Chemical looping method for producing CO from CO2

Abstract

The present invention relates to a chemical looping process for producing CO from CO, in which NH and CO are repeatedly fed to a reactor. The present invention further relates to the use of NH in a chemical looping process for producing CO from CO, and to a chemical looping reactor.

Description

[Technical Field]

[0001] In the near future, synthetic hydrocarbon fuels will be needed to decarbonize industries that are difficult to electrify. The most obvious example is aviation fuel, which will need to be blended with increasing amounts of sustainable hydrocarbons. CO2 may be used as a feedstock to produce aviation fuel and other synthetic hydrocarbon fuels. However, the yield and efficiency of CO2 as a feedstock are much lower than when using CO2. Current technological developments to improve CO2-based processes are at a low technology readiness level, and it is unclear whether they will ultimately exceed the efficiency of CO2 conversion to CO2 before producing synthetic hydrocarbons. CO2-to-CO conversion is traditionally performed in a reverse water-gas shift (RWGS) reactor, where hydrogen is used to produce water and CO2 from CO2. One of the disadvantages of the reverse water-gas shift process is the undesirable formation of methane as a byproduct. [Background technology]

[0002] Another process for converting CO2 to CO is chemical looping. Chemical looping is a two-step process in which, in the first step, a redox catalyst, typically a metal oxide, is reduced to its lower oxidation state and / or to its metallic form by a reducing agent. Typical reducing agents for converting CO2 to CO are H2 and methane. In the second step, CO2 is supplied and reduced to CO by the redox catalyst. In this way, high-purity CO can be obtained. Wenzel et al. (Biochemical Pharmacology, 17, 60-68, 2017) describes such a process.

[0003] H2 is a promising reducing agent in this process. However, local and sustainable production of H2 is problematic given the anticipated amounts of H2 required. Locations where pure CO2 is available or where CO2 can be converted into fuel-based chemicals are not accessible for cost-effective, sustainably produced H2 in large quantities. For example, large amounts of sustainable H2 are expected to be produced near the equator. Equatorial regions have abundant solar radiation, making sustainable electricity cheap. Conversely, processing facilities are often located far from the equator. Therefore, transportation and storage of H2 are unavoidable, which is not simple. H2 is known to be difficult to store and transport, particularly due to its low energy density and the safety of H2 storage. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the above, there is a need for an efficient and sustainable chemical looping process for the conversion of CO to CO that utilizes a sustainable reducing agent that is easy to store and transport. Preferably, the sustainable reducing agent is easy to use and therefore can be used directly in a chemical looping process for the conversion of CO to CO. [Means for solving the problem]

[0005] Surprisingly, the inventors have now realized that ammonia (NH3) is a good reducing agent in the process for the conversion of CO2 to CO. NH3 can be produced sustainably and is easy to transport. For example, the energy density of stored (liquid) NH3 is much higher than stored H2. Also, the storage pressure is much lower for NH3 compared to H2, and transport ships are known to integrate NH3 as an energy source for their own propulsion.

[0006] The direct use of NH in a process for converting CO to CO is particularly beneficial because it requires little or no decomposition of NH before feeding it to the reactor. NH decomposition is a process that converts NH to N and H. The decomposition of NH is an endothermic equilibrium reaction, thus requiring an undesirable recycle loop and separation of residual NH from the product stream. Conversely, in the present invention, where NH is fed directly, H is not the end product, but an intermediate product that further reacts to form HO. The conversion of H and O from the redox catalyst to HO is a non-equilibrium reaction, and therefore the overall reaction (NH and O from the redox catalyst to HO and N) is a non-equilibrium reaction. Surprisingly, this improves reaction efficiency, thereby allowing for smaller reactor volumes and eliminating or minimizing the need for recycle and separation of the remaining NH. Furthermore, when the decomposed NH3 is used as a reducing agent, an additional decomposition reactor is required, whereas in the present process, only one reactor is required, which is beneficial from the viewpoint of cost and space requirements. Furthermore, the use of one reactor facilitates process integration, thereby reducing capital and operating costs.

[0007] CO can also be produced in the water-gas shift process (CO + H ⇔ CO and H O), but in such a process undesirable methane is formed as a by-product, which is not beneficial due to the nature of chemical looping.

