Synthesis of ethanol by hydrogenation of carbon dioxide

Abstract

The present invention relates to methods for the industrial synthesis of ethanol by hydrogenation of carbon dioxide in the presence of a palladium- or iridium-based catalyst or a copper-based metal-organic framework catalyst. Different methods for purifying ethanol are described; they make it possible to obtain ethanol having a purity of 78% (by weight), 92% (by weight) or 95% (by weight).

Description

[0001] Ethanol Synthesis by Hydrogenation of Carbon Dioxide

[0002] Parent Patent Application

[0003] This patent application claims priority from French patent application number FR 24 09752 filed on September 13, 2024. The content of the French patent application is incorporated by reference in its entirety.

[0004] Technical Field

[0005] The present invention relates to the field of converting the main greenhouse gas, carbon dioxide (CO2), into valuable compounds such as fuels and basic products useful in the chemical industry. More particularly, the invention relates to improved methods for producing ethanol by catalytic hydrogenation of carbon dioxide.

[0006] Context of the invention

[0007] Carbon dioxide (CO2) is a crucial component of the Earth's carbon cycle, actively participating in the respiration of living organisms and the photosynthesis of plants. It is also produced by the combustion of fossil fuels, such as coal, natural gas, and oil, as well as by the combustion of all organic matter in general. Global levels of CO2 released into the atmosphere have been increasing dramatically since the beginning of the Industrial Revolution. In December 2023, the Earth's atmosphere contained 421 ppmv (parts per million by volume) of CO2, compared to 283 ppmv in 1839, representing an overall increase of approximately 49% in less than two centuries. As CO2 is a major greenhouse gas, its overabundance contributes to global warming and the formation of tropospheric ozone, which can have a direct and detrimental impact on ecosystems.Furthermore, ocean acidification resulting from the dissolution of atmospheric carbon dioxide could jeopardize the survival of many marine organisms before the end of the 21st century.

[0008] Reducing carbon dioxide at the source of production is particularly difficult and has generally not been successful. Carbon capture, utilization, and storage (CCUS) constitutes a range of important CO2 emission reduction technologies that play a crucial role in the transition to a net-zero carbon economy. Carbon dioxide can be converted into a wide range of marketable products, including synthetic fuels, chemicals, and many other materials. Catalytic hydrogenation of carbon dioxide is one of the most promising strategies due to its potential for large-scale conversion of CO2 into fuels and building blocks for the chemical industry.For example, the synthesis of two- or more carbon-based chemicals, such as ethanol, is a sought-after reaction because it generates a chemical of great interest due to its wide variety of applications in industry and everyday life, while reducing the impact of CO2 in the atmosphere.

[0009] Unlike methanol, the synthesis of ethanol by hydrogenation of carbon dioxide is still far from being a mature technology for industrial application because, unlike methanol synthesis, carbon-carbon (CC) coupling is required to produce this compound. CC coupling has significantly hampered the path to this reaction due to a lack of efficient catalysts. Recently, much effort has been devoted to achieving better catalytic performance in the synthesis of ethanol by CO2 hydrogenation (Asare Bediako et al., Acc. Chem. Res., 2021, 54: 2467-2476; Lou et al., Appl. Catal. B., 2021, 291: 120122; An et al., Chem. Eng. J., 2022, 433: 134606; Ye et al., J. Am. Chem. Soc., 2020, 142: 19001-19005; Wang et al., ACS Catal., 2019, 9: 11335-11340; Ding et al., Chem. 2020, 6: 2673-2689; Wang et al., ACS Catal., 2021, 11: 11742-11753).Using noble metals such as palladium (Pd) and iridium (Ir), highly selective hydrogenation of CO2 to ethanol (>90%) was achieved, but the conversion of CO2 was relatively low (<10%) (Lou et al., Appl. Catal. B., 2021, 291: 120122; Ye et al., J. Am. Chem. Soc., 2020, 142: 19001-19005; Bai et al., J. Am. Chem. Soc., 2017, 138: 6827-6830). Copper (Cu), cobalt (Co), and iron (Fe)-based catalysts have also led to higher carbon dioxide conversion (>30%) but also to unsatisfactory ethanol selectivity (<40%) (Nieskens et al., Catal. Commun., 2011, 14: 111-113; Guo et al., Catal. Lett., 2013, 143: 345-355; Kusama et al., Energy, 1997, 22: 343-348). More recently, Zou et al. (J. Mater. Chem. A, 2023, 11: 10766) demonstrated the effectiveness of monovalent copper-based catalysts in generating compounds containing two or more carbon atoms.In combination with non-thermal plasma catalysis (NTP), an effective tool known to enable CO2 hydrogenation at ambient temperature and pressure, the best-performing catalyst studied, Cu(I)-HKUST-17.5, achieved a CO2 conversion rate of 41.2% and an ethanol selectivity of up to 62.9% under ambient conditions. Potential reaction byproducts that may contribute to lower selectivity include carbon monoxide (CO), methane (CH4), isopropanol, and methanol.

[0010] Although significant progress has been made in the synthesis of ethanol by the hydrogenation of carbon dioxide, the low productivity, poor conversion, challenging reaction conditions, and / or high costs involved in the process hinder practical applications. Therefore, a more efficient strategy for the synthesis of ethanol by carbon dioxide hydrogenation remains a need in the field.

[0011] Summary of the invention

[0012] In order to develop an industrial process for producing ethanol by hydrogenating carbon dioxide, the Inventors conducted simulations of processes using two different catalysts. The efficiency of ethanol production by three processes (referred to as E1, E2, and E3 in the "Examples" section) was demonstrated. These processes yield ethanol purity ranging from 78% to 95% by weight.

[0013] The present invention thus relates to an industrial process for the production of ethanol by hydrogenation of carbon dioxide (CO2), characterized in that the process comprises the following steps:

[0014] (1) a hydrogenation reaction of CO2 with hydrogen (H2) in a reaction reactor to provide a reaction mixture, the hydrogenation reaction being carried out:

[0015] (a) at an initial reaction temperature of between 200°C and 280°C, in particular 240°C, and a reaction pressure of between 20 and 30 bar, in particular 30 bar, in the presence of a palladium- or iridium-based catalyst; or

[0016] (b) at an initial reaction temperature of between 20°C and 80°C, in particular 35°C, and a reaction pressure of between 1 and 10 bars, in particular 1 bar, in the presence of a copper-based catalyst on a metal-organic network;

[0017] (2) cooling of the reaction mixture to obtain a cooled reaction mixture; (3) flash separation of the cooled reaction mixture, the flash separation providing a gaseous phase containing unreacted CO2 and hydrogen (H2) and a liquid phase containing the ethanol produced;

[0018] (4) recycling of the gaseous phase containing unreacted CO2 and hydrogen; and

[0019] (5) a purification of the liquid phase to obtain purified ethanol.

[0020] In some embodiments, the palladium or iridium-based catalyst is Pd2:CeU2.

[0021] In some embodiments, the copper-based catalyst on a metal-organic network is the Cu(I)-HKUST-17.5 catalyst.

[0022] In some embodiments, the industrial process for producing ethanol according to the invention is characterized in that it further comprises, before the hydrogenation reaction, a conditioning step of the initially delivered CO2 and hydrogen to bring the CO2 and hydrogen to the initial reaction temperature and reaction pressure.

[0023] In some embodiments, CO2 is initially delivered at a temperature of 25°C and a pressure of 30 bars and hydrogen is initially delivered at a temperature of 40°C and a pressure of 2 bars.

[0024] In embodiments where the hydrogenation reaction is carried out at an initial reaction temperature of 240°C, and a constant reaction pressure of 30 bar, in the presence of a palladium or iridium-based catalyst: the conditioning of the initially delivered CO2 includes compression, in particular using a train of compressors, and heating to 240°C, in particular using a heat exchanger; and the conditioning of the initially delivered hydrogen includes heating to 240°C, in particular using a heat exchanger.

[0025] In embodiments where the hydrogenation reaction is carried out at an initial reaction temperature of 35°C, and a constant reaction pressure of 1 bar, in the presence of a copper-based catalyst on a metal-organic network, then: the conditioning of the initially delivered CO2 includes cooling to 35°C, in particular using a heat exchanger, and a pressure reduction, in particular using an expansion valve; and the conditioning of the hydrogen includes heating to 35°C, in particular using a heat exchanger, and a pressure reduction, in particular using an expansion valve.

[0026] When the hydrogenation reaction is carried out in the presence of a palladium or iridium-based catalyst, the by-products of the hydrogenation reaction include water, methanol, methane, and carbon monoxide.

[0027] In these embodiments (i.e. hydrogenation in the presence of a palladium or iridium-based catalyst), the industrial process for the production of ethanol can be characterized in that: in step (2), the reaction mixture is cooled to ambient temperature, in particular 20°C, using a heat exchanger; and in step (3), flash separation is carried out using a high-pressure gas-liquid separator.

[0028] In these embodiments, the industrial process for the production of ethanol can be characterized in that in the recycling step (4) the gaseous phase containing unreacted CO2 and hydrogen is recovered and heated to the initial reaction temperature, in particular using a heat exchanger, before being introduced into the reaction reactor.

[0029] Before step (4) of recycling, a portion, including 3% or less, of the gaseous phase containing unreacted CO2 and hydrogen is purged.

[0030] In some embodiments, in step (5) the purification of the liquid phase is carried out using a distillation column which separates the water and ethanol and provides ethanol having a purity of about 92% by weight.

[0031] In embodiments where the hydrogenation reaction is carried out in the presence of a copper-based catalyst on a metal-organic network, the by-products of the hydrogenation reaction include water, methanol, isopropanol, methane and carbon monoxide.

[0032] In these embodiments (i.e. hydrogenation in the presence of a copper-based catalyst on a metal-organic network), the industrial process for the production of ethanol can be characterized in that: in step (2), the reaction mixture is cooled, in particular to 0°C, using a heat exchanger; and in step (3), the flash separation is carried out using a low-pressure gas-liquid separator.

[0033] In these embodiments, in recycling step (4) the gaseous phase containing unreacted CO2 and hydrogen is recovered and heated to the initial reaction temperature, in particular using a heat exchanger, before being introduced into the reaction reactor.

[0034] Before step (4) of recycling, a portion, including 3% or less, of the gaseous phase containing unreacted CO2 and hydrogen is purged.

[0035] In these embodiments, in step (5) the purification of the liquid phase containing the ethanol produced by hydrogenation is carried out using two successive distillation columns, where: the first distillation column separates the water and the alcoholic components; and a second distillation column separates the methanol and the ethanol and provides ethanol having a purity of about 78% by weight.

