WO2018015829A1

WO2018015829A1 - Process for high-pressure hydrogenation of carbon dioxide to syngas applicable for methanol synthesis

Info

Publication number: WO2018015829A1
Application number: PCT/IB2017/053935
Authority: WO
Inventors: Aghaddin Mamedov; Clark Rea
Original assignee: Sabic Global Technologies B.V.
Priority date: 2016-07-18
Filing date: 2017-06-29
Publication date: 2018-01-25

Abstract

Processes and catalysts for the hydrogenation of carbon dioxide reaction are disclosed. A process for hydrogenation of carbon dioxide (CO₂) to produce a syngas containing composition that includes hydrogen (H₂) and carbon monoxide (CO) can include contacting a chromium oxide supported catalyst with H₂ and CO₂ at a temperature of at least 600 °C and a pressure greater than atmospheric pressure to produce the syngas containing composition.

Description

PROCESS FOR HIGH-PRESSURE HYDROGENATION OF CARBON DIOXIDE TO

SYNGAS APPLICABLE FOR METHANOL SYNTHESIS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/363,404, filed July 18, 2016, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

A. Field of the Invention

[0002] The invention generally concerns a process for hydrogenation of carbon dioxide (C0₂) to produce a synthesis gas (syngas) containing composition that includes hydrogen (H₂) and carbon monoxide (CO) in a molar ratio applicable for methanol synthesis. In particular, the process includes contacting a chromium oxide supported catalyst under high pressure isothermal conditions suitable to produce a syngas composition having a sufficient amount of H₂, CO, and carbon dioxide (C0₂) in amounts sufficient to be used in methanol synthesis.

B. Description of Related Art

[0003] Syngas (which includes carbon monoxide and hydrogen gases) is oftentimes used to produce chemicals such as methanol, tert-butyl methyl ether, ammonia, fertilizers, 2-ethyl hexanol, formaldehyde, acetic acid, and 1,4-butane diol. Syngas can be produced by common methods such as methane steam reforming technology as shown in reaction equation (1), partial oxidation of methane as shown in reaction (2), or dry reforming of methane as shown in reaction (3):

CH₄ + H₂0 ^CO + 3 H₂ ΔΗ_298Κ = 206 kJ (1)

CH + 0 ^ CO + 2H

^"2 ΔΗ_298Κ = - 8 kcal/mol (2)

CH₄ + C0₂ 2CO + 2H₂ ΔΗ_298Κ = 247 kJ (3)

While the reactions in equations (1) and (2) do not utilize carbon dioxide, equation (3) does. Commercialization attempts of the dry reforming of methane to produce syngas have suffered due to high-energy consumption, catalyst deactivation, and applicability of the syngas composition produced. Equation (4) illustrates the catalyst deactivation event due to carbonization.

CH₄ + 2C0₂ C + 2CO + 2H₂0 (4)

[0004] Other attempts to convert carbon dioxide into carbon monoxide include the catalytic reduction of carbon dioxide using hydrogen as shown in equation (5).

C0₂+ H₂ ¾ CO + H₂0 ΔΗ= 10 kcal/mol (5)

This process, which is also known as a reverse water gas shift reaction, is mildly endothermic and generally takes place at temperatures of at least about 450 °C, with C0₂ conversion of 50% at temperatures between 560 °C to 580 °C. Furthermore, some methane can be formed as a by-product due to the methanation reaction as shown in equations (6) and (7).

CO + 3 H₂ ¾ CH₄ + H₂0 (6)

C0₂ + 4 H₂ ¾ CH₄ + 2 H₂0 (7)

[0005] Various catalysts and processes have been used for the catalysis of the hydrogenation of carbon dioxide reaction. By way of example, U.S. Patent No. 8,288,446 to Mamedov et al. describes a process to make a syngas mixture that includes hydrogen, carbon monoxide and carbon dioxide with a chromia/alumina catalyst at temperatures of 300 to °C to 900 °C, at a pressure of from 0.1 to 5 MPa, at combined feed gas flow rate of 52 ml/min with a temperature of 600 °C and atmospheric pressure being preferred. In another example, U.S. Patent Application Publication No. 2015/0080482 to Mamedov et al. describes a process for the hydrogenation of carbon dioxide using a chromia/alumina supported catalyst at atmospheric pressure and a temperature of 450 °C to 1000 °C with high amounts of CO in the feed gas.

[0006] Despite the foregoing, hydrogenation of carbon dioxide processes still suffers from production of the by-product methane, processing inefficiencies, and catalyst deactivation.

