Carbon dioxide conversion method

Abstract

A method for producing synthesis gas comprises: (i) reacting at least a portion of carbon dioxide with hydrogen in a first reactor to produce a first product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; and (ii) reacting at least a portion of unreacted carbon dioxide with unreacted hydrogen in a downstream reactor of the first reactor to produce a product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen.

Description

Technology Field

[0001] Embodiments of the present invention provide a method for converting carbon dioxide, including carbon dioxide directly captured from the atmosphere, into a synthesis gas that can be useful for the production of organic molecules at an industrially useful level. Background Technology

[0002] Synthesis gas, also known as syngas, contains a mixture of hydrogen and carbon monoxide, optionally with additional residual components such as carbon dioxide, nitrogen, methane, and water. Synthesis gas has various uses, including as a reaction feed for producing organic compounds such as hydrocarbons and alcohols.

[0003] Several methods have been used to synthesize synthesis gas, including generating synthesis gas from carbon dioxide. These methods involve converting carbon dioxide into carbon monoxide via a Reverse Water-Gas Shift (RWGS) reaction. The RWGS reaction is reversible and involves reacting carbon dioxide (CO2) with hydrogen (H2) in the presence of a catalyst to produce carbon monoxide (CO) and water (H2O). Subsequently, the generated carbon monoxide can be combined with additional hydrogen to produce synthesis gas, the hydrogen can be removed, or the RWGS reaction can be carried out with an excess of H2 to remove water from the product stream and directly produce synthesis gas.

[0004] The above RWGS reaction is essentially a reversible reaction that can operate in equilibrium. The degree of CO2 conversion depends on several factors, including the feed gas composition, the catalyst used, the pressure, and the temperature at which the RWGS reaction takes place. Higher reaction temperatures generally lead to higher CO2 conversion. For example, at about 540°C, approximately 55% conversion can be achieved, whereas at about 950°C, approximately 80% conversion can be achieved.

[0005] Efforts to improve the efficiency of RWGS reactions have been technically important for extraterrestrial applications such as space travel. Given the limited resources in most extraterrestrial applications, the conservation of reactants and energy is critical to the utility of those applications. For example, the literature [ Whitlow et al. [OPERATION, MODELING AND ANALYSIS OF THE REVERSE WATER GAS SHIFT PROCESS, AIP Conference Proceedings 654, 1116(2003)] proposes reaction technologies that generate oxygen and hydrogen by extracting water from the product stream and transferring it to the electrolysis stage as a reactant. Then, unreacted carbon dioxide and hydrogen are reused in the RWGS reactor to ensure almost complete conversion of the carbon dioxide reaction feed stream.

[0006] Environmental concerns regarding atmospheric carbon dioxide levels have sparked a desire to consume carbon dioxide and thereby potentially reduce atmospheric carbon dioxide levels. For example, U.S. Patent Publication No. 2007 / 0244208 proposes converting carbon dioxide into liquid fuel. According to this method, hydrogen can be generated from water by electrolysis, and carbon dioxide can be captured in industrial processes. Carbon dioxide and hydrogen react in an RWGS reaction to produce carbon monoxide or other hydrocarbon precursors. It is suggested that the RWGS reaction can be run in reuse mode with 100% equilibrium conversion, or that the reaction can be driven by water removal. Additionally, it is suggested that heat from other process steps can be used to drive the RWGS reaction throughout the entire process. While reuse or water removal is proposed, optionally, in conjunction with heat integration, preferred embodiments use condensation to remove carbon dioxide from the product stream and return it to the RWGS reaction.

[0007] Regardless of whether the operation is performed on land or in an external environment, reusing products from the product stream back into the RWGS reactor introduces several complexities and drawbacks. For example, reuse systems require compressors, which hinder efficient use within industrial-scale operations by introducing rotating equipment that may be unreliable and require maintenance. Compressors also require electricity, which can lead to undesirable inefficiencies associated with power generation and potential CO2 or other emissions. Furthermore, processes proposed in the prior art focus on the conservation of raw materials or the formation of fuel rather than the consumption of carbon dioxide. Net CO2 removal is now more desirable than ever and presents significant technical challenges that the prior art has not addressed. The problem to be solved

[0008] Since large-scale consumption of carbon dioxide is still desirable, the continuous development of efficient industrial-scale processes is necessary to achieve carbon dioxide consumption at a level that can influence atmospheric carbon dioxide levels. means of solving the problem

[0009] One or more embodiments of the present invention provide a method for producing synthesis gas comprising: (i) reacting at least a portion of carbon dioxide with hydrogen in a first reactor to produce a first product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; and (ii) reacting at least a portion of unreacted carbon dioxide with unreacted hydrogen in a reactor downstream of the first reactor to produce a product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen.

[0010] Another embodiment of the present invention comprises: (i) providing a reactant stream containing carbon dioxide; (ii) providing a reactant stream containing hydrogen; (iii) combining the reactant stream containing carbon dioxide with the reactant stream containing hydrogen to form a mixed reactant stream; (iv) heating the mixed reactant stream to form a heated and mixed reactant stream; (v) introducing the heated and mixed reactant stream into an adiabatic reactor containing a reverse water-gas shift catalyst; (vi) reacting the hydrogen and carbon dioxide within the adiabatic reactor to form a first product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (vii) removing the first product stream from the adiabatic reactor, wherein the first product stream has a temperature T1 when discharged from the adiabatic reactor; (viii) removing at least a portion of the water in the first product stream from the first product stream to form a water-deficient first product stream; (ix) introducing the first product stream into a fired-tubular reactor containing a reverse gas conversion catalyst, wherein the fired-tubular reactor produces an exhaust stream containing carbon dioxide and excess heat; (x) heating the product stream in the fired-tubular reactor to a temperature T3 to react the carbon dioxide and hydrogen in the first product stream to form a final product stream, wherein T3 is equal to or greater than T1; (xi) sending at least a portion of the excess heat to the step of heating the mixed reactant stream to form a heated and mixed reactant stream; and (xii) sending at least a portion of the generated carbon dioxide to the adiabatic reactor or the fired-tubular reactor, thereby providing a method for producing synthesis gas.

[0011] Another embodiment of the present invention comprises: (i) providing a reactant stream containing carbon dioxide; (ii) providing a reactant stream containing hydrogen; (iii) combining the reactant stream containing carbon dioxide with the reactant stream containing hydrogen to form a mixed reactant stream; (iv) heating the mixed reactant stream to form a heated and mixed reactant stream; (v) introducing the heated and mixed reactant stream into a first adiabatic reactor containing a reverse water-gas shift catalyst; (vi) allowing the hydrogen and carbon dioxide in the first adiabatic reactor to react to form a first product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (vii) removing the first product stream from the first adiabatic reactor, wherein the first product stream has a temperature T1 when discharged from the first adiabatic reactor; (viii) removing at least a portion of the water in the first product stream from the first product stream to form a water-deficient first product stream; (ix) heating the water-deficient first product stream to form a heated water-deficient first product stream; (x) introducing the heated water-deficient initial product stream into a downstream adiabatic reactor containing a reverse water-gas shift catalyst; (xi) allowing the hydrogen and carbon dioxide to react within the downstream adiabatic reactor to form an intermediate product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (xii) removing the intermediate product stream from the downstream adiabatic reactor, wherein the intermediate product stream has a temperature T2 when discharged from the downstream adiabatic reactor; (xiii) removing at least a portion of the water in the intermediate product stream to form a water-deficient intermediate product stream;(xiv) optionally, heating the water-deficient intermediate product stream to form a water-deficient intermediate product stream heated at temperature T02; (xv) optionally, introducing the heated water-deficient intermediate product stream into a downstream adiabatic reactor containing a reverse water-gas shift catalyst and causing carbon dioxide and hydrogen in the heated water-deficient intermediate product stream to react to ultimately form a final intermediate product stream; (xvi) introducing the intermediate product stream or the final intermediate product stream into a combustion tubular reactor containing a reverse water-gas shift catalyst, wherein the combustion tubular reactor produces an exhaust stream containing carbon dioxide and excess heat; (xvii) heating the intermediate or final intermediate product stream in the combustion tubular reactor to temperature T3 to react carbon dioxide and hydrogen in the intermediate product stream or the final intermediate product stream to form a final product stream, wherein T3 is equal to or greater than T2 and T3 is equal to or greater than T1; (xviii) sending at least a portion of the excess heat to the step of heating the mixed reactant stream to form a heated mixed reactant stream, or sending it to the step of heating the first product stream to form a heated first product stream; and (xix) sending at least a portion of the generated carbon dioxide to the adiabatic reactor, the downstream adiabatic reactor, or the combustion-tubular reactor, thereby providing a method for producing synthesis gas.;

[0012] Another embodiment of the present invention comprises: (i) a first RWGS reactor comprising a reverse water-gas shift catalyst, wherein the first RWGS reactor is configured to facilitate the reaction of hydrogen and carbon dioxide to form a first product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (ii) a water removal unit located downstream of the first RWGS reactor for removing water from the first product stream; (iii) any one or more intermediate RWGS reactors arranged in series downstream of the first RWGS reactor, wherein each of the any one intermediate RWGS reactor comprises a water-gas shift catalyst, and said any one intermediate reactor facilitates the reaction of hydrogen and carbon dioxide to form an intermediate product stream and ultimately forms a final intermediate product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (iv) any water removal unit for removing water from the intermediate product stream and the final intermediate product stream; and (v) a final RWGS reactor disposed in series downstream of the first RWGS reactor and any one or more intermediate RWGS reactors, wherein the final RWGS reactor comprises a water-gas shift catalyst and is configured to facilitate the reaction of hydrogen and carbon dioxide to form a final product stream comprising carbon monoxide, water, hydrogen and carbon dioxide, thereby providing an RWGS system comprising the final RWGS reactor. Brief explanation of the drawing

