Methods of converting alkanes to alkenes and steam tolerant promoted dehydrogenation catalysts

Abstract

A method for converting alkanes to alkenes includes contacting a feed stream including alkanes with a dehydrogenation catalyst in a reaction zone in the presence of steam, and converting at least a portion of the alkanes to alkenes, thereby yielding a product stream including alkanes, alkenes, and hydrogen, wherein the reaction zone is substantially free of gaseous oxidant. The dehydrogenation catalyst includes chromium, rare earth element, and alkali metal on a silica-zirconia support, and the catalyst includes from 0.5 wt.% to 10 wt.% chromium, from 1 wt.% to 20 wt.% rare earth metal, from 0.1 wt.% to 1.5 wt.% alkali metal, at least 53.5 wt.% zirconia, and from 0.05 wt.% to 15 wt.% silica.

Description

86468-WO-PCT / DOW 86468 WO1METHODS OF CONVERTING ALKANES TO ALKENES AND STEAM TOLERANT PROMOTED DEHYDROGENATION CATALYSTSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U. S. Provisional Application Serial No.63 / 738,854 filed December 26, 2024, the contents of which are incorporated in their entirety herein.TECHNICAL FIELD

[0002] Embodiments described herein generally relate to chemical processing and, more specifically, to methods and systems for converting alkanes to alkenes.BACKGROUND

[0003] Alkenes are used for a wide range of industrial applications, including producing plastics, fuels, and various downstream chemicals. Such alkenes include C2to C4materials, including ethene, propene, and butenes (also commonly referred to as ethylene, propylene, and butylenes, respectively). A variety of processes for producing these alkenes have been developed, including petroleum cracking and various synthetic processes.

[0004] One such process for producing alkenes is alkane dehydrogenation. Conventional alkane dehydrogenation is endothermic and equilibrium limited and produces multiple moles of products per mole of reactants. Therefore, to reach economically feasible levels of alkane-to-alkene conversion, conventional non-catalytic alkane dehydrogenation necessitates the use of low pressures and high temperatures, often in excess of 800 °C, to shift the equilibrium toward the reaction products. Additionally, radical chemistry that occurs in conventional alkane dehydrogenation processes may produce coke as a byproduct. The coke may cause blockages, which may require periodic shutdowns for decoking operations.

[0005] Maintaining the low pressures and high temperatures necessary for economically feasible alkane-to-alkene conversion can be expensive. Accordingly, a need exists for methods and catalytic systems with high alkene selectivity that operate at higher pressures and lower temperatures while reaching economically feasible levels of alkane-to-alkene conversion.86468-WO-PCT / DOW 86468 WO2SUMMARY

[0006] Embodiments of the present disclosure address these and other needs by the methods of preparing dehydrogenation catalysts, and more particularly, dehydrogenation catalysts that are capable of performing dehydrogenation chemistry in the presence of steam, and methods of using such dehydrogenation catalysts. A dehydrogenation catalyst, as described herein, comprises chromium (Cr), a rare earth element, an alkali metal, and a support comprising zirconia (ZrO2) and silica (SiO2). This dehydrogenation catalyst may then be used for converting alkanes to alkenes. The dehydrogenation catalyst may be able to catalyze the conversion of alkanes to alkenes in the presence of steam.

[0007] According to one or more embodiments of the present disclosure, a method for converting alkanes to alkenes may comprise contacting a feed stream comprising alkanes with a dehydrogenation catalyst in a reaction zone in the presence of steam, and converting at least a portion of the alkanes to alkenes, thereby yielding a product stream comprising alkanes, alkenes, and hydrogen, wherein the reaction zone is substantially free of gaseous oxidant. The dehydrogenation catalyst may comprise from 0.5 wt.% to 10 wt.% chromium, from 1 wt.% to 20 wt.% rare earth element, from 0.1 wt.% to 1.5 wt.% alkali metal, and a support including at least 53.5 wt.% zirconia and from 0.05 wt.% to 15 wt.% silica.

[0008] According to one or more embodiments of the present disclosure, a method for forming a dehydrogenation catalyst may comprise obtaining a zirconia support, adding a chromium-containing precursor, a silicon-containing precursor, a rare earth element-containing precursor, and an alkali metal-containing precursor to the zirconia support to form a doped support, and drying and calcining the doped support to form the dehydrogenation catalyst.

[0009] 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 which follows in addition to the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawing, where like structure is indicated with like reference numerals and in which:86468-WO-PCT / DOW 86468 WO3

[0011] FIG. 1 is a schematic depiction of a reactor system suitable for use with a dehydrogenation catalyst, according to one or more embodiments described herein.

[0012] 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 drawings illustrate the various embodiments described herein, and together with the description, explain the principles and operations of the claimed subject matter.DETAILED DESCRIPTION

[0013] Reference will now be made in detail to embodiments of methods for preparing dehydrogenation catalysts, and more particularly, dehydrogenation catalysts that tolerate steam, and methods of using the dehydrogenation catalysts to convert alkanes to alkenes in the presence of steam. As used herein, “steam conditions” refers to reaction conditions where at least some amount of steam is present. For example, a reaction might take place under 5 volume percent (v.%) steam conditions wherein 5% of the gas volume of the reaction section would be filled with steam. The steam that leads to steam conditions may come from any source. For example, the steam that leads to steam conditions may be generated in-situ by selective hydrogen combustion materials.

[0014] As used herein, “dehydrogenation” refers to a chemical process by which hydrogen is chemically removed from a chemical compound. For example, ethane may undergo dehydrogenation to be converted to ethylene. As used herein, “dehydrogenation catalyst(s)” refers to any substance that increases the rate of a dehydrogenation reaction without itself undergoing any permanent chemical change. As used herein, “background dehydrogenation activity” refers to the dehydrogenation activity that occurs in the presence of inert material instead of a catalyst measured under the same process conditions. For example, a dehydrogenation catalyst may have an activity equal to 1.1 times background dehydrogenation activity when the dehydrogenation catalyst performs dehydrogenation at a conversion rate equal to 1.1 times the dehydrogenation activity of quartz chips under the same process conditions.

[0015] 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,86468-WO-PCT / DOW 86468 WO4propane, and butane are examples of alkanes. As used herein, “alkene(s)” refers any series of hydrocarbon molecules, where at least two of the carbon atoms are not saturated with hydrogen and share a double bond. Ethylene, propylene, 1-butene, -2-butene, and -2-butene are examples of alkenes. Alkenes include dienes, which are hydrocarbons where at least two sets of two of the carbon molecules, that may or may not be adjacent to each other, are not saturated with hydrogen and share a double bond.

[0016] As used herein, “silica-containing zirconia” refers to a zirconia where silica is present on the surface of the zirconia, and / or silica is present in the pores of the zirconia.

[0017] The use of dehydrogenation catalysts is known in the field of hydrocarbon products, such as plastics, fuels, and various downstream chemicals. For example, the Catofrn propane dehydrogenation processes from Lummus Technology and the Oleflex propane dehydrogenation processes from Honeywell employ Cr / Al2O3and Pt-Sn-based dehydrogenation catalysts, respectively. Additionally, zirconia catalysts are known for use in oxidative dehydrogenation of alkanes. In the oxidative dehydrogenation processes, alkanes are typically co-fed with a gaseous oxidant such as oxygen, air, carbon dioxide, or nitrogen oxides, thus shifting the equilibrium constraint of the dehydrogenation reaction.

[0018] Oxidative dehydrogenation occurs at the surface of the catalyst by a reaction of alkane and oxidant and generates water. The presence of water and alkanes at high temperatures can lead to reduced alkene selectivity through oxidation and reforming reactions that yield methane and carbon oxide products such as carbon monoxide and carbon dioxide. Furthermore, many oxidative dehydrogenation catalysts, when used in the absence of a gaseous oxidant in the feed stream or as a co-feed, exhibit significantly reduced activity in the presence of steam. Thus, not every oxidative dehydrogenation catalyst is a steam tolerant alkane dehydrogenation catalyst. In contrast, the dehydrogenation catalysts disclosed and described herein exhibit steam tolerance, even in the absence of a gaseous oxidant in the feed stream or as a co-feed. The preparation and composition of such dehydrogenation catalysts used in embodiments are discussed below.

[0019] Now referring to FIG. 1, a reactor system 100 that may be used with the methods of the present disclosure is shown, but other reactor systems that would be suitable for the presently disclosed methods are contemplated as suitable. FIG. 1 is a simplified system, and other systems are contemplated. Additionally, in FIG. 1, a wide variety of reactor types are contemplated as potentially suitable for the methods described herein. For example, the dehydrogenation catalysts of the present disclosure may be utilized in the systems and methods that are disclosed in at least86468-WO-PCT / DOW 86468 WO5PCT International Application No. PCT / US23 / 73963, entitled “Methods For Dehydrogenating Hydrocarbons By Thermal Dehydrogenation” and International Patent Publication WO 2020 / 046978, entitled “Methods for Dehydrogenating Hydrocarbons,” the teachings of each of which are incorporated by reference in their entirety herein. The technical aspects of these disclosures may further describe the methods and systems described herein with respect to FIG.1. Additionally, it is noted that the steps indicated by FIG. 1 are not to be interpreted as essential steps, particularly in view of the methods of the appended claims.