SUMMARY OF THE INVENTION

[0007] A discovery has been made that provides an alternate process for the production of syngas from hydrogen and carbon dioxide while producing less than 5 mol.% of methane as a by-product at elevated pressures and isothermal conditions. The discovery is premised on the use of a supported chromium oxide catalyst under isothermal conditions of at least 600 °C and a pressure greater than atmospheric pressure. Such a process has a C0₂ conversion of at least 50% and can produce syngas compositions suitable (e.g., a H₂:CO molar ratio of 4: 1 to 5 : 1) for use as an intermediate or as feed material in a subsequent methanol synthesis. The produced syngas composition also has relatively low amounts of methane (CH₄) (e.g., less than 5 mol. %), which makes it further advantageous for use in methanol synthesis.

[0008] In a particular aspect of the invention, an isothermal process for hydrogenation of carbon dioxide (C0₂) to produce a syngas containing composition that includes hydrogen (H₂) and carbon monoxide (CO) in a molar ratio (e.g., a H₂:CO molar ratio of 4: 1 to 5 : 1) suitable for methanol synthesis. The process can include contacting a chromium oxide supported catalyst with a reactant feed that includes H₂ and C0₂ at a reaction temperature of at least 600 °C to less than 660 °C, preferably 610 °C to 630 °C, more preferably 615 °C to 625 °C, or about 620 °C, and a pressure greater than atmospheric pressure, preferably greater than 2 MPa, more preferably 2 to 4 MPa, more preferably 2.5 to 3.5 MPa, or most preferably 2.5 MPa to 3 MPa to produce a product stream that includes the syngas containing composition containing H₂ and CO at a molar ratio suitable for methanol synthesis. Notably, the H₂:CO molar ratio is similar to, or the same, as the H₂:CO molar ration in syngas obtained from methane reforming. Thus, the feed can be used in a methanol plant designed to operate using syngas composition from methane reforming processes without any substantial changes in the methanol process conditions.

[0009] In the processes of the present invention, the chromium oxide catalyst can include from 5 wt.% to 30 wt. %, preferably 10 wt.% to 20 wt.%, more preferably 13 wt.% to 17 wt.% of chromium based on the total weight of the catalyst. In some embodiments, the catalyst can include from 0.2 to 30 wt. %, preferably 2 wt.% to 10 wt.%, more preferably 2 wt.%) to 5 wt.%) of lithium (Li), potassium (K), cesium (Cs) or strontium (Sr) based on the total weight of the catalyst. In some aspects of the processes of the present invention, the volume ratio of the reactants H₂ and C0₂ can be least 4: 1. In some embodiments, a combined reactant feed gas flow rate of H₂ and C0₂ can be at least 54 mL/min. In other embodiments, the H₂ gas flow rate is at least 3.5 times greater than the C0₂ gas flow rate. In another preferred aspect, the reaction conditions can include a H₂ gas flow rate of 75 mL/min to 100 mL/min, preferably 75 mL/min to 90 mL/min, a C0₂ gas flow rate of 15 mL/min to 30 mL/min, preferably 20 mL/min to 30 mL/min, a temperature of 600 °C to 650 °C, preferably 610 °C to 630 °C, and a pressure of 2.5 MPa to 3.5 MPa, preferably 2.5 MPa to 3 MPa.

[0010] Under the isothermal process conditions of the present invention, a syngas composition can be produced that includes up to 5 mol.% of alkanes (e.g., 1 to 4 mol.% or 2 to 4 mol.%) of alkanes, preferably, methane). In a preferred instance, the syngas composition includes 60 mol.% to 70 mol% H₂, 15 to 20 mol% CO, 10 to 15 mol% C0₂ and 2 to 4 mol% CH₄. In a particular instance, the product stream can include about 16.3 mol.% CO, about

12.3 mol.%) C0₂, about 2.4 mol.%> CH₄, and about 69.0 mol.%> H₂. In another embodiment, the product stream can include about 16.9 mol.%> CO, about 12.9 mol.%> C0₂, about 2.6 mol.%) CH₄, and about 67.6 mol.%> H₂. In some embodiments, the product stream can include about 16.3 mol.% CO, about 12.2 mol.% C0₂, about 2.9 mol.% CH₄, and about 68.6 mol.% H₂. In yet another embodiment, the product stream can include about 16.2 mol.%> CO, about

12.4 mol.% C0₂, about 3.2 mol.% CH₄, and about 68.2 mol.% H₂.

[0011] The following includes definitions of various terms and phrases used throughout this specification.

[0012] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%>, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

[0013] The terms "wt.%", "vol.%", or "mol.%" refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol.% of component.

