WO2018232060A2

WO2018232060A2 - Methanol production from water-splitting process

Info

Publication number: WO2018232060A2
Application number: PCT/US2018/037448
Authority: WO
Inventors: Justin R. Johnson; Sari AL-SAYEGH; Khalid ALMUSAITEER; Abdullah AL-THOBAITY; Abdullah BAUBAID
Original assignee: Sabic Global Technologies B.V.
Priority date: 2017-06-15
Filing date: 2018-06-14
Publication date: 2018-12-20
Also published as: WO2018232060A3

Abstract

Methods, processes, and systems for the production of methanol from a feed source generated from a mixture of H2(g), CO2(g), and oxygen (O2(g)) from a water-splitting process, where the mixture is outside the flammability zone of the mixture.

Description

METHANOL PRODUCTION FROM WATER-SPLITTING PROCESS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of US Provisional Patent Application No. 62/519,935 filed June 15, 2017, which is hereby incorporated by reference in its entirety for all lawful purposes.

BACKGROUND OF THE INVENTION

A. Field of the Invention

[0002] The invention generally concerns processes to produce methanol (CH₃OH) from gaseous hydrogen (¾) and carbon dioxide (C0₂) obtained from a water-splitting process.

B. Description of Related Art

[0003] Methanol is a key product used in the chemical industry. It can be used as a building block for the production of numerous commodity chemicals, for example, methyl tert-butyl ether (MTBE), acetic acid, and formaldehyde. Globally, the feedstock to produce methanol is substantially derived from hydrocarbon resources (e.g., natural gas) through reforming processes. Reforming processes can require substantial energy (heat) and contribute significant C0₂ emissions. To curb emissions and reduce the overall energy footprint, major efforts have been made to develop new reaction processes and catalysts that can effectively use C0₂ as the carbon source. As shown in reaction scheme (1), carbon dioxide can be hydrogenated in the presence of a copper catalyst to produce methanol:

[0004] Methanol can be produced using the CAMERE process (carbon dioxide hydrogenation to form methanol via a reverse-water gas shift reaction or RWGSR). In the CAMERE process, two reactors are consecutively arranged to convert carbon dioxide to CO and H20 in the first reactor by RWGSR (See, reaction scheme (2)). Water and, optionally, carbon dioxide can then be removed to form a stream rich in carbon monoxide. The enriched carbon monoxide stream can then be fed into the second reactor to produce methanol under catalytic conditions (See, reaction scheme (3)):

[0005] In this approach, RWGSR can be carried out at high temperature (> 600 °C) under catalytic conditions to obtain high C02 conversion to CO. Conversion of CO to methanol in a second reactor can lead to high methanol productivity due to the removal of water.

[0006] Hydrogen used in the methanol process can be obtained from hydrocarbon sources, which have become increasingly depleted and expensive. Water-splitting has been investigated as a source of hydrogen. However, there is currently a lack of commercial methods or technologies for purifying hydrogen gas produced via the water-splitting process. The process produces a highly explosive gas mixture, which requires using as yet undefined techniques and/or systems to separate and purify hydrogen from oxygen.

[0007] Various attempts to use hydrogen generated from a water-splitting process as a feed source in a reaction to form methanol have been described. By way of example, International Patent Application No. WO 2008054230 to Fareid et al, and U.S. Patent Application Publication Nos. 20100159352 to Gelin et al. and 20120079767 to Aplin et al. describe producing hydrogen and oxygen from water-splitting and then subsequent use of the hydrogen to produce hydrocarbons {e.g., methane), which than can be converted to methanol. In another example, U.S. Patent Application Publication No. 20100000874 to Hinman et al., describes mixing hydrogen from a water splitter with solar heated C0₂ in a reverse-water- gas-shift reactor to produce methanol. The currently known methods for separating the gas mixture produced by water lack reliability and safety, and are considered unrealistic from an engineering point of view.

[0008] While there have been various attempts to use hydrogen from water-splitting reactions, there remains a need for additional methods, processes, and systems for obtaining a sufficient amount of hydrogen from water-splitting reactions for commercial uses.

SUMMARY OF THE INVENTION

[0009] A discovery has been made that provides solutions to problems associated with the production of methanol from carbon dioxide. In particular, the discovery is premised on using hydrogen and carbon dioxide obtained from a water-splitting process that creates a product stream with oxygen and hydrogen in the same environment. The carbon dioxide is used in the water-splitting process as a flammability suppressor, which allows the oxygen to be separated from the hydrogen gas to generate a gaseous mixture that includes carbon dioxide and hydrogen. The carbon dioxide/hydrogen mixture is then provided to a methanol production unit and contacted with a catalyst to produce methanol.