[0020] Referring still to FIG. 1, the reactor system 100 may include a reaction zone 110 and a regeneration unit 120. In one or more embodiments, the reaction zone 110 may be a fluidized bed reactor. Generally, a feed stream 101 may be passed into the reaction zone 110 and be processed in the reaction zone 110 to form a product stream 102 that includes one or more olefinic compounds. As described in detail herein, according to one or more embodiments, the dehydrogenation catalyst may be cycled between the reaction zone 110 and the regeneration unit 120, where the dehydrogenation catalyst enters the reaction zone 110 in an oxygen- rich state, provides oxygen in the reactor 110, leaves the reaction zone 110 in an oxygen-diminished state, and may be regenerated to an oxygen-rich state in the regeneration unit 120.

[0021] In one or more embodiments, a method for converting alkanes to alkenes may comprise contacting a feed stream 101 comprising alkanes with a dehydrogenation catalyst in a reaction zone 110. In embodiments, the feed stream 101 may comprise C2-C4 alkanes. In embodiments, the feed stream 101 may comprise one or more hydrocarbons. As described herein, the feed stream 101 may be passed into the reaction zone 110. In one or more embodiments, the one or more hydrocarbons may comprise one or more of ethane, propane, or butane. According to one or more embodiments, the one or more hydrocarbons may comprise at least 50 wt. %, at least 60 wt. %, at least 70 wt. %, at least 80 wt. %, at least 90 wt. %, at least 95 wt. % or even at least 99 wt. % of any of ethane. In additional embodiments, the one or more hydrocarbons may comprise at least 50 wt. %, at least 60 wt. %, at least 70 wt. %, at least 80 wt. %, at least 90 wt. %, at least 95 wt. % or even at least 99 wt. % of propane. In additional embodiments, the one or more hydrocarbons may comprise at least 50 wt. %, at least 60 wt. %, at least 70 wt. %, at least 80 wt. %, at least 90 wt. %, at least 95 wt. % or even at least 99 wt. % of butane. In additional embodiments, the one or more hydrocarbons may comprise at least 50 wt. %, at least 60 wt. %, at least 70 wt. %, at least 80 wt. %, at least 90 wt. %, at least 95 wt. % or even at least 99 wt. % of the sum of ethane, propane, and butane.86468-WO-PCT / DOW 86468 WO6

[0022] In embodiments, the feed stream 101 may be contacted with the dehydrogenation catalyst for a controlled time of exposure. In embodiments, the controlled time of exposure may be selected based on the desired catalyst to feed stream mass to mass ratio. In embodiments, the controlled time of exposure may be from 1 second (sec) to 1 hour (h). In embodiments, the controlled time of exposure may be from 5 seconds (sec) to 1 h, from 10 sec to 30 minutes (min), from 15 sec to 15 min, from 20 sec to 10 min, from 25 sec to 5 min, from 25 sec to 30 sec, from 30 sec to 1 min, or any combination thereof.

[0023] In one or more embodiments, the reaction zone 110 may be a zone inside a reactor adapted to allow the feed stream 101 to be contacted with the dehydrogenation catalyst. In one or more embodiments, the reactor may be a fixed-bed reactor, including but not limited to a dual tube fixed-bed reactor or a 3 -tube fixed-bed reactor. In embodiments, the reactor may be a circulating fluidized bed reactor. In embodiments, the reactor may be two or more reactors in series or parallel, and each reactor in series or parallel may be the same type of reactor as other reactors in the series, or may be a different type of reactor from other reactors in the series. In embodiments, the reaction zone 110 may house a material that converts gaseous hydrogen to water.

[0024] In one or more embodiments, a method for converting alkanes to alkenes may comprise converting at least a portion of the alkanes to alkenes, thereby yielding a product stream 102 comprising alkanes, alkenes, and hydrogen. As used herein, “alkenes” may also be referred to as olefinic compounds, and may comprise one or more of ethylene, propylene, butylene, or styrene. The term butylene includes any isomers of butylene, such as α-butylene, cis-β-butylene, trans-β-butylene, and isobutylene.

[0025] In embodiments, the product stream 102 may comprise ethylene, propylene, butylene, hydrogen, or combinations thereof. In embodiments, the product stream 102 may comprise ethane, propane, butane, ethylene, propylene, butylene, hydrogen, or combinations thereof. In some embodiments, the product stream 102 may comprise at least 20 wt. %, at least 30 wt. %, at least 40 wt. %, at least 50 wt. %, or even at least 60 wt. % of ethylene. In additional embodiments, the product stream 102 may comprise at least 20 wt. %, at least 30 wt. %, at least 40 wt. %, at least 50 wt. %, or even at least 60 wt. % of propylene. In additional embodiments, the product stream 102 may comprise at least 20 wt. %, at least 30 wt. %, at least 40 wt. %, at least 50 wt. %, or even at least 60 wt. % of butylene. In additional embodiments, the product stream 102 may comprise at least 20 wt. %, at least 30 wt. %, at least 40 wt. %, at least 50 wt. %, or even at least 60 wt. % of the sum of one or more of ethylene, propylene, and butylene. As stated, the product stream 10286468-WO-PCT / DOW 86468 WO7may further comprise unreacted components of the feed stream 101, as well as other reaction products that are not considered olefinic compounds. The olefinic compounds may be separated from unreacted components in subsequent separation steps.

[0026] In one or more embodiments, at least a portion of the hydrogen in the product stream 102 may be combusted and yield water. In embodiments, the water may be in the form of steam. In embodiments, the steam may comprise gaseous water, liquid water, aerosolized water, or combinations thereof. Because of this hydrogen combustion, water — such as steam — will be present in the reaction zone 110 during dehydrogenation of the alkanes in the feed stream 101. In embodiments, the reaction zone 110 may comprise greater than or equal to 5 v.% steam, such as greater than or equal to 10 v.%, 15 v.%, 20 v.%, 25 v.%, 30 v.%, 35 v.%, 40 v.%, 45 v.%, or 50 v.% steam.

[0027] As mentioned above, many oxidative dehydrogenation catalysts lose conversion and selectivity when exposed to water and require a significant amount of oxidative gas to offset the loss of conversion and selectivity. Additionally, methane, carbon dioxide, and carbon monoxide may form in the product stream 102 as a result and may cause several issues, such as difficulty in separating such components from other compounds in the product stream 102 as well as the potential emission of carbon dioxide into the environment or need to sequester such carbon dioxide. For example, carbon monoxide may be an undesirable inhibitor in certain downstream unit operations like acetylene hydrogenation reactors. With this in mind, it has been found that the presently disclosed dehydrogenation catalysts may retain relatively high catalytic activity in the presence of water and retain all or some of their conversion or selectivity when the hydrogen is combusted and forms water. Therefore, the catalysts disclosed and described herein can operate in the presence of water without the addition of oxidative gas.

[0028] In one or more embodiments, the dehydrogenation catalyst may have an alkene selectivity of greater than or equal to 60 carbon mole percent (Cmol%), greater than or equal to 65 Cmol%, greater than or equal to 70 Cmol%, greater than or equal to 75 Cmol %, greater than or equal to 80 Cmol%, greater than or equal to 85 Cmol%, greater than or equal to 90 Cmol%, greater than or equal to 95 Cmol %, greater than or equal to 97 Cmol%, greater than or equal to 98 Cmol%, or greater than or equal to 99 Cmol%.

[0029] In one or more embodiments, the dehydrogenation catalyst comprises a dehydrogenation activity of greater than or equal to 1.1 times background dehydrogenation activity. In embodiments, the dehydrogenation catalyst comprises a dehydrogenation activity of86468-WO-PCT / DOW 86468 WO8greater than or equal to 1.1 times, 1.5 times, 2 times, 3 times, 4 times, 5 times, or 10 times background dehydrogenation activity.

[0030] In one or more embodiments, the dehydrogenation catalyst retains at least some dehydrogenation activity above background dehydrogenation activity under greater than or equal to 5 v.% steam conditions based on a total volume of gaseous components in the reaction zone 110. In embodiments, the dehydrogenation catalyst retains at least some dehydrogenation activity above background dehydrogenation activity under greater than or equal to 5 v.%, 10 v.%, 15 v.%, 20 v.%, 25 v.%, 30 v.%, 35 v.%, 40 v.%, 45 v.%, or 50 v.% steam conditions based on a total volume of gaseous components in the reaction zone 110. In embodiments, the dehydrogenation catalyst comprises a dehydrogenation activity of greater than or equal to 1.1 times, 1.5 times, 2 times, 3 times, 4 times, 5 times, or 10 times background dehydrogenation activity under greater than or equal to 5 v.%, 10 v.%, 15 v.%, 20 v.%, 25 v.%, 30 v.%, 35 v.%, 40 v.%, 45 v.%, or 50 v.% steam conditions based on a total volume of gaseous components in the reaction zone 110.

[0031] In one or more embodiments, the method for converting alkanes to alkenes may further comprise contacting the feed stream 101 comprising alkanes with at least one other catalyst. In embodiments, the at least one other catalyst may comprise a selective hydrogen combustion material (interchangeably called an oxygen carrier material). For example, oxygen-carrier materials such as those disclosed in U. S. App. No. 62 / 725,504, entitled “METHODS OF PRODUCING HYDROGEN-SELECTIVE OXYGEN- CARRIER MATERIALS,” fded on, August 31, 2018, and U. S. App. No. 62 / 725,508, entitled “HYDROGEN-SELECTIVE OXYGEN-CARRIER MATERIALS AND METHODS OF USE,” fded on, August 31, 2018, are contemplated as suitable for the presently disclosed processes, and the teachings of these references are incorporated by reference herein. In one or more additional embodiments, the oxygen-carrier material may include those of U. S. Pat. No. 5,430,209, U. S. Pat. No. 7,122,495, and / or WO 2018 / 232133, each of which are incorporated by reference in their entireties.

