WO2018020343A1

WO2018020343A1 - Process for producing an oxo-synthesis syngas composition by high-pressure hydrogenation over a chromium oxide/aluminum supported catalyst

Info

Publication number: WO2018020343A1
Application number: PCT/IB2017/054151
Authority: WO
Inventors: Aghaddin Mamedov; Clark Rea; Shahid Shaikh
Original assignee: Sabic Global Technologies B.V.
Priority date: 2016-07-25
Filing date: 2017-07-10
Publication date: 2018-02-01

Abstract

Processes and catalysts for the hydrogenation of carbon dioxide to produce an oxo-synthesis syngas containing composition are disclosed. The process includes contacting a chromium oxide/alumina supported catalyst with hydrogen (H₂) and CO₂ at a constant temperature or temperature range and high pressure (at least 0.5 MPa) to produce the oxo-synthesis syngas containing composition having a H₂:CO molar ratio of 1.2 or less and methane (CH₄) in an amount of at least 1 molar %.

Description

PROCESS FOR PRODUCING AN OXO-SYNTHESIS SYNGAS COMPOSITION BY HIGH-PRESSURE HYDROGENATION OVER A CHROMIUM OXIDE/ALUMINUM SUPPORTED CATALYST

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/366,218, filed July 25, 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 oxo-synthesis. In particular, the process includes contacting a chromium oxide/alumina supported catalyst under high pressure conditions suitable to produce an oxo-synthesis syngas composition having a H₂:CO molar ratio of less than 1.2 and at least 1 molar % of methane (CH₄).

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 AH₂₉8K = 206 kJ (1)

CH₄ + 0₂ CO + 2H₂ ΔΗ₂₉₈κ = - 8 kcal/mol (2) CH₄ + C0₂ - 2CO + 2H₂ AH_298K = 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.

[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 preferred process to make a syngas mixture that includes contacting a chromia/alumina catalyst with equimolar amounts of H₂ and C0₂ at 600 °C and atmospheric pressure. In this process, no methane was produced. 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 carbon monoxide (CO) in the feed gas.

[0006] Despite the foregoing, hydrogenation of carbon dioxide processes still suffer from processing inefficiencies to make syngas compositions suitable for oxo-product synthesis and catalyst deactivation.

SUMMARY OF THE INVENTION

[0007] A discovery has been made that provides a process for the production of oxo- synthesis syngas from hydrogen gas and carbon dioxide that includes at least 1 molar % of methane at elevated pressures and isothermal conditions. Notably, methane is not detrimental to an oxo-synthesis reaction so it does not need to be removed from the syngas product stream prior to use in an oxy-synthesis reaction {e.g., a hydroformylation of olefins reaction, a carbonylation of methanol reaction, or a carbonylation of olefins reaction). The discovery is premised on the use of a supported chromium oxide/alumina catalyst under isothermal conditions of at least 550 °C, a pressure of at least 0.5 MPa, and a H₂:C0₂ molar ratio of 1 or less. Such a process can surprisingly produce syngas compositions (e.g., a H₂:CO molar ratio of 1.2 or less) suitable for use as an intermediate or as feed material in the aforementioned oxo-synthesis reactions. By comparison, using syngas compositions having higher ratios of H₂:CO (e.g., greater than 1.2) for the hydrocarbonylation of propylene to butyl aldehyde reaction can result in increased concentrations of 2-ethyl hexanol from over-hydrogenation of butyl aldehyde dimer. Therefore, the process of the present invention provides an elegant alternative to the highly endothermic process of methane steam reforming to produce syngas suitable for use in oxo-product synthesis. Any unreacted C0₂ can be separated from the product gas stream by, for example, amine adsorption) to be further used for carbonylation reactions.

