Process for hydrogenation of carbon dioxide

Abstract

The present invention relates to a reaction system and process for the hydrogenation of carbon dioxide, the process comprising: (a) providing a carbon dioxide feed stream (106) at a temperature of at least 600 DEG C; (b) providing a first hydrogen feed stream (112) having a temperature of at least 600 DEG C; (c) mixing the carbon dioxide feed stream and the first hydrogen feed stream to obtain a first mixed feed stream (114); (d) optionally, heating the first mixed feed stream to a temperature of at least 800 DEG C in a first heat exchanger (136), obtaining a heated first mixed feed stream (138); (e) feeding the first mixed feed stream and / or the heated first mixed feed stream at a temperature of 800 DEG C to 1000 DEG C to a first reactor (116) in which it is contacted 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 into a reactor, wherein the mixed feed stream is brought into contact with a catalyst. Background Technology

[0002] Reforming hydrogen and carbon dioxide (also known as carbon dioxide hydrogenation or reverse water-gas shift reaction (RWGS)) offers significant economic benefits because these methods allow the production of syngas, an important basic chemical, from carbon dioxide as a starting material. Correspondingly, carbon dioxide obtained as a waste product in many processes can be chemically combined with it. This allows for a reduction in carbon dioxide emissions into the atmosphere.

[0003] Syngas, also known as synthesis gas, is a gaseous mixture containing hydrogen (H2) and carbon monoxide (CO) that can be used as a basic chemical in many industrial processes. Depending on its application, syngas has different hydrogen-to-carbon monoxide ratios. Syngas may contain additional components such as water (H2O), carbon dioxide (CO2), methane (CH4), and / or nitrogen (N2).

[0004] Various methods for producing syngas from carbon dioxide and hydrogen via a reverse water-gas shift reaction are known in the art. As an example, document WO 2021 / 062384 A1 discloses a method for producing syngas, comprising: (i) reacting at least a portion of carbon dioxide with hydrogen in an initial reactor to produce an initial product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; and (ii) reacting at least a portion of the unreacted carbon dioxide and unreacted hydrogen in a reactor downstream of the initial reactor to produce a product stream comprising carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen.

[0005] Document WO 2021 / 225643 A1 discloses a method for converting a feed gas containing carbon dioxide and hydrogen into a product gas containing carbon monoxide and water. The feed gas is electrically preheated to at least 760°C in a heat exchanger before entering an adiabatic or isothermal reactor where a catalytic RWGS reaction occurs. The resulting product mixture can be reheated in a second electric heater and fed into a second reactor for further conversion of carbon dioxide into carbon monoxide.

[0006] Document WO 2022 / 129338 discloses a method for producing syngas in a two-stage catalytic RWGS reaction while maintaining the temperature in the RWGS reactor below 700°C.

[0007] Although several process schemes for carbon dioxide hydrogenation are known and have been industrialized, improvements to the technology are still needed, especially in terms of avoiding the formation of coke and unwanted byproducts, energy consumption in such high-temperature processes, and sustainability.

[0008] The object of this invention is to provide a method for hydrogenating carbon dioxide that minimizes the formation of coke in heat exchangers and reactors. Another object of this invention is to provide a method for hydrogenating carbon dioxide that minimizes the formation of the unwanted byproduct methane. Yet another object of this invention is to provide a method for hydrogenating carbon dioxide in an energy-efficient reaction system with a compact design.

[0009] According to the invention, these tasks are accomplished by the method according to claim 1 and the reaction system according to claim 12. Advantageous variations of the method are presented in claims 2 to 11. Brief description

[0010] As used herein, the terms “have,” “include,” or “contain,” or any of their grammatical variations, are used in a non-exclusive manner. Thus, these terms can refer either to a situation where no other features exist in the entity described in the context besides those introduced by these terms, or to a situation where one or more other features exist. For example, the statements “A has B,” “A includes B,” and “A contains B” can refer either to a situation where no other elements exist in A besides B (i.e., A consists solely of B), or to a situation where entity A contains one or more other elements besides B (such as element C, elements C and D, or other elements).

[0011] Furthermore, it should be noted that the terms "at least one," "one or more," or similar expressions indicating a feature or element may appear once or more, but are typically used only once when describing the corresponding feature or element. In most cases, the expressions "at least one" or "one or more" are not repeated when referring to the corresponding feature or element, but in fact, the corresponding feature or element may appear once or more.

[0012] Furthermore, as used herein, the terms “preferredly,” “more preferably,” “particularly,” “more particularly,” “specifically,” “more specifically,” or similar terms are used in combination with optional features without limiting the possibility of alternatives. Therefore, the features introduced by these terms are optional features and are not intended to limit the scope of the claims in any way. As those skilled in the art will recognize, the invention can be practiced by using alternative features. Similarly, features introduced by phrases such as “in embodiments of the invention” are intended to be optional features and do not limit any alternative embodiments of the invention, the scope of the invention, or the possibility of combining features introduced in this way with other optional or non-optional features of the invention.

[0013] In a first aspect of the invention, a method for hydrogenating carbon dioxide includes the following steps: (a) providing a carbon dioxide feed stream at a temperature of 600°C to 1000°C; (b) providing a first hydrogen feed stream at a temperature of 600°C to 1000°C; (c) mixing the carbon dioxide feed stream and the first hydrogen feed stream to obtain a first mixed feed stream; (d) optionally, heating the first mixed feed stream to a temperature of 800°C to 1000°C in a first heat exchanger to obtain a heated first mixed feed stream; and (e) feeding the first mixed feed stream and / or the heated first mixed feed stream at a temperature of 800°C to 1000°C into a first reactor, in which the first mixed feed stream and / or the heated first mixed feed stream are contacted with a catalyst to obtain a first product stream containing at least carbon monoxide, water, and unreacted carbon dioxide.

[0014] In a second aspect of the invention, a reaction system for carbon dioxide hydrogenation includes: a first gas mixer configured to receive a carbon dioxide feed stream at a temperature of 600°C to 1000°C and a first hydrogen feed stream at a temperature of 600°C to 1000°C, and to mix the two streams to obtain a first mixed feed stream; optionally, a first heat exchanger configured to receive the first mixed feed stream and heat the first mixed feed stream to a temperature of 800°C to 1000°C to obtain a heated first mixed feed stream; and a first reactor configured to receive the first mixed feed stream and / or the heated first mixed feed stream at a temperature of 800°C to 1000°C and to contact it with a catalyst within the first reactor to obtain a first product stream containing at least carbon monoxide, water, and unreacted carbon dioxide.