[0014] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0015] The terms "inhibiting" or "reducing" or "preventing" or "avoiding" or any variation of these terms, when used in the claims and/or the specification, includes any measurable decrease or complete inhibition to achieve a desired result. [0016] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0017] The use of the words "a" or "an" when used in conjunction with the term "comprising" in the claims or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

[0018] The words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include"), or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0019] The process of the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc., disclosed throughout the specification. With respect to the transitional phase "consisting essentially of," in one non- limiting aspect, a basic and novel characteristic of the process of the present invention is the ability to hydrogenate carbon dioxide to produce syngas.

[0020] In the context of the present invention, 14 Embodiments now described. Embodiment 1 is an isothermal process for hydrogenating carbon dioxide (C0₂) to produce a syngas containing composition comprising hydrogen (H₂) and carbon monoxide (CO). The process includes the step of contacting a chromium oxide supported catalyst with a reactant feed stream comprising H₂ and C0₂ at a temperature of greater than 600 °C to less than 660 °C and a pressure greater than atmospheric pressure to produce a product stream comprising H₂ and CO at a molar ratio suitable for use in methanol synthesis. Embodiment 2 is the process of Embodiment 1, wherein the H₂:CO molar ratio is from 4: 1 to 5: 1, or preferably 4: 1 or more preferably 4.5: 1. Embodiment 3 is the process of any one of Embodiments 1 to 2, wherein the syngas composition contains up to 5 mol.% of an alkane, preferably 2 to 4 mol. %. Embodiment 4 is the process of Embodiment 3, wherein the alkane is methane (CH₄). Embodiment 5 is the process of any one of Embodiments 1 to 4, wherein the temperature is 610 °C to 630 °C, preferably 615 °C to 625 °C, or more preferably about 620 °C. Embodiment 6 is the process of any one of Embodiments 1 to 5, wherein the pressure is 2 MPa to 4 MPa, preferably 2.5 to 3.5 MPa, or more preferably 2.5MPa to 3 MPa. Embodiment 7 is the process of any one of Embodiments 1 to 6, wherein the syngas composition contains 60 mol.% to 70 mol% H₂, 15 to 20 mol% CO, 10 to 15 mol% C0₂ and 2 to 4 mol% CH₄. Embodiment 8 is the process of any one of Embodiments 1 to 7, wherein the syngas composition contains 15 mol% or less of C0₂. Embodiment 9 is the process of any one of Embodiments 1 to 8, wherein the pressure is 2 MPa to 4 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 70 to 100 mL/min and the C0₂ gas flow rate in the reactant feed stream is 15 to 30 mL/min. Embodiment 10 is the process of Embodiments 1 to 9, wherein the pressure is 2.5 MPa to 3 MPa, the H₂ gas flow rate is 75 to 85 mL/min, and the C0₂ gas flow rate is 20 to 30 mL/min. Embodiment 11 is the process of any one of Embodiments 1 to 10, wherein the volume ratio of the H₂ to C0₂ in the reactant feed stream is 2.5: 1 to 5: 1. Embodiment 12 is the process of any one of Embodiments 1 to 11, wherein the catalyst contains from 5 to 30 wt. % of chromium, preferably 10 to 20 wt.% chromium, and more preferably 13 to 17 wt.% chromium. Embodiment 13 is the process of Embodiments 1 to 12, wherein the catalyst comprises from 0.2 to 30 wt. %, preferably 2 to 10 wt.%, or more preferably 2 to 5 wt.% of at least one member selected from the group consisting of Li, K, Cs and Sr. Embodiment 14 the process of any one of Embodiments 1 to 13, wherein the C0₂ conversion is at least 50%. Embodiment 15 is the process of any one of Embodiments 1 to 14, further comprising subjecting the product feed to conditions sufficient to produce methanol.

[0021] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0023] FIG. 1 is an illustration of a process of the present invention to produce syngas using a combined C0₂ and H₂ containing reactant feed gas and the chromium oxide supported catalyst of the present invention.

[0024] FIG. 2 is an illustration of a process of the present invention to produce syngas using a H₂ reactant feed gas source, a C0₂ reactant feed gas source, and the chromium oxide supported catalyst of the present invention.

[0025] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0026] A discovery has been made that addresses the aforementioned problems and inefficiencies associated with the production of syngas from hydrogenation of carbon dioxide. The discovery is premised on the use of a chromium oxide supported catalyst in the hydrogenation of carbon dioxide reaction, which results in relatively high carbon dioxide conversions with minimal (e.g., less than 5 mol.%) or no production of alkane byproducts (e.g., methane) at elevated temperatures and pressures. Furthermore, these results can be achieved at isothermal processing conditions of at least 600 °C, preferably 610 °C to 630 °C, and greater than atmospheric pressure, preferably 2.5 MPa to 3.5 MPa or 2.5 MPa to 3 MPa. The syngas composition can have characteristics that make it acceptable for methanol production (e.g., a H₂:CO molar ratio of 2 or greater, a C0₂ amount of less than 16 mol.%, a CO amount of at least 8 mol.%, and/or a methane content of less than 5 mol.%).

