Process for conversion of carbon dioxide

Abstract

To provide a process that achieves consumption of carbon dioxide at levels that can impact atmospheric carbon dioxide levels, and that produces syngas in which carbon dioxide is converted to carbon monoxide at a high conversion rate.SOLUTION: A process for the production of syngas comprises (i) reacting at least a portion of carbon dioxide with hydrogen within an initial reactor to produce an initial product stream including carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; and (ii) reacting at least a portion of the unreacted carbon dioxide and unreacted hydrogen within a reactor downstream of the first reactor to thereby produce a product stream including carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention provide a process for converting carbon dioxide directly captured from the atmosphere into synthesis gas, which can be useful for the production of organic molecules at industrially useful levels.

Background Art

[0002] Synthesis gas, also called syngas, is a mixture of hydrogen and carbon monoxide, optionally containing additional residual components such as carbon dioxide, nitrogen, methane, and water. Syngas has several uses, including its use as a reactant feed for producing organic compounds such as hydrocarbons and alcohols.

[0003] Several methods have been used for the synthesis of syngas, including production from carbon dioxide. These processes involve converting carbon dioxide to carbon monoxide through the 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). The produced carbon monoxide can then be combined with additional hydrogen to produce syngas, hydrogen can be removed, or an excess of H2 can be used to perform the RWGS reaction to directly produce syngas while removing water from the product stream.

[0004] The RWGS reaction is a reversible reaction that can basically be operated to 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 occurs. Higher reaction temperatures generally lead to higher CO2 conversion rates. For example, a conversion rate of approximately 55% can be achieved at approximately 540°C, while a conversion rate of approximately 80% can be achieved at approximately 950°C.

[0005] Efforts to improve the efficiency of the RWGS reaction have been technically important in extraterrestrial applications such as space travel. Considering the limited resources in most extraterrestrial applications, conservation of not only energy but also reactants is crucial for the usefulness of the application. For example, Whitlow et al., Operation, Modeling and Analysis of the Reverse Water Gas Shift Process, AIP Conference Proceedings 654, 1116 (2003) proposed a reaction method in which water is withdrawn from the production stream and sent as a reactant to an electrolysis step to produce oxygen and hydrogen thereby. Further, unreacted carbon dioxide and hydrogen are recycled back to the RWGS reactor to ensure near-complete conversion of the carbon dioxide reactant feed stream.

[0006] Environmental concerns regarding atmospheric carbon dioxide levels have given rise to the desire to consume carbon dioxide and thereby potentially reduce atmospheric carbon dioxide levels. For example, U.S. Patent Application Publication No. 2007 / 0244208 proposes the conversion of carbon dioxide to liquid fuel. According to this process, hydrogen can be generated from water by electrolysis and carbon dioxide can be captured from industrial processes. Carbon dioxide and hydrogen react in the RWGS reaction to produce carbon monoxide or other hydrocarbon precursors. It is suggested that the RWGS reaction can be carried out in a recycle mode up to 100% equilibrium conversion, or alternatively the reaction can be driven by water removal. It is also suggested that heat from other process steps in the overall process can be used to drive the RWGS reaction. Recycling or water removal is proposed optionally with heat integration, but a preferred embodiment uses 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 Earth or in space, the recycling of products from the product stream back to the RWGS reactor creates several complexities and drawbacks. For example, the recycling system requires a compressor (which introduces rotating equipment that may be unreliable and require maintenance), thereby hindering its efficient use within industrial-scale operations. The compressor also requires power, which can result in undesirable inefficiencies and potential CO2 or other emissions associated with power generation. Furthermore, the processes proposed in the prior art focus more on conservation, or the production of raw materials, or fuels, rather than the consumption of carbon dioxide. Net CO2 removal is now more desirable than ever and presents important technical challenges, which are problems that the prior art has not addressed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

[0009] [Non-Patent Document 1] Whitlow et al., Operation, Modeling and Analysis of the Reverse Water Gas Shift Process, AIP Conference Proceedings 654, 1116 (2003) [Non-Patent Document 2] Keith et al., A process for Capturing CO2 from the Atmosphere, Joule (2018) [Summary of the Invention] [Problems to be Solved by the Invention]

[0010] Since large-scale consumption of carbon dioxide is still desired, there is a continuing need for the development of an efficient industrial-scale process for achieving carbon dioxide consumption at levels that can affect atmospheric carbon dioxide levels. [Means for Solving the Problems]

[0011] One or more embodiments of the present invention provide a process for producing syngas, the process comprising: (i) reacting at least a portion of carbon dioxide with hydrogen in an initial reactor to produce an initial product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; and (ii) reacting at least a portion of the unreacted carbon dioxide and unreacted hydrogen in a reactor downstream of the first reactor to thereby produce a product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen.

[0012] Another embodiment of the present invention is a process for producing singas, comprising: (i) supplying a reaction stream containing carbon dioxide; (ii) supplying a reaction stream containing hydrogen; (iii) combining the reaction stream containing carbon dioxide with the reaction stream containing hydrogen to produce a mixed reaction stream; (iv) heating the mixed reaction stream to produce a heated mixed reaction stream; (v) introducing the heated mixed reaction stream into an adiabatic reactor containing a reverse water gas shift catalyst; (vi) reacting hydrogen and carbon dioxide in the adiabatic reactor to thereby produce an initial product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (vii) removing the initial product stream from the adiabatic reactor, wherein the initial product stream has a temperature T1 when exiting the adiabatic reactor; (viii) removing at least a portion of the water in the initial product stream from the initial product stream to produce a water-depleted initial product stream; (ix) introducing the initial product stream into a combustion tube reactor containing a reverse water gas shift catalyst, wherein the combustion tube reactor produces an exhaust stream containing the produced carbon dioxide and excess heat; (x) heating the product stream in the combustion tube reactor to a temperature T3, thereby reacting the carbon dioxide and hydrogen in the initial product stream to produce a final product stream, wherein T3 is greater than or equal to T1; (xi) sending at least a portion of the excess heat to the step of heating the mixed reaction stream to produce a heated mixed reaction stream; and (xii) sending at least a portion of the produced carbon dioxide to the adiabatic reactor or the combustion tube reactor.

[0013] Yet another embodiment of the present invention is a process for producing singas, comprising: (i) supplying a reaction stream containing carbon dioxide; (ii) supplying a reaction stream containing hydrogen; (iii) combining the reaction stream containing carbon dioxide with the reaction stream containing hydrogen to produce a mixed reaction stream; (iv) heating the mixed reaction stream to produce a heated mixed reaction stream; (v) introducing the heated mixed reaction stream into an initial adiabatic reactor containing a reverse water gas shift catalyst; (vi) reacting hydrogen and carbon dioxide in the initial adiabatic reactor to thereby produce an initial product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (vii) removing the initial product stream from the initial adiabatic reactor, wherein the initial product stream has a temperature T1 when exiting the initial adiabatic reactor; (viii) removing at least a portion of the water in the initial product stream from the initial product stream to produce a water-depleted initial product stream; (ix) heating the water-depleted initial product stream to produce a heated water-depleted initial product stream; (x) introducing the heated water-depleted initial product stream into a downstream adiabatic reactor containing a reverse water gas shift catalyst; (xi) reacting hydrogen and carbon dioxide in the downstream adiabatic reactor to thereby produce an intermediate product stream containing 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 exiting the downstream adiabatic reactor; (xiii) removing at least a portion of the water in the intermediate product stream from the intermediate product stream to produce a water-depleted intermediate product stream; (xiv) optionally, heating the water-depleted intermediate product stream to produce a heated water-depleted intermediate product stream at a temperature T2'; (xv) optionally, introducing the heated water-depleted intermediate product stream into a downstream adiabatic reactor containing a reverse water gas shift catalyst and reacting carbon dioxide and hydrogen in the heated water-depleted intermediate product stream to thereby finally produce a final intermediate product stream; (xvi) introducing the intermediate product stream or the final intermediate product stream into a combustion tube reactor containing a reverse water gas shift catalyst, wherein the combustion tube reactor produces an exhaust stream containing the produced carbon dioxide and excess heat.(xvii) A step of heating an intermediate or final intermediate product stream to a temperature T3 in a combustion tube reactor, thereby reacting carbon dioxide and hydrogen in the intermediate product stream or final intermediate product stream to produce a final product stream, where T3 is greater than or equal to T2 and T3 is greater than or equal to T1; (xviii) A step of sending at least a part of the excess heat to the step of heating the mixed reaction stream to produce a heated mixed reaction stream or to the step of heating the initial product stream to produce a heated initial product stream; (xix) A step of sending at least a part of the produced carbon dioxide to the adiabatic reactor, the downstream adiabatic reactor, or the combustion tube reactor.

