See also references of EP 1720831A1
|1.||A method of making liquid alkanes, comprising the following steps: a. reacting methanesulfonic acid with a dehydrating agent, under conditions that create a methanesulfonic acid anhydride; b. reacting the methanesulfonic acid anhydride in a manner that creates a liquid alkane preparation having a purity sufficient for use as fuel.|
|2.||The method of Claim 1 wherein the methanesulfonic acid anhydride comprises sulfene, and wherein the sulfene is reacted with at least one second compound under conditions that allow the sulfene to transfer at least one methylene group into the second compound.|
|3.||A method of making olefins, comprising the step of reacting methanesulfonic acid with a dehydrating agent, under conditions that create sulfene as a reactive intermediate, and allowing the sulfene to react with itself in a manner that forms at least one olefin.|
|4.||The method of Claim 3 wherein the olefin comprises ethylene.|
|5.||A method of making cyclopropane, comprising the step of reacting methanesulfonic acid with a dehydrating agent, under conditions that create sulfene as a reactive intermediate, and allowing the sulfene to react with itself in a manner that forms ethylene, and allowing the sulfene to react with ethylene itself in a manner that forms cyclopropane.|
|6.||A method of making sulfene, comprising the step of treating methanesulfonic acid with a catalytically active surface that promotes formation of sulfene from methanesulfonic acid.|
|7.||A method of making sulfene, comprising the step of treating a methyl methanesulfonate ester with an agent that creates a sulfene ylide and releases methanol.|
Because there have been no adequate methods for converting methane gas into liquids that can be transported efficienty to commercial markets, huge volumes of methane are wasted every day, mainly by flaring or reinjection, at fields that produce crude oil. In addition, numerous gas fields are simply shut in, at numerous locations around the world.
Skilled chemists have tried for at least 100 years to develop methods for converting methane gas into various types of liquids. While various efforts in the prior art could produce relatively small quantities and low yields of methanol or other liquids, none of those efforts ever created yields that were sufficient to support commercial use at oil- producing sites. Such efforts prior to 1990 are described in reviews such as Gesser et al 1985 and Olah 1987 (full citations to all articles and books are provided below), and efforts after 1990 are described in articles such as Periana et al 1993,1998, and 2002, Basickes et al 1996, Lobree et al 2001, and Mukhopadhyay 2002 and 2003.
As a result, oil and chemical companies are making huge investments in liquified natural gas (LNG) facilities, and in a processing system known as"Fischer-Tropsch", to convert methane into liquids. However, both of those systems are very inefficient and wasteful.
LNG processing burns about 40% of a methane stream, to refrigerate the remainder to somewhere between-260 and-330°F, causing it to liquefy so it can be loaded into specialized ocean-going tankers. After a tanker reaches its destination, another large portion of the methane must be burned, to warm the remainder back up to temperatures that allow it to be handled by normal pipes and pumps. Therefore, LNG wastes roughly half of a methane stream. Nevertheless, as of mid 2004, oil companies had committed an estimated $30 billion to build LNG facilities.
Fischer-Tropsch processing burns about 30% of a methane stream, to convert the remainder into a carbon monoxide and hydrogen mix called"synthetic gas"or"syngas".
The syngas is then converted (using expensive catalysts) into heavy oils and paraffins, which then must be cracked and/or distilled to convert them into diesel fuel, heating oil, and other products. The syngas conversion, the catalyst costs, and the requirement for cracking thick and heavy oils and waxes all create inefficiencies, but as of mid 2004, companies have committed tens of billions of dollars to Fischer-Tropsch facilities.
The wastes and inefficiencies of LNG and Fischer-Tropsch systems prove the assertion that any methane-to-methanol systems previously proposed, based on small-scale laboratory work, have not been regarded as commercially practical, by any major companies. In addition, most methanol conversion systems proposed to date generate large quantities of acidic and hazardous byproducts and toxic wastes. Even if they can be recycled, byproducts and wastes are major obstacles to efficient and economic use.
A processing system that is believed to offer major improvements in the conversion of methane into methanol and other stable and easily-transported liquids is described in two Patent Cooperation Treaty applications by the same inventor herein. The first one, PCT application PCT/US03/035396, was filed on 5 November 2003 and was published in May 2004 as WO 2004/041399. The second PCT application, PCT/US04/019977, was filed on 21 June 2004.
Both of those applications were filed less than a year before the filing date herein, and both are claimed as priority documents. Therefore, even though their teachings are summarized herein in the Background section, for convenience, they are not conceded to be prior art against this invention. The contents of both of those applications are incorporated herein by reference, as though fully set forth herein.
Those two applications can be consulted for a brief history of (i) prior art efforts to convert methane into transportable liquids, such as methanol, and (ii) prior art methods for manufacturing methane-sulfonic acid (MSA, H3C-S03H). MSA, a major intermediate in various pathways disclosed herein, has been known for decades, and is sold as a commodity chemical, mainly for use in metal cleaning, electroplating, and semiconductor manufacturing.
The methane-to-methanol conversion system disclosed in those two applications is illustrated in FIGURES 1 and 2 herein, and can be briefly summarized as follows: (1) An"initiator"compound is used to trigger a reaction that will become a chain reaction that will continue indefinitely. This is accomplished by creating and using a "strong radical"that can efficiently remove a complete hydrogen atom (both a proton, and an electron) from methane, thereby creating a methane radical with an unpaired electonr, represented herein as H3C*, where * represents the unpaired electron.
Various methods and compounds for creating methyl radicals are known, and several are illustrated in FIG. 1, and described in PCT/US2004/019977. The principal method described herein and in the two prior PCT applications involves the use of a compound called Marshall's acid, the common name for peroxy-disulfuric acid, which has the formula HO3SO-OSO3H. This unstable compound is, effectively, two molecules of sulfuric acid, joined to each other through a peroxide (double-oxygen) linkage. It can be made by various methods, such as described in US patents 3,927, 189 (Jayawant 1975), 6,200, 440 (Moran et al 2001) or 6,503, 386 (Lehmann et al 2003). When subjected to mild excitation (such as by heating, or laser or ultraviolet radiation, which can use a"radical pump"or"radical gun" as described in articles such as Danon et al 1987, Peng et al 1992, Chuang et al 1999, Romm et al 2001, Schwarz-Selinger et al 2001, Blavins et al 2001, and Zhai et al 2004), the peroxide link will break. This releases two identical radicals with the formula H03SO*.
These can be regarded either as Marshall's acid radicals (since they came from Marshall's acid), or as sulfuric acid radicals (since they are sulfuric acid that is missing a hydrogen atom). These radicals are much stronger than conventional hydroxy radicals (HO*) from compounds such as hydrogen peroxide. Unlike hydroxy radicals, sulfuric acid radicals will remove hydrogen atoms from methane, to create stabilized sulfuric acid while converting the methane into methyl radicals. Because a small quantity of Marshall's acid will trigger a chain reaction that will keep going and convert a large quantity of methane into MSA and/or methanol, the amount of sulfuric acid waste will be small, if Marshall's acid is used as a radical initiator.
(2) Inside a continuous-flow reactor vessel, the unstable methyl radicals are mixed with sulfur trioxide. Since methyl radicals are not strong enough to remove anything from SO3, they will bond to it, thereby forming radicals of methane-sulfonic acid.
(3) The MSA radicals, which are quite strong, will attack fresh methane that is being continuously pumped into the reactor vessel. Each MSA radical will remove a single hydrogen atom (both proton and electron) from a methane molecule. This creates stabilized MSA, in liquid form. It also creates new methyl radicals, which will keep the chain reaction going, as long as proper quantities of methane and S03 continue to be added to the reactor vessel.
(4) In addition to continuously forming MSA as a product, liquid MSA in the reactor vessel also acts as an"amphoteric"solvent (i. e. , a solvent having two domains with different traits). The methyl domain of MSA helps methane gas dissolve and mix rapidly in the solution, while the sulfonic domain helps liquid S03 mix rapidly in the solution.
(5) Liquid MSA, which is being formed in the reactor, is continuously removed from the outlet of the reactor. It is then passed through a"cracking"vessel, which breaks it apart (this process can also be called thermolysis, since it is carried out at elevated temperatures). If carried out under proper conditions and in the presence of a suitable catalyst, the"cracking"operation causes a rearrangement of the molecule, in a way that causes the hydroxy group of the SO3H sulfonic domain of MSA to leave with the methyl group. This allows the cracking operation to release methanol (H3COH) and sulfur dioxide (SO2).
As a result, an endless cycle is carried out, using the sulfur compounds shown on the right side of FIG. 2. SO3 is pumped into the reactor, and it combines with methane gas to form MSA. The MSA is cracked, in a way that transfers a hydroxy group to the methyl carbon, to form methanol while releasing SO2. The SO2 is then passed through a separate reactor, which oxidizes it back to SO3, using oxygen from the atmosphere. The S03 is then returned to the MSA reactor, to complete the cycle.
Meanwhile, the reaction shown on the left side of FIG. 2 is not an endless cycle.
Instead, methane (a gas) is pumped into the system, and methanol (a liquid) is pumped out.
That reaction pathway is described in more detail in the two above-cited PCT applications.
It should be noted that MSA does not need to be cracked, to release methanol, to accomplish the goal of converting methane gas into a stable and transportable liquid.
Instead, as described in the PCT applications cited above, it is also possible to process MSA directly on Zeolite, SAPO, or other porous catalysts, to directly create various other compounds, without passing through methanol as an intermediate.
For convenience, the MSA intermediate is regarded as the dividing point between "upstream"and"downstream"processing. Any steps, reactors, or devices used to make or purify MSA (or its precursors, such as Marshall's acid or any other radical initiator), or to keep an MSA-forming reactor running properly, are regarded as being on the upstream side of an operation. By contrast, any steps, reactors, or devices that receive MSA as a feedstock, intermediate, or product are on the"downstream"side of an operation. The MSA-forming reactor is analogous to a dam on a river; it is neither upstream nor downstream, and instead is what creates and defines the different upstream and downstream zones. The oxidation of SO2 to S03 also is neither upstream nor downstream; in most cases, it will be carried out in a separate and isolated reactor system that will not receive or process any organic compounds at all (although it may contain organic catalysts to speed up the SO2 to S03 oxidation).
Catalytic Surfaces, Zeolites, and Monoliths Many chemical reactions involved in this invention use catalysts that are coated onto the surfaces of hard supporting materials, such as wire meshes, particulates in packed or <BR> <BR> fluidized beds, Zeolites or other porous solids, etc. "Supported" (or immobilized) catalysts are widely used in petroleum and chemical processing, since they allow expensive catalysts to be held and retained inside a reactor while large volumes of gas and/or liquid are pumped through the reactor. Accordingly, supported catalysts are well known, and are described in numerous books (such as Hayes et al 1997), articles (such as Raja et al 2000), and patents (various examples are cited below, most of which briefly mention one or more types of support and then focus on the catalysts that are coated onto the support surface).
This section contains a brief overview of three major types of catalysts, which are zeolite, SAPO, and monolith materials. This is followed by a discussion of how"ketene" compounds have been created by catalytic surfaces, which can help explain some of the principles that arise in creating a compound called"sulfene", which is important in this invention.
"Zeolite"is the common name that has been given to porous"aluminosilicate" materials that contain silicon, aluminum, and oxygen, in crystalline lattices. The lattices have molecular-sized cavities (also called cages) that are connected to each other by smaller tunnels (channels), in repeating geometric formations. The sizes of the cavities can be modified, in controlled ways, by varying the formulation of a zeolite, thereby providing a certain zeolite formulation with cavities that are an optimal size to hold a particular type of molecule that will be processed by that zeolite. In addition, the narrow tunnels between cavities are small enough to force molecules being treated to line up in certain orientations, before they can pass from one cavity to the next, driven by pressure from a gas or liquid.
In addition, the crystalline lattice that forms the cavities and tunnels can be embedded (or "doped") with catalytic atoms, ions, or molecules. Because of these factors, zeolites and other porous catalysts can cause organic molecules to react in controllable ways that cannot be easily achieved by other materials.
As one example of how zeolite materials can be used, a major advance in methanol- to-gasoline (MTG) processing was discovered in the 1970's, when Clarence Chang and his coworkers at Mobil Oil Corporation (now Exxon-Mobil) discovered that if methanol is passed through certain types of Zeolite, methylene groups (-CH2-) contributed by the methanol will begin condensing into chains, in a way that will create hydrocarbon liquids that can be used as gasoline. Early patents include US 3,899, 544 (Chang et al 1975), 4,076, 761 (Chang et al 1978) and 4,138, 442 (Chang et al 1979). Reviews include a book by Chang, Hydrocarbons From Methanol (Dekker, 1983), a chapter by Chang in Methanol Production and Use (W. Cheng & H. H. Kung, editors, Dekker, 1994), and Stocker 1999, an extensive review article that cites 350 articles published by other authors. Stocker 1999 is followed in the same journal by Keil 1999, which describes a number of commercial MTG facilities.
Zeolite materials that also contain phosphorus are often called"SAPO"materials, since they contain silicon, aluminum, phosphorus, and oxygen. During the research that followed the MTG discoveries of the early 1970's, it was discovered that processing of methanol on SAPO materials could create olefins, which are valuable unsaturated compounds that form the building blocks of plastics and polymers."Methanol-to-olefin" (MTO) processing is described in US patent 3,911, 041 (Kaeding et al 1975) and in articles such as Liu et al 1999, Sassi et al 2002, and Dubois et al 2003.
However, because their cavities are connected by tunnels,"semi-permeable"or "meso-permeable"materials such as zeolite and SAPO tend to suffer from relatively large pressure drops, if gases or liquids are pumped through them. They also tend to suffer from fouling and clogging, due to the formation of sludge-like materials and/or"coke" (solid particulates or cakes, comparable to the materials used to make charcoal briquets or activated carbon powders). Therefore, zeolite or SAPO beds usually require periodic cleaning and regeneration, usually at high temperatures.
