Method for preparing methanol through hydrogenation of oxycarbide for offshore energy island

Abstract

The invention relates to the technical field of methanol preparation through oxycarbide hydrogenation, in particular to a method for preparing methanol through oxycarbide hydrogenation for an offshore energy island. The method comprises the following steps: S1, partially reducing CO2 into CO through an electrocatalytic reduction reaction to form a CO and CO2 mixed gas with a controllable carbon-oxygen ratio, and controlling the volume ratio of CO2 / (CO2 + CO) in the mixed gas to be 10-60%; and S2, reducing the mixed gas of CO and CO2 and H2 into methanol through thermocatalysis. According to the method, green hydrogen obtained through power generation and hydrogen production of renewable energy serves as a raw material of CO2 hydrogenation reaction, methanol is prepared by combining CO2 obtained through ship flue gas CO2 capture and island air CO2 capture, the method has the advantages of being high in CO2 conversion rate, high in methanol selectivity, small in energy consumption, long in catalyst service life and the like, the renewable energy on an offshore energy island can be effectively utilized, and the method is suitable for industrial production. And ship carbon emission reduction and CO2 resource utilization are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogenation of carbon oxides to methanol, and particularly to a method for hydrogenation of carbon oxides to methanol for an offshore energy island. Background Art

[0002] Renewable energy sources such as solar energy, wind energy, and ocean energy are huge in reserves, widely distributed, and easy to obtain on islands. For this reason, in recent years, offshore energy islands integrating multiple renewable energy sources have received extensive attention. However, transmitting the electricity obtained from renewable energy on offshore energy islands to the inland through cables results in significant energy losses and high costs. How to efficiently convert the renewable energy of offshore energy islands into liquid fuels that are easy to store and transport is a major problem currently faced. CO 2 Hydrogenation to methanol can effectively utilize the green hydrogen produced from renewable energy on offshore energy islands, and combine the CO captured from ship flue gas and air capture on the island 2 to achieve the conversion and storage of renewable energy, carbon dioxide emission reduction and resource utilization, which is a potential CO 2 resource utilization route. The product methanol is an important basic raw material and fuel in the modern chemical and energy industrial structures.

[0003] However, there are still certain problems in the current technical route for hydrogenation of carbon dioxide to methanol. The single-pass conversion rate of traditional one-step CO 2 thermal catalytic methanol production is relatively low, and due to side reactions such as reverse water-gas shift and CO 2 methanation, the selectivity of methanol is poor, and the presence of by-product H 2 O easily leads to catalyst deactivation. To address the above problems, the invention patent CN112194566 discloses a device and process for hydrogenation of carbon dioxide to methanol, with the reactants being CO 2 , CO and H 2 , and using a flash tank to recycle the unreacted CO 2 , CO, H 2 . The invention patent CN114315514 discloses a method for hydrogenation of CO 2 to methanol with two reactors in series. CO 2 and H 2 are first partially converted to methanol in the first reactor, and then the unreacted CO 2 , H 2 and the generated CO in the first reactor are introduced into the second reactor for further reaction, and a recycle compressor is arranged to further process the still unreacted CO 2 , H 2 and CO. The invention patent CN105622344 discloses a "two-step method" CO that includes a reverse water-gas shift reaction and a methanol synthesis reaction2 A process for producing methanol, however, the so-called two-step reaction is actually carried out in the same reactor, and since the reverse water-gas shift reaction requires a lower pressure and a higher reaction temperature, it will lead to a lower CO 2 conversion rate and CO selectivity in the reverse water-gas shift reaction when this method is used. The above method and process are restricted by the lower single-pass CO 2 conversion rate and methanol selectivity, and both use methods such as multiple reflux and circulation to improve the conversion rate and selectivity, so it will lead to a significant increase in the energy consumption of the CO 2 hydrogenation process to produce methanol; in addition, the above methods do not consider the influence of the by-product H 2 O on the catalyst life; moreover, these processes do not clearly define the sources of CO 2 and H 2 , so they are not suitable for offshore energy islands. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for hydrogenating carbon oxides to produce methanol for an offshore energy island. This method uses green hydrogen obtained by electrolyzing renewable energy to generate hydrogen as the raw material for the CO 2 hydrogenation reaction, combines the CO 2 captured from ship flue gas and the CO 2 captured from island air to produce methanol. This method has the characteristics of high CO 2 conversion rate, high methanol selectivity, low energy consumption, long catalyst service life, etc., and can effectively utilize the renewable energy on the offshore energy island, which is beneficial to ship carbon emission reduction and CO 2 resource utilization. 2

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A method for hydrogenating carbon oxides to produce methanol for an offshore energy island, which includes the following steps:

[0007] S1. Partially reduce CO 2 to CO through an electrocatalytic reduction reaction to form a CO and CO 2 mixed gas with a controllable carbon-oxygen ratio, and control the volume ratio of CO 2 / (CO 2 +CO) to be 10%-60%;

[0008] S2. Catalytically reduce the CO and CO 2 mixed gas with H 2 to methanol through thermal catalysis;

[0009] The carbon oxide hydrogenation to methanol equipment based on this method includes realizing CO and CO 2 ​The carbon-oxygen ratio regulation module for mixed gas generation and the carbon oxide hydrogenation to methanol module for preparing methanol by thermal catalytic reduction

[0010] The carbon-oxygen ratio regulation module includes a carbon dioxide feed tank, a carbon dioxide reduction unit, and a carbon oxide storage tank connected in sequence; the captured CO 2 is transported to the carbon dioxide reduction unit through the carbon dioxide feed tank for electrocatalytic reduction, and CO 2 is partially converted to CO. The CO and CO with the regulated carbon-oxygen ratio obtained 2 The carbon oxide mixed gas is stored in the carbon oxide storage tank;

[0011] The carbon oxide hydrogenation to methanol module includes: a hydrogen feed tank, a gas mixer, a carbon oxide thermal catalytic reduction unit, a distillation column, and a methanol storage tank; the CO and CO in the carbon oxide storage tank 2 The mixed gas and H in the hydrogen feed tank 2 After mixing, pressurizing, and preheating in the gas mixer, it enters the carbon oxide thermal catalytic reduction unit to undergo a thermal catalytic reduction reaction to produce methanol. The methanol is separated, purified by the distillation column, and stored in the methanol storage tank.

[0012] Based on the regulation of the carbon-oxygen ratio of the raw material gas, the present invention efficiently converts carbon dioxide into methanol. The key point lies in the control of the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas of S1. This method effectively utilizes the renewable energy and green hydrogen obtained from the offshore energy island, combines the carbon dioxide obtained by ship carbon capture and air carbon capture, and realizes the efficient chemical conversion and utilization of carbon dioxide, contributing to carbon emission reduction.

[0013] Preferably, the CO 2 is sourced from ship flue gas CO 2 capture and energy island air CO 2 capture; the H 2 is sourced from hydrogen production by electrolyzing water from renewable energy on the energy island.

[0014] Preferably, the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas of S1 is 10% - 30%. More preferably, it is 15% - 25%, and the optimal volume ratio is 20%. In the present invention, the volume ratio of CO 2 in the mixed gas is controlled by controlling the flow rate of CO 2 introduced into the system and the magnitude of the current. 2 +CO)

[0015] Preferably, when electrocatalytic reduction is carried out in the carbon dioxide reduction unit, the CO 2The flow rate is in the range of 25 sccm to 60 sccm, and the volume ratio of CO in the mixed gas 2 / (CO 2 +CO) can be controlled within the optimal range, and the methanol synthesis efficiency is higher. More preferably, the flow rate of the introduced CO 2 is in the range of 25 sccm to 50 sccm.

