Method and reactor for obtaining methanol from carbon dioxide and hydrogen

Abstract

The present invention relates to a method and reactor for the synthesis of methanol from carbon dioxide (CO2) and hydrogen (H2), utilizing novel reactor and reaction conditions.

Description

D E S C R I P T I O NMETHOD AND REACTOR FOR OBTAINING METHANOL FROM CARBON DIOXIDE AND HYDROGENTechnical field

[0001] The present disclosure relates to the direct hydrogenation of carbon dioxide to methanol in a membrane reactor. The direct hydrogenation of carbon dioxide to methanol is a strong equilibrium-limited reaction. The continuous removal of reaction by-products is critical for reaching a higher conversion rate and for making the carbon dioxide hydrogenation process cheaper.

[0002] The present disclosure relates to a membrane reactor that allows the continuous removal of water and methanol, without allowing the permeation of the reactants, during the carbon dioxide hydrogenation to methanol process, thus significantly increasing the reaction's conversion rate.Background

[0003] Methanol is a key feedstock for the chemical industry, being one of the four major chemicals, alongside ethylene, ammonia, and propylene. Methanol is used in the production of acetic acid, formaldehyde, and plastics; it can also be used as a fuel, pure or blended with gasoline, or as a feedstock to produce biodiesel, jet fuel, and marine fuel.

[0004] The carbon dioxide hydrogenation reaction allows the production of green methanol from green hydrogen and biogenic carbon dioxide or other low-cost renewable sources of carbon dioxide. Currently, about 90 % of methanol is produced from natural gas, via syngas, at a pressure range of 5 - 10 MPa and at temperatures between 200 °C - 300 °C. The synthesis reactor is usually operated at ca. 250 °C and pressures between 5 - 10 MPa. There are three main reactions taking place during methanol production; the first two reversible reactions (equations 1 and 2) are the hydrogenation of carbon monoxide directly to methanol and the hydrogenation ofcarbon dioxide to produce methanol and water. These reactants can also undergo a third reaction termed as reverse water gas shift reaction (RWGS) (equation 3).AH°298k = -90.70 kJ mol1(1)CO2(g) + 3H2(g) CH3OH (g) + H2O (g) AH°298k = -49.51 kJ mol1(2)CO2(g) + 2H2(g) CO (g) + H2O (g) AH°298k = 41.19 kJ mol1(3)

[0005] Not only these synthesis reactions are reversible and overall exothermic, but they are also limited by thermodynamics, where low temperatures and high pressures favor higher equilibrium conversions to methanol. Even at low temperatures of about 200 °C and 5 MPa, the synthesis of methanol has a maximum conversion of ca. 80 %. However, the reaction kinetics increases with the temperature, and a minimum reaction temperature has to be ensured for industrial applications.

[0006] Though similar to the conventional synthesis of methanol from syngas, the carbon dioxide hydrogenation reaction - equation (2) - has critical differences: a) it is slower, and it has to be conducted at a higher temperature and pressure, normally at about 280 °C and above 6 MPa; b) at these conditions the equilibrium conversion is rather low, in the range of 20 %, which requires significant recirculation of reactants between the reactor and a phase separation system. The catalyst normally used is the same for carbon dioxide hydrogenation reaction and the conventional process, it is a Cu / Zn catalyst supported in alumina.

[0007] Inorganic membranes can selectively permeate one or both products from the reaction medium. It was reported that using a water permselective membrane reactor can result in a production rate increment compared to the process using a conventional reactor. Furthermore, a water-permeable membrane reactor is also beneficial in cost reduction at the separation stage of products. Modified carbon membranes and zeolites-based membranes are amongst the most promising inorganic membranes in this field. However, the experimental data available is still scarce, and these membranes have low reproducibility and high costs of production. This hinders the scale-up of membrane fabrication at the industrial level.

[0008] Perfluorinated super hydrophilic sulfonated tetrafluoroethylene-based fluoropolymer copolymer membrane has also been employed for methanol production, allowing higher methanol conversions and yield to be obtained as compared to conventional reactors. However, such membranes are unstable beyond 150 °C, hindering their applicability to methanol production that occurs above 200°C.General Description

[0009] The present disclosure relates to a novel tubular carbon dioxide hydrogenation reactor equipped with a hydrophilic membrane, offering improved reactivity and selectivity during the hydrogenation process. The reactor efficiently converts carbon dioxide (CO2) into valuable hydrocarbon products, in particular methanol, using a polymeric membrane comprising polybenzimidazole (PBI), polyetheretherketone (PEEK), or their combinations.