[0015] It has been found that heating the feed streams of reactants carbon dioxide and hydrogen to at least 600°C before mixing significantly reduces or even eliminates coking. Further heating the first mixed feed stream to temperatures above 600°C does not result in significant coking.

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

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

[0018] In another embodiment, an additional hydrogen feed stream is provided to a reaction system having at least two reaction stages. In this embodiment, the following additional steps may follow the above method steps (a) to (e): (f) mixing the first product stream with the second hydrogen feed stream to obtain a second mixed feed stream; (g) heating the second mixed feed stream to a temperature of 800°C to 1000°C in a second heat exchanger; and (h) feeding the heated second mixed feed stream into a second reactor, in which the heated second mixed feed stream is contacted with a catalyst to obtain a second product stream containing at least carbon monoxide, water, and unreacted carbon dioxide.

[0019] A suitable reaction system for performing the method according to this embodiment may include: a second heat exchanger configured to receive a second mixed feed stream as a mixture of a first product stream and a second hydrogen feed stream and to heat the second mixed feed stream to a temperature of 800°C to 1000°C; and a second reactor configured to receive the heated second mixed feed stream and to contact it with a catalyst within the second reactor to obtain a second product stream containing at least carbon monoxide, water, and unreacted carbon dioxide.

[0020] It has been found that providing an additional hydrogen feed stream during multi-stage reaction processes can significantly reduce the formation of the unwanted byproduct methane.

[0021] The second product stream can be the final product stream or an intermediate product stream that undergoes further reaction in subsequent stages of the reaction system. In the case of more than two reaction stages, each additional reaction stage can be provided with an additional hydrogen feed stream.

[0022] As used herein, the term "carbon dioxide feed stream" is a broad term and will be given its common and conventional meaning to those skilled in the art and is not limited to any particular or custom meaning. Specifically, the term may refer to, but is not limited to, any gaseous stream containing at least carbon dioxide as a reactant for the RWGS reaction.

[0023] The carbon dioxide content in the carbon dioxide feed stream 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 feed stream can depend on the configuration of the reaction system. In embodiments where the carbon dioxide feed stream is mixed with a first hydrogen feed stream and subsequently fed into a first reactor without further heating of the first mixed feed stream, the temperature of the carbon dioxide feed stream 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, at least 900°C. In this case, the temperature of the carbon dioxide feed stream can be at most 1200°C, preferably at most 1100°C, more preferably at most 1000°C.

[0025] In embodiments where the carbon dioxide feed stream is mixed with the first hydrogen feed stream and the resulting first mixed feed stream is further heated in one or more heat exchangers before entering the first reactor, the temperature of the carbon dioxide feed stream 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 this case, the temperature of the carbon dioxide feed stream can be at most 800°C, preferably at most 780°C, more preferably at most 765°C, and even more preferably at most 750°C.

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

[0027] As used herein, the term "hydrogen feed stream" is a broad term and will be given its common and conventional meaning to those skilled in the art and is not limited to any particular or custom meaning. Specifically, the term may refer to, but is not limited to, any gaseous stream containing at least hydrogen as a reactant for the RWGS reaction.

[0028] Hydrogen can be added to the reaction system at one or several different locations. The terms "first hydrogen feed stream," "second hydrogen feed stream," "additional hydrogen feed stream," or "auxiliary hydrogen feed stream" are used to distinguish hydrogen feed streams added to the reaction system at different locations (if applicable). In embodiments with more than one hydrogen feed stream, the different hydrogen feed streams can have the same or different compositions, temperatures, or pressures.

[0029] The hydrogen content in the hydrogen feed stream 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-.

[0030] The pressure of the hydrogen feed stream can be from 1 bar (absolute value) to 70 bar (absolute value), preferably from 3 bar (absolute value) to 50 bar (absolute value), more preferably from 6 bar (absolute value) to 20 bar (absolute value), for example at least 1 bar (absolute value), at least 2 bar (absolute value), at least 3 bar (absolute value), at least 4 bar (absolute value), at least 5 bar (absolute value), at least 6 bar (absolute value), and at most 70 bar (absolute value), at most 60 bar (absolute value), at most 50 bar (absolute value), at most 40 bar (absolute value), at most 30 bar (absolute value), and at most 20 bar (absolute value).

[0031] The temperature of the first hydrogen feed stream can depend on the configuration of the reaction system. In embodiments where the first hydrogen feed stream is mixed with the carbon dioxide feed stream and subsequently fed into the first reactor without further heating of the first mixed feed stream, the temperature of the first hydrogen feed stream can be at least 800°C, preferably at least 850°C, more preferably at least 900°C. In this case, the temperature of the first hydrogen feed stream can be at most 1200°C, preferably at most 1100°C, more preferably at most 1000°C.

[0032] In embodiments where a first hydrogen feed stream is mixed with a carbon dioxide feed stream and the resulting first mixed feed stream is further heated in one or more heat exchangers before entering a first reactor, the temperature of the first hydrogen feed stream 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 this case, the temperature of the first hydrogen feed stream can be at most 800°C, preferably at most 780°C, more preferably at most 765°C, and most preferably at most 750°C.

[0033] In embodiments where more than one hydrogen feed stream is supplied to the reaction system, the temperature of the second hydrogen feed stream and / or additional hydrogen feed streams 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 this case, the temperature of the first hydrogen feed stream can be at most 800°C, preferably at most 780°C, more preferably at most 765°C, and most preferably at most 750°C.

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

[0035] In some embodiments, the hydrogen preheater is a gas heater that transfers energy from burning hydrogen, hydrocarbon gases (e.g., natural gas), or mixtures thereof to a stream of cold hydrogen flowing through the preheater. In other embodiments, the hydrogen preheater is an electric heater that uses electricity to heat the stream of cold hydrogen. In one embodiment, the hydrogen preheater includes at least one tube that is heated from the outside and transfers heat through its walls to the stream of cold hydrogen flowing through it. In a variation of this embodiment, the hydrogen preheater includes multiple tubes that are heated from the outside and transfer heat through their walls to the stream of cold hydrogen flowing through them.

[0036] A hydrogen preheater may include one or more individual heaters. In the case of more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel connections. The heaters may be based on the same design principles or different design principles. For example, one heater may be an electrically operated heater, and another heater may be an open-flame heater operated by burning fuel.

