PARTICULARLY LOWER ALKANES TO ESTERS. ALCOHOLS. AND OPTIONALLY TO HYDROCARBONS

FIELD OF THE INVENTION

This invention is a process for converting hydrocarbonaceous feeds, particularly lower alkanes, into their corresponding esters and optionally into various intermediates (such as alcohols) and optionally into liquid hydrocarbons. The hydrocarbonaceous feeds are oxidatively converted to oxy-esters at high selectivity and conversion and at practical reaction rates using at least catalytic amounts qS. certain class "B" metals and/or metal ions defined by the Pearson definition as "soft" or "borderline". Desirable catalysts comprise such metals as Pd, Tl, Pt, Hg, and Au. Mercury is most desired. If so desired, the oxy-esters may be converted to alcohols or other intermediates such as halides. The oxy-esters, alcohols, and other intermediates may optionally be converted to liquid hydrocarbons such as gasoline.

BACKGROUND OF THE INVENTION

The countries of North America currently import significant portions of their needed liquid hydrocarbons from Asia and Africa. Natural gas is abundant on the

North American continent but is often present in remote locations. Although natural gas may be liquefied and transported for subsequent use, appropriate refrigeration

and compression equipment and transportation are quite expensive. Additionally, there are few economically viable technologies available for converting gaseous hydrocarbons to higher molecular weight liquid form materials. This invention includes a highly effective catalytic step useful in converting methane and other hydrocarbonaceous feeds, particularly lower alkanes, to another, more reactive form which may then be converted to normally liquid hydrocarbons. It is generally accepted that conversion of methane into a reactive intermediate is the most difficult step in the overall conversion of methane into higher molecular weight hydrocarbons (see, for instance, A.E. Shilov and A. . Shteinman, "Activation of Saturated Hydrocarbons by Metal Complexes in Solution", Kinetika i Kataliz, Vol. 18, No. 5, pp. 1129-1145, 1977).

Several documents disclose a variety of methods for activating methane to produce other higher molecular weight materials. Mobil Oil Corporation is the assignee in several U.S. patents using sulfur or certain sulfur- containing compounds as the reactants in non-catalytic reactions with methane to produce methyl intermediates which can then be converted to higher molecular weight hydrocarbons.

In U.S. Patent No. 4,543,434, Chang teaches a process using the following steps:

CH ₄ + 4S > CS ₂ + 2H ₂ S

Co or Ni CS ₂ + 3H ₂ --> CH ₃ SH + H ₂ S

HZSM-5 CH ₃ SH > [CH ₂ ] + H ₂ S

4H ₂ S -- > 4H ₂ + 4S

where " [CH ₂ ] " is a hydrocarbon having at least two carbon atoms.

Another Mobil disclosure (U.S. Patent No. 4,864,073 to Han et al.) suggests a carbonyl sulfide- based process in which methane and carbonyl sulfide are contacted in the presence of ultraviolet light under conditions sufficient to produce CH ₃ SH. No other reaction initiators are said to be present. The reaction scheme is shown to be:

CH ₄ + COS > CH ₃ SH + CO

HZSM-5 CH ₃ SH --> [CH ₂ ] + H ₂ S

(H ₂ S > S), a regeneration step

CO + S > COS

The selectivity of the first reaction is said to be high, i.e., around 81%; however, the conversion appears to be quite low.

A disclosure similar to that in Chang is found in Mobil's U.S. Patent No. 4,864,074 to Han et al. As in Chang, the methane is contacted with sulfur. The process

conditions are changed, however, so that either CS ₂ or

CH ₃ SH is formed. These sulfur compounds may then be converted in the presence of the preferred HZSM-5 zeolite catalyst to produce hydrocarbons having two or more carbon atoms. Also, as was the case with Chang, the step in which methane is converted to a methyl-sulfur compound is performed in the absence of a catalyst.

Other methods are known for producing substituted methanes which are suitable for further reaction to heavier hydrocarbons. A thermal methane chlorination process is shown in U.S. Patent No.

4,804,797 to Minet et al. A similar process is disclosed in U.S. Patent No. 3,979,470 to Firnhaber et al. although a preference for C ₃ hydrocarbon feeds is expressed. One method shown in U.S. Patent No. 4,523,040 to Olah utilizes either a solid strongly acidic catalyst or a supported Group VIII metal (particularly platinum and palladium) in the gas phase halogenation of methane to produce methyl halides. The patent indicates that monohalides are produced in 85% to 99% selectivity. Olah suggests that subsequent or concurrent catalytic hydrolysis produces methyl alcohol and/or dimethyl ether.

Production of methyl oxy-esters is not shown.

The reaction of methane with palladium (II) acetate in trifluoroacetic acid to effect the trifluoroacetoxylation of methane is shown in S^n et al. ,

"Palladium (II) Mediated Oxidative Functionalizixton of

Alkanes and Arenes", New Journal of Chemistry (1989) ,

Vol. 13, No. 10-11, pp. 756-760. A yield of 60% based on palladium was reported when the reaction was practiced using methane as the reactant. Consequently, the reaction with methane utilized palladium as a reactant and not as a catalyst. The extent of methane conversion, selectivity, and reaction rates were not stated.

The Sen et al. article has been criticized in Vargaftik et al. , "Highly Selective Partial Oxidation of Methane to Methyl Trifluoroacetate", Journal of the Chemical Society, Chemical Communications (1990) , pp. 1049-1050, to the extent that the results were not found to be reproducible. Vargaftik et al. discloses the catalytic oxy-esterification of methane to methyl trifluoroacetate with cobalt in trifluoroacetic acid but shows that palladium is not even suitable for stoichiometric methane oxidation in that process. With

Pd, less than 0.1% yield of methyl trifluoroacetate based on palladium (II) trifluoroacetate was obtained.

