Reverse water gas shift method with separate heating of the feed streams

Abstract

The present invention relates to a method and device for producing syngas by CO2 conversion, wherein CO2 (1) and H2 (2) are heated separately in a heating section (3) to produce heated CO2 (11) at a first target temperature between 700°C and 1100°C, and heated H2 (12) at a second target temperature between 700°C and 1100°C; the heated CO2 and the heated H2 are mixed to produce a mixture (4) at a third target temperature greater than 760°C and less than 1100°C; the heated CO2 and the heated H2 are introduced into a reverse water gas shift unit (7), before or after mixing; the mixture in the reverse water gas shift unit is treated to produce a CO-enriched reverse water gas shift gas (8).

Description

[0001] Reverse gas-to-water conversion process with separate heating of the feed streams

[0002] Technical field

[0003] The present invention relates to a process for producing synthesis gas ("syngas" in English terminology), composed mainly of carbon monoxide (CO) and optionally hydrogen (H2), by reaction between a stream comprising carbon dioxide (CO2) and optionally carbon monoxide and a stream comprising hydrogen.

[0004] The synthesis gas can then be used to produce alcohols, including methanol, or paraffinic hydrocarbons such as synthetic fuels, namely gasoline, kerosene, diesel, and / or other hydrocarbon products, such as naphtha, or lubricating bases, of very high quality (essentially free of sulfur, aromatics, nitrogen).

[0005] Prior art

[0006] The use of the reverse water-gas shift (RWGS) process for converting a mixture of carbon dioxide and hydrogen into synthesis gas comprising carbon monoxide and optionally H2 is known to those skilled in the art. During the RWGS reaction, carbon dioxide reacts with hydrogen to produce carbon monoxide and water (H2O): CO2 + H2 CO + H2O. A mixture of carbon monoxide and hydrogen can be obtained by operating with an excess of hydrogen or by adding additional hydrogen at the reactor outlet, so as to obtain, after condensation of the water, a mixture comprising carbon monoxide, hydrogen and optionally unconverted carbon dioxide.

[0007] The reverse water gas shift reaction is a reversible and endothermic reaction, which is favored at high temperatures. At thermodynamic equilibrium, depending on the pressure and the H2 / CO2 ratio, the conversion of carbon dioxide can reach 60% to 80% for temperatures between 800°C and 1000°C. Hydrogen can also react with carbon dioxide and / or carbon monoxide to form methane (CH4): CO2 + 4 H2 CH4 + 2 H2O; CO + 3 H2 CH4 + H2O. These reactions are exothermic and are therefore not favored at high temperatures, but are favored by a high partial pressure of hydrogen. These reactions that lead to the formation of methane consume a lot of hydrogen. When we want to produce synthesis gas for the production of synthetic fuel or methanol, we seek to limit the quantity of methane present in the synthesis gas, in order to maximize the quantity of liquid hydrocarbons synthesized.Carbon monoxide selectivity is therefore an important issue in limiting methane production and thus directing the hydrogen consumed towards the formation of carbon monoxide in order to maximize the production of liquid hydrocarbons.

[0008] Patent application WO2021225643A1 describes a process for converting a feed gas comprising carbon dioxide and hydrogen into a gaseous product comprising carbon monoxide and water wherein:

[0009] - the feed gas is heated to an inlet temperature above 760°C (1400°F) in a preheater outside a main reactor vessel to produce a heated feed gas;

[0010] - the preheater uses electricity to generate heat and produce the heated feed gas;

[0011] - the heated feed gas is sent into the main reactor vessel;

[0012] - the main reactor vessel is an adiabatic or quasi-adiabatic vessel where heat loss is minimized;

[0013] - the main reactor vessel contains a catalyst that converts the heated feed gas into product gas;

[0014] - the produced gas leaves the main reactor at an outlet temperature where the outlet temperature is lower than the inlet temperature.

[0015] The applicant has found that when heating the mixture of a flow comprising hydrogen and carbon dioxide in a metal-walled tube, methane formation occurs, the formation of methane being favored by temperatures below 700°C and being catalyzed by the nickel present in high-temperature resistant metallurgies. The presence of methane in the temperature range between 400 and 800°C induces the phenomenon of metal dusting, the degradation of metal alloys, for example based on iron or nickel, into metal dust. In particular, metal dusting is a significant local loss of thickness, generalized or in the form of pitting which, due to the diffusion of carbon in the metal, leads to the decomposition of the metal by the formation on the surface of metal particles (dust) and carbides or coke.

[0016] Furthermore, methane formation consumes hydrogen. Indeed, per mol of carbon dioxide consumed, 4 mol of hydrogen are consumed to form 1 mol of methane, while 1 mol of hydrogen is consumed to form 1 mol of carbon monoxide. The presence of methane leads to overconsumption at the electrolyzer to produce the necessary hydrogen. In addition, the exact concentration of the mixture during heating depends on the contact time with the metal wall, which requires control at the inlet of the RWGS reactor. For example, when the unit operates at reduced total flow (the so-called fallback phase during the operation of an industrial unit), the contact time is increased and methane formation is even greater.