[0027] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the Figures. A. Process to Produce Syngas

[0028] Conditions sufficient to produce syngas from the hydrogenation of C0₂ reaction include temperature, time, flow rate of feed gases, and pressure. The temperature range for the hydrogenation reaction can range from at least 600 °C, 600 °C to 655 °C, 615 °C to 630 °C, 610 °C to 625 °C, or about 620 °C and all ranges and values there between (e.g., 600 °C, 605 °C, 610 °C, 615 °C, 620 °C, 625 °C, 630 °C, 635 °C, 640 °C, 645 °C, or 655 °C). The average pressure for the hydrogenation reaction can range from above atmospheric pressure, at least 0.5 MPa, 0.5 MPa to about 6 MPa, 2 MPa to 4 MPa, 2.5 MPa to 3.5 MPa, or 2.5 MPa to 3 MPa and all pressures there between (e.g., 0.5 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, and 6 MPa). The upper limit on pressure can be determined by the reactor used. The conditions for the hydrogenation of C0₂ to syngas can be varied based on the type of the reactor used.

[0029] The combined flow rate for the for the reactants (e.g., combination of the H₂ and C0₂ flow rate) in hydrogenation reaction can range from at least 54 mL/min, 54 to 120 mL/min, 100 mL/min to 120 mL/min, 100 mL/min to 105 mL/ min or all ranges and values there between (e.g., at least 54 mL/min, 55 mL/min , 56 mL/min, 57 mL/min, 58 mL/min, 59 mL/min, 60 mL/min, 61 mL/min, 62 mL/min, 63 mL/min, 64 mL/min, 65 mL/min, 66 mL/min, 67 mL/min, 68 mL/min, 69 mL/min, 70 mL/min, 71 mL/min, 72 mL/min, 73 mL/min, 74 mL/min, 75 mL/min, 76 mL/min, 77 mL/min, 78 mL/min, 79 mL/min, 80 mL/min, 81 mL/min, 82 mL/min, 83 mL/min, 84 mL/min, 85 mL/min, 86 mL/min, 87 mL/min, 88 mL/min, 89 mL/min, 90 mL/min, 91 mL/min, 92 mL/min, 93 mL/min, 94 mL/min, 95 mL/min, 96 mL/min, 97 mL/min 98 mL/min, 99 mL/min, 100 mL/min, 101 mL/min, 102 mL/min, 103 mL/min, 104 mL/min, 105 mL/min, 106 mL/min, 107 mL/min 108 mL/min, 109 mL/min, 1 10 mL/min, 1 1 1 mL/min, 1 12 mL/min, 1 13 mL/min, 1 14 mL/min, 1 15 mL/min, 1 16 mL/min, 1 17 mL/min, 1 18 mL/min, 1 19 mL/min, or 120 mL/min). In some instances, the H₂ flow rate can range from 70 mL/min to 100 mL/min, 75 to 95 mL/min, 80 to 90 mL/min, or all ranges and values there between (e.g., 70 mL/min, 71 mL/min, 72 mL/min, 73 mL/min, 74 mL/min, 75 mL/min, 76 mL/min, 77 mL/min, 78 mL/min, 79 mL/min, 80 mL/min, 81 mL/min, 82 mL/min, 83 mL/min, 84 mL/min, 85 mL/min, 86 mL/min, 87 mL/min, 88 mL/min, 89 mL/min, 90 mL/min, 91 mL/min, 92 mL/min, 93 mL/min, 94 mL/min, 95 mL/min, 96 mL/min, 97 mL/min, 98 mL/min, 99 mL/min, or 100 mL/min). The C0₂ gas flow rate can be 15 mL/min to 30 mL/min, 20 to 30 mL/min or any range or value there between (e.g., 15 mL/min, 16 mL/min, 17 mL/min, 18 mL/min, 19 mL/min, 20 mL/min, 21 mL/min, 22 mL/min, 23 mL/min, 24 mL/min, 25 mL/min, 26 mL/min, 27 mL/min, 28 mL/min, 29 mL/min, or 30 mL/min). In a particular instance, the H₂ gas flow rate is 75 to 90 mL/min and the C0₂ gas flow rate is 20 to 30 mL/min at a pressure of 2.5 MPa to 3.5 MPa, or preferably 2.5 MPa to 3.0 MPa.

