Methods for hydrogenating carbon dioxide

Abstract

The present invention relates to a reaction system and method for hydrogenating carbon dioxide, comprising: (a) providing a carbon dioxide feedstock stream (106) at a temperature of at least 600°C; (b) providing a first hydrogen feedstock stream (112) at a temperature of at least 600°C; (c) obtaining a first mixed feedstock stream (114) by mixing the carbon dioxide feedstock stream and the first hydrogen feedstock stream; (d) optionally obtaining a heated first mixed feedstock stream (138) by heating the first mixed feedstock stream to a temperature of at least 800°C in a first heat exchanger (136); and (e) supplying the first mixed feedstock stream and / or the heated first mixed feedstock stream to a first reactor (116) at a temperature of 800°C to 1000°C and bringing it into contact with a catalyst to obtain a first product stream (118) containing at least carbon monoxide, water and unreacted carbon dioxide;

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for hydrogenating carbon dioxide, the method comprising the steps of providing a carbon dioxide feed stream and a hydrogen feed stream, mixing the two streams, and feeding the mixed feed stream to a reactor in which the mixed feed stream is brought into contact with a catalyst. BACKGROUND ART

[0002] Reforming of hydrogen and carbon dioxide, also referred to as carbon dioxide hydrogenation or reverse water-gas shift reaction (RWGS), has attracted great economic attention as these processes provide an option for preparing synthesis gas, which is an important basic chemical, using carbon dioxide as a starting material. Accordingly, it becomes possible to fix carbon dioxide obtained as waste in many processes through a chemical route. This makes it possible to reduce the emission of carbon dioxide into the atmosphere.

[0003] "Synthesis gas", also called "syngas", refers to a mixed gas containing hydrogen (H2) and carbon monoxide (CO), which can be used as a basic chemical in many industrial processes. The ratio of hydrogen to carbon monoxide in the synthesis gas varies depending on its application. The synthesis gas may further comprise components such as water (H2O), carbon dioxide (CO2), methane (CH4) and / or nitrogen (N2).

[0004] Various processes for producing synthesis gas from carbon dioxide and hydrogen via a reverse water-gas shift reaction are known in the art. For example, International Publication No. 2021 / 062384A1 discloses a process for producing syngas, which includes (i) reacting at least a portion of carbon dioxide with hydrogen in a first reactor to produce a product stream containing 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 produce a product stream containing carbon monoxide, water, unreacted carbon dioxide and unreacted hydrogen.

[0005] International Publication No. 2021 / 225643A1 discloses a process for converting a source gas containing carbon dioxide and hydrogen into a product gas containing carbon monoxide and water. The source gas is preheated electrically to at least 760°C in a heat exchanger before being introduced into an adiabatic or isothermal reactor in which the RWGS catalytic reaction takes place. The resulting product mixture can be reheated in a second electric heater and then supplied to a second reactor for further conversion of carbon dioxide into carbon monoxide.

[0006] International Publication No. 2022 / 129338 discloses a process for producing synthesis gas in a two-step RWGS catalytic reaction while maintaining the temperature of the RWGS reactor below 700°C. [Overview of the project] [Problems that the invention aims to solve]

[0007] While several process schemes for hydrogenating carbon dioxide are known and are available on an industrial scale, there is still a need to improve this technology, particularly in terms of avoiding the formation of coke and unwanted by-products, energy consumption in such high-temperature processes, and sustainability.

[0008] An object of the present invention is to provide a method for hydrogenating carbon dioxide that minimizes coke formation in heat exchangers and reactors. A further object of the present invention is to provide a method for hydrogenating carbon dioxide that minimizes the generation of methane, an unwanted by-product. A further object of the present invention is to provide a method for hydrogenating carbon dioxide in a compactly designed, energy-efficient reaction system. [Means for solving the problem]

[0009] These problems are solved according to the present invention by the method described in claim 1 and the reaction system described in claim 12. Advantageous variations of this method are shown in claims 2 to 11.

[0010] As used herein, “have,” “comprise,” or “include,” or any grammatical variations thereof, are used in a non-exclusive sense. Therefore, these terms can refer to both situations where the entity described in this context has no further features other than those introduced by these terms, and situations where one or more further features exist. For example, the expressions “A has B,” “A comprises B,” and “A includes B” can refer to both situations where A has no other elements other than B (i.e., A consists exclusively of B), and situations where the entity A has one or more further elements other than B, such as elements C, C and D, or further elements.

[0011] Furthermore, note that the terms "at least one," "one or more," or similar expressions suggesting that a feature or element may exist once or more than once are typically used only once when introducing each feature or element. When referring to each feature or element, even if each feature or element may exist once or more than once, the expressions "at least one" or "one or more" are almost never repeated.

[0012] Furthermore, the terms “preferably,” “more preferably,” “particularly,” “more specifically,” “specifically,” and “more specifically,” or similar terms used herein, are used in conjunction with optional features without limiting alternative possibilities. In other words, the features introduced by these terms are optional features and are not intended to limit the scope of the claims in any way. The present invention can also be carried out using alternative features as will be recognized by those skilled in the art. Similarly, features introduced by “in one embodiment of the present invention” or similar expressions are intended to be optional features and do not impose any limitations on alternative embodiments of the present invention, nor on the scope of the present invention, nor on the possibility of combining such introduced features with other optional or non-optional features of the present invention.

[0013] In a first embodiment of the present invention, a method for hydrogenating carbon dioxide includes the steps of (a) providing a carbon dioxide feedstock flow at a temperature of 600°C to 1000°C, (b) providing a first hydrogen feedstock flow at a temperature of 600°C to 1000°C, (c) mixing the carbon dioxide feedstock flow and the first hydrogen feedstock flow to obtain a first mixed feedstock flow, (d) optionally heating the first mixed feedstock flow to a temperature of 800°C to 1000°C in a first heat exchanger to obtain a heated first mixed feedstock flow, and (e) supplying the first mixed feedstock flow and / or the heated first mixed feedstock flow to a first reactor at a temperature of 800°C to 1000°C and bringing the first mixed feedstock flow and / or the heated first mixed feedstock flow into contact with a catalyst to obtain a first product flow containing at least carbon monoxide, water and unreacted carbon dioxide.

[0014] In a second embodiment of the present invention, a reaction system for hydrogenating carbon dioxide includes: a first gas mixer configured to receive a carbon dioxide feedstock flow at a temperature of 600°C to 1000°C and a first hydrogen feedstock flow at a temperature of 600°C to 1000°C, and to mix the two flows to obtain a first mixed feedstock flow; an optional first heat exchanger configured to receive the first mixed feedstock flow and to heat the first mixed feedstock flow to a temperature of 800°C to 1000°C to obtain a heated first mixed feedstock flow; and a first reactor configured to receive the first mixed feedstock flow and / or the heated first mixed feedstock flow at a temperature of 800°C to 1000°C, and to contact it with a catalyst in a first reactor to obtain a first product flow containing at least carbon monoxide, water, and unreacted carbon dioxide.

[0015] It was found that by heating the carbon dioxide and hydrogen feedstock flows separately to at least 600°C before mixing them, coke formation was significantly reduced or even avoided. Further heating of the first mixed feedstock flow to temperatures above 600°C did not induce significant coke formation.

[0016] The method for hydrogenating carbon dioxide may include further steps, and the reaction system for hydrogenating carbon dioxide may include further apparatus.

[0017] The first product flow may be the final product flow or an intermediate product flow that is further reacted in subsequent reaction steps. There may be one or more subsequent reaction steps. Each subsequent reaction step may include a further heat exchanger and a further reactor. In one embodiment, the hydrogenation of carbon dioxide is carried out in a two-step reaction process. In this embodiment, the reaction system includes a second heat exchanger and a second reactor. The first product flow can be heated to a temperature of 800°C to 1000°C in the second heat exchanger, and the heated flow is supplied to the second reactor, where the heated flow comes into contact with a catalyst to obtain a second product flow containing at least carbon monoxide, water and unreacted carbon dioxide.

[0018] In other embodiments, an additional hydrogen feedstock flow is provided in the reaction system, which includes at least two reaction steps. In this embodiment, steps (a) to (e) of the method described above may be further followed by (f) a step of mixing a first product flow with a second hydrogen feedstock flow to obtain a second mixed feedstock flow; (g) a step of heating the second mixed feedstock flow to a temperature of 800°C to 1000°C in a second heat exchanger; and (h) a step of supplying the heated second mixed feedstock flow to a second reactor and bringing the heated second mixed feedstock flow into contact with a catalyst to obtain a second product flow containing at least carbon monoxide, water and unreacted carbon dioxide.