[0037] In some embodiments, the first hydrogen feed stream, the second hydrogen feed stream, or both the first hydrogen feed stream and the second hydrogen feed stream are obtained by heating a cold hydrogen stream in a hydrogen preheater, in which heat is generated at least in part by electricity.

[0038] As used herein, the term "first mixed feed stream" is a broad term and will be given its common and conventional meaning to those skilled in the art and is not limited to any particular or custom meaning. Specifically, the term may refer to, but is not limited to, any gaseous stream resulting from the mixing of at least a carbon dioxide feed stream and a first hydrogen feed stream.

[0039] The mixing can be performed using any suitable equipment and methods known in the art. In some embodiments, the carbon dioxide feed stream and the first hydrogen feed stream are fed into the first gas mixer before entering the first heat exchanger. This has the advantage of avoiding unmixed H2 / CO2 pressures that could otherwise lead to reduced heat transfer in the subsequent heat exchanger. The first gas mixer can be any device suitable for mixing at least two gas streams. Preferred gas mixers are perforated plates, static mixers, and dynamic mixers, such as fans.

[0040] The temperature of the first mixed feed stream can depend on the configuration of the reaction system. In embodiments where the first mixed feed stream is fed into the first reactor without further heating, the temperature of the first mixed feed stream can be at least 800°C, preferably at least 820°C, and more preferably at least 850°C. In this case, the temperature of the first mixed feed stream can be at most 1200°C, preferably at most 1100°C, and more preferably at most 1000°C.

[0041] In embodiments where the first mixed feed stream is further heated in one or more heat exchangers before entering the first reactor, the temperature of the first mixed feed stream can be at least 600°C, preferably at least 650°C, more preferably at least 700°C. In this case, the temperature of the first mixed feed stream can be at most 800°C, preferably at most 750°C, more preferably at most 700°C.

[0042] The pressure of the first mixed feed stream is preferably from 1 bar to 70 bar, more preferably from 3 bar to 50 bar, and even more preferably from 6 bar to 20 bar, for example at least 1 bar, at least 2 bar, at least 3 bar, at least 4 bar, at least 5 bar, at least 6 bar, and at most 70 bar, at most 60 bar, at most 50 bar, at most 40 bar, at most 30 bar, and at most 20 bar.

[0043] In some embodiments, a first mixed feed stream is fed into a first heat exchanger, where it is heated to a temperature of 800°C to 1000°C, preferably 850°C to 950°C, and more preferably 880°C to 920°C to obtain a heated first mixed feed stream. The first heat exchanger may have any form, size, and design principle suitable for heating a gaseous stream containing carbon dioxide and hydrogen from a temperature range of 600°C to 800°C to a temperature range of 800°C to 1000°C.

[0044] In some embodiments, the first heat exchanger is a gas heater that transfers energy from burning hydrogen, hydrocarbon gases (e.g., natural gas), or mixtures thereof to a first mixed feed stream flowing through the first heat exchanger. In other embodiments, the first heat exchanger is an electric heater that uses electricity to heat the first mixed feed stream. In one embodiment, the first heat exchanger includes at least one tube that is heated from the outside and transfers heat through its walls to the first mixed feed stream flowing through the tube. In a variation of this embodiment, the first heat exchanger includes a plurality of tubes that are heated from the outside and transfer heat through their walls to the first mixed feed stream flowing through these tubes.

[0045] The first heat exchanger may include one or more individual heaters. In the case of more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel connections. The heaters may be based on the same design principles or different design principles. For example, one heater may be an electrically operated heater, and another heater may be an open-flame heater operated by burning fuel.

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

[0047] The first mixed feed stream and / or the heated first mixed feed stream are fed into the first reactor at a temperature of 800°C to 1000°C. In some embodiments, the first mixed feed stream is fed into the first reactor. In some embodiments, the heated first mixed feed stream is fed into the first reactor. In some embodiments, both the first mixed feed stream and the heated first mixed feed stream are fed into the first reactor.

[0048] As used herein, the term "first reactor" is a broad term and will be given its common and conventional meaning to those skilled in the art and is not limited to any particular or custom meaning. Specifically, the term may refer to, but is not limited to, any reactor suitable for performing a catalytic RWGS reaction.

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

[0050] In another embodiment, the first reactor is an adiabatic monolithic reactor. Preferably, in this case, the catalyst is applied as a carrier coating to the entire reactor. An advantage of this type of reactor is its low pressure drop between its inlet and outlet.

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

[0052] Catalysts for catalyzing RWGS reactions are known in the art. For example, document WO 2018 / 219992 A1 discloses a heterogeneous nickel and magnesium spinel catalyst for carbon dioxide hydrogenation. In some embodiments, the catalyst comprises nickel (Ni), magnesium (Mg), and aluminum (Al). Preferably, the catalyst has a nickel content in the range of 5 mol-% to 30 mol-% of the total, a magnesium content in the range of 10 mol-% to 40 mol-% of the total, and an aluminum content in the range of 40 mol-% to 70 mol-% of the total.

[0053] The catalyst can be mounted in the first reactor in any form suitable for the RWGS reaction inside the catalytic reactor. In some embodiments, the catalyst is in the form of granules, such as tetralobes or hexallobes, with or without internal pores. In some embodiments, the catalyst is in the form of extrusions, such as cylindrical or blade-shaped, such as trilobes. In some embodiments, the catalyst is mounted in the reactor as a three-dimensional porous structure.

[0054] The products of the RWGS reaction in the first reactor are discharged at least partially 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 contain other substances, such as unreacted hydrogen or reaction byproducts, such as methane.

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

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

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

[0058] In some embodiments, the first product stream is mixed with a second hydrogen feed stream to obtain a second mixed feed stream. Mixing can be performed using any suitable equipment and methods known in the art. In some embodiments, the first product stream and the second hydrogen feed stream are fed into a second gas mixer before entering a second heat exchanger. This has the advantage of avoiding unmixed H2 / CO2 pressures that could otherwise lead to reduced heat transfer in the subsequent heat exchanger. The second gas mixer can be any device suitable for mixing at least the gas streams. Preferred gas mixers are perforated plates, static mixers, and dynamic mixers, such as fans.

[0059] The temperature of the second mixed feed stream can depend on the configuration of the reaction system. In embodiments where the second mixed feed stream is fed into the second reactor without further heating, the temperature of the second mixed feed stream can be at least 800°C, preferably at least 850°C, and more preferably at least 900°C. In this case, the temperature of the second mixed feed stream can be at most 1200°C, preferably at most 1100°C, and more preferably at most 1000°C.