[0016] Preferably, the carbon dioxide reduction unit uses electrocatalytic reduction to partially reduce CO 2 to CO. The carbon dioxide reduction unit includes an electrolytic cell gas chamber, an electrolytic cell anode chamber, and an anolyte storage tank; after CO 2 is partially reduced to CO in the electrolytic cell gas chamber, it enters the carbon oxide storage tank, and the reaction electrolyte circulates between the electrolytic cell anode chamber and the anolyte storage tank;

[0017] In the electrolytic cell, it includes an anode working electrode and a cathode working electrode. The cathode working electrode for partially converting CO 2 to CO uses a gas diffusion electrode. The gas diffusion electrode is composed of a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO 2 reduction catalyst and a gas diffusion layer. The material of the gas diffusion layer is hydrophobic carbon paper or a hydrophobic / oil-repellent PTFE filter membrane to provide a catalyst loading substrate;

[0018] The carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO 2 reduction catalyst is prepared by the following method:

[0019] S1. The carbon nanotubes are heated at a temperature of 400 - 500 °C for 0.5 h - 1.5 h, cooled to room temperature, pickled for purification, washed, and freeze-dried to remove impurities contained in the carbon nanotubes;

[0020] S2. The carbon nanotubes pretreated in S1 are heated in a mixed solution of concentrated sulfuric acid with a mass concentration of 96 - 98%, sodium nitrate, and potassium permanganate to oxidize the carbon nanotubes to introduce hydroxyl groups, washed, and freeze-dried;

[0021] The oxidation treatment temperature is not higher than 45 °C; S3. The oxidized carbon nanotubes obtained in S2 are ultrasonically treated in a solvent DMF environment to load the molecular catalyst, washed, and freeze-dried;

[0022] The molecular catalyst is cobalt phthalocyanine (CoPc) or nickel phthalocyanine;

[0023] S4. The carbon nanotubes loaded with the molecular catalyst in S3 are hydrophobically modified with silane in an aqueous silane solution, heated to 45 °C - 120 °C and maintained for 2 h - 4 h, centrifuged and washed to remove unreacted reagents, and freeze-dried to obtain the carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO 2Reduction catalyst;

[0024] Preparation of aqueous silane solution: the silane content is 1 wt% - 10 wt%, the solvent is a mixture of ethanol and water with a mass ratio of 1 - 2:1, and after mixing the silane with the solvent, hydrolysis is carried out for 1 - 6 h.

[0025] Preferably, the effective working area of the gas diffusion electrode is 1 - 5 m 2 , and a large area is adopted to meet the high CO production demand.

[0026] Preferably, the carbon oxide thermocatalytic reduction unit mainly comprises a gas-solid two-phase reactor, and the reactor is a fixed-bed reactor, a fluidized-bed reactor or a slurry-bed reactor, preferably a fixed-bed reactor;

[0027] The methanol synthesis catalyst used in the gas-solid two-phase reactor of the carbon oxide thermocatalytic reduction unit is selected from Cu-ZnO-Al 2 O 3 , Cu-ZnO-ZrO 2 , Cu-ZnO-Al 2 O 3 -TiO 2 and other copper-based catalysts, preferably Cu-ZnO-Al 2 O 3 -TiO 2 catalyst. A shaped bulk catalyst is used to meet the high methanol production demand, and its particle size is

[0028] The reaction conditions of the reactor used in the carbon oxide thermocatalytic reduction unit are: the reaction pressure is 1 - 10 MPa, the reaction temperature is 180 °C - 400 °C, and the space velocity is 1000 - 20000 h -1 , and the carbon-hydrogen molar ratio of the CO, CO 2 mixed gas and H 2 is 1:2 - 1:8.

[0029] Preferably, the electrolytic cell is a flow electrolytic cell or a membrane electrode electrolytic cell, preferably a membrane electrode electrolytic cell. When using a membrane electrode electrolytic cell, there is no cathode electrolyte, and the catalytic layer of the gas diffusion electrode is directly in contact with the ion exchange membrane. The anode catalyst of the electrolytic cell uses a titanium-based metal oxide coating electrode with an iridium oxide / ruthenium oxide coating. The electrolytic cell has multiple electrolytic compartments, the number is between 10 and 30, and the number of electrolytic stacks built is between 20 and 40. The current density range during the operation of the electrolytic stack is 100 - 2000 mA / cm 2 , the annual working time range is 2500 - 3500 h, and the average CO Faraday efficiency range during the operation is 85% - 90%.

[0030] Preferably, the electrolyte in the electrolytic cell is an aqueous solution of potassium bicarbonate with a concentration of 0.1 to 1 M.

[0031] Preparation method of carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO 2 reduction catalyst:

[0032] Preferably, the mass ratio of oxidized carbon nanotubes to silane is 15 to 25:1. When the silane is selected from 1H,1H,2H,2H-perfluorodecyltriethoxysilane, the optimal mass ratio of oxidized carbon nanotubes to silane is 20:1.

[0033] In the present invention, the carbon nanotubes can be single-walled carbon nanotubes or multi-walled carbon nanotubes. Single-walled carbon nanotubes (SWCNTs) are formed by curling a single layer of graphene; multi-walled carbon nanotubes (MWCNTs) are formed by concentrically curling multiple layers of graphene, and no specific limitation is made here.

[0034] Preferably, the pickling step S1 is to heat the carbon nanotubes in a hydrochloric acid solution with a concentration of 4 to 8 mol / L at 130 to 150 °C for 2 to 3 h. Pickling is to remove possible metal impurities or other residues in the carbon nanotubes, and pickling can effectively improve the purity and quality of the carbon nanotubes.

[0035] Preferably, the reaction temperature for oxidizing the carbon nanotubes to introduce hydroxyl groups in S2 is 40 to 45 °C.

[0036] Preferably, the silane includes one or more of 1H,1H,2H,2H-perfluorodecyltriethoxysilane, 1H,1H,2H,2H-perfluorododecyltrichlorosilane, (3,3,3-trifluoropropyl)trimethoxysilane, 1-(trimethylsilyl)heptafluoropropane, 3,3,3-trifluoropropylmethyldimethoxysilane, propyltrimethoxysilane or cetyltrimethoxysilane. Preferably, it is 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

[0037] Preferably, in S4, it is heated at 40 to 50 °C for 2 to 3 h, maintained at 70 to 80 °C for 10 to 20 min, and heated to boiling and maintained for 20 to 40 min in sequence to promote the full grafting of silanol groups. The optimal conditions are to heat at 48 °C for 2.5 h, maintain at 75 °C for 15 min, and heat to boiling and maintain for 30 min.

[0038] Preferably, the process of introducing hydroxyl groups by oxidation treatment in S2 is as follows: The carbon nanotubes obtained by purification pretreatment are stirred overnight at room temperature in concentrated sulfuric acid with a mass concentration of 96-98%; when the above solution is heated to 40°C-45°C, sodium nitrate is added; while maintaining the reaction temperature below 45°C, potassium permanganate is slowly added; the dosage ratio of carbon nanotubes: 96-98% concentrated sulfuric acid: sodium nitrate: potassium permanganate is 1 g: 20 ml-23 ml: 280 mg-420 mg: 0.8 g-1.2 g; then continue to stir at 40°C-44°C, intermittently supplement an appropriate amount of water, stop heating after the reaction is sufficient, and add an appropriate amount of water and hydrogen peroxide to the system to end the reaction. The dosage ratio of carbon nanotubes: 96-98% concentrated sulfuric acid: sodium nitrate: potassium permanganate is preferably 1 g: 20 ml-23 ml: 350 mg: 1 g. According to the inventor's multiple experiments, it is found that the oxidation degree of carbon nanotubes will affect the amount of modified silane. The dosage ratio of carbon nanotubes, 96-98% concentrated sulfuric acid, sodium nitrate, and potassium permanganate is very crucial. Enhancing the oxidation degree can introduce more hydroxyl groups on the surface of carbon nanotubes, thereby grafting more silane groups and improving the hydrophobicity of silane-modified carbon nanotubes; however, excessive oxidation will damage the graphite structure of carbon nanotubes, reduce their conductivity and the loading amount of molecular catalysts, thereby affecting the catalytic performance.