[0013] FIG. 1 is a schematic diagram of a two-stage RWGS process according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a multi-stage RWGS process according to an embodiment of the present invention. FIG. 3 is a schematic diagram of an exemplary process having a single-step RWGS reaction according to Example 1 described herein. FIG. 4 is a schematic diagram of an exemplary process having a single-step RWGS reaction according to Example 2 described herein. Figure 5 is a graph plot of the single-step RWGS reaction as a function of temperature. FIG. 6 is a schematic diagram of an exemplary process having a two-step RWGS reaction according to Example 3 described herein. FIG. 7 is a schematic diagram of an exemplary process having a two-step RWGS reaction according to Examples 4, 5, and 6 described herein. FIG. 8 is a schematic diagram of an exemplary process having a three-step RWGS reaction according to Examples 7 and 8 described herein. FIG. 9 is a schematic diagram of an exemplary process having a three-step RWGS reaction according to Example 9 described herein. FIG. 10 is a graph plot of water removal (different curves) and CO2 conversion as a function of the number of RWGS reactor stages for an example. FIG. 11 is a graph plot of water removal (different curves) for an example and CO2 natural gas combustion emissions / converted CO2 as a function of the number of RWGS reactor stages. Specific details for implementing the invention

[0014] Embodiments of the present invention are based, at least in part, on the discovery of an industrially important process in which carbon dioxide is converted to carbon monoxide at an increased conversion rate while maintaining an overall balance of reaction efficiency. This process utilizes a reverse gas shift (RWGS) reaction within a multi-stage scheme that optionally includes both thermal integration and moisture removal to achieve overall process efficiency. Additionally, overall reaction efficiency is achieved by adjusting reaction conditions at each stage. Thus, while prior art suggests reusing unreacted carbon dioxide back into the RWGS reactor to induce complete conversion of carbon dioxide, the present invention achieves desirable efficiency at a significant industrial level. Furthermore, additional overall efficiency can be realized when combined with thermal integration and / or separation of components between reaction stages.

[0015] Method Overview

[0016] Phase 2 implementation form

[0017] A method according to the present invention showing a reverse gas conversion (RWGS) process (11) comprising a final RWGS reaction step (32) in series following an initial RWGS reaction step (22), which may also be referred to as a first RWGS reaction step (22), can be described with reference to FIG. 1. A carbon dioxide (CO2) stream (21) and a hydrogen (H2) stream (25) may be combined to form a mixed reactant stream (25), which is subsequently heated in a heating step (24) (e.g., in a heat exchanger). The heated and mixed reactant stream (27) is subsequently sent from the first heating step (24) to the first RWGS reaction step (22), where CO2 and H2 react in the presence of a catalyst (e.g., in an adiabatic reactor) to produce carbon monoxide (CO) and water (H2O).

[0018] Heat may be supplied to the heating stage (24) from one or more heat sources. For example, heat (29) may be supplied from a dedicated heat source (26). Alternatively, or in addition to the dedicated heat source (26), heat from a downstream process stage may be received by the heating stage (24). For example, as illustrated in FIG. 1 and described in more detail below, excess heat in the exhaust stream (31) from the final RWGS reaction stage (32) may be sent to the heating stage (24). In any such embodiment where carbon dioxide is generated at the time of heat generation, such as in the heat source (26), the generated carbon dioxide may be sent back to the first RWGS reaction stage (22), where it may be at least partially converted into carbon monoxide. For example, the stream (35) containing the generated carbon dioxide may be combined with the carbon dioxide feed stream (21), the mixed stream (25), or introduced directly into the reaction stage (22). Alternatively, the generated carbon dioxide can be sent to the final RWGS reaction step (32) or to an intermediate point of the process for conversion to carbon monoxide through the RWGS reaction.

[0019] The CO and H2O products, along with any unreacted reactants, are sent from the first RWGS reaction step (22) to the second RWGS reaction step (32) as a product stream (33). In one or more embodiments, the product stream (33) may undergo water removal within a water removal step (38) prior to the final RWGS reaction step (32), thereby the water removal step (38) produces a water-deficient product stream (33'). Subsequently, the water-deficient product stream (33') may be introduced into the final RWGS reaction step (32).

[0020] Heat (39) can be supplied from the heat source (36) to the final RWGS reaction stage (32), which generates an exhaust stream (31) containing heat not consumed by the reaction stage (32) (i.e., excess heat) and optionally generated carbon dioxide. As mentioned above, excess heat from the RWGS reaction stage (32) can be supplied to an upstream stage, e.g., a heating stage (24), through the exhaust stream (31) as illustrated in FIG. 1. Although not illustrated, excess heat in the exhaust stream (31) can be used to preheat the product streams (33, 33') before they are fed into the final RWGS reaction stage (32). As with the heat source (26), the generated carbon dioxide in the exhaust stream (31) can be sent back to the upstream RWGS reaction (e.g., the first RWGS reaction stage (22)). For example, a stream (45) containing carbon dioxide generated from an exhaust stream (31) may be combined with a carbon dioxide feed stream (21) and a mixture (25), or supplied directly to a reaction step (22).

[0021] FIG. 1 illustrates a final RWGS reaction step (32) in which heat (39) is added directly to the reaction step (32), but it will be understood that in other embodiments, the final RWGS reaction step may include an arrangement similar to that illustrated in relation to the reaction step (22) in which heating occurs before entry into the reactor. Again, those skilled in the art will understand that the preheating of the stream or the direct heating of the reactant stream during the reaction step may vary depending on the type of reactor selected (e.g., an adiabatic reactor or a non-diabatic reactor).

[0022] CO2 and H2 in the product stream (33) (or water-deficient stream (33')) react within the final RWGS reaction stage (32) to produce CO and H2O, which are discharged from the final RWGS reaction stage (32) as the final product stream (43) along with any unreacted reactants. The final product stream (43) may undergo one or more separations, for example, within a separation stage (46). For example, the separation stage (46) may remove water through the water stream (51). In addition to or instead of removing water, at least some of the hydrogen in the final product stream may be removed (e.g., through a membrane) to form a hydrogen-rich stream (53). Likewise, in addition to or instead of the separation of water and / or hydrogen, carbon dioxide may be optionally separated to produce a carbon dioxide-rich stream (55), and / or carbon monoxide may be optionally separated to produce a carbon monoxide-rich stream (57).

[0023] In one or more embodiments, the final product stream (43) is a synthesis gas stream. Those skilled in the art understand that separation and / or purification may be performed on the product stream (43) to produce a modified synthesis gas stream (61). For example, components may be recovered (e.g., recovery of H2O, H2, CO and / or CO2), purification may occur and / or the ratio of components may be manipulated to produce a modified synthesis gas stream (61). In one or more embodiments, for example, carbon dioxide contained in the stream (43) forming a carbon dioxide-rich stream (55) after the separation step may be sent back to an upstream RWGS reaction step so that at least a portion of the carbon dioxide may be converted into carbon monoxide. For example, the carbon dioxide-rich stream (55) may be combined with the carbon dioxide feed stream (21). Alternatively, the carbon dioxide-rich stream may be sent back to the final RWGS reaction step (32) or to an intermediate point in the process for the conversion of carbon dioxide into carbon monoxide via the RWGS reaction. FIG. 1 illustrates the separation step (46) as a single step, but it will be understood that multiple separation steps may exist to achieve the desired separation and / or purification.

[0024] Multi-stage process

[0025] In one or more embodiments, the method of the present invention comprises three or more reaction steps. In one or more embodiments, the final step is operated at a higher temperature than the preceding reaction step. The reaction steps preceding the final RWGS reaction step, including an initial RWGS reaction step and any intermediate RWGS reaction step, may each be performed at the same temperature. In another embodiment, one or more intermediate RWGS reaction steps are performed at a higher temperature than the initial RWGS step. In a specific embodiment, each intermediate RWGS reaction step is performed at a higher temperature than the preceding step. In yet another embodiment, each step of the multi-stage process is operated randomly with respect to temperature. In one or more embodiments, water is removed from the product stream discharged from one or more RWGS reaction steps before being transferred to a subsequent reaction step.

[0026] An exemplary multi-stage process illustrating a three-stage reaction process (111) comprising an initial RWGS reaction step (122), an intermediate RWGS reaction step (132), and a final RWGS reaction step (152) may be described with reference to FIG. 2. Although not illustrated, the process (111) may include more than one, more than three in other embodiments, more than ten in other embodiments, more than twenty in other embodiments, and more than 100 intermediate RWGS reaction steps in other embodiments. In these or other embodiments, the process (111) may include fewer than 100, fewer than 30 in other embodiments, and fewer than 10 in other embodiments. In one or more embodiments, the method of the present invention may include about 1 to about 100 intermediate RWGS reaction steps, in another embodiment about 2 to about 30 steps, and in another embodiment about 3 to about 10 steps.

