Catalyst and process for the dehydrogenation of alkanes to alkenes

Abstract

A method of converting alkanes to alkenes includes contacting a feed stream having alkanes with a dehydrogenation catalyst in a reactor. The dehydrogenation catalyst is a Molybdenum-Vanadium-Oxide (MoVyOx) based catalyst comprising tantalum (Ta), antimony (Sb), and bismuth (Bi), including oxides thereof, or tantalum (Ta), niobium (Nb), antimony (Sb), and bismuth (Bi), including oxides thereof. The dehydrogenation catalyst has a crystallographic structure with Pba2-32 space group. Upon contacting the feed stream with the dehydrogenation catalyst, at least a portion of the alkanes is converted to alkenes, thereby yielding a product stream including alkanes and alkenes.

Description

CATALYST AND PROCESS FOR THE DEHYDROGENATION OF ALKANES TO ALKENESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 641,134 filed May 1, 2024, the contents of which are incorporated in their entirety herein.FIELD

[0002] The present application is related to methods of converting alkanes to alkenes using an oxidative dehydrogenation catalyst, and in particular related to methods of converting ethane to ethylene comprising a Molybdenum-Vanadium-Oxide (MoVyOx) based catalyst that is capable of catalyzing the alkane-alkene conversion substantially in the absence of a gaseous oxidant.BACKGROUND

[0003] Alkenes are used for a wide range of industrial applications, including producing plastics, fuels, and various downstream chemicals. For example, ethylene (also referred to herein as C2H4 or ethene) is a valuable commodity chemical widely used to produce plastics such as polyethylene. Currently, the dominant pathway for ethane-ethylene conversion is steam cracking. Steam cracking of hydrocarbons is the leading technology for the production of base chemicals due to its significant process maturity. For example, steam cracking of ethane (C2H6) or naphtha to produce ethylene is generally operated between 973 K and 1223 K. This endothermic process is highly energy-intensive and accounts for up to 300 million tons of CO2 emissions annually.

[0004] Facing the growing demand for ethylene, there is a need to develop energy-efficient processes to produce ethylene with scaled-down CO2 emissions. Conventional oxidative dehydrogenation (ODH) process can undergo the ethane-ethylene conversion at a reduced temperature between 623 K and 773 K. However, the conventional ODH process for ethane- ethylene conversion requires that high purity oxygen and ethane coexistent in a reactor or a feedstream, which poses safety concerns. Further, producing high purity oxygen is very energy consuming, which is contrary to the trend toward energy efficiency. Additionally, the conventional ODH process undergoes side reactions leading to the formation of carboxyl group- containing products such as acetic acid and thus reduces the yield of the high-value ethylene. Accordingly, there is a need for an efficient method of converting ethane to ethylene with improved ethylene selectivity and yield, minimized CO2 footprint, and reduced safety risk.SUMMARY

[0005] Embodiments of the present disclosure meet these needs by using oxidative dehydrogenation catalysts that convert ethane to ethylene with a high ethylene selectivity and a low COXselectivity and, particularly, that are capable of performing the ODH reaction substantially in the absence of a gaseous oxidant. Embodiments of the oxidative dehydrogenation catalysts disclosed herein are Molybdenum- Vanadium- Oxide (MoVyOx) based catalysts comprising tantalum (Ta), antimony (Sb), and bismuth (Bi), including oxides thereof. In one or more embodiments, the oxidative dehydrogenation catalyst may comprise niobium (Nb), including oxides thereof. At least a portion of the oxidative dehydrogenation catalyst comprises a crystallographic structure with Pba2-32 space group. The disclosed oxidative dehydrogenation catalysts are capable of maintaining a conversion of ethane greater than or equal to 10 Cmol% and converting ethane to ethylene with an ethylene selectivity greater than or equal to 70 Cmol% substantially in the absence of a gaseous oxidant.

[0006] Additional features and advantages will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description that follows, the claims, as well as the appended drawings.

[0007] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawingsillustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGURE depicts X-Ray diffraction patterns for Molybdenum- Vanadium-Oxide (MoVyOx) based catalysts.DETAILED DESCRIPTION

[0009] Reference will now be made in detail to embodiments of methods of converting alkanes to alkenes, and particularly, methods of converting alkanes to alkenes that utilize oxidative dehydrogenation catalysts that can catalyze oxidative dehydrogenation substantially in the absence of a gaseous oxidant.

[0010] As used herein, “dehydrogenation” refers to a chemical process by which hydrogen is chemically removed from a chemical compound. For example, ethane (C2H6) may undergo dehydrogenation to be converted to ethylene (C2H4). As used herein, “oxidative dehydrogenation” refers to a chemical process that employs oxygen to activate the chemical removal of hydrogen from a chemical compound. As used herein, “catalyst(s)” refers to a substance that increases the rate of a reaction towards the desired product without itself undergoing any permanent chemical change or a substance that forms an intermediate by reacting with at least one reactant while forming a product and may be regenerated to its original form in temporally or spatially separated step(s).

[0011] As used herein, “alkane(s)” refers to any series of hydrocarbon molecules that consist of carbon-carbon single bonds and where the carbon structure is saturated with hydrogen. Ethane, propane, and butane are examples of alkanes. As used herein, “alkene(s)” refers any series of hydrocarbon molecules, where two of the carbon atoms are not saturated with hydrogen and share a double bond. Ethylene, propylene, 1 -butene, trans -2-butene, and cz -2-butene are examples of alkenes.

[0012] Methods disclosed and described herein generally may comprise contacting a feed stream comprising alkanes with an oxidative dehydrogenation catalyst in a reactor, wherein the oxidative dehydrogenation catalyst is a Molybdenum-Vanadium-Oxide (MoVyOx) based catalyst comprising tantalum (Ta), antimony (Sb), and bismuth (Bi), including oxides thereof; and converting at least a portion of the alkanes to alkenes, thereby yielding a product stream comprising alkanes and alkenes. In further embodiments, the oxidative dehydrogenation catalyst may further comprise niobium (Nb) and niobium oxides. It should be understood that in embodiments the oxidative dehydrogenation catalyst may be used alone or may be used with other additives.