[0019] A reaction system suitable for carrying out the method according to this embodiment may include: a second heat exchanger configured to receive a second mixed feedstock flow, which is a mixture of a first product flow and a second hydrogen feedstock flow, and to heat the second mixed feedstock flow to a temperature of 800°C to 1000°C; and a second reactor configured to receive the heated second mixed feedstock flow and to bring it into contact with a catalyst in the second reactor to obtain a second product flow containing at least carbon monoxide, water, and unreacted carbon dioxide.

[0020] It has been found that providing an additional hydrogen feedstock flow in a multi-stage reaction process can significantly reduce the production of methane, an unwanted by-product.

[0021] The second product flow may be the final product flow, or it may be an intermediate product flow that is further subjected to the reaction in subsequent reaction steps of the reaction system. If there are more than two reaction steps, an additional hydrogen raw material flow may be provided for each of the further reaction steps.

[0022] As used herein, the term “carbon dioxide feedstock flow” is a broad term and should be given its usual and customary meaning to those skilled in the art, and not limited to any special or unique meaning. Specifically, the term may refer to, but is not limited to, any gaseous flow containing at least carbon dioxide as a reactant in the RWGS reaction.

[0023] The carbon dioxide content of the carbon dioxide raw material flow can be at least 50 mol%, preferably at least 80 mol%, more preferably at least 90 mol%, most preferably at least 95 mol%, and particularly at least 99 mol%.

[0024] The temperature of the carbon dioxide raw material flow may depend on the configuration of the reaction system. In embodiments in which the carbon dioxide raw material flow is mixed with the first hydrogen raw material flow and then the first mixed raw material flow is supplied to the first reactor without further heating, the temperature of the carbon dioxide raw material flow can be at least 800°C, preferably at least 850°C, more preferably at least 900°C, for example, at least 800°C, at least 810°C, at least 820°C, at least 830°C, at least 840°C, at least 850°C, at least 860°C, at least 870°C, at least 880°C, at least 890°C, and at least 900°C. In that case, the temperature of the carbon dioxide raw material flow can be up to 1200°C, preferably up to 1100°C, and more preferably up to 1000°C.

[0025] In embodiments in which a carbon dioxide feedstock flow is mixed with a first hydrogen feedstock flow, and the resulting first mixed feedstock flow is further heated in one or more heat exchangers before flowing into the first reactor, the temperature of the carbon dioxide feedstock flow can be at least 600°C, preferably at least 620°C, more preferably at least 635°C, and even more preferably at least 650°C. In that case, the temperature of the carbon dioxide feedstock flow can be up to 800°C, preferably up to 780°C, more preferably up to 765°C, and even more preferably up to 750°C.

[0026] The pressure of the carbon dioxide feed stream can be 1 bar (absolute pressure) to 70 bar (absolute pressure), preferably 3 bar (absolute pressure) to 50 bar (absolute pressure), more preferably 6 bar (absolute pressure) to 30 bar (absolute pressure), for example, at least 1 bar (absolute pressure), at least 2 bar (absolute pressure), at least 3 bar (absolute pressure), at least 4 bar (absolute pressure), at least 5 bar (absolute pressure), at least 6 bar (absolute pressure) and at most 70 bar (absolute pressure), at most 60 bar (absolute pressure), at most 50 bar (absolute pressure), at most 40 bar (absolute pressure), at most 30 bar (absolute pressure), at most 20 bar (absolute pressure).

[0027] The term "hydrogen feed stream" as used herein is a broad term, and should be given the ordinary and customary meaning to those skilled in the art, and is not limited to a special or unique meaning. Specifically, this term may refer to, but is not limited to, any gas stream containing at least hydrogen as a reactant for the RWGS reaction.

[0028] Hydrogen can be added to the reaction system at one position or several different positions. The terms "first hydrogen feed stream", "second hydrogen feed stream", "another hydrogen feed stream" or "additional hydrogen feed stream" are used, where applicable, to distinguish hydrogen feed streams that are added to the reaction system at different positions. In embodiments where more than one hydrogen feed stream is employed, the different hydrogen feed streams may have the same or different composition, temperature or pressure.

[0029] The hydrogen content of the hydrogen feed stream may be at least 50 mol%, preferably at least 80 mol%, more preferably at least 90 mol%, most preferably at least 95 mol%, particularly at least 99 mol%.

[0030] The pressure of the hydrogen raw material flow can be 1 bar (absolute pressure) to 70 bar (absolute pressure), preferably 3 bar (absolute pressure) to 50 bar (absolute pressure), more preferably 6 bar (absolute pressure) to 20 bar (absolute pressure), for example, at least 1 bar (absolute pressure), at least 2 bar (absolute pressure), at least 3 bar (absolute pressure), at least 4 bar (absolute pressure), at least 5 bar (absolute pressure), at least 6 bar (absolute pressure), and a maximum of 70 bar (absolute pressure), a maximum of 60 bar (absolute pressure), a maximum of 50 bar (absolute pressure), a maximum of 40 bar (absolute pressure), a maximum of 30 bar (absolute pressure), and a maximum of 20 bar (absolute pressure).

[0031] The temperature of the hydrogen raw material flow may depend on the configuration of the reaction system. In an embodiment in which the first hydrogen raw material flow is mixed with the carbon dioxide raw material flow and then the first mixed raw material flow is supplied to the first reactor without further heating, the temperature of the first hydrogen raw material flow can be at least 800°C, preferably at least 850°C, and more preferably at least 900°C. In that case, the temperature of the first hydrogen raw material flow can be up to 1200°C, preferably up to 1100°C, and more preferably up to 1000°C.

[0032] In embodiments in which the first hydrogen raw material flow is mixed with the carbon dioxide raw material flow and the resulting first mixed raw material flow is further heated in one or more heat exchangers before flowing into the first reactor, the temperature of the first hydrogen raw material flow can be at least 600°C, preferably at least 620°C, more preferably at least 635°C, and most preferably at least 650°C. In that case, the temperature of the first hydrogen raw material flow can be up to 800°C, preferably up to 780°C, more preferably up to 765°C, and most preferably up to 750°C.

[0033] In embodiments where more than one hydrogen raw material flow is supplied to the reaction system, the temperature of the second hydrogen raw material flow and / or another hydrogen raw material flow can be at least 600°C, preferably at least 620°C, more preferably at least 635°C, and most preferably at least 650°C. In that case, the temperature of the first hydrogen raw material flow can be up to 800°C, preferably up to 780°C, more preferably up to 765°C, and most preferably up to 750°C.

[0034] In some embodiments, one or more of the first hydrogen source flow, the second hydrogen source flow, or another hydrogen source flow can be obtained by heating each low-temperature hydrogen flow in a hydrogen preheater. The low-temperature hydrogen flow may have the same composition as the first hydrogen source flow, the second hydrogen source flow, or each of the other hydrogen source flows. The temperature of the low-temperature hydrogen flow is preferably 0°C to 300°C, more preferably 10°C to 200°C. The pressure of the low-temperature hydrogen flow is preferably 1 bar (absolute pressure) to 70 bar (absolute pressure), more preferably 3 bar (absolute pressure) to 50 bar (absolute pressure), and even more preferably 6 bar (absolute pressure) to 20 bar (absolute pressure), for example, at least 1 bar (absolute pressure), at least 2 bar (absolute pressure), at least 3 bar (absolute pressure), at least 4 bar (absolute pressure), at least 5 bar (absolute pressure), at least 6 bar (absolute pressure) and at most 70 bar (absolute pressure), at most 60 bar (absolute pressure), at most 50 bar (absolute pressure), at most 40 bar (absolute pressure), at most 30 bar (absolute pressure), and at most 20 bar (absolute pressure). The hydrogen preheater can have any form, dimensions and design principle suitable for heating a hydrogen-containing gas flow from a temperature in the range of 0°C to 300°C to a temperature in the range of 600°C to 1000°C.