[0014] Still other embodiments of the present invention provide an RWGS system comprising: (i) An initial RWGS reactor containing a reverse water gas shift catalyst, adapted to facilitate the reaction of hydrogen and carbon dioxide to produce an initial product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (ii) A water removal unit downstream of the initial RWGS reactor for removing water from the initial product stream; (iii) One or more optional intermediate RWGS reactors placed in series downstream of the initial RWGS reactor, each containing a water gas shift catalyst and adapted to facilitate the reaction of hydrogen and carbon dioxide to produce an intermediate product stream and finally a final intermediate product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (iv) Optionally, a water removal unit for removing water from the intermediate product stream and the final intermediate product stream; (v) A final RWGS reactor downstream of the initial RWGS reactor and the one or more optional intermediate RWGS reactors and placed in series therewith, containing a water gas shift catalyst and adapted to facilitate the reaction of hydrogen and carbon dioxide to produce a final product stream containing carbon monoxide, water, hydrogen, and carbon dioxide. BRIEF DESCRIPTION OF THE DRAWINGS

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DETAILED DESCRIPTION OF THE INVENTION

[0026] 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 high conversion rates while maintaining an overall balance of reaction efficiency. This process utilizes the reverse water gas shift (RWGS) reaction within a multi-step reaction scheme that optionally includes both heat integration and water removal to achieve overall process efficiency. Further, the reaction conditions are adjusted at each stage to achieve overall reaction efficiency. Thus, while the prior art has proposed recycling unreacted carbon dioxide back to the RWGS reactor to drive complete conversion of carbon dioxide, the present invention achieves desirable efficiencies at industrially important levels. Further, when combined with heat integration and / or separation of components between reaction steps, additional overall efficiency can be realized.

[0027] Process Overview Two-Step Embodiment The process according to the present invention can be described with reference to FIG. 1, which shows a reverse water gas shift (RWGS) process 11 including an initial RWGS reaction step 22 (which may also be referred to as the first RWGS reaction step 22) and a final RWGS reaction step 32 that follows in series thereafter. A carbon dioxide (CO2) stream 21 and a hydrogen (H2) stream 23 can be combined to produce a mixed reaction stream 25, which is then heated in a heating step 24 (e.g., in a heat exchanger). The heated mixed reaction stream 27 is then 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).

[0028] Heat may be supplied to the heating step 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 step may be received by the heating step 24. For example, as shown in FIG. 1 and described in more detail below herein, excess heat in the effluent stream 31 from the final RWGS reaction step 32 can be sent to the heating step 24. In an optional embodiment where carbon dioxide is produced in the generation of heat, such as at the heat source 26, the produced carbon dioxide can be sent back to the first RWGS reaction step 22 that can convert it at least partially to carbon monoxide. For example, a stream 35 containing the produced carbon dioxide can be combined with the carbon dioxide feed stream 21, the mixed stream 25, or introduced directly into the reaction step 22. Alternatively, the produced carbon dioxide may be sent to the final RWGS reaction step 32 or to an intermediate point in the process for the conversion of carbon monoxide via the RWGS reaction.

[0029] The CO and H2O products, along with any unreacted reactants, are sent as product stream 33 from the first RWGS reaction step 22 to the second RWGS reaction step 32. In one or more embodiments, product stream 33 may undergo water removal in water removal step 38 prior to the final RWGS reaction step 32, whereby water removal step 38 produces a water-lean product stream 33'. The water-lean product stream 33' may then be introduced into the final RWGS reaction step 32.

[0030] Heat 39 may be supplied from heat source 36 to the final RWGS reaction step 32, which produces an exhaust stream 31 that includes heat not consumed by reaction step 32 (i.e., excess heat) and optionally the produced carbon dioxide. As described above, the excess heat from the RWGS reaction step 32 may be supplied to upstream steps, such as heating step 24, via exhaust stream 31 as shown in FIG. 1. Although not shown, the excess heat in exhaust stream 31 may be used to preheat product streams 33, 33' before they enter the final RWGS reaction step 32. Similar to heat source 26, the produced carbon dioxide in exhaust stream 31 can be sent back to an upstream RWGS reaction (e.g., the first RWGS reaction step 22). For example, a stream 45 containing the produced carbon dioxide from exhaust stream 31 can be combined with carbon dioxide feed stream 21, mixture 25, or supplied directly to reaction step 22.

[0031] FIG. 1 shows the final RWGS reaction step 32 with heat 39 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 the arrangement shown with respect to reaction step 22 where heating occurs before entering the reactor. Those skilled in the art will also understand that the preheating of the stream or the direct heating of the reaction stream during the reaction step may depend on the type of reactor chosen (e.g., adiabatic reactor or non-adiabatic reactor).

[0032] CO2 and H2 within the product stream 33 (or lean stream 33’) react within the final RWGS reaction step 32 to produce CO and H2O, which exit the final RWGS reaction step 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 separation step 46. For example, separation step 46 may remove water via water stream 51. In addition to or instead of water removal, at least a portion of the hydrogen within the final product stream may be removed (e.g., by a membrane) to produce a hydrogen-rich stream 53. Similarly, in addition to or instead of the separation of water and / or hydrogen, carbon dioxide may optionally be separated to produce a carbon dioxide-rich stream 55, and / or carbon monoxide may optionally be separated to produce a carbon monoxide-rich stream 57.

[0033] In one or more embodiments, the final product stream 43 is a syngas stream. Those skilled in the art will understand that separation and / or purification can be performed on the product stream 43 to produce a modified syngas stream 61. For example, components can be recovered (e.g., recovery of H2O, H2, CO, and / or CO2), purification can be performed, and / or the ratio of components can be manipulated to produce a modified syngas stream 61. In one or more embodiments, for example, after a separation step that produces a carbon dioxide-rich stream 55, the carbon dioxide contained in stream 43 can be sent back to an upstream RWGS reaction step to convert at least a portion of the carbon dioxide to carbon monoxide. For example, the carbon dioxide-rich stream 55 can 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 an intermediate point in the process for converting carbon dioxide to carbon monoxide via the RWGS reaction. Although FIG. 1 shows separation step 46 as a single step, it will be understood that multiple separation steps may be present to achieve the desired separation and / or purification.

[0034] Multi-step process In one or more embodiments, the process of the present invention includes three or more reaction steps. In one or more embodiments, the final step is operated at a higher temperature than the preceding reaction steps. The reaction steps preceding the final RWGS reaction step (which include the initial RWGS reaction step and any intermediate RWGS reaction steps) may each be carried out at the same temperature. In other embodiments, one or more of the intermediate RWGS reaction steps are carried out at a temperature above the initial RWGS step. In certain embodiments, each intermediate RWGS reaction step is carried out at a higher temperature than the preceding step. In still other embodiments, each step of the multi-step process is randomly operated with respect to temperature. In one or more embodiments, water is removed from the product stream exiting one or more of the RWGS reaction steps before being sent to a subsequent reaction step.

[0035] An exemplary multi-step process can be described with reference to FIG. 2, which shows a three-step reaction process 111 including an initial RWGS reaction step 122, an intermediate RWGS reaction step 132, and a final RWGS reaction step 152. Although not shown, process 111 may include more than 1, more than 3 in other embodiments, more than 10 in other embodiments, more than 20 in other embodiments, and more than 100 intermediate RWGS reaction steps in other embodiments. In these or other embodiments, process 111 may include less than 100, less than 30 in other embodiments, and less than 10 intermediate RWGS reaction steps in other embodiments. In one or more embodiments, the process of the present invention may include from about 1 to about 100, from about 2 to about 30 in other embodiments, and from about 3 to about 10 intermediate RWGS reaction steps.