[0010] The present disclosure pertains to the field of chemical engineering and catalysis, particularly relating to reactors and methods for carbon dioxide hydrogenation using a hydrophilic membrane. The hydrophilic membrane may further comprise inorganic loads such as metal oxides (e.g. SiCh, TiCh), phosphates (e.g. tin pyrophosphate) or zeolites to increase its hydrophilicity and permeability to water and methanol and also to increase the mechanical strength of the membrane. The reactor design and configuration focus on enhancing the reaction kinetics and product selectivity, providing a more environmentally friendly and cost-effective approach for direct hydrogenation of carbon dioxide to methanol.

[0011] The present disclosure relates to a membrane reactor that allows water and methanol removal from the reaction zone via a hydrophilic composite polymeric membrane; wherein the removal is enhanced using a condenser at the permeate side.

[0012] A tubular carbon dioxide hydrogenation reactor is a type of chemical reactor designed for the conversion of carbon dioxide (CO2) and hydrogen (H2) into valuable products through a hydrogenation process. The primary aim of this reactor is to conduct the direct hydrogenation reaction of carbon dioxide to methanol; this reaction isstrongly equilibrium-limited. For increasing the reaction conversion, selectively remove one or the two reaction products; which is the purpose of the disclosed membrane reactor. This same reactor can be used to conduct other chemical reactions with similar needs. The reactor operates under specific temperature and pressure conditions to facilitate the hydrogenation reaction. The choice of temperature and pressure depends on the type of catalyst.

[0013] After the hydrogenation reaction, the reactor needs a system to separate the resulting products from the reaction mixture. This may involve methods such as distillation, or membrane processes.

[0014] Applications of a tubular carbon dioxide hydrogenation reactor include the production of valuable chemicals like methanol, among others, that can be used as fuels or feedstock in various industries.

[0015] An aspect of the present disclosure relates to a water / methanol-permeable membrane reactor with a build in condenser at the permeate side.

[0016] Another aspect of the present disclosure relates to the use of a membrane reactor to selectively remove water and methanol to allow significantly higher equilibrium conversions.

[0017] Another aspect of the present disclosure relates to a carbon dioxide hydrogenation device (multi-tubular reactor) comprising a plurality of the tubular reactors of the present disclosure.

[0018] The advantage of the reactor of the present disclosure is that this reactor allows higher conversions of the carbon dioxide hydrogenation reaction and is especially suited for producing green methanol.

[0019] In an embodiment, the present disclosure discloses a water / methanol- permeable membrane reactor.

[0020] In an embodiment, the present disclosure discloses the use of a condenser to accelerate water removal through a water-permeable polymeric membrane and to reduce the H2 / CO2 permeation.

[0021] In an embodiment, the present disclosure discloses a modular-type reactor to scale up the technology and enhance efficiency.

[0022] In an embodiment, the present disclosure discloses a membrane reactor to increase the methanol synthesis conversion.

[0023] In an embodiment, the present disclosure discloses a membrane reactor, substrates, polymeric membrane layer, and condenser to accelerate water and methanol removal during methanol production, resulting in increased methanol yield a.

[0024] Sintered stainless steel tubes and porous ceramic tubes are the most adequate substrates for hosting the thin selective polymeric layer membrane. The porous substrate ensures mechanical stability as well as very high permeability to water and methanol.

[0025] In an embodiment, a thin selective layer of polybenzimidazole is applied either on the shell or on the bore side or shell side of the substrate, using a suitable technique, such as dip coating, spray coating, thermal spray coating, and / or flow coating. The polymeric membrane layer is applied on the bore-side of the tubular support if the pressure difference does not promote its deadhesion. Otherwise, the bore-side is the preferred side that prevents membrane wearing promoted by the catalyst particles present in the shell side; in this case, water and methanol is preferably in the vapor phase at the porosity of the supporting membrane for allowing an easy selective permeation. Inside the reactor, a proper balance between temperature and pressure is ensured. If the selective polymeric film is applied to the shell side of the membrane support, these requirements and no longer needed.

[0026] In an embodiment, contrary to prior art methanol membrane reactors which employ inorganic and perfluorosulfonic acid-based membranes, the membrane reactor of the present disclosure employs a polybenzimidazole or a composite polybenzimidazole membrane layer. Polybenzimidazole is a thermally and chemically very stable polymer, which has a tuneable permeability to water and methanol, obtained using different loads. Though pristine polybenzimidazole membranes have a high permeability to water and methanol, their permeability can be further improved byadding hydrophilic metal oxides, phosphates, and zeolites to obtain a composite polybenzimidazole membrane. The hydrophilic metal oxides, phosphates, and zeolites loads not only provide tuneable hydrophilicity but also improve the membrane strength. The membrane hydrophilicity prevents hydrogen and carbon dioxide from permeating. Liquid water, and also methanol, condenses and fills the whole porosity of the polybenzimidazole membrane, preventing the permeation of the gaseous reactants. In- situ condensation of water / methanol, within the membrane matrix, not only increases the permeability to water and methanol but also prevents hydrogen and carbon dioxide from permeating, thus increasing the membrane selectivity.