[0010] In one instance, a process for producing methanol (CH₃OH) from hydrogen (Hi(g)) and carbon dioxide (C0₂(g)) is described. The process can include: (a) obtaining a mixture of C0₂(g), and oxygen (0₂(g)) from a water-splitting process, where the mixture is outside its flammability zone, increasing the safety of the process; (b) separating 0₂(g) from the mixture to obtain a reactant stream comprising H^g) and C0₂(g); and (c) contacting the H^g) and C0₂(g) reactant stream with a catalyst under conditions suitable to produce CH₃OH. The mixture of H₂(g), C0₂(g), and 0₂(g) can include at least 70 mol.% C0₂(g), preferably about 70 to 75 mol.% C0₂(g). The H^g) and C0₂(g) reactant stream can include at least 30 mol.% Eb. All, or substantially all, of the C0₂(g), H₂(g), or both can be obtained from the water-splitting process. In the water-splitting reaction, the C0₂(g) can be used (1) as a sweep gas in the water-splitting reaction to remove produced 0₂(g) and H^g) from a reaction zone of the water-splitting reaction, and (2) as a diluent such that the mixture in step (a) is outside its flammability zone. In step (b), the 0₂(g) can be separated from the H₂(g) and C0₂(g) by passing the H^g), C0₂(g), and 0₂(g) mixture through a membrane, a pressure swing adsorption unit, a temperature swing adsorption unit, a liquid absorption unit, or a combination thereof to obtain the Fb(g) and C0₂(g) reactant stream. The H₂:C0₂ molar ratio of the H^g) and C0₂(g) reactant stream can be adjusted to a predetermined value during or after separating step (b), or both. During step (b), the fbiCC molar ratio of the H₂(g) and C0₂(g) reactant stream can be 1 : 1 to 3 : 1 , or 2 : 1 to 3 : 1 , or about 2.5: 1. In some embodiments, the gaseous H^g), C0₂(g), and 0₂(g) mixture can be compressed to about 0.1 MPa to 10 MPa, or 0.1, 1, 5, 6 or 9 MPa, prior to being separated. In step (c), conditions to produce methanol can include a temperature of at least 200 °C, or 200 °C to 500 °C, preferably 220 °C. The methanol catalyst can include at least one of an alkali metal or oxide thereof (e.g., rubidium (Rb), or strontium (Sr), or oxides thereof), an alkaline earth metal or oxide thereof (e.g., barium (Ba) or oxides thereof), a transition metal or oxide thereof (e.g., yttrium (Y), copper (Cu), nickel (Ni), titanium (Ti), zirconium (Zr), molybdenum (Mo), tungsten (W), silver (Ag), zinc (Zn), or combinations, or oxides thereof), a lanthanide or oxide thereof (e.g. lanthanum (La), cerium (Ce), terbium (Tb), ytterbium (Yb), or combinations, or oxides thereof), a post transition metal or oxide thereof (e.g., aluminum (Al) and/or bismuth (Bi) or oxides thereof). In some embodiments, the catalyst can include Ni/Zn/Zr/Ce/Y, Cu/Ti/Y, Cu/Zn/Zr/Ce/La, Mo/Zn/Zr/Ce/Y, Cu/Bi/Y, Cu/Zn/Zr/Ce/Ba/Al, or mixtures thereof. In some embodiments, the H^g) and C0₂(g) reactant stream can be contacted in step (c) with a catalyst to produce a reverse water gas shift reaction (RWGSR) stream that includes H^g), C0₂(g), carbon monoxide (CO(g)) and water. The RWGSR stream can then be contacted with a methanol catalyst to produce methanol. The methanol can be in a gaseous phase, in a liquid phase or a mixture thereof. In a preferred embodiment, the methanol is in the gaseous phase.. The RWGSR catalyst can include Cu/Zn/Al, Cu/Zn/Al/Ce/Y, Cu/Zn/Ce/Si, Cu/Zn/Al In, or mixtures thereof.

[0011] In other embodiments, systems for producing CH₃OH from a gaseous mixture of ¾ and C0₂ are described. A system can include: a water-splitting unit capable of producing a gaseous mixture of H , C0₂, and 0₂ outside the flammability limit for the mixture; a separation unit capable of receiving the gaseous mixture of H₂, C0₂, and 0₂ and separating gaseous 0₂ from the gaseous mixture to produce a gaseous reactant stream comprising H₂ and C0₂; and a methanol production unit capable of receiving the gaseous reactant stream that includes the H₂ and C0₂ and configured to produce CH₃OH. The water-splitting unit can be a photocatalytic water-splitting unit. The separation unit can include at least one separation unit capable of providing H₂ and C0₂ in a mole ratio of at least 1 : 1 to 4: 1. The methanol can include a reverse water gas shift reactor in combination with a methanol reactor or a direct hydrogenation of carbon dioxide reactor.

[0012] Other embodiments of the invention are discussed throughout this application. Any embodiment discussed with respect to one aspect of the invention applies to other aspects of the invention as well and vice versa. Each embodiment described herein is understood to be embodiments of the invention that are applicable to all aspects of the invention. It is contemplated that any embodiment discussed herein can be implemented with respect to any method or composition of the invention, and vice versa. The following includes definitions of various terms and phrases used throughout this specification.

[0013] The terms "about" or "approximately" are defined as being close to the value, term or phrase that follows, 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%.

[0014] 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 of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0015] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0016] The terms "inhibiting," "reducing," "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. [0017] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0018] The use of the words "a" or "an" when used in conjunction with any of the terms "comprising," "including," "containing," or "having" 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."

[0019] 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.

[0020] The processes 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 processes of the present invention are their abilities to separate hydrogen from oxygen in a gaseous mixture at conditions outside of the mixture's flammability zone and use the isolated hydrogen 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 a schematic of an overview of the process of the present invention to produce methanol using a water-splitting unit, a separation unit and a methanol production unit. [0024] FIG. 2 is a flammability diagram for H₂/0₂/C0₂ mixtures, respectively, at 1 bar and 25 °C. All stream compositions of the current invention are outside the explosion zone, i.e., outside flammability limits of the respective mixtures.

[0025] FIG. 3 is a schematic of an embodiment of the methanol production unit of FIG. 1.

[0026] FIG. 4 is a schematic of an embodiment of a H₂/0₂/C0₂ separation unit of the present invention.

[0027] FIG. 5 is a schematic of an embodiment of the methanol production unit using the Fb/CC feed stream from the separation unit of FIG. 4.

[0028] FIG. 6 is a schematic of embodiments of the methanol production processes using two separation plants.

[0029] FIG. 7 is a schematic of a separation plant of FIG. 6 using two membrane units.

[0030] FIG. 8 is a schematic of a direct C0₂ hydrogenation process using the feed stream produced from FIG. 7 or FIG. 10.

[0031] FIG. 9 is a schematic of a reverse WGSR in combination with a conventional methanol process using the feed stream produced from FIG. 7 or FIG. 10.

[0032] FIG. 10 is a schematic of a separation plant of FIG. 6 using three membrane units.