[0008] The invention will be discussed in more detail below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0009] [Figure 1]The figure shows a chemical looping reactor in two different modes: Mode 1 and Mode 2. Mode 1 corresponds to Step 1, and Mode 2 corresponds to Step 2. In Step 1, NH3 is supplied, and N2 and HO exit the reactor. The equations for the two reactions occurring during Step 1 are shown inside the reactor: NH3 is converted to N2 and H2, and the redox catalyst MxOy is reduced to M and HO by H2. In this figure, the redox catalyst is fully reduced in Step 1; however, the redox catalyst may not be fully reduced and may only be reduced to a lower oxidation state. In Step 2, CO2 is supplied, and CO exits the reactor. The equations for the reactions occurring during Step 2 are shown inside the reactor: CO2 is reduced to CO, and the redox catalyst is oxidized from M to MxOy. These are redox reactions. [Figure 2] The diagram shows a chemical looping reactor in two different modes: Mode 1 and Mode 2. Mode 1 corresponds to Step 1, and Mode 2 corresponds to Step 2. This reactor is a membrane reactor, and the dotted line within it represents an H2-permeable membrane. The section above the membrane is reactor Section 1, and the section below the membrane is reactor Section 2. In Step 1, NH3 is supplied, and N2 exits reactor Section 1. Simultaneously, sweeping gas A is supplied to reactor Section 2. This sweeping gas carries the H2O formed in reactor Section 2 to the outlet of reactor Section 2. The equations for the two reactions occurring during Step 1 are shown within the reactor: the conversion of NH3 to N2 and H2 in reactor Section 1, and the reduction of the redox catalyst MxOy to M and H2O by H2 in reactor Section 2. H2 travels across the membrane from Section 1 to Section 2. In this diagram, the redox catalyst is fully reduced in Step 1; however, redox catalysts may not be fully reduced and may only be reduced to a lower oxidation state. In step 2, CO2 is fed into reactor section 2 and CO exits reactor section 2. The reaction equations that occur during step 2 are shown inside the reactor: CO2 is reduced to CO, and the redox catalyst oxidizes M to MxOy (a redox reaction). No reaction occurs in section 1. [Figure 3]Figure 1 shows the concentration of CO and CO as a function of time in the outlet gas of the oxidation step in the chemical looping process of Example 2. The y-axis is the concentration of CO (filled circles) and CO (filled triangles) in volume percent, and the x-axis is time in minutes. [Figure 4] Figure 1 shows the allocation of H to N as a function of time in the outlet gas of the reduction step in the chemical looping process of Example 2. The y-axis is the volume ratio of H to N (black circles) and the x-axis is time in minutes. DETAILED DESCRIPTION OF THE INVENTION

[0010] In a first embodiment of the invention, the invention relates to the use of NH in a chemical looping process for producing CO from CO by reducing CO to CO with a redox catalyst, wherein NH and CO are repeatedly fed to a reactor containing one or more catalysts, where NH is converted to N and H, and H serves as a reducing agent for reducing the redox catalyst, and the one or more catalysts comprise a redox catalyst for converting CO to CO.

[0011] The present invention further relates to a method for producing CO from CO, wherein NH and CO are repeatedly fed to a reactor containing one or more catalysts, CO is formed in the reactor as CO is fed, and the reaction temperature is 400° C. or higher. Preferably, the one or more catalysts comprise a redox catalyst for converting CO to CO.

[0012] Preferably, for the uses and / or methods of the present invention, the one or more catalysts further comprise a catalyst for converting NH3 to N2 and H2, and / or the redox catalyst for converting CO2 to CO is also a catalyst for converting NH3 to N2 and H2. In a preferred embodiment, the one or more catalysts comprise a redox catalyst for converting CO2 to CO and a catalyst for converting NH3 to N2 and H2.

[0013] The present invention further relates to a chemical looping reactor for producing CO from CO, the reactor comprising a membrane that is permeable to H and that separates the reactor into two sections, the first section containing a catalyst for converting NH to N and H, and the second section containing a redox catalyst for converting CO to CO, the reactor comprising one or more feed inlets and one or more product outlets connected to the first section and one or more feed inlets and one or more product outlets connected to the second section.

[0014] The embodiments disclosed in this document apply to all aspects of the present invention, i.e., the use of NH in a chemical looping process for producing CO from CO, the process for producing CO from CO, and the chemical looping reactor for producing CO from CO.

[0015] CO production from CO2 Chemical looping processes are well known and are also used to produce CO from CO. In such chemical looping processes, a reactor contains a redox catalyst, and the feedstock alternates between a reducing agent and an oxidizing agent. The reducing agent reduces the redox catalyst, and the oxidizing agent oxidizes the redox catalyst; or, stated another way, the redox catalyst oxidizes the reducing agent, and the redox catalyst reduces the oxidizing agent. In the present invention, CO is the oxidizing agent, and NH is the reducing agent. NH reduces the redox catalyst in a two-step reaction mechanism: first, NH is decomposed into N and H, and then H reacts with the redox catalyst to produce HO. The timing of the feedstock switch is determined by the composition of the product stream exiting the reactor. Preferably, the feedstock is switched before it is no longer fully converted; this method prevents at least a portion of the feedstock from exiting the reactor and thereby forming the product stream. Preferably, the feed is switched before the product contains more than 10 wt. % of the feed, based on the total weight of the product stream, more preferably more than 1 wt. %, and most preferably more than 0.1 wt. % of the feed.

[0016] The present invention includes a method for producing CO from CO, wherein NH and CO are repeatedly fed to a reactor containing one or more catalysts, CO is formed in the reactor as CO is fed, and the reaction temperature is 400°C or higher.