[0013] According to embodiments, the feed stream may comprise at least one alkane. In embodiments, the feed stream may consist essentially alkanes, which herein means the feed stream may comprise at least 95 vol.% alkanes, such as at least 97 vol.% alkanes or at least 99 vol.% alkanes. In one or more embodiments, the feed stream may comprise greater than or equal to 40 vol.% alkanes, such as greater than or equal to 50 vol.% alkanes, as greater than or equal to 70 vol.% alkanes, or greater than or equal to 90 vol.% alkanes. In one or more embodiments, the feed stream may contain oxygen, steam and / or inert gas. In one or more embodiments, the feed stream may comprise greater than or equal to 40 vol.% alkanes and less than or equal to 60 vol.% oxygen, steam and / or inert gas, such as greater than or equal to 50 vol.% alkanes and less than or equal to 50 vol.% oxygen, steam and / or inert gas, greater than or equal to 70 vol.% alkanes and less than or equal to 30 vol.% oxygen, steam and / or inert gas, or greater than or equal to 90 vol.% alkanes and less than or equal to 10 vol.% oxygen, steam and / or inert gas. As used herein, the “inert gas” may be nitrogen, helium, or a combination thereof.

[0014] In further embodiments, the at least one alkane may be ethane; that is, the feed stream may consist essentially ethane, which herein means the feed stream may comprise at least 95 vol.% ethane, such as at least 97 vol.% ethane or at least 99 vol.% ethane. In one or more embodiments, the feed stream may comprise greater than or equal to 40 vol.% ethane, such as greater than or equal to 50 vol.% ethane, as greater than or equal to 70 vol.% ethane, or greater than or equal to 90 vol.% ethane. In one or more embodiments, the feed stream may comprise greater than or equal to 40 vol.% ethane and less than or equal to 60 vol.% oxygen, steam and / or inert gas, such as greater than or equal to 50 vol.% ethane and less than or equal to 50 vol.%oxygen, steam and / or inert gas, greater than or equal to 70 vol.% ethane and less than or equal to 30 vol.% oxygen, steam and / or inert gas, or greater than or equal to 90 vol.% ethane and less than or equal to 10 vol.% oxygen, steam and / or inert gas.

[0015] In one or more embodiments, the feed stream may be substantially free of a gaseous oxidant, meaning that the feed stream comprises less than 1 vol.% oxidants, such as less than 0.5 vol.% oxidants, less than 0.1 vol.% oxidants, less than 0.05 vol.% oxidants, or less than 0.01 vol.% oxidants. In embodiments, the gaseous oxidant may be O2, NO, NO2, H2O, CO2, N2O, O3, or a combination thereof.

[0016] According to embodiments, contacting the feed stream comprising alkanes with the oxidative dehydrogenation catalyst disclosed herein in a reactor may cause at least a portion of alkanes to be converted to alkenes, thereby yielding a product stream comprising alkanes and alkenes.

[0017] In one or more embodiments, the feed stream may contact with the oxidative dehydrogenation catalyst disclosed herein at a weight hourly space velocity of from 0.5 / hr to 4 / hr and a catalyst-to-alkane mass ratio of from 5:1 to 200:1. In further embodiments, the feed stream may contact with the oxidative dehydrogenation catalyst disclosed hereinat, for example, a weight hourly space velocity from 0.5 / hr to 1.5 / hr, from 1 / hr to 2 / hr, from 1 / hr to 3 / hr per hour, or from 2 / hr to 4 / hr per hour, and a catalyst-to-alkane mass ratio from 5:1 to 100:1, from 50:1 to 150:1, from 100:1 to 200:1, or from 150:1 to 200:1.

[0018] In one or more embodiments, the feed stream may enter the reactor at a temperature of from 300 °C to 600 °C, a pressure of from 0 bar(g) to 20 bar(g), and a weight hourly space velocity (WHSV) of from 0.1 / hr to 10 / hr. In further embodiments, the feed stream may enter the reactor at, for example, a temperature of from 300 °C to 500 °C, from 400 °C to 550 °C, from 450 °C to 600 °C, or from 500 °C to 600 °C; a pressure of from 0 bar(g) to 5 bar(g), from 0 bar(g) to 10 bar(g), from 0 bar(g) to 15 bar(g), from 5 bar(g) to 15 bar(g), from 10 bar(g) to 15 bar(g), from 10 bar (g) to 20 bar(g), or from 15 bar(g) to 20 bar(g); and a weight hourly space velocity (WHSV) of from 0.1 / hr to 3 / hr, from 0.1 / hr to 5 / hr, from 0.1 / hr to 7 / hr, from 3 / hr to 5 / hr, from 3 / hr to 7 / hr, from 5 / hr to 7 / hr, from 5 / hr to 10 / hr, or from 7 / hr to 10 / hr.

[0019] In one or more embodiments, the reactor may be substantially free of a gaseous oxidant.

[0020] In one or more embodiments, an oxygen stream may be added to a reaction zone. The concentration of oxygen in the oxygen stream is not particularly limited. For example, the oxygen concentration in the oxygen stream may be from 0.1 vol% to 99.9 vol%, such as from 5.0 vol% to 95.0 vol%, from 10.0 vol% to 90.0 vol%, from 15.0 vol% to 85.0 vol%, from 20.0 vol% to 80.0 vol%, from 25.0 vol% to 75.0 vol%, from 30.0 vol% to 70.0 vol%, from 35.0 vol% to 65.0 vol%, from 40.0 vol% to 60.0 vol%, or from 45.0 vol% to 55.0 vol%. In one or more embodiments, the concentration of oxygen in the oxygen stream is relatively low, such as from 0.1 vol% to 5.0 vol%, from 0.2 vol% to 5.0 vol%, from 0.5 vol% to 5.0 vol%, from 0.8 vol% to 5.0 vol%, from 1.0 vol% to 5.0 vol%, from 1.2 vol% to 5.0 vol%, from 1.5 vol% to 5.0 vol%, from 1.8 vol% to 5.0 vol%, from 2.0 vol% to 5.0 vol%, from 2.2 vol% to 5.0 vol%, from 2.5 vol% to 5.0 vol%, from 2.8 vol% to 5.0 vol%, from 3.0 vol% to 5.0 vol%, from 3.2 vol% to 5.0 vol%, from 3.5 vol% to 5.0 vol%, from 3.8 vol% to 5.0 vol%, from 4.0 vol% to 5.0 vol%, from 4.2 vol% to 5.0 vol%, from 4.5 vol% to 5.0 vol%, or from 4.8 vol% to 5.0 vol%. In embodiments, the oxygen stream may be air, which generally has an oxygen concentration of about 21.0 vol%.

