WO2025061605A1

WO2025061605A1 - Method for carbon dioxide hydrogenation

Info

Publication number: WO2025061605A1
Application number: PCT/EP2024/075758
Authority: WO
Inventors: Stefan Blei; Robert Peter Michael FRANZ; Heinz-Peter GERNER; Benjamin Frank; Peter HEIDEBRECHT; Michael Kraemer; Michael Bender; Christian Schulz; Karl-Friedrich SCHNEIDER; Virginie LANVER
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2023-09-18
Filing date: 2024-09-16
Publication date: 2025-03-27
Anticipated expiration: 2026-03-18

Abstract

The invention concerns a reaction system and a method for carbon dioxide hydrogenation comprising: (a) providing a carbon dioxide feed stream (106) at a temperature of at least 600°C; (b) providing a first hydrogen feed stream (112) at a temperature of at least 600°C; (c) mixing the carbon dioxide feed stream and the first hydrogen feed stream obtaining a first mixed feed stream (114); (d) optionally, heating the first mixed feed stream in a first heat exchanger (136) to a temperature of at least 800°C 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 from 800°C to 1000°C to a first reactor (116) where it is contacted with a catalyst to obtain a first product stream (118) containing at least carbon monoxide, water and unreacted carbon dioxide.

Description

Method for carbon dioxide hydrogenation

Description

Technical Field

The invention relates to a method for carbon dioxide hydrogenation 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 where the mixed feed stream is contacted with a catalyst.

Background Art

The reforming of hydrogen and carbon dioxide, also called carbon dioxide hydrogenation or reverse water-gas shift reaction (RWGS), is of great economic interest since these processes offer the option of preparing synthesis gas as an important base chemical with utilization of carbon dioxide as starting material. Accordingly, it would be possible to bind carbon dioxide, obtained as a waste product in numerous processes, by a chemical route. This makes it possible to reduce carbon dioxide emissions into the atmosphere.

"Synthesis gas", also termed “syngas”, refers to a gas mixture which comprises hydrogen (H2) and carbon monoxide (CO) and can be used as base chemical in a multitude of industrial processes. Depending on the use thereof, synthesis gas has different ratios of hydrogen to carbon monoxide. Synthesis gas may contain further components such as water (H2O), carbon dioxide (CO2), methane (CH4) and/or nitrogen (N2).

Different processes for the production of synthesis gas 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 process for the production of syngas, the process comprising (i) reacting at least a portion of carbon dioxide with hydrogen within an initial reactor to produce an initial product stream including carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen; and (ii) reacting at least a portion of the unreacted carbon dioxide and unreacted hydrogen within a reactor downstream of the initial reactor to thereby produce a product stream including carbon monoxide, water, unreacted carbon dioxide, and unreacted hydrogen. Document WO 2021/225643 A1 discloses a process for the conversion of a feed gas comprising carbon dioxide and hydrogen to a product gas comprising carbon monoxide and water. The feed gas is preheated to at least 760°C in a heat exchanger by electricity before entering an adiabatic or isothermal reactor where the catalyzed RWGS reaction takes place. The resulting product mixture may be re-heated in a second electric heater and be fed to a second reactor for further conversion of carbon dioxide to carbon monoxide.

Document WO 2022/129338 discloses a process for the production of synthesis gas in a two-stage catalytic RWGS reaction, whilst maintaining the temperature in the RWGS reactors below 700°C.

Even though several process schemes for hydrogenating carbon dioxide are known and available in industrial scale, there is still a need for improving the technology, especially in view of avoiding the formation of coke and unwanted byproducts, energy consumption in such a high-temperature process and sustainability aspects.

It is an object of the invention to provide a method for carbon dioxide hydrogenation that minimizes coke formation in heat exchangers and reactors. A further object of the invention is to provide a method for carbon dioxide hydrogenation that minimizes the formation of the unwanted byproduct methane. A further object of the invention is to provide a method for carbon dioxide hydrogenation in an energy efficient reaction system with a compact design.

These tasks are solved according to the invention by a method according to claim 1 and a reaction system according to claim 12. Advantageous variants of the method are presented in claims 2 to 11.

Brief Description

As used herein, the terms “have”, “comprise” or “include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions “A has B”, “A comprises B” and “A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or further elements. Further, it shall be noted that the terms “at least one”, “one or more” or similar expressions indicating that a feature or element may be present once or more than once typically are used only once when introducing the respective feature or element. In most cases, when referring to the respective feature or element, the expressions “at least one” or “one or more” are not repeated, nonwithstanding the fact that the respective feature or element may be present once or more than once.

Further, as used herein, the terms "preferably", "more preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with optional features, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Similarly, features introduced by "in an embodiment of the invention" or similar expressions are intended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such way with other optional or non-optional features of the invention.

In a first aspect of the invention, a method for carbon dioxide hydrogenation comprises the steps of (a) providing a carbon dioxide feed stream at a temperature of from 600°C to 1000°C, (b) providing a first hydrogen feed stream at a temperature of from 600°C to 1000°C, (c) mixing the carbon dioxide feed stream and the first hydrogen feed stream obtaining a first mixed feed stream, (d) optionally, heating the first mixed feed stream in a first heat exchanger to a temperature of from 800°C to 1000°C obtaining a heated first mixed feed stream, (e) feeding the first mixed feed stream and/or the heated first mixed feed stream at a temperature of from 800°C to 1000°C to a first reactor where the first mixed feed stream and/or the heated first mixed feed stream is contacted with a catalyst to obtain a first product stream containing at least carbon monoxide, water and unreacted carbon dioxide.