To minimize problems of clogging and pressure drops, many types of zeolites and similar catalytic materials have been developed that are designed to have surface activity only. Some of these materials have microscopic pores, comparable to pits, which encourage certain molecules to nestle into those pits in certain orientations, causing a certain atom or domain of the molecule to remain exposed to gases or liquids that are passed over the surface of the"charged"or"loaded"material. Other materials may be chemically treated, to bond positively-or negatively-charged atoms or groups to their surfaces, usually at a controlled density or spacing. Since these types of surface-only materials do not need to have a gas or liquid actually pass through flow channels in the material, they often are used in particulate forms, such as in packed or fluidized beds.
Alternately, a different class of catalytic supports has been developed with porous materials that have tiny flow-through channels that are essentially straight and linear, passing through the otherwise solid material. These materials, called"monoliths", are commonly manufactured in the form of round discs (often called"cakes") that will fit into cylindrical containers, which usually are provided with inlet and outlet filters to hold the monolith in place while a gas or liquid flows through it. Because the flow channels in monoliths are essentially straight, linear, and parallel, and do not have any constrictions or changes in internal size, monoliths can provide higher and faster flow rates, lower pressure drops, and fewer clogging and fouling problems, compared to zeolites or other materials having non-linear flow channels. Therefore, catalytic monoliths are often used in devices that cannot be easily or periodically shut down and cleaned out (such as catalytic converters that remove pollutant gases from automobile exhausts).
Monoliths can be prepared with various channel sizes and densities, usually expressed as channels per square inch (cpsi). Monoliths that handle gases usually have cpsi values ranging from about 400 to over 1000. Monoliths that handle liquids or foams require larger channels, with correspondingly lower cpsi numbers, to achieve an optimal balance between (i) reasonable and acceptably low"pressure drops"across the material, and (ii) desirably high levels of contact between the solid surfaces and the liquids flowing through the channels. Because thousands of flow channels pass through a monolith of any substantial size, very large total surface areas, inside the thousands of tiny flow channels, will be contacted by a gas or liquid that passes through a monolith.
The material that provides the porous supporting structure of a catalytic monolith is usually called the"support". It is sometimes referred to as the"substrate", to distinguish it from the catalytic coating material, but that term is confusing and should be avoided, since "substrate"also refers to a chemical compound that is acted upon by a catalyst, enzyme, or other chemical reagent.
In general, monolith supports must be able to withstand strong acids (which eliminates most metals and alloys) and high temperatures (which eliminates most plastics and starch-type polymers). These requirements usually lead to the use of minerals and/or ceramics, which frequently contain silicon and oxygen (often referred to as"silicate" materials), which are comparable to quartz but with porous lattices that provide flow channels. Support compounds such as cordierite, mullite, or silicon carbide are widely used, and are sold by companies such as Corning Inc. (www. corning. com) and Rauschert Process Technologies (www. rauschertus. com).
Various types of surfaces can be provided on a hard support material. One class of such surfaces is called"porous"supports, which implies irregular and uneven surfaces, which may be created by the material itself, or by surface treatment processes such as anodic or acidic etching. Alternately, "abraded"supports usually provide smoother surfaces, formed by processes comparable to sanding. The suitability of any such porous, abraded, or other support surface, for hydrocarbon or chemical processing as disclosed herein, can be evaluated through routine testing.
All of the foregoing relates to the support material, which in most cases is presumed to be chemically inert, and uninvolved in the molecular rearrangements involved in a chemical reaction. Regardless of how an inert supporting material is prepared, or what physical form it is in, the real value and functionality of any supported catalyst will depend on how the surfaces are"activated" (also called"functionalized"). This usually is done in either of two manners. In one approach, the surface of a hard and presumably inert support material is coated with catalytic atoms, ions, or groups; the term"coating"is used broadly herein, and involves plating, liquid immersion, sputter coating or other gaseous diffusion, or any other process that creates a surface layer that is somehow different from an underlying support material). The second approach involves incorporating the catalytic atoms, ions, or groups into the reagents used to form a supported catalyst, in some manner that distributes the catalytic atoms, ions, or groups throughout the resulting material. This second method is conventionally used to make zeolite, SAPO, and monolith materials that require catalytic"dopant"atoms to be positioned at regular intervals in a crystalline lattice.
Either of those two approaches can be regarded as"functionalizing"a catalyst, in a way that turns an inert supporting material into a chemically active material that can help trigger, drive, and control valuable reactions.
This is a brief and simplified overview, intended to help readers who do not specialize in these types of materials develop a basic understanding of how these types of materials are made and used. Any reader who wants more information on supported catalysts can locate numerous articles and books on the subject, and in websites that provide lecture and course notes for chemistry courses at various universities.
Chemists and researchers who specialize in working with zeolites and similar materials have formed an organization called the International Zeolite Association, which runs a highly useful website, www. iza-online. org. The IZA has been designated by the IUPAC (the International Union of Pure and Applied Chemists) as having official responsibility for nomenclature and other matters relating to zeolites and other compounds with structural lattices that enable them to function as molecular sieves and/or catalysts.
The IZA has three major working groups, devoted to structures, synthesis, and catalysis.
Anyone who wishes to identify zeolite or similar compounds that offer good candidates for processing a particular chemical (such as methanesulfonic acid, one of the key intermediates in this invention) can quickly locate experts in the field, through the IZA. In addition, any company that sells zeolite compounds for chemical processing, either as a manufacturer or distributor, will have on its staff at least one technical expert who can advise potential purchasers on: (i) which compounds offer the best candidates for early evaluation, for carrying out a particular reaction; and, (ii) the names of experts who can be consulted for more information.
At least one professional journal, Microporous and Mesoporous Materials, is entirely devoted to zeolite and similar materials, and several other journals (including the Journal of Molecular Catalysis, the Journal of Physical Chemistry, and Fuel Processing Technology) frequently publish articles on processing and research using porous catalysts. Accordingly, experts who specialize in particular formulations, or in processing certain classes of chemicals on porous catalysts, can be located by contacting an editor who works with one of those journals, or by reviewing the titles of articles that have been published in such journals.
Also, methods and machines have been developed for screening large numbers of candidate catalyst formulations, in a rapid and automated manner. These methods and machines are described in articles such as Muller et al 2003, and other articles cited therein. Such devices use, for example: (i) reactors with multiple parallel tubes, each tube containing a different candidate catalyst, or (ii) titer plates with multiple wells, each well containing a candidate catalyst. When a certain reagent is passed through or loaded into all of the tubes or wells, the product generated by each individual tube or well (and therefore by each candidate catalyst) is collected separately, and delivered to an automated analytical device, such as a mass spectrometer or chromatograph. The tubes or wells that created the highest yields of the desired compound can be identified, and the exact content of the catalysts in any tubes or wells that resulted in good and desirable yields can be identified and studied more closely. For example, the best-performing candidate catalyst from one round of tests can be used as a"baseline"or"centerpoint"material, in a subsequent round of tests that will use variants that resemble the best-performing catalyst from the previous round of screening. Those variants can include known and controlled compounds, having exact compositions; alterately or additionally, "combinatorial chemistry"methods and reagents can be used, to generate random or semi-random variants of a material that provided good results in an earlier screening test. Accordingly, these types of automated screening systems offer powerful and useful tools for rapidly identifying and/or improving porous catalyst formulations that can efficiently promote any particular desired reaction.
Another factor worth noting involves catalytic agents that use symphoric, anchimeric, or"neighboring group"effects to enable"two-handed"manipulation MSA or other compounds. MSA has two very different domains, methyl and sulfonic. In the pathway shown in FIG. 3 (discussed below), the silicate support merely uses hydroxy groups to attract and interact with MSA. More potent and efficient catalysts might be developed, by providing a catalytic surface with two different types of functional agents, allowing one type of catalytic group to attract and interact with the sulfonic portion of MSA, while the second type of catalytic group attracts and interacts with the methyl portion. This factor can be better understood, if the reader will consider additional comments in PCT application PCT/US03/35396 (published in May 2004), about the symphoric and/or anchimeric traits of a bromate-sulfate reagent that can convert methane into a methyl-bis-sulfate compound.
Surface Adsorption, Transition States, and Ketene Chemistry Once a reader has a working knowledge of how surface-active catalysts can be formulated, and how various different classes of physical configurations are known and available, the next step is to consider how gases or liquids will interact with those types of catalytic materials that are supported on monolithic, particulate, or other solid supports.
Several terms and concepts are briefly explained below, then these terms are considered in the context of a prior art method for making a compound called ketene, which is analogous in some respects to sulfene, a key intermediate in this invention.
The term"adsorbed"refers to a molecule that is closely associated with the surface of a solid material. In the types of reactions of interest herein, this"close association"will last only very brief time (typically measured in milliseconds), and it will occur solely during the transition from one state to a different state (especially in reactions that run at high temperatures). This association usually is initiated by some form of charged (positive- to-negative) attraction, in which hydrogen protons or other positively-charged ions or atoms are attracted to localized negative charges (such as unshared electron pairs, on the surfaces of exposed oxygen atoms). This charge attraction draws a liquid or gaseous compound into close proximity with certain molecules on the surface of the support material. When the "lowest energy"distance is reached, the association between the reagent and the catalytic coating then progresses through one or more types or stages of"coordinate"or "metastable"bond transitions, which may or may not rise to the strength of covalent bonding.
Because of various factors, it is not always possible to clearly and definitely categorize the various transitional molecules and bonds. For example, an atom or molecule can pass through transitional states that can be regarded as intermediate or halfway points, somewhere between an ionic state, and a radical state; similarly, the types of"coordinate" or"metastable"bonds that arise can be at an intermediate or halfway point between an ionic attraction or a covalent bond. Therefore, in any narrative descriptions herein (in Barteau's pathway for the production of ketenes, and in the Applicant's pathway for the production of sulfene), any reference to any transitional or intermediate state of any particular atom, ion, or radical can be regarded as merely a convenient reference term, comparable to an estimate or approximation, intended to provide a map or narrative description of the relevant terrain, for the use of experts who wish to analyze these types of reactions in greater detail. Much more information on intermediate states, transitional bondings, and"hybridized"valence-shell structures that can occur during the course of catalytic reactions, is available in numerous published reference works (such as, for example, March's Advanced Organic Chemistry, by M. Smith and J. March, Wylie Interscience, 2001).
It should also be kept in mind that the patent law generally does not require a theory, to explain a new invention. Instead, the patent law requires a description of a feasible method for accomplishing a desired result, in adequate detail to teach those skilled in the art how to mix the reagents, and run the process. In this invention, the result and the invention center on the conversion of MSA into sulfene, and the subsequent conversion of sulfene into other useful chemicals, such as olefins. Accordingly, any specific or postulated reaction steps, and any transitional or intermediate bondings or molecular complexes that are hypothesized, proposed, or otherwise discussed herein, are not essential to carrying out this invention. Instead, this invention resides in the recognition and disclosure of several practical and useful results (including but not limited to the realization that MSA, which can be formed from"waste"methane, can be pushed into forming a sulfene intermediate, and the sulfene will then react in ways that will form ethene or other valuable compounds).
Those and other practical teachings herein form the essence of this invention, and any discussion of postulated, hypothesized, probable, or modeled atomic or molecular interactions or transition states is offered merely as additional commentary, in the hope that such commentary might be useful to experts who wish to study and analyze these or similar reactions in greater detail. This commentary is not asserted to be the final answer or definitive theory, and instead should be regarded as suggesting certain places and references where experts might wish to look, among the huge mass of published and available material.
The concepts above, regarding liquid or gaseous chemicals that are temporarily "adsorbed"onto the activated surfaces of catalysts, in ways that: (i) promote or enable a desired reaction, and then (ii) release the product compound from the catalytic surface, can be illustrated by a discussion of"ketene"compounds, described by Mark Barteau in articles such as Barteau 1996. The simplest ketene compound is H2C=C=O. More complex ketenes also can be created, by replacing either or both of the two hydrogen atoms with other groups, to create R, R2C=C=O, where R, and R2 are variables.
In a series of reactions described in Barteau 1996, the suffix (ad) was used to indicate a compound that was temporarily"adsorbed"to the surface of a solid catalytic material. The suffix (g) referred to a compound that was released, from the catalytic surface, as a gas (in the case of water, this will be steam, since these reactions are carried out at high temperatures). The suffix"0 (/)" referred to"surface oxide anions" (i. e. , oxygen atoms or ions that are closely associated with, but not covalently bonded to, the support surface).
One reaction described in Barteau 1996 involved the processing of acetic acid, on silicate supports using catalytic surfaces that contain exposed oxygen atoms, to form ketene.
In the first step of Barteau's pathway, written as: CH3COOH + O (/)--> CH3COO (ad) + OH (ad) a molecule of acetic acid ionizes, and transfers its hydrogen proton to an oxygen atom/ion on the silicate surface. This causes the acetate ion (which has a negative charge, after losing its hydrogen proton) to be attracted to, and adsorbed onto, the support surface, which has positive charges on it due to hydrogen protons it is receiving from the acetic acid solution.
In the second step of Barteau's pathway: CH3COOH + OH (ad)--> CH3COO (ad) + H20 (g) a second molecule of acetic acid ionizes, and transfers its hydrogen proton to an adsorbed hydroxy group on the support surface. This causes the hydroxy group to be converted into a full molecule of water, which leaves the support surface, in the form of steam. The second acetate anion becomes adsorbed onto the support, which continues to have positive charges on it due to other hydrogen protons that are being donated to it by the acetic acid solution that continues to contact the support.
In the third step of Barteau's pathway: CH3COO (ad)--> H2C=C=O (g) = H (ad) + O (/) an acetate ion that was adsorbed onto the support surface rearranges its molecular configuration. A hydrogen atom (or proton) on the methyl group leaves, and becomes adsorbed on the support surface. The electron (or electron pair) that formed an H-C bond, in the acetate ion, moves around that carbon atom, and forms a double bond between the methyl carbon, and the other (carboxy) carbon. This electron shift also causes the single- bonded oxygen ion from the second (carboxy) carbon to leave the acetate ion; it will become adsorbed on the support surface, thereby regenerating that support as a catalyst, rather than as a consumed reagent.