The Varaftik et al. article discloses that although palladium is ineffective for the conversion of methane to methyl trifluoroacetate, Co can be used for this reaction. The Co is said to be catalytic in the presence of oxygen. The rate of the reaction was very low, 2.5 x 10 ^"11 mol/cc sec, (or four to five orders of magnitude away from typical commercial rates of about 10 mol/cc.sec) . Only four turnovers of the Co ion were disclosed. The extent of methane conversion was not stated. In addition to Co, other metals were suggested which were said to allow stoichiometric oxidation of methane to methyl trifluoroacetate in varying yields (based on amount of metal charged): Mn (30%), Cu (0.1%), and Pb (10%) .

A later publication by Sen et al ("Homogeneous Palladium (II) Mediated Oxidation of Methane", Platinum Metals Review, (1991), Vol 35, No. 3, pp. 126-132) discloses a catalytic system using palladium as the catalyst, peroxytrifluoroacetic acid as the oxidant, and a mixture of trifluoroacetic acid and trifluoroacetic anhydride as the solvent. The reaction rate was low (4.2

_ Q x 10 mol/cc.sec) and only 5.3 turnovers of Pd were

observed. The extent of methane conversion and selectivity were not stated.

None of these disclosures shows a process in which a hydrocarbonaceous feed, particularly a lower alkane, is oxidized to an oxy-ester intermediate using our class of catalysts, acids, and oxidants nor do they show a process combining that step with a step in which the oxy-ester intermediates so-produced are then converted into heavier liquid hydrocarbons. These disclosures further do not show processes achieving high conversion and selectivity for such a catalytic oxidation to form oxy-esters, particularly at practical reaction rates.

SUMMARY OF THE INVENTION

This invention is a catalytic oxidation process for the conversion of hydrocarbonaceous feeds, particularly lower alkanes, into oxy-esters which oxy- esters may be converted into functionalized intermediates such as alcohols, thiols, other esters, halides, and other such materials or may be converted into hydrocarbons (desirably in the gasoline boiling range) . The functionalized intermediates may also be converted into hydrocarbons via a variety of known processes, e.g., oligomerization or the like.

The first step is catalytic and involves the contacting of a hydrocarbonaceous feed (particularly a lower alkane such as methane) with: a.) particular acids, b.) a catalyst (in at least a catalytic amount) comprising a Class "B" metal from the Mendeleev table and/or Pearson "soft" and "borderline" metal cations,

c.) and one or more specific oxidizing agents.

The Class "B" metals are as described in "Inorganic Chemistry", C.S.G. Phillips and R.S.P.

Williams, Oxford University Press, 1966 at pp. 459-477. The so-called Pearson definitions of "soft" and "borderline" metal ions used in this disclosure may be found at pages 276 to 290 of "Inorganic Chemistry", James E. Huheey, Harper and Row Publishers, Second Edition,

1978. The reaction may take place at low pressures and temperatures. The preferred metal catalysts are selected from Pd, Tl, Pt, Hg, and Au; most preferred is Hg. The preferred oxidizing agents are 0 ₂ , H ₂ S0 ₄ , S0 ₃ , HN0 ₃ , and H ₂ Se0 ₄ . When a lower alkane is selected as a feed, the alkane is converted to an alkyl oxy-ester of the acid which is relatively inert to further oxidation under the reaction conditions.

The oxy-esters produced in the first step may then be converted to alcohols or to other suitable intermediates. This step may be used to regenerate the acid for recycle and reuse in the first step.

The alcohols or other intermediates may then be converted to higher hydrocarbons, preferably suitable for direct use as a fuel but at least suitable for further processing to higher hydrocarbons or chemicals. Of course, the alcohols may themselves be used directly as a fuel .

DESCRIPTION OF THE INVENTION

As noted above, this invention includes both the overall process for producing functionalized intermediates such as alcohols, thiols, other esters, halides, and other such functionalized materials or

higher hydrocarbons as well as the individual step of esterifying hydrocarbonaceous feeds, particularly lower alkanes, into oxy-esters.

By the term "hydrocarbonaceous feed", we mean 5 any molecule containing a C-H bond which is selectively oxidized to an oxy-ester using the process of this invention. These molecules may include aromatics, alkanes, alkenes, and alkynes as well as alkylaromatics and alkenyl aromatics. The hydrocarbonaceous feeds may

10 be substituted if the substituent is stable in the reaction conditions specified by the invention. For instance, substituent groups such as alcohols, thiols, ethers, amines, carboxylic acids, and other like moieties may be present on the molecule.

15 The overall process, using methane as an example of a hydrocarbonaceous feed, may be outlined in the following fashion:

. Cat. 1 . ,

20 Eq. 1 CH ₄ + oxidant + acid > oxy-ester of acid

+ reduced oxidant

Eq. 2 oxy-ester of acid + nucleophile functionalized intermediate + acid

25 Eq. 3 functionalized interm Cedatiat2e > hydrocarbon + nucleophile

Net Reaction: CH ₄ + oxidant > hydrocarbon reduced oxidant

30 First Step

The first step (utilizing the reaction of Eq. 1) involves contacting methane or other hydrocarbonaceous feed with an acid and an oxidizing agent in the presence -_ of a catalyst.

The acid HX (where X is the acid's anion) may be an organic or inorganic acid such as HN0 ₃ , H ₂ S0 ₄ , CF ₃ C0 ₂ H, CF ₃ S0 ₃ H, H ₃ P0 ₄ , H ₂ Se0 ₄ , HBr, HC1, HF, HPA's (heteropolyacids) , B(OH) ₃ or the like, anhydrides and acid salts of these acids such as H ₄ P ₂ 0 ₇ , H ₂ S ₂ 0 ₇ or the like, and mixtures of two or more of these acids or these acids and anhydrides.