[0033] 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.

DESCRIPTION

[0034] The present invention relates to processes and systems that provide solutions to the current problems associated with the production of methanol using gaseous mixtures obtained from a water-splitting process that have hydrogen and oxygen in concentrations outside the flammability limit. The discovery provides for reduction of the overall energy demand of the entire process (H₂ generation and CH₃OH generation) by removing or reducing reforming reactions to produce H₂ and/or improved production of methanol through adjustment of the C0₂ to H₂ ratio exiting the water-splitting reactor. These and other non-limiting aspects of the present invention are discussed in further detail with reference to the figures.

[0035] FIG. 1 depicts an overall system and process for producing methanol. The system 100 can include water-splitting reactor 102, separation unit 104, and methanol generation unit 106. Water-splitting unit 102 can be any water-splitting unit or system capable of splitting water into hydrogen and oxygen in the same environment and to produce a product stream that includes H₂, 0₂ and at least one diluent. Non-limiting examples of water-splitting units include at least one of a photocatalytic water-splitting unit, a thermochemical unit, or combinations thereof.

[0036] In the water-splitting process, water feed stream 108 and C0₂ stream 110 can enter water-splitting unit 102. In some embodiments, water feed stream 108 and C0₂ stream 110 can be mixed together and enter water-splitting unit 102 as one stream. In some embodiments, C0₂ stream 110 can be injected into the product stream as it exits the water- splitting unit 102. C0₂ stream 1 10 can include carbon dioxide, water vapor, or nitrogen or any other inert gas, or any mixture thereof. As shown, C0₂ stream 110 is provided in two different sections of the water-splitting reaction. C0₂ can be used as a flammability suppressant, and to allow the oxygen produced from water-splitting unit 102 to be separated from the hydrogen. The product gas produced in water-splitting unit 102 can include 50 to 80 mol .% hydrogen, greater than 0 mol.% (e.g., 1 mol.%) to 40 mol.% oxygen, and 0 to 20 mol.% carbon dioxide before injection of the C0₂. The generation of C0₂ to be injected as the flammability suppressant and separator can be from the use of sacrificial compounds used in the water-splitting process.

[0037] Since hydrogen has a wide flammability zone in comparison with other fuels, it can be combusted over a wide range of gas mixtures. Thus, hydrogen can combust in a mixture in which the gas content is less than the theoretical, stoichiometric or chemically ideal amount needed for combustion. The lower and upper flammability limits (LFL and UFL, respectively) are the limiting mixture concentrations under particular conditions that can support flame propagation and lead to an explosion. Mixture concentrations outside those limits are non-flammable. The progressive addition of a flammability suppressor (e.g., an inert gas) to the mixture creates a path for the mixture to exist outside of the flammability zone. Outside flammability zone is defined as a mixture whose components are at a concentration and condition (e.g., pressure and temperature) that will not support flame propagation. The flammability limit may be expressed as a function of pressure, temperature, and the composition of the mixture (See, for example, FIG. 2, with conditions at 1 bar and 25 °C). In FIG. 2, data point 202 is the upper flammability limit for 94% H₂ in 0₂ (about 6% 0₂). Data point 204 is the lower flammability limit for 4% ¾ in 0₂ (about 96% 0₂). Data point 206 is the extinction effect (about 73% C0₂). As a feed source is processed, its composition, temperature, and pressure can change; these differences in composition and conditions can cause the flammability limits of the H₂/0₂/C0₂ stream during processing to vary at different points along the process. To avoid the risk of fire/explosion, the H₂/0₂/C0₂ stream can be maintained above the upper explosive limit or below the lower explosion limit (both instances are conditions are outside of the flammability zone for the mixture) at all points along the process or system.

[0038] The gaseous mixture produced from the water-splitting reactor can be at, or near, atmospheric pressure, for example, the gaseous mixture can contain about 70 mol.% H₂, 25 mol.% 0₂ and 5 mol.% C0₂. The flammability of this feed source gas can be suppressed by injecting C0₂ stream 110 (flammability suppressor) to an appropriate mole percentage to bring the suppressed feed source gas outside flammability zone. The flammability of the mixtures produced during the process can be modulated by injecting a stream that includes at least 70% mol.% C0₂, at least 75 mol.% C0₂(g), at least 80 mol.% C0₂(g), at least 85 mol.% C0₂(g), at least 90 mol.% C0₂(g), at least 95 mol.% C0₂(g), 99 mol.% C0₂(g), 100 mol.% C0₂(g) or any value or range there between into the H₂/0₂ mixture or stream to create and maintain the mixture at a level outside flammability zone such that combustion of the mixture does not occur.

[0039] In some embodiments, water-splitting unit 102 can be a photocatalytic water- splitting unit. In water-splitting unit 102, water 108 can be contacted with a photocatalyst in the presence of light source to induce splitting of the water into hydrogen (Hb) and oxygen (0₂) in the same environment. In some embodiments, sacrificial agents such as methanol, ethanol, propanol, wo-propanol, «-butanol, so-butanol, ethylene glycol, propylene glycol, glycerol, oxalic acid, malonic acid, succinic acid, maleic acid, tartaric acid, citric acid and their water soluble salts can be used to increase the production of Hi. Ethanol and/or ethylene glycol are used in some instances.

[0040] Any photocatalyst that can generate Hz and 0₂ from water upon irradiation can be used. Photocatalysts are described by Liao et al. {Catalysis, 2012, 2:490), which is incorporated herein by reference. Non-limiting examples of photocatalysts include Pt/Ti0₂ based compounds, Pd/Ti0₂ based compounds, Au/Ti0₂ based compounds, Pd/Zr0₂, Pt/Zr0₂, RmO/ZrC , Cu/ZrCh, cobalt-based compositions, cadmium-based compositions, or combinations thereof.