[0027] In an embodiment, beyond the use of a hydrophilic stable membrane, the present disclosure also discloses the use of a heat exchange system at the membrane permeate side, as illustrated in Figure 1, for improving the water / methanol permeation and selectivity.

[0028] In an embodiment, for increasing the permeation driving force, the bore side of the supported membrane is colder than the shell side, this latter is in direct contact with the reaction medium.

[0029] In an embodiment, the tubular supported membrane comprises a heat exchange tube where cooling thermal fluid circulates. Since the driving force for water (and methanol) to permeate is the partial pressure, lowering the temperature at the bore side makes the water's partial pressure decrease as part of the vapor condenses.

[0030] In an embodiment, to keep the total pressure difference between the two sides of the membrane not too high, a selective polybenzimidazole layer is applied on the bore side or shell side, and an inert gas such as nitrogen is used as a sweep gas.

[0031] In an embodiment, the reactor of the present disclosure comprises a bundle of reactor tubes inserted in a thermally insulated tubular container. The thermally insulated tubular container is for the circulation of the thermal fluid for the start-up and shutdown of the reactor and also to drive out the heat produced by the methanol exothermal reaction. Each tubular reactor comprises the supported membrane, and the heat exchange tube, and is loaded with the catalytic particles in its annular volume(Figure 1). The use of a multi-tubular methanol reactor allows the reactor to be more efficient as it can handle a great variation of feed flow rate, since as the feed flow rate decreases, a reaction tube can be stepwise shouted down. Since all reaction tubes are kept at the reaction temperature, the startup of them is quite straightforward.

[0032] In an embodiment, a polymeric membrane that shows high thermal and chemical resistance, and water / methanol permeability, such as polybenzimidazole (PBI) or polyetheretherketone (PEEK) is used to overcome the limitation of current reactors, which uses super hydrophilic perfluorinated sulfonic-acid membrane which is unstable beyond 150 °C thus hindering their applicability to methanol production that occurs above 200°C.

[0033] In an embodiment, to further increase the permeability to water and methanol and selectivity, hydrophilic membranes are used. Polybenzimidazole membranes loaded with metal oxides (e.g. silicon dioxide, titanium dioxide), phosphates (e.g. tin pyrophosphate), or zeolites can be used to increase permeability to water and methanol and its mechanical strength.

[0034] Polybenzimidazole is a high-performance polymer with remarkable chemical inertness, mechanical strength (tensile strength of 160 MPa), good oxidation resistance, hydrophilic, and a glass transition temperature of 427 °C. Benefiting from its higher hardness and modulus, polybenzimidazole displays a better scratch resistance against stainless steel compared to other high-performance polymers such as polyetheretherketone (PEEK). This high-performance polymer also displays good adhesion to the substrates such as steel, even at temperatures above 280 °C. Polybenzimidazole is an ideal polymer to coat or cover steel or ceramic porous tubes and operate under high temperatures.

[0035] In an embodiment, tubular steel or ceramic porous tubes coated with a polybenzimidazole layer or loaded with hydrophilic materials, as a selective membrane for removing water and methanol from the reactor medium and then shifting the carbon dioxide hydrogenation reaction towards the reaction products is used, thus allowing conversions higher than 70 %.

[0036] An aspect of the present disclosure relates to a tubular carbon dioxide hydrogenation reactor comprising: a plurality of metal or ceramic porous tubes in the bore of the tubular reactor; a supported hydrophilic membrane selective to the reaction products, where the hydrophilic membrane is supported on the bore side or shell side of the plurality of a metal or ceramic porous tubes (or in the inner or the outer part of the plurality of a metal or ceramic porous tubes); wherein said hydrophilic membrane is a polymeric membrane comprising a material selected from: polybenzimidazole, polyetheretherketone.

[0037] In an embodiment, the tubular reactor further comprises a tubular heat exchanger inside the metal or ceramic porous tubes; wherein said heat exchanger is configured for flow of a cooling thermal fluid to lower the temperature at the bore side or the shell side of the plurality of metal or ceramic porous tubes making the partial pressure decrease and part of the vapor condenses.

[0038] In an embodiment, the reaction products are methanol.

[0039] In an embodiment, the tubular reactor further comprises a catalyst; an inlet for vapor; an outlet for vapor.

[0040] In an embodiment, the catalyst is in the annular volume of the tubular reactor.

[0041] In an embodiment, the polymeric membrane has a thickness from 1 - 100 pm, preferably from 2 - 15 pm.

[0042] In an embodiment, the polymeric membrane further comprises hydrophilic metal oxides, phosphates, or zeolites. The polymeric membrane is loaded with hydrophilic metal oxides, phosphates, or zeolites for improving its hydrophilicity and mechanical stability.