The preferred acids are strong inorganic acids (pKa < 3.0) and especially preferred are H ₂ S0 ₄ , H ₄ P ₂ 0 ₇ , and CF ₃ S0 ₃ H. For greatest efficiency the acids should be oxidation resistant: they should not be oxidized by the catalyst metal in the noted reaction medium. If such an oxidation were to occur, it would obviously result in destruction of the acid and need for additional acid processing. In addition to acting as a reactant, the acid may also be used in excess, and, in some cases as an oxidant, thereby acting as reactant (to form the oxy- ester) , solvent, and sometimes, oxidant.

The oxidizing agent should be selected from the group of 0 ₂ , H ₂ S0 ₄ , S0 ₃ , HN0 ₃ , and H ₂ Se0 ₄ - Although other oxidants are likely suitable under appropriate conditions, these are specifically capable of oxidizing the reduced form of the metal catalysts. Oxygen is preferred because of its ready availability and low cost. ^H ₂ S0 ₄ and S0 ₃ are desirable oxidants since the regeneration of the S0 ₂ produced is well known technology. The oxidant may be present in its entirety at the beginning of the reaction or (if a batch reaction is anticipated) added to the reaction as required. For instance, where H ₂ S0 ₄ is the solvent and S0 ₃ is the oxidant, the S0 ₃ is preferably added in a controlled manner to reoxidize the reduced catalyst. 0 ₂ may be used as an oxidant in a similar fashion.

Where 0 ₂ is the oxidant, the manner of accomplishing Eq. 1 is as follows:

Eq la CH ₄ + %0 ₂ + HX > CH ₃ X + H ₂ 0

Where H ₂ S0 ₄ is both the oxidant and the acid, the process for accomplishing Eq. 1 is as follows:

Eq lb CH ₄ + 2K ₂ S0 ₄ -> CH ₃ OS0 ₃ H + 2H ₂ 0 + S0 ₂

Where S0 ₃ is the oxidant and H ₂ S0 ₄ is the acid, the process for accomplishing the reaction of Eq. 1 is as follows:

Eq lcCH ₄ + S0 ₃ + H ₂ S0 ₄ > CH ₃ OS0 ₃ H + S0 ₂ + H ₂ 0

Where 0 ₂ is the oxidant and CF ₃ S0 ₃ H is the acid, the process for accomplishing the reaction of Eq. 1 is as follows:

Eq Id CH ₄ + 0 ₂ + CF ₃ S0 ₃ H > CH ₃ OS0 ₂ CF ₃ + H ₂ 0

Since this is an oxidation process, the chemical oxidizing agent may be replaced with an electrochemical system. Where the oxidation is carried out electrochemically, the process for accomplishing the reaction of Equation 1 (at the anode) is as follows:

Eq. le CH. + HX ---> CH X + 2H ⁺ + 2e ^~

The catalyst used in Eq. 1 is one or more metals selected from the Class "B" metals of the Mendeleev Table and/or metals ions that are characterized as "soft" or "borderline" by the Pearson definitions.

Suitable metal ions are the following: Cu, Zn, Pd, Ag, Cd, In, Sn, Sb, Te, Pt, Au, Hg, Tl, Pb, Bi, Ga, Ge, As, Po, Rh, Ir, Os, and Ru. The stable high oxidation states of these metals are characterized by a relatively high affinity for binding to "soft" polarizable ligands, e.g., CH ₄ . These metals bind well to organic ligands since these species are "soft" and polarizable and tend to show the following order of binding (and insolubility) to the halogens: I > Br > Cl > F. These properties are pronounced in those metal ions with electron configurations d -d and are especially so in the heavy ions, e.g., Au ¹ , Au ¹¹¹ , Hg ¹¹ , Tl ¹¹¹ , Pd ¹¹ , Pt ¹¹ and Pt ^IV . Another important characteristic of these metal ions is the relative inefficiency with which these metal ions undergo one-electron reductions while still allowing efficient two-electron reductions. For example, Hg 2+ reduces to produce Hg_, _>+ (a net 2e- change) ; Hg+ i.s not a stable species and one-electron reductions wi .th Hg2+. are not common. This is in stark contrast to metals such as Co and Mn which readily undergo le ^" reduction by one-electron changes to produce the M ¹¹ ions. Strong acids (desired for heterolytic reactions) and the corresponding anions are resistant to oxidation and more easily oxidized by one-electron than two-electron processes. Thus, the Class "B" and/or "soft" metal ions do not readily oxidize strong acid solvents or the corresponding anions but can still allow efficient reaction of methane via a two-electron heterolytic process in such media. One such metal ion, Pd 2+, is a powerful oxidant

(E° Pd ²⁺ /Pd° = 0.98 V vs. NHE) , with electronic

Q configuation d and is characterized as a "soft" metal ion by the Pearson definition. Consistent with its classification as a "soft" metal ion and high ionization

potential (19.42 eV) , Pd allows facile reactions with alkanes ("soft bases") including methane. Consistent with these "soft" properties of Pd are the well known reactions of Pd 2+ with arenes (palladation) to produce isolable phenyl-palladium species. These phenyl- palladium species further react to produce functionalized aryl species, including aryl esters, presumably by a similar process that occurs in the formation of methyl esters from methyl-palladium species. This metallation reaction of arenes has been relatively well studied compared to the corresponding reaction with alkanes. The initial important reaction with arenes is thought to proceed via an heterolytic electrophilic CH bond activation, Eq 4, and since this is similar to the processes proposed for reaction with alkanes (See,

Periana et al and Sen et al, above) , could serve as a good model for electrophilic reactions with the much more difficultly reactive alkanes, Eq 5.