[0060] In embodiments where the second mixed feed stream is further heated in one or more heat exchangers before entering the second reactor, the temperature of the second mixed feed stream can be at least 600°C, preferably at least 650°C, more preferably at least 700°C. In this case, the temperature of the second mixed feed stream can be at most 800°C, preferably at most 775°C, more preferably at most 750°C.

[0061] The pressure of the second mixed feed stream is preferably from 1 bar to 70 bar, more preferably from 3 bar to 50 bar, and even more preferably from 6 bar to 20 bar, for example at least 1 bar, at least 2 bar, at least 3 bar, at least 4 bar, at least 5 bar, at least 6 bar, and at most 70 bar, at most 60 bar, at most 50 bar, at most 40 bar, at most 30 bar, and at most 20 bar.

[0062] In some embodiments, a second mixed feed stream is fed into a second heat exchanger, where it is heated to a temperature of 800°C to 1000°C, preferably 850°C to 950°C, and more preferably 880°C to 920°C. The second heat exchanger can have any form, size, and design principle suitable for heating a gaseous stream containing carbon dioxide and hydrogen from a temperature range of 600°C to 800°C to a temperature range of 800°C to 1000°C.

[0063] In some embodiments, the second heat exchanger is a gas heater that transfers energy from burning hydrogen, hydrocarbon gases (e.g., natural gas), or mixtures thereof to a second mixed feed stream flowing through the second heat exchanger. In other embodiments, the second heat exchanger is an electric heater that uses electricity to heat the second mixed feed stream. In one embodiment, the second heat exchanger includes at least one tube that is heated from the outside and transfers heat through its walls to the second mixed feed stream flowing through the tube. In a variation of this embodiment, the second heat exchanger includes multiple tubes that are heated from the outside and transfer heat through their walls to the second mixed feed stream flowing through these tubes.

[0064] The second heat exchanger may include one or more individual heaters. In the case of more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel connections. The heaters may be based on the same design principles or different design principles. For example, one heater may be an electrically operated heater, and another heater may be an open-flame heater operated by burning fuel.

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

[0066] The heated second mixed feed stream is fed into the second reactor. As used herein, the term "second reactor" is a broad term and will be given its common and conventional meaning to those skilled in the art and is not limited to any particular or custom meaning. Specifically, the term may refer to, but is not limited to, any reactor suitable for performing a catalytic RWGS reaction.

[0067] In some embodiments, the second reactor is an adiabatic reactor. In an embodiment, the second reactor is an adiabatic fixed-bed reactor. Preferably, the ratio of the reactor's length to its diameter is greater than 1, that is, the reactor's length is greater than its diameter.

[0068] In another embodiment, the second reactor is an adiabatic monolithic reactor. Preferably, in this case, the catalyst is applied as a carrier coating to the entire reactor. An advantage of this type of reactor is its low pressure drop between its inlet and outlet.

[0069] The catalyst used in the second reactor may be the same as that used in the first reactor, or it may be a different catalyst. 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 differs in shape from the catalyst used in the first reactor. 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] The products of the RWGS reaction in the second reactor are at least partially removed 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 contain other substances, such as unreacted hydrogen or reaction byproducts, such as methane.

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

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

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

[0074] The carbon dioxide feed stream mixed with the first hydrogen feed stream can have a composition containing 90 mol-% to 100 mol-% carbon dioxide.

[0075] In some embodiments, the carbon dioxide feed stream is obtained from a crude carbon dioxide feed stream. The crude carbon dioxide feed stream may contain impurities that could poison the catalyst used in the first or second reactor. Potential contaminants in this stream that could poison the catalyst may be sulfur compounds such as H₂S, COS, or CS₂. The carbon dioxide feed stream may be subjected to pretreatment or conditioning steps.

[0076] In some embodiments, the carbon dioxide feed stream is obtained by feeding a crude carbon dioxide feed stream into a purification unit, in which potential contaminants are at least partially removed from the crude carbon dioxide feed stream.

[0077] The purification unit can contain any device suitable for removing impurities and unwanted substances from the crude carbon dioxide feed stream, particularly sulfur components. In embodiments, the purification unit contains an absorber bed, which preferably operates at elevated temperatures, particularly above 80°C. The purification unit may include additional devices, such as filter units or membrane units, which may be used alone or in combination with any other devices in the purification unit.

[0078] Depending on its source, the carbon dioxide feed stream can have any temperature and pressure suitable for conveying the gaseous stream through, for example, a pipe.

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

[0080] In some embodiments, the carbon dioxide feed preheater is a gas heater that transfers energy from burning hydrogen, hydrocarbon gases (e.g., natural gas), or mixtures thereof to the carbon dioxide feed stream flowing through the preheater. In other embodiments, the carbon dioxide feed preheater is an electric heater that uses electricity to heat the carbon dioxide feed stream. The carbon dioxide feed preheater may include at least one tube that is heated externally and transfers heat through its walls to the carbon dioxide feed stream flowing through it. The carbon dioxide feed preheater may include multiple tubes that are heated externally and transfer heat through their walls to the carbon dioxide feed stream flowing through them.

[0081] A carbon dioxide feed preheater may include one or more individual heaters. In the case of more than one heater, the heaters may be connected in series, in parallel, or in a combination of series and parallel connections. The heaters may be based on the same design principles or different design principles. For example, one heater may be an electrically operated heater, and another heater may be an open-flame heater operated by burning fuel.

[0082] In some embodiments, the carbon dioxide feed preheater is thermally integrated with other parts of the process, meaning that heat released at a certain process stage or equipment is used to heat the carbon dioxide feed stream in the carbon dioxide feed preheater.

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

[0084] In one embodiment, the product cooler includes a single cooler to cool the second product stream to a desired temperature. In another embodiment, the product cooler includes more than one cooler connected in parallel, series, or a combination of both. A suitable cooling medium can be selected depending on the temperature range of the second product stream flowing through one or more coolers and the desired outlet temperature at the respective cooler(s). Preferably, the cooling medium is selected from the group consisting of water, oil, or any process stream suitable for thermal integration.

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

[0086] In some embodiments, the carbon dioxide feed stream is obtained by heating a cold carbon dioxide stream in a carbon dioxide feed preheater, and the first product stream and / or the second product stream is cooled in a product cooler to obtain a cooled product stream, wherein at least a portion of the heat removed from the first product stream and / or the second product stream in the product cooler is transferred to the carbon dioxide feed preheater to heat the carbon dioxide feed stream.