[0035] In some embodiments, the hydrogen preheater is a gas combustion heater that transfers energy from the combustion of hydrogen, hydrocarbon gases, such as natural gas, or mixtures thereof, to a low-temperature hydrogen flow within the hydrogen preheater. In other embodiments, the hydrogen preheater is an electric heater that uses electricity to heat the low-temperature hydrogen flow. In one embodiment, the hydrogen preheater comprises at least one tube that is heated from the outside, transferring the heat to a low-temperature hydrogen flow through the tube via its walls. In a variation of this embodiment, the hydrogen preheater comprises a plurality of tubes that are heated from the outside, transferring the heat to a low-temperature hydrogen flow through the tubes via its walls.

[0036] A hydrogen preheater may include one or more individual heaters. If there is more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel. The heaters may be based on the same design principle or on different design principles. For example, one heater may be electrically operated, while the others may be combustion heaters operated by the combustion of fuel.

[0037] In some embodiments, the first hydrogen raw material flow, the second hydrogen raw material flow, or both the first and second hydrogen raw material flows are obtained by heating a low-temperature hydrogen flow in a hydrogen preheater, with at least a portion of the heat generated electrically.

[0038] As used herein, the term “first mixed feedstock flow” is a broad term and should be given the usual and customary meanings to those skilled in the art, and not limited to any special or unique meaning. Specifically, the term may refer to, but is not limited to, any gas flow obtained by mixing at least a carbon dioxide feedstock flow and a first hydrogen feedstock flow.

[0039] This mixing can be carried out by any suitable apparatus and method known in the art. In some embodiments, the carbon dioxide feedstock flow and the first hydrogen feedstock flow are supplied to a first gas mixer before flowing into the first heat exchanger. This has the advantage of avoiding a strain of unmixed H2 / CO2 that could cause a decrease in heat transfer in the subsequent heat exchanger. The first gas mixer can be any apparatus suitable for mixing at least two gas flows. Preferred gas mixers include perforated plates, static mixers and dynamic mixers, such as fans.

[0040] The temperature of the first mixed raw material flow may depend on the configuration of the reaction system. In embodiments in which the first mixed raw material flow is supplied to the first reactor without further heating, the temperature of the first mixed raw material flow can be at least 800°C, preferably at least 820°C, and more preferably at least 850°C. In that case, the temperature of the first mixed raw material flow can be up to 1200°C, preferably up to 1100°C, and more preferably up to 1000°C.

[0041] In embodiments in which the first mixed raw material flow is further heated in one or more heat exchangers before flowing into the first reactor, the temperature of the first mixed raw material flow can be at least 600°C, preferably at least 650°C, and more preferably at least 700°C. In that case, the temperature of the first mixed raw material flow can be up to 800°C, preferably up to 750°C, and more preferably up to 700°C.

[0042] The pressure of the first mixed raw material flow is preferably 1 bar (absolute pressure) to 70 bar (absolute pressure), more preferably 3 bar (absolute pressure) to 50 bar (absolute pressure), and even more preferably 6 bar (absolute pressure) to 20 bar (absolute pressure), for example, at least 1 bar (absolute pressure), at least 2 bar (absolute pressure), at least 3 bar (absolute pressure), at least 4 bar (absolute pressure), at least 5 bar (absolute pressure), at least 6 bar (absolute pressure) and a maximum of 70 bar (absolute pressure), a maximum of 60 bar (absolute pressure), a maximum of 50 bar (absolute pressure), a maximum of 40 bar (absolute pressure), a maximum of 30 bar (absolute pressure), and a maximum of 20 bar (absolute pressure).

[0043] In some embodiments, the first mixed raw material flow is supplied to a first heat exchanger and heated to a temperature of 800°C to 1000°C, preferably 850°C to 950°C, more preferably 880°C to 920°C, thereby obtaining a heated first mixed raw material flow. The first heat exchanger can have any form, dimensions, and design principle suitable for heating a gas flow containing carbon dioxide and hydrogen from a temperature in the range of 600°C to 800°C to a temperature in the range of 800°C to 1000°C.

[0044] In some embodiments, the first heat exchanger is a gas combustion heater that transfers energy from the combustion of hydrogen, hydrocarbon gases, such as natural gas, or mixtures thereof, to a first mixed feedstock flow through the first heat exchanger. In other embodiments, the first heat exchanger is an electric heater that uses electricity to heat the first mixed feedstock flow. In one embodiment, the first heat exchanger comprises at least one tube that is heated from the outside and transfers the heat to the first mixed feedstock flow through the tube via its wall. In a variation of this embodiment, the first heat exchanger comprises a plurality of tubes that are heated from the outside and transfer the heat to the first mixed feedstock flow through the tube via its wall.

[0045] The first heat exchanger may include one or more individual heaters. If there is more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel. The heaters may be based on the same design principle or on different design principles. For example, one heater may be electrically operated, while the other heaters may be combustion heaters operated by the combustion of fuel.

[0046] In some embodiments, the carbon dioxide feedstock flow contains 90 mol% to 100 mol% carbon dioxide, the first hydrogen feedstock flow contains 90 mol% to 100 mol% hydrogen, and the molar ratio of carbon dioxide to hydrogen in the first mixed feedstock flow and / or the heated first mixed feedstock flow is 0.9 to 3, preferably 1.3 to 2.5.

[0047] The first mixed raw material flow and / or the heated first mixed raw material flow are supplied to the first reactor at a temperature of 800°C to 1000°C. In some embodiments, the first mixed raw material flow is supplied to the first reactor. In some embodiments, the heated first mixed raw material flow is supplied to the first reactor. In some embodiments, both the first mixed raw material flow and the heated first mixed raw material flow are supplied to the first reactor.

[0048] As used herein, the term “first reactor” is a broad term and should be given the usual and customary meanings to those skilled in the art, and not limited to any special or unique meaning. Specifically, the term may refer to, but is not limited to, any reactor suitable for carrying out an RWGS catalytic reaction.

[0049] In some embodiments, the first reactor is an adiabatic reactor. In one embodiment, the first reactor is a fixed-bed adiabatic reactor. Preferably, the ratio of the reactor length to the diameter is greater than 1, i.e., the reactor length is longer than its diameter.

[0050] In other embodiments, the first reactor is an adiabatic reactor having a monolithic structure. Preferably, in this case, the catalyst is applied as a washcoat to the monolith. The advantage of this type of reactor is that it has low pressure drops at its inlet and outlet.

[0051] As used herein, the term "adiabatic" means that each reactor is not heated by external means. However, it is possible that the reactor may exchange heat with its environment, for example, due to a large temperature difference between the inside of the reactor and the surrounding environment. In some embodiments, the heat loss of an adiabatic reactor can be as high as 20%.

[0052] Catalysts for RWGS catalytic reactions are known in the art. For example, International Publication No. 2018 / 219992A1 discloses a heterogeneous catalyst containing nickel and magnesium spinel for the hydrogenation of carbon dioxide. In some embodiments, the catalyst comprises nickel (Ni), magnesium (Mg), and aluminum (Al). Preferably, the nickel content of the catalyst is in the range of 5 to 30 mol%, the magnesium content is in the range of 10 to 40 mol%, and the aluminum content is in the range of 40 to 70 mol%.

[0053] The catalyst can be installed in the first reactor in any form suitable for catalyzing the RWGS reaction within the reactor. In some embodiments, the catalyst is in the form of pellets, for example, having a tetrahedron or hexahedron shape, and the pellets may or may not have internal pores. In some embodiments, the catalyst is in the form of extruded material, for example, having a cylindrical or multi-lobed shape, such as a trihedron shape. In some embodiments, the catalyst is installed in the reactor as a three-dimensional porous structure.

[0054] At least a portion of the products of the RWGS reaction in the first reactor are withdrawn from the first reactor as a first product stream. This stream contains at least carbon monoxide, water, and unreacted carbon dioxide. The first product stream may also contain further substances such as unreacted hydrogen or reaction by-products such as methane.

[0055] The temperature of the first product flow is preferably 650°C to 850°C, more preferably 720°C to 850°C. The pressure of the first product flow is preferably 1 bar (absolute pressure) to 70 bar (absolute pressure), more preferably 3 bar (absolute pressure) to 50 bar (absolute pressure), and even more preferably 6 bar (absolute pressure) to 20 bar (absolute pressure), for example, at least 1 bar (absolute pressure), at least 2 bar (absolute pressure), at least 3 bar (absolute pressure), at least 4 bar (absolute pressure), at least 5 bar (absolute pressure), at least 6 bar (absolute pressure) and a maximum of 70 bar (absolute pressure), a maximum of 60 bar (absolute pressure), a maximum of 50 bar (absolute pressure), a maximum of 40 bar (absolute pressure), a maximum of 30 bar (absolute pressure), and a maximum of 20 bar (absolute pressure).