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

It has been found that separately heating the feed streams of the reactants carbon dioxide and hydrogen to a temperature of at least 600°C each before mixing them significantly reduces or even avoids the formation of coke. A further heating of the first mixed feed stream to temperatures higher than 600°C does not lead to a formation of coke in significant amounts.

The method for carbon dioxide hydrogenation may comprise further steps and the reaction system for carbon dioxide hydrogenation may comprise further apparatus.

The first product stream may be the final product stream or may be an intermediate product stream that is further reacted in subsequent reaction steps. There may be one or more subsequent reaction steps. Each subsequent reaction step may comprise a further heat exchanger and a further reactor. In one embodiment, the carbon dioxide hydrogenation is performed in a two-stage reaction process. In this embodiment, the reaction system comprises a second heat exchanger and a second reactor. The first product stream may be heated in the second heat exchanger to a temperature of from 800°C to 1000°C, the heated stream being fed to 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.

In another embodiment, an additional hydrogen feed stream is provided to a reaction system with at least two reaction stages. In this embodiment, the above-mentioned method steps (a) to (e) may be followed by the further steps of (f) mixing the first product stream with a second hydrogen feed stream obtaining a second mixed feed stream, (g) heating the second mixed feed stream in a second heat exchanger to a temperature of from 800°C to 1000°C, (h) feeding the heated second mixed feed stream to a second reactor where 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.

A suitable reaction system to perform the method according to this embodiment may comprise a second heat exchanger configured to receive a second mixed feed stream as a mixture of the first product stream and a second hydrogen feed stream and to heat the second mixed feed stream to a temperature of from 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 inside the second reactor to obtain a second product stream containing at least carbon monoxide, water and unreacted carbon dioxide.

It has been found that the provision of a further hydrogen feed stream in a multi-stage reaction process may significantly reduce the formation of the unwanted byproduct methane.

The second product stream may be the final product stream or may be an intermediate product stream that is further reacted in subsequent reaction stages of the reaction system. In case of more than two reaction stages, each further reaction stage may be provided with a further additional hydrogen feed stream.

The term “carbon dioxide feed stream” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to any gaseous stream containing at least carbon dioxide as a reactant for the RWGS reaction.

The content of carbon dioxide in the carbon dioxide 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-%, in particular at least 99 mol-%.

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

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 may be at least 600°C, preferably at least 620°C, more preferably at least 635°C, even more preferably at least 650°C. In this case, the temperature of the carbon dioxide feed stream may be at most 800°C, preferably at most 780°C, more preferably at most 765°C, even more preferably at most 750°C.

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

The term “hydrogen feed stream” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to any gaseous stream containing at least hydrogen as a reactant for the RWGS reaction.

Hydrogen may be added to the reaction system at one position or several distinct positions. The terms “first hydrogen feed stream”, “second hydrogen feed stream”, “further hydrogen feed stream” or “additional hydrogen feed stream” are used to distinguish hydrogen feed streams added to the reaction system at different positions, if applicable. In embodiments with more than one hydrogen feed stream, the different hydrogen feed streams may have the same or different composition, temperature or pressure.

The content of hydrogen in 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-%, in particular at least 99 mol-%.

The pressure of the hydrogen feed stream may be from 1 bar(abs) to 70 bar(abs), preferably from 3 bar(abs) to 50 bar(abs), more preferably from 6 bar(abs) to 20 bar(abs), for example at least 1 bar(abs), at least 2 bar(abs), at least 3 bar(abs), at least 4 bar(abs), at least 5 bar(abs), at least 6 bar(abs), and at most 70 bar(abs), at most 60 bar(abs), at most 50 bar(abs), at most 40 bar(abs), at most 30 bar(abs), at most 20 bar(abs). The temperature of the first hydrogen feed stream may 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 to the first reactor without further heating of the first mixed feed stream, the temperature of the first hydrogen feed stream may be at least 800°C, preferably at least 850°, more preferably at least 900°C. In this case, the temperature of the first hydrogen feed stream may be at most 1200°C, preferably at most 1100°C, more preferably at most 1000°C.

In embodiments where the first hydrogen feed stream is mixed with the carbon dioxide 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 first hydrogen feed stream may be at least 600°C, preferably at least 620°C, more preferably at least 635°C, most preferably at least 650°C. In this case, the temperature of the first hydrogen feed stream may be at most 800°C, preferably at most 780°C, more preferably at most 765°C, most preferably at most 750°C.

In embodiments where more than one hydrogen feed streams are provided to the reaction system, the temperature of the second hydrogen feed stream and/or of further hydrogen feed streams may be at least 600°C, preferably at least 620°C, more preferably at least 635°C, most preferably at least 650°C. In this case, the temperature of the first hydrogen feed stream may be at most 800°C, preferably at most 780°C, more preferably at most 765°C, most preferably at most 750°C.