[0032] In embodiments, the dehydrogenation catalyst and the selective hydrogen combustion materials are both present in the reaction zone 110. In embodiments, the dehydrogenation catalyst and the selective hydrogen combustion material may be present in a mass to mass ratio of from 10:1 to 1:10. In embodiments, the dehydrogenation catalyst and the selective hydrogen combustion material may be present in a mass to mass ratio of from 10:1 to 1:10, from 10:1 to 1:10, from 2:1 to 1:10, from 1:1 to 1:10, from 10:1 to 1:5, from 10:1 to 1:5, from 2:1 to 1:5, from 1:1 to 1:5, from 10:1 to 1:2, from 10:1 to 1:2, from 2:1 to 1:2, from 1:1 to 1:2, from 10:1 to 1:1,86468-WO-PCT / DOW 86468 WO9from 10:1 to 1:1, or from 2:1 to 1:1. In embodiments, the dehydrogenation catalyst and the selective hydrogen combustion material may be in contact with each other. In embodiments, the dehydrogenation catalyst and the selective hydrogen combustion material may have been mixed or otherwise combined prior to being placed in the reaction zone 110. In embodiments, the dehydrogenation catalyst and the selective hydrogen combustion material may be mixed in the reaction zone 110. In embodiments, the dehydrogenation catalyst and the selective hydrogen combustion material may be separate.

[0033] As mentioned above, many conventional alkane dehydrogenation processes, such as oxidative dehydrogenation processes, require the use of gaseous oxidants, such as oxygen, air, carbon dioxide, or nitrogen oxides, in the feed stream or as a co-feed. The term “gaseous oxidant(s)” may refer to a substance or substances other than water that may oxidize hydrogen. However, in one or more embodiments of the present disclosure, the dehydrogenation catalyst maintains the conversion of alkanes to alkenes without the presence of a gaseous oxidant in the feed stream 101 or as a co-feed. In some embodiments, the dehydrogenation catalyst maintains the conversion of alkanes to alkenes with the presence of only a small amount of a gaseous oxidant in the feed stream 101 or as a co-feed. In some embodiments, the dehydrogenation catalyst maintains the conversion of alkanes to alkenes with the presence of less than 5 v.%, less than 4 v.%, less than 3 v.%, less than 2 v.%, less than 1 v.%, less than 0.5 v.%, less than 0.25 v.%, or less than 0.1 v.% gaseous oxidant in the feed stream 101 or as a co-feed.

[0034] In one or more embodiments, the dehydrogenation catalyst and the feed stream 101 have a mass to mass ratio that is from 5:1 to 200:1. This mass ratio is defined as the ratio between the mass feed rate of catalyst to the reaction zone 110 and the mass feed rate of alkane to the reaction zone 110. In embodiments, the dehydrogenation catalyst and the feed stream have a mass to mass ratio that is from 5:1 to 200:1, from 10:1 to 200:1, from 25:1 to 200:1, from 50:1 to 200:1, from 75:1 to 200:1, from 100:1 to 200:1, from 150:1 to 200:1, from 5:1 to 150:1, from 10:1 to 150:1, from 25:1 to 150:1, from 50:1 to 150:1, from 75:1 to 150:1, from 100:1 to 150:1, from 5:1 to 100:1, from 10:1 to 100:1, from 25:1 to 100:1, from 50:1 to 100:1, from 75:1 to 100:1, from 5:1 to 75:1, from 10:1 to 75:1, from 25:1 to 75:1, from 50:1 to 75:1, from 5:1 to 50:1, from 10:1 to 50:1, from 25:1 to 50:1, from 5:1 to 25:1, from 10:1 to 25:1, or from 5:1 to 10:1.

[0035] In one or more embodiments, the dehydrogenation catalyst and the feed stream 101 may have a weight hourly space velocity (WHSV) of from 1 to 15 per hour (h-1), where WHSV is defined as the weight of the feed stream 101 flow per weight of the dehydrogenation catalyst86468-WO-PCT / DOW 86468 WO10present in the reaction zone 110 per hour. In embodiments, the dehydrogenation catalyst and the feed stream may have a WHSV of from 1 h-1to 15 h-1, from 1 h-1to 13 h-1, from 1 h-1to 12 h-1, from 1 h-1to 12 h-1, from 1 h-1to 10 h-1, from 1 h-1to 8 h-1, from 1 h-1to 5 h-1, from 1 h-1to 3 h-1, or from 1 h-1to 2 h-1.

[0036] In one or more embodiments, the converting at least a portion of the alkanes to alkenes occurs at a temperature less than or equal to 800 °C. In embodiments, the converting at least a portion of the alkanes to alkenes occurs at a temperature less than or equal to 775 °C, less than or equal to 750 °C, less than or equal to 725 °C, less than or equal to 700 °C, less than or equal to 675 °C, less than or equal to 650 °C, less than or equal to 625 °C, or less than or equal to 600 °C. Without being bound by any particular theory, it is believed that methods of converting alkanes to alkenes as described herein may operate at lower temperatures than conventional dehydrogenation processes, which typically operate at temperatures greater than 800 °C.

[0037] In one or more embodiments, the converting at least a portion of the alkanes to alkenes occurs at a pressure that is equal to atmospheric pressure. In embodiments, the converting at least a portion of the alkanes to alkenes occurs at a pressure from 1 bara (14.5 psia) to 20 bar (290.1 psia), when measured as an absolute pressure (bara). In embodiments, the converting at least a portion of the alkanes to alkenes occurs at a pressure from 1 bara to 20 bara, from 1 bara to 15 bara (217.6 psia), from 1 bara to 10 bara (145.0 psia), from 1 bara to 5 bara (72.5 psia), from 1 bara to 4 bara (58.0 psia), from 1 bara to 3 bara (43.5 psia), or from 1 bara to 2 bara (29.0 psia).

[0038] Referring again to FIG. 1, in some embodiments, the dehydrogenation catalyst may be cycled between the reaction zone 110 and a regeneration zone 120. The dehydrogenation catalyst may pass from the reaction zone 110 to the regeneration zone 120 via stream 103 and be passed from the regeneration zone 120 back to the reaction zone 110 via stream 104, and be continuously looped. In general, the dehydrogenation catalyst may enter the reaction zone 110 in an oxygen-rich state, lose some or all oxygen atoms in the reaction zone 110 (to combust with hydrogen gas), and exit the reaction zone 110 in an oxygen-diminished state via stream 103. The dehydrogenation catalyst in the oxygen-diminished state may be passed to the regeneration zone 120 where it is exposed to oxygen and regenerated into its oxygen-rich state. This dehydrogenation catalyst in the oxygen-rich state may be passed from the regeneration zone 120 via stream 104 back to the reaction zone 110.

[0039] As described herein, the dehydrogenation catalyst may be passed into the reaction zone 110 and subsequently out of the reaction zone 110. In one or more embodiments, the method of86468-WO-PCT / DOW 86468 WO11converting alkanes to alkenes may further comprise removing spent dehydrogenation catalyst from the reaction zone 110 and introducing the spent dehydrogenation catalyst into a regeneration zone 120. In embodiments, the regeneration zone 120 may be part of the reactor. In embodiments, the regeneration zone 120 may the separate from the reactor. In embodiments, the method of converting alkanes to alkenes may further comprise regenerating the spent dehydrogenation catalyst, thereby forming regenerated dehydrogenation catalyst. In embodiments, regenerating the dehydrogenation catalyst may comprise contacting the dehydrogenation catalyst with a regeneration stream comprising gaseous oxygen, air, or combinations thereof. In embodiments, the regeneration zone 120 is purged with gaseous nitrogen prior to contacting the dehydrogenation catalyst with the regeneration stream. Additionally, in the regeneration zone 120, a fuel gas may be combusted in order to heat the dehydrogenation catalyst. This heat may be the main source of heat to maintain temperatures in the reaction zone 110, which is using heat by the dehydrogenation reaction.

[0040] In embodiments, the dehydrogenation catalyst may be regenerated at a temperature of greater than or equal to 650 °C. In one or more embodiments, the dehydrogenation catalyst may be regenerated for a time of greater than or equal to 1 minute (min), greater than or equal to 5 min, greater than or equal to 10 min, greater than or equal to 30 min, greater than or equal to 45 min, greater than or equal to 1 hour (h), greater than or equal to 1.5 h, or greater than or equal to 2 h. In embodiments, the dehydrogenation catalyst may be heated prior to sending the dehydrogenation catalyst back to the reaction zone 110.