[0008] In one aspect of the current invention, an isothermal process for hydrogenating carbon dioxide (C0₂) to produce an oxo-synthesis syngas containing composition is described. The process can include contacting a chromium oxide/alumina supported catalyst with hydrogen (H₂) and C0₂ at a H₂:C0₂ molar ratio of 1 or less, a constant temperature of at least 550 °C, and a pressure of at least 0.5 MPa to produce the oxo-synthesis syngas containing composition that includes H₂ and CO at a H₂:CO molar ratio of 1.2 or less and methane (CH₄) in an amount of at least 1 molar %. In another aspect, the H₂:C0₂ reactant feed stream can have a molar ratio from 0.1 to 0.9, 0.2 to 0.8, or 0.4 to 0.7 and in some instances, does not contain CH₄. In some aspects, the reaction temperature can be from 550 °C to 675 °C, 550 °C to 600 °C, or 625 °C to 675 °C and the reaction pressure can be from 0.5 MPa to 3 MPa, 1 MPa to 3 MPa, or 2 MPa to 3 MPa. In a particular aspect, the chromium oxide/alumina supported catalyst can include from 5 to 30 wt. % of chromium (Cr), 10 to 20 wt. % of Cr, or 13 to 17 wt.% Cr, and, in some instances, from 0.2 wt.% to 30 wt.%, 2 wt.% to 10 wt.%, or 2 wt.% to 5 wt.% of at least one Column 1 or 2 metal (e.g., lithium (Li), potassium (K), cesium (Cs), strontium (Sr), or any combination thereof). In particular aspects, the reaction occurs at 550 °C to 600 °C and at a pressure of 0.9 MPa to 3.0 MPa, and the H₂ gas flow rate in the reactant feed stream can be 30 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream can be 50 to 70 mL/min. In yet another instance, the reaction can occur at 640 °C to 660 °C and a pressure of 2.5 MPa to 3 MPa, and the H₂ gas flow rate in the reactant feed stream can be 30 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream can be 50 to 70 mL/min. In still another instance, the reaction can occur at 640 °C to 660 °C and a pressure of 2.5 MPa to 3 MPa, and the H₂ gas flow rate in the reactant feed stream can be 20 to 40 mL/min and the C0₂ gas flow rate in the reactant feed stream can be 60 to 80 mL/min. The C0₂ conversion of the process can be at least 10%.

[0009] Under the isothermal process conditions of the present invention, the H₂:CO molar ratio of the produced oxo-synthesis gas can be from 0.1 to 1.2, 0.2 to 1.2, or 0.4 to 1.2. The amount of H₂ in the syngas composition can be from 1 to 40 molar %, 3 to 30 molar %, or 5 to 25 molar %, and the amount of CO in the syngas composition can be from 1 to 40 molar %, 3 to 30 molar %, or 10 to 25 molar %. In certain aspects, the amount of CH₄ in the syngas composition can be from 1 to 10 molar %, 1.5 to 8 molar %, or 1.5 to 6.5 molar %. In certain instances, the CH₄ in the syngas composition is inert and does not need to be removed for downstream oxo-synthesis reactions. In some aspects, the syngas composition further includes an amount of C0₂ from 40 to 90 molar % or 50 to 80 molar % and the syngas composition can be further processed to remove C0₂, for example, by amine adsorption. In some aspects, the syngas composition can include 15 mol.% to 21 mol.% CO, 50 mol.% to 60 mol.% C0₂, 1.5 mol.% to 2.5 mol.% CH₄, and 20 mol.% to 25 mol.% H₂. In yet another aspect, the syngas composition can include 15 mol.% to 25 mol.% CO, 50 mol.% to 60 mol.% C0₂, 3 mol.% to 10 mol.% CH₄, and 15 mol.% to 20 mol.% H₂. In still a further aspect, the syngas composition can include 5 mol.% to 10 mol.% CO, 70 mol.% to 85 mol.% C0₂, 3 mol.%) to 7 mol.% CH₄, and 3 mol.% to 7 mol.% H₂. Notably, methane is not detrimental to an oxo-synthesis reaction so removal of the methane from the syngas containing product stream is not needed. In a particular instance, the produced syngas composition can include C0₂ and the process can further include removing the C0₂ from the syngas containing product stream to obtain the oxo-synthesis syngas containing composition and providing the produced oxo-synthesis syngas to a hydroformylation of olefins reaction, a carbonylation of methanol reaction, or a carbonylation of olefins reaction. [0010] The following includes definitions of various terms and phrases used throughout this specification.