In some embodiments, any one or more of the first hydrogen feed stream, the second hydrogen feed stream or further hydrogen feed streams may be obtained by heating a respective 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 a respective further 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 stream is preferably from 1 bar(abs) to 70 bar(abs), more preferably from 3 bar(abs) to 50 bar(abs), even more preferably from 6 bar(abs) to 20 bar(abs), for example at least 1 bar(abs), at least 2 bar(abs), at least 3 bar(abs), at least 4 bar(abs), at least 5 bar(abs), at least 6 bar(abs), and at most 70 bar(abs), at most 60 bar(abs), at most 50 bar(abs), at most 40 bar(abs), at most 30 bar(abs), at most 20 bar(abs). The hydrogen preheater may have any form, dimension and design principle that is suitable to heat up a gaseous stream containing hydrogen from a temperature range of from 0°C to 300°C to a temperature range of from 600°C to 1000°C. In some embodiments, the hydrogen preheater is a gas fired heater that transfers energy from burning hydrogen, a hydrocarbon gas, for example natural gas, or a mixture thereof to the cold hydrogen stream flowing through the hydrogen preheater. In other embodiments, the hydrogen preheater is an electrical heater that uses electricity to heat up the cold hydrogen stream. In an embodiment, the hydrogen preheater comprises at least one tube that is heated from its outside and transfers the heat through the tube wall to the cold hydrogen stream flowing through the tube. In a variant of this embodiment, the hydrogen preheater comprises a multitude of tubes that are heated from their outside and transfer the heat through the tube walls to the cold hydrogen stream flowing through the tubes.

The hydrogen preheater may comprise one or more single heaters. In case of more than one heater, the heaters may be connected in series, in parallel or as combinations of in series and in parallel connections. The heaters may be based on the same design principle or on different design principles. For example, one heater may be a heater operated by electricity and another heater may be a fired heater operated by burning a fuel.

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 wherein the heat is generated at least partially by electricity.

The term "first mixed feed stream" as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to any gaseous stream resulting from mixing at least the carbon dioxide feed stream and the first hydrogen feed stream.

The mixing can be performed by any suitable apparatus and method known in the art. In some embodiments, the carbon dioxide feed stream and the first hydrogen feed stream are fed to a first gas mixer before entering the first heat exchanger. This has the advantageous effect that strains of unmixed H2/CO2 can be avoided that otherwise could cause a reduced heat transfer in the subsequent heat exchanger. The first gas mixer may be any apparatus suitable to mix at least two gas streams. Preferred gas mixers are perforated plates, static mixers and dynamic mixers, for example fans. The temperature of the first mixed feed stream may depend on the configuration of the reaction system. In embodiments where the first mixed feed stream is fed to the first reactor without further heating of the first mixed feed stream, the temperature of the first mixed feed stream may be at least 800°C, preferably at least 820°C, more preferably at least 850°C. In this case, the temperature of the first mixed feed stream may be at most 1200°C, preferably at most 1100°C, more preferably at most 1000°C.

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 may 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 may be at most 800°C, preferably at most 750°C, more preferably at most 700°C.

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

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

In some embodiments, the first heat exchanger is a gas fired heater that transfers energy from burning hydrogen, a hydrocarbon gas, for example natural gas, or a mixture thereof to the first mixed feed stream flowing through the first heat exchanger. In other embodiments, the first heat exchanger is an electrical heater that uses electricity to heat up the first mixed feed stream. In an embodiment, the first heat exchanger comprises at least one tube that is heated from its outside and transfers the heat through the tube wall to the first mixed feed stream flowing through the tube. In a variant of this embodiment, the first heat exchanger comprises a multitude of tubes that are heated from their outside and transfer the heat through the tube walls to the first mixed feed stream flowing through the tubes. The first heat exchanger may comprise one or more single heaters. In case of more than one heater, the heaters may be connected in series, in parallel or as combinations of in series and in parallel connections. The heaters may be based on the same design principle or on different design principles. For example, one heater may be a heater operated by electricity and another heater may be a fired heater operated by burning a fuel.

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

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

The term “first reactor” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to any reactor suitable to perform a catalyzed RWGS reaction.

In some embodiments, the first reactor is an adiabatic reactor. In an embodiment, the first reactor is an adiabatic fixed bed reactor. Preferably, the ratio of the length of the reactor to its diameter is larger than 1 , i.e. the reactor length is larger than its diameter.

In another embodiment, the first reactor is an adiabatic monolithic reactor. Preferably, the catalyst is applied to the monolith as a wash coat in this case. It is an advantage of this type of reactor that the pressure drop between its inlet and its outlet is low.

As used herein, the term “adiabatic” means that the respective reactor is not heated by any external means. However, the reactor may exchange heat with its environment, for example due to the large temperature difference between the inside of the reactor and its environment. In some embodiments, the heat loss of an adiabatic reactor may be up to 20%. Catalysts for catalyzing a RWGS reaction are known in the art. For example, the document WO 2018/219992 A1 discloses a heterogeneous nickel and magnesium spinel-containing 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 to 30 mol-%, a magnesium content in the range of 10 to 40 mol-% and an aluminum content in a range of 40 to 70 mol-%.

The catalyst may be installed in the first reactor in any form that is suitable to catalyze a RWGS reaction inside the reactor. In some embodiments, the catalyst has the form of pellets, for example of quadrilobed or hexalobed shape, with or without inner holes in the pellets. In some embodiments, the catalyst has the form of extrudates, for example of cylindrical shape or lobed shape, for example of trilobed shape. In some embodiments, the catalyst is installed in the reactor as a three-dimensional porous structure.