[0017] Preferably, in the first step, a feedstock containing NH3 is supplied to the reactor, and in the second step, a feedstock containing CO2 is supplied to the reactor. Thus, the present invention can also be expressed as a method for producing CO from CO2, in which NH3 and CO2 are repeatedly supplied to a reactor containing one or more catalysts, CO is formed in the reactor as CO2 is supplied, the reaction temperature is 400°C or higher, and in the first step, a feedstock containing NH3 is supplied to the reactor, and in the second step, a feedstock containing CO2 is supplied to the reactor.

[0018] Typically, the first and second steps are repeated, so that the first step is repeated after the second step, followed by the second step, etc. The feedstock for the first step, also referred to as the first feedstock, comprises NH, preferably the first feedstock comprises more than 50 wt%, more preferably more than 70 wt%, even more preferably more than 90 wt%, and most preferably more than 99 wt%, of NH, based on the total weight of the first feedstock. The feedstock for the second step, also referred to as the second feedstock, comprises CO, preferably the second feedstock comprises more than 50 wt%, more preferably more than 70 wt%, even more preferably more than 90 wt%, and most preferably more than 99 wt%, of CO, based on the total weight of the second feedstock. Preferably, the first feedstock contains NH3 in the range of 50% to 100% by weight, more preferably 70% to 100% by weight, even more preferably 90% to 100% by weight, and most preferably 99% to 100% by weight, based on the total weight of the first feedstock. The feedstock for the second step is also referred to as the second feedstock, and this second feedstock contains CO2; preferably, the second feedstock contains CO2 in the range of 50% to 100% by weight, more preferably 70% to 100% by weight, even more preferably 90% to 100% by weight, and most preferably 99% to 100% by weight, based on the total weight of the second feedstock.

[0019] In a preferred embodiment, the reactor is purged after the first step. Purging prevents any residual NH from interfering with the oxidation of the redox catalyst during step 2. Furthermore, without purging, the product of step 2 may contain NH, N, or H, which may be undesirable. The optional purge gas after the first step is referred to as a first purge gas. Preferably, the first purge gas is purged into the reactor after the step of supplying NH and before the step of supplying CO. Preferably, the first purge gas is an inert gas that does not oxidize or reduce the redox catalyst; more preferably, the first purge gas comprises one or more of N, HO, He, and Ar, and even more preferably one or more of N, He, and Ar.

[0020] In a preferred embodiment, the reactor is purged after the second step. Preferably, a second purge gas is purged after the step of supplying CO and before the step of supplying NH. Purging prevents any residual CO from interfering with the reduction of the redox catalyst during step 1. Furthermore, without purging, the product of step 1 may contain CO or CO, which may be undesirable. The optional purge gas after the second step is referred to as a second purge gas. Preferably, a second purge gas is purged into the reactor after the step of supplying CO and before the step of supplying NH. Preferably, the second purge gas is an inert gas that does not oxidize or reduce the redox catalyst; more preferably, the second purge gas comprises one or more of N, HO, He, and Ar, and even more preferably one or more of N, He, and Ar.

[0021] Typically, flow during the reaction has plug flow characteristics. As a result, component concentrations are not uniform throughout the reactor. Since the conversion of NH to N and H begins only upon entry, in parts of the reactor closer to the feedstock, insufficient H is being formed, so the reduction of the redox catalyst can occur at an undesirably slow rate.

[0022] Following this, in some reaction situations, metal catalysts can form undesirable metal nitrides that can affect the overall reaction efficiency. Metal nitride formation can be prevented by providing some additional H2 to the NH3-containing feedstock. The addition of H2 reduces the N2 partial pressure, which can then react with the nitrides to form NH3.

[0023] Therefore, to improve reactor efficiency and / or prevent nitride formation, in a preferred embodiment the first feedstock comprises H2, more preferably the first feedstock comprises in the range of 1 to 40 wt. % H2, even more preferably in the range of 2 to 20 wt. %, and most preferably in the range of 4 to 15 wt. %, based on the total weight of the first feedstock.

[0024] H2 can be formed by continuously feeding NH3 in step 1 after the redox catalyst is fully reduced. At that point, H2 is not further converted to HO and is present in the product. This H2 can be stored and mixed with the first feedstock. Alternatively, H2 can be generated by partial pre-decomposition of NH3. In this embodiment, NH3 is also preferably fed in the first step after the redox catalyst is fully reduced, and this H2 is fed to the first feedstock, preferably the first feedstock in the next iteration of the first step, or NH3 is partially decomposed before NH3 is fed to the reactor as the first feedstock.

[0025] In a preferred embodiment, the reaction temperature is between 400°C and 1200°C, preferably between 600°C and 1000°C, more preferably between 650°C and 850°C, and even more preferably between 750°C and 850°C. Higher reaction temperatures accelerate the reaction and improve its efficiency, but too high a temperature requires excessive capital and operational expenditures. Zeng et al. (Nature Reviews Chemistry, volume 2, pages 349-364, 2018) explain that the conversion of CO2 to CO in a chemical looping process is optimal from a thermodynamic standpoint between 650°C and 850°C. Wenzel et al. (Biochemical Pharmacology, 17, 60-68, 2017) show that the optimal temperature range for Fe2O3 as a redox catalyst is between 750°C and 850°C. In a preferred embodiment, the redox catalyst is Fe2O3 and the reaction temperature is in the range of 750°C to 850°C.