[0027] Referring again to FIG. 2, the CO2 stream (121) and H2 stream (123) are combined into a mixed reactant stream (125), heated in a heating step (124) to form a heated stream (127), and sent to an initial RWGS reaction step (122), where at least some of the CO2 and H2 are converted into CO and H2O in the presence of a catalyst to form a product stream (133). As in the embodiment of FIG. 1, the heating step (124) and the reaction step (122) may be combined into a single step depending on the type of reactor used. Additionally, it will be understood that in one or more embodiments, the mixed reactant stream (125) (as well as the above reactant stream (25)) may be supplied directly, and thus, the CO2 stream (121) and H2 stream (123) may optionally be absent.

[0028] The heating step (124) may receive heat from one or more heat sources. For example, heat (129) may be generated from a dedicated heat source (126). Alternatively, or in addition to the dedicated heat source (126), heat from a downstream process step may be received by the heating step (124). For example, as illustrated in FIG. 1, excess heat in the exhaust stream (131) is received from the final RWGS reaction step (152). In other examples (not illustrated), exhaust heat may be received from an intermediate RWGS reaction step (e.g., step (132)) or an intermediate heat source. In such an embodiment, where carbon dioxide is generated at the time of heat generation as in the heat source (126), the generated carbon dioxide may be sent back to the first RWGS reaction step (122), where it may be at least partially converted into carbon monoxide. For example, the generated carbon dioxide may be combined with the carbon dioxide feed stream (121) and the mixed stream (125), or introduced directly into the reaction step (122). Alternatively, the generated carbon dioxide may be sent to the final RWGS reaction step (152), or to an intermediate point in the process for conversion to carbon monoxide via the RWGS reaction.

[0029] In one or more embodiments, the product stream (133) from the initial RWGS reaction step (122) may be optionally sent to an optional water removal step (138) to produce a water-deficient product stream (133'), which may then be sent to an intermediate heating step (134) to form a heated stream (137). Heat (139) may be supplied to the heating step (136) from one or more heat sources. For example, heat (139) may be supplied from a dedicated heat source (136). Alternatively, or in addition to the dedicated heat source (136), heat may be sent from other process steps. For example, as illustrated in FIG. 2 and described in more detail below, excess heat in the exhaust stream (131) from the final RWGS reaction step (152) may be sent to the heating step (134). In an embodiment in which carbon dioxide is generated upon the generation of heat, such as from a heat source (136), the generated carbon dioxide (141) may be returned to a first RWGS reaction step (122), where it may be at least partially converted into carbon monoxide. For example, the generated carbon dioxide may be combined with a carbon dioxide feed stream (121), a mixed stream (125), or introduced directly into the reaction step (122). Alternatively, the generated carbon dioxide may be sent to a final RWGS reaction step (152), or to an intermediate point in the process for conversion into carbon monoxide via an RWGS reaction. As in the reaction step (122) and the heating step (124), the heating step (134) and the reaction step (132) may be combined into a single step depending on the type of reactor used.

[0030] The heated stream (137) is sent from the heating step (134) to the intermediate RWGS reaction step (132), where at least some of the CO2 and H2 in the heated stream (137) are converted into CO and H2O to form an intermediate product stream (143). The intermediate product stream (143) discharged from the intermediate RWGS reaction step (132) may optionally be sent to one or more additional intermediate RWGS reaction steps (not shown). In one or more embodiments, these one or more intermediate RWGS reaction steps are arranged in series. As the process stream proceeds downstream through one or more intermediate RWGS reaction steps, the process stream may undergo one or more water removal steps (not shown) before entering the subsequent intermediate RWGS reaction steps. Additionally, depending on the type of reactor used, one or more intermediate RWGS reaction steps may include preheating the stream before it enters the reaction steps, or the stream may be heated simultaneously during the intermediate RWGS reaction steps.

[0031] Ultimately, an intermediate product stream (e.g., stream (143)) from one or more intermediate RWGS reaction stages is sent to a final RWGS reaction stage (152). Before the final RWGS reaction stage (152), stream (143) may undergo any water removal stage (148) to form a water-depleted product stream (143'). The final RWGS reaction stage may receive heat (159) from a heat source (156) and produce an exhaust stream (131) that may contain excess heat and / or generated carbon dioxide. For example, excess heat in the exhaust stream (131) from the final RWGS reaction stage (152) may be sent to an upstream process stage, e.g., a heating stage (124 and / or 134). Additionally, excess heat in the exhaust stream (131) may be sent to any preceding reaction stage or used to preheat any upstream stream. When carbon dioxide is generated at the time of heat (159), such as from a heat source (156), the generated carbon dioxide may be sent to any RWGS reaction step (122), where it may be at least partially converted into carbon monoxide. For example, the generated carbon dioxide may be mixed with a carbon dioxide feed stream (121), a mixed stream (125), or introduced directly into one of the reaction steps. Alternatively, the generated carbon dioxide may be sent to a final RWGS reaction step (152), or to an intermediate point in the process for conversion into carbon monoxide via an RWGS reaction.

[0032] In the final RWGS reaction step (152), CO2 and H2 in the product stream (143) react to further produce CO and H2O, which are discharged from the final RWGS reaction step (152) into the final product stream (153) along with any unreacted reactants. The final product stream (153) may undergo one or more separations, for example, in a separation step (166). For example, the separation step (166) may remove water through a water stream (161). In addition to or instead of removing water, at least a portion of the hydrogen in the final product stream (153) may be removed to form a hydrogen-rich stream (163). Likewise, in addition to or instead of separating water and / or hydrogen, carbon dioxide may be optionally separated to produce a carbon dioxide-rich stream (165) and / or a carbon monoxide-rich stream (167).

[0033] In one or more embodiments, the final product stream (153) is a synthesis gas stream. Those skilled in the art understand that separation and / or purification may be performed on the product stream (153) to produce a modified synthesis gas stream (171). For example, components may be recovered (e.g., recovery of CO, CO2, H2, and / or H2), purification may occur and / or the ratio of components may be manipulated to produce a modified synthesis gas stream (171). In one or more embodiments, for example, carbon dioxide contained in the stream (153) which forms a carbon dioxide-rich stream (165) after the separation step may be sent back to an upstream RWGS reaction step to convert at least a portion of the carbon dioxide into carbon monoxide. For example, the carbon dioxide-rich stream (165) may be combined with the carbon dioxide feed stream (121). Alternatively, the carbon dioxide-rich stream may be sent back to the final RWGS reaction step (152), or to an intermediate point of the process for the conversion of carbon dioxide to carbon monoxide via the RWGS reaction. FIG. 2 illustrates the separation step (166) as a single step, but it will be understood that multiple separation steps may exist to achieve the desired separation and / or purification.

[0034] Reactant stream

[0035] In one or more embodiments, the method of the present invention comprises providing carbon dioxide and hydrogen at appropriate feed rates to the initial RWGS reaction step, thereby providing at least 1 mole of hydrogen to 1 mole of carbon dioxide within the initial RWGS reaction step. In these or other embodiments, an excess amount of hydrogen is supplied to the initial RWGS reaction step. For example, the feeds of hydrogen and carbon dioxide may be configured to provide a molar ratio of hydrogen to carbon dioxide greater than 1:1 to the initial RWGS reaction step, greater than 1.5:1 in other embodiments, greater than 2.5:1 in other embodiments, and greater than 5:1 in other embodiments. In one or more embodiments, the feeds of hydrogen and carbon dioxide provide a molar ratio of hydrogen to carbon dioxide of about 1:1 to about 10:1 to the initial RWGS reaction step, about 1.3:1 to about 5:1 in other embodiments, about 1.5:1 to about 4:1 in other embodiments, and about 2.5:1 to about 3.5:1 in other embodiments.

[0036] In one or more embodiments, the carbon dioxide reactant stream (e.g., stream (21, 121)) supplied to the initial RWGS reaction stage (or supplied to any pre-mixing stage where carbon dioxide and hydrogen are mixed) comprises more than 50 mol%, in another embodiment more than 85 mol%, in another embodiment more than 90 mol%, in another embodiment more than 95 mol%, in another embodiment more than 98 mol%, and in another embodiment more than 99 mol% of carbon dioxide. In one or more embodiments, the carbon dioxide reactant stream supplied to the initial RWGS reaction stage (or mixed with the hydrogen reactant stream) comprises about 50 mol% to about 100 mol%, in another embodiment about 75 mol% to about 99.9 mol%, and in another embodiment about 99 mol% to about 100 mol% of carbon dioxide.

[0037] In one or more embodiments, the hydrogen reactant stream (e.g., stream (23, 123)) supplied to the initial RWGS reaction stage (or supplied to any pre-mixing stage where carbon dioxide and hydrogen are mixed) comprises more than 50 mol%, more than 75 mol%, more than 85 mol% in another embodiment, more than 90 mol% in another embodiment, more than 95 mol% in another embodiment, more than 98 mol% in another embodiment, and more than 99 mol% in another embodiment. In one or more embodiments, the hydrogen reactant stream supplied to the initial RWGS reaction stage (or mixed with the carbon dioxide stream) comprises about 50 to about 100 mol%, about 75 to about 99.9 mol% in another embodiment, and about 99 mol% to about 100 mol% of hydrogen in another embodiment.