[0041] In embodiments, the method of converting alkanes to alkenes may further comprise regenerating the spent selective hydrogen combustion material, thereby forming regenerated selective hydrogen combustion material. Regenerating the selective hydrogen combustion material may comprise contacting the selective hydrogen combustion material with a regeneration stream comprising gaseous oxygen, air, or combinations thereof. In embodiments, the regeneration zone 120 is purged with gaseous nitrogen prior to contacting the selective hydrogen combustion material with the regeneration stream. In embodiments, the selective hydrogen combustion material may be regenerated at a temperature of greater than or equal to 650 °C. In one or more embodiments, the selective hydrogen combustion material may be regenerated for a time of greater than or equal to 1 minute (min), greater than or equal to 5 min, greater than or equal to 10 min, greater than or equal to 30 min, greater than or equal to 45 min, greater than or equal to 1 hour (h), greater than or equal to 1.5 h, or greater than or equal to 2 h. In embodiments,86468-WO-PCT / DOW 86468 WO12the selective hydrogen combustion material may be heated prior to sending the selective hydrogen combustion material back to the reaction zone 110 to close heat balance. In embodiments, the selective hydrogen combustion material and the dehydrogenation catalyst may be regenerated together.

[0042] In one or more embodiments, the method of converting alkanes to alkenes may further comprise returning regenerated dehydrogenation catalyst to the reaction zone 110 where it is contacted with the feed stream 101.

[0043] In embodiments disclosed herein, the dehydrogenation catalyst may have a particular composition. The dehydrogenation catalyst may comprise chromium, rare earth element, alkali metal, and a support comprising zirconia and silica. The dehydrogenation catalyst may comprise from 0.5 wt.% to 10 wt.% chromium, from 1 wt.% to 20 wt.% rare earth element, from 0.1 wt.% to 1.5 wt.% alkali metal, at least 53.5 wt.% zirconia, and from 0.05 wt.% to 15 wt.% silica. As described herein, the dehydrogenation catalyst comprising these components may be particularly suited for converting alkanes to alkenes to retain high alkene selectivity and yield. The dehydrogenation catalyst may also be tolerant to steam.

[0044] As stated, the dehydrogenation catalyst may comprise zirconia (ZrO2). As used herein, the zirconia used in embodiments disclosed and described herein in the dehydrogenation catalyst may be “phase pure zirconia”, which is defined herein as zirconia to which no other materials have intentionally been added during production. Thus, “phase pure zirconia” includes zirconia with small amounts of components other than zirconium (including oxides other than zirconia) that are unintentionally present in the zirconia as a natural part of the zirconia production process, such as, for example, hafnium (Hf). Accordingly, as used herein “zirconia” and “phase pure zirconia” are used interchangeably unless specifically indicated otherwise. In other embodiments, the zirconia can be non-phase pure zirconia. According to embodiments, the zirconia particles may include zirconia particles having a crystalline structure. The zirconia particles may include zirconia particles having monoclinic crystal form (also known as a baddeleyite structure), tetragonal crystal form, cubic crystal form, or combinations thereof.

[0045] In one or more embodiments, the dehydrogenation catalyst may comprise zirconia, where the zirconia acts as a metal oxide support. The term “metal oxide support” may refer to a support material that supports the other components of the dehydrogenation catalyst, for example, chromium. In embodiments, the dehydrogenation catalyst may comprise at least 53.5 wt.% zirconia, such as at least 54 wt.% zirconia, at least 56 wt.% zirconia, at least 58 wt.% zirconia, at86468-WO-PCT / DOW 86468 WO13least 60 wt.% zirconia, at least 62 wt.% zirconia, at least 64 wt.% zirconia, at least 66 wt.% zirconia, at least 68 wt.% zirconia, at least 70 wt.% zirconia, at least 72 wt.% zirconia, at least 74 wt.% zirconia, at least 76 wt.% zirconia, at least 78 wt.% zirconia, at least 80 wt.% zirconia, at least 82 wt.% zirconia, at least 84 wt.% zirconia, at least 86 wt.% zirconia, at least 88 wt.% zirconia, at least 90 wt.% zirconia, at least 92 wt.% zirconia, at least 94 wt.% zirconia, at least 96 wt.% zirconia, or even at least 98 wt.% zirconia, based on a total weight of the dehydrogenation catalyst. In embodiments, the dehydrogenation catalyst may comprise less than or equal to 98.35 wt.% zirconia, less than or equal to 98 wt.% zirconia, less than or equal to 96 wt.% zirconia, less than or equal to 94 wt.% zirconia, less than or equal to 92 wt.% zirconia, or less than or equal to 90 wt.% zirconia. In embodiments, the dehydrogenation catalyst may comprise from 73 wt.% zirconia to 98.35 wt.% zirconia.

[0046] In one or more embodiments, the dehydrogenation catalyst may comprise silica (SiO2) in the support (i.e., in the zirconia support). In embodiments, the support may comprise from 0.05 wt.% to 15 wt.% silica, such as from 0.05 wt.% to 15 wt.% silica, from 0.1 wt.% to 15 wt.% silica, from 1 wt.% to 15 wt.% silica, from 2 wt.% to 15 wt.% silica, from 4 wt.% to 15 wt.% silica, from 6 wt.% to 15 wt.% silica, from 8 wt.% to 15 wt.% silica, from 10 wt.% to 15 wt.% silica, from 12 wt.% to 15 wt.% silica, from 0.05 wt.% to 12 wt.% silica, from 0.05 wt.% to 10 wt.% silica, from 0.05 wt.% to 8 wt.% silica, from 0.05 wt.% to 6 wt.% silica, from 0.05 wt.% to 4 wt.% silica, from 0.05 wt.% to 2 wt.% silica, from 0.05 wt.% to 1 wt.% silica, or any combinations of these ranges and endpoints. In embodiments, the silica is present as the part of the metal oxide support, such as, for example, a support made from silica-containing zirconia.

[0047] The dehydrogenation catalyst may comprise chromium (Cr) in any suitable oxidation state. According to embodiments, the chromium may have an oxidation state of +2, +3, +4, +5, +6, or combinations thereof. In embodiments, the dehydrogenation catalyst may comprise chromium having a single oxidation state or the dehydrogenation catalyst may comprise chromium having different oxidation states. In one or more embodiments, the dehydrogenation catalyst comprises from 0.5 wt.% to 10 wt.% chromium based on a total weight of the dehydrogenation catalyst. In embodiments, the dehydrogenation catalyst may comprise from 0.5 wt.% to 10 wt.% chromium, such as from 0.5 wt.% to 9.5 wt.%, from 0.5 wt.% to 9 wt.%, from 0.5 wt.% to 8.5 wt.%, from 0.5 wt.% to 8 wt.%, from 0.5 wt.% to 7.5 wt.%, from 0.5 wt.% to 7 wt.%, from 0.5 wt.% to 6.5 wt.%, from 0.5 wt.% to 6 wt.%, from 0.5 wt.% to 5.5 wt.%, from 0.5 wt.% to 5 wt.%, from 0.5 wt.% to 4.5 wt.%, from 0.5 wt.% to 4 wt.%, from 0.5 wt.% to 3.5 wt.%,86468-WO-PCT / DOW 86468 WO14from 0.5 wt.% to 3 wt.%, from 0.5 wt.% to 2.5 wt.%, from 0.5 wt.% to 2 wt.%, from 0.5 wt.% to 1.5 wt.%, from 0.5 wt.% to 1 wt.%, from 1 wt.% to 10 wt.%, from 2 wt.% to 10 wt.%, from 3 wt.% to 10 wt.%, from 4 wt.% to 10 wt.%, from 5 wt.% to 10 wt.%, from 6 wt.% to 10 wt.%, from 7 wt.% to 10 wt.%, from 8 wt.% to 10 wt.%, from 9 wt.% to 10 wt.% chromium, or any combination of these ranges and endpoints, based on a total weight of the dehydrogenation catalyst.

[0048] The dehydrogenation catalyst may comprise a rare earth element. In embodiments, the rare earth element may be chosen from lanthanides, yttrium, scandium, or combinations thereof. In embodiments, the rare earth element may be chosen from yttrium, lanthanum, lutetium, or combinations thereof. In one or more embodiments, the dehydrogenation catalyst may comprise from 1 wt.% to 20 wt.% rare earth element based on a total weight of the dehydrogenation catalyst. In embodiments, the dehydrogenation catalyst may comprise from 2 wt.% to 20 wt.%, from 4 wt.% to 20 wt.%, from 6 wt.% to 20 wt.%, from 8 wt.% to 20 wt.%, from 10 wt.% to 20 wt.%, from 12 wt.% to 20 wt.%, from 14 wt.% to 20 wt.%, from 16 wt.% to 20 wt.%, from 18 wt.% to 20 wt.%, from 1 wt.% to 18 wt.%, from 1 wt.% to 16 wt.%, from 1 wt.% to 14 wt.%, from 1 wt.% to 12 wt.%, from 1 wt.% to 10 wt.%, from 1 wt.% to 8 wt.%, from 1 wt.% to 6 wt.%, from 1 wt.% to 4 wt.% rare earth element, or any combination of these ranges and endpoints, based on a total weight of the dehydrogenation catalyst. It should be understood that the dehydrogenation catalyst may comprise one or more of the rare earth element, such as, but not limited to, one or more of yttrium, lanthanum, and lutetium in any combination.