[0011] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%. [0012] 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. [0013] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0014] 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. [0015] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0016] 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." [0017] 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. [0018] 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 oxy-synthesis syngas. [0019] In the context of the present invention, 20 Embodiments are now described. Embodiment 1 is an isothermal process for hydrogenating carbon dioxide (C0₂) to produce an oxo-synthesis syngas containing composition. The process includes the step of contacting a chromium oxide/alumina supported catalyst with a reactant feed stream comprising hydrogen (H₂) and C0₂ at a H₂:C0₂ molar ratio of less than 1, wherein the reaction occurs at a constant temperature of at least 550 °C and a pressure of at least 0.5 MPa to produce the oxo-synthesis syngas containing composition including H₂ and CO at a H₂:CO molar ratio of less than 1.2 and methane (CH₄) in an amount of at least 1 molar %. Embodiment 2 is the process of Embodiment 1, wherein the H₂:C0₂ molar ratio is from 0.1 to 0.9, 0.2 to 0.8, or 0.4 to 0.7. Embodiment 3 is the process of any one of Embodiments 1 or 2, wherein the reactant feed stream does not contain CH₄. Embodiment 4 is the process of any one of Embodiments 1 to 3, wherein the reaction temperature is from 550 °C to 700 °C, or 570 °C to 590 °C, or 625 °C to 675 °C. Embodiment 5 is the process of any one of Embodiments 1 to 4, wherein the reaction pressure is from 0.5 MPa to 3 MPa, or 1 MPa to 3 MPa. Embodiment 6 is the process of any one of Embodiments 1 to 5, wherein the amount of H₂ in the syngas composition is from 1 to 40 molar %, 3 to 30 molar %, or 5 to 25 molar %. Embodiment 7 is the process of any one of Embodiments 1 to 6, wherein the amount of CO in the syngas composition is from 1 to 40 molar %, 3 to 30 molar %, or 10 to 25 molar %. Embodiment 8 is the process of any one of Embodiments 1 to 7, wherein the H₂:CO molar ratio is from 0.1 to 1.2, 0.2 to 1.2 or 0.4 to 1.2. Embodiment 9 is the process of any one of Embodiments 1 to 8, amount of CH₄ in the syngas composition is from 1 to 10 molar %, 1.5 to 8 molar %, or 1.5 to 6.5 molar %. Embodiment 10 is the process of Embodiment 9, further including the step of providing the CH₄ containing syngas composition to an oxy-synthesis process. Embodiment 11 is the process of any one of Embodiments 1 to 10, wherein the syngas composition further comprises an amount of C0₂ from 40 to 90 molar % or 50 to 80 molar %. Embodiment 12 is the process of any one of Embodiments 1 to 11, wherein the chromium oxide/alumina supported catalyst contains from 5 to 30 wt. % of chromium (Cr), 10 to 20 wt. % of Cr, or 13 to 17 wt.% Cr. Embodiment 13 is the process of Embodiment 12, wherein the catalyst contains from 0.2 wt.% to 30 wt.%, 2 wt.% to 10 wt.%, or 2 wt.% to 5 wt.% of at least one member selected from the group consisting of lithium (Li), potassium (K), cesium (Cs), and strontium (Sr). Embodiment 14 is the process of any one of Embodiments 1 to 13, wherein the C0₂ conversion is at least 10%. Embodiment 15 is the process of any one of Embodiments 1 to 14, wherein the reaction occurs at 550 °C to 600 °C and 0.9 MPa to 3 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 20 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream is 50 to 70 mL/min. Embodiment 16 is the process of Embodiment 15, wherein the syngas composition contains 15 mol.% to 21 mol.% CO, 50 mol.% to 60 mol.% C0₂, 1.5 mol.% to 2.5 mol.% CH₄, and 22 mol.% to 25 mol.% ¾. [0020] Embodiment 17 is the process of any one of Embodiments 1 to 14, wherein the reaction occurs at 640 °C to 660 °C and 2.5 MPa to 3 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 30 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream is 50 to 70 mL/min. Embodiment 18 is the process of Embodiment 17, wherein the syngas composition contains 15 mol.% to 25 mol.% CO, 50 mol.% to 60 mol.% C0₂, 5 mol.% to 10 mol.% CH₄, and 15 mol.% to 20 mol.% H₂.