[0038] In one or more embodiments, the reactant stream introduced into the first RWGS reaction step (22, 122), which may include the heated stream (27, 127) (i.e., the reactant reacted in the first reaction step) as well as the mixed stream (25, 125), comprises at least 50 mol%, in another embodiment at least 75 mol%, in another embodiment at least 90 mol%, and in another embodiment at least 95 mol% of the combined carbon dioxide and hydrogen. In these or other embodiments, the reactant stream introduced into the first RWGS reaction step (22, 122) is substantially free of methane, and contains an amount less than that which would otherwise have a significant impact on the practice of the invention. In one or more embodiments, the reactant stream introduced into the first RWGS reaction step (22, 122) is free of methane. In one or more embodiments, the reactant stream introduced into the initial RWGS reaction step (22, 122) contains less than 20 mol%, in another embodiment less than 10 mol%, in another embodiment less than 5 mol%, in another embodiment less than 2 mol%, and in another embodiment less than 1 mol% of methane.

[0039] Similarly, it is desirable to minimize methane production within the RWGS reaction. For example, the resulting product stream may contain less than 20 mol%, less than 10 mol% in another embodiment, less than 5 mol% in another embodiment, less than 2 mol% in another embodiment, and less than 1 mol% of methane in another embodiment. In one or more embodiments, the product stream is substantially methane-free, and in another embodiment, the product stream is methane-free.

[0040] RWGS process conditions

[0041] In one or more embodiments, the first heating step (24, 124) produces a heated and mixed reactant stream (27, 127) having a temperature greater than 350°C, greater than 450°C in another embodiment, greater than 500°C in another embodiment, and greater than 525°C in another embodiment (this would be the heat of the stream flowing into the first RWGS reaction step (22, 122)). In these or other embodiments, the first heating step (24, 124) produces a heated and mixed reactant stream (27, 127) having a temperature less than 700°C, less than 650°C in another embodiment, and less than 600°C in another embodiment. In one or more embodiments, the first heating step (24, 124) produces a heated and mixed reactant stream (27, 127) having a temperature of about 450 to about 700°C, in another embodiment about 500 to about 650°C, and in another embodiment about 525 to about 600°C. Similarly, any downstream intermediate reaction step including preheating of the intermediate reactant stream may be heated to a similar temperature.

[0042] In one or more embodiments, the initial RWGS reaction step (22, 122) is performed in an adiabatic state. In these or other embodiments, the initial RWGS and one or more intermediate RWGS reaction steps (132) are performed in an adiabatic state. In a specific embodiment, each of the first RWGS (22, 122) and intermediate RWGS (132) reaction steps is performed in an adiabatic state. In these or other embodiments, the initial RWGS reaction step (32, 152) is performed in an adiabatic state.

[0043] For the purposes of this specification, the temperature at which any RWGS reaction step is performed is quantified or characterized by the temperature of the product stream immediately discharged from the reaction step (e.g., the outlet temperature of the reactor at which the reaction step is performed).

[0044] In one or more embodiments, the initial reaction step (22, 122) is carried out at a temperature greater than 300°C, in another embodiment greater than 450°C, in another embodiment greater than 500°C, and in another embodiment greater than 525°C. In these or other embodiments, the initial reaction step (22, 122) is carried out at a temperature less than 1000°C, in another embodiment less than 800°C, in another embodiment less than 650°C, and in another embodiment less than 600°C. In one or more embodiments, the initial reaction step (22, 122) is carried out at a temperature of about 400 to about 1200°C, in another embodiment about 300 to about 1000°C, in another embodiment about 450 to about 800°C, in another embodiment about 500 to about 750°C, and in another embodiment about 525 to about 600°C.

[0045] In one or more embodiments, the final RWGS reaction step (32, 152) is performed at a temperature greater than 500°C, in another embodiment greater than 800°C, in another embodiment greater than 850°C, and in another embodiment greater than 900°C. In these or other embodiments, the final RWGS reaction step (32, 152) is performed at a temperature less than 1200°C, in another embodiment less than 1100°C, and in another embodiment less than 1000°C. In one or more embodiments, the final reaction step (32, 152) is performed at a temperature of about 500 to about 1200°C, in another embodiment about 800 to about 1200°C, in another embodiment about 850 to about 1100°C, and in another embodiment about 900 to about 1000°C.

[0046] In one or more embodiments, any water removal step (38, 138, 148) removes more than 10% of the water in the product stream (33), more than 25% in another embodiment, and more than 50% in another embodiment. In these or other embodiments, the water removal step (38) removes less than 100% of the water in the product stream (33), less than 90% in another embodiment, and less than 70% in another embodiment. In one or more embodiments, the water removal step (38) removes about 10 to about 100% of the water in the product stream (33, 133, 143), about 25 to about 90% in another embodiment, and about 50 to about 90% in another embodiment.

[0047] The RWGS process, including any individual steps, can be performed over a wide range of pressures, including atmospheric pressure, about 550 psi, and even up to 1000 psi or more. Typical reactor pressures can be selected to be matched with downstream use or to minimize compression. In one or more embodiments, the RWGS process is operated at a pressure of about 400 to about 600 psi.

[0048] Heating device

[0049] In such an RWGS step performed in an adiabatic state, the reactant stream may be preheated in a heating step (24, 124, 134) using suitable equipment, such as, but not limited to, a heat exchanger.

[0050] A person skilled in the art can easily determine the appropriate design configuration and material equipment requirements for a heating device (e.g., a heat exchanger) based on desired process conditions without excessive calculation or experimentation. For example, the desired temperature of a reaction step may indicate the materials that can be used to constitute the heating device or a part thereof.

[0051] Thermal energy for the RWGS reaction

[0052] Heat transferred to the reactant stream within an adiabatic reaction stage or directly to the reaction stage within a non-adiabatic reaction stage can originate from various heat sources. For example, heat can be supplied by the combustion of fossil fuels, such as natural gas. Alternatively, heat can be supplied by electrical energy. Electrical energy can originate from the combustion of fuels, for example, from various sources, such as nuclear, wind, solar, and hydroelectric power, and optionally CO2 capture. Alternatively, heat can be supplied by the combustion of carbon-free fuels, for example, hydrogen, which can generate energy without producing carbon dioxide.

[0053] As indicated above, when one or more heat sources (e.g., heat sources (126, 136, 156)) used to provide thermal energy to the RWGS reaction step generate carbon dioxide during heat generation, the generated carbon dioxide may optionally be captured and returned to the RWGS process as a reactant (e.g., returned to the carbon dioxide stream (21, 121)). In one or more embodiments, at least 20% of the carbon dioxide generated during heat generation for the RWGS reaction step of the present invention (e.g., combustion of fuel, e.g., natural gas), in another embodiment at least 50%, in another embodiment at least 70%, in another embodiment at least 85%, and in another embodiment at least 90% is captured and returned to the process as a reactant.

[0054] RWGS reactor

[0055] The RWGS reaction step of the present invention may be carried out in a vessel that allows the reaction to be performed in the presence of a catalyst while providing the ability to efficiently transfer heat to the reaction. For example, the reaction may be carried out in a fixed-bed reactor, which may also be referred to as a packed-bed reactor. When the RWGS reaction is carried out in an adiabatic state, the reactor may optionally include an insulated packed-bed vessel or tank. When the RWGS reaction is carried out in a non-adiabatic state, the reactor may include a heated packed-bed reactor, for example, a combustion tube packed-bed reactor, a radiatively heated packed-bed reactor, an electrically heated packed-bed reactor, a microwave-heated packed-bed reactor, and a convectively heated packed-bed reactor.

[0056] A person skilled in the art can easily determine the appropriate design configuration and material equipment requirements for the reactor based on the desired process conditions without excessive calculation or experimentation. For example, the desired temperature of the reaction step may indicate the materials that can be used to construct the reaction vessel or a part thereof (e.g., reaction tube). For example, if a low-temperature RWGS reaction (e.g., a reaction at a temperature below about 800°C) is required, the reactor components may be made of stainless steel or other metals or alloys capable of withstanding temperatures up to about 800°C. On the other hand, if a high-temperature RWGS reaction (e.g., a reaction above about 800°C) is required, the reactor components may be made of high-grade metals or alloys, such as nickel alloys, capable of withstanding temperatures up to about 1200°C.

[0057] The overall process design advantageously allows a portion of the necessary reaction heat (i.e., ΔHr) essential for inducing the RWGS reaction to be supplied from a lower energy system (i.e., the first low-temperature reaction stage), which reduces the amount of energy that must be transferred to the reaction within the high-temperature RWGS reaction stage, which advantageously allows for operation at a higher temperature to induce greater CO2 conversion. Thus, by operating the high-temperature RWGS reaction stage at a high temperature, the CO2 conversion of the entire process can be induced beyond the level achieved at lower temperatures, without relying on the high-temperature RWGS reaction stage to provide all the heat transfer requirements for the entire conversion reaction. Consequently, the characteristics of the high-temperature RWGS reaction stage can be favorably tailored to accommodate a lower total efficiency (duty), particularly the total heat transfer efficiency, which provides overall efficiency, especially in terms of capital cost requirements. For example, the low-temperature RWGS reaction stage can be carried out in a vessel made of a material that does not need to withstand the extremely high temperatures of the high-temperature RWGS reaction stage. In addition, considering that the high-temperature heat transfer requirement is less than when the process includes only a single RWGS reaction step, the reactor design for the high-temperature RWGS reaction step can be reduced.