[0017] Although methane can be partially converted by catalytic steam reforming within the RWGS reactor, the catalytic reforming reaction is slower and more endothermic than the RWGS reaction. Therefore, a significant concentration of methane remains at the outlet of the RWGS reactor.

[0018] The present invention aims to solve these problems related to the uncontrolled formation of methane and the phenomenon of corrosion by metallic dust in the heating system of the RWGS reactor charge.

[0019] Summary of the invention

[0020] In the context described above, a first object of the present description is to overcome the problems of the prior art and to provide a method and a device making it possible to improve the production of carbon monoxide, to limit the overconsumption of hydrogen, to limit the production of methane and to limit corrosion by metallic dusting. A second object of the present description is to be able to control the composition of the gaseous phase at the inlet of the RWGS reactor, and to be able to produce a synthesis gas of controlled composition, even when the unit operates with a reduced total flow rate.

[0021] According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by a process for producing synthesis gas by converting a feedstock comprising carbon dioxide, comprising the following steps:

[0022] - separately heating a carbon dioxide stream and a hydrogen stream in a heating section, to produce a heated carbon dioxide stream of first target temperature between 700°C and 1100°C, and a heated hydrogen stream of second target temperature between 700°C and 1100°C;

[0023] - mixing the heated carbon dioxide stream and the heated hydrogen stream, to produce a mixture with a third target temperature greater than 760°C and less than 1100°C; - introducing the heated carbon dioxide stream and the heated hydrogen stream into a reverse water gas conversion reaction unit RWGS, before or after the mixing step;

[0024] - treating the mixture in the reverse water gas conversion RWGS reaction unit to produce a RWGS gas enriched in carbon monoxide (and enriched in water and depleted in carbon dioxide and hydrogen) relative to the mixture.

[0025] According to one or more embodiments, the heated carbon dioxide stream (11) and the heated hydrogen stream (12) are mixed before or after introduction into the RWGS reaction unit (7)

[0026] According to one or more embodiments, the carbon dioxide stream (1) has an initial temperature of less than 300°C, preferably less than 250°C, preferably less than 200°C, and / or wherein the hydrogen stream (2) has an initial temperature of less than 300°C, preferably less than 200°C, preferably less than 150°C.

[0027] According to one or more embodiments, the first target temperature is between 760°C and 1100°C, preferably between 780°C and 1050°C, preferably between 800°C and 1050°C, and / or the second target temperature is between 760°C and 1100°C, preferably between 780°C and 1050°C, preferably between 800°C and 1050°C.

[0028] According to one or more embodiments, the third target temperature is greater than 760°C and less than or equal to 1100°C, preferably between 800°C and 1100°C, preferably between 880°C and 1050°C, preferably between 930°C and 1050°C, preferably between 980°C and 1050°C.

[0029] According to one or more embodiments, the heating section (3) comprises at least one first furnace (17) and / or at least one first heat exchanger (9) adapted to separately heat the carbon dioxide stream (1) and the hydrogen stream (2).

[0030] According to one or more embodiments, the mixture (4) is heated in a second furnace (5) to produce a heated mixture (6) with a fourth target temperature between 880°C and 1050°C, preferably between 930°C and 1050°C, preferably between 980°C and 1050°C.

[0031] According to one or more embodiments, the first furnace (17) and / or the second furnace (5) is a furnace powered at least in part by electrical energy and / or by a fuel. According to one or more embodiments, the heating section (3) comprises at least one first heat exchanger (9) adapted to separately heat the carbon dioxide stream (1) and the hydrogen stream (2) with the RWGS gas (8).

[0032] According to one or more embodiments, the RWGS gas (8) has an outlet temperature from the RWGS reaction unit (7) of at least 700°C, preferably at least 750°C, very preferably at least 800°C.

[0033] According to one or more embodiments, the heated carbon dioxide stream (11) and / or the heated hydrogen stream (12) after the heat exchange with the RWGS gas (8) have a temperature greater than or equal to 760°C, preferably a temperature greater than or equal to 780°C.

[0034] According to one or more embodiments, the heating section (3) comprises:

[0035] - at least one first heat exchanger (9) adapted to separately preheat the carbon dioxide stream (1) and the hydrogen stream (2) with the RWGS gas (8), and produce a preheated carbon dioxide stream (18) with a first target intermediate temperature between 80°C and 900°C, and a preheated hydrogen stream (19) with a second target intermediate temperature between 80°C and 900°C; and

[0036] - at least one first furnace (17) adapted to separately heat the preheated carbon dioxide stream (18) and / or the preheated hydrogen stream (19) and produce the heated carbon dioxide stream (11) and the heated hydrogen stream (12).

[0037] According to one or more embodiments, the RWGS gas (8) is cooled directly at the outlet of the RWGS reaction unit (7) with at least one second heat exchanger (13) to produce a warmed RWGS gas (14) having a temperature between 80°C and 800°C, preferably between 150°C and 600°C, preferably between 250°C and 400°C, the warmed RWGS gas (14) being sent into the at least one first heat exchanger (9) to separately preheat the carbon dioxide stream (1) and the hydrogen stream (2) instead of the RWGS gas (8).