[0041] Ti0₂ based compounds can be used a photocatalyst as they yield both a high quantum number and a high rate of H_ gas evolution. For example, Pt/Ti0₂ (anatase phase) is a catalyst used in water-splitting. These photocatalysts can combine with a thin NaOH aqueous layer to make a solution that can split water into H₂ and 0₂. Ti0₂ absorbs only ultraviolet light due to its large band gap (greater than 3.0 eV), but outperforms most visible light photocatalysts because it does not photocorrode as easily. Most ceramic materials have large band gaps and thus have stronger covalent bonds than other semiconductors with lower band gaps. Co-catalysts and dopants can be added to Pt loaded TiC . Non-limiting examples of co-catalysts and dopants include Pd, Rh, Au, Ni, Cu, Ag, Fe, Mo, Ru, Os, Re, V, Sr, metals or combinations thereof. Addition of NiO particles as co-catalysts assisted in ¾ production; this step can be done by using an impregnation method with an aqueous solution of Ni(N0₃)^»6H 0 and evaporating the solution in the presence of the photocatalyst. The TiO-based photocatalysts can include dye sensitizers that help absorb light. Non-limiting example of organic dyes include erosin Y, riboflavin, cyanine, cresyl violet, hemicyanine, and merocyanine.

[0042] Cobalt based compositions can include nanocrystalline cobalt (II) oxide, tiis(bipyridine) cobalt(II), compounds of cobalt ligated to certain cyclic polyamines, and certain cobaloximes. Chromophores can be connected to organic rings that complex to a cobalt atom. Processes using cobalt-based compositions can be less efficient than a platinum catalyst, however, cobalt is less expensive, potentially reducing total costs. The process can use one of two supramolecular assemblies based on Co(II)-templated coordination as photosensitizers and electron donors to a cobaloxime macrocycle.

[0043] Referring back to FIG. 1, suppressed gaseous stream 1 12 (e.g., H₂/0₂/C0₂ product stream) can exit water-splitting unit 102 and enter separation unit 104. Suppressed gaseous stream 112 can include 50 to 95 mol.%, 60 to 90 mol.%, 70 to 80 mol.% or 50 mol.%, 55 mol.%, 60 mol.%, 65 mol.%, 70 mol.%, 75 mol.%, 80 mol.%, 85 mol.%, 90 mol.%, 95 mol.%, 99 mol.% or any value or range there between of the C0₂. In one aspect, the suppressed gaseous mixture can have a hydrogen content of approximately 25 mol.% or less, or 5 to 25 mol.%, or 5 mol.%, 10 mol °/o, 15 mol.%, 20 mol.% or 25 mol.% or any value or range there between of hydrogen. It should be understood that suppressed gaseous stream 112 can pass through multiple heat exchangers, compressors, or other equipment to change the pressure and/or temperature of the stream to conditions suitable for separation in separation unit 104. Separation unit 104 can be any separation unit capable of separating 0₂ from C0₂ and H₂. Non-limiting examples of separation units include at least one membrane unit, pressure swing adsorption unit, temperature swing adsorption unit, liquid absorption units, or a combination thereof to obtain the H^g) and C0₂(g) reactant stream. In some embodiments, H₂(g), C0₂(g), and 0₂(g) stream 112 is compressed to about 0.1 MPa to 10 MPa, or 0.1, 1, 5, 6 or 9 MPa, prior to being separated. In separation unit 104, gaseous oxygen-containing stream 114 and Fb/CC reactant stream 116 can be produced. The separation process can produce a H₂/C0₂ reactant stream having a FbiCC molar ratio of 1 : 1 to 3:1, or 2: 1 to 3: 1 , or 1 : 1, 1.5: 1, 2: 1, 2.5: 1, 3: 1, or about 2.5:1. The H₂:C0₂ molar ratio of the H2(g) and C0₂(g) reactant stream can be adjusted to a predetermined value during or after separation. In some embodiments, the hydrogen can be separated from the carbon dioxide and then the components remixed at appropriate ratios of methanol synthesis. In other embodiments, additional C0₂ or H2 can be added to the reactant stream to obtain the desired H2:C0₂ ratio. As illustrated in a non-limiting manner in Examples 1-5, separation unit 104 can include one (FIG. 4) or more separation plants (FIG. 6). Each separation plant can include one or more separation units (e.g., 1 to 3 membrane units). In some embodiments, the suppressed gaseous stream 112 can be split and sent to two separation units in separation unit 104. In some embodiments, one separation plant is used.

[0044] In some embodiments, H₂/C0₂ selective membranes are used. Hydrogen/carbon dioxide selective membranes can be manufactured or be obtained from commercial sources. Non-limiting examples of commercial membrane sources are Air Products (U.S.A.), Membrane Technology Research, Inc. (U.S.A.), or the like.

[0045] Non-limiting examples of materials that compose the hydrogen separation membrane include polymeric and carbon membranes. Polymeric membranes typically achieve hydrogen selective molecular separation via control of polymer free volume. Polymeric membranes may be comprised, for example, of glassy polymers, epoxies, polysulfones, polyimides, and other materials, and may include crosslinks and matrix fillers of non-permeable (e.g., dense clay) and permeable (e.g., zeolites) varieties to modify polymer properties. Carbon membranes are generally microporous and substantially graphitic layers of carbon prepared by pyrolysis of polymer membranes or hydrocarbon layers. Carbon membranes may include carbonaceous or inorganic fillers, and are generally applicable at both low and high temperature. The hydrogen separation membrane may be a dense membrane composed only of the above-mentioned materials, or may be a dense thin membrane composed of the above-mentioned materials supported on a porous body. In the case of the former, the thickness of the hydrogen separation membrane is preferably 0.1 um or more and more preferably 0.5 um to 5 um from the viewpoints of mechanical strength and hydrogen permeability. In the case of the latter, the thickness of the thin membrane is 0.1 to 25 μιη or more and more preferably 0.1 um to 2 um from the viewpoint of processability.