Eq 4 C

Eq 5

Even though Pd is acceptable from a reactl"ity point of view, it is expensive and the reaction rate is slow from a commercial point of view. Other more active metals would be desirable, particularly for methane activation since the goal of developing an economic process based on the heterolytic electrophilic conversion of methane to methyl oxy-esters remains an important commercial goal. Using the intrinsic chemical properties of Pd discussed above as guidelines, other class "B",

"soft" metal ions with oxidation potentials >0.1 volts were identified as candidates for the conversion of methane to methyl esters: Au ¹¹¹ , Tl ¹¹¹ , Pt ^IV , Pt ¹¹ , Hg ¹¹ , Cu ¹¹ , Ag ¹ , Bi ^IV , Bi ¹¹¹ , Pb ^IV , Pb ¹¹ , Rh ¹¹¹ , Sn ^IV , Sn ¹¹ , Sb ^V , Sb ¹¹¹ , Te ^IV , Te ¹¹¹ , Ir ¹¹¹ , Ru ¹¹¹ , Ru ^IV , Ru ^VI ,

Ru ^VI1 , and Ru ^VI11 . Importantly, certain of these metal ions (Tl ¹¹¹ , Au ¹¹¹ , Pt ¹¹ , Hg ¹¹ , Pb ^IV ) are known to react with arenes by electrophilic mechanisms.

We have found that Hg ¹¹ , Tl ¹¹¹ , Pt ^IV , Pt ¹¹ Au ¹¹ , and Au ¹¹¹ are also effective ions for the selective oxidation of methane to methyl esters. Of these, Hg is the most effective, exhibiting much higher activity than Pd , and is significantly less expensive and is especially reactive in H ₂ S0 ₄ . The stoichiometry of the reaction when using H ₂ S0 ₄ is shown in Eq lb above.

The form in which the catalyst is introduced to the reaction medium is not particularly important; the requirements being only that it be in a form allowing oxidant, acid, and reactant access to the metal and that the form not restrict the ability of the catalytic metal to vary between oxidation states during the reaction. For instance, the metal may be introduced as a metal, salt, or complex into a liquid reaction medium. The catalytic metal (or metals) may be placed on the usual catalyst supports (carbon, zirconia, silica, alumina, etc.) provided that the supports do not interfere with the requirements listed above. We have found that introducing the metal to the liquid reaction medium in a form which produces a homogeneous catalyst is very desirable. The metal may be introduced to the liquid reaction medium in a convenient form such as the salt of the acid used in Eq. 1, although that is not required.

The metallic form of the catalyst may also be used. The catalyst metal concentration must be present in at least

a catalytic amount; amounts of metal ranging between 50 ppm and 1.0% by mole of the total liquid present are effective although we have found no intrinsic limitation on the metal concentration. The reaction rate is related to the concentration of the catalytic metal; higher rates result from higher metal concentration.

The esterification process conditions used in the first step are as follows:

a. temperature is greater than 50°C, preferably 50°C to 300°C, and most preferably 95°C to 200°C; b. if the hydrocarbonaceous feed is gaseous, e.g., methane, it is added at a pressure above about 50 psig, preferably above about 300 psig, and most preferably above about 450 psig; and c. oxidant (whether pure or with other inert diluents) is added in an amount sufficient to support the reaction.

These conditions result in production of the oxy-ester of the acid in a molar amount greater than the molar amount of the catalyst metal charged in the reactor therefore giving a truly catalytic process.

We have found that the catalyst metals may also be used as reactants rather than as catalysts. If the metal is to be used as a reactant rather than as a catalyst, then substantially larger amounts of the metal may be added. For instance, using Hg(OS0 ₃ H) ₂ both as the oxidant and the catalyst in the first step:

Eq. If CH ₄ + 2Hg(OS0 ₃ H) ₂ ---> CH ₃ OS0 ₃ H + Hg ₂ (OS0 ₃ H) ₂ + H ₂ S0 ₄ then the mercury compound may be regenerated according to the following equation:

Eq. lg Hg ₂ (OS0 ₃ H) ₂ + 0 ₂ ---> 2Hg(0S0 ₃ H) ₂ + H ₂ 0

The most preferred reaction situation for accomplishing Eq. 1 above is thus: the reaction is carried out in sulfuric acid, which acts as the solvent and acid and S0 ₃ is the oxidant. Mercury is the catalyst.

The concentration of Hg is as discussed generically above. The Hg is typically introduced into the reaction mixtures as HgS0 ₄ but any form of Hg is acceptable; e.g. HgCl ₂ , Hg ₂ S0 ₄ , Hg(N0 ₃ ) ₂ , Hg(CH ₃ ) ₂ , Hg(C _g H ₅ ) ₂ , Hg metal, Hg amalgams with various metals, etc. Although the metallic form of the metal permits a reaction to occur, the ionic form is presumed to be the catalytically active state and reactions with metallic Hg likely proceed first by oxidation of the metal to the ionic state. Importantly, metallic mercury is not observed in the reaction and the reaction remains homogeneous independent of its form when added to the reaction. The yield of the reaction when using mercury is sensitive to the concentration of the sulfuric acid and lower acid concentration results in lower yields. However, reaction does occur in 90% sulfuric acid and may occur in solutions as low as 50%. The fastest reactions and highest yields have been observed in 100% sulfuric acid. The reaction also occurs in sulfuric acid containing excess S0 ₃ (oleum) . However, since the water generated in the reaction (Eq 1) must be removed (to prevent hydrolysis of the CH.-OSO H and dilution of the

sulfuric acid) a preferred concentration is about 96% H ₂ S0 ₄ , since this concentration can readily be maintained by removal of water through simple distillation. The reaction may also be controlled to run at any desired concentration of H ₂ S0 ₄ by continuous, controlled addition of S0 ₃ to the reaction mixture. This addition step prevents the build-up of water, yet allows reoxidation of the catalyst, and may allow high conversion of the H ₂ S0 ₄ to the product methyl sulfate. It is desirable to use 0 ₂ as the oxidant in conjunction with H ₂ S0 ₄ as the reaction medium. This reaction is shown above. This combination avoids production of S0 ₂ and the concomitant need for its recycle by oxidation to S0 ₃ . Use of devices promoting good mixing between the gas and liquid phases is desirable.