[0038] According to one or more embodiments, the preheated carbon dioxide stream (18) has a first target intermediate temperature between 80°C and 300°C or between 80°C and 400°C and the preheated hydrogen stream (19) has a second target intermediate temperature between 80°C and 300°C or between 80°C and 400°C. According to a second aspect, the aforementioned objects, as well as other advantages, are obtained by a device for producing synthesis gas by converting a feedstock comprising carbon dioxide, comprising the following elements:

[0039] - a heating section adapted to separately heat a carbon dioxide stream and a hydrogen stream and produce a heated carbon dioxide stream with a first target temperature between 700°C and 1100°C, and a heated hydrogen stream with a second target temperature between 700°C and 1100°C;

[0040] - a reverse water gas conversion reaction unit RWGS adapted to treat a mixture comprising the heated carbon dioxide stream and the heated hydrogen stream, to produce a RWGS gas enriched in carbon monoxide (and enriched in water and depleted in carbon dioxide and hydrogen) relative to the mixture, the mixture having a third target temperature greater than 760°C and less than 1100°C, the heated carbon dioxide stream and the heated hydrogen stream being mixed before or after being introduced into the reverse water gas conversion reaction unit RWGS.

[0041] Embodiments of the device and method according to the aforementioned aspects as well as other characteristics and advantages will appear on reading the description which follows, given for illustrative and non-limiting purposes only, and with reference to the following drawings.

[0042] List of figures

[0043] Figure 1 is a simplified schematic representation of the method according to the present invention with separate heating of the charge flows.

[0044] Figure 2 is a simplified schematic representation of the method according to the present invention with separate heating of the feed streams and then heating of the mixture of feed streams.

[0045] Figure 3 is a simplified schematic representation of the process according to the present invention with separate heating of the feed streams by heat exchange with the RWGS effluent then heating of the mixture of feed streams with a furnace.

[0046] Figure 4 is a simplified schematic representation of the process according to the present invention with separate heating of the feed streams by heat exchange with the RWGS effluent then separate heating of the feed streams with a furnace.

[0047] Figure 5 is a simplified schematic representation of the process according to Figure 4 with cooling of the RWGS effluent. Description of the embodiments

[0048] Embodiments of the method according to the first aspect and the device according to the second aspect will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the device. However, it will be apparent to those skilled in the art that the device can be implemented without these specific details. In other cases, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0049] In this specification, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". In this specification, an effluent predominantly comprising a compound A corresponds to an effluent comprising at least 50% by weight of compound A. In this specification, an effluent comprising essentially or solely a compound A corresponds to an effluent comprising at least 95% by weight, preferably at least 98% by weight, very preferably at least 99% by weight, of compound A.

[0050] The present invention can be defined as a method and a device comprising a sequence of operations for producing synthesis gas, composed mainly of carbon monoxide (CO), by converting carbon dioxide (CO2) in the presence of hydrogen (H2). In particular, the method and the device for producing synthesis gas from carbon dioxide and hydrogen make it possible to guarantee the quality of the synthesis gas produced. The method and the device according to the invention make it possible in particular to reduce the quantity of methane present in the synthesis gas.

[0051] The method and device according to the invention are notably characterized in that they comprise and use at least one furnace and / or at least one charge / effluent heat exchanger and a reverse water gas conversion unit (RWGS).

[0052] The required carbon dioxide can be provided by a unit for separating a stream comprising carbon dioxide (e.g. combustion fumes) or a unit for capturing carbon dioxide (e.g. carbon dioxide present in the air).

[0053] The hydrogen required for the conversion of carbon dioxide can be produced by a water electrolysis unit, said water being able to come from the effluent of the RWGS reaction unit and optionally from downstream units (for example Fischer-Tropsch (FT) or alcohol synthesis units). Preferably, the use of the water electrolysis unit to treat the water produced by the RWGS reaction unit also makes it possible to minimize the environmental impact of the process. Thus, the process according to the invention does not require an external supply of hydrogen, for example produced by steam reforming of natural gas. The electrolyzer can preferably operate with low-carbon electricity, which contributes to the renewable nature of the synthesis gas and the hydrocarbons that will then be produced from this synthesis gas.Furthermore, the water used for hydrogen production can come at least in part from the recycling of water produced by the RWGS reaction, which has the advantage of limiting the external water supply.

[0054] With reference to Figure 1, according to the first aspect, the process for producing synthesis gas by converting a feedstock comprising carbon dioxide, comprises the following steps:

[0055] - separately heating a carbon dioxide stream 1 and a hydrogen stream 2 in a heating section 3, to produce a heated carbon dioxide stream 11 with a first target temperature between 700°C and 1100°C, and a heated hydrogen stream 12 with a second target temperature between 700°C and 1100°C;

[0056] - mixing the heated carbon dioxide stream 11 and the heated hydrogen stream 12, to produce a mixture 4 with a third target temperature greater than 760°C and less than 1100°C;

[0057] - introducing the heated carbon dioxide stream 11 and the heated hydrogen stream 12 into a reverse water gas conversion (RWGS) reaction unit 7, before or after the mixing step;

[0058] - treating mixture 4 in RWGS reaction unit 7 to produce RWGS gas 8 enriched in carbon monoxide (and enriched in water and depleted in carbon dioxide and hydrogen) relative to mixture 4.