[0046] In cases where the hydrogen separation membrane includes the dense thin membrane composed of the above-described materials and the porous body supporting the membrane thereon, the replacement of gaseous species tends to be inhibited on the side of the porous body. Thus, it is preferable for a dense thin membrane to be the side contacted with a mixed gas, and a porous body to be the side contacted with permeated hydrogen. [0047] Non-limiting examples of materials that C0₂ selective membranes can include at least one of poly(ethylene oxide) containing polymer membranes, silicon-containing polymers, and amine functionalized polymers. A commercial C0₂ selective membrane is a Polaris™ membrane (Membrane Technology and Research, Inc (MTR), U.S. A).

[0048] H₂/C0₂ reactant stream 1 16 can exit separation unit 104 and enter methanol production unit 106. In methanol production unit 106, Hz, C0₂, and optional CO can be contacted with a catalyst or a plurality of catalysts to produce product stream 118 that includes methanol. The methanol selectivity can be at least 50%, at least 60%, at least 70%, at least 80% or 100%. Product stream 118 can exit methanol production unit 106 and be collected and/or transported.

[0049] Referring to FIG. 3, methanol production unit 106 can include a direct hydrogenation of C0₂ reactor 302 and/or a RWGS reactor 304 in combination with a conventional methanol synthesis rector 306, or a combination thereof. The combination is shown in FIG. 3, however it should be understood that the direct hydrogenation of C0₂ reactor can be used separately.

[0050] In direct hydrogenation of C0₂ reactor 302, H2/CO2 reactant stream 116 can contact a direct hydrogenation of carbon dioxide catalyst under conditions sufficient to produce product stream 118 that includes methanol. Conditions sufficient for the hydrogenation of C0₂ or mixtures of CO and C0₂ to methanol include approximate temperature, time, space velocity, and pressure ranges. The temperature range for the hydrogenation reaction can range from about 200 °C to 300 °C, from about 210 °C to 280 °C, preferably from about 220 °C to about 260 °C and or 200 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C, 250 °C, 255 °C, 260 °C, 265 °C, 270 °C, 275 °C, 280 °C, 285 °C, 290 °C, 295, or 300 °C, or any range or value there between. The gas hourly space velocity (GHSV) for the hydrogenation reaction can range from about 2,500 h^'1 to about 20,000 h^'1, from about 3,000 h^_1 to about 15,000 h^_1, and preferably from about 4,000 h^_1 to about 10,000 h^_1. The average pressure for the hydrogenation reaction can range from about 0.1 MPa to about 10.0 MPa, preferably about 5.0 MPa to about 9.0 MPa , 5.5 MPa to 8.5 MPa, 6 MPa to 7 MPa and all values and ranges there between. The upper limit on pressure can be determined by the reactor used. In some embodiments, CO can be added to the H₂/C0₂ reactant stream 116. The conditions for the hydrogenation of C0₂ or mixtures of CO and C0₂ to methanol can be varied based on the type of the reactor.

[0051] The catalytic materials of the present invention have physical properties that can contribute to the catalytic properties and stability of the catalyst in the direct hydrogenation of carbon dioxide and/or mixtures of carbon dioxide and carbon monoxide to methanol. Without wishing to be bound by theory, it is believed that the properties of the catalysts of the present invention allow adsorption of the carbon dioxide, carbon monoxide, and hydrogen on the catalytic surface, thereby improving the proximity of hydrogen to carbon dioxide/carbon monoxide and reducing the production of by-products during direct hydrogenation of carbon dioxide to methanol reaction. In one aspect, the reaction can be performed where a single pass methanol selectivity is 40 to 100%, preferably 50 to 90%, or more preferably from 60 to 80%, or 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% after 300 hours or more time on stream (TOS).

[0052] The catalysts can include metal oxides that promote storing and releasing of oxygen (e.g., Zn, Zr, Ce, or combinations thereof). The metal oxides can be combined with other catalytic metals. Non-limiting examples of other catalytic metals include alkali metals, alkaline earth metals, transitions metals, lanthanides, or post-transition metals. Alkali metals can be metals from Column 1 of the Periodic Table. Non-limiting examples of alkali metals include rubidium (Rb) or cesium (Cs), or both. Alkaline earth metals can be metals from Column 2 of the Periodic Table. Non-limiting examples of alkaline earth metals include barium (Ba), strontium (Sr), or both. Transition metals can include metals from Columns 3- 12 of the Periodic Table. Non-limiting examples of transition metals include yttrium (Y), copper (Cu), nickel (Ni), titanium (Ti), zirconium (Zr), molybdenum (Mo), tungsten (W), silver (Ag), zinc (Zn), or combinations thereof. Lanthanides can include elements 57-71 of the Periodic Table. Non-limiting examples of lanthanides include lanthanum (La), cerium (Ce), terbium (Tb), ytterbium (Yb) or combinations thereof. Post-transition elements can include aluminum (Al). In some embodiments, the catalyst can be Ni/Zn/Zr/Ce/Y, Cu/Ti/Y, Cu/Zn/Zr/Ce/La, Mo/Zn/Zr/Ce/Y, Cu/Bi/Y, Cu/Zn/Zr/Ce/Ba/Al, or mixtures thereof. In other embodiments, the catalyst includes Cu, Zn, Al or oxides thereof.