The fourth step of Barteau's pathway: H (ad) + OH (ad)--> H20 (g) partially balances out the equations above, by releasing water, as a gas (steam). This water is formed from the hydrogen atom (or ion) that was adsorbed on the support surface in the third reaction step, and the hydroxy group (or ion) that was adsorbed on the support surface in the first reaction step.
It should be noted that the reactions listed above are only partially balanced; an acetate ion remains adsorbed on the support, presumably able to rearrange itself to form additional ketene while also releasing H and 0 for adsorption on the support. As noted by Barteau in the text following the reactions listed on page 1423 of his article, side reactions also occur, including unselective decarboxylation of the adsorbed acetate ions. This releases CO2, and it also deposits hydrocarbon fragments (from the methyl groups) on the support.
After studying and analyzing a number of articles, books, and patents (including the 1996 article and several other articles and patents by Barteau, and by other authors and inventors), the Applicant herein suspected that similar processes may also be able to occur if MSA (rather than acetic acid) is processed on a comparable type of support. To inquire into that possibility, he had the MSA reaction analyzed by computer modeling, with the paid assistance of a doctoral candidate who had access to powerful computers at a university. This modeling used the Amsterdam Density Functional software, release 2.3. 3, sold by Scientific Computation and Modeling (www. scm. com), described in articles such as te Velde et al 2001. The results were positive and promising, and are described below, in the Detailed Description section.
Accordingly, the remainder of this application describes and claims: (i) various enhancements of the MSA pathway, that were identified or developed by the Applicant since the filing of the earlier PCT applications. These options and enhancements include: (1) processing options that can be carried out, either by using the MSA-to-methanol system as a starting point, or by branching out from that pathway at one or more junction points (such as by converting MSA into an unstable anhydride called sulfene, H2C=SO2, which can then be processed in various ways to create stable and valuable products, such as liquid hydrocarbon condensates that can be used as fuels or feedstocks; (2) enhanced methods for oxidizing SO2 into S03, SO that the cycle of sulfur compounds, shown on the right side of FIG. 2, can be carried out more efficiently and economically; and, (3) methods and catalysts for carrying out a similar and related type of reaction, which will cause methyl radicals to react with carbon dioxide, rather than S03, in a way that will form acetic acid (a useful and valuable chemical) rather than MSA, in a way that can reduce carbon dioxide emissions into the atmosphere by exhaust gases from power plants, factories, and other sources.
One object of this invention is to disclose various enhancements and options that can be used to expand and improve upon various teachings of two previous PCT applications (serial numbers PCT/US03/035396, published as WO 2004/041399, and PCT/US2004/019977) that were previously filed by the same Applicant.
Another object of this invention is to disclose various processing pathways and options, using methane-sulfonic acid (from methane gas) as a feedstock or intermediate, to create various types of valuable organic chemicals.
Another object of this invention is to disclose processing pathways and options, using methane-sulfonic acid (from methane gas) to create an unstable anhydride intermediate called sulfene (H2C=SO2), which can be processed to create stable and valuable organic chemicals.
Another object of this invention is to disclose enhanced methods for oxidizing SO2 into S03, so that the cycling of sulfur compounds, as part of a larger processing system that converts methane into methanol or other compounds, can be carried out more efficiently and economically.
Another object of this invention is to disclose methods and catalysts for causing methyl radicals to react with carbon dioxide, to form acetic acid, thereby forming a valuable chemical while also reducing carbon dioxide emissions into the atmosphere.
These and other objects of the invention will become more apparent through the following summary, drawings, and detailed description.
SUMMARY OF THE INVENTION Enhancements and options are disclosed for chemical processing methods described previously by the Applicant, for converting methane into methanol or other organic compounds, via methyl radicals and methane-sulfonic acid (MSA). A major set of options and enhancements, which are the primary focus of the claims herein, relate to converting MSA into an unstable and highly reactive anhydride intermediate called sulfene, H2C=SO2.
This compound is a potent and useful donor of methylene groups (-CH2-), which can be used for purposes such as creating heavier liquid fuels or olefin compounds, or for creating plastic or polymeric compounds in particulate or other form. Other options and enhancements disclosed herein can be divided into four main categories: (1) various "upstream"processing options, such as improved methods for making Marshall's acid, one type of radical initiator that can be used to convert methane into MSA; (2) various "downstream"processing options, such as methods for treating MSA methyl-ester impurities that may be created during MSA cracking or other processes; and, (3) improved methods and catalysts for oxidizing SO2 into SO3, so that recycling of sulfur compounds in the MSA pathway can be carried out more efficiently.
BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 depicts several known chemical reactions that can"activate"methane (CH4) by removing a hydrogen atom (both a proton and an electron), to convert the methane into a methyl radical (H3C*, where the asterisk represents an unpaired electron).
FIGURE 2 depicts a reaction system that combines methyl radicals (H3C*) and sulfur trioxide, to form methane-sulfonic acid (MSA) by a multi-step process that creates a new methyl radical. This establishes a chain reaction, and the newly-created methyl radicals will react with newly-added SO3. MSA can be removed from the vessel and sold as a product, used as a reagent, or"cracked"to release methanol (which can be shipped as a liquid, or used as a feedstock for other reactions) and sulfur dioxide (which can be oxidized to SO3 and recycled back into the reactor).
FIGURE 3 depicts transitional intermediates that are likely to be formed if MSA is dewatered with the assistance of a silicate monolith material having hydroxy groups on its surface.
FIGURE 4 depicts a reaction of two molecules of sulfene (H2C=SO2) to form ethene, in gaseous form. This reaction releases gaseous SO2, which can be oxidized to S03 and recycled back into the reactor vessel that is used to convert methane into MSA.
FIGURE 5 depicts an alternate candidate pathway for dewatering MSA to form sulfene, using tungsto-phosphoric acid (also called phospho-tungstic acid).
FIGURE 6 depicts an alternate candidate pathway for making sulfene, using a methyl-MSA compound that is reacted with methanol, which is recovered and recycled.
FIGURE 7 depicts a pathway for using sulfene to convert ethene into cyclopropane, which can be converted into propene (propylene), propanol (propyl alcohol), or other products.
FIGURE 8 depicts a reaction pathway that proceeds through an"outer"anhydride form of MSA, formed by condensing two molecules of MSA while removing a water molecule.
FIGURE 9 depicts a potential polymerization pathway, in which sulfene will insert multiple methylene groups into a growing alkane molecule or derivative, which may be a branched alkane or derivative if certain types of diimine or other catalysts are used.
FIGURE 10 shows a pathway that enables a vandaium diformate catalyst to convert SO2 into S03, using pathways that appear from computer modeling to be thermodynamically favorable.
FIGURE 11 is a schematic depiction of a system for converting S02 to S03, which uses heat from the SO2 oxidation reaction to heat MSA from its relatively cool formation temperature, up to a much higher cracking temperature.
DETAILED DESCRIPTION As summarized above, this application focuses mainly on making and using sulfene, H2C=SO2, a highly reactive anhydride form of MSA that can be used to manufacture olefins, liquid fuels, or other valuable compounds from stranded methane gas. These disclosures are addressed in the immediately following subsections.
After that discussion of sulfene, two additional sets of disclosures are provided.
These disclosures focus on: (1) options and enhancements in"upstream"processing (i. e. , reagents, devices, and methods used to manufacture MSA as an intermediate), and (2) methods and catalysts for more efficient oxidation of SO2, to regenerate and recycle S03.
These disclosures are included herein, because they are believed to be necessary to ensure disclosure of the"best mode"for carrying out the processing methods and reagents disclosed herein.
The second reason is this: these disclosures are believed to reveal substantially improved ways of making good, efficient, humanitarian, and benevolent use of energy resources, while providing enhanced levels of environmental protection as well.
Accordingly, rather than generating a profusion of dozens of confusingly different-yet- interrelated patent applications, all of which would need to be located and studied carefully, and any of which could be written and crafted in ways deliberately intended to confuse and thwart any clear understanding (by competitors and adversaries, who often are the only ones who read such patents) of what was actually discovered and taught, the humanitarian, energy-conserving, environment-protecting goals of this technology (and of the Applicant) can be better served by compiling a number of discoveries and advancements into a small number of patent applications. By taking that approach, a single inventor can help establish a functional and efficient foundation and framework that can help support and enable a clear understanding, by all interested parties, of what is being taught, and how it can be developed as rapidly as possible into commercial and industrial use that will help the public, and the planet.
Accordingly, the following subsections focus on making and using sulfene. After those subsections, two additional section headings are provided, to cover: SYNTHESIS OF SULFENE As briefly summarized above, methods are disclosed herein for converting methane- sulfonic acid (MSA, which can be prepared from methane gas as described in PCT applications PCT/US03/035396 and PCT/US04/019977) into an"inner anhydride"called sulfene, H2C=SO2 (also called thioformaldehyde dioxide).
Sulfene is unstable, and if formed in large quantities and/or high concentrations, two molecules of sulfene will react with each other, in a rapid and highly exothermic reaction, to form ethylene (also called ethene), H2C=CH2, a valuable olefin used in the manufacture of plastics and polymers. The SO2 group in sulfene will act as a leaving group in most types of reactions, causing most sulfene reactions to release SO2 in gaseous form. This gas can be collected, oxidized back into S03, and returned to the reactor vessel that is being used to convert methane into MSA, in a recycling operation that minimizes wastes and unwanted byproducts.
Under some conditions, sulfene can be used as a"methylene transfer agent", which can insert methylene groups (which can be represented as-CH2-or as H2C : ) into other compounds, qas discussed in more detail below. This reaction can be used to convert various hydrocarbon compounds (include gaseous or other relatively light or"thin" hydrocarbons, such as short-chain hydrocarbons with 2 to 5 carbon atoms) into larger and heavier compounds, which generally will be easier to handle (since they will be less volatile) and more valuable (since they will have higher energy density). As just one example, if sulfene reacts with ethylene, the methylene group from sulfene will convert the ethylene into cyclopropane, which can be (1) used as a chemical feedstock, which will be highly reactive due to its stressed bond angles, (2) isomerized to form propylene (also called propene), another valuable olefin, or (3) hydrated to form propyl alcohol, a valuable chemical and a gasoline additive or substitute. In general, transfer of methylene groups into most types of gaseous and/or volatile hydrocarbons will decrease their volatility, making them easier to store, transport, and handle, and will also increase their energy density, utility, and value.
The conversion of MSA into sulfene requires the"dewatering"of MSA (H3C- SO3H). This"dewatering"process can also be called dehydration; however, dehydration is a broader and less precise term, and can be used when hydroxy groups (HO-) rather than complete water molecules (H2O) are removed. Accordingly, the term"dewatering"is preferred herein, to indicate that two hydrogen atoms and an oxygen atom must be removed from each molecule of MSA that is fully converted into sulfene. The term"anhydride"can also be used, to refer to molecules of MSA from which water molecules have been removed.
If desired, terms such as"inner"or"internal"dewatering or dehydration can be used, to indicate that a complete molecular equivalent of water is being (or has been) removed from a single molecule of MSA, to form sulfene. However, it should be understood that in most cases, each water molecule that is released during a dewatering process typically will contain a hydroxy group from the sulfate domain of one MSA molecule, and a hydrogen proton from the methyl domain of a different molecule of MSA.
There is also an"outer"anhydride of MSA, H3CSO2-O-SO2CH3, formed by condensing two molecules of MSA while removing a single molecule of water. Under some conditions, this intermediate can rearrange to form sulfene, while releasing MSA. Outer anhydrides of MSA can be useful, and are discussed below.
Several candidate methods for converting MSA into sulfene are disclosed herein.
Preferred methods for different manufacturing sites may depend on various factors, such as flow rates and flow rate consistency levels at that site, the purity levels and contaminant loads in the methane stream as well as the MSA intermediate, the ability of other equipment at a site to handle any wastes or unwanted byproducts that may be created by the various candidate methods, and the targeted purity levels for sulfene or downstream products that will enable operations at a particular site to be optimized on an economic basis.
Accordingly, any candidate method disclosed herein (and any other candidate method that is currently known or hereafter discovered) can be evaluated, both in batch-processing and continuous-flow modes of operation, to determine its suitability and economics for use at any particular site.
It should be recognized that until this point in time, sulfene has received little attention from chemical researchers, mainly because of two reasons: (i) it is unstable, and will not last long even when created; and, (ii) the only prior art methods for preparing it are difficult and tedious, and generate too much toxic and hazardous waste to enable sulfene manufacture to be used as a practical and economic route toward creating other valuable products. Two of the relatively few items published to date on sulfenes are: (i) chapter 17, by King and Rathore, in a book edited by Patai and Rappaport 1991, and (ii) Prajapati et al 1993, which describes a method of generating sulfene that consumes SOC12 and generates hydrochloric acid as a byproduct. To the best of the Applicant's knowledge and belief, neither of those items, both published more than a decade ago, ever led to any significant commercial or industrial interest in sulfene.
However, the level of interest in sulfenes may increase dramatically, after the disclosures herein have been made known to chemical and petroleum companies and academic researchers, since a feedstock that can be used to make sulfene (i. e. , MSA from stranded methane gas) is likely to become available soon, at lower cost, and in quantities that are many times greater than the currently-available worldwide supplies of MSA.
Accordingly, the disclosure of synthesis pathways that pass from stranded methane through MSA and then through sulfene, to creaste olefins or other highly valuable compounds, is likely to trigger substantial research interest in this field of research, and it is likely that these pathways can be supplemented and enhanced by other methods.
Accordingly, these pathways are being disclosed at an early stage of evaluation, after they apparently have been tentatively confirmed in batch processing but before they have been tested or evaluated in continuous-flow operations, to confirm that these pathways are indeed feasible, and to help researchers and engineers interested in this field of research become familiar with various factors and options.
Several of the synthesis pathways that pass through sulfene will require: (i) elevated temperatures, to overcome certain thermodynamic barriers, and (ii) active removal of water (usually in the form of steam), to pull certain reactions in the desired direction. In some pathways, water can be removed from MSA directly, as discussed relative to hydrated silica, below. Alternately, in some pathways (such as pathways involving methyl- methanesulfonate ester, or the outer anhydride of MSA), water may be removed from certain components prior to the creation of sulfene. This can provide benefits in various types of downstream processing.
