CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent

Application No. 62/355,516, filed June 28, 2016, which is hereby incorporated by reference in its entirety.

FIELD

[0002] The disclosed subject matter relates to methods and for producing olefins, such as ethylene and propylene, from light hydrocarbons.

BACKGROUND

[0003] Light olefins, including ethylene and propylene, are important petrochemical feedstocks that can be derived from light hydrocarbons, such as C2-C3 alkanes. Several technologies for producing light olefins are known in the art, for instance by fluid catalytic cracking (FCC), deep catalytic cracking (DCC), advanced catalytic olefins (ACO) processes, and olefin metathesis. Often, thermal steam cracking is used to convert saturated hydrocarbons to light olefins. Such cracking processes can create hydrogen (H ₂ ) as a byproduct, which can be separated and used as fuel, e.g., in heating applications.

[0004] However, it can be more desirable to produce a different byproduct during the manufacturing of light olefins. For example, syngas, also known as synthesis gas, can be used as a feedstock for producing higher hydrocarbons, such as fuels, as well as various other chemicals, including olefins, methanol, ethylene glycol, and aldehydes, for example by oxo- synthesis (also known as hydroformylation) and carbonylation reactions. Syngas is primarily a mixture of carbon monoxide (CO) and hydrogen (H ₂ ), and can also contain carbon dioxide (C0 ₂ ) and/or water (H ₂ 0). The composition of syngas, and particularly the stoichiometric ratio of H ₂ and C0 ₂ in the syngas, can be important in determining which materials are produced when it is used as a feedstock in subsequent chemical processes. [0005] Certain techniques for generating olefins and syngas are known in the art. For example, U. S. Patent Publication No. 2009/0152499 is directed to a process for converting a hydrocarbon and an oxygen source into an olefin and syngas in the absence of a catalyst. International Patent Publication No. WO2010/057663 relates to a process for converting light paraffins (e.g., C ₂ to C ₇ paraffins) and carbon dioxide into light olefins and syngas by oxidative dehydrogenation using a La-Mn catalyst. Chinese Patent No. CN 1087654 relates to a process for converting light paraffins and carbon dioxide to light olefins and syngas by oxidative dehydrogenation. International Patent Publication No. WO2000/015587 is directed to a method of producing a mono-olefin and syngas from a paraffin feedstock by oxidative dehydrogenation in the presence of a Pt and/or Pd catalyst.

[0006] However, there remains a need for improved techniques for producing olefins from light hydrocarbons, while simultaneously generating valuable byproducts, such as syngas. The present disclosure addresses these and other needs.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

[0007] The disclosed subject matter provides novel methods for producing olefins using an oxidative dehydrogenation reaction.

[0008] An exemplary method for producing olefins by an oxidative dehydrogenation reaction in accordance with the disclosed subject matter includes introducing a feed stream including C ₂ and C ₃ hydrocarbons and C0 ₂ to a Cr oxide catalyst modified with K and Mn, and generating a product stream therefrom including olefins and syngas, where the syngas has a molar ratio of CO to H ₂ (CO/H ₂ ) from about 1.4 to about 1.8.

[0009] In certain embodiments, the feed stream can include from about 30 mol-% to about 60 mol-% C ₂ and C ₃ hydrocarbons. The feed stream can further include from about 40 mol-%) to about 90 mol-%> C0 ₂ . In particular embodiments, the feed stream can include about 35 mol-%> C ₂ and C ₃ hydrocarbons and about 65 mol-%> C0 ₂ . In certain embodiments, the C ₂ hydrocarbons can include C ₂ H ₆ and the C ₃ hydrocarbons can include C ₃ H ₈ .

[0010] In certain embodiments, the Cr oxide catalyst can be supported on either A1 ₂ 0 ₃ or Si0 ₂ . The Cr oxide catalyst can include about 2 mol-% K, about 8 mol-% Cr, and about 15 mol-% Mn supported on Si0 ₂ .

[0011] In certain embodiments, the method can further include reacting the feed stream in the presence of the Cr oxide catalyst at a temperature from about 600°C to about 900°C. In particular embodiments, the temperature can be from about 800°C to about 830°C. In certain embodiments, the method can include reacting the feed stream in the presence of the Cr oxide catalyst at a space velocity of about 2800 h ^"1 .

[0012] In certain embodiments, least about 75 mol-% of the C ₂ H ₆ is converted. In certain embodiments, at least about 80 mol-% of the C ₃ H ₈ is converted. In certain embodiments, at least about 50 mol-% of the C0 ₂ is converted. In certain embodiments, the oxidative dehydrogenation reaction generates an olefins yield of greater than about 55%.