[0036] Referring again to FIG. 2, the CO2 stream 121 and the H2 stream 123 are combined into a mixed reaction stream 125, heated in a heating step 124 to produce a heated stream 127, and sent to an initial RWGS reaction step 122, where at least a portion of the CO2 and H2 are converted to CO and H2O in the presence of a catalyst to produce a product stream 133. Similar to 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. Also, in one or more embodiments, the mixed reaction stream 125 (as well as the reaction stream 25 described above) can be procured directly, and thus it will be understood that the CO2 stream 121 and the H2 stream 123 may optionally not be present.

[0037] The heating step 124 may receive heat from one or more heat sources. For example, heat 129 may be produced 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 shown in FIG. 1, excess heat in the exhaust stream 131 is received from the final RWGS reaction step 152. In another example (not shown), waste heat may be received from an intermediate RWGS reaction step (e.g., step 132) or an intermediate heat source. In embodiments where carbon dioxide is produced in the generation of heat, such as at the heat source 126, the produced carbon dioxide 135 can be sent back to the first RWGS reaction step 122 that can convert it at least partially to carbon monoxide. For example, the produced carbon dioxide can be combined with the carbon dioxide feed stream 121, the mixed stream 125, or introduced directly into the reaction step 122. Alternatively, the produced carbon dioxide may be sent to the final RWGS reaction step 152 or an intermediate point in the process for the conversion of carbon monoxide via the RWGS reaction.

[0038] In one or more embodiments, the product stream 133 from the initial RWGS reaction step 122 can optionally be sent to an optional water removal step 138 to produce a product stream 133' with less water, which is then sent to an intermediate heating step 134 to generate a heated stream 137. Heat 139 may be supplied to the heating step 136 from one or more heat sources. For example, the 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 shown in FIG. 2 and described in more detail below herein, excess heat in the effluent stream 131 from the final RWGS reaction step 152 can be sent to the heating step 134. In embodiments where carbon dioxide is produced in the generation of heat, such as at the heat source 136, the produced carbon dioxide 141 can be sent back to the first RWGS reaction step 122 where it can be at least partially converted to carbon monoxide. For example, the produced carbon dioxide can be combined with the carbon dioxide feed stream 121, the mixed stream 125, or introduced directly into the reaction step 122. Alternatively, the produced carbon dioxide may be sent to the final RWGS reaction step 152 or to an intermediate point in the process for the conversion of carbon dioxide to carbon monoxide via the RWGS reaction. Similar to 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.

[0039] The heating stream 137 is sent from the heating step 134 to the intermediate RWGS reaction step 132, where at least a portion of the CO2 and H2 in the heating stream 137 is converted to CO and H2O to produce an intermediate product stream 143. The intermediate product stream 143 exiting the intermediate RWGS reaction step 132 can 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 pass through one or more water removal steps (not shown) before entering a subsequent intermediate RWGS reaction step. Also, depending on the type of reactor used, one or more intermediate RWGS reaction steps may include a step of preheating the stream before entering the reaction step, or the stream may be heated simultaneously during the intermediate RWGS reaction step.

[0040] Finally, an intermediate product stream (e.g., stream 143) from one or more intermediate RWGS reaction steps is sent to the final RWGS reaction step 152. Prior to the final RWGS reaction step 152, stream 143 may pass through an optional water removal step 148 to produce a product stream 143' with reduced water. The final RWGS reaction step may receive heat 159 from a heat source 156 and produce an effluent stream 131, which may contain excess heat and / or produced carbon dioxide. For example, the excess heat in the effluent stream 131 from the final RWGS reaction step 152 can be sent to upstream process steps such as heating steps 124 and / or 134. Also, the excess heat in the effluent stream 131 can be sent to any of the preceding reaction steps, or the excess heat in the effluent stream 131 can be used to preheat any of the upstream streams. If carbon dioxide is produced in the generation of heat 159, such as at the heat source 156, the produced carbon dioxide 145 can be sent to any of the RWGS reaction steps that can convert it at least partially to carbon monoxide. For example, the produced carbon dioxide can be combined with the carbon dioxide feed stream 121, the mixed stream 125, or introduced directly into one of the reaction steps. Alternatively, the produced carbon dioxide may be sent to the final RWGS reaction step 152 or to an intermediate point in the process for conversion of carbon dioxide to carbon monoxide via the RWGS reaction.

[0041] Within the final RWGS reaction step 152, CO2 and H2 within the product stream 143 react to further produce CO and H2O, which, along with any unreacted reactants, exit the final RWGS reaction step 152 as the final product stream 153. The final product stream 153 may undergo one or more separations, for example within separation step 166. For example, the separation step 166 may remove water via the water stream 161. In addition to, or instead of, water removal, at least a portion of the hydrogen within the final product stream 153 can be removed to produce a hydrogen-rich stream 163. Similarly, in addition to, or instead of, the separation of water and / or hydrogen, carbon dioxide can optionally be separated to produce a carbon dioxide-rich stream 165, and / or a carbon monoxide-rich stream 167.

[0042] In one or more embodiments, the final product stream 153 is a syngas stream. Those skilled in the art will understand that separation and / or purification can be performed on the product stream 153 to produce a modified syngas stream 171. For example, components can be recovered (e.g., recovery of CO, CO2, H2, and / or H2O), purification can be performed, and / or the ratio of components can be manipulated to produce the modified syngas stream 171. In one or more embodiments, for example, after a separation step that produces a carbon dioxide-rich stream 165, the carbon dioxide contained within the stream 153 can be sent back to an upstream RWGS reaction step to convert at least a portion of the carbon dioxide to carbon monoxide. For example, the carbon dioxide-rich stream 165 can be combined with the carbon dioxide feed stream 121. Alternatively, the carbon dioxide-rich stream 165 may be sent back to the final RWGS reaction step 152, or to an intermediate point in the process for converting carbon dioxide to carbon monoxide via an RWGS reaction. Figure 2 shows the separation step 166 as a single step, but it will be understood that there may be multiple separation steps to achieve the desired separation and / or purification.

[0043] Reaction stream In one or more embodiments, the process of the present invention includes supplying carbon dioxide and hydrogen at an appropriate feed rate to an initial RWGS reaction step such that at least 1 mole of hydrogen is supplied per 1 mole of carbon dioxide within the initial RWGS reaction step. In these or other embodiments, excess hydrogen is supplied to the initial RWGS reaction step. For example, the feeds of hydrogen and carbon dioxide can be set to provide a molar ratio of hydrogen to carbon dioxide greater than 1:1, greater than 1.5:1 in other embodiments, greater than 2.5:1 in other embodiments, and greater than 5:1 in other embodiments for the initial RWGS reaction step. In one or more embodiments, the hydrogen and carbon dioxide feeds provide a molar ratio of hydrogen to carbon dioxide of from about 1:1 to about 10:1, from about 1.3:1 to about 5:1 in other embodiments, from about 1.5:1 to about 4:1 in other embodiments, and from about 2.5:1 to about 3.5:1 in other embodiments for the initial RWGS reaction step.

[0044] In one or more embodiments, the carbon dioxide reaction stream (e.g., stream 21, 121) fed to the initial RWGS reaction step (or fed to any pre - mixing step where carbon dioxide and hydrogen are combined) contains more than 50 mol%, more than 85 mol% in other embodiments, more than 90 mol% in other embodiments, more than 95 mol% in other embodiments, more than 98 mol% in other embodiments, and more than 99 mol% in other embodiments of carbon dioxide. In one or more embodiments, the carbon dioxide reaction stream fed to the initial RWGS reaction step (or combined with the hydrogen reaction stream) contains from about 50 mol% to about 100 mol%, from about 75 mol% to about 99.9 mol% in other embodiments, and from about 99 mol% to about 100 mol% of carbon dioxide.

[0045] In one or more embodiments, the hydrogen reaction stream (e.g., stream 23, 123) fed to the initial RWGS reaction step (or fed to any premixing step where carbon dioxide and hydrogen are combined) contains more than 50 mol%, more than 75 mol% in other embodiments, more than 85 mol% in other embodiments, more than 90 mol% in other embodiments, more than 95 mol% in other embodiments, more than 98 mol% in other embodiments, and more than 99 mol% of hydrogen. In one or more embodiments, the hydrogen reaction stream supplied to the initial RWGS reaction step (or combined with the carbon dioxide stream) contains from about 50 to about 100 mol%, from about 75 to about 99.9 mol% in other embodiments, and from about 99 mol% to about 100 mol% of hydrogen.