[0026] Preferably, the reaction pressure is in the range of 1 to 100 bar, preferably 2 to 50 bar, even more preferably 4 to 20 bar, and most preferably 5 to 10 bar. At higher pressures, higher yields can be obtained. Furthermore, higher pressures are beneficial for downstream processing of the CO formed. At pressures lower than Am, lower conversions may be obtained.

[0027] In a preferred embodiment, the reactor is electrically heated. Electrical heating is advantageous because electricity can be obtained from a sustainable source. Preferably, part of the electricity for heating is generated by a steam turbine powered at least in part by the steam produced in the reactor. Because the reaction temperature is much higher than 100°C, the H2O produced in the reactor is gaseous and therefore steam. Preferably, NH3 is used as the energy source for heating. In this embodiment, NH3 is decomposed and the resulting H2 is oxidized to generate energy for heating.

[0028] In a preferred embodiment, the one or more catalysts comprise a redox catalyst for converting CO to CO and a catalyst for converting NH to N and H; more preferably, the one or more catalysts consist of a redox catalyst for converting CO to CO and a catalyst for converting NH to N and H. Preferably, the one or more catalysts comprise a redox catalyst for converting CO to CO and a catalyst for converting NH to N and H, and the catalyst for converting CO to CO is the same catalyst as the catalyst for converting NH to N and H; more preferably, this same catalyst is iron oxide, and even more preferably, FeO, FeO, or a combination thereof. The redox catalyst for converting CO to CO can also catalyze the conversion of NH to N and H. In a preferred embodiment, the redox catalyst for converting CO to CO is also the catalyst for converting NH to N and H. In this embodiment, an additional catalyst for the conversion of NH to N and H, as defined herein, may be present.

[0029] Redox catalyst for the conversion of CO2 to CO and H2 to H2O For the conversion of CO to CO and H to HO, a redox catalyst is used, which catalyzes both the oxidation of H and the reduction of CO, simultaneously participating in the reaction by abstracting oxygen from CO and providing this oxygen to H. Therefore, this redox catalyst has two functions: as a redox catalyst and as an oxygen carrier. Therefore, in the context of a chemical looping process for converting CO to CO, the redox catalyst is also called an oxygen carrier material. In this document, both the terms "redox catalyst for converting CO to CO" and "oxygen carrier material for converting CO to CO" are used for this redox catalyst. Obviously, this redox catalyst for converting CO to CO is also a redox catalyst for converting H to HO and an oxygen carrier material for converting H to HO. The redox catalyst for converting CO to CO can exist in an oxidized or reduced state. The reduced state does not necessarily mean that the redox catalyst is fully reduced, i.e., in the reduced state, the reduced redox catalyst may still be an oxide. When species of redox catalysts for converting CO to CO are mentioned in this document, these species are mentioned in their oxidized form as metal oxides, and one of the species is mentioned in this document in its oxidation state.

[0030] Zeng et al. (Nature Reviews Chemistry, volume 2, pages 349-364 (2018)) provide a review of redox catalysts for chemical looping. Typical redox catalysts are metal oxides, with good results obtained using iron oxide and copper oxide. Zeng et al. note that adding promoters and supports is a common approach for these redox catalysts. Wenzel et al. (Journal of CO2 Utilization, Volume 17, January 2017, Pages 60-68) describe the chemical looping of CO2 and H2 to CO and HO, in which promoted iron oxide is investigated as a redox catalyst. Galvita et al. (Ind. Eng. Chem. Res. 2013, 52, 25, 8416-8426) also investigated iron oxide and promoted iron oxide redox catalysts for the chemical looping of CO2 and H2 to CO and HO.

[0031] In a preferred embodiment, the redox catalyst for converting CO2 to CO is a metal oxide, preferably the metal is a transition metal, more preferably the metal is selected from the list consisting of Cu, Fe, Mo, and W, and most preferably Fe. Even more preferably, the redox catalyst for converting CO2 to CO is Fe2O3, Fe3O4, or a mixture thereof. Fe2O3 is known to give good results in the chemical looping of CO2 and H2 to CO and H2O. In this process, Fe2O3 is reduced to Fe. Good results have also been shown with Fe3O4, where Fe3O4 is reduced to FeO. The use of Fe3O4 advantageously prevents the nitration of metallic Fe in the presence of NH3. The nitration of metallic Fe is prevented by the addition of Fe x N y The formation of Fe can reduce catalytic activity.