[0056] In embodiments where the first product flow is the final product flow, the first product flow may contain 5 mol% to 40 mol% of carbon monoxide, more preferably 15 mol% to 35 mol%, even more preferably 20 mol% to 30 mol%, 10 mol% to 45 mol%, more preferably 15 mol% to 35 mol%, even more preferably 20 mol% to 35 mol%, 10 mol% to 45 mol%, more preferably 15 mol% to 35 mol%, even more preferably 15 mol% to 30 mol%, 5 mol% to 40 mol%, more preferably 15 mol% to 35 mol%, even more preferably 20 mol% to 30 mol%, and less than 2 mol% of methane.

[0057] In embodiments where the first product flow is an intermediate product flow, the first product flow may contain 5 mol% to 40 mol% of carbon monoxide, more preferably 10 mol% to 35 mol%, even more preferably 15 mol% to 30 mol%, 5 mol% to 30 mol% of hydrogen, more preferably 5 mol% to 25 mol%, even more preferably 5 mol% to 20 mol%, 25 mol% to 65 mol% of carbon dioxide, more preferably 30 mol% to 60 mol%, even more preferably 35 mol% to 55 mol%, 5 mol% to 40 mol%, more preferably 10 mol% to 35 mol%, even more preferably 15 mol% to 30 mol%, and less than 2 mol% of methane.

[0058] In some embodiments, a second mixed feedstock flow is obtained by mixing a first product flow with a second hydrogen feedstock flow. This mixing can be carried out by any suitable apparatus and method known in the art. In some embodiments, the first product flow and the second hydrogen feedstock flow are supplied to a second gas mixer before flowing into the second heat exchanger. This has the advantage of avoiding streaky flows of unmixed H2 / CO2, which can cause a decrease in heat transfer in the subsequent heat exchanger. The second gas mixer can be any apparatus suitable for mixing the two (to) gas flows. Preferred gas mixers are perforated plates, static mixers and dynamic mixers, such as fans.

[0059] The temperature of the second mixed raw material flow may depend on the configuration of the reaction system. In embodiments in which the second mixed raw material flow is supplied to the second reactor without further heating, the temperature of the second mixed raw material flow can be at least 800°C, preferably at least 850°C, and more preferably at least 900°C. In that case, the temperature of the second mixed raw material flow can be up to 1200°C, preferably up to 1100°C, and more preferably up to 1000°C.

[0060] In embodiments in which the second mixed raw material flow is further heated in one or more heat exchangers before flowing into the second reactor, the temperature of the second mixed raw material flow can be at least 600°C, preferably at least 650°C, and more preferably at least 700°C. In that case, the temperature of the second mixed raw material flow can be up to 800°C, preferably up to 775°C, and more preferably up to 750°C.

[0061] The pressure of the second mixed raw material flow is preferably 1 bar (absolute pressure) to 70 bar (absolute pressure), more preferably 3 bar (absolute pressure) to 50 bar (absolute pressure), and even more preferably 6 bar (absolute pressure) to 20 bar (absolute pressure), for example, at least 1 bar (absolute pressure), at least 2 bar (absolute pressure), at least 3 bar (absolute pressure), at least 4 bar (absolute pressure), at least 5 bar (absolute pressure), at least 6 bar (absolute pressure) and a maximum of 70 bar (absolute pressure), a maximum of 60 bar (absolute pressure), a maximum of 50 bar (absolute pressure), a maximum of 40 bar (absolute pressure), a maximum of 30 bar (absolute pressure), and a maximum of 20 bar (absolute pressure).

[0062] In some embodiments, the second mixed feedstock flow is supplied to a second heat exchanger and heated to a temperature of 800°C to 1000°C, preferably 850°C to 950°C, more preferably 880°C to 920°C. The second heat exchanger can have any form, dimensions, and design principle suitable for heating a gas flow containing carbon dioxide and hydrogen from a temperature in the range of 600°C to 800°C to a temperature in the range of 800°C to 1000°C.

[0063] In some embodiments, the second heat exchanger is a gas combustion heater that transfers energy from the combustion of hydrogen, hydrocarbon gases, such as natural gas, or mixtures thereof, to a second mixed feedstock flow through the second heat exchanger. In other embodiments, the second heat exchanger is an electric heater that uses electricity to heat the second mixed feedstock flow. In one embodiment, the second heat exchanger comprises at least one tube that is heated from the outside, and the heat is transferred to the second mixed feedstock flow through the tube via the tube wall. In a variation of this embodiment, the second heat exchanger comprises a plurality of tubes that are heated from the outside, and the heat is transferred to the second mixed feedstock flow through the tube wall.

[0064] The second heat exchanger may include one or more individual heaters. If there is more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel. The heaters may be based on the same design principle or on different design principles. For example, one heater may be electrically operated, while the other heaters may be combustion heaters operated by the combustion of fuel.

[0065] In some embodiments, the molar ratio of carbon dioxide to hydrogen in the second mixed raw material flow and / or the heated second mixed raw material flow is 0.9 to 3, preferably 1.3 to 2.5.

[0066] The heated second mixed feedstock stream is supplied to the second reactor. The term “second reactor” as used herein is a broad term, and should be given the usual and customary meanings to those skilled in the art, and not limited to any special or unique meaning. Specifically, the term may refer to, but is not limited to, any reactor suitable for carrying out the RWGS catalytic reaction.

[0067] In some embodiments, the second reactor is an adiabatic reactor. In one embodiment, the second reactor is a fixed-bed adiabatic reactor. Preferably, the ratio of the reactor length to the diameter is greater than 1, i.e., the reactor length is longer than its diameter.

[0068] In other embodiments, the second reactor is an adiabatic reactor having a monolithic structure. Preferably, in this case, the catalyst is applied as a washcoat to the monolith. The advantage of this type of reactor is that it has low pressure drops at its inlet and outlet.

[0069] The catalyst used in the second reactor may be the same as the catalyst used in the first reactor, or it may be different. In some embodiments, the catalyst used in the second reactor is based on the same chemical substance as the catalyst used in the first reactor, but has a different shape. For example, the catalyst used in the second reactor may have a shape with a higher surface area-to-volume ratio than the catalyst used in the first reactor.

[0070] At least a portion of the products of the RWGS reaction in the second reactor are withdrawn from the second reactor as a second product stream. This stream contains at least carbon monoxide, water, and unreacted carbon dioxide. The second product stream may also contain further substances such as unreacted hydrogen or reaction byproducts such as methane.

[0071] In embodiments where the second product flow is the final product flow, the second product flow may contain 5 mol% to 40 mol% of carbon monoxide, preferably 15 mol% to 35 mol%, more preferably 20 mol% to 30 mol%, of carbon monoxide, 10 mol% to 45 mol%, preferably 15 mol% to 35 mol%, more preferably 20 mol% to 35 mol%, of hydrogen, 10 mol% to 45 mol%, preferably 15 mol% to 35 mol%, more preferably 15 mol% to 30 mol%, of carbon dioxide, 5 mol% to 40 mol%, preferably 15 mol% to 35 mol%, more preferably 20 mol% to 30 mol%, and less than 2 mol% of methane.

[0072] In embodiments where the second product flow is an intermediate product flow, the second product flow may contain 5 mol% to 40 mol% of carbon monoxide, preferably 10 mol% to 35 mol%, more preferably 15 mol% to 30 mol%, of carbon monoxide, 5 mol% to 35 mol%, preferably 5 mol% to 30 mol%, more preferably 10 mol% to 30 mol%, of hydrogen, 10 mol% to 60 mol%, preferably 15 mol% to 50 mol%, more preferably 20 mol% to 45 mol%, of water, preferably 10 mol% to 35 mol%, more preferably 15 mol% to 30 mol%, and less than 2 mol% of methane.