[0013] In the context of the present invention, Embodiments 1 to 14 are described. Embodiment 1 is a method for producing olefins by an oxidative dehydrogenation reaction, including (a) introducing a feed stream comprising C ₂ and C ₃ hydrocarbons and C0 ₂ to a Cr oxide catalyst modified with K and Mn; and (b) generating a product stream therefrom comprising olefins and syngas, wherein the syngas has a molar ratio of CO to H ₂ (CO/H ₂ ) from about 1.4 to about 1.8. Embodiment 2 is the method of Embodiment 1, wherein the feed stream includes from about 30 mol-% to about 60 mol-% C ₂ and C ₃ hydrocarbons. Embodiment 3 is the method of any one of Embodiments 1 and 2, wherein the feed stream includes from about 40 mol-% to about 90 mol-% C0 ₂ . Embodiment 4 is the method of any one of Embodiments 1 to 3, wherein the feed stream comprises about 35 mol-% C ₂ and C ₃ hydrocarbons and about 65 mol-% C0 ₂ . Embodiment 5 is the method of any one of Embodiments 1 to 4, wherein the C ₂ hydrocarbons comprise C ₂ H ₆ and the C ₃ hydrocarbons comprise C ₃ H ₈ . Embodiment 6 is the method of any one of Embodiments 1 to 5, wherein the Cr oxide catalyst is supported on either A1 ₂ 0 ₃ or Si0 ₂ . Embodiment 7 is the method of any one of Embodiments 1 to 6, wherein the Cr oxide catalyst includes about 2 wt-% K, about 8 wt-% Cr, and about 15 wt-% Mn supported on Si0 ₂ . Embodiment 8 is the method of any one of Embodiments 1 to 7, further including the step of reacting the feed stream in the presence of the Cr oxide catalyst at a temperature from about 600°C to about 900°C. Embodiment 9 is the method of any one of Embodiments 1 to 8, wherein the temperature is from about 800°C to about 830°C. Embodiment 10 is the method of any one of any one of Embodiments 1 to 9, further including the step of reacting the feed stream in the presence of the Cr oxide catalyst at a space velocity of about 2800 h ^"1 . Embodiment 11 is the method of Embodiment 5, wherein at least about 75 mol-% of the C ₂ H ₆ is converted. Embodiment 12 is the method of Embodiment 5, wherein at least about 80 mol-% of the C ₃ H ₈ is converted. Embodiment 13 is the method of any one of Embodiments 1 to 12, wherein at least about 50 mol-% of the C0 ₂ is converted. Embodiment 14 is the method of any one of Embodiments 1 to 13, wherein the oxidative dehydrogenation reaction generates an olefins yield of greater than about 55%.

[0014] The term "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0015] The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

[0016] The words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0017] The method of the present invention can "comprise," "consist essentially of," or "consist of particular steps, components, and use include the compositions such as catalysts, etc. disclosed throughout the specification.

[0018] The catalysts used in accordance with the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc. disclosed throughout the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 depicts a method of producing olefins by an oxidative dehydrogenation reaction according to one exemplary embodiment of the disclosed subject matter.

DETAILED DESCRIPTION

[0020] The presently disclosed subject matter provides methods for producing olefins from light hydrocarbons, e.g., by oxidative dehydrogenation. The methods can further be used to produce syngas in addition to olefins.

[0021] Oxidative dehydrogenation can be used to convert saturated hydrocarbons to olefins. For example, C ₂ and C ₃ paraffins, i.e., ethane (C ₂ H ₆ ) and propane (C ₃ H ₈ ), can be converted to C ₂ and C ₃ olefins, i.e., ethylene (C ₂ H ₄ ) and propylene (C ₃ ¾), as shown in Formulas 1 and 2 below:

C ₂ H _{6 <} → C ₂ ¾ + H ₂ (Formula 1)

C ₃ H _{8 <} → C ₃ ¾ + H ₂ (Formula 2)

[0022] During the dehydrogenation of saturated hydrocarbons, H ₂ is formed as a byproduct. By adding an oxidant, such as carbon dioxide (C0 ₂ ), to the dehydrogenation reaction, it is possible to oxidize the H ₂ and alter the products of the reaction. For example, C0 ₂ can react with the H ₂ to form carbon monoxide (CO) and water (H ₂ 0) in a reverse water gas shift reaction. The reverse water gas shift reaction is illustrated by Formula 3 below:

C0 ₂ + H _{2 <} → CO + H ₂ 0 (Formula 3)