[0059] 11 It is understood in the present application that, when the carbon dioxide stream 1 (or the hydrogen stream 2) is heated to reach a first (or a second) temperature less than or equal to 760°C, the hydrogen stream 2 (or the carbon dioxide stream 1) is heated to reach a second (or a first) temperature greater than 760°C, so that the mixture 4 has a third target temperature greater than 760°C.

[0060] Figure 1 shows that the heated carbon dioxide stream 11 and the heated hydrogen stream

[0061] 12 are mixed before being introduced into the RWGS reaction unit 7. It is understood that the method according to the present invention also relates to the separate introduction of the heated carbon dioxide stream 11 and the heated hydrogen stream 12 into the RWGS reaction unit 7 and then to the mixing of the heated carbon dioxide stream 11 and the heated hydrogen stream 12. According to one or more embodiments, the initial temperature (before the first separate heating step) of the carbon dioxide stream 1 is less than 300°C, preferably less than 250°C, preferably less than 200°C. According to one or more embodiments, the initial temperature of the carbon dioxide stream 1 is between -50°C and 300°C, preferably between 0°C and 250°C, preferably between 0°C and 200°C.

[0062] According to one or more embodiments, the initial temperature (before the first separate heating step) of the hydrogen stream 2 is less than 300°C, preferably less than 200°C, preferably less than 150°C. According to one or more embodiments, the initial temperature of the hydrogen stream 2 is between 10°C and 300°C, preferably between 10°C and 200°C, preferably between 10°C and 150°C.

[0063] According to one or more embodiments, the first target temperature is between 760°C and 1100°C, preferably between 780°C and 1050°C, preferably between 800°C and 1050°C. According to one or more embodiments, the second target temperature is between 760°C and 1100°C, preferably between 780°C and 1050°C, preferably between 800°C and 1050°C.

[0064] According to one or more embodiments, the third target temperature is greater than 760°C and less than or equal to 1100°C, preferably between 800°C and 1100°C, preferably between 880°C and 1050°C, preferably between 930°C and 1050°C, preferably between 980°C and 1050°C.

[0065] According to one or more embodiments, the heating section 3 comprises at least a first furnace 17 adapted to separately heat the carbon dioxide stream 1 and the hydrogen stream 2.

[0066] Referring to Figure 2, according to one or more embodiments, for example when the third target temperature is greater than 760°C and less than 880°C, the mixture 4 is heated in a second furnace 5 to produce a heated mixture 6 with a fourth target temperature between 880°C and 1050°C, preferably between 930°C and 1050°C, preferably between 980°C and 1050°C. The heated mixture 6 can be sent to the RWGS reaction unit 7 instead of the mixture 4.

[0067] According to one or more embodiments, the first furnace 17 and / or the second furnace 5 is a furnace powered at least in part by electrical energy. According to one or more embodiments, the first / second furnace is powered at least in part by a fuel. According to one or more embodiments, the first / second furnace is powered in a hybrid manner by electrical energy and by a fuel. Preferably, the first furnace 17 and / or the second furnace 5 is a furnace essentially or totally powered by electrical energy.

[0068] Advantageously, existing electric furnace technologies make it possible to achieve the target temperatures. According to one or more embodiments, the first / second electric furnace is (of) tubular technology, each flow to be heated circulating in one or more tubes, said tubes being able to be heated either by a system of electrical resistances, or by impedance. According to one or more embodiments, the first / second electric furnace is made up of electrical resistances immersed in the flows to be heated. Advantageously, the supply of calories can be carried out either by impedance, each flow then circulating in one or more metal tubes, or by means of electrical resistances which can be in contact with the circulating flows or without direct contact, the flows then circulating in a metal tube. The metallurgy of the metal tube can be adapted to the nature of the flows to be heated and to the target temperatures.

[0069] In the case of a first / second furnace fueled at least partially by a fuel, the first / second furnace is preferably fueled by a source of oxygen (air and / or oxygen produced by the electrolyser), and by at least one of the following fuels:

[0070] - a gaseous hydrocarbon effluent (“off-gas” in English terminology), such as an effluent from an FT unit treating RWGS 8 gas, or from a hydrocracking, hydrotreatment or hydroisomerization unit for paraffins produced by the FT unit, or an effluent from a methanol synthesis unit); and / or

[0071] - hydrogen, for example produced by the electrolyser.

[0072] According to one or more embodiments, the hydrocarbon gas effluent comprises at least one of the following: unconverted RWGS 8 gas, carbon dioxide, gaseous hydrocarbons, such as C1-C4 paraffins, C2-C4 olefins, and / or C1-C3 oxygenated compounds. According to one or more embodiments, when the first / second furnace is fed with the hydrocarbon gas effluent, the first / second furnace is a partial oxidation unit, in particular for producing an effluent rich in carbon monoxide, and preferably composed essentially of carbon monoxide, and optionally comprising carbon dioxide, hydrogen and water.

