Method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen

Abstract

The invention discloses a method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen, and relates to the technical field of chemical synthesis, and the method comprises the following steps: collecting industrial waste gas discharged in the production process of a lime kiln, a converter and a blast furnace coke oven of a steel mill, and carrying out pretreatment according to the gas source characteristics of the industrial waste gas to obtain pretreated waste gas; aiming at iron and steel industry tail gas with three characteristics of lime kiln waste gas, converter gas and blast furnace coke oven gas, the invention utilizes differentiated precise treatment processes, respectively adopts targeted treatment such as dust removal, oxidative conversion and tar removal, removes key impurities such as dust, carbon monoxide, tar and the like from the source, and improves the quality of iron and steel industry tail gas. Carbon monoxide is converted into carbon dioxide through subsequent treatment, the carbon dioxide amount is further increased, the problems of blockage and solvent pollution of a subsequent carbon dioxide capture system are effectively solved, stable and efficient operation of a capture unit is guaranteed, and a solid foundation is provided for continuous and reliable industrial tail gas carbon source supply.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, in particular to a method for preparing green methanol by using petrochemical tail gas carbon dioxide and green hydrogen. BACKGROUND

[0002] The demand for clean energy is increasing day by day, and green methanol, as a low-carbon fuel, has potential in energy transformation. However, the existing green methanol preparation technology has many limitations, especially in the utilization of carbon sources, reaction conditions and cost control, which seriously restricts the large-scale development of the green methanol industry. In terms of carbon source utilization, traditional green methanol preparation relies on biomass gasification or single carbon source capture. The steel industry is one of the main sources of carbon dioxide emissions in the world, and a large amount of carbon dioxide is contained in lime kiln, converter gas and blast furnace coke oven gas.

[0003] In the prior art, due to the complexity of the steel industry tail gas (including lime kiln exhaust gas, converter gas and blast furnace coke oven gas) and the presence of a large amount of dust, sulfides, nitrogen oxides, tar and carbon monoxide impurities, the traditional carbon dioxide capture and methanol synthesis system lacks effective pretreatment means for these specific impurities, resulting in easy plugging of the subsequent carbon dioxide capture system, solvent pollution, and catalyst poisoning, carbon deposition and sintering inactivation during the methanol synthesis process, thereby causing unstable operation of the entire process flow, significantly shortening the service life of the catalyst, and not meeting the methanol yield and purity standards, which seriously restricts the industrial application and economic benefits of this technical route. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a method for preparing green methanol by using petrochemical tail gas carbon dioxide and green hydrogen, which solves the problems mentioned in the background art.

[0005] To achieve the above purpose, the present application is implemented by the following technical scheme: a method for preparing green methanol by using petrochemical tail gas carbon dioxide and green hydrogen, comprising the following steps: S1, collecting industrial waste gas discharged in the production process of lime kiln, converter and blast furnace coke oven of a steel plant, pretreating the industrial waste gas according to the gas source characteristics of the industrial waste gas to obtain pretreated waste gas; S2, capturing carbon dioxide from the pretreated waste gas by using a pressure swing adsorption method or an amine absorption method to obtain crude carbon dioxide gas, and performing three-stage purification on the crude carbon dioxide gas, wherein the three-stage purification is first-stage desulfurization, second-stage denitrification and third-stage dehydration, to obtain pure carbon dioxide; S3, starting a solid oxide electrolytic cell to prepare hydrogen by electrolyzing water, and providing heating for the solid oxide electrolytic cell through a heat exchange system by using high-temperature waste gas generated by a blast furnace or a converter of a steel plant, so that the operating temperature of the solid oxide electrolytic cell is maintained at 600-800°C, and green hydrogen is obtained after completion. S4, mixing the pure carbon dioxide and the green hydrogen in a molar ratio of 1:3 or 1:4 to form a composite gas; introducing the composite gas into a multi-stage fixed bed reactor, and then adding a composite catalyst into the multi-stage fixed bed reactor, to obtain a methanol precursor after catalytic reaction; S5, discharging the methanol precursor from the multi-stage fixed bed reactor and condensing, to separate out a crude methanol liquid after condensation; then purifying the crude methanol liquid by azeotropic rectification with cyclohexane as an azeotrope agent, to obtain the green methanol.