[0058] catalyst

[0059] As indicated above, both high-temperature (e.g., above about 800°C) and low-temperature (e.g., from about 350 to about 800°C) RWGS reactions are induced by a catalyst. However, the practice of the present invention is not limited to a specific catalyst system as long as the catalyst promotes or facilitates the reverse water-gas shift reaction. Thus, any reverse water-gas shift catalyst may be referenced. Those skilled in the art understand that reaction conditions for any given RWGS reaction, in particular, can affect the selected catalyst system, and that those skilled in the art can easily select a suitable catalyst without excessive experimentation or calculation.

[0060] In one or more embodiments, a fixed-bed catalyst system is used. As understood by those skilled in the art, such a system comprises a catalyst material disposed on a suitable support material. Useful support materials are generally known in the art and include such materials that can be suitably filled into a reactor (e.g., a tubular reactor).

[0061] Useful catalysts include high-temperature shift catalysts, which are generally known in the art and are useful at higher temperatures (e.g., generally above 400°C) where reverse shift reactions are performed. Exemplary high-temperature reverse water-gas shift catalysts compositionally comprise iron oxide, chromium oxide, and optionally magnesium oxide. Another example is a catalyst based on said oxides, optionally in addition to or instead of the oxides of manganese and cesium and / or lanthanide metals, with carbonates or oxycarbonates, and optionally with platinum.

[0062] Other high-temperature conversion catalysts include those disclosed in U.S. Publications No. 2017 / 0197829, 2015 / 0080482, 2010 / 0105962, 2003 / 0113244, and 2007 / 0142482, which are incorporated herein by reference.

[0063] Water removal technology

[0064] As indicated above, the implementation of the present invention may include one or more steps for removing water from a product stream. Various techniques may be used. For example, the condensation of water from a product stream may be achieved by a condensation technique that includes the removal of heat from the product stream.

[0065] In other embodiments, water is removed without removing a significant amount of thermal energy from the product stream. For example, in one or more embodiments, water is removed by membrane separation. Those skilled in the art understand that such membrane systems may require pressure drop across the membrane, the use of a permeate sweep gas to affect water removal, and / or temperature adjustment. In other embodiments, adsorption techniques may be used. For example, solid adsorbents, metal oxide frameworks (MOFs), and zeolite imidazolate frameworks (ZIFs) may be used. Those skilled in the art will understand that such adsorption systems may require temperature and / or pressure adjustment.

[0066] In one or more embodiments, water is removed by reaction with methane through a steam reforming reaction, which may also be referred to as steam methane reforming (SMR).

[0067] carbon dioxide source

[0068] In one or more embodiments, carbon dioxide may be obtained from various point sources. In one or more embodiments, the carbon dioxide stream may originate from carbon dioxide capture processes, such as combustion operations and various industrial operations, which may be located at various point sources. Combustion processes may include, but are not limited to, coal or gas power plants, vehicle operations, and incineration or waste treatment. Industrial operations include, but are not limited to, aluminum smelting, ammonia production, hydrogen production, purification, cement production, iron smelting, alloy-iron production, steel production, lime production, and glass production. Carbon dioxide capture technologies may include, but are not limited to, absorption, adsorption, membrane separation, and cryogenic separation. For example, carbon dioxide may be absorbed using amine-based technologies.

[0069] In other embodiments, carbon dioxide can be captured from the atmosphere (i.e., not from specific point sources). Such techniques may include direct air capture (DAC), which captures carbon dioxide directly from ambient air. Useful techniques include liquid solvent absorption using amines or corrosive solutions. Other techniques include anion exchange polymer resins, metal-organic frameworks, adsorption, and membrane separation.

[0070] In a specific embodiment, a DAC using a potassium hydroxide solution is used to provide a carbon dioxide stream. For example, a useful DAC process is described in the literature [ Keith et al. A similar process is described in [A PROCESS FOR CAPTURING CO2 FROM THE ATMOSPHERE, Joule (2018)]. Similar processes are also described in U.S. Publications Nos. 2017 / 0354925, 2014 / 0271379, 2019 / 0344217, 2019 / 0359894, and 2019 / 0336909, which are incorporated herein by reference.

[0071] Since the reverse water-gas shift (RWGS) reaction process of the present invention can be designed to achieve an attractive net carbon dioxide consumption, the method of the present invention can be advantageously combined with direct air capture technology to provide an overall industrially useful level of carbon dioxide consumption.

[0072] hydrogen supply source

[0073] In one or more embodiments, the hydrogen stream may be supplied by an electrolysis process in which water undergoes electrolysis to produce hydrogen and oxygen. The electrical requirements for the electrolysis process may be provided from alternative and renewable energy sources, such as geothermal sources, solar power, wind energy, hydropower, nuclear power, waste combustion, ocean thermal—or kinetic—generation, or from off-peak power grid supply.

[0074] In another embodiment, the hydrogen stream can be supplied by reforming; for example, by steam reforming of natural gas and autothermal reforming of natural gas.

[0075] In another embodiment, the hydrogen stream may be supplied from off-gas or waste gas from another process; for example, from a hydrogen treatment process, a hydrocracking process, or other industrial processes that use or generate hydrogen.

[0076] Use of product stream

[0077] In one or more embodiments, carbon monoxide produced by the implementation of the present invention can be used as a building block for the production of various fuels and chemicals.

[0078] In one or more embodiments, the product stream produced by the practice of the present invention comprises a mixture of carbon monoxide and hydrogen, which may be referred to as synthesis gas or synthesis gas. For example, the molar ratio of carbon monoxide to hydrogen may be about 0.5:1 to about 5:1 or higher, in another embodiment about 1:1 to about 3:1, and in another embodiment about 1.5:1 to about 2.5:1. As will be understood by those skilled in the art, the feed rate of hydrogen to carbon dioxide into the method of the present invention, as well as the process arrangement (e.g., number of steps), operating conditions (e.g., temperature of the steps, water removal), and post-synthesis operation of the raw synthesis gas stream, can be adjusted to provide a product stream having a desired molar ratio of carbon monoxide to hydrogen.

[0079] In one or more embodiments, the product stream produced by the method of the present invention is a synthesis gas stream in which a Fischer-Tropsch process is carried out to produce hydrocarbons, such as diesel, gasoline, naphtha, wax, LPG, or methane.

[0080] In another embodiment, the product stream produced by the method of the present invention is a synthesis gas stream used for the production of methanol (i.e., methanol synthesis) or the synthesis of other alcohols.

[0081] A system for carrying out the method of the present invention, generally comprising RWGS reactors arranged in series with any heating and water removal unit disposed between the RWGS reactors, can be constructed by a person skilled in the art without excessive experimentation or calculation. In addition, a person skilled in the art will be able to easily select appropriate equipment, such as pipes or other conduits, so that one or more elements of the system are arranged to have fluid exchange with one another (e.g., to move materials between various reactors or to reuse specific materials within the system) and / or one or more elements of the system are arranged to have heat exchange with one another (e.g., to transfer heat between various process steps). A person skilled in the art will also be able to easily heat and cool various streams and appropriately measure this in accordance with the practice of the present invention.

[0082] To demonstrate the implementation of the present invention, the following examples were simulated. However, the examples should not be construed as limiting the scope of the invention. The claims will serve to define the invention.

[0083] Examples

[0084] Aspen Technology Inc. product, the process simulator Aspen Plus TM The example was simulated using [the method]. A summary table of the example and the results are provided in Table 10 and Figures 9 and 10.

[0085] The following specific process characteristics and parameters were common to all simulations: (1) The mixed process feed to the RWGS reactor system consisted of 1500 lbmol / hr CO2 and 4500 lbmol / hr H2 with a 3:1 H2 / CO ratio at a pressure that produced product synthesis gas at 100°F and 415 psia (considering different pressure drops across different examples); (2) CO2 may have been captured, for example, from industrial point source emissions, directly captured from ambient air (e.g., using "Direct Air Capture" or DAC" technology) and supplied via pipeline, truck, rail, vessel, or other means; (3) H2 may have been generated, for example, through water electrolysis, steam-methane reforming, partial oxidation, pyrolysis, refining operations and supplied via pipeline, truck, rail, vessel, or other means; (4) The product synthesis gas is produced at 415 psia and 100°F (after cooling); (5) Heat is provided to the process by the combustion of natural gas using ambient air in this example (e.g., preheating the feed and providing heat to induce an endothermic RWGS reaction); (6) said natural gas has a composition (in mole%) of 94.0% methane, 3.5% ethane, 1.5% propane, 0.5% nitrogen, and 0.5% carbon dioxide; (7) alternative means of providing heat (not simulated) are possible, which may include, for example, electric heating, hydrogen fuel, coal, oil, hydrocarbon fuel, other fuels, and oxygen combustion; (7) CO2 capture may optionally be included from the combustion flue gas, and the captured CO2 may optionally be used as a feed to the RWGS reactor(s); (8) The RWGS reactor is designed and operated so that the RWGS reaction approaches a state of equilibrium at the outlet of every RWGS reactor.