The product of the RWGS reaction in the first reactor is at least partially 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 contain further substances like unreacted hydrogen or byproducts of the reaction like methane.

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

In embodiments where the first product stream is the final product stream, the first product stream may contain from 5 mol-% to 40 mol-% of carbon monoxide, more preferably from 15 mol-% to 35 mol-% of carbon monoxide, even more preferably from 20 mol-% to 30 mol- % of carbon monoxide, from 10 mol-% to 45 mol-% of hydrogen, more preferably from 15 mol-% to 35 mol-% of hydrogen, even more preferably from 20 mol-% to 35 mol-% of hydrogen, from 10 mol-% to 45 mol-% of carbon dioxide, more preferably from 15 mol-% to 35 mol-% of carbon dioxide, even more preferably from 15 mol-% to 30 mol-% of carbon dioxide, from 5 mol-% to 40 mol-% of water, more preferably from 15 mol-% to 35 mol-% of water, even more preferably from 20 mol-% to 30 mol-% of water, and less than 2 mol-% of methane. In embodiments where the first product stream is an intermediate product stream, the first product stream may contain from 5 mol-% to 40 mol-% of carbon monoxide, more preferably from 10 mol-% to 35 mol-% of carbon monoxide, even more preferably from 15 mol-% to 30 mol-% of carbon monoxide, from 5 mol-% to 30 mol-% of hydrogen, more preferably from 5 mol-% to 25 mol-% of hydrogen, even more preferably from 5 mol-% to 20 mol-% of hydrogen, from 25 mol-% to 65 mol-% of carbon dioxide, more preferably from 30 mol-% to 60 mol-% of carbon dioxide, even more preferably from 35 mol-% to 55 mol-% of carbon dioxide, from 5 mol-% to 40 mol-% of water, more preferably from 10 mol-% to 35 mol-% of water, even more preferably from 15 mol-% to 30 mol-% of water, and less than 2 mol-% of methane.

In some embodiments, the first product stream is mixed with the second hydrogen feed stream to obtain a second mixed feed stream. The mixing can be performed by any suitable apparatus and method known in the art. In some embodiments, the first product stream and the second hydrogen feed stream are fed to a second gas mixer before entering the second heat exchanger. This has the advantageous effect that strains of unmixed H2/CO2 can be avoided that otherwise could cause a reduced heat transfer in the subsequent heat exchanger. The second gas mixer may be any apparatus suitable to mix at least to gas streams. Preferred gas mixers are perforated plates, static mixers and dynamic mixers, for example fans.

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

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 may 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 may be at most 800°C, preferably at most 775°C, more preferably at most 750°C.

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

In some embodiments, the second mixed feed stream is fed to the second heat exchanger where it is heated to a temperature of from 800°C to 1000°C, preferably from 850°C to 950°C, more preferably from 880°C to 920°C. The second heat exchanger may have any form, dimension and design principle that is suitable to heat up a gaseous stream containing carbon dioxide and hydrogen from a temperature range of from 600°C to 800°C to a temperature range of from 800°C to 1000°C.

In some embodiments, the second heat exchanger is a gas fired heater that transfers energy from burning hydrogen, a hydrocarbon gas, for example natural gas, or a mixture thereof to the second mixed feed stream flowing through the second heat exchanger. In other embodiments, the second heat exchanger is an electrical heater that uses electricity to heat up the second mixed feed stream. In an embodiment, the second heat exchanger comprises at least one tube that is heated from its outside and transfers the heat through the tube wall to the second mixed feed stream flowing through the tube. In a variant of this embodiment, the second heat exchanger comprises a multitude of tubes that are heated from their outside and transfer the heat through the tube walls to the second mixed feed stream flowing through the tubes.

The second heat exchanger may comprise one or more single heaters. In case of more than one heater, the heaters may be connected in series, in parallel or as combinations of in series and in parallel connections. The heaters may be based on the same design principle or on different design principles. For example, one heater may be a heater operated by electricity and another heater may be a fired heater operated by burning a fuel.

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

The heated second mixed feed stream is fed to the second reactor. The term “second reactor” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to any reactor suitable to perform a catalyzed RWGS reaction.

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 length of the reactor to its diameter is larger than 1 , i.e. the reactor length is larger than its diameter.

In another embodiment, the second reactor is an adiabatic monolithic reactor. Preferably, the catalyst is applied to the monolith as a wash coat in this case. It is an advantage of this type of reactor that the pressure drop between its inlet and its outlet is low.

The catalyst used in the second reactor may be the same catalyst as used in the first reactor or may be a different catalyst than used in the first reactor. In some embodiments the catalyst used in the second reactor is based on the same chemical substances 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 ratio of surface area to volume than the catalyst used in the first reactor.

The product of the RWGS reaction in the second reactor is at least partially 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 contain further substances like unreacted hydrogen or byproducts of the reaction like methane.

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

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

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

The carbon dioxide feed stream which is mixed with the first hydrogen feed stream may have a composition that contains from 90 mol-% to 100 mol-% of carbon dioxide.

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

In some embodiments, the carbon dioxide feed stream is obtained by feeding a raw carbon dioxide feed stream to a purification unit where potential contaminants are at least partially removed from the raw carbon dioxide feed stream.