[0006] Preferably, the gas source characteristics of the industrial waste gas are pretreated, specifically including: When the industrial waste gas is lime kiln tail gas, first passing the lime kiln tail gas through a coupled pretreatment system composed of a cyclone separator and an electrostatic precipitator in series, to reduce the dust concentration in the lime kiln tail gas to below 50 mg / m3; When the industrial waste gas is converter gas, first passing the converter gas through a selective catalytic oxidation tank filled with platinum-aluminum catalyst, to selectively oxidize carbon monoxide in the converter gas into carbon dioxide at a reaction temperature of 150-300°C; When the industrial waste gas is blast furnace coke oven gas, passing the blast furnace coke oven gas through a purifier composed of a condenser and an electric tar precipitator in series, to reduce the tar content in the blast furnace coke oven gas to below 50 mg / m3, and simultaneously remove dust.

[0007] Preferably, the crude carbon dioxide gas is subjected to three-stage purification, specifically including: First-stage desulfurization: passing the crude carbon dioxide gas through a desulfurization tower filled with zinc oxide adsorbent, to remove the total sulfur content in the crude carbon dioxide gas to , to obtain a first-stage gas; Second-stage denitrification: passing the first-stage gas after desulfurization through an adsorption tower filled with molecular sieve, to remove the nitrogen oxide content in the first-stage gas to , to obtain a second-stage gas; Third-stage dehydration: passing the second-stage gas through a drying tower filled with silica gel or the molecular sieve, to remove the moisture content in the second-stage gas to , to obtain the pure carbon dioxide.

[0008] Preferably, the multi-stage fixed bed reactor is divided into two temperature control zones: the reaction temperature of a first reaction stage of the multi-stage fixed bed reactor is 200-250°C, and the reaction temperature of a second reaction stage is 250-300°C, and the pressure of the multi-stage fixed bed reactor is .

[0009] Preferably, the composite catalyst is specifically... The composite catalyst was prepared by a co-precipitation method, and the precipitant was... The solution has a precipitation pH of 8-9, the hydrothermal aging temperature is 110-130℃, and the aging time is 10-14h.

[0010] Preferably, the carbon dioxide capture is performed using either the pressure swing adsorption (PSA) method or the amine absorption method, wherein the PSA method is preferred for the industrial waste gas from the lime kiln, and the amine absorption method is preferred for the industrial waste gas from the converter and the blast furnace / coke oven.

[0011] Preferably, the carbon dioxide capture specifically involves: When the pressure swing adsorption method is used, the adsorption pressure is: The desorption pressure is -0.08 to -0.05 MPa, and the adsorbent is 13X molecular sieve; When using the amine absorption method, a concentration of [missing information] is used. The methyldiethanolamine aqueous solution is used as the absorbent, with an absorption temperature of 40-60℃ and a regeneration temperature of 105-120℃.

[0012] Preferably, when the activity of the composite catalyst decreases to 80% of its initial activity, the composite catalyst is regenerated, specifically including: The composite catalyst with decreased activity was first purged with nitrogen gas at a temperature of 200-250°C for 2-4 hours to remove the physical adsorbates on the surface of the composite catalyst. The composite catalyst is then subjected to carbon deposition removal by burning. The composite catalyst is in an oxygen-containing environment... In the nitrogen atmosphere, with The temperature is increased to 350-400℃ at a certain rate and maintained for 4-8 hours to burn off the carbon deposits on the composite catalyst, thus completing the impurity removal process. After impurity removal, the composite catalyst is treated with a hydrogen-containing solution. The nitrogen gas is reduced at a temperature of 200-250℃ for 2-4 hours to obtain the regenerated composite catalyst.

[0013] Preferably, a pretreatment system is provided at the water inlet of the solid oxide electrolyzer to control the resistivity of the inlet water within a certain range. The medium- and high-temperature exhaust gas from the steel plant is used to preheat the incoming water to 70-90℃ through a heat exchanger.

[0014] Preferably, the current density of the solid oxide electrolytic cell is Hydrogen production power consumption The electrical energy of the solid oxide electrolyzer is generated by solar or wind power.

[0015] This invention provides a method for preparing green methanol using carbon dioxide and green hydrogen from petrochemical tail gas, which has the following beneficial effects: (1) This invention targets three types of steel industry tail gases with different characteristics: lime kiln exhaust gas, converter gas and blast furnace coke oven gas. It uses differentiated and precise treatment processes, employing targeted treatments such as dust removal, oxidation conversion and tar removal, to remove key impurities such as dust, carbon monoxide and tar from the source. Furthermore, the subsequent treatment converts carbon monoxide into carbon dioxide, further increasing the amount of carbon dioxide. This effectively avoids the problems of blockage and solvent pollution in the subsequent carbon dioxide capture system, ensuring the stable and efficient operation of the capture unit and providing a solid foundation for achieving a continuous and reliable carbon source supply for industrial tail gases.