This reaction may be carried out in a molten salt reaction medium rather than in acids as solvents (so long as the stoichiometric requirements of the reaction are met), e.g. molten KHS0 ₄ , NaHS0 ₄ , K ₂ S ₂ 0 _? , Na ₃ B0 ₃ , etc. Alternatively, solid acids may be used as the reacting acid, with or without an added liquid as solvent. Under these conditions the acid would be converted to a solid methyl ester which may then be treated with a nucleophile to release the methyl intermediate. These process variations have certain potential advantages such as lower corrosivity, lower volatility, increased reaction medium inertness, and lower overall cost.

Second Step

This step is shown above as Eq. 2. It is an optional step and is carried out generally for the purpose of replacing the oxy-ester formed in the first step with an intermediate which is both reactive in the

third step and does not substantially degrade the catalyst used in that later step. This step allows regeneration of the acid utilized in the first step for generation of the methyl ester. The methyl ester may be separated from the first step reaction media by commonly practiced steps such as flashing or distillation. However, there is no need to isolate the methyl ester since solutions of the methyl ester and acid solvent react with added nucleophile to produce an intermediate which is reactive in the third step. The nucleophile in Eq. 2 is suitably then mixed with the methyl oxy-ester (pure or in the acid solvent) to produce a "methyl intermediate". By "methyl intermediate" is meant methanol, if the nucleophile is H ₂ 0; methyl halide, if the nucleophile is a hydrogen halide such as HC1, HBr, or HI; methyl amino, if the nucleophile is NH ₃ ; methyl thiol, if the nucleophile is H ₂ S; methyl or carboxylic esters if the nucleophile is CH ₃ C0 ₂ H, HC0 ₂ H,etc; (di) -methyl sulphite if the nucleophile is H ₂ S0 ₃ or S0 ₂ ; (tri) -methyl borate if the nucleophile is B(OH) ₃ ; (di) -methyl carbonate if the nucleophile is H ₂ C0 ₃ or C0 ₂ ; methyl amines if the nucleophile is NH ₃ , CH ₃ NH ₂ , etc.; or acetonitrile if the nucleophile is HCN. Other nucleophiles can be utilized and would be known to the ordinary skilled worker but should be of a type not decomposed by reaction with the acid solvent. These reactions proceed readily to completion. An excess of the nucleophile is desirable. The preferred nucleophile is H ₂ 0 since it may also be produced in the first step. The product methanol may be used directly or may be converted to a variety of hydrocarbons in a following step or steps.

In some cases the first and second step may be combined if a suitable nucleophile is selected. For

-18- example, a mixture of H ₂ S0 ₄ and acetic acid results in the formation of methyl acetate that can be isolated by distillation during the progress of the reaction thus combining steps 1 and 2. Similarly, mixtures of H ₂ S0 ₄ 5 and HC1 result in the formation of CH ₃ C1.

Third Step

This step (shown above as Eq. 3) includes conversion of the methyl intermediate to a longer chain 10 or higher molecular weight hydrocarbon.

Suitable processes for converting methanol and other methyl intermediates to higher molecular weight hydrocarbons are found in U.S. Patent Nos. 3,894,107 and 3,979,472 to Butter et al. Butter shows the production 15 of olefinic and aromatic compounds by contacting the methyl intermediate with an aluminosilicate catalyst, preferably HZSM-5, at a temperature between 650°F and 1000°F.

Similarly, Butter suggests a process using a 20 preferable catalyst of antimony oxide and HZSM-5 at a temperature between 250°C and 700°C.

The ZSM-5 zeolite has been disclosed as a suitable molecular sieve catalyst for converting methyl alcohol into gasoline-range hydrocarbons. See, for 25 instance, U.S. Patent Nos. 3,702,886 to Argauer et al. and 3,928,483 to Chang et al.

Other processes include those described in U.S.

Patent No. 4,373,109 to Olah (bifunctional acid-base catalyzed conversion of methanol and other methyl

30 intermediates into lower olefins) ; U.S. Patent No.

4,687,875 to Currie et al. (metal coordination complexes of heteropolyacids as catalysts for converting short chain aliphatic alcohols to short chain hydrocarbons) ;

U.S. Patent No. 4,524,234 to Kaiser (production of 35

hydrocarbons preferably from methanol using aluminophosphate molecular sieves); and U.S. Patent No. 4,579,996 to Font Freide et al. (production of hydrocarbons from C ₁ to C ₄ monohaloalkanes using layered clays); etc. Each of the above is potentially suitable for the third step of this process and their contents are incorporated by notice.