[0049] The dehydrogenation catalyst may comprise an alkali metal. In embodiments, the alkali metal may be chosen from lithium, sodium, potassium, rubidium, cesium, or combinations thereof. In one or more embodiments, the dehydrogenation catalyst may comprise from 0.1 wt.% to 1.5 wt.% alkali metal. In embodiments, the dehydrogenation catalyst may comprise from 0.2 wt.% to 1.5 wt.%, from 0.4 wt.% to 1.5 wt.%, from 0.6 wt.% to 1.5 wt.%, from 0.8 wt.% to 1.5 wt.%, from 1 wt.% to 1.5 wt.%, from 1.2 wt.% to 1.5 wt.%, from 1.4 wt.% to 1.5 wt.%, from 0.1 wt.% to 1.4 wt.%, from 0.1 wt.% to 1.2 wt.%, from 0.1 wt.% to 1 wt.%, from 0.1 wt.% to 0.8 wt.%, from 0.1 wt.% to 0.6 wt.%, from 0.1 wt.% to 0.4 wt.%, from 0.1 wt.% to 0.2 wt.% alkali metal, or any combination of these ranges and endpoints, based on a total weight of the dehydrogenation catalyst. It should be understood that the dehydrogenation catalyst may comprise one or more of the alkali metals, such as one or more of lithium, sodium, potassium, rubidium, cesium in any combination. In embodiments, the alkali metal may be potassium.86468-WO-PCT / DOW 86468 WO15

[0050] The dehydrogenation catalyst may further comprise additional promoters. The dehydrogenation catalyst may further comprise an alkaline earth metal. In embodiments, the alkaline earth metal may be chosen from beryllium, magnesium, calcium, strontium, barium, radium, or combinations thereof. In embodiments, the dehydrogenation catalyst may further comprise tin, platinum, boron, lanthanum, cerium, neodymium, samarium, gadolinium, dysprosium, praseodymium, europium, or combinations thereof.

[0051] In one or more embodiments, the dehydrogenation catalysts described herein may be prepared by a variety of synthetic techniques. In embodiments, a method for forming a dehydrogenation catalyst may comprise obtaining a zirconia support, adding a chromium-containing precursor, a silicon-containing precursor, a rare earth element-containing precursor, and an alkali metal-containing precursor to the zirconia support to form a doped support, and drying and calcining the doped support to form a dehydrogenation catalyst. In embodiments, the doped support may be dried and calcined under air at a temperature of greater than or equal to 750 °C, such as greater than or equal to 800 °C, greater than or equal to 850 °C, greater than or equal to 900 °C, or greater than or equal to 950 °C. In one or more embodiments, a method for forming a dehydrogenation catalyst may further comprise preparing the zirconia support by precipitation reaction.

[0052] In embodiments, adding a chromium- containing precursor, a silicon-containing precursor, a rare earth element-containing precursor, and an alkali metal-containing precursor (together, the “precursors”) to the zirconia support may comprise a process comprising spray drying, granulation, pre-impregnation, post-impregnation, co-precipitation, or combinations thereof. It should be understood that, in embodiments, the precursors may be added in any order, together or sequentially, to the zirconia support. For example, the zirconia support may be doped with silica first and then the chromium-containing precursor, the rare earth element-containing precursor, and the alkali metal-containing precursor may be added to the zirconia support. Any order of addition of the precursors is contemplated.

[0053] In one or more embodiments, the dehydrogenation catalyst may be prepared by precipitation. For example, the dehydrogenation catalyst may be prepared by co-precipitating the zirconia support and the precursors. In embodiments, the dehydrogenation catalyst may be prepared by a combination of impregnation and precipitation. For example, the zirconia support may first be prepared by precipitation, and then the zirconia support may be impregnated with the precursors by sequential impregnation.86468-WO-PCT / DOW 86468 WO16

[0054] In one or more embodiments, the dehydrogenation catalyst may be prepared by impregnation. For example, the dehydrogenation catalyst may be prepared by impregnating a silicon-containing precursor, such as silica, to the zirconia support. The chromium-containing precursor, rare earth element-containing precursor, and the alkali metal-containing precursor may then be added to the silica-containing zirconia support by co-impregnation, sequential impregnation, or combinations thereof.

[0055] In one or more embodiments, adding the precursors to the zirconia support to form the doped support may comprise any combination of adding the precursors to the zirconia support, wherein the zirconia support is a fluidizable zirconia support, adding the precursors to the zirconia support by spray drying, or adding the precursors to the zirconia support by granulation.

[0056] In one or more embodiments, adding the precursors to the zirconia support in a fluidized bed operation, wherein the zirconia support is a fluidizable zirconia support may comprise placing the zirconia support in a fluidized bed reactor and adding the precursors to the zirconia support. In embodiments, the precursors may be a dry powder or may be part of a solution or slurry. In embodiments, the doped support prepared for use in a fluidized bed operation may be spray dried. In embodiments, adding the precursors to the zirconia support by granulation may comprise combining powdered zirconia support with powdered precursors and combining the powdered zirconia support and powdered precursors to form the doped support.

[0057] In embodiments, the surface area of the zirconia particles may be greater than or equal to 5 meters squared per gram (m2 / g). For example, the surface area of the zirconia particles may be at least 5 m2 / g, at least 10 m2 / g, at least 20 m2 / g, at least 50 m2 / g, at least 75 m2 / g, at least 100 m2 / g, at least 125 m2 / g, or at least 150 m2 / g. In embodiments, the surface area of the zirconia particle may be from 5 m2 / g to 200 m2 / g, from 10 m2 / g to 200 m2 / g, from 20 m2 / g to 200 m2 / g, such as from 30 m2 / g to 200 m2 / g, from 40 m2 / g to 200 m2 / g, from 50 m2 / g to 200 m2 / g, from 60 m2 / g to 200 m2 / g, from 70 m2 / g to 200 m2 / g, from 80 m2 / g to 200 m2 / g, from 90 m2 / g to 200 m2 / g, from 100 m2 / g to 200 m2 / g, from 110 m2 / g to 200 m2 / g, from 120 m2 / g to 200 m2 / g, from 130 m2 / g to 200 m2 / g, or from 140 m2 / g to 200 m2 / g. In embodiments, the surface area of the zirconia particles may be from 5 m2 / g to 180 m2 / g, from 5 m2 / g to 160 m2 / g, from 5 m2 / g to 140 m2 / g, from 5 m2 / g to 120 m2 / g, from 5 m2 / g to 100 m2 / g, from 5 m2 / g to 90 m2 / g, from 5 m2 / g to 80 m2 / g, from 5 m2 / g to 70 m2 / g, from 5 m2 / g to 60 m2 / g, from 5 m2 / g to 50 m2 / g, from 5 m2 / g to 40 m2 / g, from 5 m2 / g to 30 m2 / g, from 5 m2 / g to 20 m2 / g, or from 5 m2 / g to 10 m2 / g. In embodiments, the surface area of the zirconia particles may be from 10 m2 / g to 160 m2 / g, from 20 m2 / g to 130 m2 / g,86468-WO-PCT / DOW 86468 WO17from 30 m2 / g to 120 m2 / g, from 40 m2 / g to 110 m2 / g, from 50 m2 / g to 100 m2 / g, from 60 m2 / g to 90 m2 / g, or from 70 m2 / g to 80 m2 / g.

[0058] It should be understood that according to embodiments, the dehydrogenation catalyst may be made by other methods that eventually lead to intimate contact between the chromium-containing precursor, the silicon-containing precursor, the rare earth element-containing precursor, and the alkali metal-containing precursor and zirconia.EXAMPLES

[0059] The various embodiments of the present disclosure will be further clarified by the following examples. The examples are illustrative in nature and should not be understood to limit the subject matter of the present disclosure.

[0060] COMPARATIVE EXAMPLE 1

[0061] Commercially available quartz chips (Sigma- Aldrich, Quartz Fine Granular, 1.07536) were used to determine background dehydrogenation activity.

[0062] COMPARATIVE EXAMPLE 2

[0063] A Cr / ZrCh catalyst was prepared by strong electrostatic adsorption. First, 20 grams of ZrCh support (MEL XZ01501) was dispersed in 200 milliliters of water at room temperature while stirring. Then, 0.5 g of (NH4)2CrO7was added to the solution. The pH was adjusted to 5.8 with HNO3 in order to obtain a Cr loading of 0.6 wt.%. The solution was aged for 24 hours at room temperature. The resulting product was filtered, washed and dried in a static oven in air at 80 °C for 16 h. Finally, the solid was thermally treated in two consecutive steps, one at 177 °C for 2 hours, and a second at 1000 °C for 1 hour (ramp rate of 5 °C / min for both). The solid was recovered, compacted in a press at 7 tons, crushed and sized to 40-80 mesh fraction prior to testing. The Cr loading of 0.6 wt % was determined by XRF.

[0064] COMPARATIVE EXAMPLE 3

[0065] Comparative Example 3 was prepared via a similar procedure for Comparative Example 6, except that Z1O2 support is received from Norpro (SZ31164, 3 mm extrudates, monoclinic, pore volume 0.4 mL / g by water, BET surface area 100 m2 / g). This commercial support material was crushed and then sieved to 40-80 mesh size before impregnation). The loading of Cr is 2 wt.% in the final sample.