[0087] In some embodiments, the carbon dioxide feed preheater includes a first preheater that receives heat from a product cooler and a second preheater, preferably heated by electricity. Preferably, the carbon dioxide feed stream exiting the first preheater and entering the second preheater has a temperature of 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 the carbon dioxide feed preheater. Preferably, the second product stream exiting the first cooler and entering the second cooler has a temperature of 350°C to 470°C. More preferably, the first cooler is cooled by water vaporized in the first cooler to generate steam.

[0089] In some embodiments, those elements of the first heat exchanger exposed to high-temperature and / or corrosive media are made of heat-resistant materials (like certain stainless steel alloys or ceramic materials). In a preferred embodiment, the corresponding elements are made of a nickel-chromium alloy containing alloying elements (in weight percentages).

[0090] Nickel (Ni) 15 to 70

[0091] Chromium (Cr) 15 to 30

[0092] Silicon (Si) less than 2

[0093] Nickel-chromium alloys can contain other components such as carbon, manganese, titanium, copper, and iron.

[0094] In a further preferred embodiment, the elements of the first heat exchanger exposed to high-temperature and / or corrosive media are made of a nickel-iron-chromium alloy containing alloying elements (in weight percentages):

[0095] Carbon (C) content is less than 0.1%.

[0096] Silicon (Si) is less than 1

[0097] Manganese (Mn) less than 1.5

[0098] Chromium (Cr) 19 to 23

[0099] Nickel (Ni) 30 to 34

[0100] Titanium 0.15 to 0.6

[0101] Copper (Cu) less than 0.75

[0102] Iron (Fe) less than 39.5 Detailed Implementation

[0103] The invention is explained in more detail below with reference to the accompanying drawings. These drawings should be interpreted as a representation in principle. They do not constitute any limitation on the invention, such as with respect to particular dimensions or design variations. In the drawings:

[0104] Figure 1 A reaction system for carbon dioxide hydrogenation is shown as a first embodiment of the present invention.

[0105] Figure 2 A reaction system for carbon dioxide hydrogenation is shown as a second embodiment of the present invention.

[0106] Figure 3 A reaction system for carbon dioxide hydrogenation is shown as a third embodiment of the present invention.

[0107] Figure 4 A reaction system for carbon dioxide hydrogenation is shown as a fourth embodiment of the present invention.

[0108] Figure 5 A reaction system for carbon dioxide hydrogenation is shown as a fifth embodiment of the present invention.

[0109] Figure 1 A schematic diagram of a reaction system for carbon dioxide hydrogenation, as a first embodiment of the present invention, is shown. The reaction system includes a carbon dioxide feed preheater 104, a hydrogen preheater 110, and a first reactor 116.

[0110] A cold carbon dioxide stream 102 is fed into a carbon dioxide feed preheater 104 and heated therein to obtain a carbon dioxide feed stream 106 with a temperature of at least 800°C. The temperature of the cold carbon dioxide stream 102 can be in the range of 20°C to 250°C. The heating energy for the carbon dioxide feed preheater 104 is preferably provided by electricity.

[0111] A cold hydrogen stream 108 is fed into a hydrogen preheater 110 and heated therein to obtain a first hydrogen feed stream 112 with a temperature of at least 800°C. The temperature of the cold hydrogen stream 108 can be in the range of 20°C to 250°C. The heating energy for the hydrogen preheater 110 is preferably provided by electricity.

[0112] A carbon dioxide feed stream 106 and a first hydrogen feed stream 112 are mixed to obtain a first mixed feed stream 114 at a temperature of at least 800°C. This mixing can take place in a gas mixer (e.g., a static mixer). The first mixed feed stream 114 is fed into a first reactor 116 equipped with a catalyst suitable for RWGS reactions. Inside the first reactor 116, the first mixed feed stream 114 is contacted 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 contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0113] Figure 2 A schematic diagram of a reaction system for carbon dioxide hydrogenation, as a second embodiment of the present invention, is shown. The reaction system includes a carbon dioxide feed preheater 104, a hydrogen preheater 110, a first reactor 116, a further hydrogen preheater 122, a second heat exchanger 128, and a second reactor 132.

[0114] Similar to the above references Figure 1 The described method involves feeding a cold carbon dioxide stream 102 into a carbon dioxide feed preheater 104 and heating it therein to obtain a carbon dioxide feed stream 106 with a temperature of at least 800°C. The temperature of the cold carbon dioxide stream 102 can be in the range of 20°C to 250°C. The heating energy for the carbon dioxide feed preheater 104 is preferably provided by electricity.

[0115] A cold hydrogen stream 108 is fed into a hydrogen preheater 110 and heated therein to obtain a first hydrogen feed stream 112 with a temperature of at least 800°C. The temperature of the cold hydrogen stream 108 can be in the range of 20°C to 250°C. The heating energy for the hydrogen preheater 110 is preferably provided by electricity.

[0116] A carbon dioxide feed stream 106 and a first hydrogen feed stream 112 are mixed to obtain a first mixed feed stream 114 at a temperature of at least 800°C. This mixing can take place in a gas mixer (e.g., a static mixer). The first mixed feed stream 114 is fed into a first reactor 116 equipped with a catalyst suitable for RWGS reactions. Inside the first reactor 116, the first mixed feed stream 114 is contacted 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 contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0117] A separate cold hydrogen stream 120 is fed into a separate hydrogen preheater 122 and heated therein to obtain a second hydrogen feed stream 124. The temperature of the cold hydrogen stream 108 can be in the range of 20°C to 250°C, and the temperature of the second hydrogen feed stream 124 can also be in the range of 20°C to 250°C. The heating energy for the hydrogen preheater 110 is preferably provided by electricity.

[0118] The first product stream 118 and the second hydrogen feed stream 124 are mixed to obtain a second mixed feed stream 126. This second mixed feed stream is fed into 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 feed stream 130 is fed into a second reactor 132, which is also equipped with a catalyst suitable for the RWGS reaction. Inside the second reactor 132, the heated second mixed feed stream 130 is contacted with the catalyst to obtain a second product stream 134 containing at least carbon monoxide, water, and unreacted carbon dioxide. The second product stream 134 may contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0119] Figure 3 A schematic diagram of a reaction system for carbon dioxide hydrogenation, as a third embodiment of the present invention, is shown. 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.