[0021] Embodiment 19 is the process of any one of Embodiments 1 to 14, wherein the reaction occurs at 640 °C to 660 °C and 2.5 MPa to 3 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 20 to 40 mL/min and the C0₂ gas flow rate in the reactant feed stream is 60 to 80 mL/min, and wherein the syngas composition comprises 5 mol.% to 15 mol.% CO, 70 mol.% to 90 mol.% C0₂, 3 mol.% to 10 mol.% CH₄, and 3 mol.% to 7 mol.% ¾.

[0022] Embodiment 20 is the process of any one of Embodiments 1 to 19, wherein the oxo-synthesis syngas containing composition further includes C0₂ and wherein the process further includes removing the C0₂ from the oxo-synthesis syngas containing composition; and providing the oxo-synthesis syngas containing composition to a hydroformylation of olefins reaction, a carbonylation of methanol reaction, or a carbonylation of olefins reaction.

[0023] 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

[0024] 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. [0025] FIG. 1 is an illustration of a process of the present invention to produce oxo- synthesis syngas that includes methane using a combined C0₂ and H₂ containing reactant feed gas and the chromium oxide/alumina supported catalyst of the present invention.

[0026] FIG. 2 is an illustration of a process of the present invention to produce oxy- synthesis syngas that includes methane using a H₂ reactant feed gas source, a C0₂ reactant feed gas source, and the chromium oxide/alumina supported catalyst of the present invention.

[0027] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0028] A discovery has been made that addresses the aforementioned problems and inefficiencies associated with the production of oxo-synthesis syngas from hydrogenation of carbon dioxide. The discovery is premised on the use of a chromium oxide/alumina supported catalyst in the hydrogenation of carbon dioxide reaction using a H₂:C0₂ molar ratio of 1 or less. The described process results in the production of an oxo-synthesis syngas composition having a H₂:CO molar ratio of 1.2 or less and at least 1 molar % of methane (CH₄) at elevated temperatures and pressures. Furthermore, these results can be achieved at isothermal processing conditions of at least 550 °C (e.g., 550 °C to 700 °C, or 570 °C to 590 °C, or 625 °C to 675 °C), and at least 0.5 MPa, preferably from 0.5 MPa to 3.5 MPa, or more preferably 1 MPa to 3 MPa. The oxo-synthesis syngas composition can have characteristics that make it acceptable for oxo-synthesis reactions, such as hydroformylation.

[0029] 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

[0030] Conditions sufficient to produce oxo-synthesis 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 be at least 550 °C, from 550 °C to 700 °C, from 550 °C to 590 °C and all ranges and temperatures there between (e.g., 555 °C, 560 °C, 565 °C, 570 °C, 575 °C, 580 °C, 585 °C, or 590 °C) or 570 °C to 590 °C, or from 625 °C to 700 °C, from 625 °C to 675 °C and all temperatures and values there between (e.g., 630 °C, 635 °C, 640 °C, 645 °C, 650 °C, 655 °C, 655 °C, 660 °C, 665 °C, or 670 °C). The average pressure for the hydrogenation reaction can range from at least 0.5 MPa, or 0.5 MPa to 3.5 MPa, or 1 MPa to 3 MPa, and all pressures there between (e.g., 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, or 3.5 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.