[0066] COMPARATIVE EXAMPLE 486468-WO-PCT / DOW 86468 WO18

[0067] Comparative Example 4 was prepared by 2 g of ZrO2support (Norpro SZ32243, 0.4 mm spheres) was impregnated with 0.905 mL of the impregnation solution. The impregnation solution was prepared by mixing 0.4 mL of 2 M chromium (III) nitrate in deionized water, 0.075 mL of 2.12 M lanthanum (III) nitrate nonahydrate in deionized water, and 0.043 mL of deionized water. The catalyst was dried and calcined in air in a static box oven by ramping to 177 °C at 5 °C / min, held for 2 h, then ramped to 750 °C at 5 °C / min and held for 1 h prior to cooling to room temperature. The target loadings of La and Cr are 1 wt.% and 2 wt.%, respectively, in the final sample.

[0068] COMPARATIVE EXAMPLE 5

[0069] Comparative Example 5 was prepared by first adding 1 g of ZrCh support (Norpro SZ32243, 0.4 mm spheres) to 34 ml of 0.01 M chromium acetylacetonate solution in iso-butanol. The solvent was removed on a rotavap. The catalyst was dried in air at 175 °C for 2 h (ramp 5°C / min) and calcined in air at 750 °C for 1 h (ramp to 5 °C / min). The calcined catalyst was then impregned with 0.3 mL of 1 M potassium nitrate solution in deionized water. The catalyst was dried and calcined using the same temperature procedure as in the first step. The target loadings of K and Cr are 0.5 wt.% and 0.7 wt.%, respectively, in the final sample.

[0070] COMPARATIVE EXAMPLE 6

[0071] Comparative Example 6 was prepared on a Z1O2 support doped with 5 wt.% SiCh obtained from Norpro (SZ31107) and pre-sized to 20 / 60 mesh prior to impregnation. 1000 mg of the support was weighed into a 10 mL round bottom tube and then fastened into a vial plate attached to a shaker bed with the top open. An incipient wetness volume of 500 pL / g was used for all impregnations of the metal solutions. An impregnation solution of 0.3079 g chromium nitrate hydrate (Sigma- Aldrich) and 0.0129 g potassium nitrate (Sigma- Aldrich) with 1 g deionized water was prepared. This solution was added dropwise with the shaker bed in motion to promote even distribution. The sample was calcined in air in a static box oven by ramping to 177 °C at 5 °C / min, held for 2 h, then ramped to 800 °C at 5 °C / min and held for 1 h. The target loadings of K and Cr were 0.25 wt.% and 2 wt.%, respectively in the final sample.

[0072] EXAMPLE 1

[0073] Example 1 was prepared in a similar manner as Comparative Example 6 except the impregnations were completed sequentially. La was first impregnated using a solution of 0.4028 g lanthanum nitrate hexahydrate (Sigma- Aldrich) with 1 g deionized water. The sample was calcined at 800°C for 1 h. Following, Cr and K were impregnated using a solution containing86468-WO-PCT / DOW 86468 WO190.3079 g chromium nitrate hydrate (Sigma- Aldrich) and 0.0129 g potassium nitrate (Sigma-Aldrich) with 1 g deionized water. The sample was calcined in air in the static box oven at 800°C for 1 h with the same profde as Comparative Example 6. The target loadings of La, K and Cr are 7.8 wt.%, 0.25 wt.%, and 2 wt.%, respectively in the final sample.

[0074] EXAMPLE 2

[0075] Example 2 was prepared in a similar manner as Example 1 except a solution of 0.3358 g lutetium nitrate hydrate (Sigma- Aldrich) with 1 g deionized water was used instead of lanthanum nitrate hexahydrate. The sample was calcined at 800 °C for 1 h following addition of lutetium nitrate hydrate and for 8 h following addition of chromium nitrate hydrate and potassium nitrate using the same temperature profile in Comparative Example 6 except changing the hold time at 800 °C. The target loadings of Lu, K and Cr are 6.6 wt.%, 0.25 wt.%, and 2 wt.%, respectively in the final sample.

[0076] EXAMPLE 3

[0077] Example 3 was prepared in a similar manner as Example 1 except a solution of 0.3563 g yttrium nitrate hexahydrate (Sigma-Aldrich) with 1 g deionized water was used instead of lanthanum nitrate hexahydrate. The target loadings of Y, K and Cr are 4.4 wt.%, 0.25 wt.%, and 2 wt.%, respectively in the final sample.

[0078] EXAMPLE 4

[0079] Example 4 was prepared by first weighing 1000 mg of support (SiCh-doped ZrCh, SZ31107) into a 10 mL round bottom tube and then fastening the tube into a vial plate attached to a shaker bed with the top open. An incipient wetness volume of 500 pL / g was used for all impregnations of the metal solutions. An impregnation solution of 1.3432 g of lutetium nitrate hydrate (Sigma-Aldrich), 0.3079 g chromium nitrate hydrate (Sigma-Aldrich) and 0.0129 g potassium nitrate (Sigma- Aldrich) with 1 g deionized water was prepared. This solution was added dropwise with the shaker bed in motion to promote even distribution. The sample was calcined in air in a static oven at 800 °C for 8 h using the same temperature profile in Comparative Example 6 except changing the hold time at 800 °C. The target loadings of Lu, K and Cr are 15.1 wt.%, 0.25 wt.%, and 2 wt.%, respectively in the final sample.

[0080] EXAMPLE 5

[0081] Example 5 was prepared in a similar manner as Example 4 except the impregnation solution contained 1.4252 g yttrium nitrate hexahydrate (Sigma- Aldrich) with 1 g deionized water instead of lutetium nitrate hydrate. The sample was calcined at 800 °C for 8 h using the same86468-WO-PCT / DOW 86468 WO20temperature profile in Comparative Example 6 except changing the hold time at 800 °C. The target loadings of Y, K and Cr are 12.4 wt.%, 0.25 wt.%, and 2 wt.%, respectively in the final sample.

[0082] The compositions of the comparative examples and examples as prepared are summarized in Table 1.Table 1: Sample Compositions (target loadings)CompositionExample Rare Earth Alkali Metal ChromiumSupport Element (wt.%) (wt.%) (wt.%)Example 1 7.8 La 0.25 K 2.0 Cr Si-ZrO2Example 2 6.6 Lu 0.25 K 2.0 Cr Si-ZrO2Example 3 4.4 Y 0.25 K 2.0 Cr Si-ZrO2Example 4 15.1 Lu 0.25 K 2.0 Cr Si-ZrO2Example 5 12.4 Y 0.25 K 2.0 Cr Si-ZrO2CE 1 - - - - CE 2 - - 0.6 Cr ZrO2CE 3 - - 2.0 Cr ZrO2CE 4 1.0 La - 2.0 Cr ZrO2CE 5 - 0.5 K 0.7 Cr ZrO2CE 6 - 0.25 K 2.0 Cr Si-ZrO2

[0083] CATALYST CHARACTERIZATION

[0084] CATALYST PERFORMANCE TESTING

[0085] The performance of the catalysts of the examples and the comparative examples was assessed under the conditions of Table 2.Table 2: Reaction Conditions Used to Assess Catalyst PerformanceCatalystPressure Temperature Ethane H2O N2WHSV Catalyst / Ethane Condition Load(psig) (°C) [v.%] [v.%] [v.%] [h-1] (mass / mass)[g]Condition 1 29.4 700 60 20 20 0.3 12.1 11.986468-WO-PCT / DOW 86468 WO21Condition 2 29.4 725 60 20 20 0.3 12.1 11.9 Condition 3 29.4 750 60 20 20 0.3 12.1 11.9 Condition 4 44.1 700 60 20 20 0.3 12.1 11.9 Condition 5 44.1 725 60 20 20 0.3 12.1 11.9 Condition 6 44.1 750 60 20 20 0.3 12.1 11.9 Condition 7 58.8 700 60 20 20 0.3 12.1 11.9 Condition 8 58.8 725 60 20 20 0.3 12.1 11.9 Condition 9 58.8 750 60 20 20 0.3 12.1 11.9

[0086] The catalysts of the examples and the comparative examples were tested for selectivity and activity in a 3 tube fixed-bed reactor. The catalysts were sized to a 40-80 mesh size. The reactor bed comprised 300 milligrams (mg) of catalyst. In Comparative Example 1, the catalyst was replaced with quartz chips. The reactor pressure was varied between 29.4 psig to 58.8 psig and the catalysts were evaluated under the conditions summarized in Table 2.

[0087] First, the reactor was purged with nitrogen (pressure = 43.9 psia). The temperature was ramped to 700 °C under N2 flow. Reaction gas flow was set to 60% ethane - 20% H2O - 10% N2 - 10% He flow and stabilized while bypassing the reactor. Water inlet flow was controlled by a high pressure liquid chromatography (HPLC) pump. An evaporator was used to evaporate water to the gas phase. Feed analysis was performed by analyzing the feed gas composition using online gas chromatography (GC) while bypassing the reactor. The gas flow to the reactor was then switched from N2 to reaction gas flow and flowed for the prescribed amount of time (25 s on stream corresponding to catalyst / ethane mass / mass ratio of 11.9).