[0043] In an embodiment, the hydrophilic metal oxide is silicon dioxide, titanium dioxide, tin pyrophosphate, 5A-zeolite, or mixtures thereof.

[0044] In an embodiment, the heat exchange tube further comprises cooling thermal fluid.

[0045] In an embodiment, the metal or ceramic porous tube has a diameter from 4 - 20 cm, preferably from 5 - 7 cm.

[0046] In an embodiment, the tubular reactor has a diameter from 8 - 30 cm, preferably from 12 - 15 cm.

[0047] Another aspect of the present disclosure relates to a carbon dioxide hydrogenation device comprising a plurality of the tubular reactors of the present disclosure.

[0048] Another aspect of the present disclosure relates to a method for the direct hydrogenation of carbon dioxide to methanol using the tubular reactor according to any of the previous claims comprising: feeding hydrogen and carbon dioxide gas to the metal or ceramic porous tube.

[0049] In an embodiment, the direct hydrogenation of carbon dioxide to methanol further comprises the step of feeding a sweep gas to the metal or ceramic porous tubes.

[0050] In an embodiment, for the direct hydrogenation of carbon dioxide to methanol, the sweep gas is nitrogen gas.

[0051] In an embodiment, for the direct hydrogenation of carbon dioxide to methanol, the hydrogen, and carbon dioxide are fed to the reaction tube at temperatures ranging from 250 °C - 300 °C, preferably 280°C.

[0052] In an embodiment, for the direct hydrogenation of carbon dioxide to methanol, the hydrogen and carbon dioxide are fed to the metal or ceramic porous tubes at pressures ranging from 5-10 MPa, preferably 7-8 MPa.

[0053] The following claims further set out particular embodiments of the disclosure.Brief Description of the Drawings

[0054] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of the invention.

[0055] Figure 1 illustrates a simplified schematic diagram of a membrane reactor to produce methanol, with water and methanol being permeated through a supported RBI - based membrane, where the selective polymeric layer is applied on the bore side or shell side of steel sintered or porous ceramic tubes.

[0056] Figure 2 illustrates a simplified schematic diagram of a modular-type reactor to produce methanol, consisting of multiple membrane reactors inside of a shell.

[0057] Reference list(1) inlet for the reactants(2) sweep gas (optional)(3) sintered steel or porous ceramic support tube(4) heat exchange tube(5) thin polymeric membrane layer of pristine or composite PBI(6) methanol bed reactor(7) water / methanol permeation from the reaction side(8) cooling thermal fluid(9) outlet of the non-permeated reaction products(10) outlet of the permeated reaction products(11) reaction tube(12) tubular container of the reaction tubes(13) multiple reaction tubesDetailed Description

[0058] The present disclosure relates to a novel tubular carbon dioxide hydrogenation reactor equipped with a hydrophilic membrane, offering improved reactivity and selectivity during the hydrogenation process.

[0059] An aspect of the present disclosure relates to a polybenzimidazole-based membrane reactor for obtaining an efficient production of methanol from the direct hydrogenation of carbon dioxide.

[0060] Another aspect of the present disclosure relates to an efficient method of obtaining methanol from the direct hydrogenation of carbon dioxide. The method runs between 250 °C and 300 °C, preferably 280 °C, and from 5 MPa to 10 MPa. The reactor runs in the gas / vapor phase. After permeating, water and methanol will be at a lower temperature and pressure but well above ambient pressure. Removing water and methanol can be performed in vapor or liquid phases or both, but preferably it should be removed in the liquid phase to keep the pressure as high as possible. This is of particular relevance if another process is applied to this stream, such as membrane or reaction processes. Permeated conditions are at least 0.5 MPa below inside the reactor and in the range of 1 to 9 MPa, and the temperature is 5 °C to 80 °C lower than inside the reactor.

[0061] In an embodiment of the present application, a tubular 'bore & shell' type membrane reactor configuration is used for this device.

[0062] In an embodiment, the reaction tube is made of steel (11).

[0063] In an embodiment, the annular volume of the reaction tube contains the catalyst particles; the supported membrane contains in its bore side a heat exchange tube and is placed in the central part of the reaction tube.

[0064] In an embodiment, the diameter of the reaction tube is between 8 - 30 cm, preferably between 12 - 15 cm. This reaction tube holds the catalyst bed (6) and has an inlet and outlet for gases / vapor (1 and 9, respectively - Figure 1). The catalytic bed (6) is filled with a catalyst active for methanol production.

[0065] In an embodiment, hydrogen and carbon dioxide are fed to the reaction tube at temperatures ranges from 250 °C - 280 °C and pressures ranges from5 to 10 MPa. The unreacted gases and the un-permeated methanol and water leave the reactor via outlet (9) at the end of the reactor tube.