[0016] (2) The present invention uses a composite catalyst in the methanol synthesis stage. Through structural optimization, the composite catalyst has excellent anti-poisoning ability and thermal stability. It can withstand the trace amounts of sulfur, nitrogen and other poisons that may remain in the tail gas after pretreatment, and effectively inhibit carbon deposition and sintering of active components during the reaction process. This significantly extends the service life of the composite catalyst, maintains the long-term stability of catalytic activity in the reactor, and ensures that the methanol synthesis process can continuously obtain products with high yield and high selectivity.

[0017] (3) This invention systematically integrates and optimizes multiple processes such as differentiated tail gas pretreatment, efficient carbon dioxide capture and purification, energy-saving green hydrogen preparation and stable methanol synthesis and distillation, and improves the energy efficiency of the whole process through internal energy coupling. It realizes the smooth, stable and economical operation of the whole process from complex industrial tail gas to high-purity green methanol, which greatly enhances the overall industrial feasibility and economic competitiveness of this technical route. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the steps of a method for preparing green methanol using petrochemical tail gas carbon dioxide and green hydrogen according to the present invention. Figure 2 This is a flowchart of a method for preparing green methanol using petrochemical tail gas carbon dioxide and green hydrogen according to the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Please see Figure 1This invention provides a method for preparing green methanol using carbon dioxide and green hydrogen from petrochemical tail gas. To achieve the above objective, this invention employs the following technical solution, comprising the following steps: S1. Collect industrial waste gas discharged from lime kilns, converters and blast furnaces and coke ovens in steel plants during the production process, and pre-treat the waste gas according to the gas source characteristics to obtain pre-treated waste gas. S2. The pretreated waste gas is captured by pressure swing adsorption or amine absorption to obtain crude carbon dioxide gas. The crude carbon dioxide gas is then purified in three stages: primary desulfurization, secondary denitrification and tertiary dehydration, to obtain pure carbon dioxide. S3. Start the solid oxide electrolyzer to produce hydrogen by electrolyzing water, and use the high-temperature waste gas generated by the blast furnace or converter of the steel plant to heat the solid oxide electrolyzer through a heat exchange system, so that the operating temperature of the solid oxide electrolyzer is maintained at 600-800℃, and green hydrogen is obtained after completion. S4. Pure carbon dioxide and green hydrogen are mixed in a molar ratio of 1:3 or 1:4 to form a composite gas; the composite gas is introduced into a multi-stage fixed-bed reactor, and then a composite catalyst is added to the multi-stage fixed-bed reactor. After catalytic reaction, methanol precursor is obtained. S5. The methanol precursor is discharged from the multi-stage fixed-bed reactor and condensed. After condensation, crude methanol liquid is separated. The crude methanol liquid is then purified by azeotropic distillation with cyclohexane as the azeotropic agent to obtain green methanol.

[0021] In this embodiment, in step S1, a classified collection process was established for industrial waste gases generated in different production stages of the steel plant. Lime kiln waste gas was collected through high-temperature resistant pipelines, converter gas was collected through a gas holder buffer, and blast furnace coke oven gas was stored in a gas holder after preliminary cooling. In the pretreatment stage, different pretreatment units were configured according to the characteristics of the waste gases: for lime kiln waste gas, a multi-stage dust removal process was adopted; for converter gas, a catalytic oxidation reactor was set up; and for blast furnace coke oven gas, a deep purification process was adopted. These pretreatment units can be combined and used according to the actual gas source conditions to achieve flexible pretreatment of industrial waste gases, providing a foundation for subsequent high-purity carbon dioxide capture.