[0053] The catalysts can be prepared using known preparation techniques such as gel oxalate co-precipitation methods. The metals or post-transition metals used to prepare the catalyst of the present invention can be provided in varying oxidation states as metallic, oxide, hydrate, or salt forms. The catalyst precursors used in the preparation of the catalyst can be provided in stable oxidation states as complexes with monodentate, bidentate, tri dentate, or tetradentate coordinating ligands such as for example iodide, bromide, sulfide, thiocyanate, chloride, nitrate, azide, acetate, fluoride, hydroxide, oxalate, water, isothiocyanate, acetonitrile, pyridine, ammonia, ethyl enediamine, 2,2' -bipyri dine, 1,10-phenanthroline, nitrite, triphenylphosphine, cyanide, or carbon monoxide. In some embodiments, the mixed precursors used to prepare the catalysts of the current invention can be provided as acetates, nitrates, nitrate hydrates, nitrate trihydrates, nitrate pentahydrate, nitrate hexahydrates, and nitrate nonahydrate. Various commercial sources can be used to obtain the metals and metal precursors. A non-limiting example of a commercial source of the above mentioned metal precursors is Sigma Aldrich® (U.S.A.). Prior to use, the catalyst can be subjected to reducing conditions to convert the copper oxide and the other metals in the catalyst to a lower valance state (e.g., Cvf ² to Cu^÷1 and Cu° species). A non-limiting example of reducing conditions includes flowing a gaseous stream that includes hydrogen gas (e.g., a H₂ and Argon gas stream) at a temperature of 250 to 280 °C for a period of time (e.g., 1, 2, or 3 hours).

[0054] In some embodiments, Hz/CCh reactant stream 116 can exit separation unit 104 and enter RWGS reactor 304. In RWGS reactor 304, H₂/C0₂ reactant stream 116 can contact a RWGS catalyst under conditions sufficient to convert a portion of the C0₂ in the stream to CO and produce RWGS product stream 308 that includes tb, C0₂, and CO. Conditions sufficient to produce RWGS product stream 308 include approximate temperature, pressure, and space velocity ranges. Temperatures can be 300 to 400 °C, or 325 to 375 °C, or 300 °C, 325 °C, 350 °C, 375 °C, 400 °C, or any range or value there between. Pressure can range from 0.01 to 0.1 MPa, or about 0.02 MPa. The mole ratio of the to C0₂ can be adjusted in and/or after separation unit 104 to be 1 :2 to 1 :5, or about 1 :4. The RWGS catalyst can be any conventional RWGS catalyst, for example a copper containing catalyst supported on Al, CuNi/C, CuNi/Al₂0₃, Ni-Mo/Al₂0₃ catalyst, a Zn/Al₂0₃ catalyst and the like. A non-limiting example of a commercial RWGS supplier is Clariant® (U.S.A.).

[0055] RWGS product stream 308 can exit RWGS reactor 304 and enter methanol reactor 306. In methanol reactor 306, RWGS product stream 308 can contact a methanol catalyst to produce product stream 118 that includes methanol. Conditions to produce methanol can include a temperature of at least 200 °C, or 200 °C to 500 °C, or 200 °C, 250 °C, 300 °C, 400 °C, 450 °C, 500 °C or any range or value there between. In some embodiments, the temperature is about 220 °C. The methanol catalyst can be a commercial catalyst. Non- limiting examples of methanol catalysis include Cu/Zn/Al, Cu/Zn/Al/Ce/Y, Cu/Zn/Ce/Si, Cu/Zn/Al/In, or mixtures thereof. A non-limiting example of a commercial RWGS supplier is Johnson Matthey® (U.S.A.) sold under the tradename KATALCO®.

[0056] Various inter-stage units are not described, however, it should be understood that the various gas processing units can be included such as, but not limited to, compressors, vacuum pumps, blowers, heat exchangers, condensers, filters, dryers, distillation columns, flash drums, coolers, control valves, mixers, separators, or combinations thereof.

EXAMPLES

[0057] 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

(Methanol Production from a Water-Splitting Process)

[0058] Methanol production from a water-splitting process was simulated using ASPEN PLUS software, including custom membrane models developed using Aspen Custom Modeler. FIG. 4 and FIG. 5 are schematics depicting the separation unit and methanol production unit of the example. Separation unit included first membrane separator 402, second membrane unit 404, and oxygen separation unit 406. In the simulation, suppressed H^g), C0₂(g), and 0₂(g) stream 112 was passed through at least one heat exchanger and at least one compressor to bring the temperature and pressure of suppressed gaseous stream 112 to 150 °C and 1.23 MPa respectively. Suppressed gaseous stream 112 include 16.0 mol.% ¾, 8.0 mol.% 0₂, and 76.0 mol.% C0₂. This combination can occur in many different ways (e.g., using a mixer to combine the streams or feeding both into the first membrane separator 402). In this example, the streams were combined in a mixer before being sent to the first membrane separator 402, which was a H₂ selective membrane. In first membrane separator 402, retentate stream 412, enriched in C0₂ and 0₂, and permeate stream 414, enriched in H₂, were generated. Retentate stream 412 included 1.5 mol.% Ffc, 9.9 mol.% 0₂, and 88.6 mol.% C0₂. Permeate stream 414 included 39.7 mol.% Hi, 1.8 mol.% 0₂, and 58.5 mol.% C0₂. Permeate stream 414 exited first membrane separator 402 and was passed through at least one heat exchanger and at least one compressor to bring the temperature and pressure of permeate stream 414 to 150 °C and 1.30 MPa, respectively before the permeate stream entered the second membrane separator 404. In membrane separator 404, recycled retentate stream 416 and the permeate stream 418 were produced. Permeate stream 418 included 75.0 mol.% ¾, 0.3 mol.% 0₂, and 24.7 mol.% C0₂. Recycle stream 416 was combined sent to second membrane separator 402. Permeate stream 418 entered 0₂ separator 406. In this simulation, 0₂ separator 418 was a catalytic converter, which produced water from the residual 0₂, stoichiometric amounts of ¾, and yielded methanol feed stream 116. Methanol feed stream 116 included 74.7 mol.% Hi, 24.8 mol.% C0₂, and 0.5 mol.% H2O. Conditions of each stream are listed in Table 1.