Three main categories of candidate pathways are described below, for synthesizing sulfene. Each candidate pathway is discussed under its own subsection.
CANDIDATE PATHWAY #1 : SOLID-SUPPORTED CATALYSTS The first candidate pathway disclosed herein for dewatering MSA to form sulfene uses catalytic materials on the surfaces of solid supports. Catalysts that are coated onto (or otherwise made accessible on) the surfaces of solid support materials are widely used in the petroleum and chemical industries, because they allow expensive catalytic materials to be retained inside a reactor while large volumes of gas or liquid are pumped through the reactor. As discussed in the Background section, the types of solid-support catalysts disclosed herein can be provided in any of several candidate forms, such as: (i) "monolith" materials, with essentially linear and parallel flow channels passing through a highly porous material that can be manufactured in a"cake"or similar form that can be placed inside a reactor device, or (ii) particulate materials, which can be loaded into a packed bed, fluidized bed, stirred reactor, or comparable device.
The conversion of MSA into sulfene will be comparable in some respects to the conversion of acetic acid into ketene (H2C=C=O), which is summarized in the Background section by describing certain reactions disclosed in Barteau 1996. After studying and analyzing a number of published articles by Barteau, and other articles and patents by other authors and inventors, the Applicant herein suspected that similar processes may occur if MSA (rather than acetic acid) is processed on a suitable supported catalyst.
To evaluate that possibility, he had the MSA reaction analyzed by computer modeling, using the Amsterdam Density Functional software, release 2.3. 3, sold by Scientific Computation and Modeling (www. scm. com), described in articles such as te Velde et al 2001.
Results from that computer modeling are provided in FIG. 3, which depicts a three- dimensional model of how a molecule of MSA can interact with a silicate support that has hydroxy groups exposed on its surface, represented by (Si (OH) 3) 2O.
In the initial step of this series of reactions, one of the double-bonded oxygens of the sulfate portion of MSA is attracted to one of the hydrogen protons on the silicate support, and the hydrogen proton on the hydroxy group of the sulfate portion of MSA is attracted to one of the oxygen atoms in one of the hydroxy groups on the silicate support. At the same time, a coordinate bond between the two silicon atoms is also disrupted or reconfigured.
This combination of steps forms an adsorbate, in which MSA has become closely associated with the silicate surface. This attraction and affiliation is an exothermic reaction that occurs spontaneously, with a axe value of-10.72 kcal/mol (kilocalories per mole). The term E refers to bonding energies, which correspond to H (enthalpy) values when certain"zero point energy" (ZPE) corrections are made, as known to those skilled in the art.
In the second step, which will occur only at elevated temperatures, a water molecule will leave, most likely containing a hydroxy group that initially was on the silicate support, along with a hydrogen proton or atom from the sulfate group of the MSA. This leads to formation of a silicon-oxygen-sulfur linkage, on the right side of the molecule shown in FIG. 3. This reaction is endothermic, which means it requires energy input, with a calculated value of E = 10.79 kcal/mole. Since that figure is nearly equal to the exothermic energy release of the initial step, the net result is nearly"thermoneutral", and it will occur on an equilibrium basis, at high temperatures. This equilibrium can be shifted and pulled in the desired direction, to provide greater yields, by actively removing from the reactor vessel any water that is released (in the form of steam) from that reaction.
Accordingly, the first and second steps, taken together as described above and illustrated in FIG. 3, can be written as follows: H3C-SO3H + OH (ad)--> CH3SO3 (ad) + H2O In the next step of the reaction, the MSA residue will pivot and swing around an "axle"that is provided by the silicon-oxygen-sulfur linkage, until one of the positively- charged hydrogen protons, on the methyl group of the MSA residue, approaches a negatively-charged hydroxy group, which might be bonded to the same silicon atom that the sulfur is bonded to, but which more likely will be bonded to some other nearby silicon atom in the matrix of the silicate support.
In the fourth step, three proton and electron shifts take place, which function together to set the stage for the disengagement of sulfene from the substrate. In one shift, the hydrogen proton that formed the bridge between the methyl group of MSA, and the hydroxy group of the substrate, shifts toward the hydroxy group of the substrate, thereby weakening its bond and its attraction to the carbon atom of the MSA. In a second coordinated shift, the electron pair that previously formed the carbon-hydrogen bond (which has now become weakened because of the hydrogen proton's attraction to the hydroxy group on the substrate) will be pulled toward the electronegative sulfur atom. This sets up the formation of a double bond between the carbon atom and the sulfur atom. In the third coordinated shift, this formation of the double bond between the sulfur and the carbon will weaken the single bond between the sulfur atom, and the oxygen atom that forms the sulfur-oxygen-silicon linkage.
After these three shifts occur, in what can be regarded as the fourth step of the reaction, the fifth step can occur, in which the MSA residue will detach from the silicate support, in a way that creates a double bond between the carbon and the sulfur. The hydrogen proton from the methyl group, and the oxygen atom from the sulfate group, will both be left behind, adsorbed on the solid support material. When this detachment occurs, the H2C=SO2 molecule that remains from the original MSA has become sulfene.
The detachment of the sulfene from the solid support will leave a polarized condition on the support, with a positive charge on the hydroxy group that received a hydrogen proton from the methyl group of MSA, and a negative charge on the oxygen atom that was donated by the sulfate group of MSA. Under the acidic conditions that will exist in the system (due to the continued addition of fresh MSA, an acid, to the system), those localized charges can be resolved in any of numerous ways involving migrating or mobilized protons, in ways that will regenerate the hydroxy groups on the support, and restore the silicate support, thereby rendering it a catalyst, rather than a consumed reagent.
Accordingly, when the third, fourth, and fifth steps in the pathway are combined together and written in the aggregate, they become: CH3SO3 (ad)--> CH2SO2 + OH (ad) When this reaction is combined with the reaction above, and then balanced by eliminating identical items on the left and right sides, the net result of both reactions becomes: CH3SO3H--> CH2SO2 + H20 (released as gas/steam) Table 1 provides the AH (change in enthalpy) values and the A G (change in Gibbs free energy) values for the formation of ethene via either of two routes: (1) from acetic acid via ketene, as described in Barteau 1996, for comparative purposes; and, (2) from MSA via sulfene, as disclosed herein. These units are in kilocalories per mole, but since two moles of sulfene make only one mole of ethene, attention needs to be paid to whether the one- mole compound is on the left or the right side of the reaction arrow, as discussed in more detail following the table.
Both sets of values were calculated at 3 different temperatures, which are 300,600, and 900 Kelvin. The Kelvin scale begins at theoretical absolute zero, at which all atomic motion completely stops. A Kelvin temperature can be converted into centigrade by subtracting 273.15 ; therefore, the modeling temperatures were equal to 26.85, 326.85, and 626. 85°C. Those temperatures are equal to 80,620, and 1130°, in the Fahrenheit scale, which is mentioned to emphasize the range they cover, and to point out that the lowest modeled temperature (which is close to room temperature) would not be useful or practical for manufacturing ethene from MSA, since the initial barrier to reach sulfene is too high.
TABLE 1 THERMODYNAMICS OF KETENE OR SULFENE REACTIONS Ketene reactions H G-300K G-600K G-900K CH3COOH-> H2C=C=O + 30.66 18.36 4.5-8. 82 H20 2H2C=C=O-> C2H4 + 2CO 5.61-3. 63-12.08-19. 87 Sulfene reactions CH3S03H-> H2C=SO2 + H20 34.83 23.30 11.79 1.12 2CH3SO3H-> 2H2C=SO2 + 69.66 2 H20 2H2C = SO2-> C2H4 + 2SO2-54. 09-66.67-77. 68-87.85 S02 +'/202-> S03-20. 86 Overall reaction:-26. 15 2CH3SO3H + °2-> CH, + 2H20 +2S03 The conversion of MSA to sulfene will require a very hot reactor. One candidate class of reactors that can handle such temperatures includes reactors that contain monolith supports, made of quartz-like but porous silicate materials having essentially linear and parallel flow channels, as described in the Background section.
It should also be noted that many scientific articles refer to"adiabatic"monolithic reactors. The term"adiabatic"indicates that a reaction is carried out without adding external heat to the reactor, and without using heat exchangers or other means to actively draw heat away from the reactor vessel. When used during research, that approach can simplify and clarify various data and calculations. However, when highly exothermic (heat- generating and heat-releasing) reactions are carried out on a commercial scale, in large manufacturing operations, it would be wasteful to let the heat simply dissipate, rather than putting it to productive use. Therefore, it is presumed that in most industrial operations, any reactor that generates intense heat from an exothermic reaction will be surrounded by some type of heat exchanger, and will not be run as an adiabatic process.
If the sulfane that is generated in this manner is converted into ethene, as shown in FIG. 4, that reaction will be extremely rapid and exothermic, and it will release energy, calculated as a AH value-54.09 kcal/mol for each mole of ethene created. However, it requires two moles of sulfene to create a mole of ethene. Therefore, the endothermic (energy-consuming) AH value of 34.83, for creating a mole of sulfene from MSA, must be doubled, when overall energy requirements are considered. This leads to an endothermic value of 69.66 for creating two moles of sulfene, followed by a-54.09"partial payback"of energy that is released when the two moles of sulfene are combined to form one mole of ethene.
That leaves a net energy consumption requirement of 15.57 kcal/mole for producing ethene from MSA; however, the calculations do not stop there. Two moles of SO2 will be released by the sulfene-to-ethene reaction, and the SO2 must be oxidized back into S03, which will be recycled back into the reactor that is converting methane into MSA. The oxidation of SO2 to S03 is highly exothermic, releasing-20.86 kcal/mole, and that value is doubled (to-41.72 kcal) when two moles of SO2 are oxidized. Therefore, the entire system, which starts with MSA and ends with ethene and S03, is exothermic, and yields a net energy release of-26.15 kcal/mole, when two moles of MSA are converted into one mole of ethene and two moles of S03.
These computer-modeled numbers were calculated based on a simple and non-optimized solid support, involving nothing more than hydroxy groups on a silicate material. Now that a pathway has been disclosed for converting methane gas (which is wasted by flaring and reinjection, at rates of roughly $100 million worth of methane, every day) into ethene (a highly valuable olefin), via MSA and sulfene intermediates, those who specialize in designing and testing solid catalytic materials (including silicates, cordierite, mullite, silicon carbide, etc. ) can identify and optimize various combinations of supports and activating agents that are likely to create solid catalysts that can increase the yields, selectivity, processing rates, and other desired traits of these reactions.
CANDIDATE PATHWAY #2 : BIFUNCTIONAL (FRIEDEL-CRAFTS) CATALYSTS Anyone attempting to develop improved catalysts for use as disclosed herein should also consider"bi-functional"catalysts that use symphoric, anchimeric, and/or"neighboring group"effects to increase their ability to manipulate MSA. Such catalysts are also referred to as Friedel-Crafts catalysts (described in various patents and articles, such as US patent 2,334, 565), as acid-base (or acidic-alkaline) catalysts, or by similar terms. These catalysts presumably should be affixed to solid supports, to enable them to be retained inside a reactor vessel while large quantities of gas or liquid are being pumped through the vessel.
Therefore, these types of catalysts can be regarded as a subset of Candidate Pathway #1, discussed in the preceding subsection, and they build upon and extend the teachings of that prior subsection.
In layman's terms, bifunctional catalysts can be regarded as"two-handed"catalysts.
By way of analogy, most people cannot securely grip and hold a basketball with just one hand; however, nearly anyone can do it, using two hands. Similarly, it is easier (and faster) to cut a piece of steak, or an uncooked carrot or potato, if someone uses one hand (either with or without a fork) to hold the food stationary, while using the other hand to hold and use a knife.
In analogous ways, "two-handed"catalysts can attract, grasp, and manipulate some types of molecules more rapidly, efficiently, and securely than catalysts having only one type of active site or group. This is especially true with a molecule such as MSA, which has methyl and sulfonic domains that are very different from each other.
Therefore, rather than using a silicate support that only has hydroxy groups as the active sites (as described in the first candidate pathway, above), more efficient catalysts can be developed by providing a catalytic surface with two or more types of functional groups, allowing one type of group to attract and interact with the sulfonic domain of MSA, while a different group attracts and interacts with the methyl domain.
In general, most bi-functional catalysts use either or both of the following: (1) two distinct mechanisms that occur in sequence, usually quite rapidly (such as within nano-, micro-, or milliseconds); and/or, (2) anchimeric, symphoric, or neighboring group effects, in which a partial shift in one part of a molecule enables and promotes a secondary shift in another part of the molecule. In either case, an initial reaction or shift usually avoids or minimizes some type of transitional barrier that otherwise would hinder or block the second part of the desired reaction.
This approach to using bi-functional catalysts can be illustrated by a description of how a"hetero-polyacid"compound, such as tungsto-phosphoric acid (also called phospho-tungstic acid) can function in a desired manner, in a liquid solution. This teaching can then be adapted for use with immobilized catalysts on solid supports.
Hetero-polyacid compounds usually are formed by combining two or more types of salts, then using a strong acid to acidify the salt mixture. For example, tungsto-phosphoric acid can be created by: (1) mixing a tungsten salt such as sodium tungstate dihydrate, Na2W042H2, with a sodium phosphate hydrate such as Na2HPO4 12H2O, in distilled water; (2) adding concentrated hydrochloric acid, slowly and with vigorous stirring; (3) evaporating the water under a vacuum; (4) extracting tungsto-phosphoric acid from the residue, using a solvent such as ethyl alcohol; and, (5) removing the solvent under a vacuum, to provide a crystalline acid. This mixture will contains various species that can be represented as WO, (W is the symbol for tungsten) and HYPO, where x, y, and z are variable numbers (usually but not always represented as integers). If desired, the acid mixture can be represented by one or more dominant species, such as WO3 H3PO3. This compound is sold by Alfa-Aesar (www. alfa. com). Additional information is contained in sources such as US patent 3,974, 232 (Aizawa et al 1976, assigned to Toray Industries), which describes both (i) the dehydration of cyclohexanol into cyclohexene, and (ii) the use of other hetero-polyacid compounds, such as tungsto-silicic acid, molybdo-silicic acid, and molybdo-phosphoric acid.