[0030] In another aspect, the reaction can be carried out over the chromium oxide supported catalyst of the current invention having particular syngas selectivity and conversion results. Therefore, in one aspect, the reaction can be performed with a C0₂ conversion of at least 50 mol.%, at least 60 mol.%, at least 70 mol.%, at least 80 mol.% or at least 99 mol.%. The method can further include collecting or storing the produced syngas along with using the produced syngas as a feed source, solvent, or a commercial product. Prior to use, the catalyst can be subjected to reducing conditions to convert the chromium oxide and the other metals in the catalyst to a lower valance state or the metallic form. A non-limiting example of reducing conditions includes flowing a gaseous stream that includes a hydrogen gas or a hydrogen gas containing mixture (e.g., a H₂ and argon gas stream) at a temperature of 500 °C to 700 °C for a period of time (e.g., 1 to 8 hours) under atmospheric pressure over the catalyst.

[0031] Referring to FIG. 1, a system 100 is illustrated, which can be used to convert a reactant gas stream of carbon dioxide (C0₂) and hydrogen (H₂) into syngas using the chromium oxide supported catalyst of the present invention to produce a product stream having a composition suitable for methanol synthesis. The system 100 can include a combined reactant gas source 102, a reactor 104, and a collection device 106. The combined reactant gas source 102 can be configured to be in fluid communication with the reactor 104 via an inlet 108 on the reactor. The combined reactant gas source 102 can be configured such that it regulates the amount of reactant feed (e.g., C0₂ and H₂) entering the reactor 104. As shown, the combined reactant gas source 102 is one unit feeding into one inlet 108. By comparison, FIG. 2 depicts a system 200 for the process of the present invention having two feed inlets. As shown in FIG. 2, a hydrogen gas reactant feed source 202 and a carbon dioxide reactant gas feed source 204 are in fluid communication with reactor 104 via hydrogen gas inlet 206 and carbon dioxide gas inlet 208, respectively. It should be understood that the number of inlets and/or separate feed sources can be adjusted to reactor sizes and/or configurations. The reactor 104 can include a reaction zone 1 10 having the chromium oxide supported catalyst 112 of the present invention. The reactor can include various automated and/or manual controllers, valves, heat exchangers, gauges, etc., for the operation of the reactor. The reactor can have insulation and/or heat exchangers to heat or cool the reactor as desired. The amounts of the reactant feed and the chromium oxide catalyst 112 used can be modified as desired to achieve a given amount of product produced by the systems 100 or 200. In a preferred aspect, a continuous flow reactor can be used. Non-limiting examples of continuous flow metal reactors include fixed-bed reactors, fluidized reactors, bubbling bed reactors, slurry reactors, rotating kiln reactors, moving bed reactors or any combinations thereof when two or more reactors are used. The reactor can made of materials that are corrosion and oxidation resistant. By way of example, the reactor can be lined with, or made from, Inconel, or be a quartz reactor. In some embodiments, the reactant gas is preheated prior to being fed to the reactor. In some embodiments, the reactant gas is preheated prior to being fed to the reactor. In some embodiments, reaction zone 110 is a multi-zone reactor with different stages of heating in each zone. The reactor 104 can include an outlet 114 configured to be in fluid communication with the reaction zone 110 and configured to remove a first product stream comprising syngas from the reaction zone. Reaction zone 110 can further include the reactant feed and the first product stream. The products produced can include hydrogen and carbon monoxide. The product stream can also include unreacted carbon dioxide, water, and less than 5 mol.% of alkanes {e.g., methane). In some aspects, the catalyst can be included in the product stream. The collection device 106 can be in fluid communication with the reactor 104 via the product outlet 114. Reactant gas inlets 108, 206, and 208, and the outlet 114 can be opened and closed as desired. The collection device 106 can be configured to store, further process, or transfer desired reaction products {e.g., syngas) for other uses. In a non-limiting example, collection device 106 can be a separation unit or a series of separation units that are capable of separating the gaseous components from each other {e.g., separate carbon dioxide or water from the stream). Water can be removed from the product stream with any suitable method known in the art, {e.g., condensation, liquid/gas separation, etc.).

[0032] Any unreacted reactant gas can be recycled and included in the reactant feed to maximize the overall conversion of C0₂ to syngas, which increases the efficiency and commercial value of the C0₂ to syngas conversion process of the present invention. The resulting syngas can be sold, stored or used in other processing units {e.g., methanol processing unit) as a feed source. Still further, the systems 100 or 200 can also include a heating/cooling source (not shown). The heating/cooling source can be configured to heat or cool the reaction zone 1 10 to a temperature sufficient (e.g., at least 600 °C or 600 °C to 650 °C) to convert C0₂ in the reactant feed to syngas via hydrogenation. Non-limiting examples of a heating/cooling source can be a temperature controlled furnace or an external, electrical heating block, heating coils, or a heat exchanger.