Table 1

[0059] Referring to FIG. 5, methanol feed stream 1 16 was passed through at least one heat exchanger and at least one compressor, and combined with recycle stream 520 to bring the temperature and pressure of the entering feed to reactor 502 to 210 °C and 7.50 MPa respectively. Feed stream 1 16 included 74.7 mol.% Hi, 24.8 mol.% C0₂, and 0.5 mol.% H₂0, but upon combination with recycle stream 520, the composition of the stream fed into reactor 502 became 82.8 mol.% Hi, 13.5 mol.% CC 0.1 mol.% H2O, 3.4 mol.% CO, and the remaining 0.3 mol.% CH₃OH. This combination can occur many different ways. In a non- limiting example, a mixer was used to combine the streams for feeding both into the reactor 502. In this example, the streams were combined into a mixer and passed through another heat exchanger to bring the stream temperature to 210 °C before entering reactor 502.

[0060] Methanol was produced in the reactor 502, and exiting crude methanol stream 518 was sent to a cooler, reducing the temperature to 35 °C. Crude methanol stream 518 included 77.0 mol.% Hi, 10.3 mol.% C0₂, 4.5 mol.% HiO, 3.7 mol.% CO, and 4.6 mol.% CH3OH. After exiting the cooler, crude methanol stream 518 was sent to separation unit 504 to begin the separation of methanol from the mixture, which in this example was a flash drum. Flash drum 504 produced flashed stream 522, which was sent to unit 506, and overhead stream 520, which can be split as pictured in FIG. 5. In this example, a portion of the overhead stream 520 leaving 106 was sent to a flare, which was consistent with engineering safety practices. The flare stream 520 had a total flow rate of 6.00 kmol/hr, or 46.83 kg/hr, and the recycle stream 520 had a total flow rate of 594.22 kmol/hr, or 4,667.41 kg/hr. The composition of these streams was 84.4 mol.% ¾, 11.1 mol.% C0₂, 0.1 mol.% KtO, 3.7 mol.% CO, and the remaining 0.3 mol.% CH₃OH.

[0061] Flashed stream 522 was sent to secondary separation unit 506, which in this example was another flash drum. Before entering the flash drum, stream 522 was sent through a control valve to decrease the pressure to 0.120 MPa. The composition of stream 522 was 2.0 mol.% H₂, 3.0 mol.% C0₂, 48.1 mol °/o Ή2Ο, 0.1 mol.% CO, and the remaining 46.8 mol.% CH3OH. Flash drum 506 yielded stream 524, which included 36.5 mol.% H₂, 50.3 mol.% C0₂, 1.9 mol.% Ή2Ο, 2.3 mol.% CO, and the remaining 9.1 mol.% CH₃OH, and stream 526, which was sent to a heater before undergoing more separation in unit 508. Stream 526 included 0.3 mol.% C0₂, 50.7 mol.% Ή2Ο, and 48.9 mol.% CH3OH. The temperature of stream 526 after the heat exchanger was 80 °C.

[0062] Separation unit 508 was a distillation column in this example, which yielded stream 528 and water stream 530, which included 100.0 mol.% Ή2Ο. Stream 528, comprised of 0.7 mol.% C0₂, 99.3 mol.% CH3OH, and trace amounts of CO and H2, was sent through a compressor and cooler before entering the final separation unit 510, in this example as another flash drum. The temperature and pressure of stream 528 before entering final separation unit 510 was 50 °C and 0.12 MPa respectively. The streams exiting final separation unit 510 were stream 532 and methanol product stream 118. Stream 532 was composed of 2.7 mol.% ¾ 41.4 mol.% C0₂, 0.2 mol.% CO, and the remaining 55.7 mol.% CH3OH. Stream 1 18 was composed of 0.3 mol.% C0₂ and the remaining 99.7 mol.% CH3OH. Conditions of each stream are listed below in Table 2, with "TRACE" representing trace amounts of the compound.

Examples 2-5

(Methanol Production from a Water-Splitting Process)

[0063] Methanol production from a water-splitting process was simulated using ASPEN PLUS software, including custom membrane models developed using Aspen Custom Modeler. FIG. 6 is an overall schematic for Examples 2-5. In Examples 2-5, suppressed gaseous stream 112 included 16.0 mol.% Fb, 8.0 mol.% 0₂, and 76.0 mol.% C0₂ and was sent to separation unit 104 that included two separation plants, Separation Plant 1 and Separation Plant 2. The suppressed gaseous stream was split and sent to both separation units. However, it should be understood that one separation plant can be used. Referring to FIG. 7 for Examples 1 and 2, separation plant 1 included 2 membrane units (membrane 1 and 2 (Ml and M2). Ml had an Area of 6200 m² and M2 had an area of 1300 m². Table 3 lists the conditions of each stream for the separation process The stream generated from separation plant 1 was sent to a direct C0₂ hydrogenation plant (Example 2, FIG. 8, Route 1) and/or to a reverse WGSR plant and then to a conventional methanol process (Example 3, FIG. 9, Route 2), or both. Route 1 includes the following equipment: reactor: catalyst = 700 kg (Example 2), 720 kg (Example 4), reactor dimension = 4.30m * 0.44m; distillation column: reflux ratio = 1.1, No. of stages was 29. Table 4 list the conditions and mole fraction (%) of each stream for Route 1. Table 5 li st the conditions and mole fraction (%) of each stream for these plants for Route 2.

[0064] Referring to FIGS. 6 and 10, separation plant 2 can include 3 membrane units, M3, M4 and M5. M3 had an Area of 5800 m², M4 had an area of 700 m² and M5 had an area of 2000 m². Table 6 lists the conditions of each stream for the separation process. The stream generated from separation plant 2 as sent to a direct C0₂ hydrogenation plant (Example 4) and/or to a reverse WGSR plant and then to a conventional methanol process (Example 5). Tables 4-5 list the conditions of each stream for these processes for Examples 4 and 5, which were the same as for Examples 2 and 3.