[0086] Example 1: Single-step RWGS reaction at 1742°F (950°C)

[0087] The single-stage RWGS process of this embodiment is illustrated in FIG. 3. The mixed H2+CO2 feed is preheated to 1000°F (538°C) and supplied to a combustion tubular RWGS reactor (a design similar to a well-known steam methane reformer for generating hydrogen from steam and methane). The RWGS reactor is operated at a high outlet temperature of 1742°F (950°C), which represents the operating temperature for expensive high-nickel alloy tubes in a combustion tubular RWGS reactor. The CO2 conversion rate through RWGS is 80%. The product synthesis gas contains 94% H2+CO on a dry basis and with an H2:CO ratio of 2.75:1. Combustion of 291 lbmol / hr of natural gas fuel produces 310 lbmol / hr of CO2 contained in the flue gas. Additional thermal and mass balance data are provided in Table 1.

[0088]

[0089] Example 2: Single-stage RWGS at 1000℉ (538℃)

[0090] The single-stage RWGS process of this embodiment is illustrated in FIG. 4. The mixed H2+ CO2 feed is preheated to 1000°F (538°C) and supplied to a fired heater-style RWGS reactor (designed similar to a well-known typical smelter furnace). The RWGS reactor is operated at a low outlet temperature of 1000°F (538°C), which represents the operating temperature for low-cost stainless steel tubing in a fired heater-style RWGS reactor; alternative low-temperature RWGS process configurations (not illustrated) may include waste heat recovery (e.g., no dedicated combustion) and / or an adiabatic reactor (e.g., packed bed). The CO2 conversion rate through the single-stage RWGS is 54%. The product synthesis gas contains 87% H2+ CO on a dry basis and with an H2:CO ratio of 4.58:1. Combustion of 166 lbmol / hr of natural gas fuel produces 177 lbmol / hr of CO2 contained in the flue gas. Additional heat and mass balance data are provided in Table 2.

[0091]

[0092] Data from Examples 1 and 2 show that CO2 conversion via the RWGS reaction through a single-step RWGS process for a given feed (in this case, 1500 lbmol / hr CO2 and 4500 lbmol / hr H2) under similar operating conditions is a strong function of the RWGS reactor outlet temperature, as exemplified by comparing Example 1 at 1742℉, which shows 80% CO2 conversion, to Example 2 at 1000℉, which shows 54% CO2 conversion.

[0093] Additional simulation results of a single-stage RWGS process operated at RWGS reactor outlet temperatures ranging from 400℉ to 2400℉ are shown in Table 3 and Figure 5.

[0094]

[0095] Example 3: Two-stage RWGS at 1742℉ and 1742℉ with water knockout via cooling and condensation

[0096] The two-stage RWGS process of this embodiment is illustrated in FIG. 6. A mixed H2+ CO2 feed is preheated to 1000°F and supplied to a first-stage combustion tubular RWGS reactor in which the RWGS reactor operates at a high outlet temperature of 1742°F (950°C). The synthesis gas is cooled to 100°F, and a large amount of water formed by the RWGS reaction in the first RWGS reactor stage (which is present in the synthesis gas effluent of the first RWGS reactor stage) is condensed and removed (99.2% removed). The synthesis gas is reheated to 1000°F and supplied to a second-stage combustion tubular RWGS reactor in which the RWGS reactor operates again at a high outlet temperature of 1742°F (950°C). The total CO2 conversion rates through RWGS in the effluents of the first and second-stage RWGS reactors are 80% and 95%, respectively. The product synthesis gas contains 98% H2+ CO on a dry basis and with an H2:CO ratio of 2.16:1.

[0097] The two-stage RWGS product synthesis gas of Example 3, having a larger CO2 conversion rate, a larger H2+CO content (target synthesis reactant), and an H2:CO ratio close to 2 (typical target H2+CO ratio for Fischer-Tropsch synthesis, methanol synthesis, and other synthesis reactions), is an improvement over the single-stage RWGS product synthesis gas of Examples 1 and 2. Combustion of 291 lbmol / hr natural gas fuel from Stage 1 produces 310 lbmol / hr of CO2 contained in the flue gas from Stage 1. Combustion of 183 lbmol / hr natural gas fuel in Stage 2 produces 195 lbmol / hr of CO2 contained in the flue gas from Stage 2. Additional thermal and mass balance data are provided in Table 4.

[0098] The additional practical value of a two (or multiple) stage RWGS reactor process is recognized when the two stages are designed differently or operated under different operating conditions (where metallurgical and / or building materials are involved). A wide range of different design and operating conditions are possible. The design of different stages where water is removed and heat is integrated and / or combined (where building materials are involved), and the operation of the stages at different RWGS reactor outlet temperatures, are of particular interest, as will be shown in the following additional examples.

[0099]

[0100] Example 4: Two-stage RWGS at 1000℉ and 1742℉ with thermal integration and no inter-stage water removal

[0101] The two-stage RWGS process of this embodiment is illustrated in FIG. 7. A mixed H2+CO2 feed is preheated to 1249°F and supplied to an adiabatic RWGS reactor (e.g., a packed catalyst bed). Sufficient RWGS catalyst is supplied to approach the equilibrium state of the RWGS reaction, and the reacted gas is discharged from the first-stage RWGS reactor at 1000°F. An alternative design (not illustrated) for a convectively heated RWGS reactor may have been used to achieve similar (or improved) CO2 conversion. The effluent gas from the first-stage RWGS reactor is supplied to a second-stage combustion tubular RWGS reactor. The second-stage RWGS reactor operates at a high outlet temperature of 1742°F (950°C). Without inter-stage water removal, the total CO2 conversion results are similar to the consecutive combination of Examples 2 and 1 at 54% and 80%, respectively. Similar to Example 1, burning 291 lbmol / hr of natural gas fuel produces 310 lbmol / hr of CO2 contained in the flue gas. Additional heat and mass balance data are provided in Table 5.

[0102] The CO2 conversion rate of Example 5 is similar to that of Example 1, but the significant advantage of Example 5 (compared to Example 1) lies in the low-cost equipment design and metallurgy (or building materials) of the 1-stage RWGS related to low-temperature operation and packed-bed reactor design. Less conversion occurs in the 2nd stage, and the size of the expensive combustion tubular RWGS reactor with expensive high-nickel alloy tubes is significantly reduced (compared to Example 1).

[0103]

[0104] Example 5: Two-stage RWGS at 1000℉ and 1742℉ using thermally integrated and high-temperature membranes with 50% inter-stage water removal

[0105] The two-stage RWGS process of this embodiment is illustrated in FIG. 7. This embodiment 5 is similar to the preceding embodiment 4, except that 50% of the water formed by the RWGS reaction in the first RWGS reactor stage (which is present in the synthesis gas effluent of the first RWGS reactor stage) is removed using a hot membrane system. The total CO2 conversion rates through RWGS in the effluents of the first and second stage RWGS reactors are 54% and 84% (respectively). The product synthesis gas contains 95% H2+CO on a dry basis and with an H2:CO ratio of 2.55:1. Combustion of 285 lbmol / hr of natural gas fuel produces 304 lbmol / hr of CO2 contained in the flue gas. Additional thermal and mass balance data are provided in Table 6.

[0106] The benefits of the low-cost equipment design (discussed above in Example 4) also apply to this Example 5. In addition, compared to Example 4, the CO2 conversion rate increases from 80% to 84%; and a beneficial reduction in total heat transfer efficiency (resulting in smaller equipment), fuel combustion, and CO2 contained in the flue gas is recognized. Compared to the single-stage RGWS designs of Examples 1 and 2, both cost and performance are improved.

[0107]

[0108] Example 6: Two-stage RWGS at 1000℉ and 1742℉ with 90% inter-stage water removal using thermally integrated high-temperature adsorbents

[0109] The two-stage RWGS process of this example is illustrated in FIG. 7. This Example 6 is similar to the preceding Example 5, except that 90% of the water formed by the RWGS reaction in the first RWGS reactor stage (which is present in the synthesis gas effluent of the first RWGS reactor stage) is removed using a high-temperature adsorbent system. The total CO2 conversion rates through RWGS in the effluents of the first and second stage RWGS reactors are 54% and 88% (respectively). The product synthesis gas contains 96% H2+CO on a dry basis and with an H2:CO ratio of 2.39:1. Combustion of 280 lbmol / hr of natural gas fuel produces 299 lbmol / hr of CO2 contained in the flue gas. Additional thermal and mass balance data are provided in Table 7.

[0110] The benefits of the low-cost equipment design (discussed above in Example 4) also apply to this Example 6. Compared to Example 5, the CO2 conversion rate increases from 84% to 88%; and a beneficial reduction in total heat transfer efficiency (resulting in smaller equipment), fuel combustion, and CO2 contained in the flue gas is recognized. Compared to the single-stage RGWS designs of Examples 1 and 2, both cost and performance are improved.