If tungsto-phosphoric acid is mixed with MSA under suitable conditions and pressures, at least some of the MSA is likely to react with the acid in a manner shown in FIG. 5. In one part of the reaction, tungsten trioxide (W03) will extract a hydrogen atom from the methyl portion of the MSA. In a second part of the reaction, phosphoric acid will donate a hydrogen to the sulfate group on the MSA, causing it to become an ionic group with an extra hydrogen proton,-SO2OH2+. The-OH2 group will then leave, as water (i. e., as steam, if the reaction is carried out at high temperature), leaving behind an ionic sulfate group,-S02'. This generates a transitional MSA ion that is likely to rearrange into sulfene, while releasing water, as shown in FIG. 5. These reactions also allow positively-charged tungsten ions (W03H+) and negatively-charged phosphate ions (H2PO3-) to reassociate, through ionic attraction, to reform a tungsto-phosphoric acid mixture. Accordingly, this compound functions as a catalyst, rather than as a consumed reagent.
To render it useful for continuous-flow processing of liquids or gases, bifunctional catalysts can be immobilized on solid supports, to prevent the catalyst from being washed out of a reactor by the gas or liquid flowing through the reactor. Immobilization of a bi-functional catalysts can be accomplished by using and/or adapting various synthesis routes that are already known to skilled experts who specialize in creating and testing new types of zeolites and other semi-permeable catalysts. As one example, the"SAPO"class of zeolite catalysts already contains phosphorus atoms, in an aluminosilicate matrix.
Therefore, an activating agent can be used to donate tungsten atoms or groups in a manner that will coat the accessible surfaces of a SAPO material, in a manner that will create immobilized groups that are similar to tungsto-phosphoric acid mixtures as described above.
Alternately, if desired, a donor compound can be added to a reagent mixture that is being used to synthesize a porous catalyst. However, this approach tends to make less efficient use of an expensive"dopant"compound, since much of the dopant is likely to be inaccessible, inside the final material, rather than merely coated onto accessible surfaces.
Examples of hydrocarbon processing using bi-functional catalysts are provided in numerous published articles. As one example, scheme III shown on page 427 of Olah 1987 represents two sequential reactions that are triggered, first, by an acidic domain of a catalyst, and second, by an alkaline domain of the same catalyst material. Olah et al 1984 (entitled, "Onium Ylide Chemistry: 1. Bifunctional Acid-Base-Catalyzed Conversion of...") contains more information on this subject.
It should also be noted that many metal oxide catalysts (such as vanadium oxide catalysts, platinum oxide catalysts, etc. ) act as bi-functional catalysts, in which a vanadium, platinum, or other metal atom interacts with one domain of a compound being treated, while one or more oxygen atoms bonded to the metal atom interact with a different domain of the compound being treated.
Accordingly, since MSA has two different domains that will respond differently to different catalytic sites, bi-functional catalysts hold exceptionally good promise for converting MSA into sulfene, in ways that adapt and extend the teachings set forth above, concerning solid-supported catalysts in general.
CANDIDATE PATHWAY #3 : MSA METHYL ESTER PATHWAY During the course of the laboratory research that confirmed the computer-modeled MSA-forming pathway shown in FIG. 2, a question arose as to whether the MSA was (or might be, under certain conditions) contaminated by a methyl-methanesulfonate ester, with a structure shown at the top of FIG. 6. That question triggered some additional analysis and computer modeling, as well as a careful rereading of every patent issued to Snyder and Grosse in the early 1950's.
That work eventually resulted in a postulated pathway that (according to the computer modeling results) appears to offer an improved pathway to sulfene, with lower thermodynamic hurdles than candidate pathway 1, above.
This candidate pathway is illustrated in FIG. 6. It is commenced by reacting MSA with methanol, in the presence of a dehydration catalyst (various metals, such as aluminum, beryllium, silver, and copper offer candidates for evaluation for such use), in order to deliberately convert the MSA into the methyl-methanesulfonate (MMS) ester. This dehydration reaction will be carried out at an elevated temperature, and the water that is released will be removed from the reactor, as steam. Additional information that can shed additional light on this dehydration reaction, and on catalysts that can promote it, can be gleaned from US patent 2,553, 576 (Grosse & Snyder, 1951).
The MMS ester compound is then treated with a highly polarized metallic salt, such as a zinc halide, such as zinc chloride, ZnC12, which can act as a"Friedel-Crafts"catalyst.
As suggested by various comments in US patent 2,492, 984 (Grosse & Snyder, 1950), when those comments are combined with and interpreted in the light of a modern understanding of"ylide"compounds and structures (which are briefly summarized below), the metal halide will effectively pry off the-OCH3 (methoxy) group from the sulfate group. This methoxy group will then react with a hydrogen proton, which will be available from one or more other sources in the reactor vessel (such as from a methyl group on MSA or MMS, which will be releasing protons as they convert from an H3C-methyl group into an H2C= sulfene group). The reaction of the methoxy group with a hydrogen proton completes the re-formation and release of methanol, which is recycled back into the dehydration reactor.
The release of methanol, from the the MMS ester, leaves behind an"ylide"form of sulfene, as the residue. Various candidate solvents can be tested, to deterine which solvent (s) can maximize the yields of this reaction. Tetrahydrofuran, dimethylsulfoxide, and other candidate solvents can provide a range of polarity levels, which will merit evaluation for such use. In general, the preferred solvent selected for a particular manufacturing facility is likely to depend on the operating temperature that is used, at that site. Solvents with lower polarity levels can be used to slow down SO2 removal, in ways that can be used to control reaction kinetics, to maximize desired yields.
The sulfene ylide compound will react with sulfene to form ethylene, a valuable olefin used to make plastics and polymers. These reactions are complex, involving various types of pi and sigma bonds. They potentially involve four-member"dimer"intermediates that will decompose at suitable temperatures, enabling the SO2 groups to act as leaving groups while ethylene is formed (for more information on such dimers, chapter 17 by King and Rathore, from Patai and Rappaport 1991, and Arnaud et al 1999, should be consulted.
However, computer modeling indicates that sulfene is sufficiently electronegative and reactive that it is likely to avoid any thermodynamic barriers, and may bypass any such dimer formation. This modeling further supports the conclusion that sulfene may be one of the most active and effective methylene transfer agents ever identified, and may open up exceptionally efficient pathways to various types of hydrocarbon chemistry that have not previously been available. In addition, various options can be evaluated for controlling the levels of sulfene reactivity, including, for example: (i) carrying out such reactions at low temperatures, under reduced pressures, and/or in the presence of various solvents that will help sustain reactions at lower rates; and, (ii) modifying MSA, prior to dewatering it, in ways that may, for example, modify one or more of the oxygen atoms on the sulfonic group.
If the ethylene remains in solution while additional sulfene is being formed, at least some of the ethylene is likely to react with sulfene, to form cyclopropane. This is a relatively unstable molecule, due to the fact that its bond angles are stressed, at 60 degrees, compared to the normal 109.5 degrees for unstressed bonds in an aliphatic chain.
Accordingly, cyclopropane can be isomerized by steps such as mild heating, to form propylene (a valuable olefin that is easier to handle and transport than ethylene), or it can be reacted with water to convert it into propyl alcohol, which makes a very good gasoline additive or substitute, with an energy density higher than methanol or ethanol.
While the modeling data generated to date rely on various assumptions, and are not regarded or represented as final and authoritative, a comparison of certain numbers for different pathways that were generated using fairly consistent assumptions can provide some indication of the relative merits of the MMS-plus-methanol pathway, compared to the first pathway described above, using a silicate support with exposed hydroxy groups. Under standard conditions, at 300 degrees Kelvin, the dehydration reaction (to reach the MMS compound and release steam) showed an endothermic H value of +11. 7 kcal/mol, and a Gibbs free energy value of AG 12.3 kcal/mol, and the reaction that released methanol and formed sulfene ylide showed an endothermic value of AH = +23.1 kcal/mol, and a Gibbs free energy value of G = 11 kcal/mol. For comparison, MSA conversion on silica with hydroxy groups showed an endothermic value of AH = +34.8 kcal/mol, and a Gibbs free energy value Of AG = 23.3 kcal/mol.
The fact that all three of the candidate pathways disclosed above, for making sulfene, regenerate their starting materials, and treat those materials as catalysts rather than consumed reagents, deserves attention, especially when compared to pathways reported in the prior art, which could generate sulfene only by consuming reagents and generated unwanted byproducts (as one example, Prajapati et al 1993 describes a method of generating sulfene which consumed SOC12, and generated hydrochloric acid). Since catalytic processes are generally superior to processes that generate unwanted wastes (especially acidic and/or salt wastes), it is believed that this invention discloses a new and useful improvement in synthesizing sulfene, regardless of what is subsequently done with the sulfene.
With regard to all of the candidate pathways listed above, the enthalpy calculations in Table 1 merit consideration, and certain factors that dwell within those numbers should be noted in specific. The conversion of MSA into sulfene is endothermic, and requires energy to drive it, at a AH value calculated as 34.83 kcal/mole. However, the AH value for subsequently converting sulfene into ethene is exothermic, and releases 54.09 kcal/mol. The net release of energy is about 20 kcal/mol, to move from MSA to ethene. This is a crucial factor that sits at the heart of this aspect of the invention, and all of the candidate pathways disclosed herein should be regarded as ways to drive the MSA dewatering reaction over an initial"hump", so that the reaction can reach the downhill slope of the energy curve, where it will continue on its own, releasing substantial net energy.
Accordingly, a proper understanding of this invention herein should not focus solely on converting methane or MSA into sulfene, since sulfene is an unstable high-energy intermediate. Instead, this invention discloses a useful pathway for converting methane or MSA into olefins or other valuable and useful products, by passing through sulfene, an intermediate that effectively provides a pathway for making olefins and other materials, with lower thermodynamic barriers than other alternative pathways.
It also should be emphasized that the candidate pathways described above are not regarded as exhaustive or exclusive. Instead, other candidate pathways for reaching sulfene, or for reaching other useful intermediates that can be converted into olefins or other valuable products, are likely to be recognized by those skilled in the art, after the chemical pathways and commercial prospects for converting stranded and wasted methane into MSA, then sulfene, and then ethylene, have been disclosed.
USE OF SULFENE AND OTHER YLIDES; METHYLENE TRANSFER AGENTS In addition to being useful for the manufacture of ethylene, sulfene may be potentially useful as a"methylene transfer agent" (MTA) in various other situations. This potential utility will be limited by the tendency of sulfene to react with itself, rapidly and exothermically, to form ethylene; nevertheless, by controlling reaction conditions such as temperatures, pressures, and ratios of reagents, it may be possible and practical to induce sulfene to react with various other compounds, in various ways and at commercial levels.
Cyclopropane offers a good example, since it can be formed by reacting ethylene (formed by condensing sulfene, or by any other known method) with additional sulfene. If a fixed quantity of sulfene is placed or created in a closed reactor, much of the sulfene is likely to form ethylene, fairly rapidly; then, as the ratio of ethylene to sulfene in the reactor rises, the remaining sulfene will become more likely to react with the growing quantity of ethylene, than with the dwindling quantity of remaining sulfene. In a similar manner, if a gaseous ethylene feedstock is continuously fed into a reactor along with a limited quantity of sulfene, at least some of the sulfene will react with the ethylene.
Accordingly, FIG. 7 depicts a reaction pathway for using sulfene to convert ethylene into cyclopropane. Briefly, when a molecule of sulfene contacts a compound having a double bond, the sulfur dioxide group from the sulfene will leave, and the methylene group (which has two unshared electrons, and which can be represented as either H2C : or-CH2-) will react with the double bond, in a way that generates a triangular structure, as shown in FIG. 7. If the reagent with the double bond comprises ethylene, the triangular product will be cyclopropane, which is useful and valuable because it is highly reactive, due to the fact that its bonds are stressed at 60 degree angles in a planar structure (by contrast, the conventional bond angle in alkane molecules is 109.5 degrees).
If a limited and appropriate amount of energy is put into cyclopropane, the cyclopropane can overcome a transitional energy barrier and undergo an isomerization reaction, as shown in the lower portion of FIG. 8, to form propylene (also called propene), H2C=CH-CH3. This is a valuable olefin, useful for making polypropylene and other plastics and polymers. Since propylene is larger and heavier than ethylene, it is less volatile, and more inclined to behave as a liquid rather than a gas, at temperatures and pressures that can be achieved more easily and at less expense than required for ethylene.
Propylene can be stored and transported as a liquid, using tanks that can operate at lower operating pressures and/or warmer temperatures than required to store or transport ethylene as a liquid. Therefore, ethylene-to-propylene conversion, using sulfene as shown in FIG. 7, may have important commercial implications.
Alternately, cyclopropane can be reacted with water, in a manner that breaks one of the stressed triangular bonds, in a way that creates propyl alcohol (also called propanol).
This reaction can be referred to either as hydrolysis (since one of the carbon-carbon bonds is broken), or as hydration (since the components of a water molecule are being added to the cyclopropane). Propyl alcohol is a clean-burning fuel, which can be used as a gasoline additive or substitute with higher energy content than methanol or ethanol, and it has other valuable uses as a chemical feedstock, skin disinfectant, etc.
Prior to these discoveries and disclosures, sulfene has not received any close or careful attention by chemists, for three main reasons: (i) it is highly reactive, unstable, and short-lived; (ii) it is very difficult to store or transport, and, (iii) it was difficult to synthesize, and the known methods created serious problems of toxic and hazardous wastes.
However, if efficient and economic methods for manufacturing sulfene from stranded methane (which currently is being wasted and destroyed in huge volumes, every day) are made available by the discoveries and disclosures of the Applicant, sulfene will deserve and receive much more attention and analysis.
In particular, sulfene can be regarded and used as a dipolar compound that has both "super-nucleophile"and"super-electrophile"traits. This gives it an exceptionally potent ability to react with double bonds, in ways that can avoid the destruction and elimination of the double bonds.