[0036] In some of these embodiments, in step (5), the purification of the liquid phase is carried out using two distillation columns and one extractive distillation column, where: a first distillation column separates the water and the alcoholic components; an extractive distillation column using ethylene glycol, in particular ethylene glycol at 95% by weight, as the driving agent, this column separating the alcoholic components from a water / ethylene glycol mixture; and a second distillation column separates the methanol and ethanol and provides ethanol having a purity of about 95% by weight.

[0037] In these embodiments, the process further includes a step of recycling ethylene glycol.

[0038] In order to minimize the energy impact of ethanol synthesis from CO2, the present inventors have also modified the ethanol production methods described herein by partially or fully electrifying the industrial process. In particular, they have shown that partial electrification (i.e., affecting only the distillation step) allows for a 20% reduction in the non-electrical heat demand of the process, and that full electrification leads to a complete reduction in the non-electrical heat demand of the process while producing ethanol with a purity of approximately 70% by weight, a purity sufficient for many applications.

[0039] Thus, in certain embodiments of an ethanol production process according to the present invention, in particular an ethanol production process in which the ethanol is purified by column distillation, the process is characterized in that the distillation step of the ethanol produced is electrified, preferably by a system comprising an open-loop heat pump.

[0040] In some embodiments, the system including the open-loop heat pump comprises: a compressor placed at the top of the distillation column; a reboiler placed at the bottom of the distillation column; and two heat exchangers, a first heat exchanger and a second heat exchanger, placed between the high-pressure gas-liquid separator and the distillation column.

[0041] In some embodiments: the flow from the top of the distillation column is compressed by the compressor and the thermal energy of the compressed flow is used to power the reboiler and to heat the liquid phase containing the ethanol produced obtained in step (3) at the second heat exchanger before the heated liquid phase containing the ethanol produced enters the distillation column; the thermal energy of the water flow exiting the reboiler is used to preheat the liquid phase containing the ethanol produced at the first heat exchanger before the preheated liquid phase containing the ethanol produced is directed to the second heat exchanger.

[0042] In some of these embodiments, the non-electrical heat demand of the process is 20% lower than the non-electrical heat demand of the process without the open-loop heat pump system. The ethanol produced has a purity of approximately 70% by weight or higher.

[0043] In some embodiments, the ethanol production process according to the present invention is fully electrified. In some embodiments, the total electrification of the process includes: electrification of the ethanol production distillation step by a system comprising an open-loop heat pump (as described above); thermal integration of the conditioning of the initially delivered CO2 and hydrogen to provide a mixture of conditioned CO2 and H2; and placement of an electric heater between the inlet of the conditioned CO2 and H2 mixture and the reaction reactor, where the electric heater provides the energy input not supplied by thermal integration.

[0044] In some of these embodiments, the non-electrical heat demand of the process is zero. The ethanol produced has a purity of approximately 70% by weight or more.

[0045] A more detailed description of some preferred embodiments of the invention is given below.

[0046] Brief Description of the Figures

[0047] Figure 1: Process El: Scheme of ethanol production by hydrogenation of CO2 in the presence of a palladium (Pd) or iridium (Ir) based catalyst, in particular the Pd2:CeU2 catalyst.

[0048] Figure 2: Process E2: Schematic of ethanol production by hydrogenation of CO2 in the presence of the Cu(I)-HKUST-17.5 catalyst to obtain a pure ethanol of approximately 78% by weight.

[0049] Figure 3: Process E3: Schematic of ethanol production by hydrogenation of CO2 in the presence of the Cu(I)-HKUST-17.5 catalyst to obtain a pure ethanol of approximately 95% by weight.

[0050] Figure 4: Separation (purification) units for process E2 (left) and for process E3 (right).

[0051] Figure 5: Diagram of ethanol production (70% w / w) with the distillation part of the process electrified (without heat integration).

[0052] Figure 6: Diagram of fully electrified ethanol (70% w / w) production with total heat integration.

[0053] Figure 7: Energy demand for ethanol production for three configurations: a non-electrified ethanol production process (70% w / w), an ethanol production process (70% w / w) with the distillation part of the process electrified (without heat integration), and a fully electrified 70% w / w production process with total heat integration.

[0054] Detailed Description

[0055] As mentioned above, the present invention relates to a method for synthesizing ethanol, and more particularly to an industrial process for producing ethanol. The terms “industrial process for producing ethanol,” “industrial method for producing ethanol,” and “industrial synthesis of ethanol” are used interchangeably herein. They refer to a method or process of a chemical nature for producing ethanol in large quantities and under technically and economically acceptable conditions. For example, such a method can enable the production of a quantity of ethanol ranging from 1 kt / year to 1000 kt / year or more for a production unit, for example, approximately 100 kt / year, approximately 200 kt / year, approximately 300 kt / year, approximately 400 kt / year, approximately 500 kt / year, approximately 600 kt / year, approximately 700 kt / year, approximately 800 kt / year, approximately 900 kt / year or more for a production unit.An industrial method for producing ethanol according to the present invention is preferably implemented in a suitable plant. In what follows, the term “industrial” is very often omitted.

[0056] 1 - Production of Ethanol by Catalytic Hydrogenation of Carbon Dioxide

[0057] A method for producing ethanol according to the present invention is based on the catalytic hydrogenation of carbon dioxide. The term “hydrogenation,” as used here, has its meaning known in the art and designates a chemical reaction that consists of the addition of a molecule of dihydrogen (H2) to another compound. Hydrogenation generally requires catalysis, as uncatalyzed hydrogenation reactions require very high temperatures. Thus, the term “catalytic hydrogenation,” as used here, designates hydrogenation carried out in the presence of a catalyst.

[0058] 1. Catalytic Hydrogenation of Carbon Dioxide

[0059] In the context of the present invention, the hydrogenation of carbon dioxide to produce ethanol is carried out according to the following reaction:

[0060] 2 CO2 + 6 H2C2H5OH + 3 H2O in the presence of a catalyst. a. Carbon Dioxide

[0061] As used here, the term “carbon dioxide” refers to the molecule with the formula CO2, also called carbonic gas or carbonic anhydride, which appears as a colorless and odorless gas under normal / ambient temperature and pressure conditions.

[0062] The carbon dioxide that can be used in the context of the present invention may have been generated by any process. For example, the CO2 used in a method according to the present invention may have been generated by an industrial process (such as during electricity production, steel or cement production, textile, chemical, or petrochemical industry processes, etc.). Carbon dioxide can be captured from these stationary sources (factories or power plants). Several methods of CO2 capture in industry are known:

[0063] (1) Post-combustion capture, which consists of recovering CO2 by scrubbing the flue gases emitted by combustion with a solvent. This technique is the best known and most widely used.

[0064] (2) Pre-combustion carbon capture involves decarbonizing the fuel before combustion by transforming it into a synthesis gas composed of hydrogen (H2), water, and carbon monoxide. Steam is then introduced into this synthesis gas to produce CO2 and hydrogen (H2), which can be separated using a solvent. This technology is currently considered too expensive.

[0065] (3) Oxy-combustion capture involves burning carbonaceous fuels in the presence of pure oxygen instead of air, thus producing flue gases with a higher CO2 concentration. The main problem with this technology is the cost of producing pure oxygen, which is generally obtained by cryogenic distillation of air.

[0066] Alternatively, the CO2 used in a method according to the present invention may have been captured directly from the atmosphere. Carbon dioxide can be extracted from the atmosphere either by a liquid solvent or by a solid absorbent, from which it is then released by heating. There are currently 19 direct air CO2 capture facilities in operation worldwide, with a limited capacity of 9,000 tonnes of CO2 per year.

[0067] In general, the use of CO2 in a method according to the present invention makes it possible to reduce its presence in the atmosphere. b. Hydrogen

[0068] As used here, the term “hydrogen” refers to dihydrogen, H2, which is the molecular form of the element hydrogen and exists as a gas under normal / ambient temperature and pressure conditions. Hydrogen does not have a direct greenhouse effect but is an indirect climate gas that induces perturbations of methane, ozone, and water vapor in the atmosphere—three potent greenhouse gases.

[0069] The hydrogen (H2) that can be used in the context of the present invention can be produced by any method known in the art. For example, hydrogen can be produced by steam reforming of natural gas (mainly methane) with carbon sequestration (so-called "blue" hydrogen) or without carbon sequestration (so-called "gray" hydrogen), or by electrolysis of water powered by renewable energy (so-called "green" hydrogen). The hydrogen can also be low-carbon hydrogen produced from nuclear sources. c. Palladium- or iridium-based catalyst

[0070] The production of ethanol by CO2 hydrogenation according to the invention is carried out in the presence of a palladium- or iridium-based catalyst. As used here, the term “catalyst” has its meaning known in the art and designates a compound that accelerates a chemical reaction or causes it to occur.

[0071] In some embodiments, the catalyst used in a hydrogenation method according to the present invention is a palladium (Pd) or iridium (Ir) based hydrogenation catalyst. Any palladium or iridium based hydrogenation catalyst, and in particular any palladium or iridium based carbon dioxide hydrogenation catalyst, may be used in the context of the present invention. In some parts of this document, the term “Pd-Ir catalyst” is used. This term refers to a palladium or iridium based CO2 hydrogenation catalyst.

[0072] In some embodiments, the palladium-based catalyst is a palladium / cerium dioxide catalyst of formula Pd2:CeU2. This catalyst was described by Lou et al. (Appl. Catal. B., 2021, 291: 120122) as providing the best results for ethanol production by carbon dioxide hydrogenation with an ethanol selectivity of 99.2% and a CO2 conversion of 9.2%, with almost no by-products. In other embodiments, the palladium-based catalyst is in the form of highly ordered palladium and copper nanoparticles of formula Pd2Cu Ns / P25, which were described by Bai et al. (J. Am. Chem. Soc., 2017, 139: 6827-6830) as enabling optimized ethanol production efficiency by carbon dioxide hydrogenation and as exhibiting ethanol selectivity of up to 92.0%.

[0073] In other embodiments, the iridium-based catalyst is In-ImCl, which incorporates two active catalytic centers by anchoring monatomic iridium (In) to the indium(III) oxide (ImO) support. This catalyst was described by Ye et al. (J. Am. Chem. Soc., 2020, 142: 19001-19005) as efficient for the hydrogenation of CO2, offering high ethanol selectivity of over 99%.