[0066] In an embodiment, in the bore side or shell side of the tubular reactor, at the center, a porous steel or ceramic tube (3) with a preferred diameter between 4 - 20 cm, preferably between 5 and 7 cm, is inserted. This tube is coated or covered with pristine PBI or composite PBI-based membranes (5). The preferred membrane thickness is between 1 - 100 pm and more preferentially between 2 and 15 pm, to ensure easier water vapor permeation without adversely affecting the physical properties of the membrane. The membrane is applied on the inorganic porous substrate (5) using a coating technique such as dip coating, blade coating, spray coating, thermal spray coating, flow coating, and spin coating.

[0067] In an embodiment, polybenzimidazole powder and / or polybenzimidazole solution are used to produce polybenzimidazole membranes. Polybenzimidazole solution is obtained using dimethylacetamide (DMAc) as a solvent. The polymer mass fraction in the solvent is kept between 10-15 % to prepare the solution.

[0068] In an embodiment, polybenzimidazole membranes are coated / covered preferentially on the bore side of the tubular substrate that is facing the reaction site (5).

[0069] In an embodiment, to prepare the composite PBI membranes, nano-sized hydrophilic, such as silicon dioxide, titanium dioxide, zeolite, or like hydrophilic thermally stable inorganic fillers are slowly added to the polybenzimidazole solution and stirred to avoid agglomeration inside the polybenzimidazole solution.

[0070] In an embodiment, a heat exchange tube (4) is placed in the center of the reaction tube to cool the permeated stream (7) and then improve the permeation of water and methanol.

[0071] In an embodiment, the diameter of the heat exchange tube is between 2 and 10 cm, preferably between 2.5 and 3.5 cm.

[0072] In an embodiment of the present application, water and methanol removal is achieved due to the pressure and temperature difference between the two sides of the membrane.

[0073] In an embodiment, the shell reactor (11, 6) side comprises a catalyst and is operated from 5-10 MPa and from 250 °C and 300 °C while the bore is from 1 to 9 MPa and at least 0.5 MPa below the reaction medium and from 5 °C and 80 °C below the reaction medium (7). These partial pressure and temperature differences make water and methanol removal possible through the membrane. Removed products from the reaction side exist from the outlet provided for this particular purpose.

[0074] In an embodiment, the shell reactor runs from 250 °C - 300 °C and from 5 tolO MPa, and more preferentially from 270 °C and 280 °C and 7 to 8 MPa, in the vapor phase, so optimum catalytic activity and stability are ensured.

[0075] In an embodiment, cooling thermal fluid circulates continuously inside the heat exchange tube placed inside the reactor. Cooling the permeated stream makes the permeation driving force higher and partially dissipates the heat of the exothermal reaction. The composite polybenzimidazole-based membrane is super hydrophilic, so water and methanol are in a condensed phase. This prevents hydrogen and carbon dioxide to permeate. However, for water and methanol being in a condensed phase inside the membrane, they should be only slightly above their condensation conditions inside the reaction medium. The condenser, inside the porous inorganic supporting membrane, also makes the temperature at polybenzimidazole-based (PBI-based) membrane film lower, contributing for the water and methanol inside this membrane to be in a condensed state.

[0076] In an embodiment, the membrane reactors may be assembled inside a container through which flows a thermal fluid for controlling the temperature of the shell side tubular reactors; as previously mentioned, there is a temperature gradient between the shell side of the tubular reactors and the surface temperature at the polybenzimidazole -based membrane so that hydrogen and carbon dioxide would not permeate the membrane.

[0077] In an embodiment, the temperature difference is between 2 °C and 30 °C, preferably between 5 °C and 20 °C, more preferably about 15 °C, even more preferably10 °C.

[0078] These multiple membrane modules allow easy scaling up the methanol production.Example 1

[0079] The relationship between methanol conversion and system pressure was studied by varying the operating pressure of the system. The sintered steel tube (3), with a 5 cm internal diameter illustrated in Figure 1 was deep coated on its outer wall with 15 wt. % polybenzimidazole solution. This solution was prepared from commercial polybenzimidazole powder, which was slowly added to the dimethylacetamide under stirring; the solution was heated at 110 °C for 2 h to obtain a viscous polymer solution. The coated substrate was then dried in a vacuum oven at 120 °C for 3 h to remove the solvent. The coating method was optimized to achieve a polybenzimidazole membrane thickness of (10 ± 0.5) pm. The tubular membrane was placed in the center of the reaction tube as illustrated in Figure 1. 1 g of copper oxide / zinc oxide / aluminium oxide catalyst (6) in the reaction tube (11) was reduced in-situ between 160 °C - 250 °C with a temperature ramp of 2 °C-min-1. Flowing hydrogen (10 ml-min-1) and nitrogen (190 ml-min-1) were used as a reduction medium. After the catalyst activation, the reaction tube was flushed with nitrogen (50 ml-min-1) for 30 min to remove adsorbed hydrogen. The temperature was then set to 270 °C using electric heaters controlled by a proportional-integral-derivative controller with temperature information provided by thermocouples near to the cylinder wall. A mixture of hydrogen and carbon dioxide was constantly fed to the inlet (1) of the reaction tube with a feed flow rate of 5000 h1(GHSV). The reaction tube was pressurized with reactant gases at 6Mpa, 7 MPa, and 8 MPa, and maintained with the use of a back pressure regulator. The products were analyzed with an online gas chromatograph. The product was analyzed every 20 min until the steady-state is achieved. The obtained average methanol conversion in this membrane reactor was 41.2 % (6 MPa), 73.7 % (7 MPa), and 83.3 % (8 MPa). From the experiments performed, it was observed that by increasing the operating pressure, the methanol conversion also increases. The pressure shifts the equilibrium of the methanol reaction (equation 2) to the product side, which has a lower number of moles. Additionally, the lower operating pressures are attributed to low driving forces acrossthe membrane (lowered water and methanol permeation). At increased pressure, with higher product removal, the reaction is shifted towards the product side.Example 2