[0039] Preparation of the cathode working electrode:

[0040] Preferably, for the preparation of the cathode working electrode: Catalyst ink is prepared with Nafion ionomer, and the dosage of Nafion ionomer is 10% ± 2% of the mass of the carbon fluoride chain-modified carbon-based hydrophobic electrocatalytic CO 2 reduction catalyst. After the obtained catalyst ink is ultrasonically dispersed, the catalyst ink is loaded on the gas diffusion layer until the loading amount of the catalyst reaches 1-3 mg / cm 2 , to obtain a cathode working electrode for the partial conversion of CO 2 to CO.

[0041] A carbon oxide hydrogenation to methanol device based on the method of the present invention. The carbon oxide hydrogenation to methanol device includes a carbon-oxygen ratio regulation module for realizing the generation of a CO and CO 2 mixed gas and a carbon oxide hydrogenation to methanol module for thermally catalytic reduction to prepare methanol. The carbon-oxygen ratio regulation module includes a carbon dioxide feed tank, a carbon dioxide reduction unit, and a carbon oxide storage tank connected in sequence; the captured CO 2 is transported to the carbon dioxide reduction unit through the carbon dioxide feed tank for electrocatalytic reduction, and CO 2 is partially converted to CO. The CO and CO after the carbon-oxygen ratio is regulated 2The carbon oxide mixture is stored in a carbon oxide storage tank; the carbon oxide hydrogenation to methanol module includes: a hydrogen feed tank, a gas mixer, a carbon oxide thermal catalytic reduction unit, a distillation column, and a methanol storage tank; the CO and CO in the carbon oxide storage tank 2 in the mixed gas and the H in the hydrogen feed tank 2 After mixing, pressurizing, and preheating in the gas mixer, it enters the carbon oxide thermal catalytic reduction unit, where a thermal catalytic reduction reaction occurs to produce methanol. The methanol is separated, purified by the distillation column, and then stored in the methanol storage tank.

[0042] Preferably, the carbon dioxide reduction unit uses electrocatalytic reduction to partially reduce CO 2 to CO. The carbon dioxide reduction unit includes an electrolytic cell gas chamber, an electrolytic cell anode chamber, and an anolyte storage tank; CO 2 After being partially reduced to CO in the electrolytic cell gas chamber, it enters the carbon oxide storage tank, and the reaction electrolyte circulates between the electrolytic cell anode chamber and the anolyte storage tank; in the electrolytic cell, it includes an anode working electrode and a cathode working electrode. CO 2 The cathode working electrode for partially converting to CO uses a gas diffusion electrode, and the gas diffusion electrode is composed of a carbon fluoride chain-modified carbon-based hydrophobic electrocatalytic CO 2 reduction catalyst and a gas diffusion layer. The material of the gas diffusion layer is hydrophobic carbon paper or a hydrophobic / oil-repellent PTFE filter membrane to provide a catalyst loading substrate.

[0043] The beneficial effects of the present invention are:

[0044] 1) The present invention makes full use of abundant renewable energy sources such as solar energy, wind energy, and ocean energy on the offshore energy island as the main energy sources for processes such as electrolyzing water to produce hydrogen and CO 2 reduction. At the same time, it couples the ship's CO 2 capture and the capture of air CO on the offshore energy island 2 to achieve the resource utilization of CO 2 conversion to methanol, so as to meet the energy-saving and carbon-reduction requirements of the island and the ship;

[0045] 2) The present invention uses a carbon fluoride chain-modified carbon-based hydrophobic electrocatalytic CO 2 reduction catalyst to electrocatalytically reduce CO 2 partially to CO, improving the CO 2 conversion rate and stability. Compared with conventional catalysts, it can achieve a CO selectivity close to 100% at a certain current density, and can stably operate at a higher current density to easily obtain a CO and CO 2 mixed gas with a controllable carbon-oxygen ratio, and use it as a raw material for carbon oxide hydrogenation to methanol;

[0046] 3) The coupling system proposed by the present invention has the characteristics of high single-pass conversion rate of CO and high methanol selectivity in the absence of external CO input, reducing the number of material circulation times. Compared with the traditional CO hydrogenation method for producing methanol, it can effectively reduce energy consumption. The energy consumption for producing methanol by the direct hydrogenation route of carbon dioxide is 39.7 GJ / t methanol, while the energy consumption for producing methanol by this route is 37.1 GJ / t methanol. 2 4) The carbon dioxide reduction device in the present invention can improve the carbon dioxide conversion rate and effectively reduce the generation of common by-product H₂O in the process of one-step hydrogenation of carbon dioxide to methanol, inhibiting the catalyst deactivation phenomenon caused by H₂O and improving the service life of the catalyst. 2 5) The reaction conditions required for the method of converting carbon dioxide to methanol proposed by the present invention are mild. Compared with the traditional CO hydrogenation method for producing methanol, the reaction pressure and temperature are lower, which can effectively reduce energy consumption.

[0047] 4) The carbon dioxide reduction device in the present invention can increase the carbon dioxide conversion rate and effectively reduce the formation of the common by-product H₂O in the process of one-step hydrogenation of carbon dioxide to methanol, inhibiting the catalyst deactivation phenomenon caused by H₂O and increasing the service life of the catalyst. 2 O, inhibiting the catalyst deactivation phenomenon caused by H 2 O and increasing the service life of the catalyst.

[0048] 5) The reaction conditions required for the method of converting carbon dioxide to methanol proposed by the present invention are mild. Compared with the traditional CO 2 hydrogenation method for producing methanol, the reaction pressure and temperature are lower, which can effectively reduce energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is the reaction flow chart of carbon dioxide conversion to methanol for an offshore energy island, where the label descriptions are as follows:

[0050] Carbon dioxide feed tank 1, carbon dioxide reduction unit 2, carbon oxide storage tank 3, hydrogen feed tank 4, gas mixer 5, carbon oxide thermal catalytic reduction unit 6, distillation column 7, methanol storage tank 8, methanol separator 9, crude methanol flash evaporator 10;

[0051] Figure 2 is the structural schematic diagram of the carbon dioxide reduction unit, where the bracket descriptions are as follows: electrolytic cell gas chamber 11, electrolytic cell anode chamber 12, anode electrolyte storage tank 13;

[0052] Figure 3 is the graph of the electrolytic cell voltage change with time during the electrocatalytic reduction of carbon dioxide to carbon monoxide in Application Example 1;

[0053] Figure 4 is the test result of the electrocatalytic carbon dioxide reduction stability in Application Example 1;

[0054] Figure 5 is the graph of the mixed gas ratio change with the carbon dioxide flow rate after electrocatalytic reduction of carbon dioxide;

[0055] Figure 6 is the influence of the catalytic effect of hydrogenation of carbon dioxide to methanol with different CO / CO 2 ratios;

[0056] Figure 7SEM image of carbon nanotubes after oxidation;

[0057] Figure 8 SEM image of carbon nanotubes loaded with molecular catalyst and hydrophobically modified;

[0058] Figure 9 Catalytic performance of carbon nanotube molecular catalysts without and with hydrophobic modification at different current densities. Detailed implementation manners

[0059] The technical solutions of the present invention will be further specifically described below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any formal modification and / or change made to the present invention will fall within the protection scope of the present invention.

[0060] In the present invention, unless otherwise specified, all parts and percentages are in weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0061] The reagents used in the following embodiments can be purchased from a conventional biochemical reagent store unless otherwise specified.

[0062] YLS-30T carbon paper, that is, the carbon paper substrate of the fuel cell gas diffusion layer, is commercially available.