[0021] The oxygen stream may, in embodiments, be added to the reaction zone sequentially to the feed stream, such that the feed stream and the oxygen stream are not added to the reaction zone at the same time. It should be understood that in embodiments, the oxygen stream may be added at various points within the reaction process. This may be accomplished by introducing the oxygen stream into the reaction zone at different locations within the reaction zone and / or introducing the oxygen stream at different time periods while the reaction is taking place.

[0022] In one or more embodiments, the oxygen stream is added to the reaction zone simultaneously to the feed stream. In such embodiments, the volume ratio of oxygen (in the oxygen stream) to alkanes (in the feed stream) in the reaction zone is from greater 0.0 to 1.0, from 0.1 to 1.0, from 0.2 to 1.0, from 0.3 to 1.0, from 0.4 to 1.0, from 0.5 to 1.0, from 0.6 to 1.0, from 0.7 to 1.0, from 0.8 to 1.0, from 0.9 to 1.0, or from greater than 0.0 to 0.2, from 0.0 to 0.3, from 0.0 to 0.4, from 0.0 to 0.5, from 0.0 to 0.6, from 0.0 to 0.7, from 0.0 to 0.8, or from 0.0 to 0.9.

[0023] The reactor is not particularly limited and any type of reactor allowing for cyclic or continuous operation of the dehydrogenation process may be used in embodiments. In embodiments, the reactor may be a fixed bed reactor, a fluidized bed reactor, a moving bed reactor, a bubbling bed reactor, circulating fluidized reactor, reverse flow reactor, or an ebullated (bubbling) bed reactor. In embodiments, a reaction zone can be all or apportion of the reactor. The reaction zone is not particularly limited to a single reactor and can consist of multiple reactors in either series or parallel configuration.

[0024] Reference will now be made in detail to embodiments of oxidative dehydrogenation catalysts that are capable of catalyzing the alkane-alkene conversion substantially in the absence of a gaseous oxidant.

[0025] Using oxidative dehydrogenation catalysts disclosed herein convert alkanes to alkenes, and particularly, ethane to ethylene, substantially in the absence of a gaseous oxidant at a temperature similar to or lower than conventional ODH processes. These oxidative dehydrogenation catalysts comprise lattice oxygen species. Without being bound by any particular theory, lattice oxygen can activate alkanes, thus this particular dehydrogenation process is termed lattice oxidative dehydrogenation or TODh.

[0026] It has been observed that previously known molybdenum-vanadium oxide based catalysts may be capable of catalyzing both ODH and TODh processes. However, when known molybdenum vanadium oxide catalysts convert ethane in TODh processes, they usually demonstrate low activity yet still may cause overoxidation of fed ethane to COX, thereby leading to low C2H4 yield. Without being bound by any particular theory, it is believed that low conversion may be a result of low catalyst stability caused by the chemical changes, reduction, and volatilization of elements such as tellurium, which is generally encountered when these catalysts are operated in a cyclic redox mode or in conditions with low partial pressure of O2 typically at the bottom sections of fixed bed reactors.

[0027] Further, maintaining high conversion of ethane (more than 10 Cmol%) and high selectivity to C2H4 (more than 70 Cmol%) under relevant conditions is a general issue for oxidative dehydrogenation processes to compete with and outperform commercial steam cracking.

[0028] It has unexpectedly been found that combining tantalum (Ta) with antimony (Sb) and bismuth (Bi), including oxides thereof, or with niobium (Nb), antimony (Sb), and bismuth (Bi), including oxides thereof, allows the development of a structurally robust material that could withstand reduction (i.e., ethane feed) and oxidation (i.e., controlled re-oxidation) cycling with significantly improved activity and presenting high ethylene selectivity with limited COXformation. According to embodiments disclosed and described herein, the oxidative dehydrogenation catalysts may comprise Molybdenum-Vanadium-Oxide (MoVyOx) based catalysts comprising Ta, Sb, and Bi, including oxides thereof, or Ta, Nb, Sb, and Bi, including oxides thereof. Embodiments of the oxidative dehydrogenation catalyst include MoVyOxbased catalysts that are a physical mixture of MoVyOx, tantalum oxides, antimony oxides, and bismuth oxides. In one or more embodiments, the oxidative dehydrogenation catalyst is a MoVyOxbased catalyst that has a formula MoVyXaShbBicOx, wherein X is Ta or Ta and Nb. In embodiments, the disclosed oxidative dehydrogenation catalyst may be substantially free of tellurium (Te), meaning that the oxidative dehydrogenation catalyst comprises less than 0.001 wt.% Te or a Te / Mo ratio below 0.01.

[0029] In one or more embodiments, the oxidative dehydrogenation catalyst may comprise a physical mixture of MoVyOx, tantalum oxides, antimony oxides, and bismuth oxides or a physical mixture of MoVyOx, tantalum oxides, niobium oxides, antimony oxides, and bismuth oxides.

[0030] In embodiments, vanadium may comprise from 2 wt.% to 16.4 wt.% of the oxidative dehydrogenation catalyst, such as from 2 wt.% to 8 wt.%, from 2 wt.% to 10 wt.%, from 4 wt.% to 16.4 wt.%, from 4 wt.% to 13 wt.%, from 4 wt.% to 8 wt.%, from 4 wt.% to 10 wt.%, from 10 wt.% to 16.4 wt.%, from 8 wt.% to 13 wt.%, or from 8 wt.% to 16.4 wt.%.