B. Catalyst and Preparation Thereof

[0033] The catalyst can include chromium (Cr) as the catalytic active metal. The chromium can be in the form of one or more oxides (e.g., Cr₂0₃, Cr0₂, and CrO) on a metal oxide support (e.g., alumina, A1₂0₃). The catalyst can also include a promotor (e.g., alkali metal, alkaline earth metals, or both), a binder material, or usual impurities, as known to the skilled person.

[0034] The chromium (Cr) content of the catalyst can be 5 to 30 wt.%, 10 to 20 wt.%, or 13 to 17 wt. %, or any range or value there between (e.g., 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 1 1 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, or 30 wt.%).

[0035] The catalyst can also include at least one alkali metal (metal from Column 1 of the Periodic Table) or alkaline earth metal (metal from Column 2 of the Periodic Table) as a promoter. Non-limiting examples of alkali metal include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or any combination thereof. Non-limiting examples of alkaline earth metals include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The alkali metal or alkaline earth metal content can be 0.2 to 30 wt.%, 2 to 10 wt.%), or 2 to 5 wt. %, or any range or value there between (e.g., 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 1 1 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.%, or 30 wt.%). In a preferred aspect, the promoter can be Li, K, Cs, Sr, or any combination thereof. Without wishing to be bound by theory, it is believed that the inclusion of an alkali metal or alkaline earth metal can suppress coke formation and/or methanation reactions, thereby improving the catalyst stability /life-time and reducing the amount of unwanted by-products. [0036] The catalyst used in the process according to the invention can have alumina as carrier or support material. Without wishing to be bound to any theory, it is believed that chemical interactions between chromium and alumina lead to structural properties (e.g., spinel type structures) that enhance catalytic performance in the targeted reaction. In some instances, the catalyst has a surface area of at least 50 m²/g.

[0037] The catalyst composition according to the invention may further contain an inert binder or support material other than alumina (e.g., silica or titanium oxides).

[0038] The catalyst that is used in the process of the invention may be prepared by any conventional catalyst synthesis method as known in the art or obtained from a commercial source. Non-limiting examples of chromium oxide catalyst include catalysts sold under the tradename CATOFIN® (Clariant, U.S.A.). A non-limiting example of preparation of the catalyst can include making aqueous solutions of the desired metal components, for example from their nitrate or other soluble salt, mixing the solutions with alumina, forming a solid catalyst precursor by precipitation (or impregnation) followed by removing water and drying, and then calcining the precursor composition by a thermal treatment in the presence of oxygen. The catalyst may be applied in the process of the invention in various geometric forms, for example as spherical pellets.

C. Reactants and Products

[0039] Carbon dioxide gas and hydrogen gas can be obtained from various sources. In one non-limiting instance, the carbon dioxide can be obtained from a waste or recycle gas stream (e.g., from a plant on the same site such as from ammonia synthesis, or a reverse water gas shift reaction) or after recovering the carbon dioxide from a gas stream. A benefit of recycling such carbon dioxide as a starting material in the process of the invention is that it can reduce the amount of carbon dioxide emitted to the atmosphere (e.g., from a chemical production site). The hydrogen can be from various sources, including streams coming from other chemical processes, like water splitting (e.g., photocatalysis, electrolysis, or the like), additional syngas production, ethane cracking, methanol synthesis, or conversion of methane to aromatics. The volume ratio of H₂:C0₂ reactant gas for the hydrogenation reaction can range from 2.5 : 1 to 5 : 1, from 3 : 1 to 4: 1. In one instance the reactant gas stream includes 40 to 90 vol.% H₂, 10 to 35 vol.% C0₂, or 65 to 85 vol.% H₂, and 20 to 30 vol.% C0₂, preferably, 84 vol.% H₂ and 21 vol.% C0₂ or 78.7 vol.% H₂ and 26.2 vol.% C0₂. In some embodiments, the streams are not combined. In these instances, the hydrogen and carbon dioxide can be delivered at the same H₂:C0₂ ratios and volume percentages such as those discussed above for a combined reactant stream. In some examples, the remainder of the reactant gas stream can include another gas or gases provided the gas or gases are inert, such as argon (Ar), nitrogen (N₂), or methane and further provided that they do not negatively affect the reaction. All possible percentages of C0₂ plus H₂ plus inert gas in the current embodiments can have the described H₂:C0₂ ratios herein. Preferably, the reactant mixture is highly pure and substantially devoid of water or steam. In some embodiments, the carbon dioxide can be dried prior to use (e.g., pass through a drying media) or contain a minimal amount of water or no water at all.