[0032] In a preferred embodiment, the redox catalyst for converting CO to CO is promoted by a metal promoter, preferably the promoter is selected from the list consisting of alkali metals, rare earth metals, and their oxides, more preferably the promoter is selected from the list consisting of K, Na, Ba, Cs, Li, La, Ce, Al, Ca, Ti, and their oxides, even more preferably the promoter is Ce or its oxide. Preferably the amount of promoter is in the range of 0.01 to 20 wt % based on the total weight of the unsupported catalyst, more preferably in the range of 0.1 to 10 wt % based on the total weight of the unsupported catalyst. A promoter is a substance that enhances the catalytic effect of the catalyst.

[0033] In a preferred embodiment, the redox catalyst for converting CO to CO is mounted on a support. The support can stabilize the size and / or morphology of the metal particles and increase the exposure of their active sites. The support can also affect the catalytic performance. Providing a support improves thermal stability and prevents sintering. Preferably, the support material is a metal oxide or carbon-based support; more preferably, the support material is selected from the list consisting of Al2O3, SiO2, CeO2, MgO, La2O3, TiO2, YO3, ZrO2, CeZrO2, SBA-15, ZSM-5, carbon nanotubes, C, and graphite; most preferably, the support material is SiO2.

[0034] Catalyst for converting NH3 to N2 and H2 Catalysts for converting NH3 to N2 and H2 are well known in the art. Lucentini et al. (Ind. Eng. Chem. Res. 2021, 60, 18560-18611) provide an overview of such catalysts. Regarding the selection of a catalyst for converting NH3 to N2 and H2, those skilled in the art will know the appropriate materials and conditions from this and other publications. Transition metals are typically used. The reaction is catalyzed by the non-oxidized form of the metal catalyst, although oxidized metals may also function as catalysts. For example, from the metallurgical (steelmaking) field, Hosokai et al. (Environ. Sci. Technol. 2011, 45, 821-826) disclose Fe2O3 and Fe3O4 to catalyze the thermal decomposition of NH3 to H2 and N2, where the formed H2 subsequently reduces the iron oxide to iron. Hosokai et al. report that this is the dominant NH3 decomposition pathway at temperatures above 530°C. Furthermore, Hosokai et al. report that no iron nitride is observed at temperatures of 600°C and 700°C.

[0035] In a preferred embodiment, the catalyst for converting NH to N and H is a metal catalyst or an oxide thereof, preferably a transition metal catalyst or an oxide thereof, more preferably a metal catalyst or an oxide thereof, wherein the metal is selected from the list consisting of Ru, Ni, Rh, Co, Ir, Fe, Pt, Cr, Pd, Cu, Ag, Mo, Gd, and combinations thereof, even more preferably a metal catalyst or an oxide thereof, wherein the metal is selected from the list consisting of Ni, Ru, and Fe.

[0036] In a particularly preferred embodiment, the catalyst for converting NH to N and H is iron oxide. Such a catalyst is also the redox catalyst for converting CO to CO, and advantageously, in the case of the process by using iron oxide, only one catalyst is required. Obviously, in this embodiment, the redox catalyst for converting CO to CO is also iron oxide.

[0037] Good results have been obtained by adding a promoter to the catalyst (Lucentini et al. (Ind. Eng. Chem. Res. 2021, 60, 18560-18611). A promoter is a substance that enhances the catalytic effect of the catalyst. In a preferred embodiment, the catalyst for converting NH to N and H is promoted by a metal promoter, preferably selected from the list consisting of alkali metals, rare earth metals, and their oxides, more preferably selected from the list consisting of K, Na, Ba, Cs, Li, La, Ce, Al, Ca, Ti, and their oxides. Preferably, the amount of promoter is in the range of 0.01 to 20 wt. % based on the total weight of the unsupported catalyst, more preferably in the range of 0.1 to 10 wt. % based on the total weight of the unsupported catalyst.

[0038] In a preferred embodiment, the catalyst for converting NH3 to N2 and H2 is mounted on a support. The support can stabilize the size and / or morphology of the metal particles and increase the exposure of their active sites. The support can also affect the catalytic performance. Providing a support improves thermal stability and prevents sintering. Preferably, the support material is a metal oxide or carbon-based support, more preferably the support material is selected from the list consisting of Al2O3, SiO2, CeO2, MgO, La2O3, TiO2, YO3, ZrO2, CeZrO2, SBA-15, ZSM-5, carbon nanotubes, C, and graphite, and most preferably the support material is SiO2. SiO2 is easy to manufacture, has high stability, and is low cost.

[0039] Membranes and Membrane Reactors In a preferred embodiment, the reactor is a membrane reactor containing an H2-permeable membrane. The H2-permeable membrane separates the reactor into two sections. The first section is on a first side of the H2-permeable membrane, and the second section is on a second side of the H2-permeable membrane. In this embodiment, during the reduction of the redox catalyst, H2 is produced on one side of the H2-permeable membrane by the decomposition of ammonia. The H2 permeates the membrane and reduces the redox catalyst on the other side of the membrane to form H2O. In this way, N2 does not come into contact with the redox catalyst, which can be beneficial for preventing nitrification. Furthermore, the membrane reactor delivers concentrated N2 that does not require further separation or concentration. Furthermore, greater flexibility in the selection of the NH3 decomposition catalyst and the redox catalyst is possible because these catalysts are completely separated.