[0031] In embodiments, tantalum or tantalum and niobium may comprise from 0.06 wt.% to 10.8 wt.% of the oxidative dehydrogenation catalyst, such as from 0.06 wt.% to 5.4 wt.%, from 0.06 wt.% to 7.5 wt.%, from 0.06 wt.% to 2.8 wt.%, from 0.5 wt.% to 10.8 wt.%, from 0.5 wt.% to 5.4 wt.%, 0.5 wt.% to 2.8 wt.%, from 1 wt.% to 7.5 wt.%, from 1 wt.% to 10.8 wt.%, from 5 wt.% to 8 wt.%, from 5 wt.% to 10.8 wt.%, or from 7 wt.% to 10.8 wt.%.

[0032] In embodiments, antimony may comprise from 0.09 wt.% to 14 wt.% of the oxidative dehydrogenation catalyst, such as from 0.09 wt.% to 10.2 wt.%, from 0.09 wt.% to 5.1 wt.%,from 1.5 wt.% to 5.1 wt.%, from 1.5 wt.% to 7.5 wt.%, from 1.5 wt.% to 10.2 wt.%, from 5.1 wt.% to 10.2 wt.%, from 5.1 wt.% to 14 wt.%, from 7.5 wt.% to 14 wt.%, or from 10.2 wt.% to14 wt.%.

[0033] In embodiments, bismuth may comprise from 0.2 wt.% to 22 wt.% of the oxidative dehydrogenation catalyst, such as from 0.2 wt.% to 11.5 wt.%, from 0.2 wt.% to 17.6 wt.%, from0.2 wt.% to 19.8 wt.% from 0.2 wt.% to 5.6 wt.%, from 0.2 wt.% to 1.9 wt.%, from 1.9 wt.% to11.5 wt.% from 1.9 wt.% to 19.8 wt.%, from 5.6 wt.% to 11.5 wt.%, from 5.6 wt.% to 17.6 wt.%, from 5.6 wt.% to 22 wt.%, from 7.7 wt.% to 22 wt.%, from 7.7 wt.% to 17.6 wt.%, from 11.5 wt.% to 17.6 wt.%, from 11.5 wt.% to 22 wt.%, or from 17.6 wt.% to 22 wt.%.

[0034] In further embodiments, the oxidative dehydrogenation catalyst may comprise vanadium from 4 wt.% to 16.4 wt.%, tantalum or tantalum and niobium from 0.1 wt.% to 20 wt.%, antimony from 0.6 wt.% to 10 wt.%, and bismuth from 2.6 wt.% to 17.6 wt.%.

[0035] In further embodiments, the oxidative dehydrogenation catalyst may comprise vanadium from 4 wt.% to 13 wt.%, tantalum or tantalum and niobium from 0.06 wt.% to 7.5 wt.%, antimony from 0.09 wt.% to 5.1 wt.%, and bismuth from 7.7 wt.% to 17.6 wt.%

[0036] In one or more embodiments, the oxidative dehydrogenation catalyst may have a formula MoVyXaShbBicOx, wherein X is Ta or Ta and Nb. The atomic ratios of V, X, Sb, and Bi are determined using Mo as the basis; that is, Mo has a composition ratio of 1.0. The composition ratio of O is x, which is the oxygen content required to charge-balance the structure. In embodiments, vanadium may have a composition ratio y that is from 0.1 to 0.6; tantalum or tantalum and niobium may have a composition ratio a from 0.001 to 0.1; antimony may have a composition ratio b from 0.002 to 0.2; and bismuth may have a composition ratio c from 0.002 to 0.2.

[0037] In further embodiments, vanadium may have a composition ratio y that is from 0.1 to 0.6, such as from 0.1 to 0.2, from 0.1 to 0.3, from 0.1 to 0.4, from 0.2 to 0.4, from 0.2 to 0.6, or from 0.3 to 0.6.

[0038] In further embodiments, tantalum or tantalum and niobium may have a composition ratio a from 0.001 to 0.1, such as from 0.001 to 0.01, from 0.001 to 0.05, from 0.001 to 0.075,from 0.001 to 0.1, from 0.005 to 0.05, from 0.005 to 0.075, from 0.005 to 0.1, or from 0.075 to 0.1.

[0039] In further embodiments, antimony may have a composition ratio b from 0.002 to 0.2, such as from 0.01 to 0.2, from 0.01 to 0.1, from 0.05 to 0.15, from 0.05 to 0.2, from 0.05 to 0.1, or from 0.1 to 0.2.

[0040] In further embodiments, bismuth may have a composition ratio c from 0.002 to 0.2, such as from 0.01 to 0.2, from 0.01 to 0.1, from 0.05 to 0.2, from 0.05 to 0.1, or from 0.1 to 0.2.

[0041] For example, the oxidative dehydrogenation catalyst having a formula MoVyXaShbBicOx, wherein X is Ta or Ta and Nb, may comprise vanadium with a composition ratio y that is from 0.2 to 0.5, tantalum or tantalum and niobium with a composition ratio a from 0.005 to 0.075, antimony with a composition ratio b from 0.05 to 0.15, and bismuth with a composition ratio c from 0.05 to 0.15.

[0042] The oxidative dehydrogenation catalyst having a formula MoVyXaShbBicOx, wherein X is Ta or Ta and Nb, may comprises a plurality of phases. The phase of the oxidative dehydrogenation catalyst disclosed and described herein can, in embodiments, be measured using x-ray diffraction (XRD). For instance, and as would be understood by a skilled artisan, the relative intensity of XRD peaks at various angles can be used to describe the phase(s) of the oxidative dehydrogenation catalyst.

[0043] In one or more embodiments, the oxidative dehydrogenation catalyst may comprise at least a Pba2-32 space group crystal structure. This structure replaces the volatile Te with a more stable Bi, Sb, and Ta or Ta and Nb, which allows for improved stability over the known MoVNbTeOx catalysts while providing improved alkane conversion. For instance, in embodiments the oxidative dehydrogenation catalyst disclosed and described herein is both active (greater than 10% ethane conversion), selective (greater than 70 Cmol% ethylene selectivity), and renders stable performance under relevant reaction conditions.