The purification unit may contain any apparatus that is suitable to remove impurities and unwanted substances from the raw carbon dioxide feed stream, in particular to remove sulfur components from the raw carbon dioxide feed stream. In an embodiment, the purification unit contains an absorber bed, the absorber bed preferably being operated at elevated temperatures, in particular at temperatures above 80°C. The purification unit may contain further apparatuses like filter units or membrane units, either used alone or in combination with any other apparatus in the purification unit. Depending on its origin, the carbon dioxide feed stream may have any temperature and pressure suitable for transporting the gaseous stream through a pipeline for example.

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 from 20°C to 250°C, more preferably from 50°C to 200°C. The pressure of the cold carbon dioxide stream is preferably from 1 bar(abs) to 70 bar(abs), more preferably from 2 bar(abs) to 30 bar(abs). The carbon dioxide feed preheater may have any form, dimension and design principle that is suitable to heat up a gaseous stream containing carbon dioxide from a temperature range of from 20°C to 250°C to a temperature range of from 600°C to 1000°C.

In some embodiments, the carbon dioxide feed preheater is a gas fired heater that transfers energy from burning hydrogen, a hydrocarbon gas, for example natural gas, or a mixture thereof to the carbon dioxide feed stream flowing through the carbon dioxide feed preheater. In other embodiments, the carbon dioxide feed preheater is an electrical heater that uses electricity to heat up the carbon dioxide feed stream. The carbon dioxide feed preheater may comprise at least one tube that is heated from its outside and transfers the heat through the tube wall to the carbon dioxide feed stream flowing through the tube. The carbon dioxide feed preheater may comprise a multitude of tubes that are heated from their outside and transfer the heat through the tube walls to the carbon dioxide feed stream flowing through the tubes.

The carbon dioxide feed preheater may comprise one or more single heaters. In case of more than one heater, the heaters may be connected in series, in parallel or as combinations of in series and in parallel connections. The heaters may be based on the same design principle or on different design principles. For example, one heater may be a heater operated by electricity and another heater may be a fired heater operated by burning a fuel.

In some embodiments, the carbon dioxide feed preheater is heat integrated with other parts of the process in the sense that heat released at a certain process stage or apparatus is used to heat the carbon dioxide feed stream in the carbon dioxide feed preheater.

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, dimension and design principle that is suitable to cool down a gaseous stream containing at least carbon monoxide, water and carbon dioxide from a temperature range of from 650°C to 850°C to a temperature range of from 10°C to 100°C.

In one embodiment, the product cooler comprises one single cooler to cool down the second product stream to the desired temperature. In another embodiment, the product cooler comprises more than one cooler connected in parallel, in series or partly in parallel and partly in series. Depending on the temperature range of the second product stream flowing through the one or more coolers and the desired outlet temperature at the respective cooler(s), a suitable cooling medium can be chosen. Preferably, the cooling medium is selected from the group consisting of water, oil, or any process stream suitable for heat integration.

In some embodiments, the heating medium used to cool at least one cooler of the product cooler is water. Preferably, the water at least partially vaporizes during the cooling process, and the resulting steam is used as a heating medium, either in a different part of the process for carbon dioxide hydrogenation or in another process.

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, where at least part 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.

In some embodiments, the carbon dioxide feed preheater comprises a first preheater that receives the heat from the product cooler and a second preheater that is preferably heated by electricity. Preferably, the carbon dioxide feed stream leaving the first preheater and entering the second preheater has a temperature of from 300°C to 450°C.

In some embodiments, the product cooler comprises at least a first cooler and a second cooler, the latter delivering the heat to the carbon dioxide feed preheater. Preferably, the second product stream leaving the first cooler and entering the second cooler has a temperature of from 350°C to 470°C. It is further preferred that the first cooler is cooled by water that vaporizes in the first cooler to produce steam. In some embodiments, those elements of the first heat exchanger that are exposed to the high temperatures and/or corrosive media are made of a heat-resistant material like certain stainless steel alloys or a ceramic material. In a preferred embodiment, the respective elements are constructed from a nickel chrome alloy containing the alloying elements (proportions in % by weight): nickel (Ni) 15 to 70 chromium (Cr) 15 to 30 silicon (Si) less than 2

The nickel chrome alloy may contain further components, for example carbon, manganese, titanium, copper, iron.

In a further preferred embodiment, the elements of the first heat exchanger that are exposed to the high temperatures and/or corrosive media are made of a nickel iron chrome alloy containing the alloying elements (proportions in % by weight): carbon (C) less than 0.1 silicon (Si) less than 1 manganese (Mn) less than 1.5 chromium (Cr) 19 to 23 nickel (Ni) 30 to 34 titanium 0.15 to 0.6 copper (Cu) less than 0.75 iron (Fe) less than 39.5

Detailed Description

The invention is explained in more detail below with reference to the drawings. The drawings are to be interpreted as in-principle presentation. They do not constitute any restriction of the invention, for example with regard to specific dimensions or design variants. In the figures:

Fig. 1 shows a reaction system for carbon dioxide hydrogenation as a first embodiment of the invention.

Fig. 2 shows a reaction system for carbon dioxide hydrogenation as a second embodiment of the invention.

Fig. 3 shows a reaction system for carbon dioxide hydrogenation as a third embodiment of the invention. Fig. 4 shows a reaction system for carbon dioxide hydrogenation as a fourth embodiment of the invention.

Fig. 5 shows a reaction system for carbon dioxide hydrogenation as a fifth embodiment of the invention.