[0040] Preferably, the membrane is selective to H. By selective to H, it is meant that no significant amount of other components other than H permeates the membrane. Preferably, greater than 90 wt. % of the components permeating the membrane is H, more preferably greater than 99 wt. % of the components permeating the membrane.

[0041] In embodiments where the reactor is a membrane reactor, during the reduction of the redox catalyst, a sweep gas is preferably supplied to the portion of the reactor containing the redox catalyst. In this manner, the HO formed is discharged from this portion of the reactor. The portion of the reactor containing the redox catalyst is referred to as the second portion. Preferably, the sweep gas is an inert gas such that oxidation or reduction of the redox catalyst does not occur; more preferably, the sweep gas comprises one or more of N, HO, He, and Ar, and even more preferably, one or more of N, He, and Ar. In a preferred embodiment, the sweep gas is the same as the second purge gas.

[0042] Membranes permeable to H2 are well known in the art, as described, for example, by Ockwig et al. (Chemical Reviews, 107(10), 4078-4110). Metallic, ceramic, and carbon membranes are most suitable for the temperature range envisioned by the present method. Dong et al. (Journal of Membrane Science, volume 629, 1 July 2021, 119281) describe zeolite membranes, carbon molecular sieve membranes, and Pd / Ag membranes for removing H2 during the catalytic decomposition of ammonia. Sitar et al. (Journal of Membrane Science, volume 644, 15 February 2022, 120147) describe Pd and zeolite membranes for removing H2 during the catalytic decomposition of ammonia.

[0043] In a preferred embodiment, the H2-permeable membrane is selected from the group consisting of metal membranes, ceramic membranes, and carbon membranes. Preferably, the H2-permeable membrane is a ceramic membrane or a carbon membrane, more preferably a dense or porous ceramic membrane or a porous carbon membrane, and even more preferably a dense ceramic membrane or a porous carbon membrane. Dense and porous membranes are well known in the art. Preferably, in this embodiment, the metal membrane is a Pd, Pd / Ag, Ta, V, Nb, or alloy membrane, where the alloy includes V, Cr, Ti, Ni, Al, Fe, Zr, Mo, or Co. Preferably, in this embodiment, the ceramic membrane is a silica, alumina, zirconia, titania, or zeolite membrane.

[0044] In a preferred embodiment, the reactor in the context of the present invention is a membrane reactor comprising a membrane permeable to H, which separates the reactor into two sections: in the first section, a catalyst for converting NH to N and H is present, and in the second section, a redox catalyst for converting CO to CO is present. The first section of the membrane reactor is fed with NH and the second section is fed with CO. Any suitable membrane reactor can be selected. Preferably, the membrane reactor is a tubular membrane reactor or a plate-on-plate membrane reactor. Preferably, the reactor is a chemical loop reactor. Preferably, the reactor comprises one or more feed inlets and one or more product outlets connected to the first section, and one or more feed inlets and one or more product outlets connected to the second section.

[0045] General definition In this document and its claims, the verb "comprise" and its conjugations are used in their open-ended sense, meaning that items following the word are included, but items not expressly mentioned are not excluded. Furthermore, the reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one element is present, unless the context clearly requires that only one element be present. Thus, the indefinite article "a" or "an" typically means "at least one." When used in connection with a numerical value (e.g., about 10), the word "about" or "approximately" preferably means that the value can be 1% more or less than the specified value.

[0046] The present invention has been described above with reference to a number of exemplary embodiments. Modifications and substitutions of several parts or elements are possible and fall within the scope of protection defined in the appended claims. All literature and patent citations are incorporated herein by reference.

[0047] Chemical elements contained in this document are described by their chemical element symbols. Compounds in this document are described in chemical formula format using chemical element symbols. For metal species, the symbol M is used. Some chemical formulas used in this document are: hydrogen = H2, carbon monoxide = CO, carbon dioxide = CO2, water = H2O, and ammonia = NH3. When the term metal oxide or chemical species is mentioned, the stoichiometric ratio between the metal and the oxide is not limited and can be any known ratio. For example, iron oxide includes FeO, Fe2O3, Fe3O4, and other known iron oxides. For some metal oxides, only one stoichiometric ratio is known, and therefore the metal oxide is limited to that stoichiometric ratio. For example, zinc oxide is ZnO. [Example]

[0048] Example 1 Figure 1 shows a first general embodiment of the present invention. In a first reduction step, NH3 is fed to the reactor, thereby reducing the redox catalyst. In this first step, NH3 is converted to H2 and N2, which is then converted to H2 by the redox catalyst M2. x O y NH3 is converted to HO by the redox catalyst M, thereby forming reduced redox catalyst M and HO. Optionally, the reduced redox catalyst is still a metal oxide. The conversion of NH3 to H2 and N2 may be catalyzed by the redox catalyst or by another catalyst for converting the NH3 present in the reactor to N2 and H2. The product stream of this first step contains N2 and HO, which can be easily separated by condensing the HO. A concentrated N2 product is obtained. Furthermore, the heat of this product stream can be utilized, for example, to directly heat the feedstock or to generate electricity in a generator. The electricity can be used to heat the feedstock or the reactor.