Indeed, in addition to regarding sulfene as a dipolar compound (due to the differences between the CH2 component and the SO2 component), a methylene radical, by itself, can be regarded as a dipolar and bi-functional agent that is both a super-nucleophile, and a super-electrophile. On one level, a methylene radical has two extra and unpaired electrons exposed on its surface, and those electrons will aggressively seek out and bind to the positively-charged nucleus of another carbon atom. That makes methylene radicals highly potent nucleophiles. However, at the same time, a methylene radical is missing two electrons from its valence shell, and it will aggressively seek out and bind to an electron- rich structure which can help it fill those gaps (such as a double bond, in an olefin molecule). That makes methylene radicals highly potent electrophiles.
These combined traits are believed to make sulfene a highly potent"methylene transfer agent", which can insert-CH2-groups into various types of compounds. In one particular type of reaction that is likely to become of scientific and commercial interest, it is believed that sulfene will be able to insert methylene groups into olefins, without destroying the double-bonded constituents of the targeted olefins. As such, it is believed to be able to convert propene into butene, butene into pentene, pentene into hexene, etc. , by chain-lengthening reactions in which the sulfene is most likely to react with the electron- rich double bond, in each step of the reaction. The initial step in a"methylene insertion" reaction will create a three-membered ring, comparable to a cyclopropane molecule that has a"tail"attached to one of the three carbons. The ring having three carbon atoms (with stressed bonds, having bond angles of 60 degrees) can then be induced (such as by moderate heating) to cross a relatively low transitional energy barrier, in a way that isomerizes the three-member ring to form an"alpha"olefin, with the double bond positioned between the first and second carbon atoms in the chain. This isomerization form is believed to be preferred over a 2,3-olefin formation, because the #3 carbon atom in a three-membered ring (i. e. , the carbon atom that has a hydrocarbon"tail"attached to it) will be less electron-rich, and less likely to participate in the formation of a double-bond.
By screening and optimizing different zeolite or other porous catalyst formulations, and by manipulating the use of"seeding"compounds that can serve in a manner comparable to"condensation nuclei", this approach can be used to manufacture liquid mixtures that will be comparable to"fractions"that can be obtained by distillation or other conventional hydrocarbon processing, with sufficient quality and consistency to enable their use as gasoline or other fuels, or as fuel additives, blending agents, etc. , without requiring distillation or other purification (although distillation or other purification can be provided, if desired, to increase the purity and value of any resulting product (s) ). In some cases, it likely will also be possible to generate liquids that are sufficiently enriched in one or more dominant compounds that they can be used as chemical feedstocks, either without additional purification, or after purification by means such as by distillation, molecular sieves, etc.
It also is likely and anticipated that methods will become known and available (such as by manipulating temperature, pressure, and time conditions, catalyst formulations, and/or condensation nuclei) for manufacturing various different categories of liquid hydrocarbons, including straight-chain alkanes, branched alkanes, alkenes (also called olefins), cycloalkanes and cycloalkenes, aromatics, and possibly even substituted hydrocarbons (such as halogenated or oxygenated derivatives, etc.).
As a demonstration of that potential, some of the initial tests carried out to date, described in Example, indicate that under some conditions, methane reagents that have passed through MSA and then sulfene intermediates have generated liquid hydrocarbon mixtures that qualify as naphtha-type mixtures (generally defined as a crude oil fraction that can be obtained by distillation, containing molecules within the C4 through C12 range).
This result indicates that this approach may offer the most efficient and economical method ever discovered to date, for converting methane gas into liquid hydrocarbons that can be used for high-quality gasoline or other fuels, or for chemical feedstocks (which can be especially valuable if a double bond remains present in the hydrocarbon molecules).
In addition, early tests involving different conditions, described in Example indicate that under some conditions, sulfene-containing preparations can generate solid polymeric materials. Such plastic and/or polymeric materials, when manufactured in this manner at methane-producing sites, have a wide range of uses; for example, they can be stored and transported in particulate form, in ways that allow them to be melted and molded into desired shapes, at a factory.
Because of the reactivity of sulfene, it is likely that most commercial-scale reactions involving sulfene will generate a mixture of products, rather than a single relatively pure product. However, various types of separation processes (such as distillation, centrifugation, molecular sieves, etc. ) can be used to separate mixed product streams into relatively pure product fractions, if desired. Accordingly, preferred product mixtures or purified product streams will depend more heavily on economic factors and preferences than on technical constraints. It should also be noted that the presence of a substantial quantity of cyclopropane and/or propene, in a liquid or gaseous mixture that also contains ethene, is likely to lower the vapor pressure of the ethene, in ways that will make it more efficient and economic to transport a mixture in liquid form. Similar effects occur with other hydrocarbons, including"liquified natural gas" (LNG) mixtures, in which butane and/or pentane effectively help to"solubilize"propane in a liquid mixture. This allows large quantities of propane to be stored and transported, in LNG mixtures, at pressures substantially lower than would be required for propane alone.
Therefore, the ability to use sulfene in various types of chemical synthesis and manufacturing operations, and the economic, technical, and commercial possibilities that will become available if reactions that pass through sulfene as a reactive and unstable intermediate can be efficiently and economically carried out in large quantities by the methods disclosed herein, appear to have the potential to open up a number of new pathways and fields, in organic chemistry. These options and opportunities will merit careful evaluation, after the disclosures herein have been revealed to chemists who are skilled in these branches of organic chemistry.
YLIDES AND CARBANIONS Chemists interested in sulfene chemistry should understand (or at least study) compounds called ylides and ylids, and so-called"Wittig reactions" (named after Georg Wittig, a German chemist who won the Nobel Prize in 1979).
A complete analysis of ylid and ylide chemistry is beyond the scope of this application; however, they are discussed in detail in various review articles (e. g. , Li et al<BR> 1997 and Lakeev 2001), and full-length books (e. g. , Trost 1975, Clark 2002, and Bertrand<BR> 2002).
Very briefly, ylides and ylids that are of interest herein will have a"carbanion", a term that combines"carbon"with"anion". This refers to what is, in effect, a carbon atom with an unshared electron pair. This unshared electron pair is created by positioning the carbon atom next to a positively-charged"hetero-atom", which will donate one of its electrons to the carbon atom (a more complete description of this electron shift requires an analysis of electron valence shells, "p"and"d"orbitals, pi bonding, etc. ). In most cases of commercial interest, the heteroatom will be sulfur, nitrogen, or phosphorus, although some chemists regard oxygen as also having sufficient strength to form compounds that can behave as ylides under at least some conditions).
Ylides and other compounds that contain negatively-charged, electron-rich "carbanions"are relevant to the manufacture of olefins, for the following reason: if two molecules that contain electron-rich"carbanions"react with each other, the electron-rich "carbanions"in the reagent molecules are likely to form an electron-rich double bond, between the two carbon atoms, in a new molecule created by the reaction, while the positively-charged heteroatoms act as leaving groups.
Examples of ylide chemistry are discussed in Corey et al 1965, which addresses two particular ylides: dimethylsulfonium methylide, (CH3) 2S=CH2, and dimethyloxosulfonium methylide, (CH3) 2S (O) =CH2 (the parentheses around the oxygen atom, in the oxosulfonium ylide, indicate that the oxygen is double-bonded to the sulfur atom, rather than being positioned between the sulfur and carbon atoms). In both of those ylide compounds, the bond between the sulfur atom and the carbon atom can be written in any of three ways (often called"canonical"forms, comparable to a musical piece such as"Pachelbel's Canon", in which the same melody is played repeatedly, but in slightly different ways).
One written version depicts a standard double bond, such as RR2S=CH2. A second written version depicts a single bond with charge indicators, RlR2S+-C-H2. A third written version combines those two formats, and depicts a double bond with charge indicators, R, R2S+=C H2 The term"resonating structure"is often used to describe electron configurations that cannot be cleanly represented as one particular form. Most commonly, resonating (or resonant) electron structures can have either or both of: (i) two distinctly different forms which will shift back and forth, to coexist with each other, in equilibrium; or, (ii) a quasi- stable intermediate form, located somewhere between the two ends of the continuum, and having some combination of mid-point properties. Resonating electron structures are fairly common in chemistry, and are used to explain a wide variety of semi-stable molecules, including carbon monoxide, sulfur dioxide, and molecules that shift back and forth between "tautomeric"forms (such as sugar molecules, which shift back and forth between rings, and straight chains).
One set of teachings in Corey et al 1965 is worth noting. When Corey et al used the reagents described in the lower right column of page 1363 to synthesize dimethylsulfonium methylide (which Corey et al described as CH3) 2S'== C-H2, shown as compound XIII in the left column of page 1356), the temperature of the reaction mixture rose slightly, and released a gas, most of which evolved within 5 minutes. That gas was passed through a bromine solution, and the resulting gas was analyzed and found to be ethylene dibromide.
This indicated that the gas, released by spontaneous exothermic decomposition of Corey's methylide compound (which contained the S+=C-ylide structure) was ethylene, and the dimethylsulfide group of the ylide compound acted as a leaving group. That report provides additional support for the assertion that sulfene will spontaneously react with itself, in a way that releases ethylene.
The disclosures herein also suggest that dewatering of other alkane-sulfonic acids (such as ethanesulfonic acid, propanesulfonic acid, etc. ), using agents and methods such as described above to create sulfene analogs or other ylide compounds, can provide useful approaches to manufacturing other types of longer and heavier olefins.
Accordingly, the disclosures herein can be combined with additional disclosures (already published in the art) involving ylides, ylids, and Wittig reactions, in ways that will enable commercial and industrial adaptation of sulfene and sulfene-analog chemistry for use with additional types of ylids and ylides, in ways that will become apparent to those skilled in that particular field of chemistry, after they have analyzed and evaluated the disclosures herein.
"OUTER"ANHYDRIDES Analysis of another article (Karger and Mazur 1971, entitled, "Mixed sulfonic- carboxylic anhydrides: I. Synthesis and thermal stability. New synthesis of sulfonic anhydrides") suggested to the Applicant herein that certain additional processes might also be involved (or might be created, by controlling reaction conditions) in the formation of sulfene from MSA, and in subsequent polymerization reactions involving the sulfene.
Karger and Mazur worked with MSA (which is listed as their formula CH3SO3H a number of times, such as in their Tables I and II on page 530); however, they were combining MSA with various acid chloride compounds, in ways that displaced the chloride moieties and created various ether and/or ester linkages in the resulting anhydrides. One passage on page 531 is worth particular attention. It reports, "Thus, methanesulfonic anhydrides decomposed only above 250°" (it should be noted that that phrase is ambiguous; it may refer to only those anhydrides that would decompose only above the 250°C temperature, or it may refer to all anhydrides, if treated at temperatures above 250°C)"to give methanesulfonic acid (70%), residual intractable polymer (15%), and sulfene which presumably did not survive its conditions of generation (equation 8). "Their equation 8 was: CH3SO2oSo2CH3---> CH3SO3H + (CH2=SO2) at 250°C.
Two reaction pathways that offer candidate mechanisms for explaining the formation and then destruction of the MSA"outer anhydride"are shown in FIG. 8. The first reaction in FIG. 8 shows a condensation step involving two molecules of MSA, which creates an "outer anhydride"of MSA (shown as the starting reagent in Karger's Equation 8) while releasing a molecule of water. To create this condensate, the sulfate group on a first molecule of MSA releases a hydrogen proton, and the sulfate group on a second molecule of MSA releases a hydroxy group. These two reactions join the MSA residues together through a single-bonded oxygen linkage, which can be regarded as an ether bond (or thioether bond, since the oxygen atom links two sulfur atoms), or as an ester (or thioester) bond, since the sulfur atoms also have double-bonded oxygen atoms. Presumably, this reaction can be promoted by dehydrating agents such as mentioned elsewhere herein, and in various passages in Karger et al 1971.
In Step 2 in FIG. 8, which likely will occur only at relatively high temperatures, the "outer anhydride"molecule rearranges. This reaction is postulated to involve: (i) release of a hydrogen proton from the methyl group of the anhydride; (ii) migration of the electrons from the C-H bond over to the C-S bond, thereby forming a double bond; and, (iii) breakage of the S-O linkage, in the presence of protons in the acidic MSA solution. It is possible but not especially likely that the same hydrogen proton from a particular molecule will bond to the oxygen atom from an S-O linkage that is being broken in that same molecule. In addition to generating sulfene, as shown in FIG. 8, the rearrangement in step 2 also regenerates and releases a molecule of MSA.
It is also worth noting that because of how the"outer anhydride"breaks apart, it might be useful as a radical initiator compound, to trigger the conversion of methane into methyl radicals, during the processing that converts methane into MSA as shown in FIGS.
1 and 2. If the"outer anhydride"compound is broken apart by means such as passing it across a heating element in a device such as"radical gun", it may release at least one and possibly two"strong radical initiator"compounds that can efficiently remove hydrogen atoms from methane. This possibility is especially interesting because its products may be able to reform MSA, rather than creating a sulfuric acid waste, which will be created if Marshall's acid is used.
Additional comments on sulfene formation, and on Karger et al 1971, are provided in King and Rathore 1991. Those comments, while focusing on different aspects of the chemistry (such as IR spectroscopy of sulfene at low temperatures) are nevertheless believed to be consistent with all disclosures and postulated mechanisms herein.
POLYMERIZATION AND DENDRIMERS As mentioned above, one comment made in passing by Karger et al 1971 reported, on page 531, "a black intractable polymeric solid, which gave no acid reaction on boiling with water, was the only nonvolatile product". The yield of Karger's polymer was low (15%), their compound was never analyzed, and it clearly did not teach or suggest any practical way to manufacture a commercially viable polymer. Their publication occurred more than 30 years ago, and it never led to any commercialization.
However, the discoveries and disclosures of the Applicant herein appear to be approaching a point where practical and efficient methods can now be disclosed for manufacturing various types of polymers from methane, via MSA and MSA anhydrides. In particular, the Applicant herein believes and anticipates that polymeric material can be created by repeated insertions of methylene groups (-CH2-) into growing carbon chains, as indicated in FIG. 9. It is possible that methylene groups can be inserted into the carbon- sulfur bond, shown in the MSA molecule that serves as the starting point for the chain- lengthening reaction; however, computer modeling indicates that the more likely point of insertion appears to be at a carbon-hydrogen bond in the methyl group.