[0111]

[0112] Example 7: Three-stage RWGS at 1000℉, 1000℉, and 1742℉ with 50% inter-stage water removal using thermally integrated high-temperature adsorbents

[0113] The three-stage RWGS process of this embodiment is illustrated in FIG. 8. A mixed H2+CO2 feed is preheated to 1249°F and supplied to an adiabatic RWGS reactor (e.g., a packed catalyst bed). Sufficient RWGS catalyst is supplied to bring the RWGS reaction close to equilibrium, and the reacted gas is discharged from the first-stage RWGS reactor at 1000°F. 50% of the water formed by the RWGS reaction in the first-stage RWGS reactor (present in the synthesis gas effluent of the first-stage RWGS reactor) is removed using a high-temperature adsorbent system. The water-deficient first-stage RWGS reactor effluent is reheated to 1047°F and supplied to the second-stage adiabatic RWGS reactor; again, sufficient RWGS catalyst is supplied to bring the RWGS reaction close to equilibrium, and the reacted gas is discharged from the second-stage RWGS reactor at 1000°F. Fifty percent of the water present in the synthesis gas effluent of the second RWGS reactor stage is removed using a high-temperature adsorbent system. The water-deficient effluent from the second RWGS reactor is fed to the third combustion tubular RWGS reactor. The third RWGS reactor is operated at a high outlet temperature of 1742°F (950°C). The total CO2 conversion rates through RWGS from the effluents of the first, second, and third RWGS reactors are 54%, 63%, and 88%, respectively. The product synthesis gas contains 96% H2+CO on a dry basis and with an H2:CO ratio of 2.42:1. Combustion of 281 lbmol / hr of natural gas fuel produces 300 lbmol / hr of CO2 contained in the flue gas. Additional thermal and mass balance data are provided in Table 8.

[0114] The benefits of the low-cost equipment design (discussed above in Example 4) also apply to this Example 7. Compared to the two-stage Example 5, the CO2 conversion rate increases from 84% to 88%; and beneficial reductions in total heat transfer efficiency (resulting in smaller equipment), fuel combustion, and CO2 contained in the flue gas are recognized. Compared to the single-stage RGWS designs of Examples 1 and 2, both cost and performance are improved.

[0115] Additional steps (e.g., 4, 5, 100+) are possible. The benefits of a highly integrated multi-step system applicable to large-scale systems are particularly advantageous in small-scale systems where efficient and / or advanced manufacturing and assembly technologies (e.g., 3D printing, etching, iterative parts, factory manufacturing) can be used to minimize manufacturing costs.

[0116]

[0117] Example 8: 3-stage RWGS at 1000℉, 1000℉, and 1742℉ with 90% inter-stage water removal using thermally integrated and high-temperature membranes

[0118] The three-stage RWGS process of this example is illustrated in FIG. 8. This example 8 is similar to the preceding example 7, except that 90% of the water (formed by the RWGS reaction) present in the synthesis gas effluent of the first and second RWGS reactor stages is removed using a high-temperature membrane system. The total CO2 conversion rates in the effluents of the first, second, and third RWGS reactors are 54%, 71%, and 93% (respectively). The product synthesis gas contains 98% H2+CO on a dry basis and with an H2:CO ratio of 2.24:1. Combustion of 277 lbmol / hr of natural gas fuel produces 295 lbmol / hr of CO2 contained in the flue gas. Additional thermal and mass balance data are provided in Table 9.

[0119] The benefits of the low-cost equipment design (discussed above in Example 4) also apply to this Example 8. Compared to the three-stage Example 7, the CO2 conversion rate increases from 88% to 93%; and beneficial reductions in total heat transfer efficiency (resulting in smaller equipment), fuel combustion, and CO2 contained in the flue gas are recognized. Compared to the two-stage Example 6, the CO2 conversion rate increases from 88% to 93%; and beneficial reductions in total heat transfer efficiency (resulting in smaller equipment), fuel combustion, and CO2 contained in the flue gas are recognized. Compared to the single-stage RGWS designs of Examples 1 and 2, both cost and performance are improved.

[0120]

[0121] Example 9: 90% inter-step moisture removal using thermally integrated and high-temperature membranes and 90% CO from flue gas 2 H is captured and H is used so that the product synthesis gas H2 / CO ratio = 2.0. 2 3-stage RWGS at 1000℉, 1000℉, and 1742℉ with adjustable supply

[0122] The three-stage RWGS process of this embodiment is illustrated in FIG. 9. This embodiment 9 is similar to the preceding embodiment 8, except that a CO2 capture system (e.g., an amine system or another capture system) is added to the flue gas. 90% of the CO2 contained in the flue gas is captured from the flue gas, compressed (not illustrated), and blended with a fresh CO2 feed into the RWGS reactor system. The H2 feed into the RWGS reactor system is adjusted to obtain a specific target H2:CO ratio in the product synthesis gas, which is 2.0 in this embodiment 9. The total CO2 conversion rates in the effluents of the first, second, and third stage RWGS reactors are 42%, 63%, and 90% (respectively). The product synthesis gas contains 97% H2+CO on a dry basis and with an H2:CO ratio of 2.00:1. Combustion of 317 lbmol / hr of natural gas fuel produces 338 lbmol / hr of CO2 in the flue gas before the CO2 capture system and 34 lbmol / hr of CO2 in the flue gas after the CO2 capture system. Additional heat and mass balance data are provided in Table 10.

[0123] Compared to Example 8, the CO2 contained in the flue gas following the CO2 capture system is significantly reduced from 295 lbmol / hr to 34 lbmol / hr, the CO + H2 contained in the product synthesis gas is nominally increased by 10% from 4500 lbmol / hr to 4955 lbmol / hr, and a target H2:CO ratio of 2.0 is achieved in the product synthesis gas. As exemplified in this example, adjustments to the H2 feed flow, CO2 feed flow, CO2 capture and / or reuse flow, as well as other operating parameters within the RWGS reactor system (e.g., temperature, pressure, moisture removal), can be used to control the production and quality of the product synthesis gas, including the production rate of the product synthesis gas, the H2:CO ratio of the product synthesis gas, and the molar percentage of H2+ CO in the product synthesis gas. A portion of the product synthesis gas may be reused into the RWGS reactor system (e.g., as a feed within the RWGS process or as an intermediate point), the removal and / or addition of components (e.g., from the product synthesis gas), and / or other purification methods known in the art may also be used to affect the product synthesis gas.

[0124]

[0125] A summary of the example simulations is presented in Table 10. Plots of water removal (different curves), CO2 conversion (Fig. 10), and CO2 natural gas combustion emissions / converted CO2 (Fig. 11) as a function of the number of RWGS reactor stages are shown in Figs. 10 and 11. The example clearly demonstrates the advantages of a multi-stage RWGS reactor in which water is removed between stages, particularly when water removal is performed on-site and in conjunction with heat integration. CO2 emissions may be further reduced and / or avoided by other heating means (e.g., electricity, H2 combustion, waste heat integration, etc.) and / or by CO2 capture from flue gas.

[0126] Various modifications and alterations that do not depart from the scope and spirit of the present invention will be apparent to those skilled in the art. The present invention should not be formally limited to the exemplary embodiments described herein.