[0049] In the second oxidation step, the reduced redox catalyst M is oxidized by CO to form CO and the oxidized redox catalyst M. x O yThis second product stream contains a high concentration of CO, or even consists entirely of CO, eliminating the need for further separation of this stream. This CO can be readily used for further processing without the need for additional separation or concentration steps. The concentration of CO in the second product is directly related to the CO concentration in the feedstock.

[0050] Figure 2 shows a second specific embodiment of the invention, in which there is an H2-permeable membrane separating the reactor into two sections (dotted line): in the first section of the reactor there is a catalyst for converting NH3 to N2 and H2, and in the second section, separated from the first section by the H2-permeable membrane, there is a redox catalyst for converting CO2 to CO.

[0051] In the first reduction step, NH3 is fed to a first part of the reactor, thereby reducing the redox catalyst, and a sweep gas A is fed to a second part of the reactor. In this first step, NH3 is converted to H2 and N2 in the first part of the reactor. The formed H2 permeates the membrane and reaches the second part of the reactor. Subsequently, the redox catalyst M is reduced in this second part of the reactor. x O y The H2 is converted to HO by the HO gas, thereby forming a reduced redox catalyst M and HO. In some cases, the reduced redox catalyst is still a metal oxide. A sweeping gas carries away the formed HO. The heat contained in the HO stream leaving the reactor can be utilized, for example, to directly heat the feedstock or to generate electricity in a generator. The electricity can be used to heat the feedstock or the reactor. A concentrated N2 product is also obtained from the first portion of the reactor. In this embodiment, it is not necessary to remove HO from the N2 stream.

[0052] In the second oxidation step, CO is supplied to the second portion of the reactor, and the reduced redox catalyst M is oxidized by CO, and the CO and the oxidized redox catalyst M are x Oy is formed. The second product stream contains a high concentration of CO, or even consists entirely of CO, eliminating the need for further separation of this stream. This CO can be readily used for further processing without the need for further separation or concentration steps. The concentration of CO in the second product is directly related to the CO concentration in the feedstock.

[0053] Example 2 Iron powder (supplied by Riogen) was ground and sieved to a particle size of 500 μm. 1.5 grams of iron powder, which serves as the redox catalyst in the reduced state, was placed in a tubular reactor with a working volume of 6.5 ml. The reactor was made from Hastelloy. To obtain isothermal reaction conditions, the reactor was placed in an oven. A micro-GC (Agilent, type 490) was attached to the outlet to analyze the reaction products. The micro-GC was calibrated with a synthetic gas mixture containing the gas to be measured.

[0054] The reactor was maintained at 750 °C and 1 bar and flushed with a constant stream of He. In the first step, the feed was switched to CO2 at 3 nL / h. The concentrations of CO and CO2 in the outlet stream were measured (Figure 3). An initial increase in CO concentration and a decrease in CO2 concentration were observed during the first 3 min. This initial increase was followed by a period in which the CO concentration remained constant at approximately 65 vol% CO, and the CO2 concentration remained constant at approximately 35 vol% CO. Apparently, the redox reaction with iron powder converted most of the CO2 to CO, yielding iron oxide powder and CO as reaction products. Subsequently, the CO2 concentration gradually decreased to 0 vol% CO, and the CO2 concentration gradually increased to 100 vol% CO. This decrease was caused by a gradual increase in the amount of oxidized iron in the reactor, which could not be reduced with CO2.

[0055] In the next step, the CO2 feed was stopped, and the reactor was flushed with He (helium). Subsequently, the feed was switched to NH3 at 3 nL / h. The concentrations of N2 and H2 in the outlet were measured, and the measured H2 to N2 ratio is plotted in Figure 4. The NH3 concentration in the outlet was also measured in addition to N2 and H2. The NH3 concentration rapidly dropped below the detection limit. Qualitative evaluation of the presence of water in the reaction product revealed a significant amount of water in the outlet stream. Furthermore, a camp trap placed before the micro-GC was found to capture some of the water in the reaction product. As can be seen in Figure 4, the initial stoichiometry of H2:N2 (approximately 2:1) is lower than that in NH3. This is because some of the formed H2 is further converted to HO via a redox reaction using an iron oxide redox catalyst. Once the redox catalyst is fully reduced, the H2:N2 stoichiometry increases to about 3:1, but further reduction of the redox catalyst is not possible because H2 cannot react to form HO. Interestingly, the time required to fully oxidize the redox catalyst is approximately the same as the time to fully reduce the redox catalyst, which can be advantageous for process design in a continuous process.