[0046] In one or more embodiments, the reaction stream introduced into the initial RWGS reaction steps 22, 122 (which may include the mixed stream 25, 125 and the heated stream 27, 127) (i.e., the reactants to be reacted within the initial reaction step) contains at least 50 mol%, at least 75 mol% in other embodiments, at least 90 mol% in other embodiments, and at least 95 mol% of combined carbon dioxide and hydrogen. In these or other embodiments, the reaction stream introduced into the initial RWGS reaction steps 22, 122 contains substantially no methane, i.e., contains less than an amount that would otherwise significantly affect the practice of the present invention. In one or more embodiments, the reaction stream introduced into the initial RWGS reaction steps 22, 122 contains no methane. In one or more embodiments, the reaction stream introduced into the initial RWGS reaction steps 22, 122 contains less than 20 mol%, less than 10 mol% in other embodiments, less than 5 mol% in other embodiments, less than 2 mol% in other embodiments, and less than 1 mol% of methane.

[0047] Similarly, it is desirable to minimize the production of methane within the RWGS reaction. For example, the product stream produced may contain less than 20 mol%, in other embodiments less than 10 mol%, in other embodiments less than 5 mol%, in other embodiments less than 2 mol%, in other embodiments less than 1 mol% methane. In one or more embodiments, the product stream may be substantially free of methane, and in other embodiments the product stream may be methane-free.

[0048] RWGS process conditions In one or more embodiments, the first heating step 24, 124 produces a heated mixed reaction stream 27, 127 having a temperature above 350 °C, in other embodiments above 450 °C, in other embodiments above 500 °C, in other embodiments above 525 °C, which serves as the heat for the stream entering the first RWGS reaction step 22, 122. In these or other embodiments, the first heating step 24, 124 produces a heated mixed reaction stream 27, 127 having a temperature below 700 °C, in other embodiments below 650 °C, in other embodiments below 600 °C. In one or more embodiments, the first heating step 24, 124 produces a heated mixed reaction stream 27, 127 having a temperature of about 450 to about 700 °C, in other embodiments about 500 to about 650 °C, in other embodiments about 525 to about 600 °C. Similarly, any downstream intermediate reaction step, including preheating of the intermediate reaction stream, may be heated to a similar temperature.

[0049] In one or more embodiments, the initial RWGS reaction step (22, 122) is carried out adiabatically. In these or other embodiments, one or more of the initial RWGS and intermediate RWGS reaction steps (132) are carried out adiabatically. In certain embodiments, each of the first RWGS (22, 122) and intermediate RWGS (132) reaction steps is carried out adiabatically. In these or other embodiments, the final RWGS step (32, 152) is carried out adiabatically.

[0050] In this specification, the temperature at which any of the RWGS reaction steps occur is quantified or characterized by the temperature of the product stream immediately exiting the reaction step (e.g., the outlet temperature of the reactor in which the reaction step occurs).

[0051] In one or more embodiments, the initial reaction steps 22, 122 occur at a temperature greater than 300 °C, in other embodiments greater than 450 °C, in other embodiments greater than 500 °C, and in other embodiments greater than 525 °C. In these or other embodiments, the initial reaction steps 22, 122 occur at a temperature less than 1000 °C, in other embodiments less than 800 °C, in other embodiments less than 650 °C, and in other embodiments less than 600 °C. In one or more embodiments, the initial reaction steps 22, 122 occur at a temperature of about 400 to about 1200 °C, in other embodiments about 300 to about 1000 °C, in other embodiments about 450 to about 800 °C, in other embodiments about 500 to about 750 °C, and in other embodiments about 525 to about 600 °C.

[0052] In one or more embodiments, the final RWGS reaction steps 32, 152 occur at a temperature greater than 500 °C, in other embodiments greater than 800 °C, in other embodiments greater than 850 °C, and in other embodiments greater than 900 °C. In these or other embodiments, the final RWGS reaction steps 32, 152 occur at a temperature less than 1200 °C, in other embodiments less than 1100 °C, and in other embodiments less than 1000 °C. In one or more embodiments, the final reaction steps 32, 152 occur at a temperature of about 500 to about 1200 °C, in other embodiments about 800 to about 1200 °C, in other embodiments about 850 to about 1100 °C, and in other embodiments about 900 to about 1000 °C.

[0053] In one or more embodiments, the optional water removal step 38 (as well as 138, 148) removes more than 10%, in other embodiments more than 25%, and in other embodiments more than 50% of the water in the product stream 33. In these or other embodiments, the water removal step 38 removes less than 100%, in other embodiments less than 90%, and in other embodiments less than 70% of the water in the product stream 33. In one or more embodiments, the water removal step 38 removes from about 10% to about 100%, in other embodiments from about 25% to about 90%, and in other embodiments from about 50% to about 90% of the water in the product streams 33, 133, 143.

[0054] The RWGS process, including any of its individual steps, may be carried out over a wide range of pressures including from atmospheric pressure to about 550 psi and further up to 1000 psi or more. The typical reactor pressure can be selected to be compatible 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.

[0055] Heating device In the RWGS step carried out adiabatically, the reaction stream can be preheated, such as in the heating steps 24, 124, 134, using suitable equipment such as, but not limited to, heat exchangers.

[0056] One of ordinary skill in the art can readily determine the appropriate design configuration and material equipment requirements for the heating device (e.g., heat exchanger) based on the desired process conditions without undue calculation or experimentation. For example, the desired temperature of the reaction step can determine the material that can be used to construct the heating device or a portion thereof.

[0057] Thermal energy to the RWGS reaction The heat sent to the reaction stream in the adiabatic reaction step, or the heat sent directly to the reaction step in the non-adiabatic reaction step, can be obtained from various heat sources. For example, the heat can be supplied by the combustion of fossil fuels such as natural gas. Alternatively, the heat can be supplied by electrical energy. For example, the electrical energy can be derived from various sources such as nuclear power, wind power, solar power, hydropower, and the combustion of fuels, optionally with CO2 capture. Instead, the heat can be supplied by the combustion of carbon-free fuels such as hydrogen, which can produce energy without generating carbon dioxide.

[0058] As shown above, if one or more heat sources (e.g., heat sources 126, 136, 156) used to supply thermal energy to the RWGS reaction step generate carbon dioxide during heat generation, the generated carbon dioxide can be optionally captured and returned as a reactant to the RWGS process (e.g., returned to carbon dioxide streams 21, 121). In one or more embodiments, at least 20% of the carbon dioxide produced in the generation of heat for the RWGS reaction step of the present invention (e.g., combustion of fuels such as natural gas), at least 50% in other embodiments, at least 70% in other embodiments, at least 85% in other embodiments, and at least 90% in other embodiments is captured and returned to the process as a reactant.

[0059] RWGS reactor The RWGS reaction step of the present invention can be carried out in a vessel that enables the reaction to occur 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 called a packed-bed reactor). If the RWGS reaction is carried out adiabatically, the reactor may optionally include an adiabatic packed-bed vessel or tank. If the RWGS reaction is carried out non-adiabatically, the reactor may include a heated packed-bed reactor, such as a combustion-tube type packed-bed reactor, a radiation-heated packed-bed reactor, an electrically heated packed-bed reactor, a microwave-heated packed-bed reactor, and a convectively heated packed-bed reactor.

[0060] One of ordinary skill in the art can readily determine the appropriate design configuration and material equipment requirements for a reactor based on the desired process conditions without undue calculation or experimentation. For example, the desired temperature of the reaction step can determine the materials that can be used to construct the reaction vessel, or a portion thereof (e.g., the reaction tube). For example, when a low-temperature RWGS reaction is desired (e.g., a reaction at a temperature of less than about 800° C.), the reactor components can be constructed of stainless steel or other metals or alloys that can withstand a temperature of up to about 800° C. On the other hand, when a high-temperature RWGS reaction is desired (e.g., a reaction of greater than about 800° C.), the reactor components can be constructed of high-grade metals or alloys, such as nickel alloys, that can withstand a temperature of up to about 1200° C.