[0073] With reference to Figure 3, according to one or more embodiments, the heating section 3 comprises at least one first heat exchanger 9. According to one or more embodiments, the at least one first heat exchanger 9 comprises one or more heat exchangers (e.g., a train of heat exchangers) adapted to separately heat each of the streams by heat exchange with the RWGS gas 8, for example directly at the outlet of the RWGS reaction unit 7, and produce a cooled RWGS gas 10. According to one or more embodiments, the at least one first heat exchanger 9 is adapted to heat in parallel the carbon dioxide stream 1 and the hydrogen stream 2. For example, the RWGS gas 8 can be divided into two streams, one heating the carbon dioxide stream 1 by means of one or more heat exchangers, the other heating the hydrogen stream 2 by means of another or other heat exchangers.According to one or more embodiments, the at least one first heat exchanger 9 comprises at least one multi-service heat exchanger, i.e., a heat exchanger adapted to heat at least two separate fluids in parallel. According to one or more embodiments, the at least one first heat exchanger 9 is adapted to heat the carbon dioxide stream 1 and the hydrogen stream 2 in series, for example, the RWGS gas 8 heats the carbon dioxide stream 1 then the hydrogen stream 2, or the hydrogen stream 2 then the carbon dioxide stream 1, by means of one or more heat exchangers. According to one or more embodiments, the at least one first heat exchanger 9 comprises at least one plate heat exchanger (e.g. for temperatures below 400°C) and / or at least one shell-and-tube heat exchanger (e.g. for temperatures greater than or equal to 400°C).

[0074] According to one or more embodiments, the RWGS gas 8 has an outlet temperature from the RWGS reaction unit 7 (lower than the third target temperature) of at least 700°C, preferably at least 750°C, very preferably at least 800°C, for example a temperature between 800°C and 1050°C, preferably a temperature between 800°C and 1000°C, preferably a temperature between 800°C and 900°C. According to one or more embodiments, the temperature difference between the inlet gas in the RWGS reaction unit 7 (mixture 4 or heated mixture 6) and the RWGS gas 8 is at least 10°C, preferably at least 40°C, very preferably at least 50°C, for example a temperature difference between 50°C and 200°C, preferably a temperature between 60°C and 195°C, preferably a temperature between 80°C and 190°C.It is understood that the temperature of the inlet gas in the reaction unit of RWGS 7 is higher than that of the gas of RWGS 8.

[0075] According to one or more embodiments, the heated carbon dioxide stream 11 and / or the heated hydrogen stream 12 after the heat exchange with the RWGS gas 8 have a temperature greater than or equal to 760°C, preferably a temperature greater than or equal to 780°C. With reference to FIG. 4, according to one or more embodiments, the heating section 3 comprises:

[0076] - at least one first heat exchanger 9 adapted to separately preheat the carbon dioxide stream 1 and the hydrogen stream 2 and produce a preheated carbon dioxide stream 18 with a first target intermediate temperature between 80°C and 900°C, for example a temperature greater than or equal to 280°C, preferably a temperature greater than or equal to 380°C and a preheated hydrogen stream 19 with a second target intermediate temperature between 80°C and 900°C, for example a temperature greater than or equal to 280°C, preferably a temperature greater than or equal to 380°C; and

[0077] - at least one first furnace 17 adapted to separately heat the preheated carbon dioxide stream 18 and / or the preheated hydrogen stream 19 and produce the heated carbon dioxide stream 11 and the heated hydrogen stream 12. It is understood that the first target intermediate temperature is lower than the first target temperature and that the second target intermediate temperature is lower than the second target temperature. It is also understood that the embodiments as shown in Figure 4 make it possible to use a second furnace 5 to heat the mixture 4 and produce a heated mixture 6 as described above.

[0078] With reference to Figure 5, according to one or more embodiments, the RWGS gas 8 is cooled directly at the outlet of the RWGS reaction unit 7 with at least one second heat exchanger 13 to produce a warmed RWGS gas 14. For example, the at least one second heat exchanger 13 can be used to produce water vapor 16 from a water supply 15. According to one or more embodiments, the warmed RWGS gas 14 has a temperature (e.g. outlet of the second heat exchanger 13) of between 80°C and 800°C, preferably between 150°C and 600°C, preferably between 250°C and 400°C. According to one or more embodiments, the water vapor 16 has a temperature (e.g. outlet of second heat exchanger 13) of between 120°C and 400°C, preferably between 130°C and 350°C, preferably between 130°C and 300°C.

[0079] Advantageously, the warmed RWGS gas 14 can be used instead of the RWGS gas 8 sent to the first heat exchanger 9 to separately preheat the carbon dioxide stream 1 and the hydrogen stream 2 and produce the preheated carbon dioxide stream 18 with a first target intermediate temperature of between 80°C and 300°C or between 80°C and 400°C and the preheated hydrogen stream 19 with a second target intermediate temperature of between 80°C and 300°C or between 80°C and 400°C. Advantageously, it is possible to use a first furnace 17 adapted to treat one or more loads whose inlet temperature in the first furnace 17 is less than or equal to 300°C or 400°C, the at least one first furnace 17 being adapted to heat (separately) the preheated carbon dioxide stream 18 and / or the preheated hydrogen stream 19 and produce the heated carbon dioxide stream 11 and the heated hydrogen stream 12.It is also understood that the embodiments as shown in Figure 5 allow a second oven 5 to be used to heat the mixture 4 and produce a heated mixture 6 as described above.