[0056] Several cycles were performed in which CO2 and NH3 were fed instead; the exhaust gas compositions of these cycles were identical, indicating that decomposition of the redox catalyst did not occur. Furthermore, the experiment was repeated at a temperature of 850 °C using the same experimental setup. Visual inspection revealed that some sintering had occurred, but even at this temperature, good conversion was observed for both the reduction of CO2 and the decomposition and oxidation of NH3. Sintering can be prevented by using a supported redox catalyst. Alternative redox catalysts, such as W or Mo, can also be used in this process.

[0057] This example demonstrates a chemical looping process in which a pre-decomposition step of NH is not necessary because NH is converted to HO and N. The reduced redox catalyst can then be used to convert CO to CO. This process can be further improved by conventional optimization, such as increasing the conversion of H to HO and / or CO to CO.

Claims

1. CO ２ 1. A method for producing CO from NH ３ and CO ２ is repeatedly supplied, and CO ２ is supplied to the reactor, CO is formed in the reactor when the reaction temperature is 400° C. or higher, and the one or more catalysts ２ a redox catalyst for converting CO.

2. The one or more catalysts are selected from the group consisting of NH ３ N ２ and H ２ and / or said CO ２ The redox catalyst for converting NH ３ N ２ and H ２ 10. The process of claim 1, which is also a catalyst for converting

3. The CO ２ 3. The method of claim 1 or 2, wherein the redox catalyst for converting to CO is a metal oxide, preferably the metal is a transition metal, more preferably the metal is selected from the list consisting of Cu, Fe, Mo, and W.

4. NH ３ N ２ and H ２ 4. The method of claim 2 or 3, wherein the catalyst for converting HCl to HCl is a metal catalyst or an oxide thereof, preferably a transition metal catalyst or an oxide thereof, more preferably a metal catalyst or an oxide thereof, wherein the metal is selected from the list consisting of Ce, Zr, Ru, Ni, Rh, Co, Ir, Fe, Pt, Cr, Pd, Cu, Ag, Mo, Gd, and combinations thereof, and even more preferably a metal catalyst or an oxide thereof, wherein the metal is selected from the list consisting of Ce, Ni, Ru, and Fe.

5. The CO ２ The redox catalyst for converting NH ３ N ２ and H ２ and preferably this catalyst is iron oxide.

6. A method according to any one of claims 1 to 5, wherein one or more of said one or more catalysts is mounted on a support, preferably said support being in particulate form.

7. The material of the support is a metal oxide or a carbon-based support, and more preferably, the support is Al ２ O ３ , SiO ２ , CeO ２ , MgO, La ２ O ３ , TiO ２ , Y ２ O ３ , ZrO ２ , CeZrO ２ 7. The method of claim 6, wherein the cellulose acylate is selected from the list consisting of SBA-15, ZSM-5, carbon nanotubes, C, and graphite.

8. The reactor is ２ is a membrane reactor containing a permeable membrane, and H ２ A permeable membrane separates the reactor into two sections, the first section contains NH ３ is supplied to this part, and NH ３ N ２ and H ２ and in the second portion there is a catalyst for converting CO ２ is supplied to this part, and CO ２ 8. The method of claim 1, wherein a redox catalyst is present to convert CO.

9. The H ２ The permeable membrane is selected from the list of metal membranes, ceramic membranes, and carbon membranes, and preferably ２ The method according to claim 8, wherein the permeable membrane is a ceramic membrane or a carbon membrane, more preferably a dense or porous ceramic membrane or a porous carbon membrane, and even more preferably a dense ceramic membrane or a porous carbon membrane.

10. 10. The method according to any one of claims 1 to 9, wherein the reactor is electrically heated, preferably part of the electricity for heating is generated by a steam turbine powered at least in part by steam produced in the reactor.

11. 11. The method of any one of claims 1 to 10, wherein the reaction temperature is in the range of 400°C to 1200°C, preferably in the range of 600°C to 1000°C, more preferably in the range of 650°C to 850°C, and even more preferably in the range of 750°C to 850°C.

12. The process according to any one of claims 1 to 11, wherein the reaction pressure is in the range of from 1 to 100 bar, preferably from 2 to 50 bar, even more preferably from 4 to 20 bar, most preferably from 5 to 10 bar.

13. A membrane, ２ a membrane permeable to CO separating the reactor into two sections; ２ 1. A chemical loop reactor for producing CO from a first portion comprising NH ３ N ２ and H ２ and the second portion comprises a catalyst for converting CO ２ a redox catalyst for converting HCl to CO, the reactor comprising one or more feed inlets and one or more product outlets connected to the first section, and one or more feed inlets and one or more product outlets connected to the second section.

14. Redox-catalyzed CO ２ CO by reduction to CO ２ NH in a chemical looping process for producing CO from ３ Use of NH ３ and CO ２ is repeatedly fed to a reactor containing one or more catalysts, and NH ３ N ２ and H ２ is converted to H ２ is a reducing agent that reduces the redox catalyst, and the one or more catalysts are ２ a redox catalyst for converting HCl to CO.

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