Claims

1. A process for producing methanol (CH₃OH) from hydrogen (H^g)) and carbon dioxide (C0₂(g)), the process comprising:

(a) obtaining a mixture of H₂(g), C0₂(g), and oxygen (0₂(g)) from a water-splitting process, wherein the mixture is outside the flammability zone of the mixture;

(b) separating 0₂(g) from the mixture to obtain a reactant stream comprising H₂(g) and C0₂(g); and

(c) contacting the H₂(g) and C0₂(g) reactant stream with a catalyst under conditions suitable to produce CH3OH.

2. The process of claim 1, wherein the mixture of H^g), C0₂(g), and 0₂(g) comprises at least 70 mol.% C0₂(g), preferably about 70 to 75 mol.% C0₂(g).

3. The process of any one of claims 1 to 2, wherein the H^g) and C0₂(g) reactant stream comprising at least 30 mol.% H₂.

4. The process of any one of claims 1 to 3, wherein the catalyst comprises at least one of an alkali metal or oxide thereof, an alkaline earth metal or oxide thereof, a transition metal or oxide thereof, a lanthanide or oxide thereof, a post transition metal or oxide thereof, or combinations thereof.

5. The process of claim 4, wherein:

the alkali metal or alkaline earth metal is rubidium (Rb), strontium (Sr), or barium (Ba), or combinations thereof;

the transition metal is yttrium (Y), copper (Cu), nickel (Ni), titanium (Ti), zirconium (Zr), molybdenum (Mo), tungsten (W), silver (Ag), zinc (Zn), or combinations thereof; the lanthanide is lanthanum (La), cerium (Ce), terbium (Tb), ytterbium (Yb), or combinations thereof;

the post transition metal is aluminum (Al), bismuth (Bi), or combinations thereof.

6. The process of any one of claims 4 to 5, wherein the catalyst is Ni/Zn/Zr/Ce/Y, Cu/Ti/Y, Cu/Zn/Zr/Ce/La, Mo/Zn/Zr/Ce/Y, Cu/Bi/Y, Cu/Zn/Zr/Ce/Ba/Al, or mixtures thereof.

7. The process of claim 1, wherein the catalyst comprises Cu, Zn, and Al or oxides thereof.

8. The process of any one of claims 1 to 7, wherein separating step (b) comprises passing the mixture through a membrane unit, a pressure swing adsorption unit, a temperature swing adsorption unit, a liquid absorption units, or a combination thereof to obtain the ¾(g) and C0₂(g) reactant stream.

9. The process of any one of claims 1 to 8, further comprising adjusting the H^CCte molar ratio of the H.(g) and C0₂(g) reactant stream to a predetermined value during or after separating step (b), or both.

10. The process claim 9, wherein the HziCCh molar of the H^g) and C0₂(g) reactant stream is 1 : 1 to 3: 1, or 2: 1 to 3: 1, or about 2.5: 1 during step (b).

11. The process of claim 10, wherein the H₂(g) and C0₂(g) reactant stream is contacted with a catalyst to produce a reverse water gas shift reaction (RWGSR) stream comprising H^g), C0₂(g), carbon monoxide (CO(g)) and water, and wherein the RWGSR stream is contacted with a methanol catalyst to produce methanol.

12. The process of claim 1 1 , wherein the methanol catalyst is Cu/Zn/Al, Cu/Zn/Al/Ce/Y, Cu/Zn/Ce/Si, Cu/Zn/Al/In, or mixtures thereof.

13. The process of any one of claims 1 to 9, wherein the H^g) and C0₂(g) reactant stream in step (b) has a E :C0₂ molar of at least 3:1, preferably 4: 1.

14. The process of claim 13, further comprising providing carbon monoxide to the H^g) and C0₂(g) reactant stream .

15. The process of any one of claims 1 to 14, wherein all, or substantially all, of the C0₂(g), H^g), or both is/are obtained from the water-splitting reaction, and wherein the C0₂(g) is used (1) as a sweep gas in the water-splitting reaction to remove produced 0₂(g) and H_(g) from a reaction zone of the water-splitting reaction and (2) as a diluent such that the mixture in step (a) is outside the flammability limit of the mixture.

16. The process of any one of claims 1 to 15 wherein H₂(g), C0₂(g), and 0₂(g) mixture is compressed to about 0.1 MPa to 10 MPa, or 0.1, 1, 5, 6 or 9 MPa, prior to being separated, and/or wherein the conditions to produce methanol comprise a temperature of at least 200 °C, or 200 °C to 500 °C, preferably 220 °C.

17. A system for producing methanol (CH₃OH) from a gaseous mixture of hydrogen (H₂) and carbon dioxide (C0₂), the system comprising:

(a) a water-splitting unit capable of producing a gaseous mixture of H^g), C0₂(g), and oxygen (0₂)(g) outside the flammability limit for the mixture;

(b) a separation unit capable of receiving the gaseous mixture of H^g), CC (g), and 0₂(g) and separating gaseous 0₂(g) from the gaseous mixture to produce a gaseous reactant stream comprising H^g) and C0₂(g); and

(c) a methanol unit capable of receiving the gaseous reactant stream comprising the H^g) and C0₂(g) and configured to produce CH3OH.

18. The system of claim 17, wherein the water-splitting unit is a photocatalytic water- splitting unit, a thermochemical unit, or combinations thereof.

19. The system of any one of claims 17 to 18, wherein the separation unit comprises at least one separation unit capable of providing H^g) and C0₂(g) in a H2:C0₂ mole ratio of at least 1 : 1 to 4: 1.

20. The system of any one of claims 17 to 18, wherein the methanol production unit is a reverse water gas shift reactor in combination with a methanol reactor or a direct hydrogenation of carbon dioxide reactor.