[0080] According to one or more embodiments, the RWGS reaction unit 7 comprises at least one reactor used under at least one of the following operating conditions:

[0081] - temperature between 700°C and 1200°C, preferably between 800°C and 1100°C, and even more preferably between 850°C and 1050°C;

[0082] - pressure between 0.1 MPa and 10 MPa, preferably between 0.1 MPa and 5 MPa, and more preferably between 0.1 MPa and 3.5 MPa;

[0083] - space velocity of the gas at the reactor inlet between 2000 NL / kg ca ta / h and 40000 NL / kgcata / h;

[0084] - catalyst based on the elements Ni, Cu, Fe, Co or precious metals such as Pt, Pd, Ru, Ag and Au. According to one or more embodiments, the catalyst for the RWGS reaction comprises a support, for example based on alumina, silica, silica-alumina, alumina-silica. According to one or more embodiments, the catalyst has a ring or cylinder shape. Advantageously, the RWGS reaction unit 7 comprises a catalytic bed allowing a carbon dioxide conversion of at least 60%, preferably at least 65%, preferably at least 67%.

[0085] According to one or more embodiments, the at least one reactor of the RWGS reaction unit 7 is an adiabatic reactor. Advantageously, the low heat loss or even the absence of heat loss in the adiabatic reactor is ensured by any thermal insulation means known to those skilled in the art. For example, the insulation of the adiabatic reactor can be carried out from the outside of the metal wall of the adiabatic reactor, and in this case, the metal wall is in a metallurgy resistant to temperature and gases containing CO, hydrogen and water, possibly covered with a coating (e.g. layer < 1 mm) against coking and metal dusting (e.g. coating based on Al, Cr or Si which is then oxidized in situ to form a layer of AI2O3 oxide. For example, the insulation of the adiabatic reactor can be carried out from the inside of the metal wall of the adiabatic reactor, with one or more layers of insulating materials.According to one or more embodiments, the amount of hydrogen at the inlet of the RWGS reaction unit 7 is adjusted so that the H2 / CO molar ratio at the outlet of the RWGS reaction unit 7 is compatible with the need for a downstream FT unit (not described) or an alcohol synthesis unit (not described). According to one or more embodiments, the amount of hydrogen at the inlet of the RWGS reaction unit 7 is controlled so that the H2 / CO molar ratio at the outlet of the RWGS reaction unit 7 is between 0.5 and 4, preferably between 1 and 3, more preferably between 1.5 and 2.5.According to one or more embodiments, a portion of the hydrogen required for the FT synthesis or the alcohol synthesis may be supplied downstream of the RWGS reaction unit 7, for example by mixing a make-up hydrogen source with the RWGS effluent (8, 10 or 14), before or after heat exchange with the feedstock streams of the RWGS reaction unit 7. The addition of hydrogen may be carried out, for example, downstream of a water separation unit (defined below) adapted to separate water contained in the RWGS effluent. Advantageously, the addition of hydrogen is carried out upstream of one of the FT units or the alcohol synthesis unit.

[0086] According to one or more embodiments, the RWGS gas (8, 10 or 14), and preferably the cooled RWGS gas 10, is sent to the water separation unit (not described), to separate at least partially or completely the water present in the RWGS gas and produce a water-depleted RWGS gas. Advantageously, the water-depleted RWGS gas comprises essentially carbon monoxide, optionally carbon dioxide (residual) and optionally hydrogen (when hydrogen is in excess). For example, the RWGS gas can be cooled to a condensation temperature allowing condensation and the water present in the RWGS gas.

[0087] According to one or more embodiments, the water electrolysis unit treats at least in part the water separated from the water-depleted RWGS gas and / or separated from an effluent from a downstream unit (e.g. for the production of paraffinic hydrocarbons or alcohols) to produce at least in part the hydrogen stream 2. The water electrolysis unit may optionally treat in part or completely water from a make-up line.

[0088] According to one or more embodiments, the water electrolysis unit comprises at least one alkaline electrolyzer. Other electrolyzer technologies may be used for the water electrolysis unit, such as proton exchange membrane electrolysis (PEM), solid oxide electrolysis (SOE), or anion exchange membrane electrolysis (AEM). The operating conditions (temperature, pressure, nature of the electrolyte, electrodes and diaphragm / membrane) are then specific to each technology.