[0023] Accordingly, the oxidative dehydrogenation of C ₂ H ₆ and C ₃ H ₈ in the presence of C0 ₂ can be represented overall by Formulas 4 and 5 below:

2C ₂ H ₆ + C0 _{2 <} → 2C ₂ H ₄ + CO + H ₂ + H ₂ 0 (Formula 4)

2C ₃ H ₈ + C0 _{2 <} → 2C ₃ H ₆ + CO + H ₂ + H ₂ 0 (Formula 5)

[0024] As shown in Formulas 4 and 5, the total reaction will result in a mixture of olefins (i.e., C ₂ H ₄ and C ₃ ¾) and syngas (primarily a mixture of CO and H ₂ ). These reactions are equilibrium-driven, and can be performed under conditions resulting in only partial conversion of C0 ₂ and H ₂ , and thus the product stream can include C0 ₂ and H ₂ , as well as olefins, CO, and H ₂ 0. Moreover, by adjusting the stoichiometric ratio of C0 ₂ in the feed stream, it is possible to obtain syngas having various molar ratios of CO to H ₂ (CO/H ₂ ).

[0025] The use of oxidative dehydrogenation in the presence of C0 ₂ can have advantages over certain conventional techniques. For example, unlike steam cracking, which produces a significant amount of H ₂ byproduct and can result in the accumulation of coke (i.e., carbonaceous) deposits, oxidative dehydrogenation can be used to generate syngas and results in less coke formation. For further example, oxidative conversion of hydrocarbons, which can result in full oxidation to C0 ₂ and as a result, partial loss of the feed stock. On the contrary, oxidative dehydrogenation can be used to generate olefins without creating deep oxidation products, such as C0 ₂ . Furthermore, compared to oxidation reactions, oxidative dehydrogenation is less prone to cause heat runaway from oxidation by molecular oxygen.

[0026] Accordingly, the presently disclosed methods can use oxidative dehydrogenation to generate olefins and syngas from a hydrocarbon feed stream. For the purpose of illustration and not limitation, FIG. 1 is a schematic representation of a method according to a non-limiting embodiment of the disclosed subject matter. The method 100 can include introducing a feed stream comprising C ₂ and C ₃ hydrocarbons and C0 ₂ to a Cr oxide catalyst 101 and generating a product stream therefrom comprising olefins and syngas 102.

[0027] As embodied herein, the feed stream can include C ₂ and C ₃ hydrocarbons. The hydrocarbons can be sourced from a C ₂ and/or C ₃ fraction, e.g., derived from natural gas or petroleum processing. In certain embodiments, the C ₂ hydrocarbons can include ethane (i.e., C ₂ H ₆ ). In certain embodiments, the C ₃ hydrocarbons can include propane (i.e., C ₃ H ₆ ).

[0028] In certain embodiments, the feed stream can further include C0 ₂ . The C0 ₂ in the feed stream can originate from various sources. For example, C0 ₂ can be sourced from other chemical processes, e.g., as a waste product, and/or unconverted C0 ₂ can be recovered from the product stream and recycled to the feed stream. "Feed stream," as used herein, can refer to a single feed stream or multiple feed streams, which can be combined before or during the oxidative dehydrogenation reaction. For example, the feed stream can be a single mixture of hydrocarbons and C0 ₂ . Alternatively or additionally, multiple feed streams containing one or more types of hydrocarbons and/or C0 ₂ can be provided.

[0029] As embodied herein, the feed stream can further include additional components, including heavier hydrocarbons (i.e., C ₄ and heavier hydrocarbons), and unsaturated C ₂ and C ₃ hydrocarbons, e.g., ethylene, propylene, and/or acetylene.

[0030] In certain embodiments, the feed stream can include from about 10 mol-% to about 60 mol-%, or from about 20 mol-% to about 50 mol-%, or from about 30 mol-% to about 40 mol-%, or about 35 mol-% C ₂ and C ₃ hydrocarbons. In certain embodiments, about 50 mol-%) of the hydrocarbons can be C ₂ hydrocarbons (e.g., C ₂ H ₆ ) and about 50 mol-%> of the hydrocarbons can be C ₃ hydrocarbons (e.g., C ₃ H ₈ ). Thus, the feed stream can comprise from about 15 mol-%> to about 30-mol%> C ₂ hydrocarbons and from about 15 mol-%> to about 30 mol%> C ₃ hydrocarbons. The feed stream can further include from about 40 mol-%> to about 90 mol-%>, or from about 50 mol-%> to about 80 mol-%>, or from about 60 mol-%> to about 70 mol-%, or about 65 mol-% C0 ₂ .