[0031] 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 70 to 130 mL/min, 80 mL/min to 1 10 mL/min, 90 mL/min to 105 mL/ min or all ranges and values there between (e.g., at least 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, 120 mL/min, 121 mL/min, 122 mL/min, 123 mL/min, 124 mL/min, 125 mL/min, 126 mL/min, 127 mL/min, 128 mL/min, 129 mL/min, or 130 mL/min). In some instances, the H₂ gas flow rate can range from 20 mL/min to 50 mL/min, 30 to 50 mL/min, or any range or value there between (e.g., 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, 30 mL/min, 31 mL/min, 32 mL/min, 33 mL/min, 34 mL/min, 35 mL/min, 36 mL/min, 37 mL/min, 38 mL/min, 39 mL/min, 40 mL/min, 41 mL/min, 42 mL/min, 43 mL/min, 44 mL/min, 45 mL/min, 46 mL/min, 47 mL/min, 48 mL/min, or 49 mL/min). The C0₂ flow rate can range from 50 mL/min to 80 mL/min, 60 to 70 mL/min, or all ranges and values there between (e.g., 50 mL/min, 51 mL/min, 52 mL/min, 53 mL/min, 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, or 79 mL/min). In a particular instance, the H₂ gas flow rate in the reactant feed stream is 30 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream is 50 to 70 mL/min at a reaction temperature of 550 °C to 600 °C and a reaction pressure from 0.9 MPa to 3 MPa. In another instance, the H₂ gas flow rate in the reactant feed stream is 30 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream is 50 to 70 mL/min at a reaction temperature of 640 °C to 660 °C and a reaction pressure of 2.5 MPa to 3 MPa. In yet another instance, the H₂ gas flow rate in the reactant feed stream is 20 to 40 mL/min and the C0₂ gas flow rate in the reactant feed stream is 60 to 80 mL/min at a reaction temperature of 640 °C to 660 °C and a reaction pressure of 2.5 MPa to 3 MPa.

[0032] In another aspect, the reaction can be carried out over the chromium oxide/alumina supported catalyst of the current invention having particular oxo-synthesis syngas selectivity and conversion results. Therefore, in one aspect, the reaction can be performed with a C0₂ conversion of at least 10 mol.%, at least 20 mol.%, at least 30 mol.%, 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 oxo-synthesis syngas along with using the produced oxo-synthesis syngas as a feed source, solvent, or a commercial product in oxo-synthesis reactions. Non-limiting examples of oxo-synthesis reactions include hydroformylation of olefins, carbonylation of methanol, or carbonylation of olefins. 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.

[0033] 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/alumina supported catalyst of the present invention. The produced syngas can be suitable for oxo-synthesis reactions. 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 110 having the chromium oxide/alumina 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/alumina 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 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 be made of materials that are corrosion and/or 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, 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 that includes oxo-synthesis 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, carbon monoxide, and at least 1 molar% of alkanes (e.g., methane). The product stream can also include unreacted carbon dioxide and water. 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., oxo- synthesis 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 C0₂ 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.). C0₂ can be removed or scrubbed from the product stream with any suitable method known in the art (e.g., physical absorption, chemical absorption, adsorption, membrane or supercritical technologies, etc.). A preferred method of removing C0₂ can be adsorption, such as an amine-based chemical adsorbent, an amine- impregnated adsorbent, or an amine-grafted adsorbent.

[0034] Without being limited by theory, any unreacted reactant gas can be recycled and included in the reactant feed to maximize the overall conversion of C0₂ to oxo-synthesis syngas. This increases the efficiency and commercial value of the C0₂ to oxo-synthesis syngas conversion process of the present invention. The resulting oxo-synthesis syngas can be sold, stored, or used in other processing units (e.g., hydroformylation 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 550 °C) to convert C0₂ in the reactant feed to oxo-synthesis 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

[0035] 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.

[0036] 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.%) [0037] The catalyst can also include at least one alkali metal or alkaline earth metal 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. [0038] 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. [0039] 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).

[0040] 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/alumina 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

[0041] 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 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 molar ratio of H₂:C0₂ in the reactant stream can be 1 or less. In some embodiments, the H₂:C0₂ molar ratio can be from 0.1 : 1 to 0.9: 1, from 0.2: 1 to 0.8: 1, or 0.4: 1 to 0.7: 1. The volume ratio of H₂:C0₂ reactant gas for the hydrogenation reaction can range from 0.2: 1 to 0.8: 1, from 0.3 : 1 to 0.7: 1. In one instance the reactant gas stream includes 30 to 50 vol.% H₂ and 50 to 70 vol.% C0₂, or 20 to 30 vol.% H₂, and 60 to 80 vol.% C0₂, preferably, 40 vol.% H₂ and 60 vol.% C0₂ or 30 vol.% H₂ and 70 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 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.