[0120] The cold hydrogen stream 108 is preheated to a temperature of 600°C to 800°C in a hydrogen preheater 110 and split into a first hydrogen feed stream 112 and a second hydrogen feed stream 124. Alternatively, the cold hydrogen stream 108 can be initially split into two separate streams, each preheated to a temperature of 600°C to 800°C in the hydrogen preheater 110, producing the first hydrogen feed stream 112 and the second hydrogen feed stream 124. Heating energy is preferably provided by electricity. The first hydrogen feed stream 112 is mixed with a carbon dioxide feed stream 106 provided at a temperature of 600°C to 800°C. The resulting first mixed feed stream 114 is fed into a first heat exchanger 136, where it is heated to a temperature of 800°C to 1000°C. The heated first mixed feed stream 138 is fed into a first reactor 116 equipped with a catalyst suitable for RWGS reactions. Inside the first reactor 116, a heated first mixed feed stream 138 is contacted with a catalyst to obtain a first product stream 118 containing at least carbon monoxide, water, and unreacted carbon dioxide. The first product stream 118 may contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0121] The first product stream 118 is mixed with the second hydrogen feed stream 124 to obtain a second mixed feed stream 126. The second mixed feed stream is fed into a 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 combustion of a hydrocarbon-containing gas (e.g., natural gas, a hydrogen-containing gas, or a gas containing both hydrocarbons and hydrogen). The heated second mixed feed stream 130 is fed into a second reactor 132, which is also equipped with a catalyst suitable for the RWGS reaction. Inside the second reactor 132, the heated second mixed feed stream 130 is contacted with the catalyst to obtain a second product stream 134 containing at least carbon monoxide, water, and unreacted carbon dioxide. The second product stream 134 may contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0122] Figure 4 A schematic diagram of a reaction system for carbon dioxide hydrogenation, as a fourth embodiment of the present invention, is shown. The reaction system includes a hydrogen preheater 110, a purification unit 142, a carbon dioxide feed 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.

[0123] The crude carbon dioxide feed stream 140 is fed into a purification unit 142, where contaminants that could poison the catalyst ultimately contained in the crude carbon dioxide feed stream 140 are at least partially removed. The thus purified cold carbon dioxide stream 102 is preheated in a carbon dioxide feed preheater 104 to obtain a carbon dioxide feed stream 106 at a temperature of 600°C to 800°C.

[0124] The cold hydrogen stream 108 is preheated to a temperature of 600°C to 800°C in a hydrogen preheater 110 and split into a first hydrogen feed stream 112 and a second hydrogen feed stream 124. Alternatively, the cold hydrogen stream 108 can be initially split into two separate streams, each preheated to a temperature of 600°C to 800°C in the hydrogen preheater 110, producing the first hydrogen feed stream 112 and the second hydrogen feed stream 124. Heating energy is preferably provided by electricity. The first hydrogen feed stream 112 is mixed with a carbon dioxide feed stream 106. The resulting first mixed feed stream 114 is fed into a first heat exchanger 136, where it is heated to a temperature of 800°C to 1000°C. The heated first mixed feed stream 138 is fed into a first reactor 116 equipped with a catalyst suitable for RWGS reactions. Inside the first reactor 116, a heated first mixed feed stream 138 is contacted with a catalyst to obtain a first product stream 118 containing at least carbon monoxide, water, and unreacted carbon dioxide. The first product stream 118 may contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0125] The first product stream 118 is mixed with the second hydrogen feed stream 124 to obtain a second mixed feed stream 126. The second mixed feed stream is fed into a 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 combustion of a hydrocarbon-containing gas (e.g., natural gas, a hydrogen-containing gas, or a gas containing both hydrocarbons and hydrogen). The heated second mixed feed stream 130 is fed into a second reactor 132, which is also equipped with a catalyst suitable for the RWGS reaction. Inside the second reactor 132, the heated second mixed feed stream 130 is contacted with the catalyst to obtain a second product stream 134 containing at least carbon monoxide, water, and unreacted carbon dioxide. The second product stream 134 may contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0126] The second product stream 134 is cooled in the product cooler 144 to obtain a cooled product stream 146, wherein at least a portion of the heat removed from the second product stream 134 in the product cooler 144 is transferred to the carbon dioxide feed preheater 104 to heat the carbon dioxide feed stream 106. Figure 4 The dashed lines in the diagram represent heat transfer.

[0127] Figure 5A schematic diagram of a reaction system for carbon dioxide hydrogenation, as a fifth embodiment of the present invention, is shown. The reaction system includes a carbon dioxide feed preheater 104, a hydrogen preheater 110, a further hydrogen preheater 122, a first heat exchanger 136, a first reactor 116, a second heat exchanger 128, a second reactor 132, and a product cooler 144. In this example, the feed preheaters include two separate heaters for each feed stream: a first carbon dioxide feed preheater 104A and a subsequent second carbon dioxide feed preheater 104B, a first hydrogen preheater 110A and a subsequent second hydrogen preheater 110B, and a first further hydrogen preheater 122A and a subsequent second further hydrogen preheater 122B.

[0128] A cold carbon dioxide stream 102 is fed into a carbon dioxide feed preheater 104 and heated therein to obtain a carbon dioxide feed stream 106 with a temperature of at least 600°C. The temperature of the cold carbon dioxide stream 102 can be in the range of 20°C to 250°C. A cold hydrogen stream 108 is fed into a hydrogen preheater 110 and heated therein to obtain a first hydrogen feed stream 112 with a temperature of at least 600°C. The temperature of the cold hydrogen stream 108 can be in the range of 20°C to 250°C.

[0129] A carbon dioxide feed stream 106 and a first hydrogen feed stream 112 are mixed to obtain a first mixed feed stream 114 at a temperature of at least 800°C. This mixing can take place in a gas mixer (e.g., a static mixer). The first mixed feed stream 114 is fed to a first heat exchanger 136, where it is heated to a temperature of 800°C to 1000°C. The heated first mixed feed stream 138 is fed to a first reactor 116 equipped with a catalyst suitable for RWGS reactions. Inside the first reactor 116, the heated first mixed feed stream 138 is contacted 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 contain additional components, such as unreacted hydrogen, nitrogen, or methane.

[0130] An additional cold hydrogen stream 120 is fed into a separate hydrogen preheater 122 and heated therein to obtain a second hydrogen feed stream 124. The temperature of the cold hydrogen stream 108 can be in the range of 20°C to 250°C, and the temperature of the second hydrogen feed stream 124 can also be in the range of 20°C to 250°C.