[0061] An integrated process design advantageously enables a portion of the heat of reaction (i.e., ΔHr) required to drive the RWGS reaction to be supplied from a lower energy system (i.e., a first low-temperature reaction step), which advantageously functions at a higher temperature and thereby reduces the amount of energy that must be transferred to the reaction within the high-temperature RWGS reaction step that drives further CO2 conversion. Thus, by operating the high-temperature RWGS reaction step at a high temperature, the overall CO2 conversion of the process can be advanced beyond the level achieved at lower temperatures without relying on the high-temperature RWGS reaction step to meet all of the heat transfer requirements of the conversion reaction. As a result, the characteristics of the high-temperature RWGS reaction step can be advantageously adjusted to accommodate a smaller load, particularly a heat transfer load, which realizes the overall efficiency, particularly in terms of capital cost requirements. For example, the low-temperature RWGS reaction step can be carried out in a vessel constructed of materials that do not need to withstand the extremely high temperatures of the high-temperature RWGS reaction step. Further, considering that the high-temperature heat transfer requirements are lower than when only one RWGS reaction step is involved in the process, the scale of the reactor design for the high-temperature RWGS reaction step can be reduced.

[0062] Catalyst As indicated above, both high temperature (e.g., above about 800 °C) and low temperature (e.g., about 350 - about 800 °C) RWGS reactions are catalytically promoted. However, the practice of the present invention is not limited to a particular catalyst system so long as the catalyst promotes or otherwise facilitates the reverse water gas shift reaction. Accordingly, reference can be made to reverse water gas shift catalysts. Those skilled in the art will understand that reaction conditions, particularly for any given RWGS reaction, can affect the catalyst system selected, and those skilled in the art will be able to readily select an appropriate catalyst without undue experimentation or calculation.

[0063] In one or more embodiments, a fixed bed catalyst system is used. As will be appreciated by those skilled in the art, this system includes a catalyst material disposed on a suitable support material. Useful support materials are generally known in the art and include materials that can be suitably packed into a reactor (e.g., a tubular reactor).

[0064] 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 the reverse shift reaction occurs. Exemplary high temperature reverse water gas shift catalysts compositionally include iron oxide, chromium oxide, and optionally magnesium oxide. Another example is a catalyst based on oxides of manganese and cesium and / or lanthanide series metals that optionally includes carbonates or oxycarbonates in addition to or instead of oxides and optionally includes platinum together.

[0065] Other high temperature shift catalysts include those disclosed in U.S. Patent Application Publication Nos. 2017 / 0197829, 2015 / 0080482, 2010 / 0105962, 2003 / 0113244, and 2007 / 0142482, which are incorporated herein by reference.

[0066] Water removal method As indicated above, the practice of the present invention may include one or more steps for the removal of water from the product stream. Several techniques can be used. For example, the condensation of water from the product stream can be achieved by a condensation method that involves the removal of heat from the product stream.

[0067] 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 will understand that these membrane systems may require pressure loss across the membrane, the use of a permeate sweep gas that affects water removal, and / or temperature control. In other embodiments, an adsorption method may be used. For example, solid sorbents, metal-organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) may be used. Those skilled in the art will understand that these absorption systems may require temperature control and / or pressure control.

[0068] In one or more embodiments, water is removed by reaction with methane via a steam reforming reaction (which may also be referred to as steam methane reforming (SMR)).

[0069] Carbon dioxide source In one or more embodiments, carbon dioxide can be obtained from various point sources. In one or more embodiments, the carbon dioxide stream can be derived from a carbon dioxide capture process that can be located at various point sources such as combustion operations and various industrial operations. Combustion processes 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, refining, cement production, iron smelting, ferroalloy production, steel production, lime production, and glass production. Carbon dioxide capture techniques can include, but are not limited to, absorption, adsorption, membrane separation, and cryogenic separation. For example, carbon dioxide can be absorbed using amine-based technologies.

[0070] In other embodiments, carbon dioxide can be captured from ambient air (i.e., not at a specific point source). This technique can include direct air capture (DAC), which captures carbon dioxide directly from ambient air. Useful techniques include liquid solvent absorption using an amine or caustic solution. Other techniques include anion exchange polymer resins, metal organic frameworks, adsorption, and membrane separation.

[0071] In certain embodiments, DAC using a potassium hydroxide solution is used to supply a carbon dioxide stream. For example, a useful DAC process is described in Keith et al., A process for Capturing CO2 from the Atmosphere, Joule (2018). Similar processes are also described in U.S. Patent Application Publication Nos. 2017 / 0354925, 2014 / 0271379, 2019 / 0344217, 2019 / 0359894, 2019 / 0336909, which are incorporated herein by reference.

[0072] 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 process of the present invention can be advantageously combined with a direct air capture method, thereby achieving an overall industrially useful carbon dioxide consumption level.

[0073] Hydrogen source 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 required amount of electricity for the electrolysis process may be supplied from alternative and renewable energy sources such as geothermal sources, solar power, wind energy, hydropower, nuclear power, waste combustion, ocean thermal energy conversion or kinematic power generation, or from an off-peak power grid supply.

[0074] In other embodiments, the hydrogen stream may be supplied by reforming, for example, steam reforming of natural gas and autothermal reforming of natural gas.

[0075] In other embodiments, the hydrogen stream may be supplied from off-gas or waste gas from another process, such as a hydrogenation process, a hydrocracking process, or other industrial processes that use or produce hydrogen.

[0076] Use of the product stream In one or more embodiments, the carbon monoxide produced by the implementation of the present invention can be used as a building block for producing various fuels and chemicals.

[0077] In one or more embodiments, the product stream produced by the implementation of the present invention contains a mixture of carbon monoxide and hydrogen, which may be referred to as synthesis gas or syngas. For example, the molar ratio of carbon monoxide to hydrogen may be from about 0.5:1 to about 5:1 or more, in other embodiments from about 1:1 to about 3:1, and in other embodiments from about 1.5:1 to about 2.5:1. As those skilled in the art will understand, the feed rate of hydrogen to carbon dioxide into the process of the present invention, as well as the configured process (e.g., the number of stages), operating conditions (e.g., the temperature of the stages, water removal), and post-synthesis operations of the raw syngas stream, can be adjusted to supply a product stream having the desired molar ratio of carbon monoxide to hydrogen.

[0078] In one or more embodiments, the product stream produced by the process of the present invention is a syngas stream that can be subjected to a Fischer-Tropsch process to produce hydrocarbons such as diesel oil, gasoline, naphtha, wax, LPG, or methane.

[0079] In other embodiments, the product stream produced by the process of the present invention is a syngas stream used in the production of methanol (i.e., methanol synthesis) or other alcohol syntheses.

[0080] A system for carrying out the process of the present invention (this system generally includes RWGS reactors arranged in series, together with an optional heating and water removal unit located between the RWGS reactors) can be configured by a person skilled in the art without undue experimentation or calculation. In this regard, a person skilled in the art can easily select appropriate equipment, such as pipes or other conduits, and arrange one or more elements of the system that are in fluid communication with each other (for example, to move materials between various reactors or to recycle certain materials within the system), and / or one or more elements of the system that are in thermal communication with each other (for example, 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 make appropriate measurements thereof in accordance with the practice of the present invention.

[0081] To illustrate the practice of the present invention, the following examples were simulated. However, the examples should not be regarded as limiting the scope of the present invention. The claims serve to define the present invention.

Examples

[0082] The examples were simulated using the process simulator Aspen Plus (trademark) manufactured by Aspen Technology Inc. An overview table of the examples and results is described in Table 10 and FIGS. 9 and 10.