Integrated Process Where the process steps outlined as Eqs. 1-3 above are integrated, as might be done in an operating plant where CH ₄ is the hydrocarbonaceous feed, 0 ₂ is the oxidant, and HY is a nucleophile, the overall process scheme is as follows:

CH ₄ + &0 ₂ + HX > CH ₃ X + H ₂ 0

CH ₃ X + HY > CH ₃ Y + HX

CH ₃ Y > [CH ₂ 3 + HY

Net Reaction: CH ₄ + %0 ₂ > [CH ₂ ] + H ₂ 0

Where H ₂ S0 ₄ is both the oxidant and the acid and water is the nucleophile, the process for accomplishing the overall process is as follows:

CH ₄ + 2 H ₂ S0 ₄ > CH ₃ 0S0 ₃ H + 2 H ₂ 0 + S0 ₂

S0 ₂ + 0 ₂ + H ₂ 0 > H ₂ S0

CH ₃ OS0 ₃ H H ₂ 0 > CH ₃ 0H + H ₂ S0 ₄

CH ₃ OH > [CH ₂ ] + H ₂ 0

Net Reaction: CH ₄ + 0 ₂ > [CH ₂ ] + H ₂ 0

It should be understood that the first two reactions expressed immediately above are equivalent in sum to Eq. 1 of the overall process.

Where S0 ₃ is the oxidant, H ₂ S0 ₄ is the acid, and water is the nucleophile, the process for accomplishing the overall process is as follows:

CH ₄ + S0 ₃ + H ₂ S0 ₄ • > CH ₃ OS0 ₃ H + S0 ₂ so ₂ + 14 ₂ > so ₃

CH ₃ OS0 ₃ H + H ₂ 0 > CH ₃ 0H + H ₂ S0 ₄

CH ₃ OH > [CH ₂ ] + H ₂ 0

Net Reaction: CH ₄ + 0 ₂ > [CH ₂ 3 + H ₂ 0

It should be understood that the first two reactions expressed immediately above are equivalent in sum to Eq. 1 of the overall process.

Where 0 ₂ is the oxident, CF ₃ S0 ₃ H is the acid, and water is the nucleophile, the process is as follows:

CH ₄ + 0 ₂ + CF ₃ S0 ₃ H > CH ₃ OS0 ₂ CF ₃ + H ₂ 0

CH ₃ 0S0 ₂ CF ₃ + H ₂ 0 > CH ₃ OH + CF ₃ S0 ₃ H CH ₃ OH > [CH ₂ ] + H ₂ 0

Net Reaction: CH ₄ + -£0 ₂ ---> [CH ₂ 1 + H ₂ 0

These reaction schemes permit regeneration and recycle of the acid and, in some instances, the auxiliary oxidant, which makes the process more economical. Some acids require additional steps to separate the nuecleophile but such steps are known to the ordinarily skilled worker.

EXAMPLES These examples are intended to show portions of the overall inventive process, in particular the esterification reaction utilizing methane as the reactant. The remainder of the process steps are easily selectable from known processes.

Example 1 This example shows the use of a palladium catalyst, S0 ₃ as oxidant, and H ₂ S0 ₄ as the acid in esterifying methane.

A 100 ml glass reactor having an integral heater-stirrer was loaded with 15 ml of oleum (20% S0 ₃ ) and 0.0304 gm PdS0 ₄ - 2H ₂ 0 (1.27xl0 ^~4 mol) . The system was purged with N ₂ and pressured to 100 psig with CH ₄ .

The stirrer and heater were started. During heat-up, the pressure was adjusted to maintain about 100 psig. The reaction was carried out at about 100°C and 100 psig. After about three hours, the reactor was cooled to about

25°C, the pressure bled down, and samples of the gaseous effluent taken. Samples of the reactor solution (in range of color from orange to red without black precipitate) were also taken. The gases in the reactor were analyzed using a gas chromatograph and the gas remaining in the reactor contained CH ₄ , 2.96x10 -4 mols carbon di.oxide and

9.28x10 ^"3 mols S0 ₂ .

The reaction produced a large amount of S0 ₂ caused by the reoxidation of Pd . The yield of the methyl ester CH ₃ OS0 ₃ H was 3.6X10 mols as determined by saponification of the reaction samples and subsequent analysis of the released CH ₃ OH. This shows a 2834% yield on palladium and verifies that palladium is catalytic in

-22- the process. The yield of methyl ester was also confirmed by H-NMR (using internal standards in coaxial tubes) .

Example 2

This example demonstrates the use of H ₂ S0 ₄ both as an oxidant and as esterfying acid in the reaction.

The process of Example 1 was repeated except that S0 ₃ was omitted. An amount of 8.5 ml of H ₂ S0 ₄ was 10 used both as the acid and oxidant. The PdS0 ₄ ^■ 2H ₂ 0 was added in an amount of 0.0035 gm (1.5x10 mol)

The gas chromatograph data showed 6.64x10 -4 mols of S0 _o in the reactor along with 2.85x10 -4 mols carbon dioxide. The yield of CH ₃ 0S0 ₃ H was 1.46x10 -4

15 mols or a 970% yield on the amount of palladium present in the reactor. The reaction was catalytic in the palladium metal.

Example 3

20 This example shows the use of 0 ₂ as the oxidant, H ₂ S0 ₄ as the esterfying acid, and palladium as the catalyst. In addition, the process is a continuous feed operation rather than a batch operation as shown in Examples 1 and 2.

25 A 150 ml TEFLON-lined reactor having an integral heater-stirrer was loaded with 20 ml of H ₂ S0 ₄ and 0.478 gm (2xl0 ^~3 mol) PdS0 ₄ ' 2H ₂ 0. The system was purged with N ₂ and pressured to 600 psig with CH ₄ . The stirrer and heater were started. The reaction was

30 carried out at 175°C. The effluent gas was continuously sampled. The feed gases were introduced at 20 cc/minute of 0 ₂ (8.9x10~ ⁴ mol/minute) and 80 cc/minute of CH ₄ (3.6x10 mol/minute) .