[0042] 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. 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 oxo-synthesis syngas composition is used in the hydroformylation of olefins(e.g., production of C₂+ alcohols, ethers, and the like). By way of example, the molar H₂:CO ratio can be about 0.1 to 1.2, 0.2 to 0.9, preferably 0.4 to 0.7, which is suitable for oxo-synthesis to avoid over-hydrogenation. The amount of H₂ in the syngas composition can be from 1 to 40 molar %, 3 to 30 molar %, or 5 to 25 molar % and the amount of CO in the syngas composition can be from 1 to 40 molar %, 3 to 30 molar %, or 10 to 25 molar %. In some instances, a purge gas from the oxo-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 C0₂ can be removed (e.g., by amine adsorption). The amount of alkane (e.g., methane) produced in the process of the present reaction can be at least 1 molar %, 1 to 10 molar %, 1.5 to 8 molar %, or 1.5 to 6.5 molar % based on the total moles of components in the product stream. In a particular instance, the product stream can include 5 molar % to 25 molar % H₂, 10 to 25 molar % CO, 50 to 80 molar % C0₂ and 1.5 to 6.6 molar % CH₄. In a particular instance, the product stream can include 19.9 or 19.4 molar % CO, about 55 or 56.8 molar % C0₂, about 1.8 or 2.2 molar % CH₄, and about 23.3 or 21.5 molar % H₂. In another embodiment, the product stream can include about 19.6 molar % CO, about 55.6 molar % C0₂, about 2.2 to 2.3 molar % CH₄, and about 22.5 molar % H₂. In some embodiments, the product stream can include about 21.2 or 20.9 molar % CO, about 53.9 or 54.9 molar % C0₂, about 6.0 or 6.1 molar % CH₄, and about 18.1 or 18.9 molar % H₂. In yet another embodiment, the product stream can include about 10.4 molar % CO, about 78.4 molar % C0₂, about 6.1 molar % CH₄, and about 5.1 molar % ¾. EXAMPLES

[0043] 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)

[0044] A commercial chromium/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 used was 20-50 mesh and contains about 13 wt.% of Cr.

[0045] 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 + %C¾ + %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)

[0046] The general procedure of Example 1 was followed with the following conditions: a pressure of 1 MPa, a temperature of 580 °C, a H₂ flow rate of 40 cubic centimeter (cc)/min, and a C0₂ flow rate of 60 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)

[0047] The general procedure of Example 1 was followed using the following conditions: a pressure of 2.8 MPa, a temperature of 580 °C, a H₂ flow rate of 40 cc/min, and a C0₂ flow rate of 60 cc/min. Results are listed in Table 2.

Table 2

Example 4

(Process for Hydrogenation of Carbon Dioxide)

[0048] The general procedure of Example 1 was followed using the following conditions: a pressure of 2.8 MPa, a temperature of 650 °C, a H₂ flow rate of 40 cc/min, and a C0₂ flow rate of 60 cc/min. Results are listed in Table 3.

Table 3

Example 5

(Process for Hydrogenation of Carbon Dioxide)

[0049] The general procedure of Example 1 was followed using the following conditions: a pressure of 2.8 MPa, a temperature of 650 °C, a H₂ flow rate of 30 cc/min, and a C0₂ flow rate of 70 cc/min. Results are listed in Table 4.

Table 4

[0050] As can be seen from the Examples, the hydrogenation of C0₂ at high pressure provides a product gas stream composition that contains H₂, CO, CH₄, and C0₂, with a H₂:CO molar ratio of less than 1.2 and CH₄ in an amount of at least 1 molar %, which is suitable for use in production of oxo-synthesis reactions (e.g., hydroformylation of olefins, carbonylation of methanol, and carbonylation of olefins). In preferred instances, CH₄ can remain in the product gas stream but C0₂ is first removed from the product gas stream for oxo-synthesis reactions.

Claims

1. An isothermal process for hydrogenating carbon dioxide (C0₂) to produce an oxo- synthesis syngas containing composition, the process comprising contacting a chromium oxide/alumina supported catalyst with a reactant feed stream comprising hydrogen (H₂) and C0₂ at a H₂:C0₂ molar ratio of less than 1, wherein the reaction occurs at a constant temperature of at least 550 °C and a pressure of at least 0.5 MPa to produce the oxo-synthesis syngas containing composition comprising H₂ and CO at a H₂:CO molar ratio of less than 1.2 and methane (CH₄) in an amount of at least 1 molar %.