[0083] The following characteristics and parameters of the specific process were common to all simulations: (1) The mixed process feed to the RWGS reactor system consisted of 1500 lbmol / hr of CO2 and 4500 lbmol / hr of H2 at a pressure (considering different pressure losses through different examples) that produced product syngas with an H2 / CO ratio of 3:1, 100°F, and 415 psia; (2) CO2 could be captured, for example, from industrial point source emissions, directly from ambient air (e.g., captured using direct air capture, i.e., “DAC” technology), and procured via pipeline, truck, railroad, ship, or other means; (3) H2 could be produced, for example, via electrolysis of water, steam methane reforming, partial oxidation, pyrolysis, through purification operations, and procured via pipeline, truck, railroad, ship, or other means; (4) The product syngas was produced at 415 psia and 100°F (after cooling); (5) In these examples, heat was supplied to the process by combustion of natural gas with ambient air (e.g., to preheat the feed and supply heat to drive the endothermic RWGS reaction); (6) The natural gas had the following composition: 94.0% methane, 3.5% ethane, 1.5% propane, 0.5% nitrogen, and 0.5% carbon dioxide (composition in mole% units); (7) Alternative means of supplying heat (not simulated) were possible and could include, for example, electric heating, hydrogen fuel, coal, oil, hydrocarbon fuel, other fuels, oxy-fuel combustion; (8) CO2 capture could optionally be included from combustion flue gas, and the captured CO2 could optionally be used as feed to the RWGS reactor; (9) The RWGS reactor was designed and operated such that the RWGS reaction was very close to equilibrium at the outlet of all RWGS reactors. [Comparative Example 1]

[0084] One-step RWGS reaction at 1742°F (950°C) The single-stage RWGS process of this example is shown in Figure 3. A mixed H2+CO2 feed is preheated to 1000°F (538°C) and fed to a combustion-tube type RWGS reactor (similar in design to a steam-methane reformer for producing hydrogen from steam and methane, the design of which is well-known). The RWGS reactor is operated at a high outlet temperature of 1742°F (950°C) representative of the operating temperature of the expensive high-nickel alloy tubes in the combustion-tube type RWGS reactor. The CO2 conversion rate via RWGS is 80%. The product syngas contains 94% H2+CO at a H2:CO ratio of 2.75:1 on a dry basis. The combustion of 291 lbmol / h of natural gas fuel produces 310 lbmol / h of CO2 contained in the flue gas. Additional heat and material balance data are listed in Table 1.

Table 1

[0085] Single-stage RWGS at 1000°F (538°C) The single-stage RWGS process of this example is shown in Figure 4. A mixed H2+CO2 feed is preheated to 1000°F (538°C) and fed to a combustion-heater type RWGS reactor (similar in design to a typical purification combustion heater, the design of which is well-known). The RWGS reactor is operated at a low outlet temperature of 1000°F (538°C) representative of the operating temperature of the low-cost stainless steel tubes in the combustion-heater type RWGS reactor, and an alternative low-temperature RWGS process configuration (not shown) may include waste heat recovery (e.g., without dedicated combustion) and / or an adiabatic reactor (e.g., a packed bed). The CO2 conversion rate via this single-stage RWGS is 54%. The product syngas contains 87% H2+CO at a H2:CO ratio of 4.58:1 on a dry basis. The combustion of 166 lbmol / h of natural gas fuel produces 177 lbmol / h of CO2 contained in the flue gas. Additional heat and material balance data are listed in Table 2.

Table 2

[0086] Data from Comparative Examples 1 and 2 show that the CO2 conversion rate via the RWGS reaction through a one - step RWGS process for a given feed (in this case 1500 lbmol / h of CO2 and 4500 lbmol / h of H2) under similar operating conditions is a strong function of the RWGS reactor outlet temperature, as shown by the comparison of Comparative Example 1 at 1742°F showing an 80% CO2 conversion rate versus Comparative Example 2 at 1000°F showing a 54% CO2 conversion rate.

[0087] Additional simulation results for a one - step RWGS process operated at RWGS reactor outlet temperatures ranging from 400°F to 2400°F are shown in Table 3 and Figure 5.

Table 3

[0088] Two - step RWGS at 1742°F and 1742°F with water knockout via cooling and condensation The two - step RWGS process of this example is shown in Figure 6. A mixed H2 + CO2 feed is pre - heated to 1000°F and fed to a first - stage combustion - tube - type RWGS reactor where the RWGS reactor is operated at a high outlet temperature of 1742°F (950°C). The syngas is cooled to 100°F and much of the water (present in the syngas effluent of the first RWGS reactor stage) produced by the RWGS reaction in the first RWGS reactor stage is condensed and removed (99.2% removal). The syngas is reheated again to 1000°F and fed to a second - stage combustion - tube - type RWGS reactor where the RWGS reactor is operated again at a high outlet temperature of 1742°F (950°C). The overall CO2 conversion rate via RWGS in the effluents of the first and second - stage RWGS reactors is 80% and 95% respectively. The product syngas contains 98% H2 + CO with a H2:CO ratio of 2.16:1 on a dry basis.

[0089] The two-stage RWGS product syngas of Example 3 is improved compared to the single-stage RWGS product syngas of Comparative Examples 1 and 2, having a higher CO2 conversion rate, a higher H2+CO content (the target synthesis reactant), and an H2:CO ratio close to 2 (a typical target H2:CO ratio for Fischer-Tropsch synthesis, methanol synthesis, and other synthesis reactions). The combustion of 291 lbmol / hour of natural gas fuel during the first stage produces 310 lbmol / hour of CO2 contained in the flue gas from the first stage. The combustion of 183 lbmol / hour of natural gas fuel during the second stage produces 195 lbmol / hour of CO2 contained in the flue gas from the second stage. Additional heat and material balance data are provided in Table 4.

[0090] Additional utility of the two (or multi)-stage RWGS reactor process is recognized when the stages are designed differently (including metallurgy and / or construction materials) or operated at different operating conditions. A wide range of different designs and operating conditions are possible. Different designs of the stages (including and / or construction materials), including water removal, including heat integration, operation of the stages at different RWGS reactor outlet temperatures, and / or combinations are of particular interest as shown in the following additional examples. [Table 4] [Example 4]

[0091] Two-stage RWGS at 1000°F and 1742°F, including heat integration and not including inter-stage water removal The two - stage RWGS process of this example is shown in Figure 7. A mixed H2+CO2 feed is preheated to 1249°F and fed to an adiabatic RWGS reactor (e.g., a packed catalyst bed). Sufficient RWGS catalyst is supplied to get very close to the equilibrium of the RWGS reaction, and the reacted gas exits the first - stage RWGS reactor at 1000°F. An alternative design (not shown) could have used a convective - heated RWGS reactor to achieve a similar (or improved) CO2 conversion rate. The first - stage RWGS reactor effluent gas is fed to a second - stage combustion - tube - type RWGS reactor. The second - stage RWGS reactor is operated at a high outlet temperature of 1742°F (950°C). Without inter - stage water removal, the overall CO2 conversion rate results are 54% and 80% respectively, similar to the series combination of Comparative Example 2 and 1. Similar to Comparative Example 1, the combustion of 291 lbmol / h of natural gas fuel produces 310 lbmol / h of CO2 contained in the flue gas. Additional heat and material balance data are described in Table 5.

[0092] The CO2 conversion rate of this Example 5 is similar to that of Comparative Example 1, but the significant benefit of this Example 5 (compared to Comparative Example 1) lies in the lower - cost equipment design and metallurgy (or construction materials) of the first RWGS stage related to its low - temperature operation and packed - bed reactor design. Less conversion occurs during the second stage, and the size of the expensive combustion - tube - type RWGS reactor, which includes high - nickel alloy tubes, is significantly reduced (compared to Comparative Example 1).

Table 5

[0093] Two - stage RWGS at 1000°F and 1742°F, including heat integration and 50% inter - stage water removal using a high - temperature membrane The two - stage RWGS process of this example is shown in Figure 7. This Example 5 is similar to the previous Example 4. However, it is excepted that 50% of the water generated by the RWGS reaction during the first RWGS reactor stage (present in the syngas effluent during the first RWGS reactor stage) is removed using a high - temperature membrane system. The overall CO2 conversion rate via RWGS in the effluents of the first and second stage RWGS reactors is 54% and 84% respectively. The product syngas contains 95% H2 + CO at a H2:CO ratio of 2.55:1 on a dry basis. The combustion of 285 lbmol / h of natural gas fuel produces 304 lbmol / h of CO2 contained in the flue gas. Additional heat and material balance data are described in Table 6.