[0073] The temperature of the second product flow is preferably 650°C to 850°C, more preferably 750°C to 850°C. The pressure of the second product flow is preferably 1 bar (absolute pressure) to 70 bar (absolute pressure), more preferably 3 bar (absolute pressure) to 50 bar (absolute pressure), and even more preferably 6 bar (absolute pressure) to 20 bar (absolute pressure), for example, at least 1 bar (absolute pressure), at least 2 bar (absolute pressure), at least 3 bar (absolute pressure), at least 4 bar (absolute pressure), at least 5 bar (absolute pressure), at least 6 bar (absolute pressure) and a maximum of 70 bar (absolute pressure), a maximum of 60 bar (absolute pressure), a maximum of 50 bar (absolute pressure), a maximum of 40 bar (absolute pressure), a maximum of 30 bar (absolute pressure), and a maximum of 20 bar (absolute pressure).

[0074] The carbon dioxide raw material flow mixed with the first hydrogen raw material flow may have a composition containing 90 mol% to 100 mol% carbon dioxide.

[0075] In some embodiments, the carbon dioxide feedstock flow is obtained from a crude carbon dioxide feedstock flow. The crude carbon dioxide feedstock flow may contain impurities that can poison the catalyst used in the first or second reactor. Potential catalyst poisons in this flow include sulfur compounds such as H2S, COS, and CS2. The carbon dioxide feedstock flow may be subjected to a pretreatment or conditioning step.

[0076] In some embodiments, the carbon dioxide raw material flow is obtained by supplying a crude carbon dioxide raw material flow to a purification unit and removing at least some of the impurities that may be present in the crude carbon dioxide raw material flow.

[0077] The purification unit may include any devices suitable for removing impurities and unwanted substances from the crude carbon dioxide raw material flow, in particular any devices suitable for removing sulfur components from the crude carbon dioxide raw material flow. In one embodiment, the purification unit includes an adsorption bed, which is preferably operated at a high temperature, particularly above 80°C. The purification unit may include further devices such as a filtration unit or a membrane unit, which may be used alone or in combination with any other devices within the purification unit.

[0078] Depending on its origin, the carbon dioxide raw material flow can have any temperature and pressure suitable for transporting the gas flow, for example, through a conduit.

[0079] In some embodiments, the carbon dioxide feedstock flow is obtained by heating a low-temperature carbon dioxide flow in a carbon dioxide feedstock preheater. The low-temperature carbon dioxide flow may have the same composition as the carbon dioxide feedstock flow. The temperature of the low-temperature carbon dioxide flow is preferably 20°C to 250°C, more preferably 50°C to 200°C. The pressure of the low-temperature carbon dioxide flow is preferably 1 bar (absolute pressure) to 70 bar (absolute pressure), more preferably 2 bar (absolute pressure) to 30 bar (absolute pressure). The carbon dioxide feedstock preheater may have any form, dimensions, and design principle suitable for heating a carbon dioxide-containing gas flow from a temperature in the range of 20°C to 250°C to a temperature in the range of 600°C to 1000°C.

[0080] In some embodiments, the carbon dioxide raw material preheater is a gas combustion heater that transfers energy from the combustion of hydrogen, hydrocarbon gases, such as natural gas, or mixtures thereof, to a carbon dioxide raw material flow within the carbon dioxide raw material preheater. In other embodiments, the carbon dioxide raw material preheater is an electric heater that uses electricity to heat the carbon dioxide raw material flow. The carbon dioxide raw material preheater may comprise at least one tube that is heated from the outside, transferring the heat to the carbon dioxide raw material flowing through the tube via the tube wall. The carbon dioxide raw material preheater may comprise multiple tubes that are heated from the outside, transferring the heat to the carbon dioxide raw material flowing through the tube wall.

[0081] A carbon dioxide raw material preheater may include one or more individual heaters. If there is more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel. The heaters may be based on the same design principle or on different design principles. For example, one heater may be electrically operated, while the other heaters may be combustion heaters operated by the combustion of fuel.

[0082] In some embodiments, the carbon dioxide raw material preheater is thermally integrated with other parts of the process, in the sense that the heat released in a particular process stage or apparatus is used in the carbon dioxide raw material preheater to heat the carbon dioxide raw material flow.

[0083] In some embodiments, a cooled product flow is obtained by cooling the second product flow in a product cooler. The product cooler can have any form, dimensions and design principle suitable for cooling a gaseous flow containing at least carbon monoxide, water and carbon dioxide from a temperature of 650°C to 850°C to a temperature of 10°C to 100°C.

[0084] In one embodiment, the product cooler includes one separate cooler for cooling the second product flow to a desired temperature. In other embodiments, the product cooler includes one or more coolers connected in parallel, in series, or partially in parallel and partially in series. A suitable cooling medium can be selected depending on the temperature range of the second product flow flowing through one or more coolers and the desired outlet temperature of each cooler. Preferably, the cooling medium is selected from the group consisting of water, oil, or any flow in the process suitable for thermal integration.

[0085] In some embodiments, the heating medium for cooling at least one of the condensers of the product condenser is water. Preferably, at least a portion of the water evaporates during the cooling process, and the resulting water vapor is used as a heating medium in other parts of the carbon dioxide hydrogenation process or in another process.

[0086] In some embodiments, the carbon dioxide feedstock flow is obtained by heating a low-temperature carbon dioxide flow in a carbon dioxide feedstock preheater, the first product flow and / or second product flow are cooled in a product cooler to obtain a cooled product flow, and at least some of the heat removed from the first product flow and / or second product flow in the product cooler is transferred to the carbon dioxide feedstock preheater to heat the carbon dioxide feedstock flow.

[0087] In some embodiments, the carbon dioxide raw material preheater includes a first preheater that receives heat from a product cooler and a second preheater that is preferably heated electrically. Preferably, the temperature of the carbon dioxide raw material flow flowing out of the first preheater and into the second preheater is 300°C to 450°C.

[0088] In some embodiments, the product cooler includes at least a first cooler and a second cooler, the second cooler transferring heat to a carbon dioxide raw material preheater. Preferably, the temperature of the second product flow flowing out of the first cooler and into the second cooler is 350°C to 470°C. More preferably, the first cooler is cooled with water, which evaporates within the first cooler to produce water vapor.

[0089] In some embodiments, components of the first heat exchanger exposed to high temperatures and / or corrosive media are made from heat-resistant materials such as specific stainless steel alloys or ceramic materials. In preferred embodiments, each component is made from a nickel-chromium alloy containing the following alloying elements (ratios in weight percent): Nickel (Ni): 15-70 Chromium (Cr): 15-30 Silicon (Si): Less than 2.

[0090] Nickel-chromium alloys may contain additional components, such as carbon, manganese, titanium, copper, and iron.

[0091] In a further preferred embodiment, the components of the first heat exchanger, which are exposed to high temperatures and / or corrosive media, are made from a nickel-iron-chromium alloy containing the following alloying elements (in weight percent): Carbon (C): Less than 0.1 Silicon (Si): Less than 1 Manganese (Mn): Less than 1.5 Chromium (Cr): 19-23 Nickel (Ni): 30-34 Titanium: 0.15~0.6 Copper (Cu): Less than 0.75 Iron (Fe): Less than 39.5.

[0092] The present invention will be described in further detail below with reference to the drawings. The drawings should be interpreted as illustrative of the principle. They do not limit the present invention, for example, in terms of specific dimensions or design variations. [Brief explanation of the drawing]

[0093] [Figure 1] This figure shows a reaction system for hydrogenating carbon dioxide, which is a first embodiment of the present invention. [Figure 2] This figure shows a reaction system for hydrogenating carbon dioxide, which is a second embodiment of the present invention. [Figure 3] This figure shows a reaction system for hydrogenating carbon dioxide, which is a third embodiment of the present invention. [Figure 4] This figure shows a reaction system for hydrogenating carbon dioxide, which is a fourth embodiment of the present invention. [Figure 5] This figure shows a reaction system for hydrogenating carbon dioxide, which is a fifth embodiment of the present invention. [Modes for carrying out the invention]

[0094] Figure 1 shows a schematic diagram of a reaction system for hydrogenating carbon dioxide, which is a first embodiment of the present invention. The reaction system includes a carbon dioxide raw material preheater 104, a hydrogen preheater 110, and a first reactor 116.

[0095] A low-temperature carbon dioxide stream 102 is supplied to a carbon dioxide raw material preheater 104, where it is heated to obtain a carbon dioxide raw material stream 106 with a temperature of at least 800°C. The temperature of the low-temperature carbon dioxide stream 102 can be in the range of 20°C to 250°C. The heating energy for the carbon dioxide raw material preheater 104 is preferably provided by electricity.