[0080] The effect of the operating pressure on methanol conversion was evaluated at three different temperatures. These tests were designed to assess the effect of temperature on membrane permeation performance; three different temperatures were considered, 260 °C, 270 °C, and 280 °C. The experiments were conducted in a membrane reactor as illustrated in Figure 1. The sintered steel tube (3) was deep coated on its outer wall with 15 wt.% polybenzimidazole solution. A commercial polybenzimidazole powder was slowly added to the dimethylacetamide under stirring. The solution was heated at 110 °C for 2 h to obtain a viscous polymer solution. The coated substrate was dried in a vacuum oven at 120 °C for 3 h to remove the solvent. The coating method was optimized to achieve a polybenzimidazole membrane thickness of (10 ± 0.5) pm. The tubular membrane was placed in the center of the reaction tube as illustrated in Figure 1. The annular volume of the reactor (11) was filled with 1 g of copper oxide / zinc oxide / aluminium oxide catalyst (6), reduced in-situ between 160 °C - 250 °C with a temperature ramp of 2 °C-min-1, under a reducing atmosphere made of 10 ml-min1of hydrogen and 190 ml-min1of nitrogen. After the catalyst activation, the reaction tube was flushed with nitrogen (50 ml-min-1) for 30 min to remove the adsorbed hydrogen. The temperature was then set to 260 °C, 270 °C, and 280 °C using electric heaters controlled by a proportional-integral-derivative controller with temperature information provided by the thermocouples near the cylinder wall. A mixture of hydrogen and carbon dioxide was constantly fed to the inlet (1) of the reaction tube with a feed flow rate of 5000 h1(GHSV). The reaction tube was pressurized with reactant gases at 7.5 MPa, and maintained with the use of a back pressure regulator. The products were analyzed with an online gas chromatograph every 20 min until reaching the steady-state. The obtained average methanol conversion was 53.8 % (260 °C), 75.7 % (270 °C), and 81.2 % (280 °C). There was a peak in the methanol conversion with the temperature (at 280 °C), and then it dropped. For a conventional fixed-bed reactor, as the temperature increases, the RWGS reaction (equation 3) becomes more relevant.This leads the methanol and water production to decrease. However, herein, constant removal of methanol and water from the reaction zone ensured minimum to no RWGS reaction. This led to an increase in methanol conversion even at high temperatures.Example 3

[0081] The effect of polybenzimidazole-based membrane thickness on the methanol conversion was also tested using three different membrane thicknesses, 5 pm, 10 pm, and 15 pm. These tests were designed to assess the membrane permeation and its importance for product removal during methanol synthesis. The porous (sintered) steel tube (3), with a 5 cm internal diameter, is illustrated in Figure 1. It was deep coated on its outer wall with 15 wt.% polybenzimidazole solution; a commercial polybenzimidazole powder was slowly added to the dimethylacetamide under stirring. The solution was heated at 110 °C for 2 h to obtain a viscous polymer solution. The coated substrate was dried in a vacuum oven at 120 °C for 3 h to remove the solvent. The coating method was optimized to achieve a membrane thickness of (5 ± 0.5) pm, of (10 ± 0.5) pm, and of (15 ± 0.5) pm. The tubular membrane was placed in the center of the reaction tube, as illustrated in Figure 1. l g of CuO / ZnO / AI2O3 catalyst (6) was loaded in the annular volume of the reaction tube (11) and reduced in-situ between 160 °C - 250 °C with a temperature ramp of 2 “C-min1. Hydrogen (10 ml-min1) and nitrogen (190 ml-min-1) were fed as reduction medium. After the catalyst activation, the reaction tube was flushed with nitrogen (50 ml-min-1) for 30 min to remove adsorbed hydrogen. The temperature was then set to 280 °C using electric heaters, controlled by a proportional- integral-derivative controller with temperature information provided by thermocouples placed near the cylinder wall. A mixture of hydrogen and carbon dioxide was constantly fed to the inlet (1) of the reaction tube with a feed flow rate of 5000 h1(GHSV). The reaction tube was pressurized with reactant gases at 7.5 MPa; and maintained using a back pressure regulator. The reaction products were analyzed every 20 min until the steady state is achieved. The average methanol conversion in this membrane reactor was 80.3 % (5 pm), 76.7 % (10 pm), and 73.7 % (15 pm). Reducing the membrane wall thickness is beneficial as the permeating flow through the membrane increases. As moreproduct is removed from the reaction tube, the reaction shifts towards the product side, which increases the methanol conversion.