[0074] In some preferred embodiments, the catalyst used in the production of ethanol by hydrogenation of carbon dioxide is Pd2:CeU2. d. Copper-based catalyst on a metal-organic lattice

[0075] In some embodiments, the catalyst used in a method for producing ethanol by hydrogenating carbon dioxide according to the present invention is a copper-based catalyst on a metal-organic framework. As used here, the term “metal-organic framework” (MOF) refers to a crystalline hybrid porous solid composed of metal ions or clusters coordinated to organic ligands to form one-, two-, or three-dimensional structures. Metal-organic frameworks exhibit, in particular, a very high specific surface area due to their nanoporous structure. Copper-based catalysts on a metal-organic network are known in the art and have found many applications (Aquilla-Rosas et al., Chem. Commun. (Camb), 2023, 59(79): 11753- 11766; Ha Huu Do et al., Beilstein J. Nanotechnol., 2023, 14: 904-911; Sun et al., J. Inorg. Biochem., 2021, 225: 11599).

[0076] In some embodiments, the copper-based catalyst on a metal-organic network is Cu(I)-HKUST17.5. The terms “Cu(I)-HKUST17.5” and “Cu(I)-HKUST-17.5” are used interchangeably here. They refer to a copper(I) catalyst based on HKUST-1, a metal-organic network. Cu(I)-HKUST-17.5 is described in Zou et al., J. Mater. Chem. A, 2023, 11: 10766. HKUST-1 (also called MOF-199 or Cu-BTC) is a well-known coordination porous polymer (CPP) that has been extensively studied as a heterogeneous catalyst. HKUST-1 has the formula Cu3(BTC)2(H2O)s, where BTC is 1,3,5-benzene tricarboxylate. It is constructed with Cu(II) cations that are coordinated to carboxylate ligands and water. HKUST-1 can be synthesized by any method known in the art. For example, HKUST-1 can be synthesized by applying a classical hydrothermal method previously described (Chui et al., Science, 1999, 283: 1148-1150) and used by Zou et al. (J.(Mater. Chem. A, 2023, 11: 10766). Thus, in such a method and on a laboratory scale, BTC (5 mmol) is dissolved in a mixed solution containing anhydrous ethanol (15 mL) and N,N-dimethylformamide (DMF) (15 mL). Copper nitrate hydrate (9 mmol) is dissolved in deionized water (15 mL), and the mixture is added to the above solution. The entire mixture is then transferred to a 100 mL Teflon autoclave maintained at 100°C for 12 hours. After cooling to room temperature, the resulting blue crystals are filtered and then treated with DMF and ethanol for 24 hours to remove any unreacted chemicals. The resulting solids are dried at 80°C to obtain the expected HKUST-1. A person skilled in the art is able to adapt this method for the synthesis of larger quantities of HKUST-1.Alternatively, KHUST-1 is available for sale, for example, from CD Bioparticles (Shirley, NY, USA), NovoMOF (Zofingen, Switzerland), Sigma-Aldrich (St. Louis, MI, USA, sold as Basolite C300 and produced by BASF) and ASC Material (Los Angeles, CA, USA, sold as Cu-BTC).

[0077] The Cu(I)-HKUST-17.5 catalyst can be synthesized by any suitable method known in the art, such as the method described in Zou et al., J. Mater. Chem. A, 2023, 11: 10766 and Qi et al., Angew. Chem., Int. Ed., 2019, 58: 10104-10109. In this method, 0.15 g of HKUST-1 is transferred into a quartz vessel inside a Teflon-lined stainless steel autoclave (100 mL capacity) containing 20 mL of ethanol in the bottom to prevent contact between the solid and the ethanol. The autoclave is heated to 200°C and maintained at this temperature for a predetermined time. Next, the autoclave is rapidly cooled to room temperature, and the powder is transferred to a container and evacuated to remove residual ethanol. The resulting samples are designated Cu(I)-HKUST-n, where n is the autoclave processing time, which can range from 0 to 27.5 hours. Therefore, Cu(I)-HKUST-17.The 5 used in the context of the ethanol production method described here is obtained by using a treatment at 200°C for 17.5 hours. Those skilled in the art can adapt this method to produce larger quantities of Cu(I)-HKUST-17.5.

[0078] 2. Ethanol Production Reaction by Catalytic Hydrogenation of Carbon Dioxide

[0079] The main reaction for the production of ethanol by catalytic hydrogenation of carbon dioxide is as follows:

[0080] 2 CO2 + 6 H2C2H5OH + 3 H2O.

[0081] This main reaction is accompanied by secondary reactions in the case of both types of catalysts (palladium- or iridium-based catalyst and copper-based catalyst on a metal-organic network). These common secondary reactions are: which produce carbon monoxide (CO), methanol (CH3OH), water (H2O) and methane (CH4) as by-products.

[0082] When the hydrogenation catalyst is Cu(l)-HKUST-17.5, an additional side reaction is present:

[0083] 3 CO2 + 9 H2C(CH3)2OH + 5 H2O which produces isopropanol (C(CH3)2OH) and water as byproducts. a. Gaseous Reactants

[0084] The ethanol production reaction by catalytic hydrogenation of carbon dioxide according to a method of the invention is carried out in stoichiometric proportions. Those skilled in the art know that stoichiometric proportions are achieved when the initial amounts of reactants are in proportion to their number or stoichiometric coefficient. The ethanol production reaction according to the present invention is therefore carried out starting from the following stoichiometric proportions: 2 moles of CO2 to 6 moles of hydrogen (H2) (according to the main reaction described above).

[0085] Depending on the desired quantities of ethanol, a person skilled in the art can determine the initial quantities of CO2 and H2 to be used. In a method according to the invention, hydrogen (H2) and carbon dioxide are initially delivered at any suitable temperature and pressure. For example, in some embodiments, hydrogen is initially delivered at a temperature of 25°C and a pressure of 30 bar, while carbon dioxide is initially delivered at a temperature of 40°C and a pressure of 2 bar. b. Catalyst

[0086] In the catalytic hydrogenation of carbon dioxide for the production of ethanol according to the invention, the catalyst (whether a palladium- or iridium-based catalyst, or a copper-based catalyst on a metal-organic network) is present in a catalytic amount or an amount greater than a catalytic amount. The term “catalytic amount,” as used here, has its meaning known in the art and designates an amount sufficient to permit catalysis, that is, to allow a significant acceleration of a reaction. A person skilled in the art can determine, through routine experiments, a catalytic amount as a function of the reaction and the catalyst used. c. Reaction

[0087] In general, the present invention relates to an industrial process for the production of ethanol by hydrogenation of carbon dioxide, characterized in that the industrial process comprises:

[0088] (1) a hydrogenation reaction of CO2 with hydrogen (H2) in a reaction reactor to provide a reaction mixture, the hydrogenation reaction being carried out;

[0089] (a) at an initial reaction temperature of between 200°C and 280°C, in particular 240°C, and a reaction pressure of between 20 and 40 bar, in particular 30 bar, in the presence of a palladium- or iridium-based catalyst; or

[0090] (b) at an initial reaction temperature of between 20°C and 80°C, in particular 35°C, and a reaction pressure of between 1 and 10 bars, in particular 1 bar, in the presence of a copper-based catalyst on a metal-organic network.

[0091] (2) a cooling of the reaction mixture;

[0092] (3) flash separation of the cooled reaction mixture, which provides a gaseous phase containing unreacted CO2 and hydrogen (H2) and a liquid phase containing the ethanol produced; (4) recycling of the gaseous phase containing unreacted CO2 and hydrogen (H2); and

[0093] (5) a purification of the liquid phase to obtain purified ethanol.

[0094] Differences in conditions and catalysts result in reaction mixtures containing different by-products in varying quantities, necessitating the development of different separation or purification methods. The characteristics of these various methods are described below.

[0095] II - Production of Ethanol by Hydrogenation of CO2 in the Presence of a Palladium or Iridium-Based Catalyst

[0096] The production of ethanol by catalytic hydrogenation of carbon dioxide according to the present invention can be divided into two stages: the ethanol production reaction and the purification of the ethanol produced.

[0097] 1. Ethanol Production Reaction by Hydrogenation of CO2 in the Presence of a Palladium or Iridium-Based Catalyst

[0098] The ethanol production reaction includes conditioning each of the two initially supplied gases (CO2 and H2) to bring them to the initial reaction temperature and pressure; and the reaction of the two gases in the presence of the catalyst. a. Conditioning of CO2 and H2

[0099] In the method according to the invention, carried out in the presence of a palladium or iridium-based catalyst, the reaction of the two gases takes place at an initial reaction temperature between 200°C and 280°C, in particular 240°C, and a reaction pressure between 20 and 40 bar, in particular 30 bar. Before being introduced into the reactor where the hydrogenation reaction is to take place, each of the two initially delivered gases must be conditioned to reach these initial reaction temperature and reaction pressure conditions. As used herein, the term “initially delivered CO2 or H2” refers to the CO2 or H2 that is brought to the plant and introduced into the ethanol production facility before these two gases are brought into contact. The conditioning of each of the two gases takes place in the ethanol production facility and can be carried out using any suitable method known in art.For example, when the initial reaction temperature is 240°C and the reaction pressure is 30 bar, hydrogen (H2), which is initially delivered at a temperature of 25°C and a pressure of 30 bar, is conditioned by heating in a heat exchanger to a temperature of 240°C; and carbon dioxide, which is initially delivered at a temperature of 40°C and a pressure of 2 bar, is conditioned by compression to 30 bar using a train of compressors (for example, two successive compressors), then by heating in a heat exchanger to a temperature of 240°C. b. Reaction of CO2 and H2.

[0100] Conditioned CO2 and H2 gases are mixed and then introduced into the reaction reactor. In the presence of a palladium or iridium-based catalyst, the hydrogenation reaction takes place at an initial reaction temperature between 200°C and 280°C, for example, approximately 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, or approximately 280°C, particularly 240°C. As used here, the term "initial reaction temperature" refers to the initial temperature of the hydrogenation reaction. Depending on the type of reactor (adiabatic or isothermal), the temperature within the reactor may change during the reaction. In the presence of a palladium or iridium-based catalyst, the hydrogenation reaction takes place at a reaction pressure between 20 and 40 bars, for example about 20 bars, about 25 bars, about 30 bars, about 35 bars, about 40 bars, especially 30 bars.

[0101] The reaction mixture obtained by the catalytic hydrogenation reaction in the presence of a palladium-based catalyst (Pd2:CeU2) contains ethanol (CH3CH2OH), carbon monoxide (CO), methanol (CH3OH), methane (CH4) and water (H2O), as well as unreacted carbon dioxide and hydrogen (H2).