[0063] Nafion ionomer, the aqueous solution is Nafion TM Polymer dispersant, that is, Nafion 117 solution (Maclean N831951 Nafion 117 perfluorinated resin solution, ∼5% in a mixture of lower aliphatic alcohols and water), Cas No.: 31175-20-9, is commercially available.

[0064] The anode working electrode uses a titanium-based metal oxide coated electrode, purchased from Shaanxi Youchuang Environmental Protection Technology Co., Ltd., an electrolytic water titanium electrode, which is commercially available.

[0065] 1. Synthesize methanol catalyst: The methanol synthesis catalyst in the gas-solid two-phase fixed bed reactor used in the carbon oxide thermal catalytic reduction unit is a Cu-ZnO-Al 2 O 3 -TiO 2 type copper-based catalyst. The catalyst powder is prepared by the co-precipitation method, and its typical preparation process is as follows: Take a certain amount of Cu(NO 3 ) 2 ·3H 2O, Zn(NO 3 ) 2 ·6H 2 O, Al(NO 3 ) 3 ·9H 2 O and Ti(SO 4 ) 2 were added to deionized water and stirred for 1 h to completely dissolve and mix evenly. Subsequently, an aqueous solution of Na 2 CO 3 (0.5 mol / L) was added dropwise to the mixed solution until the pH of the solution reached 8, and stirring and aging were continued at 70 °C for 2 h. After the reaction, the precipitate was filtered and washed several times, then placed in an oven at 110 °C for drying for 12 h. The dried solid was placed in a muffle furnace and calcined at 350 °C for 3 h (heating rate: 2 °C / min) to obtain Cu-ZnO-Al 2 O 3 -TiO 2 catalyst powder. The prepared catalyst powder was pressed into a shaped catalyst after tabletting.

[0066] 2. Preparation of the cathode working electrode

[0067] A preparation method of a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO 2 reduction catalyst, the specific steps are as follows:

[0068] 1. Purification of carbon nanotubes

[0069] 1 g of a commercially available carbon nanotube sample was placed in a muffle furnace, heated at 500 °C for 60 min and then the heating was stopped. After cooling to room temperature, the sample was taken out. The above carbon nanotubes were placed in a 250 ml flask and 70 ml of 6 mol / L hydrochloric acid solution was added to ensure sufficient contact between the carbon nanotubes and the hydrochloric acid solution. It was heated at 140 °C for 2 h using an oil bath and then cooled to room temperature. After centrifugal washing with ultrapure water three times, it was put into a freeze dryer for freeze-drying to obtain a purified carbon nanotube sample.

[0070] 2. Oxidation of carbon nanotubes

[0071] Put 1 g of purified carbon nanotubes into a 250 ml round-bottom flask, add 23 ml of concentrated sulfuric acid (mass concentration about 98%), and stir overnight at room temperature; transfer the above solution to a water bath and heat it. When the temperature rises to 40 °C, add 350 mg of sodium nitrate; slowly add 1 g of potassium permanganate while keeping the reaction temperature below 45 °C; continue to stir the solution at 40 °C for 30 min; then add 3 ml of water to the flask, add another 3 ml of water after 5 min. After another 5 min, add 40 ml of water; after 15 min, remove the flask from the water bath, add 140 ml of water and 10 ml of hydrogen peroxide with a mass concentration of 30% to end the reaction; wash the oxidized carbon nanotubes by repeatedly using a HCl solution with a mass concentration of 5% and water, and then perform freeze-drying to obtain the oxidized carbon nanotubes.

[0072] 3. Loading of molecular catalyst

[0073] Ultrasonically disperse 30 mg of oxidized carbon nanotubes in 20 ml of DMF for 1 h using an ultrasonic dispersion device with a power of 1800 W to obtain a CNT suspension.

[0074] Ultrasonically disperse 3 mg of CoPc in another 10 ml of DMF, then add it to the above CNT suspension, further ultrasonically disperse for 1 h and stir at room temperature for 24 h. The obtained solid is separated by centrifugation and centrifugally washed with DMF, ethanol and water, and freeze-dried to obtain CO 2 Reduced catalyst CoPc MDE-O.

[0075] 4. Hydrophobic modification of carbon nanotubes

[0076] Take 1H,1H,2H,2H-perfluorodecyltriethoxysilane as an example for the hydrophobic modification of carbon nanotubes.

[0077] Prepare a mixed solution of ethanol and water, in which the mass ratio of ethanol to water is 1.5:1; add the 1H,1H,2H,2H-perfluorodecyltriethoxysilane solution to the above ethanol solution, the concentration of 1H,1H,2H,2H-perfluorodecyltriethoxysilane is 3 wt%, and stir at room temperature for 2 h to promote the hydrolysis of 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

[0078] CoPc MDE-O was added to the hydrolyzed 1H,1H,2H,2H-perfluorodecyltriethoxysilane solution, where the mass ratio of CoPc MDE-O to 1H,1H,2H,2H-perfluorodecyltriethoxysilane was 20:1, and it was stirred for 2.5 h under a water bath at 48 °C; the suspension of CoPc MDE-O and 1H,1H,2H,2H-perfluorodecyltriethoxysilane was heated to 75 °C and maintained for 15 min to graft 1H,1H,2H,2H-perfluorodecyltriethoxysilane onto the surface of CoPc MDE-O, and the grafted CoPc MDE-O was heated to boiling and maintained for 30 min to promote further grafting of silanol groups. The treated CoPc MDE-O was centrifugally washed three times in an ethanol solution to remove the unreacted 1H,1H,2H,2H-perfluorodecyltriethoxysilane reagent and then freeze-dried to obtain the final product CoPc MDE-1.0Si-1.

[0079] The SEM image of the oxidized carbon nanotubes obtained in Step 2 is shown in Figure 7 , and the SEM image of the carbon nanotubes loaded with molecular catalysts and hydrophobically modified is shown in Figure 8 . Referring to Figure 7 As shown, the diameter of the oxidized carbon nanotubes prepared in this example did not change significantly, and no obvious structural damage or deformation was observed under the electron microscope, and it was able to maintain its original structural characteristics and morphology, proving that the carbon nanotubes maintained their structural stability during the oxidation process. Referring to Figure 8 As shown, the hydrophobically modified carbon nanotubes prepared in this example still maintained their original morphology despite the silane modification, were evenly arranged on the carbon paper surface, and there were no obvious defects in the overall structure, indicating that the silane grafting process did not affect the structural characteristics of the carbon nanotubes.

[0080] Test Example 1

[0081] Preparation of CoPc MDE catalyst (comparative example): Place 1 g of a commercially available carbon nanotube sample in a muffle furnace, heat it at 500 °C for 60 min, then stop heating, and take out the sample after cooling to room temperature. Place the above carbon nanotubes in a 250 ml flask and add 70 ml of 6 mol / L hydrochloric acid solution to ensure full contact between the carbon nanotubes and the hydrochloric acid solution. Heat it at 140 °C for 2 h using an oil bath, then cool to room temperature, wash it three times by centrifugation with ultrapure water, and put it into a freeze dryer to obtain a purified carbon nanotube sample after freeze-drying. Ultrasonically disperse 30 mg of the obtained carbon nanotubes (without oxidation treatment) in 20 ml of DMF for 1 h using an ultrasonic dispersion device with a power of 1800 W to obtain a CNT suspension. Ultrasonically disperse 3 mg of CoPc in another 10 ml of DMF, then add it to the above CNT suspension, further ultrasonically disperse for 1 h and stir at room temperature for 24 h. The obtained solid is separated by centrifugation and centrifugally washed with DMF, ethanol, and water, and then freeze-dried to obtain the CO 2 reduced catalyst CoPc MDE.