[0044] According to embodiments, the oxidative dehydrogenation catalyst disclosed herein maintains its cyclic performance despite longer exposure to continuous ethane feed and higher operating temperatures, such as from 300 °C to 600 °C.

[0045] In one or more embodiments, the oxidative dehydrogenation catalyst may convert at least a portion of ethane to ethylene with an ethylene selectivity greater than or equal to 70 Cmol% by contacting the feed stream comprising ethane with the oxidative dehydrogenation catalyst in the reactor at a temperature that is from 300 °C to 600 °C; a pressure that is from 0 bar(g) to 20 bar(g); and an alkane weight hourly space velocity (WHSV) that is from 0.1 / hr to 10 / hr. For example, the temperature may be of from 300 °C to 500 °C, from 400 °C to 550 °C, from 450 °C to 600 °C, or from 500 °C to 600 °C. For example, the pressure may be of from 0 bar(g) to 5 bar(g), from 0 bar(g) to 10 bar(g), from 0 bar(g) to 15 bar(g), from 5 bar(g) to 15 bar(g), from 10 bar(g) to 15 bar(g), from 10 bar (g) to 20 bar(g), or from 15 bar(g) to 20 bar(g). For example, the weight hourly space velocity (WHSV) may be of from 0.1 / hr to 3 / hr, from 0.1 / hr to 5 / hr, from 0.1 / hr to 7 / hr, from 3 / hr to 5 / hr, from 3 / hr to 7 / hr, from 5 / hr to 7 / hr, from 5 / hr to 10 / hr, or from 7 / hr to 10 / hr.

[0046] Under these process conditions, the oxidative dehydrogenation catalyst may convert at least a portion of ethane to ethylene with an ethane conversion greater than or equal to 10 Cmol% and a COXselectivity less than or equal to 25 Cmol%. In further embodiments, the ethane conversion may be greater than or equal to 20 Cmol% or 30 Cmol%, and the COXselectivity may be less than or equal to 20 Cmol%, or less than or equal to 15 Cmol%.

[0047] The disclosed oxidative dehydrogenation catalysts may be synthesized through a convectional hydrothermal synthesis method. According to embodiments, methods of forming the oxidative dehydrogenation catalyst disclosed herein may comprise adding a molybdenum- containing compound, a vanadium-containing compound, a bismuth-containing compound, a tantalum-containing compound, an antimony-containing compound, and one or more organic acids to a mixture of alkylene glycol and water to form a starting mixture, wherein the starting mixture may comprise at least one of molybdenum trioxide (MoOs) and vanadium pentoxide (V2O5); treating the starting mixture by hydrothermal synthesis at a hydrothermal synthesis temperature that is from 150 °C to 250 °C; and separating a retentate from retained liquids, wherein the retentate comprises the disclosed oxidative dehydrogenation catalyst. In further embodiments, the methods of forming the oxidative dehydrogenation catalyst disclosed herein may further comprise adding a niobium-containing compound.

[0048] In one or more embodiments, the tantalum-containing compound may comprise at least one of tantalum(V) oxide and tantalum(V) ethoxide; the niobium-containing compound may comprise at least one of ammonium niobate(V) oxalate, niobium(V) oxide, hydrated niobium(V) oxide also known as niobic acid, niobium(V) ethoxide, niobium(II) oxide, niobium(IV) oxide; the antimony-containing compound may comprise at least one of antimony(III) oxide and antimony(V) oxide; and the bismuth-containing compound may comprise bismuth(III) oxide. In further embodiments, the one or more organic acids may comprise at least one of citric acid (CeHsCh), oxalic acid (C2H2O4), and mixtures thereof, and the alkylene glycol is ethylene glycol (C2H6O2).

[0049] In one or more embodiments, the method of forming the disclosed oxidative dehydrogenation catalyst may further comprise heat-treating the retentate at a temperature that is from 450 °C to 550 °C with a constant flow of nitrogen at a flow rate sufficient to maintain substantially oxygen free environment, for example, greater than or equal to 10 cm3 / s.

[0050] Reference will now be made in detail to embodiments of the product stream yielded by the alkane-to alkene conversion utilizing the MoVyOxbased catalysts disclosed herein.

[0051] According to embodiments, the product stream may comprise at least one alkene. In one or more embodiments, the product stream may comprise greater than or equal to 3 vol.% alkenes, such as 10 vol.% alkenes, 20 vol.% alkenes, or 30 vol.% alkenes. In one or more embodiments, the at least one alkenes may consist essentially ethylene, such that the product stream may comprise greater than or equal to 3 vol.% ethylene, such as 10 vol.% ethylene, 20 vol.% ethylene, or 30 vol.% ethylene.

[0052] The product stream may further comprise at least one of oxygenates, carbon monoxide, carbon dioxide, steam, and wherein the product stream is further processed to remove the at least one of at least one of oxygenates, carbon monoxide, carbon dioxide, steam, and alkanes from the product stream.

[0053] In further embodiments, the product stream may comprise less than or equal to 25 vol.% gaseous COX, such as less than or equal to 18 vol.% or less than or equal to 10 vol.%. The gaseous COXmay be CO, CO2, or a combination thereof.

[0054] In further embodiments, the product stream may be substantially free of an oxygenated molecule or molecules containing at least one oxygenated functional group, such as a carboxyl group, a carbonyl group, a hydroxyl group, a ketone group, and / or an epoxy group, meaning that the product stream comprises less than 1 vol.% an oxygenated molecule such as a carboxyl molecule, a carbonyl molecule, or an alcohol molecule. In one or more embodiments, the carboxyl molecule, the carbonyl molecule, or the alcohol molecule may be acetic acid, acetaldehyde, methanol, ethanol, or other light-weight molecule containing at least one carboxyl (-COOH), carbonyl (-C=O), or hydroxyl (-OH) group.

[0055] Reference will now be made in detail to embodiments of regenerating spent dehydrogenation catalysts and forming regenerated dehydrogenation catalysts.