35

At about two hours, the molar ratio of CH ₄ /0 ₂ stabilized at about 4/1 and the system pressure stabilized at 625 psig. After about six hours the reaction was terminated by cooling the reactor to 50°C. Gas chromatograph analysis of the gases showed

_-a that, on the average, 7.59x10 mols of carbon dioxide and 9.28x10 mols of S0 ₂ were produced. The yield of CH ₃ 0S0 ₃ H was 5.0x10 ^"3 mols for a yield of 250% based on the amount of palladium present. Again, this demonstrates the palladium metal to be catalytic in this process.

Example 4

This example shows the catalytic esterification of methane using CF ₃ S0 ₃ H (triflic acid) as the acid, 0 ₂ as the oxidant, and palladium as the catalyst.

A 50 ml Hastalloy C reactor equipped with a stirrer was loaded with 30 ml of triflic acid, 0.2 ml H ₂ 0, and 0.25 g of palladium black (Pd ) . The reactor was pressured to 500 psig with pure 0 ₂ , heated to 180°C, and stirred for two hours to convert the palladium black to the catalytically active form.

The reactor was cooled and purged with N ₂ to remove the 0 ₂ . The reactor was pressured to 1000 psig with CH ₄ . A flow of 200 standard cc/minute of CH ₄ was then established. The gas leaving the reactor was scrubbed using aqueous Na ₂ C0 ₃ . A flow of 50 standard cc/minute of 0 ₂ was then introduced, the reactor heated to 180°C, and stirring commenced. The exiting gases were periodically analyzed for carbon dioxide and other product gases. The reaction was terminated at three hours by stopping the gas flows and allowing the reactor to cool to room temperature. The reactor head space was vented through the Na _^ CO-, trap. The contents of the ^J

reactor, Na ₂ C0 ₃ trap, and the exit gases were analyzed for methyl triflate, methanol, carbon dioxide, and other products.

The only carbon-containing products were methanol, methyl triflate, and carbon dioxide. Less than 5% of the methane consumed was converted to carbon dioxide. The sum of the amounts of methyl ester (methyl triflate) found in the reactor and methanol found in the Na ₂ C0 ₃ trap (due to in situ saponification) was calculated to produce a yield of 500% based on palladium.

Example 5

This is a comparative example which shows the need for an oxidant in the process in order to obtain catalysis with respect to palladium. Specifically, methane was used as the lower alkane, CF ₃ S0 ₃ H (triflic acid) as the acid, and palladium as the oxidant.

A 50 ml Hastalloy C reactor equipped with a stirrer was loaded with 30 ml of triflic acid (CF ₃ S0 ₃ H) ,

0.2 ml H ₂ 0, and 0.25 g of palladium black (Pd°) . The reactor was pressured to 500 psig with pure 0 ₂ , heated to

180°C, and stirred for two hours to convert the palladium black to the oxidant. The reactor was cooled and purged with N ₂ to remove the 0 ₂ . The reactor was pressured to 600 psig with CH ₄ . In Example 4, 50 cc/minute of 0 ₂ was introduced into the reactor; oxygen was not included in this example. The reactor was heated to 180°C, the pressure adjusted to 1000 psig with CH ₄ and stirring commenced.

The reaction was terminated at three hours by allowing the reactor to cool to room temperature. The reactor head space was vented through a Na C0, trap. The ^{z J}

contents of the reactor, Na ₂ C0 ₃ trap, and the exit gases were analyzed for methyl triflate, methanol, carbon dioxide, and other products.

The only carbon-containing products were methanol, methyl triflate, and carbon dioxide. Only trace amounts of carbon dioxide were detected. The sum of the amounts of methyl ester (methyl triflate) found in the reactor and methanol found in the Na ₂ C0 ₃ trap (due to in situ saponification) provided a yield of 92% based on palladium. Without the added oxidant (such as 0 ₂ as used in Example 4) the palladium was not catalytic.

Example 6

The following examples (A. through I.) show the catalytic effect of mercury in our inventive process.

A. A 50 ml high pressure reactor was charged with 25 ml of 100% H ₂ S0 ₄ and 2.0 g of HgS0 ₄ (270 mM) . The contents of the reactor were stirred, the reactor was flushed with methane and heated to 188°C under 1800 psig of methane. After l hr the reactor was cooled to room temperature. A gas sample of the gas in the reactor was obtained for gas chromatographic analysis and an aliquot of the reaction mixture was qualitatively analyzed for methyl sulfate by

13 C NMR and ιH NMR. A second aliquot was first diluted with 3 volumes of water and the resulting solution heated in a sealed container for 2 hrs. The resulting solution was quantitatively analyzed for free CH ₃ 0H by HPLC using an ion exclusion column with an eluant of

0.01% H ₂ S0 ₄ in H ₂ 0 and a refractive index detector. Based on the high pressure liquid

chromatography ("HPLC") and nuclear magnetic resonance ("NMR") analyses, the yield of methyl sulfate was 746 mol% (25 mmoles, 1008 mM, Table I, entry 1) based on HgS0 ₄ added (assuming that the reaction proceeds via the Hg redox couple

Hg _?+/Hg,2+) . This corresponds to a

^Δ _ ₇ productivity rate of 2.8 x 10 mol. of oxy- ester/cc of reaction volume - sec based on the conversion of methane to methyl sulfate. Trace levels of acetic acid and dimethylether were detected. Gas chromatographic analysis showed that copious amounts of S0 ₂ and trace levels of C0 ₂ were produced.

B. To show the effect of HgS0 ₄ concentration, the general procedure of example A was repeated both with 1000 mM and 100 mM of HgS0 ₄ for 60 minutes under 510 psig of methane. The results shown in Table I (entries 2 and 3) demonstrate that the higher concentrations of HgS0 ₄ result in higher yields of methyl sulfate over the same reaction time.