[0031] As used herein, the term "about" or "approximately" means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, "about" can mean a range of up to 20%, up to 10%, up to 5%), and or up to 1% of a given value.

[0032] As embodied herein, the feed stream can be introduced to a Cr oxide catalyst, e.g., as modified with K and Mn, for the oxidative dehydrogenation reaction. The oxidative dehydrogenation can be performed under any suitable reaction conditions. For example, the reaction can be performed at a temperature ranging from about 600°C to about 900°C, or from about 700°C to about 850°C, or from about 800°C to about 830°C. The pressure can range from atmospheric pressure to about 5 bar. The weight hourly space velocity (WHSV) of the reaction can be from about 1500 h ^"1 to about 4500 h ^"1 , or from about 2000 h ^"1 to about 3500 h ^"1 , from about 2500 h ^"1 to about 3000 h ^"1 , or about 2800 h ^"1 .

[0033] For example, and not limitation, the reaction can be performed in any reactor type known in the art to be suitable for the oxidative dehydrogenation of a hydrocarbon stream. For example, but not by way of limitation, the reactor can be a fixed bed reactor, such as a tubular fixed bed reactor or multi-tubular fixed bed reactor, or fluidized bed reactor. The dimensions and structure of the reactor of the presently disclosed subject matter can vary depending on the capacity of the reactor. The capacity of the reactor can be determined by the reaction rate, the stoichiometric quantities of the reactants and/or the feed stream flow rate.

[0034] The catalyst for use in the presently disclosed subject matter can be a modified chromium (Cr) oxide catalyst. The Cr can be supported on a variety of oxide materials, including, but not limited to aluminum oxide (alumina), magnesia, silica, titania, zirconia, and mixtures or combinations thereof. In certain embodiments, the support material is alumina (AI ₂ O ₃ ) or silica (Si0 ₂ ). In particular embodiments, the catalyst is a modified Cr/Si0 ₂ catalyst.

[0035] A Cr oxide catalyst can be an effective catalyst for the dehydrogenation of C ₂ and C ₃ hydrocarbons, e.g., as depicted by Formulas 1 and 2 described above. However, a bifunctional catalyst is preferred for the simultaneous activation of the hydrocarbons and C0 ₂ , as in oxidative dehydrogenation. For example, the Cr oxide catalyst can be modified with a basic element to form a redox system. Such a redox system can further reduce the accumulation of coke deposits on the Cr oxide catalyst. By way of example, and not limitation, suitable basic elements for use in the redox system include alkali metals, such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs), or rare earth elements such as lanthanum (La) or gadolinium (Gd). In particular embodiments, the Cr oxide catalyst is modified with K.

[0036] Additionally or alternatively, the Cr oxide catalyst can include one or more promoters. In certain embodiments, the one or more promoters can increase activation of C0 ₂ , e.g., to promote the generation of syngas. For example, and not limitation, manganese (II) oxide (MnO) can be a suitable promoter. Because the Mn of MnO is a basic element, MnO can further activate C0 ₂ through the formation of surface carbonates, as demonstrated in Formulas 6 and 7 below. Surface carbonates can block the surface of the Cr oxide catalyst to prevent oxide phase formation that can reduce catalyst activity.

MnO + C0 _{2 <} → MnCO (Formula 6)

3MnC0 ₃ Mn ₃ 0 ₄ + 2C0 ₂ + CO (Formula 7)

[0037] In certain embodiments, a catalyst according to the disclosed subject matter can be a Cr oxide catalyst modified with at least two additional elements. For example, the Cr oxide catalyst can be modified with K and Mn. In particular embodiments, the catalyst can be K- Cr-Mn/Si0 ₂ . In certain embodiments, a K-Cr-Mn/Si0 ₂ catalyst can include from about 0.5 wt-% to about 5 wt-%, or about 2 wt-% K and further include from about 5 wt-% to about 25 wt-%), or about 15 wt-%> Mn. The K-Cr-Mn/Si0 ₂ catalyst can also include from about 2 wt-%> to about 15 wt-%), or about 8 wt-%> Cr.

[0038] The presently disclosed method can be used to generate a product stream including olefins, e.g., ethylene and propylene, and syngas (i.e., CO and H ₂ ). The product stream can further include additional components, such as unconverted reactants and intermediates, including C ₂ and C ₃ hydrocarbons and C0 ₂ . In certain embodiments, the product stream can further include H ₂ 0 and/or methane (CH ₄ ).