[0056] In both ODH and LODh processes, spent dehydrogenation catalysts are likely to lose lattice oxygen as a result of the conversion. The lost lattice oxygen can be regenerated by reoxidizing the catalysts with a gaseous oxidant, such as air or oxygen, in a spatially or temporally separated step. By avoiding co-feeding a gaseous oxidant and highly flammable ethane, safety risks are significantly reduced. Further, by using a gaseous oxidant such as air to regenerate the catalysts, the need for separate, energy-consuming O2 production can be avoided.

[0057] According to embodiments, methods of converting alkanes to alkenes may further comprise contacting spent dehydrogenation catalyst with a regenerative stream, thereby regenerating the spent dehydrogenation catalyst and forming regenerated dehydrogenation catalyst, wherein the regenerative stream may comprise oxygen. In one or more embodiments, the regenerative stream may comprise from 2 vol.% to 22 vol.% oxygen, such as from 2 vol.% to 10 vol.% oxygen, from 7 vol.% to 12 vol.% oxygen, from 7 vol.% to 17 vol.%, from 7 vol.% to 22 vol.% oxygen, from 12 vol.% to 17 vol.% oxygen, from 12 vol.% to 22 vol.% oxygen, or from 17 vol.% to 22 vol.% oxygen. The regenerative stream may be diluted or undiluted air.

[0058] In one or more embodiments, contacting spent dehydrogenation catalyst with a regenerative stream may comprise introducing the regenerative stream and the spent dehydrogenation catalyst into a regeneration zone at a temperature of from 300 °C to 600 °C and a pressure of from 0 bar(g) (0 kPa) to 21 bar(g) (2100 kPa). For example, the temperature may be of from 300 °C to 500 °C, from 400 °C to 550 °C, from 450 °C to 600 °C, or from 500 °C to 600°C. For example, the pressure may be of from 0 bar(g) to 6 bar(g), from 0 bar(g) to 11 bar(g), from 0 bar(g) to 17 bar(g), from 6 bar(g) to 17 bar(g), from 11 bar(g) to 17 bar(g), from 11 bar (g) to 21 bar(g), or from 17 bar(g) to 21 bar(g).

[0059] The regenerative stream may, in embodiments, be added to the reactor sequentially to the feed stream, such that alkanes and gaseous oxidants are not present in the reaction zone at the same time. It should be understood that, in embodiments, the regenerative stream may be added at various points within the reaction process. This may be accomplished by introducing the regenerative stream into the reactor at different locations within the reactor and / or introducing the regenerative stream at different time periods while the reaction is taking place.

[0060] In one or more embodiments, the regenerative stream may contact with the spent dehydrogenation catalyst at a weight hourly space velocity of 0.5 to 4 per hour.

[0061] According to embodiments, contacting the spent dehydrogenation catalyst with the regenerative stream regenerates the spent dehydrogenation catalysts, thereby forming regenerated dehydrogenation catalysts that can be used in the reaction zone to aid the conversion of alkanes to alkenes.

[0062] In embodiments, upon contacting the spent dehydrogenation catalyst with the regenerative stream it would replenish the structure with oxygen in the process recovering from 0.05 wt.% to 5 wt.% of the spent dehydrogenation catalyst.

[0063] In embodiments, the regenerated dehydrogenation catalyst may comprise a recovered maximum activity that is from 50 % to 100 % of the maximum activity of a pre-regenerated, unspent dehydrogenation catalyst measured after several redox cycles (e.g. 30 redox cycles). For example, the recovered maximum activity may be from 50 % to 80 %, from 70 % to 90 %, or from 60 % to 75% of the maximum activity of the pre-regenerated, unspent dehydrogenation catalyst.EXAMPLES

[0064] Embodiments will be further clarified by the following examples.

[0065] Following examples describe the preparation of the MoVyOx-based catalysts disclosed and described herein as well as comparative MoVyOx-based catalysts free of Ta. A comparison of the conversion of ethane to ethylene using the examples and comparative examples is also provided.

[0066] Preparation of MoVyOx-Based Catalysts

[0067] The MoVyOx-based catalysts disclosed herein are prepared by hydrothermal synthesis. The preparation details for each example is now provided. The starting materials are listed in Table 1. The compositions for examples and comparative examples are provided in Table 2.

[0068] Table 1. Fist of starting materials.

[0069] Table 2. Composition of metal oxide slurry for El, E2, CE1, and CE2.

[0070] Example 1 (El): MoVo 49Tao 06Sbo 05Bio 11Ox

[0071] The first example (El) was a MoVyOx-based catalyst comprising Ta, Sb, and Bi, including oxides thereof, prepared by hydrothermal synthesis. The amounts of materials used for preparing El are presented in Table 2. First, a slurry of the metal oxides was prepared. The metal oxides were added to a 45 cm3Teflon-insert autoclave (Model 4744 General Purpose Acid Digestion Vessel, Parr). The metal oxides were mixed with deionized H2O and stirred using a Teflon-coated magnetic stirrer at a speed of 13.3 rotations per second to form the slurry. While the slurry was under stirring, ethylene glycol, followed by oxalic acid, and citric acid were added into the slurry. After being stirred for at least 10 minutes (360 seconds), the autoclave was sealed and latched on to a rotating shaft oven.

[0072] For the hydrothermal synthesis, temperature was increased at 3 °C / min (0.05 K / s) to 200 °C (473 K) and kept at this temperature for 48 hours (172800 seconds). During thehydrothermal synthesis, the autoclaves were tumbled over a horizontal axis at a speed of 10 rotations per minute (0.17 rotations per second). The obtained material was fdtered over a 0.45 pm fdter paper and washed with at least 90 cm3of deionized water by pouring over the retentate. The retentate was dried in stagnant air overnight in an oven maintained at 85 °C (358 K).

[0073] The dried sample was heat-treated in a sealed metal bucket inside an oven with a constant flow of N2 (>16 cm3 / s measured at ambient conditions). The heat-treatment procedure consisted of ramping the temperature to 450 °C (723 K) at 5 °C / min (0.083 K / s) and holding the temperature at 450 °C (723 K) for 2 hours (7200 seconds) before cool down.