[0102] This reaction mixture is cooled to ambient temperature, for example using a heat exchanger. In some embodiments, the ambient temperature to which the reaction mixture is cooled is 20°C.

[0103] The cooled reaction mixture is then conveyed to a high-pressure gas-liquid separator. A high-pressure gas-liquid separator is typically used to rapidly vaporize a high-pressure fluid stream containing vapor / gas and condensate (a process known as flash separation). A high-pressure gas-liquid separator generally consists of a high-pressure inlet, an inner chamber, an upper vapor or gas discharge port, and a lower condensate or liquid discharge port. A high-pressure gas-liquid separator efficiently and safely reduces the pressure in the fluid stream, thereby enabling the recovery of produced vapors / gases and the collection of chemicals from the condensate stream.In the context of the present invention, thanks to the high-pressure gas-liquid separator, a portion of the unreacted gases (CO2 and H2) is recovered and recycled, another portion is purged, and the recovered liquid phase containing ethanol is sent to the purification unit. c. Recycling of CO2 and H2.

[0104] The gas stream from the high-pressure gas-liquid separator (containing unreacted carbon dioxide and hydrogen (H2), as well as impurities such as CH4 and CO) is recovered and heated to the initial reaction temperature using a heat exchanger before being recycled, i.e., introduced into the reactor where ethanol production takes place. In some embodiments, a compressor is present in the recycling loop (before the introduction of this gas stream into the reactor) to increase the pressure of the gas stream to the reaction pressure.

[0105] To prevent the accumulation of potential inert contaminants (such as CH4 and CO) in the recirculation loop, a percentage of the gas stream from the high-pressure gas-liquid separator is purged. For example, 3%, or less than 3% (e.g., 2.5%, 2%, 1.5%, 1%, or less than 1%), of the gas stream may be purged.

[0106] 2. Purification of the Ethanol Product

[0107] The liquid phase recovered from the outlet of the high-pressure gas-liquid separator, containing the produced ethanol and water, is sent to the purification unit. In the context of this method of the invention, the purification unit consists of a distillation column. This distillation column separates the water from the ethanol and produces three streams in total: two liquid streams (water at the bottom and ethanol at the top) and a vapor stream containing CO2 released by the expansion of the liquid (which does not need to be recycled given the minimal quantities of CO2). A person skilled in the art can select a distillation column capable of achieving this goal. Table 2 in the "Examples" section below provides the possible characteristics of such a distillation column.

[0108] As shown in the Examples, with a selectivity for ethanol of 99.2% and a carbon dioxide conversion of 9.2%, this method of producing ethanol by hydrogenation of CO2 in the presence of a palladium or iridium-based catalyst (in particular in the presence of the Pd2:CeU2 catalyst) makes it possible to obtain ethanol that is 92.05% pure (by weight in water).

[0109] III - Production of Ethanol by Hydrogenation of Carbon Dioxide in the Presence of a Copper-Based Catalyst on a Metallo-Organic Network

[0110] The production of ethanol by catalytic hydrogenation of carbon dioxide in the presence of a copper-based catalyst on a metal-organic network according to the present invention can be divided into two stages: the ethanol production reaction and the purification of the ethanol produced.

[0111] 1. Ethanol Production Reaction by CO2 Hydrogenation in the Presence of a Copper-Based Catalyst on a Metallo-Organic Lattice

[0112] The ethanol production reaction includes conditioning each of the two gases (CO2 and H2) to the initial reaction temperature and reaction pressure; and reacting the two gases in the presence of the catalyst in a reaction reactor at an initial reaction temperature between 20°C and 80°C, in particular 35°C, and a reaction pressure between 1 and 10 bar, in particular 1 bar. a. Conditioning of CO2 and H2

[0113] Before being introduced into the reaction reactor, each of the two gases must be conditioned to achieve the initial reaction temperature and reaction pressure conditions. The conditioning of each of the two gases can be carried out using any suitable method known in art.

[0114] For example, when the hydrogenation reaction is carried out at an initial reaction temperature of 35°C and a reaction pressure of 1 bar, the hydrogen (H2), which is initially supplied at a temperature of 25°C and a pressure of 30 bar, is conditioned by heating in a heat exchanger to 35°C and subjected to an expansion valve, which reduces its pressure to 1 bar; and the carbon dioxide, which is initially supplied at a temperature of 40°C and a pressure of 2 bar, is conditioned by a heat exchanger to 35°C. b. Reaction of CO2 and H2

[0115] Conditioned CO2 and H2 gases are mixed and then introduced into the reaction reactor. In the presence of a copper-based catalyst on a metallo-organic network, the hydrogenation reaction takes place at an initial reaction temperature between 20°C and 80°C, for example approximately 20°C, approximately 25°C, approximately 30°C, approximately 35°C, approximately 40°C, approximately 45°C, approximately 50°C, approximately 55°C, approximately 60°C, approximately 65°C, approximately 70°C, approximately 75°C, or approximately 80°C, in particular 35°C, and a reaction pressure between 1 and 10 bars, for example approximately 1 bar, approximately 2 bars, approximately 3 bars, approximately 4 bars, approximately 5 bars, approximately 6 bars, approximately 7 bars, approximately 8 bars, approximately 9 bars, or approximately 10 bars, in particular 1 bar.

[0116] The reaction mixture obtained by the catalytic hydrogenation reaction in the presence of a copper-based catalyst on a metal-organic network contains ethanol (CH3CH2OH), carbon monoxide (CO), methanol (CH3OH), methane (CH4), water (H2O), isopropanol (C(CH3)2OH), as well as unreacted carbon dioxide and hydrogen (H2).

[0117] This reaction mixture is cooled to a low temperature, in particular 0°C, for example using a heat exchanger.

[0118] The cooled reaction mixture is then conveyed to a low-pressure gas-liquid separator. A low-pressure gas-liquid separator is identical to a high-pressure gas-liquid separator except that it operates at low pressure. In the context of the present invention, thanks to the low-pressure gas-liquid separator, some of the unreacted gases (CO2 and H2) are recycled, some are purged, and the recovered liquid phase containing ethanol is sent to the purification unit. c. CO2 and H2 Recycling

[0119] The gas stream from the low-pressure gas-liquid separator (containing unreacted carbon dioxide and hydrogen (H2) and impurities such as CH4 and CO) is separated and heated to the initial reaction temperature of between 20°C and 40°C, specifically 35°C, using a heat exchanger before being recycled, i.e., reintroduced into the reaction reactor where ethanol production takes place. In some embodiments, a compressor may be present in the recycling loop (before the introduction of this gas stream into the reactor).

[0120] To prevent the accumulation of potential inert contaminants (such as CH4 and CO) in the recycling loop, a percentage of the gas stream from the low-pressure gas-liquid separator is purged. For example, 3%, or less than 3% (e.g., 2.5%, 2%, 1.5%, 1%, or less than 1%), of the gas stream may be purged. d. Liquid Stream Recovery and Ethanol Purification

[0121] The liquid phase recovered at the outlet of the low pressure gas-liquid separator, which contains the ethanol produced, water, methanol and isopropanol, is cooled, notably to 30°C, using a heat exchanger and sent to the purification unit.

[0122] Due to lower ethanol selectivity (62.9%) in the presence of a copper-based catalyst on a metal-organic network such as Cu(I)-HKUST-17.5 compared to a palladium- or iridium-based catalyst such as Pd2:CeU2, and therefore a greater quantity of by-products (or impurities), a more complex separation process is required. Two purification processes are described here: the first (process E2) yields ethanol with a purity of 78% by weight, and the second (process E3) yields ethanol with a purity of 95% by weight.

[0123] 2. First Process for Purifying the Ethanol Produced

[0124] In this process, the purification unit consists of two distillation columns.

[0125] The first distillation column separates water from the alcoholic components (ethanol, methanol, isopropanol) and produces three streams in total: two liquid streams (water at the bottom and alcoholic compounds at the top) and a gaseous stream containing impurities. This first distillation column operates at 1 bar with negligible pressure loss. The second distillation column separates ethanol from methanol and produces two streams in total: a liquid stream (ethanol with a very low concentration of isopropanol) exiting the column at the bottom and a methanol vapor stream exiting the column at the top. This second column also operates at 1 bar with negligible pressure loss. Those skilled in the art can select distillation columns to achieve this goal. Table 5 in the "Examples" section provides the possible characteristics of such distillation columns.

[0126] As the Examples show, with a selectivity for ethanol of 62.9% and a CO2 conversion of 41.2%, this method of producing ethanol by hydrogenation of carbon dioxide in the presence of Cu(I)-KHUST-17.5 including the separation process described makes it possible to obtain ethanol pure at 78% (by weight in water).

[0127] 3. Second Process for Purifying the Ethanol Produced

[0128] In this process, the purification unit consists of three distillation columns and one extractive distillation column, each of the columns operating at 1 bar.

[0129] The first column is identical to the first distillation column of process E2. It allows the separation of water and alcoholic components (ethanol, methanol, isopropanol) and produces three streams in total: two liquid streams (water at the bottom and alcoholic compounds at the top) and one gaseous stream containing impurities.

[0130] The second column is an extractive distillation column. As used here, the term “extractive distillation” has its meaning known in the art and refers to a distillation process used to separate azeotropic mixtures or mixtures containing compounds with similar boiling points—these two types of mixtures cannot be separated by conventional distillation. Extractive distillation uses an additive, called a driving agent, which increases the volatility of one of the components or strongly alters the activity coefficients of the substances to be separated in different directions. In the context of the present invention, the second column is an extractive distillation column using an ethylene glycol stream, in particular a 95% by weight ethylene glycol stream, as the driving agent.Ethylene glycol drives water down the extractive distillation column while the alcoholic components exit from the top of this column.

[0131] The alcoholic components exiting the extractive distillation column at the top are conveyed to the second distillation column, which separates the ethanol and methanol. This column produces two streams: a liquid stream (ethanol with a very low concentration of isopropanol) exiting the column at the bottom, and a methanol vapor stream exiting the column at the top.

[0132] Ethylene glycol can be recycled. In this recycling step, the ethylene glycol and water mixture exiting the extractive distillation column at the bottom is fed into the third distillation column, which separates the ethylene glycol from the water. The recovered ethylene glycol is cooled to 30°C in a heat exchanger. After the possible addition of more water and ethylene glycol to the cooled ethylene glycol, the resulting solvent is fed back into the extractive distillation column. This addition ensures a solvent with a composition identical, or substantially identical, to the composition of the initial entrainment solvent (e.g., ethylene glycol at 95% by weight).