[0088] Then, the reactor was purged with N2 for 2 min and then switched to air for regeneration for 6 min followed by a subsequent N2 purge for 2 min. This completes a single cycle at a given temperature set point. Regeneration of the catalyst after exposure to ethane-containing feed was performed at the same temperature as the corresponding reaction step. Each sample was evaluated under the conditions specified in Table 2. For each condition and each temperature set point, 3 cycles (reaction-purge-regeneration) were completed. The average values were then calculated and reported in Table 3.86468-WO-PCT / DOW 86468 WO22

[0089] Alkane conversion and carbon based selectivities are calculated using the following equations:Sj (Cmol%) = [αj · ηi, out / Σ αj · ηi, out] · 100 (Equation 1)Carbon Balance (%) = Σ αj · ηi,out / ηC2H6,in · 100 (Equation 2)Ethane Conversion (%) = [(ηC2H6, in – ηC2H6, out) / ηC2H6, in] · 100 (Equation 3) Reforming Product sei. (Cmol%) = SCH4+ Sco + Sco2(Equation 4) where “q, in” is defined as the molar inlet flow of the component (mol / min), “r|, out” is the molar outlet flow of the component (mol / min), “Sj” is defined as the carbon based selectivity to product j (%), and “aj” the number of carbon atoms for product).Table 3: Performance Data for the ExamplesReforming Ethylene Carbon Ethane Conversion Ethylene Sei.Condition Example Product Sei. Yield Balance (%) (Cmol%)(Cmol%) (Cmol%) (%) 1 Example 1 13.9 90.8 8.8 12.6 101.0 1 Example 2 17.2 87.3 12.4 15.0 101.5 1 Example s 17.4 87.8 12.1 15.2 101.4 1 Example 4 12.7 91.0 8.9 11.5 101.7 1 Example 5 13.4 92.4 7.4 12.4 101.5 1 CE 1 2.6 98.5 1.0 2.6 101.1 1 CE 2 16.5 80.0 19.8 13.2 101.4 1 CE 3 33.1 43.8 55.2 14.5 102.0 1 CE 4 29.2 55.1 44.3 16.1 102.1 1 CE 5 6.6 81.8 17.5 5.4 101.4 1 CE 6 24.8 83.8 16.0 20.8 97.1 2 Example 1 21.3 89.7 9.8 19.1 101.8 2 Example 2 26.4 83.9 15.1 22.1 101.7 2 Example s 26.3 84.8 14.7 22.3 101.6 2 Example 4 21.4 88.9 10.8 19.0 101.6 2 Example s 20.8 91.1 8.5 18.9 101.8 2 CE 1 7.3 97.1 1.2 7.1 101.2 2 CE 2 26.0 74.0 25.5 19.2 101.9 2 CE 3 46.1 34.2 64.7 15.8 100.0 2 CE 4 41.5 42.9 56.2 17.8 99.686468-WO-PCT / DOW 86468 WO232 CE 5 12.9 83.1 15.7 10.7 101.2 2 CE 6 27.9 79.6 20.0 22.2 106.4 3 Example 1 32.7 86.2 12.5 28.2 101.5 3 Example 2 37.8 78.6 20.3 29.7 101.3 3 Example s 37.2 78.9 19.8 29.3 102.0 3 Example 4 34.4 85.3 13.8 29.3 98.9 3 Example s 30.9 87.8 10.9 27.1 101.6 3 CE 1 15.8 95.9 1.8 15.2 101.3 3 CE 2 37.8 64.5 34.3 24.4 101.0 3 CE 3 54.3 37.9 60.8 20.6 96.4 3 CE 4 36.6 38.6 60.3 14.1 101.1 3 CE 5 22.5 79.5 18.6 17.9 101.8 3 CE 6 44.1 73.2 25.7 32.3 96.4 4 Example 1 12.2 92.2 7.0 11.3 101.6 4 Example 2 16.0 87.8 11.6 14.1 101.6 4 Example s 15.9 88.7 10.8 14.1 101.4 4 Example 4 14.1 90.7 8.8 12.8 101.7 4 Example s 12.3 93.3 6.4 11.4 101.6 4 CE 1 3.6 97.7 1.1 3.5 101.3 4 CE 2 16.6 76.1 23.4 12.6 101.5 4 CE 3 27.5 45.2 53.7 12.4 101.6 4 CE 4 24.9 53.6 45.5 13.4 101.7 4 CE 5 6.7 85.2 14.1 5.7 101.4 4 CE 6 18.8 83.7 15.7 15.7 101.7 5 Example 1 21.0 88.3 9.9 18.6 101.8 5 Example 2 25.5 82.2 16.6 20.9 101.7 5 Example s 24.8 82.5 15.6 20.5 101.9 5 Example 4 22.7 86.6 12.4 19.6 101.5 5 Example s 20.3 89.4 8.9 18.1 101.8 5 CE 1 9.2 95.2 1.5 8.8 101.5 5 CE 2 25.9 66.3 32.4 17.2 101.7 5 CE 3 41.2 30.4 68.4 12.5 100.7 5 CE 4 36.6 38.6 60.3 14.1 101.1 5 CE 5 13.8 81.6 17.0 11.3 101.5 5 CE 6 27.7 76.8 22.0 21.3 102.0 6 Example 1 32.2 82.5 15.0 26.6 101.7 6 Example 2 35.9 73.8 24.5 26.5 101.2 6 Example s 34.5 74.2 23.8 25.6 102.586468-WO-PCT / DOW 86468 WO246 Example 4 33.0 79.7 18.4 26.3 101.3 6 Example s 30.4 84.1 13.3 25.6 101.9 6 CE 1 19.3 92.8 2.5 17.9 100.6 6 CE 2 36.2 55.4 42.6 20.0 101.5 6 CE 3 51.8 31.7 66.9 16.4 96.0 6 CE 4 49.6 32.9 65.5 16.3 97.0 6 CE 5 24.5 75.1 22.1 18.4 101.7 6 CE 6 37.7 66.4 31.8 25.0 101.7 7 Example 1 12.3 90.9 7.8 11.2 101.6 7 Example 2 16.1 85.4 13.0 13.8 101.7 7 Example s 15.3 86.2 11.9 13.2 102.0 7 Example 4 13.7 88.9 9.7 12.2 102.0 7 Example s 12.6 91.8 7.4 11.6 101.6 7 CE 1 4.3 96.9 1.2 4.1 101.4 7 CE 2 16.4 71.7 27.5 11.8 101.3 7 CE 3 25.4 40.4 58.4 10.3 101.6 7 CE 4 27.7 48.1 50.8 13.3 95.6 7 CE 5 7.4 83.7 15.3 6.2 101.5 7 CE 6 17.8 80.9 18.0 14.4 101.8 8 Example 1 20.2 86.9 10.0 17.5 101.9 8 Example 2 24.3 80.6 17.1 19.5 101.7 8 Example s 21.3 81.4 15.8 17.4 104.7 8 Example 4 21.4 85.1 12.5 18.2 102.1 8 Example 5 20.0 87.0 9.9 17.4 102.1 8 CE 1 10.1 94.1 1.8 9.5 101.9 8 CE 2 25.3 59.9 38.0 15.1 101.3 8 CE 3 37.3 29.0 69.7 10.8 100.7 8 CE 4 33.4 36.0 62.5 12.0 101.0 8 CE 5 14.8 78.0 18.9 11.5 102.1 8 CE 6 25.5 74.2 23.9 18.9 102.0 9 Example 1 29.9 82.0 14.1 24.5 101.7 9 Example 2 33.3 73.4 23.6 24.4 101.4 9 Example s 32.4 74.4 22.3 24.1 101.4 9 Example 4 30.7 79.5 17.3 24.4 101.5 9 Example s 29.0 82.3 14.3 23.9 101.8 9 CE 1 20.1 91.2 3.2 18.3 101.8 9 CE 2 34.8 49.0 48.3 17.0 101.3 9 CE 3 48.3 28.4 70.0 13.7 97.486468-WO-PCT / DOW 86468 WO259 CE 4 45.8 30.1 68.5 13.8 98.2 9 CE 5 25.3 71.8 25.2 18.2 101.5 9 CE 6 34.3 64.6 32.7 22.2 101.7

[0090] As shown in Table 3, Examples 1-5 demonstrate that catalysts containing chromium, a rare earth element, an alkali metal, silica and zirconia demonstrate high activity under varying dehydrogenation conditions and retain some or all of their activity in the presence of 20% steam by volume. The catalysts of the examples also demonstrate substantial activity above the background dehydrogenation activity (as measured in Comparative Example (CE) 1 by using quartz chips in lieu of a catalyst).

[0091] Comparative Examples 2 and 3 are Cr-ZrCh catalysts. As shown in Table 3, these catalysts exhibit greater activity than Comparative Example 1, which contains quartz chips. Thus, Cr and ZrCh are believed to be important elements of a steam tolerant catalyst.

[0092] Comparative Example 4 is a Cr-ZrCh catalyst and includes La, a rare earth element. As shown in Table 3, ethane conversion increases and ethylene yield is generally maintained compared to Comparative Example 2, which is similar to Comparative Example 4 but does not contain a rare earth element. However, ethylene conversion decreases with the presence of only a rare earth element. Comparative Example 5 is a Cr-ZrCL catalyst and includes K, an alkali metal. As shown in Table 3, ethane conversion and, under most conditions, ethylene yield decreases with the presence of only an alkali metal. Thus, Comparative Examples 4 and 5 show that the presence of both an alkali metal and a rare earth element are important for improving overall catalytic performance.

[0093] Comparative Example 6 is a K-Cr-Si-ZrCh catalyst. As shown in Table 3, Comparative Example 6 has improved ethane conversion and ethylene yield than Comparative Example 5, which is a K-Cr-ZrCh catalyst. Ethylene selectivity is only slightly lower under most conditions than Comparative Example 5. Thus, it is believed that Si improves and / or maintains catalytic activity of a dehydrogenation catalyst.