[0082] Where ranges are given, endpoints are included. Furthermore, it is to be understood that unless otherwise indicated or otherwise evident from the context and / or the understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value within the stated ranges in different embodiments of the invention, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. It is also to be understood that unless otherwise indicated or otherwise evident from the context and / or the understanding of one of ordinary skill in the art, values expressed as ranges can assume any subrange within the given range, wherein the endpoints of the subrange are expressed to the same degree of accuracy as the tenth of the unit of the lower limit of the range.

[0083] The embodiments described above are combinable.

[0084] The term "comprising" whenever used in this document, is intended to indicate the presence of stated features, integers, steps, and components, but not to preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0085] The following claims further set out particular embodiments of the disclosure.References1. Bertau M, Offermanns H, Plass L, Schmidt F, Wernicke HJ. Methanol: The basic chemical and energy feedstock of the future: Asinger's vision today. Methanol: The Basic Chemical and Energy Feedstock of the Future: Asinger's Vision Today. 2014. i- xxxi.2. Dalena F, Senatore A, Basile M, Knani S, Basile A, lulianelli A. Advances in methanol production and utilization, with particular emphasis toward hydrogen generation via membrane reactor technology. Membranes (Basel). 2018;8(4).3. Gallucci F. Inorganic Membrane Reactors for Methanol Synthesis [Internet], Methanol: Science and Engineering. Elsevier B.V.; 2018. 493-518 p. Available from: http: / / dx.doi.org / 10.1016 / B978-0-444-63903-5.00018-2Iyer SS, Renganathan T, Pushpavanam S, Vasudeva Kumar M, Kaisare N. Generalized thermodynamic analysis of methanol synthesis: Effect of feed composition. J CO2 Util [Internet], 2015;10:95-104. Available from: http: / / dx.doi.Org / 10.1016 / j.jcou.2015.01.006 Samimi F, Hamedi N, Rahimpour MR. Green Methanol Production Process from Indirect CO2 Conversion: RWGS Reactor versus RWGS Membrane Reactor. J Environ Chem Eng [Internet], 2019;7(l):102813. Available from: https: / / doi.Org / 10.1016 / j.jece.2018.102813 Wu J, Saito M, Takeuchi M, Watanabe T. The stability of Cu / ZnO-based catalysts in methanol synthesis from a C02-rich feed and from a CO-rich feed. Appl Catal A Gen. 2001;218(l- 2):235-40. Farsi M, Jahanmiri A. Methanol production in an optimized dual-membrane fixed-bed reactor. Chem Eng Process Process Intensif [Internet], 2011;50(ll-12):1177-85. Available from: http: / / dx.doi.Org / 10.1016 / j.cep.2011.08.011 Struis RPWJ, Stucki S, Wiedorn M. A membrane reactor for methanol synthesis. J Memb Sci. 1996;113(l):93-100. Quartarone E, Angioni S, Mustarelli P. Polymer and composite membranes for protonconducting, high-temperature fuel cells: A critical review. Materials (Basel). 2017;10(7). Akhtar FH, Kumar M, Villalobos LF, Vovusha H, Shevate R, Schwingenschlbgl U, et al. Polybenzimidazole-based mixed membranes with exceptionally high water vapor permeability and selectivity. J Mater Chem A. 2017;5(41):21807-19. Sun X, Simonsen SC, Norby T, Chatzitakis A. Composite Membranes for High Temperature PEM Fuel Cells and Electrolysers: A Critical Review. Membr [Internet], 2019 / 07 / 25. 2019;9(7). Available from: internal-pdf: / / 65.187.203.140 / Composite Membranes for High Temperature PEM F.pdf Kyriacos D. High-Temperature Engineering Thermoplastics [Internet], Brydson's Plastics Materials: Eighth Edition. Elsevier Ltd; 2017. 545-615 p. Available from: http: / / dx.doi.org / 10.1016 / B978-0-323-35824-8.00021-9 Moon JD, Borjigin H, Liu R, Joseph RM, Riffle JS, Freeman BD, et al. Impact of humidity on gas transport in polybenzimidazole membranes. J Memb Sci [Internet], 2021;639(August):119758. Available from: https: / / doi.Org / 10.1016 / j.memsci.2021.119758 Chen X, Zhang Y, Ribeiorinha P, Li H, Kong X, Boaventura M. A proton conductor electrolyte based on molten CsH5(PO4)2 for intermediate-temperature fuel cells. RSC Adv [Internet], 8(10):5225-32. Available from: internal-pdf: / / 0450074186 / A proton conductor electrolyte based on molten.pdfJean-Fulcrand A, Masen MA, Bremner T, Wong JSS. High temperature tribological properties of polybenzimidazole (PBI). Polymer (Guildf) [Internet], 2017;128:159-68. Available from: https: / / doi.Org / 10.1016 / j.polymer.2017.09.026 Iqbal HMS, Bhowmik S, Benedictus R. Process optimization of solvent based polybenzimidazole adhesive for aerospace applications. Int J Adhes Adhes [Internet], 2014;48:188-93. Available from: http: / / dx.doi.Org / 10.1016 / j.ijadhadh.2013.09.031 Bos MJ, Brilman DWF. A novel condensation reactor for efficient CO2 to methanol conversion for storage of renewable electric energy. Chem Eng J [Internet], 2015;278:527- 32. Available from: http: / / dx.doi.Org / 10.1016 / j.cej.2014.10.059