[0133] A person skilled in the art can select distillation and extractive distillation columns to achieve the goals described above. Table 5 in the "Examples" section provides the possible characteristics of such columns.

[0134] As the Examples show, with an ethanol selectivity of 62.9% and a CO2 conversion of 41.2%, this method of producing ethanol by hydrogenation of carbon dioxide in the presence of Cu(I)-KHUST-17.5 including the purification process (E3) described makes it possible to obtain 95% pure ethanol (by weight in water).

[0135] IV - Minimizing the Energy and Environmental Impact of Ethanol Production by Carbon Dioxide Hydrogenation in the Presence of a Catalyst

[0136] The present inventors have shown that a process for producing ethanol by hydrogenating carbon dioxide in the presence of a catalyst can be modified to reduce its energy and environmental impact. This improvement was designed by the inventors with the aim of producing ethanol with a purity of approximately 70% by weight, a purity sufficient for certain ethanol applications (see Example 2 below). However, it is possible to design such an improvement with the aim of obtaining ethanol with a purity exceeding 70% by weight (for example, 90% or 95% by weight).

[0137] In particular, the present inventors have shown that electrifying the distillation portion of the production process reduces non-electrical heat demand by 20%. Combining electrification of the distillation portion of the ethanol production process with thermal integration resulted in a complete reduction of the process's non-electrical heat demand.

[0138] Thus, in certain embodiments of an ethanol production method according to the invention, the industrial process is partially or totally electrified. Partial electrification of the industrial process relates to the purification step of the ethanol produced, and more specifically, the distillation step. Total electrification relates to the entire ethanol production process, including the distillation step.

[0139] As used here, the term “electrification of an industrial process” refers to the conversion of a process dependent on non-electrical energy sources (particularly fossil fuels such as natural gas) into an electrically powered solution. Preferably, electrification techniques rely on low-carbon electricity. The term “low-carbon electricity” refers to electricity produced from non-fossil primary energy sources, that is, electricity from renewable or nuclear sources (which therefore has the advantage of emitting little or no carbon dioxide).

[0140] 1. Electrification of the Distillation Section of the Ethanol Production Process

[0141] The electrification of the distillation section of a CO2 hydrogenation ethanol production process according to the present invention can be carried out by any method known to those skilled in the art. All the ethanol production processes described herein [i.e., Process E1 (Figure 1, palladium (Pd) or iridium (Ir) based catalyst, in particular Pd2:CeU2), Process E2 (Figure 2, Cu(I)-HKUST-17.5 catalyst for obtaining approximately 78% pure ethanol by weight), and Process E3 (Figure 3, Cu(I)-HKUST-17.5 catalyst for obtaining approximately 95% pure ethanol by weight)] can be electrified. In some preferred embodiments, the ethanol production process is Process E1

[0142] In some embodiments, the electrification of the distillation stage of the ethanol production process is achieved using a system comprising an open-loop heat pump. As used here, the term “heat pump” refers to any thermomechanical heat transfer system that uses a compressible fluid to transfer thermal energy from one or more heat sources to one or more heat sinks. A heat pump is referred to as open-loop when this compressible fluid includes one or more process fluids, typically originating from a column. A heat pump is referred to as closed-loop when the compressible fluid includes one or more heat transfer fluids circulating independently of the column.

[0143] In general, the open-loop heat pump system used in an ethanol production process according to the present invention recovers heat from a condenser located at the top of the distillation column and increases its temperature in order to supply it to the reboiler of the distillation column.

[0144] Thus, in certain embodiments, the system comprising the open-loop heat pump used in the distillation step of an ethanol production process according to the present invention (in particular in the distillation step of Process El) comprises: a compressor placed at the top of the distillation column; a reboiler placed at the bottom of the distillation column; and two heat exchangers, a first heat exchanger and a second heat exchanger, placed between the high-pressure gas-liquid separator and the distillation column.

[0145] In the open-loop heat pump system, the compressor recovers the overhead flow from the distillation column and compresses it to a higher pressure. In some embodiments, the pressure increase due to compression is between 0.5 and 4 bar, for example, between 1 and 2 bar. In some embodiments, the compressed overhead flow from the distillation column increases from a pressure of 1 bar to a pressure of 2.3 bar per compression.

[0146] The thermal energy of the compressed stream is recovered to power the reboiler and thus provide the heat required by the distillation column. As used here, the term “reboiler” has its well-known meaning in the field and refers to a device whose purpose is to partially vaporize the bottom of the distillation column in order to generate the vapor phase that will perform the fractionation in the exhaust section of the distillation column. A reboiler is a type of heat exchanger that supplies heat to the bottom of a distillation column.

[0147] The thermal energy of the compressed flow is also used to heat the feed (i.e., the liquid phase containing the ethanol produced in step (3) of the process) entering the distillation column at the second heat exchanger of the system comprising the open-loop heat pump.

[0148] The heat from the water stream (~99°C) exiting the reboiler is used to preheat the load at the first heat exchanger before it is directed to the second heat exchanger.

[0149] Table 11 in the Examples presents a comparison of the energy demands before and after electrification of the distillation stage of the CO2 hydrogenation ethanol production process according to the invention.

[0150] 2. Total Electrification of the Ethanol Production Process

[0151] The complete electrification of the industrial ethanol production process according to the present invention consists of electrifying the distillation step of the process as described above and electrifying the remaining steps of the process. This latter electrification can be carried out by any method known to those skilled in the art. For example, it can include the application of thermal integration, that is, a process of optimizing energy consumption within a system by reusing the heat generated by one part of the process to improve another. Thermal integration aims to save energy, reduce costs, and decrease environmental impact through efficient heat management within industrial processes. Electrification can be supplemented by the addition of electric heating to meet any residual thermal requirements not addressed by thermal integration.

[0152] Thus, in certain embodiments, the complete electrification of the ethanol production process includes optimizing a network of heat exchangers at the reaction reactor where the hydrogenation of CO2 with hydrogen (H2) takes place. Preferably, the optimization of the heat exchanger network is carried out using the pinch method. As used here, the term “pinch method” (Pinch Technology) has its well-established meaning in the art and designates an integration method that optimizes both thermodynamically and economically the energy recovery possibilities (waste heat) of any type of industrial process by incorporating heat recovery elements (exchangers and / or heat pumps).In certain embodiments, the complete electrification of the industrial ethanol production process according to the present invention comprises: (1) electrification of the distillation step of the ethanol production process using a system comprising an open-loop heat pump, and (2) thermal integration of the conditioning of the initially delivered CO2 and hydrogen, and the addition of an electric heater upstream of the reaction reactor to provide the energy input not supplied by thermal integration. The thermal integration of the CO2 and H2 conditioning and the addition of the electric heater lead to optimized conditioning of the CO2 and hydrogen (H2) before they enter the reaction reactor.

[0153] In some embodiments: a first heat exchanger is placed between the two CO2 compression stages so as to recover the heat of compression to preheat the incoming hydrogen; an electric heater is placed between the incoming preheated carbon dioxide and hydrogen and the reaction reactor, where the electric heater provides the additional energy not supplied by thermal integration; and a second heat exchanger is placed between the conditioned CO2 and H2 mixture and the electric heater so as to heat the CO2 and H2 mixture to the maximum using the heat available in the system.

[0154] Table 12 in Examples and Figure 7 present a comparison of the energy demands before and after electrification of the distillation stage of the CO2 hydrogenation ethanol production process according to the invention and after thermal integration and total electrification.

[0155] Unless otherwise defined, all technical and scientific terms used in the Description have the same meaning as that commonly understood by an ordinary specialist in the field to which this invention belongs. Likewise, all publications, patent applications, patents, and other references mentioned herein are incorporated by reference. Examples

[0156] The following examples describe certain embodiments of the present invention. However, it is understood that the examples and figures are presented for illustrative purposes only and do not in any way limit the scope of the invention.

[0157] Simulations were performed using commercial process analysis and synthesis software. The processes described here were designed to produce approximately 100 kt / year of ethanol in a plant operating 8000 hours per year.

[0158] Example 1

[0159] 1 - Production of Ethanol by Hydrogenation of Carbon Dioxide

[0160] Two catalysts were studied for the production of ethanol by CO2 hydrogenation. These two catalysts are a palladium (Pd) or iridium (Ir)-based catalyst (referred to here as Pd-Ir) and Cu(I)-HKUST17.5. Their operating conditions are presented in Table 1 below. One, Cu(I)-HKUST17.5, was reported to lead to lower ethanol purity but exhibits higher conversion than the other, Pd-Ir. To better understand the trade-offs between selectivity and conversion, a process model was developed for each of the two catalysts. The two process models share a common component, which is presented first below. The specific characteristics associated with each process, which mainly concern the purification step, are then described.

[0161] Table 1. Operating conditions; ethanol selectivity and CO2 conversion rate reported for each of the Pd-Ir and Cu-HKUST17.5 catalysts.

[0162] The hydrogenation processes were designed based on the basic scheme presented by He et al. (Journal of CO2 Utilization, 2017, 19: 157-164), regardless of the catalyst. The Soave-Redlich-Kwong (PSRK) predictive properties method was used in the hydrogenation processes to predict the thermodynamic properties of the chemical systems. This method was used in both processes for their entire basic scheme as a first approximation. However, its validity for modeling the separation sections, including the distillation units, will need to be validated in subsequent work.

[0163] The carbon dioxide (CO2) and hydrogen (H2) streams are conditioned to meet reaction conditions before entering the reactor. The stoichiometry, conversion, and selectivity of the process are well established and are specified as such in the reactor model, which does not need to calculate equilibrium conditions. H2 is initially delivered at 30 bar and 25°C, based on the output of a proton exchange membrane electrolyzer for water electrolysis (He et al., Chemical Engineering Research and Design, 2023, 195: 106-115), while CO2 is delivered at 40°C and 2 bar instead of 25°C and 1 bar. Flash separation is used after the reactor to remove unreacted gas. This gas is then recycled back to the reactor inlet, with a purge, to prevent the accumulation of potential inert contaminants.

[0164] After separating the unreacted gas in the first flash separation, further separation units (flash units 2 and 3 and the distillation column) are used to further separate the remaining unreacted gas and to separate the water from the ethanol. The goal is to obtain high-purity ethanol. For subsequent models, the separation process is adjusted: different units are used depending on the catalyst and the desired final ethanol purity. The catalyst significantly influences the selectivity for ethanol and the CO2 conversion, thus affecting the ethanol purity. Depending on the impurities present, the separation units must be adapted. The specific separation processes associated with each model / catalyst are detailed in the following sections dedicated to each catalyst.