[0094] Examples 1-5 show that the combination of chromium, a rare earth element, an alkali metal, and Si-ZrCh improve overall catalytic performance. Examples 1-5 have a substantially improved ethylene selectivity than Comparative Examples 2-6 and a substantially improved ethane conversion than Comparative Example 1. Additionally, ethylene yield of Examples 1 -5 generally improves or is maintained compared to Comparative Examples 1-6. Thus, it is believed86468-WO-PCT / DOW 86468 WO26that the combination of chromium, a rare earth element, an alkali metal, and Si-ZrCh result in a dehydrogenation catalyst with improved ethylene selectivity and catalytic activity in steam conditions.

[0095] The present disclosure includes numerous aspects, including aspects 1-15 described herein.

[0096] Aspect 1. A method for converting alkanes to alkenes, the method comprising: contacting a feed stream comprising alkanes with a dehydrogenation catalyst in a reaction zone in the presence of steam, wherein the dehydrogenation catalyst comprises chromium, rare earth element, and alkali metal on a silica-zirconia support, wherein the catalyst comprises: from 0.5 wt.% to 10 wt.% chromium; from 1 wt.% to 20 wt.% rare earth element; from 0.1 wt.% to 1.5 wt.% alkali metal; at least 53.5 wt.% zirconia, and from 0.05 wt.% to 15 wt.% silica; and converting at least a portion of the alkanes to alkenes, thereby yielding a product stream comprising alkanes, alkenes, and hydrogen; wherein the reaction zone is substantially free of gaseous oxidant.

[0097] Aspect 2. The method of aspect 1, wherein the rare earth element is chosen from lanthanides, yttrium, scandium, or combinations thereof..

[0098] Aspect 3. The method of any of the preceding aspects, wherein the alkali metal is chosen from lithium, sodium, potassium, rubidium, cesium, or combinations thereof.

[0099] Aspect 4. The method of any of the preceding aspects, wherein the dehydrogenation catalyst further comprises an alkaline earth metal, tin, platinum, boron, lanthanum, cerium, neodymium, samarium, gadolinium, dysprosium, praseodymium, europium, or combinations thereof.

[0100] Aspect 5. The method of aspect 1, further comprising combusting at least a portion of the hydrogen to yield steam.

[0101] Aspect 6. The method of any of the preceding aspects, wherein the dehydrogenation catalyst comprises an alkene selectivity greater than or equal to 60 Cmol%.

[0102] Aspect 7. The method of any of the preceding aspects, wherein the reaction zone comprises greater than or equal to 5 v.% steam.

[0103] Aspect 8. The method of any of the preceding aspects, further comprising contacting the feed stream comprising alkanes with a selective hydrogen combustion material, wherein the dehydrogenation catalyst and the selective hydrogen combustion material are both present in the reaction zone.86468-WO-PCT / DOW 86468 WO27

[0104] Aspect 9. The method of any of the preceding aspects, wherein the dehydrogenation catalyst comprises from 0.5 wt.% to 5 wt.% chromium based on a total weight of the dehydrogenation catalyst.

[0105] Aspect 10. The method of any of the preceding aspects, wherein the dehydrogenation catalyst and the feed stream have a mass to mass ratio that is from 5:1 to 200:1.

[0106] Aspect 11. The method of any of the preceding aspects, wherein the converting at least a portion of the alkanes to alkenes occurs at a temperature that is less than or equal to 800 °C, a pressure from 1 bara to 20 bara, and a WHSV of from 1 h'1to 15 h'1.

[0107] Aspect 12. The method of any of the preceding aspects, wherein the method further comprises: removing spent dehydrogenation catalyst from the reaction zone; introducing the spent dehydrogenation catalyst into a regeneration zone; regenerating the spent dehydrogenation catalyst, thereby forming regenerated dehydrogenation catalyst; and returning regenerated dehydrogenation catalyst to the reaction zone where it is contacted with the feed stream.

[0108] Aspect 13. A method for forming a dehydrogenation catalyst, the method comprising: obtaining a zirconia support; adding a chromium- containing precursor, a silicon-containing precursor, a rare earth element-containing precursor, and an alkali metal-containing precursor to the zirconia support to form a doped support; and drying and calcining the doped support to form the dehydrogenation catalyst.

[0109] Aspect 14. The method of aspect 13, wherein adding the chromium- containing precursor, the silicon-containing precursor, the rare earth element-containing precursor, and the alkali metal-containing precursor to the zirconia support is a process comprising spray drying, granulation, pre-impregnation, post-impregnation, co-precipitation, or combinations thereof.

[0110] Aspect 15. The method of aspect 1, wherein the rare earth element-containing precursor comprises yttrium, lanthanum, lutetium, or combinations thereof and the alkali metal-containing precursor lithium, sodium, potassium, rubidium, cesium, or combinations thereof.

[0111] The subject matter of the present disclosure has been described in detail and by reference to specific embodiments. It should be understood that any detailed description of a component or feature of an embodiment does not necessarily imply that the component or feature is essential to the particular embodiment or to any other embodiment. Further, it should be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter.86468-WO-PCT / DOW 86468 WO28

[0112] It is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present technology, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.”

[0113] It should be understood that where a first component is described as “comprising” a second component, it is contemplated that, in embodiments, the first component “consists” or “consists essentially of’ that second component. It should further be understood that where a first component is described as “comprising” a second component, it is contemplated that, in embodiments, the first component comprises at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or even at least 99% that second component (where % can be weight % or molar %).

[0114] It is also noted that recitations herein of “at least one” component, element, etc., should not be used to create an inference that the alternative use of the articles “a” or “an” should be limited to a single component, element, etc.

Claims

86468-WO-PCT / DOW 86468 WO29CLAIMS1. A method for converting alkanes to alkenes, the method comprising:contacting a feed stream comprising alkanes with a dehydrogenation catalyst in a reaction zone in the presence of steam, wherein the dehydrogenation catalyst comprises chromium, rare earth element, and alkali metal on a silica-zirconia support, wherein the catalyst comprises:from 0.5 wt.% to 10 wt.% chromium;from 1 wt.% to 20 wt.% rare earth element;from 0.1 wt.% to 1.5 wt.% alkali metal;at least 53.5 wt.% zirconia; andfrom 0.05 wt.% to 15 wt.% silica; andconverting at least a portion of the alkanes to alkenes, thereby yielding a product stream comprising alkanes, alkenes, and hydrogen;wherein the reaction zone is substantially free of gaseous oxidant.

2. The method of claim 1, wherein the rare earth element is chosen from lanthanides, yttrium, scandium, or combinations thereof.

3. The method of any of the preceding claims, wherein the alkali metal is chosen from lithium, sodium, potassium, rubidium, cesium, or combinations thereof.

4. The method of any of the preceding claims, wherein the dehydrogenation catalyst further comprises an alkaline earth metal, tin, platinum, boron, lanthanum, cerium, neodymium, samarium, gadolinium, dysprosium, praseodymium, europium, or combinations thereof.

5. The method of any of the previous claims, further comprising combusting at least a portion of the hydrogen to yield steam.

6. The method of any of the preceding claims, wherein the dehydrogenation catalyst comprises an alkene selectivity greater than or equal to 60 Cmol%.

7. The method of any of the preceding claims, wherein the reaction zone comprises greater than or equal to 5 v.% steam.86468-WO-PCT / DOW 86468 WO308. The method of any of the preceding claims, further comprising contacting the feed stream comprising alkanes with a selective hydrogen combustion material, wherein the dehydrogenation catalyst and the selective hydrogen combustion material are both present in the reaction zone.

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

10. The method of any of the preceding claims, wherein the converting at least a portion of the alkanes to alkenes occurs at a temperature that is less than or equal to 800 °C, a pressure from 1 bara to 20 bara, and a WHSV of from 1 h'1to 15 h'1.

11. The method of any of the preceding claims, wherein the method further comprises:removing spent dehydrogenation catalyst from the reaction zone;introducing the spent dehydrogenation catalyst into a regeneration zone; regenerating the spent dehydrogenation catalyst, thereby forming regenerated dehydrogenation catalyst; andreturning regenerated dehydrogenation catalyst to the reaction zone where it is contacted with the feed stream.

12. A method for forming a dehydrogenation catalyst, the method comprising:adding a chromium- containing precursor, a rare earth element-containing precursor, and an alkali metal-containing precursor to a silica-zirconia support to form a doped silica-zirconia support; anddrying and calcining the doped silica-zirconia support to form the dehydrogenation catalyst.

13. The method of claim 13, further comprising adding a silicon-containing precursor to a zirconia support to form the silica-zirconia support.

14. The method of claim 13, wherein adding the chromium-containing precursor, the rare earth element-containing precursor, and the alkali metal- containing precursor to the zirconia support is86468-WO-PCT / DOW 86468 WO31a process comprising spray drying, granulation, pre-impregnation, post-impregnation, co-precipitation, or combinations thereof.

15. The method of any one of claims 12 to 14, wherein the rare earth element-containing precursor comprises lanthanides, yttrium, scandium, or combinations thereof and the alkali metal-containing precursor lithium, sodium, potassium, rubidium, cesium, or combinations thereof.

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