[0082] Prepare catalyst inks from the prepared CoPc MDE-1.0Si-1 and CoPc MDE and further prepare a working electrode with a working area of 1 cm 2 . In 1 M KHCO 3 solution, test the catalytic performance of the two catalytic electrodes of CoPc MDE-1.0Si-1 and CoPcMDE at different current densities. The specific steps are as follows:

[0083] S1. Prepare the catalyst ink

[0084] The preparation method of CoPc MDE catalyst ink is as follows: Weigh 8 mg of CoPc MDE catalyst powder and disperse it in 3.6 ml of isopropanol, and then add 0.8 mg of Nafion ionomer (10 wt% of the catalyst dosage, added in the form of Nafion TM polymer dispersant);

[0085] The preparation method of CoPc MDE-1.0Si-1 catalyst ink is as follows: Weigh 8 mg of CoPc MDE-1.0Si-1 catalyst powder and disperse it in 3.6 ml of isopropanol, and then add 0.8 mg of Nafion ionomer (10 wt% of the catalyst dosage, added in the form of Nafion TM polymer dispersant);

[0086] S2. Prepare the working electrode

[0087] After the catalyst ink prepared in S1 is dispersed under high-power ultrasound for 1 h, load the catalyst ink on YLS-30T carbon paper until the catalyst loading reaches 1 mg / cm2 Among them, the loading method can be the drop coating method or the spraying method. In this embodiment, the drop coating method is adopted; a heating table at 40 °C is used to heat the YLS-30T carbon paper to promote the volatilization of isopropanol during the electrode preparation process.

[0088] The test results of the catalytic performance of carbon nanotube molecular catalysts without hydrophobic modification and with hydrophobic modification at different current densities are as Figure 9 shown. CoPc MDE-1.0Si-1 exhibits excellent catalytic performance at each current density, and the Faraday efficiency of CO always remains above 98%; in contrast, due to the difficulty of effectively maintaining the hydrophobicity of the electrode, CoPc MDE can achieve a CO Faraday efficiency of more than 95% at current densities of 150 and 200 mA / cm 2 However, as the current density gradually increases from 250 mA / cm 2 to 2 350 mA / cm, its Faraday efficiency gradually decreases to 88%.

[0089] In the following tests, the cathode working electrode prepared with the CoPc MDE-1.0Si-1 catalyst of this embodiment is used.

[0090] The core of the present invention lies in providing a method for hydrogenating carbon oxides to methanol for an offshore energy island, which converts carbon dioxide into methanol by regulating the carbon-oxygen ratio of the raw material gas. Specifically, it includes: S1. Partially reducing CO 2 to CO through an electrocatalytic reduction reaction to form a CO, CO 2 mixed gas with a controllable carbon-oxygen ratio, and controlling the volume ratio of CO 2 / (CO 2 +CO) to be 10% - 60%; S2. Thermally catalyzing the reduction of the CO, CO 2 mixed gas and H 2 to methanol.

[0091] The carbon oxide hydrogenation to methanol equipment based on this method includes a carbon-oxygen ratio regulation module and a carbon oxide hydrogenation to methanol module, and the structural schematic diagrams are as Figure 1 and Figure 2 shown.

[0092] The carbon-oxygen ratio regulation module includes a carbon dioxide feed tank 1, a carbon dioxide reduction unit 2, and a carbon oxide storage tank 3 connected in sequence. Among them, the carbon dioxide from ship flue gas capture and energy island air capture is stored in the carbon dioxide feed tank. The captured CO 2 is transported to the carbon dioxide reduction unit through the carbon dioxide feed tank for electrocatalytic reduction, and CO 2 is partially converted to CO, and the obtained CO, CO 2The carbon oxide mixture is stored in the carbon oxide storage tank 3.

[0093] The carbon oxide hydrogenation to methanol module includes a hydrogen feed tank 4, a gas mixer 5, a carbon oxide thermal catalytic reduction unit 6, a distillation column 7, and a methanol storage tank 8. The hydrogen in the hydrogen feed tank is sourced from hydrogen production by electrolyzing water with renewable energy on the energy island. The CO and CO 2 in the carbon oxide storage tank 3 2 mixed gas and the H 2 in the hydrogen feed tank 4

[0094] After being mixed, pressurized, and preheated in the gas mixer 5, it enters the carbon oxide thermal catalytic reduction unit 6, where a thermal catalytic reduction reaction occurs to produce methanol. The crude methanol is separated and purified by the distillation column 7 to obtain refined methanol and stored in the methanol storage tank 8. The H 2 is sourced from hydrogen production by electrolyzing water with renewable energy on the energy island. 2 The carbon dioxide reduction unit 2 partially reduces CO 2 to CO by electrocatalytic reduction. The carbon dioxide reduction unit 2 includes an electrolytic cell gas chamber 11, an electrolytic cell anode chamber 12, and an anolyte storage tank 13. Among them, carbon dioxide is partially reduced to carbon monoxide in the electrolytic cell gas chamber and then enters the carbon oxide storage tank 3, and the reaction electrolyte circulates between the electrolytic cell anode chamber 12 and the anolyte storage tank 13. In the electrolytic cell, it includes an anode working electrode and a cathode working electrode. The cathode working electrode for partially converting CO

[0095] to CO uses a gas diffusion electrode. The gas diffusion electrode is composed of a carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO

[0096] reduction catalyst and a gas diffusion layer. The material of the gas diffusion layer is hydrophobic carbon paper or a hydrophobic / oil-repellent PTFE filter membrane to provide a catalyst loading substrate. 2 / (CO 2 +CO) has a volume ratio of 10% - 30%. More preferably, it is 15% - 25%, and the optimal volume ratio is 20%. In the present invention, the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas is controlled by controlling the flow rate of CO 2 introduced into the system and the magnitude of the current.

[0097] As a preferred implementation, the electrolyte in the electrolytic cell is a 0.1 - 1M aqueous potassium bicarbonate solution. In the following examples, the electrolyte is a 0.5M aqueous potassium bicarbonate solution.

[0098] Test Example: CO Introduced into the System 2 Effect of Flow Rate on the Volume Ratio of CO in the Mixed Gas 2 / (CO 2 +CO)

[0099] In the present invention, by controlling the flow rate of CO introduced into the system 2 and the magnitude of the current, the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas is controlled. The effective working area of the cathode working electrode is 25 cm 2 ; under the condition that the current density is 200 mA / cm 2 , and the electrolytic cell voltage is 2.2 - 2.6 V, the flow rate of CO introduced into the carbon dioxide reduction unit 1 from the carbon dioxide feed tank is controlled by a flow meter within the range of 25 sccm to 300 sccm. The proportion of the gas components at the outlet of the electrolytic cell in the carbon dioxide reduction unit is detected. The result of the change in the proportion of the mixed gas obtained after electrocatalytic reduction of carbon dioxide with the change in the flow rate of carbon dioxide is as 2 shown; according to Figure 5 it can be known that when the flow rate of CO Figure 5 introduced into the carbon dioxide feed tank 1 is 50 sccm, the proportion of CO 2 in the mixed gas after the reaction is close to 20%, and the by-product H 2 is still at a relatively low level, which is most suitable for the subsequent methanol synthesis step. 2

[0100] Therefore, by controlling the flow rate of CO introduced during electrocatalytic reduction in the carbon dioxide reduction unit within the range of 25 sccm to 50 sccm, the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas can be controlled within the optimal range, and the methanol synthesis efficiency is also higher. 2

[0101] Test Example: Investigation of the Catalytic Effect of Hydrogenation of Carbon Dioxide to Methanol with Different CO / CO 2 Ratios

[0102] In the carbon oxide thermocatalytic reduction unit 6, a gas-solid two-phase fixed-bed reactor is used. In the fixed-bed reactor, the methanol synthesis catalyst of Cu-ZnO-Al 2 O 3 -TiO 2 is tested with different mixed gas ratios. The specific method is as follows: After pre-reducing with hydrogen at 300 °C for 3 h, the gas flowing through the fixed-bed reactor is switched to a mixed gas of different ratios of CO 2 / CO / H 2 and the pressure is increased to 5 MPa for performance testing. The CO in the mixed gas​​2 The proportion in carbon oxides is 0-100% respectively, H 2 The volume of is three times the volume of CO 2 The sum of twice the volume of CO gas and the total flow rate of the mixed gas remains unchanged before and after switching different proportions.