2. The process of claim 1, wherein the H₂:C0₂ molar ratio is from 0.1 to 0.9, 0.2 to 0.8, or 0.4 to 0.7.

3. The process of any one of claims 1 or 2, wherein the reactant feed stream does not contain CH₄.

4. The process of any one of claims 1 or 2, wherein the reaction temperature is from 550 °C to 700 °C, or 570 °C to 590 °C, or 625 °C to 675 °C.

5. The process of any one of claims 1 or 2, wherein the reaction pressure is from 0.5 MPa to 3 MPa, or 1 MPa to 3 MPa.

6. The process of any one of claims 1 or 2, wherein the amount of H₂ in the syngas composition is from 1 to 40 molar %, 3 to 30 molar %, or 5 to 25 molar %.

7. The process of any one of claims 1 or 2, wherein the amount of CO in the syngas composition is from 1 to 40 molar %, 3 to 30 molar %, or 10 to 25 molar %.

8. The process of any one of claims 1 or 2, wherein the H₂:CO molar ratio is from 0.1 to 1.2, 0.2 to 1.2 or 0.4 to 1.2.

9. The process of any one of claims 1 or 2, amount of CH₄ in the syngas composition is from 1 to 10 molar %, 1.5 to 8 molar %, or 1.5 to 6.5 molar %.

10. The process of claim 9, further comprising providing the CH₄ containing syngas composition to an oxy-synthesis process.

11. The process of any one of claims 1 or 2, wherein the syngas composition further comprises an amount of C0₂ from 40 to 90 molar % or 50 to 80 molar %.

12. The process of any one of claims 1 or 2, wherein the chromium oxide/alumina supported catalyst comprises from 5 to 30 wt. % of chromium (Cr), 10 to 20 wt. % of Cr, or 13 to 17 wt.% Cr.

13. The process of claim 12, wherein the catalyst comprises from 0.2 wt.% to 30 wt.%, 2 wt.%) to 10 wt.%), or 2 wt.%) to 5 wt.% of at least one member selected from the group consisting of lithium (Li), potassium (K), cesium (Cs), and strontium (Sr).

14. The process of any one of claims 1 or 2, wherein the C0₂ conversion is at least 10%>.

15. The process of any one of claims 1 or 2, wherein the reaction occurs at 550 °C to 600 °C and 0.9 MPa to 3 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 20 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream is 50 to 70 mL/min.

16. The process of claim 15, wherein the syngas composition comprises 15 mol.%> to 21 mol.% CO, 50 mol.% to 60 mol.% C0₂, 1.5 mol.% to 2.5 mol.% CH₄, and 22 mol.% to 25 mol.% H₂.

17. The process of any one of claims 1 or 2, wherein the reaction occurs at 640 °C to 660 °C and 2.5 MPa to 3 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 30 to 50 mL/min and the C0₂ gas flow rate in the reactant feed stream is 50 to 70 mL/min.

18. The process of claim 17, wherein the syngas composition comprises 15 mol.%> to 25 mol.% CO, 50 mol.% to 60 mol.% C0₂, 5 mol.% to 10 mol.% CH₄, and 15 mol.% to 20 mol.% H₂.

19. The process of any one of claims 1 or 2, wherein the reaction occurs at 640 °C to 660 °C and 2.5 MPa to 3 MPa, and wherein the H₂ gas flow rate in the reactant feed stream is 20 to 40 mL/min and the C0₂ gas flow rate in the reactant feed stream is 60 to 80 mL/min, and wherein the syngas composition comprises 5 mol.%> to 15 mol.%> CO, 70 mol.% to 90 mol.% C0₂, 3 mol.% to 10 mol.% CH₄, and 3 mol.% to 7 mol.% ¾.

20. The process of any one of claims 1 or 2, wherein the oxo-synthesis syngas containing composition further includes C0₂ and wherein the process further comprises:

removing the C0₂ from the oxo-synthesis syngas containing composition; and providing the oxo-synthesis syngas containing composition to a hydroformylation of olefins reaction, a carbonylation of methanol reaction, or a carbonylation of olefins reaction.