Fig. 1 shows a schematic view of a reaction system for carbon dioxide hydrogenation as a first embodiment of the invention. The reaction system comprises a carbon dioxide feed preheater 104, a hydrogen preheater 110 and a first reactor 116.

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

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

The carbon dioxide feed stream 106 and the first hydrogen feed stream 112 are mixed to obtain a first mixed feed stream 114 with a temperature of at least 800°C. Mixing may be performed in a gas mixer, for example a static mixer. The first mixed feed stream 114 is fed to the first reactor 116 that is equipped with a catalyst suitable for a RWGS reaction. 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 further components like unreacted hydrogen, nitrogen or methane.

Fig. 2 shows a schematic view of a reaction system for carbon dioxide hydrogenation as a second embodiment of the invention. The reaction system comprises 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.

Similar to the process described above with reference to Fig. 1 , a cold carbon dioxide stream 102 is fed to the carbon dioxide feed preheater 104 and heated therein to obtain a carbon dioxide feed stream 106 at a temperature of at least 800°C. The temperature of the cold carbon dioxide stream 102 may be in the range from 20°C to 250°C. The heating energy for the carbon dioxide feed preheater 104 is preferably provided by electricity.

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

The first product stream 118 and the second hydrogen feed streams 124 are mixed to obtain a second mixed feed stream 126 that is fed to the second heat exchanger 128 where it is heated to a temperature of from 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 to the second reactor 132 that is also equipped with a catalyst suitable for a 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 further components like unreacted hydrogen, nitrogen or methane.

Fig. 3 shows a schematic view of a reaction system for carbon dioxide hydrogenation as a third embodiment of the invention. The reaction system comprises a hydrogen preheater 110, a first heat exchanger 136, a first reactor 116, a second heat exchanger 128 and a second reactor 132.

A cold hydrogen stream 108 is preheated in the hydrogen preheater 110 to a temperature of from 600°C to 800°C and is split in a first hydrogen feed stream 112 and a second hydrogen feed stream 124. The cold hydrogen stream 108 may also be split first into two separate streams that are preheated in the hydrogen preheater 110 to a temperature of from 600°C to 800°C each, yielding a first hydrogen feed stream 112 and a second hydrogen feed stream 124. The heating energy is preferably provided by electricity. The first hydrogen feed stream 112 is mixed with a carbon dioxide feed stream 106 that is provided at a temperature of from 600°C to 800°C. The resulting first mixed feed stream 114 is fed to the first heat exchanger 136 where it is heated to a temperature of from 800°C to 1000°C. The heated first mixed feed stream 138 is fed to the first reactor 116 that is equipped with a catalyst suitable for a RWGS reaction. 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 further components like unreacted hydrogen, nitrogen or methane.

The first product stream 118 is mixed with the second hydrogen feed stream 124 to obtain a second mixed feed stream 126 that is fed to a second heat exchanger 128 where it is heated to a temperature of from 800°C to 1000°C. The heating energy for the first heat exchanger 136 and for the second heat exchanger 128 is preferably provided by burning a hydrocarbon containing gas, for example natural gas, a gas containing hydrogen, or a gas containing hydrocarbons and hydrogen. The heated second mixed feed stream 130 is fed to the second reactor 132 that is also equipped with a catalyst suitable for a 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 further components like unreacted hydrogen, nitrogen or methane.

Fig. 4 shows a schematic view of a reaction system for carbon dioxide hydrogenation as a fourth embodiment of the invention. The reaction system comprises 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. A raw carbon dioxide feed stream 140 is fed to the purification unit 142 where contaminants that might poison the catalyst eventually contained in the raw carbon dioxide feed stream 140 are at least partially removed. The thus purified cold carbon dioxide stream 102 is preheated in the carbon dioxide feed preheater 104 to obtain a carbon dioxide feed stream 106 having a temperature of from 600°C to 800°C.

A cold hydrogen stream 108 is preheated in the hydrogen preheater 110 to a temperature of from 600°C to 800°C and is split in a first hydrogen feed stream 112 and a second hydrogen feed stream 124. The cold hydrogen stream 108 may also be split first into two separate streams that are preheated in the hydrogen preheater 110 to a temperature of from 600°C to 800°C each, yielding a first hydrogen feed stream 112 and a second hydrogen feed stream 124. The heating energy is preferably provided by electricity. The first hydrogen feed stream 112 is mixed with the carbon dioxide feed stream 106. The resulting first mixed feed stream 114 is fed to the first heat exchanger 136 where it is heated to a temperature of from 800°C to 1000°C. The heated first mixed feed stream 138 is fed to the first reactor 116 that is equipped with a catalyst suitable for a RWGS reaction. 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 further components like unreacted hydrogen, nitrogen or methane.

The second product stream 134 is cooled in a product cooler 144 to obtain a cooled product stream 146, wherein at least part 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. The dashed line in Fig. 4 symbolizes the heat transfer.

Fig. 5 shows a schematic view of a reaction system for carbon dioxide hydrogenation as a fifth embodiment of the invention. The reaction system comprises 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 comprise 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, as well as a first further hydrogen preheater 122A and a subsequent second further hydrogen preheater 122B.