Regardless of which bond provides the particular insertion site, a hard polymeric compound was indeed observed, when the"outer anhydride"of MSA (purchased in crystalline form, from Aldrich Chemicals) was heated to a temperature higher than 250°C, under nitrogen gas. The decomposition created both a clear liquid, and a black solid. Both the liquid and the residue were chemically analyzed. The clear liquid was found to consist mainly of MSA and cycloalkanes. The black solid was found to contain cyclic hydrocarbons, naphthenics, and a relatively high quantity of aromatic structures. Some of the aromatic rings were bridged by sulfonate or methylene bridges, and some of the aromatic rings had cyclopropane rings attached to them.
Based on those results combined with other teachings herein, it is believed and anticipated that practical means for making commercial quantities of hydrocarbon liquids that can be used as fuels, and possibly as chemical feedstocks, can now be identified and developed, using pathways that pass through MSA, MSA esters, and/or MSA anhydrides, by using steps that include the following: a. creating a preparation that contains sulfene and/or MSA outer anhydride, mixed with a suitable solvent having a boiling point higher than the decomposition temperature of the sulfene or sulfene-containing starting material (dimethyl sulfoxide offers one candidate for early evaluation, and other solvents with higher boiling points are known); and, b. heating the preparation, while bubbling nitrogen gas up through it at rates that will remove the desired products as they are being formed, without allowing them to continue to rearrange until they form aromatic rings.
In addition, it is believed and anticipated that practical means for making commercial quantities of solid polymers can now be identified and developed, using pathways that pass through MSA and MSA anhydrides, by using steps that include the following: a. creating a preparation that contains (i) sulfene and/or MSA outer anhydride, and (ii) any other desired starting reagent (such as a styrene precursor, acrylate precursor, vinyl precursor, etc. ), in a suitable solvent having a boiling point higher than the decomposition temperature of the starting mixture; and, b. subjecting the preparation to a"cooking"reaction (i. e. , involving a controlled temperature-pressure-time combination) that forms a desired solid, while bubbling an inert gas (such as nitrogen or CO2) through the mixture at rates that are sufficient to remove the desired products before they form aromatic rings.
In either type of system, the use of solvents with boiling points that are well above the heating temperatures being used, combined with the use of gas"sweep"systems to promptly remove desired products in gaseous phase as they are formed, provides a useful and flexible means for controlling the reactions.
On the subject of reactions that can create hydrocarbon chains by insertion of methylene groups, a report by Michalak and Ziegler 2003 should also be noted. This report indicates that branched polymers can be created, in controllable manners, by using certain types of catalysts, such as nickel-diimine or palladium diimine.
This approach to controlling the branching of hydrocarbon chains that are being formed has a number of important commercial implications. One application worth noting relates to the manufacture of liquid fuels having higher energy density per volume, as well as higher quality (including higher"octane"ratings, for gasoline). These aspects, involving increased value and utility, arise from two facts. First, in a hydrocarbon liquid, molecules that have some degree of branching tend to fit together better (allowing greater weight per volume) than entirely linear molecules. Second, molecules that have some degree of branching are not as long as straight-chain molecules, for a given number of carbon atoms, and there is less chance that the"far end"of some particular molecule will be pushed away, in unburned form, when one of the molecules goes through rapid and explosive but imperfect combustion. As an illustration of this phenomenon, the molecule with the gold- standard"100"octane rating is 2,2, 4-trimethyl pentane, rather than straight-chain octane.
Other potential applications (including the manufacture of various types of plastics and polymers, including isotactic, atactic, or other"designed"polymers) will be recognized by those skilled in the art, after they have studied the properties and potentials of sulfene as a methylene transfer agent.
Two additional classes of reactions also should be noted, involving C=O double bonds, generally referred to as carbonyl bonds or groups. If sulfene transfers a methylene group into an aldehyde group (i. e. , a carbonyl group located at the end of a carbon chain)<BR> or into a ketone group (i. e. , a carbonyl group located in the middle of a carbon chain), the insertion will create a three-membered oxirane or epoxide ring, which will include the carbon atom that had the carbonyl group. Epoxide and oxirane rings are unstable and reactive, due to their stressed bond angles. This makes them useful reactants in certain types of chemical processing, if they can be used rapidly after they are generated, before they have time to spontaneously decompose.
It should also be noted that sulfene may become useful in modifying the surfaces of various types of silicate materials that will have special properties or uses following such treatments. Examples of such candidate uses include semiconductors, and an emerging category of materials that are creating new types of interfaces and interactions between biological materials (such as antibody fragments or other proteins, DNA segments, etc.) and nonbiological materials, for purposes such as diagnostic, therapeutic, or other analytical, processing, medical, or other physico-chemical uses. Anyone interested in this category of uses should study Lie et al 2002, including passages such as the first full paragraph on page 116, which discusses the formation of direct silicon-carbon bonds rather than silicon-oxygen-carbon linkages, and the last paragraph in column 1 of page 117, which discusses the possible insertion of methylene groups (-CH2-) into silicon-silicon bonds.
"UPSTREAM"OPTIONS AND ENHANCEMENTS In addition to the discussion of synthesis and use of MSA and its esters and anhydrides, in the foregoing sections, this application also contains a number of teachings on other aspects of the overall system. As described near the start of the"Detailed Discussion"section, these disclosures are intended to help ensure that any and all "disclosure of the best mode"requirements for valid patents are satisfied, since they relate to improved ways for designing and operating complete and functional systems that can take methane gas all the way to liquid fuels, olefins, polymers, and other valuable compounds.
The disclosures in this subsection relate to"upstream"processing, i. e. , steps that help promote the synthesis of MSA, the crucial intermediate, from methane. These "upstream"options and enhancements include the following: (1) It is believed and anticipated that if carbon dioxide (CO2) is pressurized to a point that causes it to become a supercritical liquid, it may be able to increase the solubility of methane gas, in a liquid solution of S03 and MSA. If this is confirmed in continuous- flow testing, the use of supercritical liquid COZ may be able to increase and improve the mass transfer rates that will transfer gaseous methane into a liquid solution. This may be able to increase the speed and efficiency of the reaction that converts methane into MSA.
(2) It is believed and anticipated that it may be possible to adapt either the inner anhydride of MSA (i. e. , sulfene), or the outer anhydride of MSA, for use as a radical initiator compound, instead of Marshall's acid or various other radical initiators that will generate acidic waste byproducts. Briefly, a radical initiator compound that can efficiently remove a hydrogen atom (both a proton, and an electron) from methane, thereby converting the methane into a methyl radical, H3C*, is necessary to launch the chain reaction that will convert methane into MSA, as shown in FIG. 2. As described above, sulfene can release methylene radicals. These radicals can be regarded as"double-strong"radicals, since they have not just one, but two unpaired electrons.
When a methylene radical (with two unpaired electrons) reacts with methane, the "double-strong"methylene radical is likely to remove a single hydrogen atom from methane. This will balance out the two molecules, making them equal, thereby creating two methyl radicals, H3C*. Each of these methyl radicals will be able to combine with sulfur trioxide, SO3, to form MSA radicals, as shown in FIG. 2, and the MSA radicals will then remove hydrogens from fresh methane, to form stable MSA while creating new methyl radicals that will keep the chain reaction going.
Accordingly, if sulfene (in gaseous, mist, or similar form) can be injected into a methane stream, it may be an effective and useful radical initiator compound, which may eliminate or reduce the need for Marshall's acid, halogen gases, or other compounds that would likely create acidic wastes.
If desired, an MSA anhydride can be pumped out of a device (which can be called a "radical gun") having a nozzle that contains a very hot electric filament or other heating element (which can be embedded in a quartz tube or other protective device, if desired) that will break apart the radical-releasing molecules as they pass across the heating element.
These types of devices are described in numerous articles, including Danon et al 1987, Peng et al 1992, Chuang et al 1999, Romm et al 2001, Schwarz-Selinger et al 2001, Blavins et al 2001, and Zhai et al 2004. Similar devices can be constructed and tested, which will pass a selected radical-releasing compound through a nozzle or other component having a zone that is subjected to high levels of ultraviolet, tuned laser, or other radiation (or, indeed, any other form of energy input).
(3) One or more types of borate compounds (such as trimethyl borate, or borate anhydride), if properly utilized in the MSA reactor vessel, may be able to help promote the synthesis of MSA, mainly by reducing unwanted S03 reactions (such as the formation of CHX (SOy),, H polymers and other species, where x, y, and n are variables). In addition to helping to minimize and prevent the formation of unwanted methyl-sulfonate species, the borate compound can also help maintain S03 molecules in their aplha and gamma forms, which can help improve the overall conversion of S03 to MSA. Such borate compounds can be coated onto immobilized or particulate surfaces, to ensure that they remain inside the MSA reactor.
(4) If quantities of both liquid and gaseous S03 are pumped into the MSA reactor vessel (either separately, through different inlet nozzles, or in a mixed and entrained stream, or in any other suitable manner), the mixed liquid and gas streams may be able to react with methane gas, in the liquid/gas mixtures and interfaces that will be present inside the reactor, in ways that will increase the rates of MSA formation.
(4) It may be possible to use methods for breaking apart a radical initiator (such as Marshall's acid), using methods such as photolysis, in ways that create or preserve certain types of electron"spin"in the two radicals that are formed when the radical initiator breaks apart. This is analogous to creating one radical with an electron having a"right-handed" spin, while the other radical has an electron with a"left-handed"spin. This can be important, because two right-handed radicals cannot recombine with each other, and two left-handed radicals cannot recombine with each other, in ways that would reform the initiator and"quench"it as a radical. In other words, a left-handed spinning radical must combine with a right-handed spining radical, to recombine. This approach suggests useful methods (such as continuing to shine light having a radical-breaking wavelength) into an MSA reactor vessel), through one or more transparent panels in one or more walls of the reactor.
By contrast, breakage of a radical initiator by means such as heating provides less of this useful effect, and allows radicals to recombine more readily.
These factors are discussed in more detail under the term"solvent cage"effects, in various chemical articles. If those factors are recognized and understood, they can be put to good use in the systems disclosed herein.
(5) It may be possible to create MSA, in bulk quantities, by using one or more types of surface-active radical initiators, comparable to the immobilized catalytic compounds described by Barteau 1996 (for the formation of ketene, as described in the Background section) or described herein, in the passages on candidate pathways for making sulfene.
This approach is supported by those teachings, combined with the additional teachings of Lie et al 2002, which is entitled, "Photochemical reaction of diazomethane with hydrogen- terminated silicon surfaces", describing work done in the laboratories of Benjamin Horrocks and Andrew Holton, at the University of Newcastle upon Tyne, in Great Britain.
The Lie et al 2002 article describes highly complex and sophisticated chemistry that was done using light-activated molecules on silicon surfaces. Thus type of photo-catalyzed chemistry is used to create the extraordinarily tiny circuitry in integrated circuits, and there is no reason to suspect or assume that this class of chemistry could be adapted and converted into efficient methods for mass-manufacture of liquid chemicals, at the scales involved in methane conversion.
Nevertheless, various factors discussed herein led the Applicant's to carefully study various articles on chemical treatment of semiconductor surfaces (such as Barteau 1996 and Lie et al 2002), and those articles triggered several insights by the Applicant, into ways that certain chemical reactions and pathways used in preparing semiconductor surfaces might be adapted and expanded to enable the handling and processing of bulk liquids, such as methane, MSA, and sulfene.
In particular, certain passages in Lie et al 2002 (especially a passage that begins with the first full paragraph in column 2 of page 113) state or imply that certain types of radical species can be generated, at or near the surfaces of silicon-containing materials, when compounds such as diazomethane are activated by using certain conditions (mainly involving ultraviolet light radiation, when semiconductor manufacturing is involved). Those passages, combined with additional teachings in Barteau 1996 and other articles, have suggested to the Applicant that if certain types of solid materials are surface-treated in certain ways, the resulting surface-treated supports may be able to function as efficient removers of hydrogen atoms (both protons and electrons) from lower alkyl molecules such as methane, or from other compounds (such as azomethane, sulfene, ketene, etc. ) that can<BR> subsequently function as"strong radical initiators" (i. e. , compounds that can efficiently remove hydrogen atoms from methane or other lower alkanes). This would generate methyl radicals, in quantities that may be able to initiate the methane-to-MSA conversion reaction shown in FIG. 2, without requiring a slow and steady input of radicals from a radical initiator compound such as Marshall's acid or a halogen gas.
Accordingly, this approach offers a promising candidate pathway for use as disclosed herein. Those skilled in this field of art can better understand and evaluate these comments if they study Lie et al 2002, Barteau 1996, and other published works cited by those authors, especially including the items cited as footnotes 22,33-34, and 41-52 by Lie et al.
IMPROVED CONVERSION OF SO2 INTO S03 The process illustrated in FIG. 2 pumps S03 into an MSA-forming reactor, and removes SO2 from an MSA cracker. To keep that sulfur cycle running, SO2 that emerges from the MSA cracker to be oxidized back into S03. While that is a well-known process, used at numerous facilities aorund the world, the volumes that will be involved, in methane-to-methanol conversion, are likely to dwarf any SO2 oxidizers that have ever been builf. As mentioned in the Background section, roughly $100 million worth of methane is wasted by flaring or reinjection, every day. Those are huge volumes of methane, and correspondingly huge volumes of SO2 will need to be converted into S03, every day. To illustrate the volumes involved, it has been estimated that the volume of SO2 to S03 conversion to handle the methane gas output from even a single large oil field, in the Middle East, will require an SO2 to S03 processing facility that is roughly five times larger than the largest facility that currently exists anywhere in the world.
Accordingly, this application discloses what is believed to offer potentially important improvements, not just over standard V205 systems, but also over several items of recent art that offer their own improvements over V205 systems. Accordingly, this aspect of the invention requires a brief overview of several recent advances in SO2 to S03 processing.