[0103] Different CO / CO 2 The influence results of the catalytic effect of carbon dioxide hydrogenation to methanol at different ratios are as follows Figure 6 As shown, according to the results, the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas is 10%-30% with better effect, and the methanol yield is 1.7-2.6g MeOH g cat -1 h -1 ; The optimal volume ratio is 20%, and the methanol yield can reach 2.6g MeOH g cat -1 h -1 .

[0104] Example 1

[0105] A method for hydrogenating carbon oxides to methanol for an offshore energy island, which converts carbon dioxide into methanol by regulating the carbon-oxygen ratio of the raw material gas. Specifically, it includes: S1. Partially reducing CO 2 to CO through an electrocatalytic reduction reaction to form a CO, CO 2 mixed gas with a controllable carbon-oxygen ratio, and controlling the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas to 20%; S2. Thermally catalyzing the CO, CO 2 mixed gas and H 2 to methanol. The carbon oxide hydrogenation to methanol equipment used includes a carbon-oxygen ratio regulation module and a carbon oxide hydrogenation to methanol module. The structural schematic diagrams are as shown in Figure 1 and Figure 2 shown, and the specific structure is as described above.

[0106] Example 2

[0107] A method for hydrogenating carbon oxides to methanol for an offshore energy island, which is the same as Example 1 in detail, except that: the volume ratio of CO 2 / (CO 2 +CO) in the mixed gas is controlled to 40%.

[0108] Comparative example Ordinary catalyst without coupling the carbon-oxygen ratio regulation module

[0109] Only using the carbon oxide hydrogenation to methanol module for thermocatalytic reduction to prepare methanol described in the present invention, the methanol synthesis catalyst is Cu-ZnO-Al 2 O 3 , commercially available (SCST-253 type low-pressure methanol synthesis catalyst from Sichuan Shutai Chemical Industry).

[0110] The comparison of the carbon conversion rate and methanol yield of the carbon oxide thermocatalytic reduction unit in the above comparative examples and Examples 1-2 is shown in Table 1. According to the results, when not combining the CO generated by the carbon dioxide reduction unit as the raw material gas for thermocatalytic reduction transposition, that is, when the proportion of CO in the carbon oxide is 100%, the carbon conversion rate and methanol yield of the ordinary methanol synthesis catalyst are lower at higher temperatures, while when coupling the CO obtained by reducing the modified gas diffusion electrode as the raw material gas, higher carbon conversion rate and methanol yield are achieved at lower temperatures. 2 When the proportion of CO in the carbon oxide is 100%, the carbon conversion rate and methanol yield of the ordinary methanol synthesis catalyst are lower at higher temperatures, while when coupling the CO obtained by reducing the modified gas diffusion electrode as the raw material gas, higher carbon conversion rate and methanol yield are achieved at lower temperatures.

[0111] Table 1

[0112]

[0113] Application Example 1 Methanol synthesis method for converting 1000 tons of carbon dioxide to methanol Electrochemical reduction of CO 2 to produce CO, taking an annual methanol production of 1000t as an example

[0114] A method for hydrogenating carbon oxides to methanol for an offshore energy island, realized by using the aforementioned carbon oxide hydrogenation to methanol equipment, and the specific steps are as follows:

[0115] S1. Partially reduce CO 2 to CO through an electrocatalytic reduction reaction to form a CO, CO 2 mixed gas with a controllable carbon-oxygen ratio, and control the volume ratio of CO 2 / (CO 2 +CO) to be about 10%:

[0116] The catalytic electrolysis reaction is carried out at room temperature. The electrolytic cell device used is a membrane electrode electrolytic cell, using the cathode working electrode and anode working electrode described in Example 1. The effective working area of the cathode working electrode is 1m 2 ; an anion exchange membrane is used to separate the cathode and the anode. The electrolytic cell has 15 electrolysis compartments, and the number of electrolytic stacks built is 20. When the electrolytic stack works, the current density is 700mA / cm 2 , the annual working time is greater than or equal to 3000h, and the average Faraday efficiency of CO during operation is greater than or equal to 90%. The flow rate of CO 2 introduced into the electrolytic stack is 1184Nm 3 / h. Under the above working conditions, it is detected that about 90% of CO 2The single-pass conversion rate and provide CO for the carbon oxide storage tank 3 2 / (CO 2 +CO) to provide a mixed gas with a volume ratio of about 10%.

[0117] S2. Catalytically reduce the CO, CO 2 mixed gas with H 2 to methanol by thermal catalytic reduction:

[0118] The catalytic synthesis of methanol reaction is carried out at 250 °C, and a fixed-bed reactor containing 72 reaction tubes with a diameter of 50 mm is used for the synthesis of methanol from the mixed gas. The Cu-ZnO-Al 2 O 3 -TiO 2 type copper-based catalyst is loaded in the fixed-bed reactor to form a catalyst bed layer. The catalyst loading height is 600 mm, and the loading volume is 0.085 m 3 .

[0119] The raw material gas is provided by mixing the mixed gas provided by the carbon oxide storage tank and the hydrogen provided by the hydrogen feed tank in proportion in a gas mixer. The molar ratio of the raw material gas is n(CO 2 ): n(CO): n(H 2 ) = 0.1:0.9:2.1.

[0120] The raw material gas coming out of the gas mixer is preheated to the reaction temperature of 250 °C, and then fed into the fixed-bed reactor for catalytic reaction. The reaction volume space velocity is 15000 h -1 , and the reaction pressure is controlled at 5 MPa. The annual working hours of the fixed bed are greater than or equal to 7200 h. Under the above working conditions, the average carbon single-pass conversion rate is about 33%, the methanol selectivity is about 78%, and the main by-product is CO. The mixed gas after the reaction is continuously discharged at the reactor outlet, and the crude methanol obtained by condensation is separated and purified by a distillation column and then sent to the methanol storage tank 8 for storage.

[0121] The variation of the cell voltage of the electrocatalytic carbon dioxide reduction to carbon monoxide electrolyzer with time is as shown in Figure 3 . According to Figure 3 , at a current density of 200 mA / cm 2 , the electrolyzer voltage is relatively stable and the electrolyzer energy consumption is low;

[0122] The results of the electrocatalytic carbon dioxide reduction stability test are as shown in Figure 4 . According to Figure 4 , it can be seen that the performance of the gas diffusion electrode in reducing CO 2 to generate CO does not decrease significantly after running for a long time, and the stability performance is good. Application Example 2. The synthesis method for converting thousands of tons of carbon dioxide to methanol. Electrocatalytic CO 2Reductive production of CO, taking an annual methanol output of 5000 t as an example

[0123] A method for hydrogenating carbon oxides to methanol for an offshore energy island is realized by using the aforementioned carbon oxide hydrogenation to methanol equipment. The specific steps are the same as those in Application Example 1, except that:

[0124] The cathode working electrode and the anode working electrode of the membrane electrode electrolyzer are the same as those in Application Example 1, but the effective working area of the cathode working electrode is 2.5 m 2 ; The electrolyzer has 20 electrolysis compartments, and the number of electrolysis stacks built is 25. When the electrolysis stack is working, the current density is 1000 mA / cm 2 . The CO 2 flow rate into the electrolysis stack is 6044 Nm 3 / h. Under the above working conditions, about 80% of the CO 2 single-pass conversion rate can be achieved, and CO 2 / (CO 2 ) with a volume ratio of about 20% of the mixed gas is provided for the carbon oxide storage tank 3.