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

The carbon dioxide feed stream 106 and the first hydrogen feed stream 112 are mixed to obtain a first mixed feed stream 114 with a temperature of at least 800°C. Mixing may be performed in a gas mixer, for example a static mixer. The first mixed feed stream 114 is fed to the first heat exchanger 136 where it is heated to a temperature of from 800°C to 1000°C. The heated first mixed feed stream 138 is fed to the first reactor 116 that is equipped with a catalyst suitable for a RWGS reaction. 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 further components like unreacted hydrogen, nitrogen or methane.

A further cold hydrogen stream 120 is fed to the further hydrogen preheater 122 and heated therein to obtain a second hydrogen feed stream 124. The temperature of the cold hydrogen stream 108 may be in the range from 20°C to 250°C, the temperature of the second hydrogen feed stream 124 may be in the range from 20°C to 250°C. The first product stream 118 and the second hydrogen feed streams 124 are mixed to obtain a second mixed feed stream 126 that is fed to the second heat exchanger 128 where it is heated to a temperature of from 800°C to 1000°C. The heated second mixed feed stream 130 is fed to the second reactor 132 that is also equipped with a catalyst suitable for a 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 further components like unreacted hydrogen, nitrogen or methane. The second product stream 134 is cooled in a product cooler 144 to obtain a cooled product stream 146.

In this example, the heating energy needed to heat the feed streams is provided from different sources. The first hydrogen preheater 110A and the first further hydrogen preheater 122A are preferably heated by electric energy. The cold hydrogen streams 108 and the further cold hydrogen stream 120 may be heated by the first heaters to a temperature in the range of from 500°C to 650°C. The second hydrogen preheater 110B and the second further hydrogen preheater 122B may be heated by electric energy or by burning hydrogen or a hydrocarbon containing gas, for example natural gas.

The first heat exchanger 136 and the second heat exchanger 128 may be electric heaters or fired heaters in which a fuel like hydrogen or a hydrocarbon containing gas, for example natural gas, are burned to produce the heating energy.

The carbon dioxide feed preheater 104 may comprise electric heaters, fired heaters or heat exchangers that transfer energy from other heat exchangers to the cold carbon dioxide stream 102 via heat integration. The first carbon dioxide feed preheater 104A may, for example, be heat integrated with the product cooler 144 such that at least part 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. The dashed lines in Fig. 5 symbolize the heat transfer. The second carbon dioxide feed preheater 104B may be heated by using the flue gas of fired heaters of the reaction system or external sources of high-temperature flue gases.

Further heat integration schemes are possible, in the embodiment shown in Fig. 5 as well as in any other embodiment. For example, in case of a fired first heat exchanger 136 and/or a fired second heat exchanger 128, the hot flue gas leaving these heat exchangers may be used to heat any of the feed preheaters. The feed preheaters may also be subdivided into multiple units to allow for additional electrical heating if heat integration with hot flue gas for example is not sufficient.

Example 1

As an example, a reaction system as shown in Fig. 3 was simulated in the commercially available simulation tool Aspen Plus V14 by AspenTech (20 Crosby Drive, Bedford, MA 01730, U.S.A., www.aspentech.com). The simulation tool is equation-based and uses physical property data by AspenTech. The SRK property model included in the software package was used for the simulation. The “Heater” model was used in Aspen for blocks 110, 136 and 128. Blocks 116 and 132 were modelled as equilibrium reactors “REquil”.

A carbon dioxide feed stream 106 with a temperature of 700°C and a first hydrogen feed stream 112 with a temperature of 700°C were mixed to obtain a first mixed feed stream 114. The molar ratio of hydrogen to carbon dioxide in the first mixed feed stream was 0.67. The first mixed feed stream was fed to a first heat exchanger 136 where it was heated to obtain a heated first mixed feed stream 138 with a temperature of 890°C. The pressure of the heated first mixed feed stream was 13 bar(abs).

The heated first mixed feed stream was fed to a first reactor 116. The first reactor was operated in an adiabatic mode. For the simulation, thermodynamic equilibrium for the following reactions was assumed:

CO₂ + H₂ H₂O + CO

A first product stream 118 was withdrawn from the first reactor 116 at a temperature of 762°C and a pressure of 11 .5 bar(abs). The conversion of CO₂ was 36.6%, methane was formed with a yield of 1.3%.

The first product stream 118 was mixed with a 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 was 1.46. The second mixed feed stream was fed to a second heat exchanger 128 where it was heated to obtain a heated second mixed feed stream 130 with a temperature of 895°C. The pressure of the heated second mixed feed stream was 11.5 bar(abs). The heated second mixed feed stream was fed to a second reactor 132 that was also operated in an adiabatic. Again, thermodynamic equilibrium for the above-mentioned reactions was assumed.

A second product stream 134 was withdrawn from the second reactor 132 at a temperature of 835°C and a pressure of 10 bar(abs). The overall conversion of CO2 was 56.7%, methane was formed with a yield of 1.8%.

Example 2

A pure carbon dioxide feed stream was fed to a first heated tube at ambient temperature, a pressure of 18 bar(abs) and a flow rate of 75 ml(n)/min and was heated to a temperature of 700°C. A pure hydrogen feed stream was fed to a second heated tube at ambient temperature, a pressure of 18 bar(abs) and a flow rate of 75 ml(n)/min and was heated to a temperature of 700°C. Both tubes were made from a nickel-chrome-iron alloy (material number 2.4816). The heated carbon dioxide stream and the heated hydrogen stream were subsequently mixed, and the resulting heated mixed feed stream was fed to a reaction tube made of the same material as the heating tubes. The reaction tube was located in a tubular furnace that provided temperature zones of 800 and 850°C, respectively. Each temperature zone of the reaction tube was equipped with 5 metal platelet samples of 5 mm x 5 mm, respectively, including different alloys and stainless steel compositions to test their suitability as a construction material under RWGS reaction conditions. The platelets were fixed in a bed of 3 mm quartz beads.