One major set of advances relates to using relatively small"monolith"catalysts, rather than large towers, for SO2 to S03 conversion. As described elsewhere herein, monoliths are hard but porous materials with essentially linear and parallel flow channels, usually ranging from about 100 channels per square inch (cpsi) for liquids, up to 1000 or more cpsi for gases. Their use in SO2 to S03 conversion is described in patents such as US 5,264, 200 (Felthouse et al 1993). Other materials that can provide solid supports for catalytic materials include woven glass fibers (e. g. , Bal'zhinimaev et al 2003), and zeolite-<BR> type porous materials (e. g. , US patent 6,500, 402, Winkler et al 2002). Other relevant patents that address fluid-handling and heat-exchanging machinery include US 6,572, 835 (MacArthur et al 2003).
Another interesting research lead involves the use of activated carbon as a catalyst, as described in US 6,521, 200 (Silveston et al 2003). One interesting aspect of that work is its assertion that SO2 to S03 conversion can be carried out at relatively low temperatures, ranging from room temperature up to about 60°C. It should be noted that room temperature conversion of SO2 to S03 was initially described in Davtyan 1955 (published in Russian), and subsequently in Hartman et al 1972.
Accordingly, those publications indicate that improved methods and catalysts already have recently been discovered, mainly in academic laboratories and small companies, for conversion of SO2 to S03. However, those recent advances have not yet been widely noticed or adopted by industry, presumably because of two clusters of reasons. The first set of reasons centers on the fact that a large network (or"base") of existing V205 systems already exists, and has been running for years. People and companies already know how to keep those systems running, and if a system suffers an upset, local operators and available experts know how to get it running again, quickly. Replacement of those existing systems, and training people not just to run them but also to diagnose and correct any upsets and malfunctions, would be very expensive. The second cluster of reasons centers on the fact that the SO2 to S03 reaction is highly exothermic. Since it releases a lot of heat and energy, which can be captured and used for steam generation or other useful purposes, there has been no motivation or incentive for industrial companies that already own and ru vos systems to invest in other systems that might be smaller, faster, or more efficient.
However, that situation will change dramatically, with the advent of a new process for converting methane to methanol in huge quantities, using methods that will require equally huge quantities of SO2 to be oxidized to SOg. Accordingly, the disclosure of new methane conversion systems will require a careful reappraisal of the best recently-identified technology for oxidizing SO2 into S03.
As part of that reappraisal, the Applicant herein discloses what may offer another potentially important advance in high-efficiency conversion of SO2 into S03. This disclosure is based on computer modeling which indicates two potentially important results.
First, a new class of vanadium catalysts, including vanadium diformate and halogenated analogs of vanadium diformate (such as vanadium fluoro-or perfluoro- diformate, in which some or all of the hydrogen atoms have been replaced by fluorine atoms), may be able to offer a better catalytic pathway from SO2 to S03, using steps and intermediates such as illustrated in FIG. 10.
Accordingly, it is disclosed herien that vanadium formate catalysts (or any other vanadium catalyst) can be coated onto activated carbon, for use (which may include low temperature use) in converting SO2 to S03. In addition, reports by others (Fonseca et al 2003, which involved adsorption rates of SO2 from exhaust gases) suggest that the presence of a vanadium catalyst, on activated carbon, can increase the adsorption of SO2 onto the catalytic surfaces, compared to activated carbon surfaces without vanadium. Accordingly, the disclosures herein, involving improved vanadium diformate catalysts on activated carbon, are believed capable of providing substantial improvements in rates and efficiencies. This type of processing preferably should be carried out in an aprotic medium, where the solvent has a low dielectric constant, such as supercritical CO2, to help promote rapid desorption of S03 away from catalytic sites, and to prevent the hindrance of vanadium catalytic sites, as can occur with solvents having higher dielectric constants.
Other catalyst formulations that may deserve to be reevaluated, in light of the approaching demand for improved ways to convert SO2 to S03 in methane conversion systems, are described in US patent 2,418, 851 (Rosenblatt et al, 1947), which disclosed that mixtures of platinum and palladium were substantially more effective than either metal by itself in converting SO2 to S03, and in US patent 6,500, 402 (Winkler et al 2002), which discloses that relatively inexpensive iron catalysts can be used to convert SO2 to S03 at temperatures greater than 700°C, which is higher than can be withstood continuously by most soft and/or noble metals. Although the highest reported yield in US 6,500, 402 was 77 % (see Table 1, in column 3), that yield may be sufficient for operations as described herein, if the SO2 and S03 output streams are separated, and if unreacted SO2 is returned to the reactor for another pass. Alternately, that type of"first-pass"processing may be able to get most of the work done in a relatively inexpensive manner, in ways that can be followed and supplemented by"polishing"steps that will take the outputs to higher levels and percentages using smaller quantities of more expensive catalysts.
These types of catalysts should be evaluated for use in conventional towers, in smaller monolith reactors, in packed and fluidized beds, and in any other type of processing vessel or reactor that may be of interest. They can be evaluated at any desired temperature, and either with or without supercritical carbon dioxide as a solvent.
The preferred choice of operating parameters (which will include a chosen operating temperature, and any heat exchangers or other subsystems that may be used tp actively remove heat from the SO2 to S03 conversion reactor) will be determined by economic rather than technical factors. If a system is run at a relatively low temperature, it can be cooled by using seawater or other means that may be available at that site.
However, it should also be noted that if an SO2 to S03 conversion reactor is run at a higher temeprature, the heat it generates may be useful, for heating MSA from a relatively cool formation temperature (such as roughly 50°C), to a much higher cracking temperature (which is likely to exceed 250 or 300°C).
Accordingly, SO2 catalytic oxidation reactors that are run at high temepratures can be placed inside tubular structures, which can be surrounded by annular or other flow channels that will carry liquid MSA, preferably in a counterflow direction. This can provide an efficient heat exchange mechanism, allowing heat that is released by SO2 oxidation, inside the inner reactor tube, to be transferred to the MSA liquid in the annular space, to heat the MSA liquid up to cracking temperatures.
Accordingly, FIG. 11 is a schematic depiction of a system for converting S02 to S03, using: (i) an oxidizing reactor that contains a catalyst on a monolithic, fiberglass, or other porous support; (ii) a heat exchanger that allows heat from the SO2 to S03 reaction to heat MSA from its formation temperature (about 50°C) to its cracking temperature (more than 300°C) ; (iii) an S03 condenser, to allow liquid S03 to be collected and pumped back into the MSA reactor; and (iv) a device for separating SO2 from remnants of the air that was used as an oxygen source, allowing purified SO2 to be returned to the catalytic reactor for another conversion pass.
EXAMPLES EXAMPLE 1: MAKING AND CRACKING MSA Methods and reagents used to make Marshall's acid and MSA in laboratory conditions, using a batch reactors, have already been described in PCT applications PCT/US03/035396 (published in May 2004 as WO 2004/041399) and PCT/US04/019977, both filed by the same Applicant herein. Therefore, those descriptions will not be repeated herein.
To crack MSA in a manner that releases methanol and SO2, nitrogen gas (N2) at a flow rate of 6 to 8 mL/second was passed through a gas bubbler containing 10.0-15. 0 g of MSA at 120-140°C. The outlet of the bubbler was connected to a quartz tube with an inner diameter of 2 cm and a length of 20 cm, which (except for short inlet and outlet segments) passed through a furnace In various different tests, the tube was either empty, or a 10 cm length of the tube was loaded with 4 to 8 mesh zeolite beads (Davison Chemicals, code number 54208080237). The outlet of the tube was connected to two bubblers, each containing 5.0 g of D20 (i. e. , water containing the heavier deuterium isotope of hydrogen, for analysis using H-nuclear magnetic resonance) at 4-6°C, for trapping any emerging liquids.
When the tube did not contain zeolite packing, significant quantities of the methyl ester of MSA (a byproduct that was unwanted, in these particular tests) were obtained.
However, when zeolite packing was provided in the tubes and the furnace was run at 385°C, the yield of methanol increased greatly, and reportedly approached 100%.
EXAMPLE 2: SYNTHESIS OF ETHYLENE AND LIQUID ALKANES ON HYDROXYLATED SILICATE MONOLITH The Applicant purchased (from Vesuvius Hi-Tech Ceramics) the same type of"low surface area reticulated silica monolith"described in Barteau 1996, and processed an MSA preparation (purchased from Aldrich Chemical) on it, using reflux temperatures for several hours. Analysis of the gases that emerged from the refluxing liquid, using lH-NMR, 13C- NMR, and gas chromatography, indicated that the gases contained ethylene, and liquid alkanes.
The presence of those compounds in those gases indicated that: (i) when MSA is processed on a suitable activated surface, it can pass through intermediates that will create olefins (such as ethylene) and higher alkanes; (ii) the postulated mechanisms and molecular rearrangements described herein have received experimental support; and, (iii) methods for creating olefins and alkanes from MSA can indeed be provided, by one or more pathways that apparently use MSA anhydride intermediates, apparently including sulfene.
EXAMPLE 3: DECOMPOSITION OF MSA OUTER ANHYDRIDE The Applicant purchased the MSA"outer anhydride"compound, in crystalline form, from Aldrich Chemical. In a reaction beaker, it was heated until the crystals melted and then began to form a clear liquid over a black solid. The liquid and the solid were analyzed, using lH-NMR, l3C-NMR, and gas chromatography. The results indicated that the clear liquid consisted mainly of MSA and cycloalkanes. The black solid was found to contain cyclic hydrocarbons, naphthenics, and a relatively high quantity of aromatic structures. Some of the aromatic rings were bridged by sulfonate or methylene bridges, and some of the aromatic rings had cyclopropane rings attached to them.
Those results provide experimental support for various postulated mechanisms and molecular rearrangements described herein, and confirm that methods for creating olefins, alkanes (including cycloalkanes), and aromatics from MSA can be provided, by one or more pathways that apparently use MSA anhydride intermediates.
Thus, there has been shown and described a new and useful means for synthesizing higher alkanes from methane, via pathways that involve MSA and MSA anhydrides, and there have also been disclosed various addiitonal enhancements in this system. Although this invention has been exemplified for purposes of illustration and description by reference to certain specific embodiments, it will be apparent to those skilled in the art that various modifications, alterations, and equivalents of the illustrated examples are possible. Any such changes which derive directly from the teachings herein, and which do not depart from the spirit and scope of the invention, are deemed to be covered by this invention.
REFERENCES <BR> <BR> Basickes, N. , et al, J Am Chem Soc 118 : 13111 (1996)<BR> Blavins, J. J. , et al, J Org Chem 66: 4285 (2001)<BR> Broekhuis, R. R. , et al, Catalysts Today 69: 887 (2001)<BR> Chuang, T. J. , et al, J Electron Spectroscopy & Related Phenomena 98-99 : 149 (1999)<BR> Danon, A. , et al, Rev Sci Instrum 58 : 1724 (1987)<BR> Dubois, D. R. , et al, Fuel Proc. Technology 83 : 203 (2003)<BR> Dunn, J. P. , et al, Applied Catalysis B: Environmental 19: 103 (1998)<BR> Gesser, H. D. , et al, Chem Rev 85 : 235 (1985) Giakoumelou, I., et al, Catalysis Letters 78 : 209 (2002) Gilbert, G. E., Sulfonation and Related Reactions (Interscience Publishers, 1965) Gilson, T. R., J Solid State Chemistry 117 : 136 (1995) <BR> <BR> Hayes, R. E. , et al, Introduction to Catalytic Combustion (Gordon & Breach Science Publ., Amsterdam, 1997) Keil, F. J., Microporous and Mesoporous Materials 29.-49 (1999) <BR> <BR> Lefferts, L. , et al, Applied Catalysis 23: 385 (1986)<BR> Li, P. , et al, Surface Science 380 : 530 (1997)<BR> Li, A-H, . et al, Chem Rev 97 : 2341 (1997)<BR> Lie, L. H. , et al,, J Phys Chem B 106 : 113 (2002) Liu, W., AIChE Journal 48 : 1519 (2002) Liu, W. , et al, Ind Eng Chem Res 41 : (2002) Liu, Z. and Liang, J., Current Opinion in Solid State and Materials Science 4 : 80 (1999) <BR> <BR> Liu, H. , et al, J Catalysis 208 : 1 (2002)<BR> Lobree, L. J. , et al, Ind Eng Chem Res 40 : 736 (2001)<BR> Mukhopadhyay, S. , et al, Angew Chem Int Ed 42 : 2990 (2003)<BR> Mukhopadhyay, S. , et al, Amer Chem Soc 2002 : A-E (2002)<BR> Muller, A. , et al, Catalysis Today 81 : 337 (2003)<BR> Olah, G. A. , et al, J Amer Chem Soc 106 : 2143 (1984) Olah, G. A., Acc Chem Res 20 : 422 (1987) Peng, X-D. , et al, Rev Sci Instrum 63: 3930 (1992)<BR> Periana, R. A. , et al, Science 259 : 340 (1993)<BR> Periana, R. A. , et al, Chem Commun 2002 : 2376 (2002)<BR> Periana, R. A. , et al, Science 280 : 560 (1998)<BR> Porcelli, R. V. , et al, Hydrocarbon Proc., March 1986 : 37 (1986)<BR> Raja, L. L. , et al, Catalysis Today 59 : 47 (2000)<BR> Romm, L. , et al, J Phys Chem A 105 : 7025 (2001)<BR> Sagawa, K. , et al, J Catalysis 131 : 482 (1991)<BR> Sassi, A. , J Phys Chem B 106 : 8768 (2002)<BR> Stocker, M. , Microporous Mesoporous Materials 29: 3 (1999)<BR> Tatibouet, J. M. , et al, J Catalysis 161 : 873 (1966)<BR> Tatibouet, J. M. , et al, Applied Catalysis 148 : 213 (1996)<BR> te Velde, G. , et al, J Comput Chem 22: 931 (2001)<BR> Won, T-J. , et al, Inorganic Chemistry 34 : 4499 (1995)<BR> Zhai, R-S. , et al, preprint downloaded from American Chemical Society website (Langmuir), 2004 Zhou, X. , et al, Chem Commun : 2294 (2003)
Next Patent: METHOD FOR THE CATALYTIC HYDROGENATION OF ALKYNE COMPOUNDS