[0040] The process of the present invention can produce a product stream that includes a mixture of H₂ and CO having a molar H₂:CO ratio suitable as an intermediate or as feed material in a subsequent synthesis to form a chemical product or a plurality of chemical products to produce one or more chemical products. Non-limiting examples of synthesis include methanol production, olefin synthesis, aromatics production, hydroformylation of olefins, carbonylation of methanol, and carbonylation of olefins. Non-limiting examples of products that can be produced include aliphatic oxygenates, methanol, olefin synthesis, aromatics production, carbonylation of methanol, carbonylation of olefins, or reduction of iron oxide in steel production. In a preferred embodiment, the syngas composition is used in a methanol synthesis to produce methanol. By way of example, the molar H₂:CO ratio can be about 1.9: 1 to 5 : 1, 2: 1 to 4: 1, 4: 1 to 5 : 1, or preferably 4: 1 to 4.5 : 1, which is suitable for the production of methanol from syngas. In some instances, a purge gas from the methanol synthesis reaction, containing hydrogen and carbon dioxide, is recycled back to the carbon dioxide hydrogenation step. In embodiments, when C0₂ is present in the product stream, the process can produce a mixture suitable for the production of methanol having at least 2 mol.% of C0₂ up to 16 mol.% C0₂. The amount of alkane (e.g., methane) produced in the process of the present reaction can be less than 5 mol.%, less than 4 mol.%, 3 mol.%, 2 mol.%), 1 mol.%) or 0 mol.%> or 2 mol.%> to 4 mol.%> based on the total moles of components in the product stream. In a particular instance, the product stream can include 60 mol.%> to 70 mol% H₂, 15 to 20 mol% CO, 10 to 15 mol% C0₂ and 2 to 4 mol% CH₄. In a particular instance, the product stream can include about 16.3 mol.% CO, about 12.3 mol.% C0₂, about 2.4 mol.%) CH₄, and about 69.0 mol.% H₂. In another embodiment, the product stream can include about 16.9 mol.% CO, about 12.9 mol.% C0₂, about 2.6 mol.% CH₄, and about 67.6 mol.% H₂. In some embodiments, the product stream can include about 16.3 mol.% CO, about 12.2 mol.% C0₂, about 2.9 mol.% CH₄, and about 68.6 mol.% H₂. In yet another embodiment, the product stream can include about 16.2 mol.% CO, about 12.4 mol.% C0₂, about 3.2 mol.% CH₄, and about 68.2 mol.% H₂.

EXAMPLES

[0041] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters, which can be changed or modified to yield essentially the same results.

Example 1

(General Process for Hydrogenation of Carbon Dioxide)

[0042] A commercial chromia/alumina dehydrogenation catalyst, marketed by Clariant (USA) as Catofin® for dehydrogenation of propane or iso-butane, was applied as catalyst composition in this experiment. This catalyst contains about 13 to 17 wt.% of Cr.

[0043] General Procedure. Catalyst testing was performed in a high throughput metal reactor system. The reactors are fixed bed type reactor with a 2.5 cm inner diameter and 40 cm in length. Gas flow rates were regulated using two mass flow controllers. Reactor pressure was maintained by using a back pressure regulator. The reactor temperature was maintained by an external, electrical heating block. The effluent of the reactors was connected to a gas chromatograph for online gas analysis using a molecular sieve and Hayesep D column and thermal conductivity detector (TCD). The catalyst (3 mL) was placed on top of inert material inside the reactor. Prior to the reaction test, the catalyst was reduced at 600 °C under 25 vol.% H₂ in Ar for 2 h. In all examples, C0₂ conversion was calculated by the following formula.

C0₂ conversion, % mol = (%CO + %CH₄) / (%CO + %CH₄ + %C0₂) (8) which presents the reactions of equations (5) and (7) discussed above

C0₂+ H₂ ¾ CO + H₂0 (5)

C0₂ + 4 H₂ ¾ CH₄ + 2 H₂0 (7) Therefore, equation (8) presents the sum of all carbon, products divided by the total number of carbons.

Example 2

(Process for Hydrogenation of Carbon Dioxide)

[0044] The general procedure of Example 1 was followed with the following conditions: a pressure of 2.8 MPa, a temperature of 620 °C, a H₂ flow rate of 78.7 cubic centimeter (cc)/min, and a C0₂ flow rate of 26.2 cc/min. Time on stream (TOS), molar percentage of components in the product stream and percent (%) carbon dioxide conversion and results are listed in Table 1.

Table 1

*Time on Stream

Example 3

(Process for Hydrogenation of Carbon Dioxide)

[0045] The general procedure of Example 1 was followed using the following conditions: a pressure of 2.8 MPa, a temperature of 620 °C, a H₂ flow rate of 84 cc/min and a C0₂ flow rate of 21 cc/min. Results are listed in Table 2.