[0165] 2 - Catalyst: Pd-Ir

[0166] For the Pd-Ir catalyst, the process scheme (El) used is shown in Figure 1. The hydrogen stream is heated to 240°C in a heat exchanger (HTX3 in Figure 1), while the carbon dioxide stream is compressed to 30 bar using a compressor train (COMP1 and COMP2 in Figure 1) and heated to 240°C. The isothermal reaction reactor (REACT in Figure 1) operates at 240°C and 30 bar, with a CO2 conversion rate of 9.2%. The selectivity for ethanol, carbon monoxide (CO), methanol (CH3OH), and methane (CH4) is 99.2%, 0.2667%, 0.2667%, and 0.2667%, respectively.

[0167] The reaction between CO2 and H2 occurs in stoichiometric proportions: 2 moles of CO2 for every 6 moles of hydrogen (H2). The main and secondary reactions are as follows:

[0168] Main reaction:

[0169] 2 CO2+ 6 H2C2H5OH + 3 H2O AH°™ (298K) = -215.42 kJ / mol

[0170] Side effects:

[0171] CO2 + H2CO + H2O AH 0 ™ (298K) = 41 kJ / mol

[0172] CO2+ 3 H2CH3OH + H2O AH°™ (298K) = -49.5 kJ / mol

[0173] CO2+ 4 H2CH4+ 2 H2O AH°™ (298K) = -165 kJ / mol

[0174] The resulting reaction mixture is cooled to 20°C in the heat exchanger (HTX4 in Figure 1) and directed to the high-pressure gas-liquid separator (SEP LV HP in Figure 1). The gas stream (Gas in Figure 1) from the SEP LV HP unit is separated and heated to 240°C for recycling into the reactor. To prevent the accumulation of potential contaminants in the recycling loop, 3% of the stream is purged as a first approach. However, this leads to a significant reagent loss, so further studies should aim to reduce this loss. Additionally, a compressor for the recycling loop would be necessary but is neglected in the first approach due to the relatively small pressure drops expected in the reactor operating at 30 bar.

[0175] Returning to the gas-liquid separator, the liquid stream (Liquid in Figure 1) is depressurized to 1 bar and sent to the distillation unit (DIST 1 in Figure 1), the specifications of which are presented in Table 2 below. The distillation column is designed to separate water from ethanol and produces three streams in total: two liquid streams (water at the bottom and ethanol at the top) and a vapor stream containing CO2 released at the top of the column (Impurities in Figure 1). Due to the minimal amount of CO2 in this stream, its recycling is considered inefficient compared to the energy required for compression and the equipment costs. Table 2. Summary of the specifications of the distillation column used in the production of ethanol by hydrogenation of carbon dioxide in the presence of the Pd-Ir catalyst (Process El).

[0176] The overall mass balance of process El is as follows. For 36,158 kg / h of CO2 and 4,882 kg / h of H2, the reaction (after distillation) produced 16,734 kg / h (94% by weight) of water and 114.67 kt / yr (92% by weight) of ethanol, and distillation resulted in 633 kg / h (93% by weight) of CO2. Purging removed 9,338 kg / h (87% by weight) of CO2.

[0177] Table 3 below provides additional results concerning the hydrogenation reaction. Table 3. Specifications of the product obtained by hydrogenation of CO2 in the presence of the Pd-Ir catalyst (Process El)

[0178] The purity of the ethanol obtained by hydrogenating CO2 in the presence of the Pd-Ir catalyst is satisfactory. Dilution with water is not a problem at this concentration. The distillation column proves sufficient to achieve the desired ethanol purity.

[0179] 3 - Catalyst: Cu(I)-HKUST17.5

[0180] The use of the Cu(I)-HKUST17.5 catalyst in the production of ethanol by carbon dioxide hydrogenation requires a more complex separation process than using Pd-Ir. This is due to the selectivity for ethanol, which in the presence of Cu(I)-HKUST17.5 is fixed at 62.9%, indicating that more water and impurities are introduced into the ethanol after the reaction. Separating the water is difficult due to the presence of an azeotrope between water and ethanol. While simple distillation can yield relatively good ethanol purity, the literature suggests that for higher ethanol purity, extractive distillation using ethylene glycol is commonly employed.

[0181] Here, two process schemes are presented: they use the same reactor and the same catalyst for the hydrogenation of CO2 but different methods for the purification (separation) process: one of the processes called E2, which is shown in Figure 2, aims to obtain an ethanol with a lower purity (78% by weight) and the other process called E3, which is shown in Figure 3, aims to obtain an ethanol with a higher purity (95% by weight).

[0182] For each process (E2 and E3), the hydrogen (H2) and carbon dioxide streams are conditioned at 1 bar and 35°C for hydrogenation using heat exchangers and expansion valves. The reactants are mixed with the recycled stream and enter the isothermal reaction reactor (REACT in Figures 2 and 3). The temperature of the isothermal reactor is set at 35°C. The CO2 conversion rate is set at 41.2%. The mass selectivity is given in Table 4 below.

[0183] Table 4. Selectivity of the product for the production of ethanol by hydrogenation of CO2 in the presence of the catalyst Cu(I)-HKUST17.5.

[0184] The reaction between CO2 and H2 occurs in stoichiometric proportions: 2 moles of CO2 for 6 moles of H2. The primary and secondary reactions are identical to those of hydrogenation in the presence of the Pd-Ir catalyst, the only difference being the presence of an additional secondary reaction producing isopropanol. Additional secondary reaction:

[0185] 3 CO2+ 9 H2C(CH3)2OH + 5H2O AH 0™ (298K) = -94.6 kJ / mol. After the reaction, the reaction mixture is cooled to 0°C by a heat exchanger (HTX3 in Figures 2 and 3) and directed to the low-pressure liquid-gas separator tank (SEP LV LP in Figures 2 and 3). The unreacted gases (Gas 1 in Figures 2 and 3) recovered from the top of the low-pressure flash tank are recycled. Before recycling, these gases undergo a 3% flow reduction. They then pass through a heat exchanger, reaching a temperature of 35°C. Again, the compression costs for the recycling loop were initially neglected, although the pressure drops in the process can now be significant compared to the operating pressure. The liquid stream exiting the SEP LV LP unit is cooled to 30°C before entering the remaining separation units. The separation part of each process (E2 and E3) is shown in Figure 4 to facilitate their comparison.

[0186] In process E2, two distillation columns in series are modeled. The first distillation column (DIST 1 on the left side of Figure 4) separates water from the alcoholic components (methanol, ethanol, and isopropanol), and the second distillation column (DIST 2 on the left side of Figure 4) separates ethanol from methanol. DIST 1 operates at 1 bar with negligible pressure loss. Three streams leave the DIST 1 distillation column: the water stream (Water on the left side of Figure 4), the liquid stream containing alcohols (Alcohols on the left side of Figure 4), and a gaseous stream with impurities (Gas 2 on the left side of Figure 4). DIST 2 also operates at 1 bar with no pressure loss; the ethanol stream (with a very low concentration of isopropanol) exits the column from the bottom, while the methanol vapor exits from the top.

[0187] In process E3, three distillation columns (DIST 1, DIST 2, and DIST 3 on the right side of Figure 4) are present. In addition, an extractive distillation column (EXT-DIST on the right side of Figure 4) is used in the system. Each column operates at 1 bar. The specifications for DIST 1 are the same for processes E2 and E3. In the EXT-DIST extractive distillation column, a 95% wt. ethylene glycol stream enters at the third stage (stage counting starts at the top of the column), while the alcohol and water mixture is introduced above the 20th stage. emeThe process involves two stages. Ethylene glycol extracts water to the bottom of the column, while the alcoholic components (methanol, ethanol, isopropanol) rise to the top. The ethylene glycol and water leaving the top of the extractive distillation column then enter the DIST 3 distillation column. In DIST 3, the water is separated from the ethylene glycol. The ethylene glycol stream exiting DIST 3 is cooled to 30°C in a heat exchanger (HTX6 on the right side of Figure 4) for recycling to the extractive distillation column. For the process to continue, a feed of 0.4 kg / h of ethylene glycol and 18 kg / h of water is required and mixed with the recycled solvent. The final distillation column, DIST 2, is used to separate the ethanol and methanol. The specifications of all columns are shown in Table 5.

[0188] The overall mass balance of each process E2 and E3 is provided below, and Table 6 presents additional results concerning the hydrogenation reactions for each of the processes.

[0189] Table 5. Specifications of the columns used in the purification steps of the production of ethanol by hydrogenation of carbon dioxide in the presence of the catalyst Cu(I)-HKUST17.5 in processes E2 and E3. distill. = distillation; distill, extract. = extractive distillation; déhyd. = dehydration.

[0190] The overall mass balance of process E2 is as follows: for 45,404 kg / h of CO2 and 5,597 kg / h of H2, the reaction produced 2.6 kg / h of the gaseous fraction Gas 2 (on the left side of Figure 4) (48% by weight of CO and 34% by weight of CO2), 23,534 kg / h of the Water fraction (on the left side of Figure 4) (94% by weight of H2O), and 136.92 kt / year of ethanol (78% by weight). The purge removed 7,747 kg / h (64% by weight) of CO.

[0191] The overall mass balance of process E3 is as follows: for 46,466 kg / h of CO2, 5,598 kg / h of hydrogen, 0.4 kg / h of ethylene glycol (Ethylene glycol on the right side of Figure 4) and 18 kg / h of water (Water 3 on the right side of Figure 4), the reaction produced 2.5 kg / h of the gaseous fraction Gas 2 (48% by weight of CO and 35% by weight of CO2), 23,544 kg / h of water (94% by weight) at the Water 1 level (on the right side of Figure 4) and 2,060 kg / h of water (95% by weight) at the Water 2 level (on the right side of Figure 4), 4,458 kg / h of methanol (83% by weight) and 105.62 kt / year of ethanol (95% by weight). The purge removed 9223 kg / h (64% by weight) of CO.

[0192] Table 6. Specifications of the product obtained by hydrogenation of CO2 in the presence of the catalyst Cu(I)-HKUST17.5 (Process E2 and Process E3). mass flow rate; tr = trace

[0193] The efficiency of ethanol production by carbon dioxide hydrogenation is demonstrated for processes E1, E2, and E3. Process E3 yields the highest purity ethanol but has a higher isopropanol content. Process E1 has the lowest impurity content, with the remaining compound consisting primarily of water. In process E2, the ethanol purity is acceptable (see below), although a significant amount of methanol is still present in the final product. In summary, the purity levels are considered satisfactory for all three processes. Analyzing the energy consumption and costs associated with each option can help identify the optimal process for ethanol production by CO2 hydrogenation based on the intended use.