[0125] The catalyst for synthesizing methanol is the same as that in Application Example 1. The catalytic synthesis of methanol reaction is carried out in a fixed-bed reactor containing 275 reaction tubes with a diameter of 50 mm for the synthesis of methanol from the mixed gas. The height of the catalyst packing is 600 mm, and the packing volume is 0.324 m 3 . The raw material gas is provided after being mixed in the carbon oxide storage tank. The molar ratio of the composition of the inlet raw material gas is n(CO 2 ): n(CO): n(H 2 ) = 0.2: 0.8: 2.2, and the reaction volume space velocity is 20000 h -1 Under the above working conditions, the average single-pass conversion rate of carbon is about 40%, the methanol selectivity is 85%, and the main by-product is CO.

[0126] Electrocatalytic CO 2 reductive production of CO for the 10,000-ton methanol synthesis method from carbon dioxide conversion in Application Example 3, taking an annual methanol output of 10000 t as an example

[0127] A method for hydrogenating carbon oxides to methanol for an offshore energy island is realized by using the aforementioned carbon oxide hydrogenation to methanol equipment. The specific steps are the same as those in Application Example 1, except that:

[0128] The cathode working electrode and the anode working electrode of the membrane electrode electrolyzer are the same as those in Application Example 1, but the effective working area of the cathode working electrode is 4 m 2 , and the current density when the electrolysis stack is working is 1600 mA / cm 2 . The CO 2 flow rate into the electrolysis stack is 10315 Nm 3 / h, under the above working conditions, about 70% of CO 2 single-pass conversion rate can be achieved, and a mixed gas with a volume ratio of CO 2 / (CO 2 +CO) of about 30% is provided for the carbon oxide storage tank 3.

[0129] The catalyst for synthesizing methanol is the same as that in Application Example 1. The catalytic synthesis of methanol reaction is carried out in a fixed-bed reactor containing 630 reaction tubes with a diameter of 50 mm for synthesizing methanol from the mixed gas. The catalyst filling height is 600 mm, and the filling volume is 0.742 m 3 . The raw material gas is provided after being mixed by the carbon oxide storage tank. The composition molar ratio of the inlet raw material gas is n(CO 2 ):n(CO):n(H 2 ) = 0.3:0.7:2.3, and the reaction volume space velocity is 18000 h -1 Under the above working conditions, the average carbon single-pass conversion rate is about 32%, the methanol selectivity is about 72%, and the by-product is mainly CO. Application Example 4 Ten-thousand-ton scale carbon dioxide conversion to methanol synthesis method Electro-catalytic CO 2 reduction to CO, taking the annual methanol production of 5000 t as an example

[0130] A method for hydrogenating carbon oxides to methanol for an offshore energy island is realized by using the aforementioned carbon oxide hydrogenation to methanol equipment. The specific steps are the same as those in Application Example 1, except that:

[0131] The cathode working electrode of the membrane electrode electrolytic cell uses a nano-silver catalyst to replace the CoPc MDE-1.0Si-1 catalyst, and the anode working electrode is the same as the preparation method in Application Example 1. The effective working area of the cathode working electrode is 2.5 m 2 ; the electrolytic cell has 20 electrolysis compartments, and the number of electrolytic stacks built is 25. The current density during the operation of the electrolytic stack is 900 mA / cm 2 . The flow rate of CO 2 introduced into the electrolytic stack is 6044 Nm 3 / h, under the above working conditions, about 70% of CO 2 single-pass conversion rate can be achieved, and a mixed gas with a volume ratio of CO 2 / (CO 2 +CO) of about 30% is provided for the carbon oxide storage tank 3.

[0132] The catalyst for synthesizing methanol is the same as that in Application Example 1. The catalytic synthesis of methanol reaction is carried out in a fixed-bed reactor containing 275 reaction tubes with a diameter of 50 mm for synthesizing methanol from the mixed gas. The catalyst filling height is 600 mm, and the filling volume is 0.324 m 3 . The raw material gas is provided after being mixed by the carbon oxide storage tank. The composition molar of the inlet raw material gas is n(CO2 )): n(CO): n(H 2 ) = 0.3:0.7:2.3, and the reaction volume space velocity is 20,000 h -1 Under the above working conditions, the average single-pass carbon conversion rate is about 33%, the methanol selectivity is about 75%, and the main by-product is CO.

[0133] Application Examples 1-4 prove that the coupling of carbon dioxide reduction and thermal catalytic reduction of carbon oxides is more efficient in carbon utilization in the reaction of converting carbon dioxide to methanol, and can improve the methanol yield per unit time.

[0134] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and reference can be made to the description of the method part for the relevant parts.

[0135] The above has introduced in detail a method for hydrogenating carbon oxides to methanol for an offshore energy island provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for producing methanol by hydrogenating carbon oxides for offshore energy islands, characterized in that The method comprises the following steps: S1. Partially reduce CO2 to CO through electrocatalytic reduction reaction to form a CO / CO2 mixed gas with a controllable carbon-oxygen ratio, and control the volume ratio of CO2 / (CO2+CO) in the mixed gas to be 10%-60%; S2, reducing the CO, CO2 mixed gas and H2 into methanol through thermal catalysis; The carbon oxide hydrogenation methanol production equipment based on this method includes a carbon-oxygen ratio control module for realizing the generation of CO and CO2 mixed gas and a carbon oxide hydrogenation methanol production module for preparing methanol by thermal catalytic reduction. The carbon-oxygen ratio control module comprises a carbon dioxide feed tank (1), a carbon dioxide reduction unit (2) and a carbon oxide storage tank (3) which are connected in sequence; the captured CO2 is transported to the carbon dioxide reduction unit via the carbon dioxide feed tank for electrocatalytic reduction, and part of the CO2 is converted into CO, and the obtained CO, CO2 and carbon oxide mixed gas after the carbon-oxygen ratio is controlled is stored in the carbon oxide storage tank (3); The carbon oxide hydrogenation to methanol module comprises: a hydrogen feed tank (4), a gas mixer (5), a carbon oxide thermal catalytic reduction unit (6), a distillation tower (7) and a methanol storage tank (8); the CO and CO2 mixed gas in the carbon oxide storage tank (3) and the H2 in the hydrogen feed tank (4) are mixed, pressurized and preheated in the gas mixer (5) and then enter the carbon oxide thermal catalytic reduction unit (6), where a thermal catalytic reduction reaction occurs to generate methanol, which is separated and purified in the distillation tower (7) and then stored in the methanol storage tank (8).

2. The method for producing methanol by hydrogenation of carbon oxides for offshore energy islands according to claim 1, characterized in that: The CO2 comes from the capture of CO2 from ship flue gas and CO2 from the air on the energy island; the H2 comes from the electrolysis of water to produce hydrogen from renewable energy on the energy island.

3. The method for producing methanol by hydrogenating carbon oxides for offshore energy islands according to claim 1, characterized in that: The volume ratio of CO2 / (CO2+CO) in the mixed gas of S1 is 10%-30%.