Table 2

TOS, hour Concentration, % mol % C0₂ Conversion

CO co₂ CH₄ H₂

6 16.3 12.2 2.9 68.6 61.2

12 16.2 12.4 3.2 68.2 61.0 Example 4

(Process for Hydrogenation of Carbon Dioxide)

[0046] The general procedure of Example 1 was followed using the following conditions: a pressure of 2.65 MPa, a temperature of 660 °C, a H₂ flow rate of 100 cc/min and a C0₂ flow rate of 25 cc/min. Results are listed in Table 3.

Table 3

Example 5

(Process for Hydrogenation of Carbon Dioxide)

[0047] The general procedure of Example 1 was followed using the following conditions: a pressure of 2.8 MPa, a temperature of 600 °C, a H2 flow rate of 78.7 cc/min and a C02 flow rate of 26.2 cc/min. Results are listed in Table 4.

Table 4

[0048] From the comparison of Example 4 with Examples 2 and 3, it was determined that the high temperature (660 °C) was not as efficient for producing syngas, as a majority of the carbon dioxide converts to methane, as illustrated by the high amounts of methane present in the syngas (Example 4). From the comparison of Example 5 with Examples 2 and 3, it was determined that temperatures of 600 °C or less are not as efficient for producing the syngas compositions, as the syngas composition includes at least 16 mol% C0₂ and less than 12 mol% CO (Example 5). Syngas having amounts of methane over 5 mol% and amounts of C0₂ over 15 mol% are not conducive for use in methanol synthesis reactions. [0049] By comparison, Examples 2 and 3 provide processing conditions allowing for syngas production having a methane content of 2 to 4 %, with a C0₂ conversion of at least 50 mol.%, and a CO content of at least 12 mol%. The amount of methane in the produced syngas composition is similar to the content of methane present in product streams obtain from methane reforming syngas reactions. Syngas produced at the conditions of Examples 2 and 3 with the catalyst of the present invention is suitable for use as an intermediate or as feed material in a subsequent synthesis (e.g., methanol production) to form a chemical product or a plurality of chemical products (e.g., methanol).

Claims

1. An isothermal process for hydrogenating carbon dioxide (C0₂) to produce a syngas containing composition comprising hydrogen (H₂) and carbon monoxide (CO), the process comprising contacting a chromium oxide supported catalyst with a reactant feed stream comprising H₂ and C0₂ at a temperature of greater than 600 °C to less than 660 °C and a pressure greater than atmospheric pressure to produce a product stream comprising H₂ and CO at a molar ratio suitable for use in methanol synthesis.

2. The process of claim 1, wherein the H₂:CO molar ratio is from 4: 1 to 5: 1, or 4: 1 or 4.5: 1.

3. The process of claims 1 or 2, wherein the syngas composition comprises up to 5 mol.% of an alkane, preferably 2 to 4 mol. %.

4. The process of claim 3, wherein the alkane is methane (CH₄).

5. The process of any one of claim 1 or 2, wherein the temperature is 610 °C to 630 °C, preferably 615 °C to 625 °C, or about 620 °C.

6. The process of any one of claims 1 or 2, wherein the pressure is 2 MPa to 4 MPa, preferably 2.5 to 3.5 MPa, or more preferably 2.5MPa to 3 MPa.

7. The process of any one of claims 1 or 2, wherein the syngas composition comprises 60 mol.% to 70 mol% H₂, 15 to 20 mol% CO, 10 to 15 mol% C0₂ and 2 to 4 mol% CH₄.

8. The process of any one of claims 1 or 2, wherein the syngas composition comprises 15 mol% or less of C0₂.

9. The process of any one of claims 1 or 2, wherein the pressure is 2 MPa to 4 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 70 to 100 mL/min and the C0₂ gas flow rate in the reactant feed stream is 15 to 30 mL/min.

10. The process of claim 1 or 2, wherein the pressure is 2.5 MPa to 3 MPa, the H₂ gas flow rate is 75 to 85 mL/min, and the C0₂ gas flow rate is 20 to 30 mL/min.

11. The process of any one of claims 1 or 2, wherein the volume ratio of the H₂ to C0₂ in the reactant feed stream is 2.5 : 1 to 5: 1.

12. The process of any one of claims 1 or 2, wherein the catalyst contains from 5 to 30 wt.

% of chromium, preferably 10 to 20 wt.% chromium, more preferably 13 to 17 wt.% chromium

13. The process of claim 1 or 2, wherein the catalyst comprises from 0.2 to 30 wt. %, preferably 2 to 10 wt.%, or more preferably 2 to 5 wt.% of at least one member selected from the group consisting of Li, K, Cs and Sr.

14. The process of any one of claims 1 or 2, wherein the C0₂ conversion is at least 50%.

15. The process of any one of claims 1 or 2, further comprising subjecting the product feed to conditions sufficient to produce methanol.