[0131] A first product stream 118 and a second hydrogen feed stream 124 are mixed to obtain a second mixed feed stream 126. This second mixed feed stream is fed into a second heat exchanger 128, where it is heated to a temperature of 800°C to 1000°C. The heated second mixed feed stream 130 is fed into a second reactor 132, which is also equipped with a catalyst suitable for RWGS reactions. Inside the second reactor 132, the heated second mixed feed stream 130 is contacted with the catalyst to obtain a second product stream 134 containing at least carbon monoxide, water, and unreacted carbon dioxide. The second product stream 134 may contain additional components, such as unreacted hydrogen, nitrogen, or methane. The second product stream 134 is cooled in a product cooler 144 to obtain a cooled product stream 146.

[0132] In this example, the heating energy required to heat the feed stream is provided from different sources. The first hydrogen preheater 110A and the first additional hydrogen preheater 122A are preferably heated by electrical energy. The cold hydrogen stream 108 and the additional cold hydrogen stream 120 can be heated to a temperature in the range of 500°C to 650°C by the first heater. The second hydrogen preheater 110B and the second additional hydrogen preheater 122B can be heated by electrical energy or by burning hydrogen or a hydrocarbon-containing gas (e.g., natural gas).

[0133] The first heat exchanger 136 and the second heat exchanger 128 can be electric heaters or open flame heaters, in which fuels such as hydrogen or hydrocarbon-containing gases (e.g., natural gas) are burned to generate heating energy.

[0134] The carbon dioxide feed preheater 104 may include an electric heater, an open flame heater, or a heat exchanger that transfers energy from other heat exchangers to the cold carbon dioxide stream 102 via thermal integration. The first carbon dioxide feed preheater 104A may be thermally integrated, for example, with the product cooler 144, such that at least a portion of the heat removed from the second product stream 134 in the product cooler 144 is transferred to the carbon dioxide feed preheater 104 to heat the carbon dioxide feed stream 106. Figure 5 The dashed lines in the diagram represent heat transfer. The second carbon dioxide feed preheater 104B can be heated by an external source, such as flue gas from the open flame heater of the reaction system or high-temperature flue gas.

[0135] exist Figure 5 In the illustrated embodiments, and in any other embodiments, additional thermal integration schemes are possible. For example, in the case of the open-flame first heat exchanger 136 and / or the open-flame second heat exchanger 128, the hot flue gas exiting these heat exchangers can be used to heat either of the feed preheaters. The feed preheater can also be subdivided into multiple units to allow for additional electric heating, for example, in cases where thermal integration with the hot flue gas is insufficient.

[0136] Example 1

[0137] As an example, the commercial simulation tool Aspen Plus V14, manufactured by AspenTech (20 Crosby Drive, Bedford, 01730, MA, www.aspentech.com), provides examples of simulations such as... Figure 3 The reaction system shown was simulated. The simulation tool is equation-based, using physical property data produced by AspenTech. The simulation was performed using the SRK property model included in the software package. In Aspen, boxes 110, 136, and 128 use the "heater" model. Boxes 116 and 132 are modeled as a balanced reactor "REquil".

[0138] A carbon dioxide feed stream 106 at 700°C and a first hydrogen feed stream 112 at 700°C are mixed to obtain a first mixed feed stream 114. The molar ratio of hydrogen to carbon dioxide in the first mixed feed stream is 0.67. The first mixed feed stream is fed into a first heat exchanger 136, where it is heated to obtain a heated first mixed feed stream 138 at 890°C. The pressure of the heated first mixed feed stream is 13 bar (absolute value).

[0139] The heated first mixed feed stream is fed into the first reactor 116. The first reactor operates in adiabatic mode. For the simulation, it is assumed that the following reaction reaches thermodynamic equilibrium:

[0140]

[0141] The first product stream 118 is withdrawn from the first reactor 116 at a temperature of 762°C and a pressure of 11.5 bar (absolute value). The CO2 conversion rate is 36.6%, forming methane in a yield of 1.3%.

[0142] The first product stream 118 is mixed with the second hydrogen feed stream 124 to obtain a second mixed feed stream 126. The molar ratio of hydrogen to carbon dioxide in the second mixed feed stream is 1.46. The second mixed feed stream is fed into a second heat exchanger 128, where it is heated to obtain a heated second mixed feed stream 130 at a temperature of 895°C. The pressure of the heated second mixed feed stream is 11.5 bar (absolute value).

[0143] The heated second mixed feed stream is fed into the second reactor 132, which also operates under adiabatic conditions. Again, it is assumed that the above reaction reaches thermodynamic equilibrium.

[0144] The second product stream 134 is withdrawn from the second reactor 132 at a temperature of 835°C and a pressure of 10 bar (absolute). The overall CO2 conversion rate is 56.7%, forming methane in a yield of 1.8%.

[0145] Example 2

[0146] A pure carbon dioxide feed stream was fed into the first heated tube at ambient temperature, a pressure of 18 bar (absolute value), and a flow rate of 75 ml(n) / min, and heated to 700°C. A pure hydrogen feed stream was fed into the second heated tube at ambient temperature, a pressure of 18 bar (absolute value), and a flow rate of 75 ml(n) / min, and heated to 700°C. Both tubes were made of nickel-chromium-iron alloy (material number 2.4816). The heated carbon dioxide and hydrogen streams were then mixed, and the resulting heated mixed feed stream was fed into a reaction tube made of the same material as the heating tubes. The reaction tubes were located in a tube furnace providing temperature zones of 800°C and 850°C, respectively. Each temperature zone of the reaction tube was equipped with five 5 mm x 5 mm metal sheet samples, including different alloy and stainless steel compositions, to test their suitability as building materials under RWGS reaction conditions. The sheets were fixed in a 3 mm bed of quartz beads.

[0147] The experiment ran for over 2000 hours. During this period, the pressure drop across the entire apparatus (i.e., the heating and reaction tubes) remained almost constant. No carbon buildup or other harmful blockages in the tubes were observed.

[0148] Comparison Examples

[0149] In a separate experiment, pure carbon dioxide and pure hydrogen feed streams, as in Example 2, were mixed at ambient temperature. The mixed feed stream was fed into a heated reaction tube at a pressure of 18 bar (absolute) and a flow rate of 150 ml(n) / min. The reaction tube was made of the same nickel-chromium-iron alloy (material number 2.4816) used in Example 2. The reaction tube was located in a tube furnace that provided temperature zones of 325°C, 400°C, 475°C, 550°C, 625°C, 700°C, 750°C, 800°C, and 850°C. Each temperature zone of the reaction tube was equipped with five 5 mm x 5 mm metal sheet samples, including different alloy and stainless steel compositions, to test their suitability as building materials under RWGS reaction conditions. The sheets were fixed in a 3 mm bed of quartz beads.