4. The method for producing methanol by hydrogenating carbon oxides for an offshore energy island according to claim 1, characterized in that: The carbon dioxide reduction unit uses an electrocatalytic reduction method to partially reduce CO2 to CO. The carbon dioxide reduction unit comprises an electrolytic cell gas chamber (11), an electrolytic cell anode chamber (12), and an anode electrolyte storage tank (13). After CO2 is partially reduced to CO in the electrolytic cell gas chamber, it enters the carbon oxide storage tank (3), and the reaction electrolyte circulates between the electrolytic cell anode chamber (12) and the anode electrolyte storage tank (13). The electrolyzer comprises an anode working electrode and a cathode working electrode. The cathode working electrode for partially converting CO2 into CO adopts a gas diffusion electrode. The gas diffusion electrode is composed of a carbon-based hydrophobic electrocatalytic CO2 reduction catalyst modified by a carbon-fluorine chain and a gas diffusion layer. The material of the gas diffusion layer is a hydrophobic carbon paper or a hydrophobic / oleophobic PTFE filter membrane to provide a catalyst loading substrate. The carbon-fluorine chain modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst is prepared by the following method: S1, heating the carbon nanotubes at 400-500°C for 0.5-1.5h, cooling to room temperature, washing after acid washing, and freeze drying to remove impurities contained in the carbon nanotubes; S2, heating the carbon nanotubes obtained by the pretreatment in S1 in a mixed solution of concentrated sulfuric acid, sodium nitrate and potassium permanganate with a mass concentration of 96-98% to perform oxidation treatment on the carbon nanotubes to introduce hydroxyl groups, washing and freeze-drying; The oxidation treatment temperature is not higher than 45°C; S3, subjecting the oxidized carbon nanotubes obtained by the treatment in S2 to ultrasonic treatment in a DMF solvent environment to load the molecular catalyst, washing, and freeze-drying; The molecular catalyst is cobalt phthalocyanine (CoPc) or nickel phthalocyanine; S4, hydrophobically modifying the oxidized carbon nanotubes loaded with molecular catalysts in S3 by using silane in a silane aqueous solution, heating to 45°C-120°C for 2h-4h, centrifugally washing to remove unreacted reagents, and freeze-drying to obtain a carbon-fluorine chain-modified carbon-based hydrophobic electrocatalytic CO2 reduction catalyst; Preparation of silane aqueous solution: the silane content is 1wt%~10wt%, the solvent is a mixture of ethanol and water in a mass ratio of 1~2:1, and the silane and the solvent are mixed and hydrolyzed for 1~6 hours.

5. The method for producing methanol by hydrogenating carbon oxides for offshore energy islands according to claim 1, characterized in that: The carbon oxide thermal catalytic reduction unit (6) mainly comprises a gas-solid two-phase reactor, which is a fixed bed reactor, a fluidized bed reactor or a slurry bed reactor; The methanol synthesis catalyst used in the gas-solid two-phase reactor used in the carbon oxide thermal catalytic reduction unit (6) is selected from copper-based catalysts such as Cu-ZnO-Al2O3, Cu-ZnO-ZrO2, Cu-ZnO-Al2O3-TiO2, etc.; The reaction conditions of the reactor used in the carbon oxide thermal catalytic reduction unit (6) are: reaction pressure of 1-10 MPa, reaction temperature of 180°C-400°C, space velocity of 1000-20000 h -1 The carbon-hydrogen molar ratio of CO, CO2 mixed gas and H2 is 1:2-1:

8.

6. The method for producing methanol by hydrogenation of carbon oxides for offshore energy islands according to claim 4, characterized in that In the preparation method of the carbon-based hydrophobic electrocatalytic CO2 reduction catalyst modified by a carbon-fluorine chain: S1, the acid washing step is to heat the carbon nanotubes in a 4-8 mol / L hydrochloric acid solution at 130-150°C for 2h-3h; In S2, the carbon nanotubes are oxidized to introduce hydroxyl groups at a reaction temperature of 40-45° C. In S2, the oxidized carbon nanotubes are repeatedly washed with a 5% mass concentration HCl solution and water; In S4, the mixture is heated at 40-50°C for 2-3 h, maintained at 70-80°C for 10-20 min, and heated to boiling and maintained for 20-40 min to promote sufficient grafting of silanol groups; The silane includes one or more of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, 1H, 1H, 2H, 2H-perfluorododecyltrichlorosilane, (3, 3, 3-trifluoropropyl)trimethoxysilane, 1-(trimethylsilyl)heptafluoropropane, 3, 3, 3-trifluoropropylmethyldimethoxysilane, propyltrimethoxysilane or hexadecyltrimethoxysilane.

7. The method for producing methanol by hydrogenation of carbon oxides for offshore energy islands according to claim 4, characterized in that In the preparation method of the carbon-based hydrophobic electrocatalytic CO2 reduction catalyst modified by a carbon-fluorine chain: The process of introducing hydroxyl groups by oxidation treatment in S2 is: stirring the purified pretreated carbon nanotubes in 96-98% concentrated sulfuric acid at room temperature overnight; adding sodium nitrate when the solution is heated to 40°C-45°C; slowly adding potassium permanganate while keeping the reaction temperature below 45°C; Carbon nanotubes: 96~98% concentrated sulfuric acid: sodium nitrate: potassium permanganate. The usage ratio is 1g: 20ml~23ml: 280mg~420mg: 0.8g~1.2g; Then continue stirring at 40°C~44°C, add appropriate amount of water intermittently, stop heating after the reaction is sufficient, and add appropriate amount of water and hydrogen peroxide to the system to terminate the reaction.

8. The method for producing methanol by hydrogenation of carbon oxides for offshore energy islands according to claim 4, characterized in that Preparation of cathode working electrode: Catalyst ink was prepared with Nafion ionomer, the amount of Nafion ionomer used was 10%±2% of the mass of the carbon-based hydrophobic electrocatalytic CO2 reduction catalyst modified by the carbon fluorine chain, and the obtained catalyst ink was ultrasonically dispersed and then loaded on the gas diffusion layer until the catalyst loading reached 1-3 mg / cm 2 , obtaining a cathode working electrode for partial conversion of CO2 into CO.

9. A carbon oxide hydrogenation to methanol device based on the carbon oxide hydrogenation to methanol method for offshore energy islands according to claim 1, characterized in that The carbon oxide hydrogenation methanol production equipment comprises a carbon-oxygen ratio control module for realizing the generation of CO and CO2 mixed gas and a carbon oxide hydrogenation methanol production module for preparing methanol by thermal catalytic reduction. The carbon-oxygen ratio control module comprises a carbon dioxide feed tank (1), a carbon dioxide reduction unit (2) and a carbon oxide storage tank (3) which are connected in sequence; the captured CO2 is transported to the carbon dioxide reduction unit via the carbon dioxide feed tank for electrocatalytic reduction, and part of the CO2 is converted into CO, and the obtained CO, CO2 and carbon oxide mixed gas after the carbon-oxygen ratio is controlled is stored in the carbon oxide storage tank (3); The carbon oxide hydrogenation to methanol module comprises: a hydrogen feed tank (4), a gas mixer (5), a carbon oxide thermal catalytic reduction unit (6), a distillation tower (7) and a methanol storage tank (8); the CO and CO2 mixed gas in the carbon oxide storage tank (3) and the H2 in the hydrogen feed tank (4) are mixed, pressurized and preheated in the gas mixer (5) and then enter the carbon oxide thermal catalytic reduction unit (6), where a thermal catalytic reduction reaction occurs to generate methanol, which is separated and purified in the distillation tower (7) and then stored in the methanol storage tank (8).

10. The carbon oxide hydrogenation to methanol equipment according to claim 9, characterized in that: The carbon dioxide reduction unit uses an electrocatalytic reduction method to partially reduce CO2 to CO. The carbon dioxide reduction unit comprises an electrolytic cell gas chamber (11), an electrolytic cell anode chamber (12), and an anode electrolyte storage tank (13). After CO2 is partially reduced to CO in the electrolytic cell gas chamber, it enters the carbon oxide storage tank (3), and the reaction electrolyte circulates between the electrolytic cell anode chamber (12) and the anode electrolyte storage tank (13). The electrolytic cell comprises an anode working electrode and a cathode working electrode. The cathode working electrode for partially converting CO2 into CO adopts a gas diffusion electrode. The gas diffusion electrode is composed of a carbon-based hydrophobic electrocatalytic CO2 reduction catalyst modified by a carbon fluorine chain and a gas diffusion layer. The material of the gas diffusion layer is hydrophobic carbon paper or a hydrophobic / oleophobic PTFE filter membrane to provide a catalyst loading substrate.

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