[0094] The benefits of lower - cost equipment design (discussed above in Example 4) also apply to this Example 5. Further, compared to Example 4, the CO2 conversion rate increases from 80% to 84%, and beneficial reductions are observed in the heat transfer load (resulting in a smaller facility), fuel combustion, and CO2 contained in the flue gas. Both cost and performance are improved compared to the single - stage RGWS designs of Comparative Examples 1 and 2.

Table 6

[0095] Two - stage RWGS at 1000°F and 1742°F with 90% inter - stage water removal using heat - integrated and high - temperature sorbents The two - stage RWGS process of this example is shown in Figure 7. This Example 6 is similar to the previous Example 5. However, it is excepted that 90% of the water generated by the RWGS reaction during the first RWGS reactor stage (present in the syngas effluent during the first RWGS reactor stage) is removed using a high - temperature adsorbent system. The overall CO2 conversion rate via RWGS in the effluents of the first and second stage RWGS reactors is 54% and 88% respectively. The product syngas contains 96% H2 + CO with an H2:CO ratio of 2.39:1 on a dry basis. The combustion of 280 lbmol / h of natural gas fuel produces 299 lbmol / h of CO2 contained in the flue gas. Additional heat and material balance data are described in Table 7.

[0096] The benefits of lower - 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 beneficial reductions are observed in the heat transfer load (resulting in a smaller facility), fuel combustion, and CO2 contained in the flue gas. Both cost and performance are improved compared to the single - stage RGWS designs of Comparative Examples 1 and 2.

Table 7

[0097] Three - stage RWGS at 1000°F, 1000°F, and 1742°F, including heat integration and 50% inter - stage water removal using a high - temperature adsorbent The three-stage RWGS process of this example is shown in Figure 8. A mixed H2+CO2 feed is preheated to 1249°F and fed to an adiabatic RWGS reactor (e.g., a packed catalyst bed). Sufficient RWGS catalyst is provided to get very close to the equilibrium of the RWGS reaction, and the reacted gas exits the first-stage RWGS reactor at 1000°F. 50% of the water produced by the RWGS reaction during the first RWGS reactor stage (present in the syngas effluent of the first RWGS reactor stage) is removed using a high-temperature adsorbent system. The water-lean first-stage RWGS reactor effluent gas is reheated to 1047°F and fed to the second-stage adiabatic RWGS reactor, and again, sufficient RWGS catalyst is provided to get very close to the equilibrium of the RWGS reaction, and the reacted gas exits the second-stage RWGS reactor at 1000°F. 50% of the water present in the syngas effluent of the second RWGS reactor stage is removed using a high-temperature adsorbent system. The water-lean second-stage RWGS reactor effluent gas is fed to the third-stage combustion-tubular RWGS reactor. The third-stage RWGS reactor is operated at a high outlet temperature of 1742°F (950°C). The overall CO2 conversion via RWGS in the effluents of the first, second, and third-stage RWGS reactors is 54%, 63%, and 88% respectively. The product syngas contains 96% H2+CO with an H2:CO ratio of 2.42:1 on a dry basis. The combustion of 281 lbmol / h of natural gas fuel results in 300 lbmol / h of CO2 contained in the flue gas. Additional heat and material balance data are described in Table 8.

[0098] The benefits of lower-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 are observed in the heat transfer load (resulting in a smaller facility), fuel combustion, and CO2 contained in the flue gas. Both cost and performance are improved compared to the single-stage RGWS designs of Comparative Examples 1 and 2.

[0099] Additional stages (e.g., 4, 5, 100+) are possible. The benefits of a highly integrated multi-stage system, while applicable to large-scale systems, are particularly advantageous in small-scale systems where efficient and / or advanced manufacturing and assembly techniques (e.g., 3D printing, etching, repeat parts, factory manufacturing) can be used, for example, to minimize manufacturing costs.

Table 8

[0100] Three-stage RWGS at 1000°F, 1000°F, and 1742°F, including heat integration and 90% inter-stage water removal using a high-temperature membrane The three-stage RWGS process of this example is shown in Figure 8. This Example 8 is similar to the previous Example 7, except that 90% of the water (produced by the RWGS reaction) present in the syngas effluent during the first and second RWGS reactor stages is removed using a high-temperature membrane system. The overall CO2 conversion rates in the effluents of the first, second, and third stage RWGS reactors are 54%, 71%, and 93% respectively. The product syngas contains 98% H2+CO at a H2:CO ratio of 2.24:1 on a dry basis. Combustion of 277 lbmol / hr of natural gas fuel produces 295 lbmol / hr of CO2 contained in the flue gas. Additional heat and material balance data are described in Table 9.

[0101] The benefits of lower-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 are observed in the heat transfer load (resulting in a smaller facility), fuel combustion, and CO2 contained in the flue gas. Compared to the two-stage Example 6, the CO2 conversion rate increases from 88% to 93%, and beneficial reductions are observed in the heat transfer load (resulting in a smaller facility), fuel combustion, and CO2 contained in the flue gas. Both cost and performance are improved compared to the single-stage RGWS designs of Comparative Examples 1 and 2.

Table 9

[0102] Three-stage RWGS at 1000°F, 1000°F, and 1742°F, including heat integration, 90% inter-stage water removal using a high-temperature membrane, 90% CO2 capture from flue gas, and H2 feed adjustment to achieve a product syngas H2 / CO ratio = 2.0 The three-stage RWGS process of this example is shown in Figure 9. This Example 9 is similar to the previous Example 8. However, except that a CO2 capture system (e.g., an amine-based or other CO2 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 shown), and blended with the fresh CO2 feed to the RWGS reactor system. The H2 feed to the RWGS reactor system is adjusted to achieve the specified target H2:CO ratio (which is 2.0 in this Example 9) in the product syngas. The overall CO2 conversion rates in the effluents of the first, second, and third stage RWGS reactors are 42%, 63%, and 90% respectively. The product syngas contains 97% H2+CO at a H2:CO ratio of 2.00:1 on a dry basis. Combustion of 317 lbmol / h of natural gas fuel produces 338 lbmol / h of CO2 contained in the flue gas before the CO2 capture system and 34 lbmol / h of CO2 contained in the flue gas after the CO2 capture system. Additional heat and material balance data are listed in Table 10.

[0103] Compared to Example 8, the CO2 contained in the flue gas after the CO2 capture system is significantly reduced from 295 lbmol / hour to 34 lbmol / hour, and the CO + H2 contained in the product syngas nominally increases by 10% from 4500 lbmol / hour to 4955 lbmol / hour, and a target H2:CO ratio of 2.0 is achieved in the product syngas. As illustrated by this example, by using the adjustment of the H2 feed stream, CO2 feed stream, CO2 capture and / or recycle stream, and other operating parameters (such as temperature, pressure, water removal) in the RWGS reactor system, the production rate of the product syngas, the H2:CO ratio of the product syngas, and the molar percentage of H2 + CO in the product syngas can be controlled, including. Recycling a portion of the product syngas to the RWGS reactor system (e.g., to the feed or an intermediate point during the RWGS process), removing and / or adding components (e.g., from the product syngas), and / or using other purification methods known in the art may also affect the product syngas.

Table 10

[0104] An overview of the example simulations is shown in Table 10. Plots of the CO2 conversion rate (Figure 10) and CO2 natural gas bleed / converted CO2 (Figure 11) versus water removal (different curves) and the number of RWGS reactor stages are shown in Figures 10 and 11. The examples clearly show the benefits of a multi-stage RWGS reactor including inter-stage water removal, especially when water removal is carried out in situ with heat integration. CO2 emissions can be further reduced and / or avoided by other heating means (such as electricity, H2 combustion, waste heat integration, etc.) and / or by CO2 capture from the flue gas.

[0105] Various modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The invention should not be unduly limited to the exemplary embodiments described herein.

Claims

1. A process for producing singas, comprising: (i) reacting at least a portion of carbon dioxide with hydrogen in an initial reactor to produce an initial product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; (ii) reacting at least a portion of the unreacted carbon dioxide and the unreacted hydrogen in a reactor downstream of the initial reactor, thereby producing a product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; wherein the initial product stream has a temperature T1 when it exits the initial reactor, the product stream has a temperature T2 when it exits the downstream reactor, T2 > T1, T1 is from 300 to 1000 °C, and T2 is from 500 to 1200 °C; the initial reactor is an adiabatic reactor and the downstream reactor is a non-adiabatic combustion tube reactor. A process.