[0096] The low-temperature hydrogen flow 108 is supplied to the hydrogen preheater 110, where it is heated to produce a first hydrogen raw material flow 112 with a temperature of at least 800°C. The temperature of the low-temperature hydrogen flow 108 can be 20°C to 250°C. The heating energy for the hydrogen preheater 110 is preferably provided by electricity.

[0097] The carbon dioxide feedstock stream 106 and the first hydrogen feedstock stream 112 are mixed to obtain a first mixed feedstock stream 114 with a temperature of at least 800°C. Mixing can be carried out in a gas mixer, such as a static mixer. The first mixed feedstock stream 114 is supplied to a first reactor 116 equipped with a catalyst suitable for the RWGS reaction. The contact of the first mixed feedstock stream 114 with the catalyst in the first reactor 116 yields a first product stream 118 containing at least carbon monoxide, water, and unreacted carbon dioxide. The first product stream 118 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0098] Figure 2 shows a schematic diagram of a reaction system for hydrogenating carbon dioxide, which is a second embodiment of the present invention. The reaction system includes a carbon dioxide raw material preheater 104, a hydrogen preheater 110, a first reactor 116, another hydrogen preheater 122, a second heat exchanger 128, and a second reactor 132.

[0099] Similar to the process described above with reference to Figure 1, the low-temperature carbon dioxide stream 102 is supplied to the carbon dioxide raw material preheater 104, where it is heated to obtain a carbon dioxide raw material stream 106 with a temperature of at least 800°C. The temperature of the low-temperature carbon dioxide stream 102 can be in the range of 20°C to 250°C. The heating energy for the carbon dioxide raw material preheater 104 is preferably provided by electricity.

[0100] The low-temperature hydrogen flow 108 is supplied to the hydrogen preheater 110, where it is heated to produce a first hydrogen raw material flow 112 with a temperature of at least 800°C. The temperature of the low-temperature hydrogen flow 108 can be 20°C to 250°C. The heating energy for the hydrogen preheater 110 is preferably provided by electricity.

[0101] The carbon dioxide feedstock stream 106 and the first hydrogen feedstock stream 112 are mixed to obtain a first mixed feedstock stream 114 with a temperature of at least 800°C. Mixing can be carried out in a gas mixer, such as a static mixer. The first mixed feedstock stream 114 is supplied to a first reactor 116 equipped with a catalyst suitable for the RWGS reaction. The contact of the first mixed feedstock stream 114 with the catalyst in the first reactor 116 yields a first product stream 118 containing at least carbon monoxide, water, and unreacted carbon dioxide. The first product stream 118 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0102] Another low-temperature hydrogen flow 120 is supplied to another hydrogen preheater 122, where it is heated to produce a second hydrogen raw material flow 124. The temperature of the low-temperature hydrogen flow 108 can be in the range of 20°C to 250°C, and the temperature of the second hydrogen raw material flow 124 can be in the range of 20°C to 250°C. The heating energy for the hydrogen preheater 110 is preferably provided by electricity.

[0103] The first product flow 118 is mixed with the second hydrogen feedstock flow 124 to obtain a second mixed feedstock flow 126, which is supplied to a second heat exchanger 128, where it is heated to a temperature of 800°C to 1000°C. The heating energy for the second heat exchanger 128 is preferably provided by electricity. The heated second mixed feedstock flow 130 is supplied to a second reactor 132, which also contains a catalyst suitable for the RWGS reaction. The heated second mixed feedstock flow 130 comes into contact with the catalyst in the second reactor 132 to obtain a second product flow 134 containing at least carbon monoxide, water, and unreacted carbon dioxide. The second product flow 134 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0104] Figure 3 shows a schematic diagram of a reaction system for hydrogenating carbon dioxide, which is a third embodiment of the present invention. The reaction system includes a hydrogen preheater 110, a first heat exchanger 136, a first reactor 116, a second heat exchanger 128, and a second reactor 132.

[0105] The low-temperature hydrogen stream 108 is preheated to a temperature of 600°C to 800°C in the hydrogen preheater 110 and divided into a first hydrogen raw material stream 112 and a second hydrogen raw material stream 124. Alternatively, the low-temperature hydrogen stream 108 may be first divided into two separate streams, and then each stream may be preheated to a temperature of 600°C to 800°C in the hydrogen preheater 110 to obtain the first hydrogen raw material stream 112 and the second hydrogen raw material stream 124. The heating energy is preferably provided by electricity. The first hydrogen raw material stream 112 is mixed with a carbon dioxide raw material stream 106 provided at a temperature of 600°C to 800°C. The resulting first mixed raw material stream 114 is supplied to the first heat exchanger 136, where it is heated to a temperature of 800°C to 1000°C. The heated first mixed raw material stream 138 is supplied to the first reactor 116, which is equipped with a catalyst suitable for the RWGS reaction. The heated first mixed raw material flow 138 comes into contact with the catalyst in the first reactor 116 to produce a first product flow 118 containing at least carbon monoxide, water, and unreacted carbon dioxide. The first product flow 118 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0106] The first product flow 118 is mixed with the second hydrogen feedstock flow 124 to obtain a second mixed feedstock flow 126, which is supplied to the second heat exchanger 128, where it is heated to a temperature of 800°C to 1000°C. The heating energy for the first heat exchanger 136 and the second heat exchanger 128 is preferably provided by burning a hydrocarbon-containing gas, such as natural gas, a hydrogen-containing gas, or a gas containing hydrocarbons and hydrogen. The heated second mixed feedstock flow 130 is supplied to the second reactor 132, which also contains a catalyst suitable for the RWGS reaction. The heated second mixed feedstock flow 130 comes into contact with the catalyst in the second reactor 132 to obtain a second product flow 134 containing at least carbon monoxide, water, and unreacted carbon dioxide. The second product flow 134 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0107] Figure 4 shows a schematic diagram of a reaction system for hydrogenating carbon dioxide, which is a fourth embodiment of the present invention. The reaction system includes a hydrogen preheater 110, a purification unit 142, a carbon dioxide raw material preheater 104, a first heat exchanger 136, a first reactor 116, a second heat exchanger 128, a second reactor 132, and a product cooler 144.

[0108] The crude carbon dioxide raw material flow 140 is supplied to the purification unit 142, where at least some of the impurities that may be present in the crude carbon dioxide raw material flow 140 and could poison the catalyst are removed. The purified low-temperature carbon dioxide flow 102 is then preheated in the carbon dioxide raw material preheater 104 to obtain a carbon dioxide raw material flow 106 with a temperature of 600°C to 800°C.

[0109] The low-temperature hydrogen stream 108 is preheated to a temperature of 600°C to 800°C in the hydrogen preheater 110 and divided into a first hydrogen raw material stream 112 and a second hydrogen raw material stream 124. Alternatively, the low-temperature hydrogen stream 108 may be first divided into two separate streams, and then each stream may be preheated to a temperature of 600°C to 800°C in the hydrogen preheater 110 to obtain the first hydrogen raw material stream 112 and the second hydrogen raw material stream 124. The heating energy is preferably provided by electricity. The first hydrogen raw material stream 112 is mixed with the carbon dioxide raw material stream 106. The resulting first mixed raw material stream 114 is supplied to the first heat exchanger 136, where it is heated to a temperature of 800°C to 1000°C. The heated first mixed raw material stream 138 is supplied to the first reactor 116, which is equipped with a catalyst suitable for the RWGS reaction. The heated first mixed raw material flow 138 comes into contact with the catalyst in the first reactor 116 to produce a first product flow 118 containing at least carbon monoxide, water, and unreacted carbon dioxide. The first product flow 118 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0110] The first product flow 118 is mixed with the second hydrogen feedstock flow 124 to obtain a second mixed feedstock flow 126, which is supplied to the second heat exchanger 128, where it is heated to a temperature of 800°C to 1000°C. The heating energy for the first heat exchanger 136 and the second heat exchanger 128 is preferably provided by burning a hydrocarbon-containing gas, such as natural gas, a hydrogen-containing gas, or a gas containing hydrocarbons and hydrogen. The heated second mixed feedstock flow 130 is supplied to the second reactor 132, which also contains a catalyst suitable for the RWGS reaction. The heated second mixed feedstock flow 130 comes into contact with the catalyst in the second reactor 132 to obtain a second product flow 134 containing at least carbon monoxide, water, and unreacted carbon dioxide. The second product flow 134 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0111] Cooled product flow 146 is obtained by cooling the second product flow 134 in the product cooler 144, and at least some of the heat removed from the second product flow 134 in the product cooler 144 is transferred to the carbon dioxide feedstock preheater 104 to heat the carbon dioxide feedstock flow 106. The dashed lines in Figure 4 represent heat transfer.