[0089] According to one or more embodiments, the water electrolysis unit comprises at least one reactor used in at least one of the following operating conditions: Alkaline type electrolyzer:

[0090] - temperature between 60°C and 90°C,

[0091] - pressure between 0.1 MPa and 20 MPa, preferably between 0.1 MPa and 4 MPa,

[0092] - electrolyte comprising KOH,

[0093] - electrodes comprising a metal alloy,

[0094] - diaphragm comprising asbestos, polytetrafluoroethylene and / or nickel oxide;

[0095] Proton exchange membrane (PEM) electrolyzer:

[0096] - temperature between 50°C and 80°C,

[0097] - pressure between 0.1 MPa and 20 MPa, preferably between 1.8 MPa and 5.5 MPa,

[0098] - electrolyte comprising a polymer membrane,

[0099] - electrodes comprising a metal alloy;

[0100] Solid Oxide Electrolyzer (SOE):

[0101] - temperature between 800°C and 900°C,

[0102] - pressure between 0.1 MPa and 2 MPa, preferably between 0.1 MPa and 0.5 MPa,

[0103] - electrolyte comprising a ceramic membrane (eg perovskite type), - electrodes comprising a metal alloy;

[0104] Anion exchange membrane (AEM) type electrolyzer:

[0105] - temperature between 50°C and 70°C,

[0106] - pressure between 0.1 MPa and 20 MPa, preferably between 0.1 MPa and 3.5 MPa,

[0107] - electrolyte comprising a polymer membrane,

[0108] - electrodes comprising a metal alloy.

[0109] According to one or more embodiments, the hydrogen stream 2 produced by the water electrolysis unit comprises between 99.5% by weight and 99.999% by weight of hydrogen (after drying). According to one or more embodiments, the carbon dioxide-rich effluent 1 is purified before being introduced into the RWGS reaction unit 7. According to one or more embodiments, the carbon dioxide-rich effluent 1 is purified in the heating section 3. For example, the carbon dioxide-rich effluent 1 may be purified before or after being introduced into the first heat exchanger 9. It is preferable that the carbon dioxide-rich effluent 1 is purified before being introduced into the first furnace 17 or the second furnace 5. According to one or more embodiments, the carbon dioxide-rich effluent 1 is purified before being introduced into the heating section 3.

[0110] According to one or more embodiments, the RWGS gas 8 is purified before being introduced into the reaction unit for the synthesis of paraffinic hydrocarbons or alcohols, for example upstream or downstream of a water separation unit arranged between the RWGS reaction unit 7 and said reaction unit for the synthesis of paraffinic hydrocarbons or alcohols. According to one or more embodiments, the water effluent recovered by separation on the RWGS gas 8 is purified before being introduced into the water electrolysis unit.

[0111] The effluent purification stages aim to at least partially eliminate sulfur and nitrogen compounds, halogens, heavy metals and transition metals. The main gas purification technologies are: adsorption, absorption, catalytic reactions.

[0112] Examples

[0113] Example 1 not in accordance with the invention - common heating

[0114] In Example 1, not in accordance with the invention, 1000 kg / h of carbon dioxide and 88.6 kg / h of hydrogen are mixed at low temperature (15°C) in order to produce a RWGS gas having an H2 / CO ratio of 2.1. The mixture is then heated to reach a mixing temperature of 1000°C. The mixture thus heated is sent to a RWGS reaction unit reactor.

[0115] As shown in Table 1, 350.2 kg / h of carbon monoxide, 271.6 kg / h of water and 20.6 kg / h of methane are produced at the reactor outlet. The RWGS gas also includes 393.2 kg / h of carbon dioxide and 53.0 kg / h of unconverted hydrogen. Table 1

[0116] The production of one mole of methane consumes between 3 and 4 moles of hydrogen. That is, to produce 20.6 kg / h of methane, between 7.7 kg / h and 10.3 kg / h of hydrogen are consumed, which corresponds to an additional electrical consumption (compared to a case without methane production) of more than 0.5 MW for a conventional electrolyser, for example of the PEM type, for a total consumption of 5 MW to produce 88.6 kg / h of hydrogen, or 10% of the electrical consumption.

[0117] Example 2 according to the invention - separate heating over the entire range

[0118] In Example 2, according to the invention, 1000 kg / h of carbon dioxide and 97.2 kg / h of hydrogen are sent to a RWGS reaction unit reactor in order to produce a RWGS gas having an H2 / CO ratio of 2.1. To do this, the carbon dioxide stream 1 and the hydrogen stream 2 are heated separately to reach a first target temperature of 1000°C and a second target temperature of 1000°C. The heated carbon dioxide stream 11 and the heated hydrogen stream 12 are then mixed to produce a mixture 4 with a third target temperature of 1000°C. The mixture 4 is sent to the RWGS reaction unit reactor.

[0119] As shown in Table 2, 424.9 kg / h of carbon monoxide, 286.3 kg / h of water and 5.8 kg / h of methane are produced at the reactor outlet. The RWGS gas also includes 316.5 kg / h of carbon dioxide and 64.2 kg / h of unconverted hydrogen. Table 2

[0120] In this example 2, the carbon dioxide stream 1 and the hydrogen stream 2 are heated separately up to 1000°C. No reaction took place between the carbon dioxide and the hydrogen below 1000°C. It follows that the lines and equipment are not degraded by metal dusting.

[0121] The production of one mole of methane consumes between 3 and 4 moles of hydrogen. That is, to produce 5.8 kg / h of methane, between 2.2 kg / h and 2.9 kg / h of hydrogen are consumed, which corresponds to an additional electrical consumption (compared to a case without methane production) of approximately 0.15 MW for the same PEM type electrolyser, for a total consumption of 5.5 MW to produce 97.2 kg / h of hydrogen, or 3% of the electrical consumption.