[0194] The results of processes E2 and E3 show disparities, the main difference being the reduction in water and methanol content in the ethanol product streams. It is important to note that both processes produce ethanol containing isopropanol. The presence of isopropanol in ethanol is not problematic if the ethanol is intended for use in the culture of the yeast Saccharomyces cerevisiae. Indeed, during the culture of Saccharomyces cerevisiae, isopropanol can be generated as a byproduct, indicating the bacterium's tolerance to isopropanol. However, it is essential to emphasize that isopropanol becomes toxic to the bacterium when its concentration exceeds 3 g / L. The maximum level of isopropanol impurities observed in process E2 is considered acceptable.Using an appropriate dilution approach, this level of impurities would result in a concentration of 2.5 g / L of isopropanol in the bioreactor, which is below the specified requirement.

[0195] Example 2: Electrification of Ethanol Production by CO2 Hydrogenation

[0196] 1 - State of the Art

[0197] There are several ways to produce ethanol. One involves using biotechnology and fermenting biological substrates, such as corn or sugarcane. Another process involves catalytically hydrating ethylene (see, for example, Ayaou et al., Ethanol production by catalytic hydration of ethylene. Integrated project in Chemical Engineering, University of Liege, 2020, see internet: chemeng.uliege.be / upload / docs / application / pdf / 2020-06 / article_publication_ethanol.pdf). Finally, ethanol can also be produced from synthesis gas, specifically from a mixture of CO, CO2, and hydrogen (see, for example, Miranda et al., J. Clean. Prod., 2020, 269, 122978). The direct production of alcohols from CO and H2 has been practiced since the mid-1920s (Kanso et al., J. CO2 Util., 2025, 96: 103108), but the production of ethanol from CO2 and hydrogen (H2) has only recently been studied.

[0198] Regardless of the production process, a purification step is necessary to produce high-purity ethanol. The liquid effluent from the (bio)reactor, typically an ethanol-water mixture, is then sent to a downstream separation train that incorporates one or more distillation columns, depending on the desired purity. Since the ethanol-water mixture has an azeotropic point, an extractive distillation column may be required to achieve ethanol purities above the azeotropic point (-95.5% by weight of ethanol). Extractive distillation uses a selective solvent, such as ethylene glycol, to achieve the required ethanol purity. A representative process flow diagram of such a process is presented, for example, by Kanso et al. (J. CO2 Util., 2025, 96: 103108). This process yields ethanol with a purity of 99.9%. However, this high purity is not always necessary.Indeed, the purity may remain below the azeotropic point for many ethanol applications. In particular, for some uses, an ethanol purity of 70% by weight is sufficient.

[0199] An approach to electrifying ethanol production via fermentation was described by Rispoli et al. (Energies, 2021, 14(21): 7267). In their work, a mechanical vapor compression (MVC) system was integrated into the atmospheric rectification column. This rectification column is used to separate a water-ethanol stream containing 33 wt% ethanol into a distillate containing 94.4 wt% ethanol. In this case, the column includes two condensers and a reboiler. Despite this difference, the study remains highly relevant for evaluating reboiler electrification strategies. In the scheme proposed by Rispoli et al., the MVC is installed downstream of the first condenser, where the vapor stream is compressed to 4 bar. The compressed vapor is then reused to power the reboiler, thus fully meeting the column's heat requirements.This design eliminates the need for external steam and reduces the demand for cooling water.

[0200] The aim of this example is to combine an ethanol synthesis process based on the use of CO2 and hydrogen with an innovative process design to obtain an ethanol production process with minimal energy and environmental impact. As the results obtained below demonstrate, the combination of the two processes leads to a 100% electrified, high-energy-efficiency process capable of converting captured CO2 into ethanol.

[0201] 2 - Modeling

[0202] The hydrogenation of CO2 to ethanol is described by the following reaction:

[0203] 2 CO2 + 6 H2C2H5OH + 3 H2O AH 0 ™ (298K) = -215.42 kJ / mol

[0204] This reaction is exothermic and therefore thermodynamically favored at low temperatures. However, high temperatures are necessary to overcome the stability of the CO2 molecule and achieve reasonable kinetics. Several catalysts have been studied for this hydrogenation pathway. In Example 1, two types of catalysts were identified, and a process was developed for each. On the one hand, a copper-based catalyst was considered for non-thermal plasma conversion at ambient temperature and pressure. On the other hand, a Pd-Ir catalyst was identified to operate at 30 bar and 240°C. The first type of catalyst exhibits high conversion but low selectivity, while the second type of catalyst exhibits a relatively low conversion rate but high selectivity for ethanol (da Silva et al., Appli. Catal. B Environ., 2023, 324: 122221).

[0205] The hydrogenation process using the two types of catalysts was modeled using commercial process analysis and synthesis software, based on first-principles thermodynamics and incorporating detailed mass and energy balances. The target ethanol production capacity was approximately 100 kt / year. The process flow diagram for the Pd-Ir catalyst is presented in Figure 1, with a detailed description provided in Example 1.

[0206] Simulation results indicated a final ethanol production of 116 kt / year, with a mass purity of 92%.

[0207] The next step in the study aimed to improve the overall efficiency of the process, while specifically targeting purity requirements. In this context, the proposed improvement involves electrifying the distillation step by integrating a heat pump into the process design. Furthermore, the target ethanol purity was set at 70% (w / w) (instead of 90%) to meet the industrial requirements of the intended ethanol applications. This purity level is considered acceptable provided the ethanol is blended with a majority of water. Residual impurities must remain comparable to those obtained in the previous configuration. Detailed specifications are presented in Table 7 below:

[0208] Table 7. Purity of the product stream (90% EtOH w / w)

[0209] The first step in improving the process was to identify the impact on impurities of a target ethanol purity of 70% instead of 90%. To this end, the process setup was maintained, with adjustments only to the operating parameters to achieve the desired purity. The resulting impurity levels are shown in Table 8. Table 8. Product stream purity (70% EtOH w / w)

[0210] The purity of the ethanol obtained meets the target requirements, with impurity levels slightly lower than those of the previous configuration. The overall performance of the distillation column can therefore be evaluated to establish the basic requirements for producing 70% pure ethanol. These results are summarized in Table 9 below, where they are compared to previous results for 90% pure ethanol.

[0211] Table 9. Comparison of distillation column specifications for ethanol production without thermal integration for different purity levels (70% vs 90% EtOH w / w)

[0212] A slight reduction in energy demand is observed, accompanied by an increase in ethanol flow rate (the ethanol flow rate indicated in the table only takes into account the ethanol present in the product stream, and not the entire ethanol-water mixture). This increase in ethanol flow rate is independent of the chosen purity specification and could be further improved by optimizing the distillation operating conditions to minimize ethanol losses.

[0213] Based on these results, a heat recovery system was designed to minimize the energy demand of the process, and in particular to minimize the energy demand of the purification section. This system consists of an open-loop heat pump that recovers heat from the condenser of the distillation column and raises its temperature to supply it to the column's reboiler. The resulting configuration is illustrated in Figure 5. In this configuration, the overhead flow of the distillation column is compressed to a higher pressure by a compressor (COMP3 in Figure 5), and its thermal energy is then recovered to provide the heat required by the column. This configuration is inspired by that described by Kiss et al. (Energy Efficient Bioethanol Purification by Heat Pump Assisted Extraction Distillation, in: Gemaey et al. (Eds.), Computer Aided Chemical Engineering, Elsevier, 2015, pp. 1307-1312).A closer examination of the configuration shows that the heat from the overhead flow is used not only to power the reboiler (Reboiler in Figure 5), but also to preheat the feed entering the distillation column (HTX7 in Figure 5). In addition, heat is recovered from the bottomwater flow in the heat exchanger HTX6 (in Figure 5), which exits the column at the reboiler temperature (99°C). This configuration operates as an open-loop heat pump. Instead of using an external working fluid, a process fluid is used as the working fluid to transfer heat directly to the process.

[0214] One limitation of this configuration is the increased pressure in the compressor and the associated increase in electrical power demand. Furthermore, as noted by Kiss et al. (Energy Efficient Bioethanol Purification by Heat Pump Assisted Extraction Distillation, in: Gemaey et al. (Eds.), Computer Aided Chemical Engineering, Elsevier, 2015, pp. 1307-1312), the compressor discharge temperature must not exceed 150°C for material compatibility and safety reasons, which limits the maximum compressor discharge pressure. In the present configuration, the final pressure of the compressor outlet flow is 2.3 bar, allowing a maximum temperature of 149°C. The temperature of the condenser at the top of the system is 55°C, which meets the 70% purity requirement by weight. This temperature could potentially be adjusted depending on the target purity.An overview of the resulting thermal requirements of the distillation column is presented in Table 10.

[0215] Table 10. Specifications of the distillation column for the production of ethanol (70% w / w) with heat integration (from the distillation section) The thermal energy demand of the distillation column is reduced from approximately 11,000 kW to zero, while cooling requirements are significantly decreased from approximately 10,000 kW to 221 kW. Cooling water can be used for this purpose, with minimal cost and environmental impact. However, electrifying this distillation unit requires an additional 1,060 kW of electrical power. Therefore, the entire heating load of the distillation column is covered by heat transfer within the distillation system.

[0216] Beyond the distillation column alone, Table 11 below shows the difference between the system configuration before and after electrification of the distillation section, in a configuration without thermal integration.

[0217] Table 11. Comparison of energy demand before and after electrification of the distillation section, without thermal integration

[0218] Total energy demand of the process

[0219] To achieve complete electrification of the process, the remaining sections of the system were examined for further energy optimization. Thermal integration, in particular, can contribute to a significant reduction in the process's energy demand by coupling heat sources to heat sinks. Typically, thermal integration is studied before electrification. However, in some cases where the purification section cannot be integrated with the synthesis section (for example, due to steps taking place in remote units or low-temperature ethanol synthesis with limited thermal integration potential), the electrification route can be implemented independently of process integration. It is also possible to implement energy integration first, and then electrification to meet the remaining energy demand.

[0220] In this case, thermal integration was applied taking into account the already electrified purification section, resulting in the process configuration shown in Figure 6. Optimizing a heat exchanger network using the pinch method leads to a reduction in the residual heat demand from 51,471 kW to 1,276 kW for the entire system. The remaining heating demand is used to increase the reactor inlet gas temperature from 235°C to 240°C (electric heater in Figure 6). This cannot be supplied by industrial heat, as no source is available at such a high temperature. In this electrified context, the 1,276 kW can be provided by an electric heater, enabling fully electrified operation.