[0039] In certain embodiments, the syngas of the product stream can have a ratio of CO to H ₂ (CO/H ₂ ) from about 1.4 to about 1.8, or from about 1.5 to about 1.7. In certain embodiments, the conversion of C ₂ hydrocarbons (e.g., C ₂ H ₆ ) can be greater than about 65 mol-%), greater than about 70 mol-%>, or greater than about 75 mol-%>. In certain embodiments, the conversion of C ₃ hydrocarbons (e.g., C ₃ H ₈ ) can be greater than about 60 mol-%), greater than about 70 mol-%>, or greater than about 80 mol-%>. In certain embodiments, the conversion of C0 ₂ can be greater than about 40 mol-%>, greater than about 45 mol-%>, or greater than about 50 mol-%>. The presently disclosed methods of oxidative dehydrogenation can generate an olefins yield of greater than about 45%, greater than about 50%), or greater than about 55%.

[0040] The presently disclosed methods can be used to generate a product stream suitable for a variety of applications. For example, a product stream including a mixture of olefins and syngas can be used directly for hydro-carbonylation reactions, e.g., involving oxo-synthesis. Alternatively, the olefins and syngas can be separated and used in multiple applications. By way of example, and not limitation, the generated propylene can be used for the hydro-carbonylation of propylene to butyl aldehyde, which can be further converted to 2- ethylhexanol (2-EH). For further example, the syngas can be used in the production of monoethylene glycol (MEG) or methanol carbonylation. Excess hydrogen can be separated and used, for example, as fuel.

[0041] The methods and systems of the presently disclosed subject matter provide advantages over certain existing technologies. Exemplary advantages include efficient conversion of light hydrocarbons to olefins while creating a valuable syngas byproduct. Additional advantages include increased conversion of light hydrocarbons and olefins yield.

[0042] The presently disclosed subject matter will be further understood with reference to the following examples. The following examples are merely illustrative of the presently disclosed subject matter and should not be considered as limitations in any way.

EXAMPLE 1. OXIDATIVE DEHYDROGENATION OF A 0-C¾ FRACTION

[0043] In this Example, a C ₂ -C ₃ fraction including C ₂ and C ₃ alkanes was dehydrogenated in the presence of C0 ₂ . The catalyst used was 2%K-8%Cr-15%Mn/Si0 ₂ (by weight). Catalyst loading was 8 mL. The space velocity of the reaction was 2800 h ^"1 . The feed stream contained 35 mol-% of the C ₂ -C ₃ fraction and 65 mol-% C0 ₂ . The feed stream was provided to a fixed bed reactor at a flow rate or 373 cc/min. The fixed bed reactor included a 15mm ID. quartz reactor that was heated by an electrical furnace. The C ₂ -C ₃ fraction contained 50 mol-% C ₂ H ₆ and 50 mol-% C ₃ H ₈ .

[0044] The reaction was carried out at a temperature of 800°C. The product composition was analyzed with a Gas Chromatograph having columns with Porapak Q and a Molecular Sieve with a thermal conductivity detector (TCD). The conversion of C ₂ H ₆ was 70.5 mol-% and the conversion of C ₃ H ₈ was 74.6 mol-%. C0 ₂ conversion was 44.2 mol-%. The product stream contained ethylene (C ₂ H ₄ ), propylene (C ₃ H ₆ ), CO, H ₂ , and CH ₄ . The CO to H ₂ ratio (CO/H ₂ ) in the product stream was 1.5. The C ₂ and C ₃ olefins yield was 56%. These data show that oxidative dehydrogenation with a K-Cr-Mn/Si0 ₂ catalyst can efficiently convert a hydrocarbon stream to olefins and syngas.

EXAMPLE 2. OXIDATIVE DEHYDROGENATION OF A C7.-C1 FRACTION

[0045] In this Example, a C2-C3 fraction was dehydrogenated in the presence of C0 ₂ under the same conditions and using the same methods described in Example 1, but at a temperature of 830°C.

[0046] The conversion of C ₂ H ₆ was 78.0 mol-% and the conversion of C ₃ H ₈ was 80.5 mol-%. C0 ₂ conversion was 50.0 mol-%. The product stream contained ethylene (C ₂ H ₄ ), propylene (C ₃ H ₆ ), CO, H ₂ , and CH ₄ . The CO to H ₂ ratio (CO/H ₂ ) in the product stream was 1.7. The C ₂ and C ₃ olefins yield was 61%. Accordingly, oxidative dehydrogenation can be used with a K-Cr-Mn-/Si0 ₂ catalyst to convert a hydrocarbon stream to olefins and syngas with high conversion and olefins yield.

* * *

[0047] In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having other combinations of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

[0048] It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.