[0074] The heat-treated material was compacted under 7 tonne pressure and sieved to 177 - 400 pm (40-80 mesh) prior to loading in the reactor. The finely powdered catalysts were analyzed with X-ray diffraction (see FIGURE).

[0075] Example 2 (E2): MoV0.2Ta0.005Sb0.05Bi0.11Ox

[0076] The second example (E2) was a MoVyOx-based catalyst comprising Ta, Sb, and Bi, including oxides thereof, prepared by the method generally described in Example 1. The amounts of materials used for preparing E2 are presented in Table 2. During the hydrothermal synthesis, the autoclaves were tumbled over a horizontal axis at a speed of 0.17 rotations per second.

[0077] Comparative Example 1 (CE1): MoVo 55Sbo 05Bio 11Ox

[0078] The first comparative example (CE1) was a MoVyOx-based catalyst comprising only Sb, and Bi, including oxides thereof, prepared by the method generally described in Example 1. The amounts of materials used for preparing CE1 are presented in Table 2. During the hydrothermal synthesis, the autoclaves were tumbled over a horizontal axis at a speed of 0.17 rotations per second.

[0079] Comparative Example 2 (CE2): MoVo2Nho 005Sho 05Bio 11Ox

[0080] The second comparative example was a MoVyOx-based catalyst comprising Nb, Sb, and Bi, including oxides thereof, prepared by hydrothermal synthesis.

[0081] Four batches of slurries of metal oxides were prepared as generally described in Example 1. The amounts of materials added for the four different batches are presented in Table 2. The four batches of slurries undergo the hydrothermal synthesis as generally described in Example 1 to obtain four batches of retentates. The four batches of retentates were dried overnight in an oven maintained at 85 °C (358 K).

[0082] After drying, all four batches of CE2 retentates were homogenized by physical mixing. A 2 g aliquot was washed further with 20 cm3of deionized H2O in a microwave synthesis apparatus (Anton Paar Monowave 450) using a sealed 30 cm3vial. The microwave washing procedure consisted of stirring the sample at 300 rotations per minute (5 rotations per second) and increasing the temperature to 70 °C (343 K) from ambient temperature in 10 minutes (600 seconds). This temperature was held for 3 hours (10800 s) under continuous stirring before cooled down to 45 °C (318 K). After being cooled down, 25 cm3to 30 cm3methanol was added to the slurry. Precipitation of solids was achieved by a centrifuge operated for 10 minutes (600 seconds) at 3000 rotations per minute (50 rotations per second). The supernatant was discarded. The steps of adding methanol, centrifugation, and disposal of the supernatant liquid were repeated three times. The wet samples were flushed out of the centrifuge tubes with additional methanol into a drying cup. The sample was allowed to dry at ambient conditions in a fume hood.

[0083] The dried samples were heat-treated in a sealed metal bucket inside an oven with a constant flow of N2 (>16 cm3 / s measured at ambient conditions). The heat-treatment procedure consisted of ramping the temperature to 450 °C (723 K) at 5 °C / min (0.083 K / s) and holding the temperature at 450 °C (723 K) for 2 hours (7200 seconds) before cool down.

[0084] The heat-treated material was compacted under 7 tonne pressure and sieved to 177 - 400 pm (40-80 mesh) prior to loading in the reactor. The fines were analyzed with X-ray diffraction (see FIGURE). As shown in FIGURE, the catalyst comprises a plurality of crystal structures, some of which may have coincidental x-ray diffraction on certain angles.

[0085] Characterization of MoVyOx-Based Catalysts

[0086] MoVyOx-based catalysts were characterized by X-Ray diffraction analysis (XRD). (See FIGURE) XRD of finely powdered catalysts (approximately 100 mg, less than177 pm) were obtained using a Broker D8 Discover diffractometer working at 40 mA and 40 kV using a graphite monochromator and Cu Kot 1,2 source (I = 1.5418 A) and Vantec 500 General Area Diffraction Detector System (GADDS) detector at ambient temperature and pressure. The diffracto grams were recorded for 20 angles ranging from 2° to 80° with a step size of 0.0195° and an integration step size of 0.5 s.

[0087] The XRD results show that apart from the Pba2-32 space group, several other phases co-exist within the samples. As shown in FIGURE, at least a portion of the oxidative dehydrogenation catalyst has a crystallographic structure with Pba2-32 space group characterized by reflections determined with Cu-KaX-ray diffraction (XRD) as follows:

[0088] An analysis of peak broadening shows that the crystallite size is typically greater than 50 nm for all examples.

[0089] Catalyst Performance Testing

[0090] Performance testing was performed in a fixed bed high-throughput reactor setup from Sintef (High Pressure Reactor Assembly Module), with parallel SS316 reactor tubes (I.D. 3 mm) located in a heated block. For catalytic testing, 350 mg of catalyst particles of 40-80 mesh size were loaded in the reactor. The total pressure was kept constant at 1.5 bar(g) (250 kPa) with a back pressure regulator, and the temperature was kept constant at 450 °C (723 K).

[0091] In the EODh mode of operation, first, the reactor was purged with nitrogen gas (N2) for 10 minutes (600 seconds) at a flow rate of 10 ml / min (0.167 cm3 / s) measured at ambient conditions before introducing a feed stream comprising 50 vol.% of C2H6 and 50 vol.% of I h / He. The feed stream entered the reactor and contacted with the catalysts for 6 minutes (360 seconds)at a flow rate of 15 ml / min (0.25 cm3 / s) measured at ambient conditions at a weight hourly space velocity (WHSV) close to 1.6 / hr. Next, the reactor was purged again with nitrogen gas (N2) for 10 minutes (600 seconds) at a flow rate of 10 ml / min (0.167 cm3 / s) measured at ambient conditions before regenerating the spent catalysts. The spent catalysts were regenerated by contacting a regenerative stream comprising 2.5 vol.% of O2 inN2 for 75 minutes (4500 seconds) at a flow rate of 10 ml / min (0.167 cm3 / s) measured at ambient conditions. This completed a single cycle and a new cycle began. The same cycle was repeated at least 34 times for each measurement.