[0221] Table 12 below summarizes the energy demand associated with the different ethanol production configurations. The results indicate that complete electrification is feasible, provided that the remaining 1,276 kW of heat is supplied by an electric heater. Under these conditions, the total electrical demand of the process amounts to 5,092 kW (3,816 + 1,276 kW), with no remaining heat requirement. Figure 6 illustrates the evolution of the energy demand through the different stages of the process. An initial 20% reduction in non-electrical heat demand is achieved through electrification of the distillation section, followed by a complete reduction of non-electrical heat demand when energy integration is implemented in combination with the use of an electric heater.

[0222] Table 12. Energy demand for ethanol production (70% w / w) for different configurations

[0223] Conclusions

[0224] The work of these inventors proposes a process combining several innovations:

[0225] The use of CO2 as a feedstock to produce ethanol from CO2 and low-carbon hydrogen, thus enabling the production of fully synthetic ethanol; the complete electrification of the purification section (ethanol distillation), allowing the production of ethanol with a purity greater than or equal to 70% by weight and below the azeotropic point (95.5% by weight). This does not preclude the possibility of exceeding the azeotropic point with additional purification units; and

[0226] Minimal energy demand thanks to the integration of heat, allowing complete electrification of the heating needs of the CO2 to ethanol conversion process.

[0227] Thanks to these improvements, beyond raw materials, ethanol synthesis now requires energy solely in the form of electricity, at a rate of approximately 0.34 kWh per kilogram of ethanol, equivalent to 1.22 MJ / kg of ethanol (5092 kW / 121,000 t per year, assuming 8000 operating hours per year). Furthermore, some of the waste heat from the process can be recovered, for example, to produce steam or electricity via an organic Rankine cycle. Compared to alternative pathways, the energy requirements of the process described here are significantly lower. For example, the ethylene hydration pathway leads to an energy demand of 62 MJ / kg EtOH (Ayaou et al., 2020, see online: chemeng.uliege.be / upload / docs / application / pdf / 2020-06 / article_publication_ethanol).(pdf)), while synthesis from biomass varies between 15 and 150 MJ / kg of ethanol and synthesis from coal amounts to approximately 80 MJ / kg EtOH (Li and Cheng, Applied Energy, 2020, 277: 115574). A more detailed comparison might be needed to ensure that similar limits are taken into account (equivalent inputs and outputs in the different processes), but these results already appear very promising.

[0228] In conclusion, the electrified process enables the production of ethanol from CO2, while providing an innovative way to valorize captured CO2 and a significant reduction in energy demand through advanced energy integration.

Claims

Demands 1. An industrial process for the production of ethanol by hydrogenation of carbon dioxide (CO2), characterized in that the process comprises the following steps: (1) a hydrogenation reaction of CO2 with hydrogen (H2) in a reaction reactor to provide a reaction mixture, the hydrogenation reaction being carried out: (a) at an initial reaction temperature of between 200°C and 280°C, in particular 240°C, and a reaction pressure of between 20 and 40 bar, in particular 30 bar, in the presence of a palladium- or iridium-based catalyst; or (b) at an initial reaction temperature of between 20°C and 80°C, in particular 35°C, and a reaction pressure of between 1 and 10 bars, in particular 1 bar, in the presence of a copper-based catalyst on a metal-organic network; (2) cooling of the reaction mixture to obtain a cooled reaction mixture; (3) a flash separation of the cooled reaction mixture, the flash separation providing a gaseous phase containing unreacted CO2 and hydrogen (H2) and a liquid phase containing the ethanol produced; (4) recycling of the gaseous phase containing unreacted CO2 and hydrogen; and (5) a purification of the liquid phase to obtain purified ethanol.

2. Industrial process for the production of ethanol according to claim 1, characterized in that the palladium or iridium-based catalyst is Pd2:CeO2.

3. Industrial process for the production of ethanol according to claim 1, characterized in that the copper-based catalyst on a metallo-organic network is the Cu(I)-HKUST-17.5 catalyst.

4. An industrial process for the production of ethanol according to any one of claims 1 to 3, characterized in that the process further comprises, before the hydrogenation reaction, a conditioning step of the initially delivered CO2 and hydrogen to bring the CO2 and hydrogen to the initial reaction temperature and reaction pressure.

5. Industrial process for the production of ethanol according to any one of claims 1 to 4, characterized in that CO2 is initially delivered at a temperature of 25°C and a pressure of 30 bars and hydrogen is initially delivered at a temperature of 40°C and a pressure of 2 bars.

6. Industrial process for the production of ethanol according to claim 5, characterized in that if the hydrogenation reaction is carried out at an initial reaction temperature of 240°C and a reaction pressure of 30 bar in the presence of a palladium or iridium-based catalyst: the conditioning of the CO2 initially delivered includes compression using a train of compressors, and heating to 240°C, in particular using a heat exchanger; and the conditioning of the hydrogen initially delivered includes heating to 240°C, in particular using a heat exchanger.

7. Industrial process for the production of ethanol according to claim 5, characterized in that if the hydrogenation reaction is carried out at an initial reaction temperature of 35°C and a reaction pressure of 1 bar in the presence of a copper-based catalyst on a metallo-organic network: the conditioning of the CO2 initially delivered includes cooling to 35°C, in particular using a heat exchanger, and a pressure reduction, in particular using an expansion valve; and the conditioning of the hydrogen includes heating to 35°C, in particular using a heat exchanger, and a pressure reduction, in particular using an expansion valve.

8. An industrial process for the production of ethanol according to any one of claims 1, 2, and 4-6, characterized in that the hydrogenation reaction is carried out in the presence of a palladium or iridium-based catalyst and in that: in step (2), the reaction mixture is cooled to ambient temperature, in particular 20°C, using a heat exchanger; and in step (3), the flash separation is carried out using a high-pressure gas-liquid separator.

9. Industrial process for the production of ethanol according to claim 8, characterized in that in the recycling step (4) the gaseous phase containing unreacted CO2 and hydrogen is recovered and heated to the initial reaction temperature, in particular using a heat exchanger, before being introduced into the reaction reactor.

10. Industrial process for the production of ethanol according to claim 9, characterized in that, before the recycling step (4), a portion, in particular 3% or less, of the gaseous phase containing unreacted CO2 and hydrogen is purged.

11. Industrial process for the production of ethanol according to any one of claims 8 to 10, characterized in that in step (5) the purification of the liquid phase is carried out using a distillation column which separates water, a by-product of the hydrogenation reaction and ethanol, thus providing ethanol having a purity of 92% by weight.

12. Industrial process for the production of ethanol according to any one of claims 1, 3-5 and 7, characterized in that the hydrogenation reaction is carried out in the presence of a copper-based catalyst on a metallo-organic network, and in that: in step (2), the reaction mixture is cooled, in particular to 0°C, using a heat exchanger; and in step (3), the flash separation is carried out using a low-pressure gas-liquid separator.

13. An industrial process for the production of ethanol according to claim 12, characterized in that in recycling step (4) the gaseous phase containing unreacted CO2 and hydrogen is recovered and heated to the initial reaction temperature, notably using a heat exchanger, before being introduced into the reaction reactor.

14. Industrial process for the production of ethanol according to claim 12 or claim 13, characterized in that, before the recycling step (4), a portion, in particular 3% or less, of the gaseous phase containing unreacted CO2 and hydrogen is purged.

15. An industrial process for producing ethanol according to any one of claims 12 to 14, characterized in that in step (5) the purification of the liquid phase containing the ethanol produced by hydrogenation is carried out using two successive distillation columns, where: a first distillation column separates water, a by-product of the hydrogenation reaction, and the alcoholic components, the alcoholic components comprising the ethanol produced by hydrogenation and methanol and isopropanol, by-products of the hydrogenation reaction; and a second distillation column separates the methanol and ethanol, thus providing ethanol having a purity of 78% by weight.

16. An industrial process for producing ethanol according to any one of claims 12 to 14, characterized in that in step (5) the purification of the liquid phase is carried out using two distillation columns and one extractive distillation column, wherein: a first distillation column separates water, a by-product of the hydrogenation reaction, and the alcoholic components, the alcoholic components comprising ethanol produced by hydrogenation and methanol and isopropanol, by-products of the hydrogenation reaction; an extractive distillation column using ethylene glycol, in particular ethylene glycol at 95% by weight, as a driving agent, this column separating the alcoholic components from a water / ethylene glycol mixture; and a second distillation column separates the methanol and ethanol, thus providing ethanol having a purity of 95% by weight.

17. Industrial process for the production of ethanol according to claim 16, characterized in that the process further comprises a step of recycling ethylene glycol.

18. Industrial process for producing ethanol according to any one of claims 11 and 15-17, characterized in that the distillation step of the ethanol produced is electrified, preferably by a system comprising an open-loop heat pump.

19. Industrial process for the production of ethanol according to claim 18, characterized in that the system comprising the open-loop heat pump includes: a compressor placed at the top of the distillation column; a reboiler placed at the bottom of the distillation column; and two heat exchangers, a first heat exchanger and a second heat exchanger, placed between the high-pressure gas-liquid separator and the distillation column.

20. Industrial process for the production of ethanol according to claim 19, characterized in that: the flow from the top of the distillation column is compressed by the compressor and the thermal energy of the compressed flow is used to power the reboiler and to heat the liquid phase containing the ethanol produced obtained in step (3) at the second heat exchanger before the entry of said heated liquid phase containing the ethanol produced into the distillation column; Athe thermal energy of the water flow exiting the reboiler is used to preheat said liquid phase containing the ethanol produced at the first heat exchanger before the preheated liquid phase containing the ethanol produced is directed to the second heat exchanger, and characterized in that the ethanol produced has a purity of about 70% by weight or more, and the non-electrical heat demand of the process is 20% lower than the non-electrical heat demand of the process in the absence of the system including the open-loop heat pump.

21. Industrial process for the production of ethanol according to any one of claims 18 to 20, characterized in that the process is fully electrified.

22. Industrial process for the production of ethanol according to the process of claim 21, characterized in that: the conditioning of the initially delivered CO2 and of the initially delivered hydrogen is optimized by thermal integration to provide a mixture of conditioned CO2 and H2; and an electric heater is placed between the arrival of the mixture of conditioned CO2 and H2 and the reaction reactor to provide the energy input not supplied by thermal integration.

23. Industrial process for the production of ethanol according to the process of claim 22, characterized in that the ethanol produced has a purity of about 70% by weight or more, and the non-electrical thermal demand of the process is zero.

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