[0122] The total consumption of the electrolyser in Example 2 is 10% higher than in Example 1 for a 20% higher production of RWGS gas (having an H2 / CO ratio of 2.1). It is therefore preferable to limit the interaction between carbon dioxide and hydrogen before reaching a temperature favourable to the RWGS reaction, finally to improve the production of carbon monoxide, to limit the excess electricity consumption of the electrolyser, to limit the production of methane and to limit metal dusting.

Claims

Claims 1. Process for producing synthesis gas by converting a feedstock comprising carbon dioxide, comprising the following steps: - separately heating a carbon dioxide stream (1) and a hydrogen stream (2) in a heating section (3), to produce a heated carbon dioxide stream (11) with a first target temperature between 700°C and 1100°C, and a heated hydrogen stream (12) with a second target temperature between 700°C and 1100°C; - mixing the heated carbon dioxide stream (11) and the heated hydrogen stream (12), to produce a mixture (4) with a third target temperature greater than 760°C and less than 1100°C; - introducing the heated carbon dioxide stream (11) and the heated hydrogen stream (12) into a reverse water gas conversion reaction unit (7), before or after the mixing step; - treating the mixture (4) in the reverse water gas conversion reaction unit (7) to produce a reverse water gas conversion gas (8) enriched in carbon monoxide relative to the mixture (4).

2. A method according to claim 1, wherein the heated carbon dioxide stream (11) and the heated hydrogen stream (12) are mixed before introduction into the reverse water gas conversion reaction unit (7).

3. Method according to claim 1 or claim 2, wherein the carbon dioxide stream (1) has an initial temperature below 300°C, preferably below 250°C, preferably below 200°C, and / or wherein the hydrogen stream (2) has an initial temperature below 300°C, preferably below 200°C, preferably below 150°C.

4. Method according to any one of the preceding claims, wherein the first target temperature is between 760°C and 1100°C, preferably between 780°C and 1050°C, preferably between 800°C and 1050°C, and / or the second target temperature is between 760°C and 1100°C, preferably between 780°C and 1050°C, preferably between 800°C and 1050°C.

5. Method according to any one of the preceding claims, wherein the third target temperature is between 800°C and 1100°C, preferably between 880°C and 1050°C, preferably between 930°C and 1050°C, preferably between 980°C and 1050°C.

6. Method according to any one of the preceding claims, wherein the heating section (3) comprises at least one first furnace (17) and / or at least one first heat exchanger (9) adapted to separately heat the carbon dioxide stream (1) and the hydrogen stream (2).

7. A method according to any one of the preceding claims, wherein the mixture (4) is heated in a second furnace (5) to produce a heated mixture (6) with a fourth target temperature of between 880°C and 1050°C, preferably between 930°C and 1050°C, preferably between 980°C and 1050°C.

8. Method according to claim 6 or claim 7, wherein the first furnace (17) and / or the second furnace (5) is a furnace powered at least in part by electrical energy and / or by a fuel.

9. A method according to any one of the preceding claims, wherein the heating section (3) comprises at least one first heat exchanger (9) adapted to separately heat the carbon dioxide stream (1) and the hydrogen stream (2) with the reverse water gas conversion gas (8).

10. The method of claim 9, wherein the reverse water gas shift gas (8) has an outlet temperature from the reverse water gas shift reaction unit (7) of at least 700°C, preferably at least 750°C, most preferably at least 800°C.

11. A method according to claim 9 or claim 10, wherein the heated carbon dioxide stream (11) and / or the heated hydrogen stream (12) after heat exchange with the reverse water gas conversion gas (8) have a temperature greater than or equal to 760°C, preferably a temperature greater than or equal to 780°C.

12. A method according to any preceding claim, wherein the heating section (3) comprises: - at least one first heat exchanger (9) adapted to separately preheat the carbon dioxide stream (1) and the hydrogen stream (2) with the reverse water gas conversion gas (8), and produce a preheated carbon dioxide stream (18) with a first target intermediate temperature between 80°C and 900°C, and a preheated hydrogen stream (19) with a second target intermediate temperature between 80°C and 900°C; and - at least one first furnace (17) adapted to separately heat the preheated carbon dioxide stream (18) and / or the preheated hydrogen stream (19) and produce the heated carbon dioxide stream (11) and the heated hydrogen stream (12).

13. The method of claim 12, wherein the reverse water gas conversion gas (8) is cooled directly at the outlet of the reaction unit (7) with at least one second heat exchanger (13) to produce a warmed reverse water gas conversion gas (14) having a temperature between 80°C and 800°C, preferably between 150°C and 600°C, preferably between 250°C and 400°C, the warmed reverse water gas conversion gas (14) being sent to the at least one first heat exchanger (9) to separately preheat the carbon dioxide stream (1) and the hydrogen stream (2) instead of the reverse water gas conversion gas (8).

14. The method of claim 13, wherein the preheated carbon dioxide stream (18) has a first target intermediate temperature of between 80°C and 300°C or between 80°C and 400°C and the preheated hydrogen stream (19) has a second target intermediate temperature of between 80°C and 300°C or between 80°C and 400°C.

Images