C. To show the greater effectiveness of Hg as compared to Pd , the general procedure of example A was repeated but with 165 mM of PdS0 ₄ and 100 mM HgS0 ₄ for 180 minutes under 400 psig of methane. The results shown in Table I (entries 4 and 5) demonstrate that, under identical conditions, the HgS0 ₄ system is about

17 times more active than the PdS0 ₄ system for the production of methyl sulfate.

D. As a "blank" run, the procedure of Example C was repeated but without added PdS0 ₄ or HgS0 ₄ . As may be seen from the results in Table I

(entry 6) no methyl sulfate was produced in the reaction.

E. To show the effect of acid concentration, the general procedure of Example A was twice repeated but with 90% (wt) H ₂ S0 ₄ (remainder H ₂ 0) and 100% (wt) H ₂ S0 ₄ , 100 mM HgS0 ₄ , and 510 to 560 psig of methane for two hours. The results shown in Table I (entries 7 and 8) demonstrate that the yield of methyl sulfate was 464 mol% based on HgS0 ₄ added in the 100% ^H 2 ^S0 4 ^{and 155 mol% in tile 90} * ^H 2 ^S0 4 ^s Y ^{s em} -

F. To show the effect of temperature, the general procedure of Example A was repeated at 140°C, 160°C, 180°C and 200°C with lOOmM HgS0 ₄ for two hours under 510 psig of methane. The results shown in Table I (entries 8, 9, 10 and 11) demonstrate that increasing temperatures from 140°-180° lead to increased yields of methyl sulfate. At 200°C, a loss in yield was observed.

G. To show the effect of methane pressure, the general procedure of Example A was repeated with lOOmM HgS0 ₄ at methane pressures from 360 psig to 1820 psig. The results shown in Table

I (entries 12 and 13) demonstrate that the yield of methyl sulfate increases at higher pressures.

H. To show that the reaction proceeds in other acids, the general procedure of Example A was repeated in pyrophosphoric acid and trifluoromethanesulfonic acids. The results shown in Table I (entries 14 and 15) demonstrate that the reaction can be successfully carried out in pyrophosphoric acid and trifluoromethanesulfonic acids.

I. To show that the reaction proceeds with different forms of Hg, the general procedure of Example A was repeated variously using HgO, HgCl ₂ , Hg ₂ S0 ₄ , and Hg metal in place of HgS0 ₄ . The results shown in Table I (entries 16, 17, 18, and 19) demonstrate that these forms of Hg also leads to formation of methyl esters.

TABLE I

Entry Metal [Metal] Acid Temp Rxn Time [ [CCHH ₄ ,]] [[CCHH..OOHH]]

S Saalltt (mM) (°C) (min) (psig) (mM)

1 HgSO, 270 H ₂ S0 ₄ 180 60 1800 1008

(100%)

HgSO, 100 H ₂ S0 ₄ 180 60 510

247

(100%)

3 HgSO. 1000 H,SO. 180 60 510 378 ^{4 4}

(100%)

4 PdS0 ₄ 165 ^H 2 ^{S0 180 180 0} °

50

(100%) 5 HgS0 ₄ 100 ^H 2 ^{S0 180 180} 400 526

(100%)

6 H ₂ S0 ₄ 180 180 400

0

(100%)

7 HgS0 ₄ 100 ^H 2 ^S0 4 ¹⁸ ° ¹² ° ⁵⁶⁰ 155

(90%)

8 HgS0 ₄ 100 ^H 2 ^S0 4 ^{180 12} ° ⁵¹⁰ 64 (100%) HgSO. 100 H S0 _Δ 140 120 510 6 ^

(100%)

_vjf.ii lA-iie ι _π ₄ j [CH.OH]

( in) (psig) (mM)

120 510 464

120 510 16

120 510 121

120 510 452

60 360 187

60 1Θ20 394

114 400 26

TABLE I (cont.)

Entry Metal [Metal] Acid Temp Rxn Time [CH ₄ ] [CH ₃ OH] Salt (mM) (°C) (min) (psig) (mM)

H 180 120 900 112

(100%)

18 HgO 155 H ₂ S0 ₄ 180 180 510 200 (100%)

19 Hg ₂ SO, 51 H ₂ S0 ₄ 180 180 920 609 (100%)

-30-

This example demonstrates that other class "B" metals and/or Pearson "soft" metal ions can be utilized in our process for the selective oxidation of methane, 5 the general procedure of Example 6 (entry A.) was repeated variously using the metals shown in Table II (entries 1 - 4) . The metals Tl, Pt, and Au successfully facilitated the oxidation of methane to the methyl esters. Although the molar amount of methyl ester

10 produced in entries 1 - 4 was less than the amount of metal present in the reaction medium (the metal could therefore be considered either a reactant or a catalyst) , it is apparent that the use of oxygen to oxidize these metals would result in a process utilizing the metals in

15 a truly catalytic fashion.

20

25

30

35

ESHEET

vo t t

(J-i o Ul o Ul Ul

Table II

Entry Metal [Metal] Acid Temp Rxn Time [CH ₄ ] [CH ₃ 0H] Salt (mM) c) (min) (psig) (mM)

^T1 2°3 100 CF ₃ S0 ₃ H 170 120 500 123 (100%)

2 ^τl 2°3 ⁵⁰ H ₂ S0 ₄ 180 180 400 38

(100%)

PtO, 62 H ₂ S0 ₄ 180 185 400 48 (100%)

Au (0H) ₃ 100 H ₂ S0 ₄ 180 120 920 94 (100%)

-32-

The invention has been shown both by description and by example. The examples are only examples; they should not be used in any fashion to limit the scope of the invention otherwise described here.

Additionally, it should be clear that one having ordinary skill in this art would envision equivalents to the processes described in the claims that follow and these equivalents would be within the scope and spirit of the claimed invention.