Claims

Claim 1 A method for producing synthesis gas, the method comprising: (i) reacting at least a portion of carbon dioxide with hydrogen in a first reactor to produce a first product stream comprising carbon monoxide, water, unreacted carbon dioxide and unreacted hydrogen; and (ii) reacting at least a portion of unreacted carbon dioxide with unreacted hydrogen in a reactor downstream of the first reactor to produce a product stream comprising carbon monoxide, water, unreacted carbon dioxide and unreacted hydrogen, wherein the first product stream has a temperature T1 when discharged from the first reactor and the product stream has a temperature T2 when discharged from the downstream reactor, wherein T2 > T1, T1 is 300 to 1,000 °C, and T2 is 500 to 1,200 °C. Claim 2 A method for producing synthesis gas according to claim 1, wherein the carbon dioxide and hydrogen account for at least 50 mol% of the reactants in the first reactor. Claim 3 A method for producing synthesis gas according to paragraph 2, wherein the reactor contains less than 10 mol% of methane with respect to the total mole of reactants in the first reactor. Claim 4 delete Claim 5 A method for producing synthesis gas according to claim 1, wherein T1 is 450 to 800°C and T2 is 800 to 1,200°C. Claim 6 A method for producing synthesis gas according to claim 1, wherein the reactor downstream of the first reactor is a final reactor in series, and the product stream produced by the final reactor is a final product stream, and the method further comprises the step of reacting unreacted carbon dioxide and unreacted hydrogen in the initial product stream in one or more reactors disposed between the first reactor and the final reactor. Claim 7 A method for producing synthesis gas according to claim 6, wherein one or more reactors disposed between the first reactor and the final reactor produce a final intermediate product stream comprising carbon monoxide, water, unreacted hydrogen and unreacted carbon dioxide, and the unreacted hydrogen and unreacted carbon dioxide in the final intermediate product stream react in the final reactor. Claim 8 A method for producing synthesis gas according to claim 6, further comprising: (i) a step of removing at least a portion of water from the initial product stream prior to the step of reacting at least a portion of unreacted carbon dioxide with unreacted hydrogen in the final reactor; or (ii) a step of removing at least a portion of water from the intermediate product stream prior to the step of reacting unreacted carbon dioxide with unreacted hydrogen in one or more reactors disposed between the first reactor and the final reactor; wherein the intermediate product stream is an exhaust stream produced by any one of the one or more reactors disposed between the first reactor and the final reactor. Claim 9 A method for producing synthesis gas according to claim 1, wherein the step of reacting at least a portion of carbon dioxide with hydrogen in the first reactor is performed in an adiabatic state. Claim 10 A method for producing synthesis gas according to claim 6, further comprising the step of introducing heat into the final reactor. Claim 11 A method for producing synthesis gas according to claim 6, wherein the final reactor is a fired-tubular reactor. Claim 12 A method for producing synthesis gas according to claim 1, further comprising: (i) providing a stream containing carbon dioxide; (ii) providing a stream containing hydrogen; (iii) combining the stream containing carbon dioxide with the stream containing hydrogen to form a reaction mixture; (iv) optionally heating the reaction mixture to form a heated reaction mixture; and (v) introducing at least one of the reaction mixture and the heated reaction mixture into the first reactor. Claim 13 A method for producing synthesis gas according to claim 12, wherein the hydrogen-containing stream contains more than 90 mol% hydrogen and the carbon dioxide-containing stream contains more than 90 mol% carbon dioxide. Claim 14 A method for producing synthesis gas according to claim 12, wherein the hydrogen-containing stream contains more than 98 mol% hydrogen and the carbon dioxide-containing stream contains more than 98 mol% carbon dioxide. Claim 15 A method for producing synthesis gas according to claim 10, wherein the step of introducing heat into the final reactor further comprises the step of producing carbon dioxide and producing an exhaust stream containing CO2, capturing at least a portion of the CO2 contained in the exhaust stream to form a captured stream containing CO2, and further comprising the step of introducing at least a portion of the CO2 contained in the captured stream into the final reactor or an upstream step of the final reactor to convert carbon monoxide. Claim 16 A method for producing synthesis gas according to claim 15, wherein the step of capturing at least a portion of the exhaust CO2 stream comprises capturing at least 50% of the carbon dioxide produced to generate heat. Claim 17 A method for producing synthesis gas according to claim 15, wherein the step of capturing at least a portion of the exhaust CO2 stream comprises capturing at least 90% of the carbon dioxide produced to generate heat. Claim 18 A method for producing synthesis gas according to claim 6, wherein the final product stream comprises carbon monoxide and hydrogen. Claim 19 A method for producing synthesis gas according to claim 6, wherein the final product stream is a synthesis gas stream. Claim 20 A method for producing synthesis gas according to claim 6, further comprising the step of converting at least a portion of the final product stream into hydrocarbons. Claim 21 A method for producing synthesis gas according to claim 6, further comprising the step of converting at least a portion of the final product stream into methanol. Claim 22 A method for producing synthesis gas according to claim 6, further comprising the step of converting at least a portion of the final product stream into alcohol. Claim 23 A method for producing synthesis gas according to claim 12, wherein the step of reacting at least a portion of unreacted carbon dioxide with unreacted hydrogen produces an exhaust stream containing excess heat, and further comprises the step of (i) transferring the excess heat to at least one of a carbon dioxide-containing feed stream and the reaction mixture prior to the step of reacting at least a portion of carbon dioxide with hydrogen in the first reactor. Claim 24 A method for producing synthesis gas according to claim 10, wherein the step of introducing heat into the final reactor comprises introducing heat from a carbon-free heat source. Claim 25 A method for producing synthetic gas according to claim 24, wherein the carbon-free heat source comprises at least one of electric power, nuclear power, wind power, solar power, hydropower, combustion of hydrogen, and combustion of carbon-free fuel. Claim 26 A method for producing synthesis gas according to claim 1, further comprising the step of capturing carbon dioxide from a point source to form a captured stream containing a carbon dioxide stream, and further comprising the step of introducing at least a portion of the captured stream containing carbon dioxide into the first reactor. Claim 27 A method for producing synthesis gas according to paragraph 26, wherein the point source of pollution is an industrial source of carbon dioxide or a power plant. Claim 28 A method for producing synthesis gas according to claim 1, further comprising the step of capturing carbon dioxide from the atmosphere to form a direct air-captured stream containing carbon dioxide, and further comprising the step of introducing at least a portion of the direct air-captured stream containing carbon dioxide into the first reactor. Claim 29 A method for generating synthesis gas, wherein the method comprises: (i) providing a reactant stream containing carbon dioxide; (ii) providing a reactant stream containing hydrogen; (iii) combining the reactant stream containing carbon dioxide with the reactant stream containing hydrogen to form a mixed reactant stream; (iv) heating the mixed reactant stream to form a heated and mixed reactant stream; (v) introducing the heated and mixed reactant stream into an adiabatic reactor containing a reverse water-gas shift catalyst; (vi) allowing the hydrogen and carbon dioxide to react within the adiabatic reactor to form a first product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (vii) removing the first product stream from the adiabatic reactor, wherein the first product stream has a temperature T1 when discharged from the adiabatic reactor; (viii) removing at least a portion of the water in the first product stream from the first product stream to form a water-deficient first product stream; (ix) introducing the first product stream into a combustion tubular reactor containing a reverse water-gas shift catalyst, wherein, A method for producing synthesis gas comprising: (x) a step of producing an exhaust stream containing carbon dioxide and excess heat generated by the combustion tubular reactor; (x) a step of heating the product stream to a temperature T3 within the combustion tubular reactor to react the carbon dioxide and hydrogen in the first product stream to form a final product stream, wherein T3 is equal to or greater than T1; (xi) a step of sending at least a portion of the excess heat to the step of heating the mixed reactant stream to form a heated and mixed reactant stream; and (xii) a step of sending at least a portion of the generated carbon dioxide to the adiabatic reactor or to the combustion tubular reactor. Claim 30 A method for generating synthesis gas comprising: (i) providing a reactant stream containing carbon dioxide; (ii) providing a reactant stream containing hydrogen; (iii) combining the reactant stream containing carbon dioxide with the reactant stream containing hydrogen to form a mixed reactant stream; (iv) heating the mixed reactant stream to form a heated and mixed reactant stream; (v) introducing the heated and mixed reactant stream into a first adiabatic reactor containing a reverse water-gas shift catalyst; (vi) allowing the hydrogen and carbon dioxide to react within the first adiabatic reactor to form a first product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (vii) removing the first product stream from the first adiabatic reactor, wherein the first product stream has a temperature T1 when discharged from the first adiabatic reactor; (viii) removing at least a portion of the water in the first product stream to form a water-deficient first product stream; (ix) heating the water-deficient first product stream to form a heated water-deficient first product stream. Step; (x) introducing the heated water-deficient initial product stream into a downstream adiabatic reactor containing a reverse water-gas shift catalyst; (xi) allowing the hydrogen and carbon dioxide to react within the downstream adiabatic reactor to form an intermediate product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (xii) removing the intermediate product stream from the downstream adiabatic reactor, wherein the intermediate product stream has a temperature T2 when discharged from the downstream adiabatic reactor; (xiii) removing at least a portion of the water in the intermediate product stream to form a water-deficient intermediate product stream;(xiv) optionally, heating the water-deficient intermediate product stream to form a water-deficient intermediate product stream heated at temperature T02; (xv) optionally, introducing the heated water-deficient intermediate product stream into a downstream adiabatic reactor containing a reverse water-gas shift catalyst and allowing carbon dioxide and hydrogen in the heated water-deficient intermediate product stream to react to ultimately form a final intermediate product; (xvi) introducing the intermediate product stream or the final intermediate product stream into a combustion tubular reactor containing a reverse water-gas shift catalyst, wherein the combustion tubular reactor generates an exhaust stream containing the generated carbon dioxide and excess heat; (xvii) heating the intermediate or final intermediate product stream in the combustion tubular reactor to temperature T3 so that carbon dioxide and hydrogen in the intermediate product stream or the final intermediate product stream react to form a final product stream, wherein T3 is equal to or greater than T2 and T3 is equal to or greater than T1; (xviii) sending at least a portion of the excess heat to the step of heating the mixed reactant stream to form a heated and mixed reactant stream, or sending it to the step of heating the initial product stream to form a heated initial product stream; and (xix) sending at least a portion of the generated carbon dioxide to the adiabatic reactor, the downstream adiabatic reactor, or the combustion tubular reactor, a method for producing synthesis gas.; Claim 31 As an RWGS system, (i) a first RWGS reactor comprising a reverse water-gas shift catalyst, wherein the first RWGS reactor is an adiabatic reactor configured to facilitate the reaction of hydrogen and carbon dioxide to form a first product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (ii) a water removal unit located downstream of the first RWGS reactor for removing water from the first product stream; (iii) any one or more intermediate RWGS reactors arranged in series downstream of the first RWGS reactor, wherein each of the any one intermediate RWGS reactor comprises a water-gas shift catalyst, and said any one intermediate reactor is configured to facilitate the reaction of hydrogen and carbon dioxide to form an intermediate product stream and ultimately form a final intermediate product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (iv) any water removal unit for removing water from the intermediate product stream and the final intermediate product stream; and (v) a final RWGS reactor disposed in series downstream of the first RWGS reactor and any one or more intermediate RWGS reactors, wherein the final RWGS reactor is a fired-tubular reactor comprising a water-gas shift catalyst, and the final RWGS reactor is configured to facilitate the reaction of hydrogen and carbon dioxide to form a final product stream comprising carbon monoxide, water, hydrogen and carbon dioxide, the RWGS system comprising the final RWGS reactor. Claim 32 An RWGS system according to claim 31, further comprising a heat source that exchanges heat with the final RWGS reactor, and an exhaust conduit that exchanges heat with one or more upstream heat sources. Claim 33 An RWGS system according to claim 32, further comprising a carbon dioxide capture unit, wherein the carbon dioxide capture unit is fluidly connected to the exhaust conduit and configured to remove carbon dioxide from the exhaust gas discharged from the heat source.

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