[0150] During the experiment's run, the pressure drop across the reaction tube steadily increased, indicating increased carbon buildup within the tube. After 24 hours of operation, the experiment was forced to stop due to complete blockage of the reaction tube. Inspection of the reaction tube revealed a thick layer of carbon deposits covering the inner surface of the tube, including the thin sheet.

[0151] List of reference numerals used in the figures:

[0152] 102…Cold carbon dioxide flow

[0153] 104…Carbon Dioxide Feed Preheater

[0154] 106…Carbon dioxide feed stream

[0155] 108…Cold hydrogen gas flow

[0156] 110… Hydrogen preheater

[0157] 112…First hydrogen feed stream

[0158] 114…First Mixed Feed Flow

[0159] 116…First Reactor

[0160] 118…First Product Flow

[0161] 120…another stream of cold hydrogen

[0162] 122…another hydrogen preheater

[0163] 124…Second hydrogen feed stream

[0164] 126…Second Mixed Feed Flow

[0165] 128…Second heat exchanger

[0166] 130… The second mixed feed stream after heating

[0167] 132…Second reactor

[0168] 134…Second Product Flow

[0169] 136…First heat exchanger

[0170] 138…The first mixed feed stream after heating

[0171] 140…crude carbon dioxide feed stream

[0172] 142…Purification Unit

[0173] 144…Product Cooler

[0174] 146…The cooled product stream.

Claims

1. A method for hydrogenating carbon dioxide, the method comprising the following steps: (a) Provide a carbon dioxide feed stream at a temperature of 600°C to 1000°C (106); (b) Provide a first hydrogen feed stream (112) at a temperature of 600°C to 1000°C; (c) The carbon dioxide feed stream (106) and the first hydrogen feed stream (112) are mixed to obtain a first mixed feed stream (114). (d) Optionally, the first mixed feed stream (114) is heated to a temperature of 800°C to 1000°C in the first heat exchanger (136) to obtain a heated first mixed feed stream (138). (e) The first mixed feed stream (114) and / or the heated first mixed feed stream (138) at a temperature of 800°C to 1000°C are fed into a first reactor (116), in which the first mixed feed stream (114) and / or the heated first mixed feed stream (138) are contacted with a catalyst to obtain a first product stream (118) containing at least carbon monoxide, water and unreacted carbon dioxide.

2. The method of claim 1, further comprising the following steps: (f) The first product stream (118) is mixed with the second hydrogen feed stream (124) to obtain a second mixed feed stream (126). (g) The second mixed feed stream (126) is heated to a temperature of 800°C to 1000°C in the second heat exchanger (128); (h) The heated second mixed feed stream (130) is fed into the second reactor (132), in which the heated second mixed feed stream (130) is contacted with a catalyst to obtain a second product stream (134) containing at least carbon monoxide, water and unreacted carbon dioxide.

3. The method as described in claim 1 or 2, characterized in that, The carbon dioxide feed stream (106) contains 90 mol-% to 100 mol-% carbon dioxide, the first hydrogen feed stream (112) contains 90 mol-% to 100 mol-% hydrogen, and the molar ratio of carbon dioxide to hydrogen in the first mixed feed stream (114) and / or the heated first mixed feed stream (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-% carbon monoxide and less than 2 mol-% methane.

5. The method according to any one of claims 1 to 4, characterized in that, Both the first hydrogen feed stream (112) and the second hydrogen feed stream (124) are obtained by heating the cold hydrogen stream (108) in a hydrogen preheater (110), in which heat is generated at least in part by electricity.

6. The method according to any one of claims 1 to 5, characterized in that, The carbon dioxide feed stream (106) is obtained by feeding a crude carbon dioxide feed stream (140) into a purification unit (142), in which potential contaminants are at least partially removed from the crude carbon dioxide feed stream (140).

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

8. The method as described in claim 7, characterized in that, The carbon dioxide feed preheater (104) includes a first preheater that receives heat from the product cooler (144) and a second preheater that is preferably heated by electricity, wherein the carbon dioxide feed stream leaving the first preheater and entering the second preheater has a temperature of 300°C to 450°C.

9. The method as described in claim 7 or 8, characterized in that, The product cooler (144) includes a first cooler and a second cooler, the second cooler transferring heat to the carbon dioxide feed preheater (104), wherein the second product stream exiting the first cooler and entering the second cooler has a temperature of 350°C to 470°C.

10. The method as described in claim 9, characterized in that, The first cooler is cooled by water, which vaporizes in the first cooler to produce steam.

11. The method according to any one of claims 1 to 10, characterized in that, The carbon dioxide feed stream (106) and the first hydrogen feed stream (112) and / or the first product stream (118) and the second hydrogen feed stream (124) are fed into the gas mixer before entering the first reactor (116), the first heat exchanger (136) and / or the second heat exchanger (128).

12. A reaction system for hydrogenation of carbon dioxide, comprising: A first gas mixer is configured to receive a carbon dioxide feed stream (106) at a temperature of 600°C to 1000°C and a first hydrogen feed stream (112) at a temperature of 600°C to 1000°C, and to mix the two streams to obtain a first mixed feed stream (114). Optionally, a first heat exchanger (136) is configured to receive the first mixed feed stream (114) and heat the first mixed feed stream to a temperature of 800°C to 1000°C to obtain a heated first mixed feed stream (138); and A first reactor (116) is configured to receive the first mixed feed stream (114) and / or the heated first mixed feed stream (138) at a temperature of 800°C to 1000°C, and to contact it with a catalyst within the first reactor (116) to obtain a first product stream (118) containing at least carbon monoxide, water and unreacted carbon dioxide.

13. The reaction system as described in claim 12, characterized in that, The reaction system further includes: A second heat exchanger (128) is configured to receive a second mixed feed stream (126) which is a mixture of the first product stream (118) and the second hydrogen feed stream (124), and to heat the second mixed feed stream (126) to a temperature of 800°C to 1000°C; and A second reactor (132) is configured to receive a heated second mixed feed stream (130) and contact it with a catalyst inside the second reactor (132) to obtain a second product stream (134) containing at least carbon monoxide, water and unreacted carbon dioxide.

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