[0112] Figure 5 shows a schematic diagram of a reaction system for hydrogenating carbon dioxide, which is a fifth embodiment of the present invention. The reaction system includes a carbon dioxide feedstock preheater 104, a hydrogen preheater 110, another hydrogen preheater 122, a first heat exchanger 136, a first reactor 116, a second heat exchanger 128, a second reactor 132, and a product condenser 144. In this example, the feedstock preheaters include two separate heaters for each feedstock flow: a first carbon dioxide feedstock preheater 104A and a subsequent second carbon dioxide feedstock preheater 104B, a first hydrogen preheater 110A and a subsequent second hydrogen preheater 110B, and another first hydrogen preheater 122A and another subsequent second hydrogen preheater 122B.

[0113] The low-temperature carbon dioxide stream 102 is supplied to the carbon dioxide raw material preheater 104, where it is heated to obtain a carbon dioxide raw material stream 106 with a temperature of at least 600°C. The temperature of the low-temperature carbon dioxide stream 102 can be in the range of 20°C to 250°C. The low-temperature hydrogen stream 108 is supplied to the hydrogen preheater 110, where it is heated to obtain a first hydrogen raw material stream 112 with a temperature of at least 600°C. The temperature of the low-temperature hydrogen stream 108 can be in the range of 20°C to 250°C.

[0114] The carbon dioxide feedstock stream 106 and the first hydrogen feedstock stream 112 are mixed to obtain a first mixed feedstock stream 114 having a temperature of at least 800°C. Mixing can be carried out in a gas mixer, such as a static mixer. The first mixed feedstock stream 114 is supplied to a first heat exchanger 136, where it is heated to a temperature of 800°C to 1000°C. The heated first mixed feedstock stream 138 is supplied to a first reactor 116 equipped with a catalyst suitable for the RWGS reaction. In the first reactor 116, the heated first mixed feedstock stream 138 comes into contact with the catalyst to obtain a first product stream 118 containing at least carbon monoxide, water, and unreacted carbon dioxide. The first product stream 118 may also contain further components such as unreacted hydrogen, nitrogen, or methane.

[0115] Another low-temperature hydrogen flow 120 is supplied to another hydrogen preheater 122, where it is heated to produce a second hydrogen raw material flow 124. The temperature of the low-temperature hydrogen flow 108 can be in the range of 20°C to 250°C, and the temperature of the second hydrogen raw material flow 124 can be in the range of 20°C to 250°C.

[0116] The first product flow 118 is mixed with the second hydrogen feedstock flow 124 to obtain the second mixed feedstock flow 126, which is supplied to the second heat exchanger 128, where it is heated to a temperature of 800°C to 1000°C. The heated second mixed feedstock flow 130 is supplied to the second reactor 132, which also contains a catalyst suitable for the RWGS reaction. The heated second mixed feedstock flow 130 comes into contact with the catalyst in the second reactor 132 to obtain the second product flow 134, which contains at least carbon monoxide, water, and unreacted carbon dioxide. The second product flow 134 may also contain further components such as unreacted hydrogen, nitrogen, or methane. The second product flow 134 is cooled in the product cooler 144 to obtain the cooled product flow 146.

[0117] In this example, the energy required to heat the raw material flow is provided from various sources. The first hydrogen preheater 110A and another first hydrogen preheater 122A are preferably heated by electrical energy. The low-temperature hydrogen flow 108 and another low-temperature hydrogen flow 120 can be heated by the first heater to temperatures in the range of 500°C to 650°C. The second hydrogen preheater 110B and another second hydrogen preheater 122B can be heated by electrical energy or by combustion of a hydrogen or hydrocarbon-containing gas, such as natural gas.

[0118] The first heat exchanger 136 and the second heat exchanger 128 may be electric heaters, or they may be combustion heaters that generate heating energy by burning a fuel such as hydrogen or hydrocarbon-containing gas, for example, natural gas.

[0119] The carbon dioxide raw material preheater 104 may include an electric heater, a combustion heater, or a heat exchanger that transfers energy from another heat exchanger to the low-temperature carbon dioxide flow 102 via thermal integration. The first carbon dioxide raw material preheater 104A may, for example, thermally integrate with the product cooler 144 so that at least some of the heat removed from the second product flow 134 in the product cooler 144 is transferred to the carbon dioxide raw material preheater 104 to heat the carbon dioxide raw material flow 106. The dashed lines in Figure 5 represent heat transfer. The second carbon dioxide raw material preheater 104B may be heated using the combustion exhaust gas from the combustion heater of the reaction system or using an external source of high-temperature combustion exhaust gas.

[0120] In the embodiment shown in Figure 5 and any other embodiment, other thermal integration schemes may be used. For example, if a combustion-type first heat exchanger 136 and / or a combustion-type second heat exchanger 128 are used, the high-temperature combustion exhaust gas discharged from these heat exchangers can be used to heat either of the raw material preheaters. The raw material preheater may also be subdivided into multiple units, for example, to allow for additional electric heating if thermal integration with the high-temperature combustion exhaust gas is insufficient. [Examples]

[0121] Example 1 As an example, the reaction system shown in Figure 3 was simulated using Aspen Plus V14, a commercially available simulation tool from AspenTech (20 Crosby Drive, Bedford, MA 01730, USA, www.aspentech.com). This simulation tool is equation-based and uses AspenTech's physical property data. The simulation used a physical property model based on SRK included in the software package. In Aspen, the "Heater" model was used for blocks 110, 136, and 128. Blocks 116 and 132 were modeled as the equilibrium reactor "REquil".

[0122] A first mixed raw material flow 114 was obtained by mixing a carbon dioxide raw material flow 106 with a temperature of 700°C and a first hydrogen raw material flow 112 with a temperature of 700°C. The molar ratio of hydrogen to carbon dioxide in the first mixed raw material flow was set to 0.67. The first mixed raw material flow was supplied to a first heat exchanger 136, where it was heated to obtain a heated first mixed raw material flow 138 with a temperature of 890°C. The pressure of the heated first mixed raw material flow was set to 13 bar (absolute pressure).

[0123] A heated first mixed raw material flow was supplied to the first reactor 116. The first reactor was operated in an adiabatic manner. In the simulation, thermodynamic equilibrium was assumed for the following reactions: [ka]

[0124] The first product stream 118, withdrawn from the first reactor 116, had a temperature of 762°C and a pressure of 11.5 bar (absolute pressure). The conversion rate of CO2 was 36.6%, and methane was produced in a yield of 1.3%.

[0125] The first product flow 118 was mixed with the second hydrogen raw material flow 124 to obtain the second mixed raw material flow 126. The molar ratio of hydrogen to carbon dioxide in the second mixed raw material flow was set to 1.46. The second mixed raw material flow was supplied to the second heat exchanger 128 and heated there to obtain a heated second mixed raw material flow 130 with a temperature of 895°C. The pressure of the heated second mixed raw material flow was set to 11.5 bar (absolute pressure).

[0126] The heated second mixed raw material flow was supplied to the second reactor 132, which was also operated adiabatically. Here, as before, thermodynamic equilibrium was assumed for the reaction described above.

[0127] The second product stream 134, withdrawn from the second reactor 132, had a temperature of 835°C and a pressure of 10 bar (absolute pressure). The total conversion rate of CO2 was 56.7%, and methane was produced in a yield of 1.8%.