2. The process according to claim 1, wherein the carbon dioxide and the hydrogen comprise at least 50 mol% of the reactants in the initial reactor.

3. The downstream reactor is a final reactor in series, the product stream produced by the final reactor is a final product stream, and the process further comprises reacting unreacted carbon dioxide and unreacted hydrogen in the initial product stream in one or more reactors located between the initial reactor and the final reactor. The process according to claim 1.

4. The process according to claim 3, further comprising (i) removing at least a portion of the water from the initial product stream before the step of reacting at least a portion of the unreacted carbon dioxide and the unreacted hydrogen in the final reactor, or (ii) removing at least a portion of the water from an intermediate product stream before the step of reacting unreacted carbon dioxide and unreacted hydrogen in one or more reactors located between the initial reactor and the final reactor.

5. The process further comprises introducing heat into the final reactor, the step of introducing heat into the final reactor generates carbon dioxide and produces an exhaust stream containing carbon dioxide, the process comprises capturing at least a portion of the carbon dioxide contained in the exhaust stream to generate a capture stream containing carbon dioxide. The process according to claim 3, further comprising introducing at least a portion of the carbon dioxide contained in the capture stream into the final reactor or into a step upstream of the final reactor for conversion to carbon monoxide.

6. The process according to claim 3, further comprising converting at least a portion of the final product stream into at least one of a hydrocarbon and an alcohol.

7. The step of reacting at least a portion of the carbon dioxide with hydrogen produces an effluent stream containing excess heat, The process according to claim 1, further comprising transferring the excess heat to at least one of the carbon dioxide-containing feed stream and the mixed reaction stream in which the carbon dioxide-containing feed stream and the hydrogen stream are combined, prior to the step of reacting at least a portion of the carbon dioxide with hydrogen in an initial reactor.

8. The step of introducing heat into the final reactor includes introducing heat from a carbon-free heat source, The process according to claim 5, wherein the carbon-free heat source includes at least one of electricity, nuclear power, wind power, solar power, hydropower, combustion of hydrogen, and combustion of carbon-free fuel.

9. Capturing carbon dioxide from ambient air to produce a direct air capture stream containing carbon dioxide, and The process according to claim 1, further comprising introducing at least a portion of the direct air capture stream containing carbon dioxide into the initial reactor.

10. A process for producing syngas, comprising: (i) supplying a reaction stream containing carbon dioxide; (ii) supplying a reaction stream containing hydrogen; (iii) combining the reaction stream containing carbon dioxide with the reaction stream containing hydrogen to produce a mixed reaction stream; (iv) heating the mixed reaction stream to produce a heated mixed reaction stream; (v) introducing the heated mixed reaction stream into an adiabatic reactor containing a reverse water gas shift catalyst; (vi) reacting the hydrogen and the carbon dioxide in the adiabatic reactor to thereby produce an initial product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; (vii) removing the initial product stream from the adiabatic reactor, wherein the initial product stream has a temperature T1 when exiting the adiabatic reactor. Step (viii) of removing at least a portion of the water in the initial product stream from the initial product stream to produce a water-lean initial product stream; Step (ix) of introducing the initial product stream into a non-adiabatic combustion tube reactor containing a reverse water gas shift catalyst, the combustion tube reactor producing an exhaust stream containing produced carbon dioxide and excess heat; Step (x) of heating the initial product stream to a temperature T3 within the combustion tube reactor, thereby reacting the carbon dioxide and the hydrogen within the initial product stream to produce a final product stream, where T3 is greater than or equal to T1; Step (xi) of sending at least a portion of the excess heat to the step of heating the mixed reaction stream to produce a heated mixed reaction stream; Step (xii) of sending at least a portion of the produced carbon dioxide to the adiabatic reactor or the combustion tube reactor; A process comprising. Claim 11 A process for producing syngas, comprising: Step (i) of supplying a reaction stream containing carbon dioxide; Step (ii) of supplying a reaction stream containing hydrogen; Step (iii) of combining the reaction stream containing carbon dioxide with the reaction stream containing hydrogen to produce a mixed reaction stream; Step (iv) of heating the mixed reaction stream to produce a heated mixed reaction stream; Step (v) of introducing the heated mixed reaction stream into an initial adiabatic reactor containing a reverse water gas shift catalyst; Step (vi) of reacting the hydrogen and the carbon dioxide within the initial adiabatic reactor, thereby producing an initial product stream containing carbon monoxide, water, hydrogen, and carbon dioxide; Step (vii) of removing the initial product stream from the initial adiabatic reactor, the initial product stream having a temperature T1 when exiting the initial adiabatic reactor; Step (viii) of removing at least a portion of the water in the initial product stream from the initial product stream to produce a water-lean initial product stream; Step (ix) of heating the water-lean initial product stream to produce a heated water-lean initial product stream; Step (x) of introducing the heated water-lean initial product stream into a downstream adiabatic reactor containing a reverse water gas shift catalyst; (xi) reacting the hydrogen and the carbon dioxide in the downstream adiabatic reactor to thereby produce an intermediate product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (xii) removing the intermediate product stream from the downstream adiabatic reactor, the intermediate product stream having a temperature T2 when it exits the downstream adiabatic reactor; (xiii) removing at least a portion of the water in the intermediate product stream to produce an intermediate product stream having a low water content; (xiv) introducing the intermediate product stream having a low water content into a non-adiabatic combustion tube reactor containing a reverse water gas shift catalyst, the combustion tube reactor producing an exhaust stream containing produced carbon dioxide and excess heat; (xv) heating the intermediate product stream having a low water content in the combustion tube reactor to a temperature T3, thereby reacting the carbon dioxide and the hydrogen in the intermediate product stream having a low water content to produce a final product stream, where T3 is greater than or equal to T2 and T3 is greater than or equal to T1; (xvi) sending at least a portion of the excess heat to the step of heating the mixed reaction stream to produce a heated mixed reaction stream or to the step of heating the initial product stream having a low water content to produce a heated initial product stream having a low water content; (xvii) sending at least a portion of the produced carbon dioxide to the initial adiabatic reactor, the downstream adiabatic reactor, or the combustion tube reactor A process comprising.

12. (i) An initial RWGS reactor containing a reverse water gas shift catalyst, adapted to facilitate the reaction of hydrogen and carbon dioxide, and producing an initial product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; (ii) A water removal unit downstream of the initial RWGS reactor for removing water from the initial product stream; (iii) A final RWGS reactor downstream of the initial RWGS reactor and serially and finally positioned relative to the initial RWGS reactor, containing a water gas shift catalyst, adapted to facilitate the reaction of hydrogen and carbon dioxide, and producing a final product stream comprising carbon monoxide, water, hydrogen, and carbon dioxide; Comprising, The initial RWGS reactor is an adiabatic reactor, and the final RWGS reactor is a non-adiabatic combustion tube reactor. RWGS system.

13. The system according to claim 12, further comprising a heat source in thermal communication with the final RWGS reactor, the heat source including an exhaust conduit in thermal communication with one or more upstream heat sources.

14. The system according to claim 13, further comprising a carbon dioxide capture unit, the carbon dioxide capture unit being in fluid communication with the exhaust conduit and adapted to remove carbon dioxide from the exhaust gas exiting the heat source.

15. The system of claim 12, further comprising one or more intermediate RWGS reactors placed in series with and downstream of the initial RWGS reactor, each of the intermediate RWGS reactors including an aqueous gas shift catalyst, the intermediate RWGS reactors being adapted to facilitate the reaction of hydrogen and carbon dioxide to produce an intermediate product stream and ultimately a final intermediate product stream containing carbon monoxide, water, hydrogen, and carbon dioxide, and comprising a water removal unit for removing water from the intermediate product stream and the final intermediate product stream.

16. heating the intermediate product stream with low water content to a temperature T2'; then introducing it into an adiabatic reactor containing a reverse aqueous gas shift catalyst downstream; and reacting the carbon dioxide and hydrogen in the intermediate product stream with low water content before introducing the intermediate product with low water content into the combustion tube reactor. The process of claim 11, comprising.

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