[0092] To determine the zero time, viz. the time when ethane contacts the catalyst, the entire reactor effluent stream was directed to the thermal conductivity detector (TCD) of the gas chromatograph (GC). The zero time was estimated by switching the flow from N2 to C2H6 at 353 K and 250 kPa. The point at which the TCD signal reaches 75% of its asymptotic values is assumed to be the zero time. The measurement was repeated 10 times and the average zero time was used for further calculations.

[0093] The catalyst / ethane ratio (g / g) is calculated based on the time-on-stream (TOS, seconds) in which the GC analyses the reactor effluent, using Equation (1):where mcataiyst is defined as the catalyst mass, r|in(C2H6), in is the inlet molar flow rate of ethane (mol / s) and MW(C2H6) is the molecular weight of ethane (30 g / mol).

[0094] The ethane conversion, carbon-based selectivity, and ethylene yield are calculated using Equations (2) to (4):T(C2H4) (%) = (S(C2H4) ■ X(C2H6)) / 100 (Eq. 4) where X(C2H6) is defined as the C2H6 conversion (%), pin is defined as the inlet molar flow rate of the component (mol / s), r|out is the outlet molar flow rate of the component (mol / s), Sj is definedas the carbon based selectivity to product j (Cmol%), otj is the number of carbon atoms for product j. Carbon balance for all experiments was within 95-105% for all experiments.

[0095] The results of performance test are reported in Table 3. A comparison of El and CE1 shows that catalysts without Ta (CE1) has 27% lower (relative) C2H4 yield and 3 percentage points lower C2H4 selectivity. A comparison of E2 and CE2 shows that catalysts with Nb (CE2) instead of Ta (E2) has 4% lower (relative) C2H4 yield and more than 2 percentage points lower C2H4 selectivity. Further, negligible deactivation of the catalyst was observed during the duration of performance test.

[0096] Table 3. Performance Data for the Examples

[0097] Accordingly, the above results show the use of the Molybdenum- Vanadium-Oxide (MoVyOx) based catalysts disclosed and described hereinabove to convert alkanes to alkenes.

[0098] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

CLAIMS1. A method of converting alkane to alkene, comprising: contacting a feed stream comprising alkanes with an oxidative dehydrogenation catalyst in a reactor, wherein the oxidative dehydrogenation catalyst is a Molybdenum-Vanadium-Oxide (MoVyOx) based catalyst comprising tantalum (Ta), antimony (Sb), and bismuth (Bi), including oxides thereof, and at least a portion of the oxidative dehydrogenation catalyst has a crystallographic structure with Pba2-32 space group, and converting at least a portion of the alkanes to alkenes, thereby yielding a product stream comprising the alkenes.

2. The method of claim 1, wherein the oxidative dehydrogenation catalyst further comprises niobium (Nb) and niobium oxides.

3. The method of any of the preceding claims, wherein the oxidative dehydrogenation catalyst is substantially free of tellurium (Te).

4. The method of any of the preceding claims, wherein the oxidative dehydrogenation catalyst comprises: a physical mixture of MoVyOx, tantalum oxides, antimony oxides, and bismuth oxides; or a physical mixture of MoVyOx, tantalum oxides, niobium oxides, antimony oxides, and bismuth oxides.

5. The method of claim 4, wherein vanadium comprises 2 wt.% to 16.4 wt.% of the oxidative dehydrogenation catalyst; tantalum comprises 0.06 wt.% to 10.8 wt.% of the oxidative dehydrogenation catalyst; antimony comprises 0.09 wt.% to 14 wt.% of the oxidative dehydrogenation catalyst; and bismuth comprises 0.2 wt.% to 22 wt.% of the oxidative dehydrogenation catalyst.

6. The method of any one of claims 1 to 3, wherein the oxidative dehydrogenation catalyst has a formula MoVyXaShbBicOx, whereinX is Ta or Ta and Nb; y is from 0.1 to 0.6; a is from 0.001 to 0.1; b is from 0.002 to 0.2; c is from 0.002 to 0.2; and x is an oxygen content required to charge-balance the structure.

7. The method of any one of the preceding claims, wherein the at least a portion of the oxidative dehydrogenation catalyst has the crystallographic structure with Pba2-32 space group characterized by reflections determined with Cu-KaX-ray diffraction (XRD) as follows:

8. The method of any of the preceding claims, wherein the feed stream and / or the reactor are substantially free of a gaseous oxidant; or the feed stream and / or the reactor comprise oxygen.

9. The method of any of the preceding claims, wherein the feed stream comprise greater than or equal to 40 vol.% the alkanes.

10. The method of any of the preceding claims, wherein the alkanes comprises ethane; and converting at least a portion of ethane to ethylene comprises contacting the feed stream comprising ethane with the oxidative dehydrogenation catalyst in the reactor at a temperature that is from 300 °C to 600 °C; a pressure that is from 0 bar(g) to 20 bar(g); and an alkane weight hourly space velocity (WHSV) that is from 0.1 / hr to 10 / hr.

11. The method of any of the preceding claims, wherein the oxidative dehydrogenation catalyst and the feed stream have a catalyst-to-alkane mass ratio that is from 5:1 to 200:1.

12. The method of any of the preceding claims, further comprising contacting spent dehydrogenation catalyst with a regenerative stream, thereby regenerating the spent dehydrogenation catalyst and forming regenerated dehydrogenation catalyst, wherein the regenerative stream comprises oxygen.

13. The method of claim 12, wherein the regenerative stream is diluted or undiluted air.

14. The method of claims 12 or 13, wherein contacting the spent dehydrogenation catalyst with the regenerative stream comprises introducing the regenerative stream and the spent dehydrogenation catalyst into a regeneration zone at a temperature of from 300 °C to 600 °C and a pressure of from from 0 bar(g) (0 kPa) to 21 bar(g) (2100 kPa).

15. The method of any of the preceding claims, wherein the product stream further comprises at least one of oxygenated molecule, carbon monoxide, carbon dioxide, and wherein the product stream is further processed to remove the at least one of oxygenated molecule, carbon monoxide, carbon dioxide, and alkanes from the product stream.

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