[0128] Example 2 A high-purity carbon dioxide feedstock stream was supplied to a heated first tube at ambient temperature, pressure of 18 bar (absolute pressure), and flow rate of 75 ml(n) / min, heating to 700°C. A high-purity hydrogen feedstock stream was supplied to a heated second tube at ambient temperature, pressure of 18 bar (absolute pressure), and flow rate of 75 ml(n) / min, heating to 700°C. Both tubes were made from nickel-chromium-iron alloy (material number 2.4816). The heated carbon dioxide stream and the heated hydrogen stream were then mixed, and the resulting heated mixed feedstock stream was supplied to a reaction tube made from the same material as the heating tubes. The reaction tubes were placed in tubular furnaces providing temperature compartments of 800°C and 850°C, respectively. To test the suitability of the materials as constituent materials under RWGS reaction conditions, five 5mm x 5mm metal plate samples, each containing different alloys and stainless steels of different compositions, were placed in each temperature compartment of the reaction tube. The plates were fixed in a 3mm quartz bead bed.

[0129] This experiment was run for over 2000 hours. During this period of operation, the pressure drop throughout the entire apparatus, namely the heating tubes and reaction tubes, remained nearly constant. No coke formation or other undesirable tube blockages were observed.

[0130] Comparative Example In further experiments, high-purity carbon dioxide and high-purity hydrogen raw material flows were mixed at ambient temperature according to Example 2. This mixed raw material flow was supplied to a heated reaction tube at a pressure of 18 bar (absolute pressure) and a flow rate of 150 ml(n) / min. The reaction tube was made from the same nickel-chromium-iron alloy (material number 2.4816) as in Example 2. The reaction tube was placed in a tubular furnace providing temperature compartments of 325°C, 400°C, 475°C, 550°C, 625°C, 700°C, 750°C, 800°C, and 850°C, respectively. To test the suitability of the materials as constituents under RWGS reaction conditions, five 5 mm × 5 mm metal plate samples, each containing different alloys and stainless steel of different compositions, were placed in each temperature compartment of the reaction tube. The plates were fixed in a 3 mm quartz bead bed.

[0131] During the experiment's operation, the pressure drop throughout the reaction tube steadily increased, suggesting that coke formation within the tube was increasing. After 24 hours of operation, the reaction tube became completely blocked, and the experiment had to be stopped. Inspection of the reaction tube revealed that the inner surface of the tube, including the small plates, was covered with a thick layer of coke. [Explanation of symbols]

[0132] 102 Low-temperature carbon dioxide flow 104 Carbon Dioxide Raw Material Preheater 106 Carbon dioxide raw material flow 108 Low-temperature hydrogen flow 110 Hydrogen preheater 112 First Hydrogen Raw Material Flow 114 First Mixed Raw Material Flow 116 Reactor No. 1 118 First product flow 120 Another low-temperature hydrogen stream 122 Another hydrogen preheater 124 Second hydrogen raw material flow 126 Second Mixing Material Flow 128 Second heat exchanger 130 Heated second mixed raw material flow 132 Reactor No. 2 134 Second product flow 136 1st heat exchanger 138 Heated first mixed raw material flow 140 Crude carbon dioxide raw material flow 142 Purification Unit 144 Product Cooler 146 Cooled product flow

Claims

1. A method for hydrogenating carbon dioxide: (a) The step of providing a carbon dioxide raw material flow (106) at a temperature of 600°C to 1000°C; (b) The step of providing a first hydrogen raw material flow (112) at a temperature of 600°C to 1000°C; (c) The step of obtaining a first mixed raw material flow (114) by mixing the carbon dioxide raw material flow (106) and the first hydrogen raw material flow (112); (d) optionally heating the first mixed raw material flow (114) to a temperature of 800°C to 1000°C in a first heat exchanger (136) to obtain a heated first mixed raw material flow (138); (e) supplying the first mixed raw material flow (114) and / or the heated first mixed raw material flow (138) to a first reactor (116) at a temperature of 800°C to 1000°C, and bringing the first mixed raw material flow (114) and / or the heated first mixed raw material flow (138) into contact with a catalyst to obtain a first product flow (118) containing at least carbon monoxide, water and unreacted carbon dioxide; A method that includes this.

2. (f) The step of obtaining a second mixed raw material flow (126) by mixing the first product flow (118) with a second hydrogen raw material flow (124); (g) The step of heating the second mixed raw material flow (126) to a temperature of 800°C to 1000°C in the second heat exchanger (128); (h) The steps of supplying the heated second mixed raw material flow (130) to a second reactor (132) and bringing the heated second mixed raw material flow (130) into contact with a catalyst to obtain a second product flow (134) containing at least carbon monoxide, water and unreacted carbon dioxide; The method according to claim 1, further comprising:

3. The method according to claim 1 or 2, characterized in that the carbon dioxide raw material flow (106) contains 90 mol% to 100 mol% carbon dioxide, the first hydrogen raw material flow (112) contains 90 mol% to 100 mol% hydrogen, and the molar ratio of carbon dioxide to hydrogen in the first mixed raw material flow (114) and / or the heated first mixed raw material flow (138) is 0.9 to 3, preferably 1.3 to 2.

5.

4. The method according to any one of claims 1 to 3, characterized in that the first product stream (118) and / or the second product stream (134) contain 10 mol% to 40 mol% of carbon monoxide and less than 2 mol% of methane.

5. The method according to any one of claims 1 to 4, characterized in that both the first hydrogen raw material flow (112) and the second hydrogen raw material flow (124) are obtained by heating a low-temperature hydrogen flow (108) in a hydrogen preheater (110), and at least a portion of the heat is generated by electricity.

6. The method according to any one of claims 1 to 5, characterized in that the carbon dioxide raw material flow (106) is obtained by supplying a crude carbon dioxide raw material flow (140) to a purification unit (142) and removing at least a portion of any impurities that may be present in the crude carbon dioxide raw material flow (140).

7. The method according to any one of claims 1 to 6, characterized in that the carbon dioxide raw material flow (106) is obtained by heating a low-temperature carbon dioxide flow (102) in a carbon dioxide raw material preheater (104), and the first product flow (118) and / or the second product flow (134) are cooled in a product cooler (144) to obtain a cooled product flow (146), and at least a portion of the heat removed from the first product flow (118) and / or the second product flow (134) in the product cooler (144) is transferred to the carbon dioxide raw material preheater (104) to heat the carbon dioxide raw material flow (106).

8. The method according to claim 7, wherein the carbon dioxide raw material preheater (104) includes a first preheater that receives heat from the product cooler (144) and a second preheater that is preferably heated by electricity, and the temperature of the carbon dioxide raw material flow that flows out of the first preheater and into the second preheater is 300°C to 450°C.

9. The method according to claim 7 or 8, characterized in that the product cooler (144) includes a first cooler and a second cooler that transfer heat to the carbon dioxide raw material preheater (104), and the temperature of the second product flow flowing out of the first cooler and into the second cooler is 350°C to 470°C.

10. The method according to claim 9, characterized in that the first cooler is cooled with water, and the water evaporates within the first cooler to generate water vapor.

11. The method according to any one of claims 1 to 10, characterized in that (a) the carbon dioxide raw material flow (106) and the first hydrogen raw material flow (112) and / or (b) the first product flow (118) and the second hydrogen raw material flow (124) are supplied to a gas mixer before flowing into the first reactor (116), the first heat exchanger (136) and / or the second heat exchanger (128).

12. This is a reaction system for hydrogenating carbon dioxide: A first gas mixer configured to receive a carbon dioxide raw material flow (106) at a temperature of 600°C to 1000°C and a first hydrogen raw material flow (112) at a temperature of 600°C to 1000°C, and to mix the two flows to obtain a first mixed raw material flow (114); An optional first heat exchanger (136) configured to receive the first mixed raw material flow (114) and heat the first mixed raw material flow to a temperature of 800°C to 1000°C to obtain a heated first mixed raw material flow (138); The first reactor (116) is configured to receive the first mixed raw material flow (114) and / or the heated first mixed raw material flow (138) at a temperature of 800°C to 1000°C and to bring it into contact with a catalyst in the first reactor (116) to obtain a first product flow (118) containing at least carbon monoxide, water and unreacted carbon dioxide; A reaction system that includes this.

13. The aforementioned reaction system is: A second heat exchanger (128) configured to receive a second mixed raw material flow (126) as a mixture of the first product flow (118) and the second hydrogen raw material flow (124), and to heat the second mixed raw material flow (126) to a temperature of 800°C to 1000°C; The second reactor (132) is configured to receive the heated second mixed raw material flow (130) and bring it into contact with the catalyst in the second reactor (132) to obtain a second product flow (134) containing at least carbon monoxide, water and unreacted carbon dioxide; The reaction system according to claim 12, further comprising the following:

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