Claims

C L A I M S1. A tubular carbon dioxide hydrogenation reactor comprising: a plurality of metal or ceramic porous tubes in the bore of the tubular reactor; a supported hydrophilic membrane selective to the reaction products, where the hydrophilic membrane is supported on the bore side or shell side of the plurality of a metal or ceramic porous tubes; wherein said hydrophilic membrane is a polymeric membrane comprising a material selected from: polybenzimidazole, polyetheretherketone; wherein the polymeric membrane further comprises hydrophilic metal oxides, selected from the list consisting of: silicon dioxide, titanium dioxide, or phosphates, tin pyrophosphate, or mixtures thereof.

2. The tubular reactor according to the previous claim further comprising a tubular heat exchanger inside of the plurality of metal or ceramic porous tubes; wherein said heat exchanger is configured for flow of a cooling thermal fluid in order to lower the temperature at the bore side or the shell side of the plurality of metal or ceramic porous tubes making the partial pressure decrease and part of the vapor condenses.

3. The tubular reactor according to any of the previous claims, wherein the temperature difference between bore side and shell side of the plurality of metal or ceramic porous tubes ranges from 2 °C to 30 °C, preferably from 5 °C to 20 °C, more preferably about 10 to 15 °C.

4. The tubular reactor according to any of the previous claims, wherein the reaction products are methanol.

5. The tubular reactor, according to any of the previous claims comprising a catalyst; an inlet for gas / vapor; an outlet for gas / vapor.

6. The tubular reactor, according to any of the previous claims, wherein the catalyst is in the annular volume of the tubular reactor.

7. The tubular reactor according to any of the previous claims, wherein the polymeric membrane has a thickness from 1 - 100 pm, preferably from 2 - 15 pm; more preferably 5 - 10 pm.

8. The tubular reactor according to any of the previous claims, wherein the polymeric membrane further comprises phosphates, or zeolites.

9. The tubular reactor according to any of the previous claims, wherein the heat exchange tube further comprises cooling thermal fluid.

10. The tubular reactor according to any of the previous claims, wherein the metal or ceramic porous tube has a diameter from 4 - 20 cm, preferably from 5 - 7 cm.

11. The tubular reactor according to any of the previous claims, wherein the tubular reactor has a diameter from 8 - 30 cm, preferably from 12 - 15 cm.

12. A carbon dioxide hydrogenation device comprising a plurality of the tubular reactors according to any of the previous claims.

13. A method for the direct hydrogenation of carbon dioxide to methanol using the tubular reactor according to any of the previous claims comprising: feeding hydrogen and carbon dioxide gas to the metal or ceramic porous tube.

14. The method for the direct hydrogenation of carbon dioxide to methanol according to the previous claim further comprising the step of feeding a sweep gas to the metal or ceramic porous tubes.

15. The method for the direct hydrogenation of carbon dioxide to methanol according to the previous claim, wherein the sweep gas is nitrogen gas.

16. The method for the direct hydrogenation of carbon dioxide to methanol according to any of the previous claims 13-15, wherein the hydrogen and carbon dioxide arefed to the reaction tube at temperatures ranging from 250 °C - 300 °C, preferably 280°C.

17. The method direct hydrogenation of carbon dioxide to methanol according to any of the previous claims 13-16, wherein the hydrogen and carbon dioxide are fed to the metal or ceramic porous tubes at pressures ranging from 5 MPa - 10 MPa, preferably 7 MPa-8 MPa.

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