The experiment was run for more than 2000 hours. During this runtime, the pressure drop over the whole apparatus, i.e. the heating tubes and the reaction tube, was nearly constant. No coke formation or other detrimental blocking of the tubes was observed.

Comparative Example

In a further experiment, a pure carbon dioxide feed stream and a pure hydrogen feed stream according to Example 2 were mixed at ambient temperature. The mixed feed stream was fed to a heated reaction tube at a pressure of 18 bar(abs) and a flow rate of 150 ml(n)/min. The reaction tube was made from the same nickel-chrome-iron alloy (material number 2.4816) as used in Example 2. The reaction tube was located in a tubular 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, respectively. Each temperature zone of the reaction tube was equipped with 5 metal platelet samples of 5 mm x 5 mm, respectively, including different alloys and stainless steel compositions to test their suitability as a construction material under RWGS reaction conditions. The platelets were fixed in a bed of 3 mm quartz beads.

During the runtime of the experiment, the pressure drop over the reaction tube steadily increased, indicating an increasing coke formation inside the reaction tube. After 24 hours of operation, the experiment had to be stopped as the reaction tube was totally blocked. By inspection of the reaction tube it was found that the inner surface of the tube including the platelets were covered with a thick layer of coke.

List of reference numerals used:

102 ... cold carbon dioxide stream

104 ... carbon dioxide feed preheater

106 ... carbon dioxide feed stream

108 ... cold hydrogen stream

110 ... hydrogen preheater

112 ... first hydrogen feed stream

114 ... first mixed feed stream

116 ... first reactor

118 ... first product stream

120 ... further cold hydrogen stream

122 ... further hydrogen preheater

124 ... second hydrogen feed stream

126 ... second mixed feed stream

128 ... second heat exchanger

130 ... heated second mixed feed stream

132 ... second reactor

134 ... second product stream

136 ... first heat exchanger

138 ... heated first mixed feed stream

140 ... raw carbon dioxide feed stream

142 ... purification unit

144 ... product cooler

146 ... cooled product stream

Claims

1. A method for carbon dioxide hydrogenation comprising the steps of:

(a) providing a carbon dioxide feed stream (106) at a temperature of from 600°C to 1000°C;

(b) providing a first hydrogen feed stream (112) at a temperature of from 600°C to 1000°C;

(c) mixing the carbon dioxide feed stream (106) and the first hydrogen feed stream (112) obtaining a first mixed feed stream (114);

(d) optionally, heating the first mixed feed stream (114) in a first heat exchanger (136) to a temperature of from 800°C to 1000°C obtaining a heated first mixed feed stream (138);

(e) feeding the first mixed feed stream (114) and/or the heated first mixed feed stream (138) at a temperature of from 800°C to 1000°C to a first reactor (116) where the first mixed feed stream (114) and/or the 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.

2. The method of claim 1 , the method further comprising the steps of:

(f) mixing the first product stream (118) with a second hydrogen feed stream (124) obtaining a second mixed feed stream (126);

(g) heating the second mixed feed stream (126) in a second heat exchanger (128) to a temperature of from 800°C to 1000°C;

(h) feeding the heated second mixed feed stream (130) to a second reactor (132) where 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 of claim 1 or 2, characterized in that the carbon dioxide feed stream (106) contains from 90 mol-% to 100 mol-% of carbon dioxide, the first hydrogen feed stream (112) contains from 90 mol-% to 100 mol-% of hydrogen, and that 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 from 0.9 to 3, preferably from 1.3 to 2.5.

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

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

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

7. The method of 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 that the first product stream (118) and/or the second product stream (134) is cooled in a product cooler (144) to obtain a cooled product stream (146), wherein at least part 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 of claim 7, characterized in that the carbon dioxide feed preheater (104) comprises a first preheater that receives the 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 from 300°C to 450°C.

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

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

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

12. A reaction system for carbon dioxide hydrogenation comprising: a first gas mixer configured to receive a carbon dioxide feed stream (106) at a temperature of from 600°C to 1000°C and a first hydrogen feed stream (112) at a temperature of from 600°C to 1000°C and to mix the two streams obtaining a first mixed feed stream (114); optionally, a first heat exchanger (136) configured to receive the first mixed feed stream (114) and to heat the first mixed feed stream to a temperature of from 800°C to 1000°C obtaining a heated first mixed feed stream (138); and a first reactor (116) configured to receive the first mixed feed stream (114) and/or the heated first mixed feed stream (138) at a temperature of from 800°C to 1000°C and to contact it with a catalyst inside 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 of claim 12, characterized in that the reaction system further comprises a second heat exchanger (128) configured to receive a second mixed feed stream (126) as a mixture of the first product stream (118) and a second hydrogen feed stream (124) and to heat the second mixed feed stream (126) to a temperature of from 800°C to 1000°C; and a second reactor (132) configured to receive the heated second mixed feed stream (130) and to 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.