[0022] The carbon dioxide capture system employs a modular design, allowing for flexible selection of pressure swing adsorption (PSA) or amine absorption processes based on the carbon dioxide concentration in the waste gas. The three-stage purification system is arranged in series, with buffer tanks and monitoring points between each stage to ensure purification efficiency. The desulfurization tower uses multi-layer zinc oxide adsorbent, the denitrification tower uses molecular sieves, and the dehydration tower operates in a dual-tower alternating mode to ensure continuous production. The solid oxide electrolysis system is interconnected with the steel plant's waste heat recovery pipeline. The solid oxide electrolysis cell uses a tubular structure, with the cathode and anode using nickel-zirconia composite material and perovskite material, respectively. Multi-stage heat exchange design is utilized to fully leverage the heat from industrial waste gas at different temperature ranges, achieving cascaded energy utilization and enhancing the adaptability of waste heat recovery. During methanol synthesis, each reaction section of the multi-stage fixed-bed reactor is equipped with an independent temperature control unit. The composite catalyst is loaded into each bed layer of a multi-stage fixed-bed reactor using a layered loading method. The loading amount of different beds can be adjusted according to the reaction progress. This enables the resource utilization of industrial waste gas from steel plants. Each 10,000 tons of green methanol consumes approximately 80,000 tons of carbon dioxide, reducing greenhouse gas emissions and aligning with the "dual carbon" target. At the same time, green hydrogen production relies on waste heat and renewable energy from steel plants, reducing hydrogen production energy consumption. Compared with traditional water electrolysis hydrogen production, energy consumption is significantly reduced. The green methanol product collected from waste gas has high purity and can be directly used as fuel or chemical raw material, with significant economic value. The entire preparation process has a more efficient and accurate green methanol production effect. At the same time, relying on the steel plant's own waste resources, it can achieve efficient resource utilization and reduce production costs, reduce waste gas emissions, and meet the requirements of carbon emission reduction and green production.

[0023] Example 2 Pretreatment is performed based on the characteristics of the industrial waste gas source. Specifically, when the industrial waste gas is lime kiln tail gas, it is first passed through a coupled pretreatment system consisting of a cyclone separator and an electrostatic precipitator connected in series to reduce the dust concentration in the lime kiln tail gas to a level that is not too high. The following steps are taken when the industrial waste gas is converter gas: First, the converter gas is passed through a selective catalytic oxidation tank equipped with a platinum-aluminum catalyst, where a catalytic reaction is performed at a reaction temperature of 150-300℃ to selectively oxidize carbon monoxide in the converter gas to carbon dioxide. Second, when the industrial waste gas is blast furnace coke oven gas, it is passed through a purifier consisting of a condenser and an electrostatic precipitator connected in series to reduce the tar content in the blast furnace coke oven gas to a minimum. The following steps are taken to remove dust at the same time.

[0024] The crude carbon dioxide gas undergoes a three-stage purification process, specifically: Stage 1 desulfurization: The crude carbon dioxide gas is passed through a desulfurization tower filled with zinc oxide adsorbent to remove the total sulfur content of the crude carbon dioxide gas. A first-order gas is obtained; Secondary denitrification: The desulfurized primary gas is passed through an adsorption tower packed with molecular sieves to remove nitrogen oxides from the primary gas. The process involves two stages: First, a secondary gas is obtained; then, a tertiary dehydration stage is performed, passing the secondary gas through a drying tower filled with silica gel or molecular sieves to remove moisture. After completion, pure carbon dioxide is obtained. When the activity of the composite catalyst decreases to 80% of its initial activity, the composite catalyst is regenerated. Specifically, the catalyst with decreased activity is first purged with nitrogen at 200-250℃ for 2-4 hours to remove physical adsorbates on the surface of the composite catalyst. Then, the composite catalyst is subjected to carbon deposition removal by burning off the carbon deposits in an oxygen-containing environment. In a nitrogen atmosphere, with The temperature is increased to 350-400℃ at a certain rate and maintained for 4-8 hours to burn off the carbon deposits on the composite catalyst, thus completing the impurity removal process. After impurity removal, the composite catalyst is treated with a hydrogen-containing solution. Nitrogen gas is reduced at a temperature of 200-250℃ for 2-4 hours to obtain the regenerated composite catalyst.

[0025] In this embodiment, during the pretreatment of exhaust gas, a coupled system of cyclone separator and electrostatic precipitator is used to address the high dust content of the lime kiln exhaust gas. The cyclone separator adopts a multi-tube structure and can handle an air volume of up to [missing information]. Electrostatic precipitators use high-frequency power supplies, which can stably control the dust concentration at a certain level. the following.

[0026] For the pretreatment of converter gas, selective catalytic oxidation employs a radial reactor design, with the following loading... Catalyst, space velocity controlled at It is also equipped with a preheating device, which uses the sensible heat of converter gas to heat the inlet gas to the reaction temperature. Through catalyst and reaction, carbon monoxide can be efficiently converted into carbon dioxide gas, while avoiding excessive oxidation to generate nitrogen oxides, thus achieving efficient utilization of waste gas.

[0027] The purification of blast furnace coke oven gas adopts a combined condensation-electrostatic precipitator process. The condenser uses a multi-stage cooling method: first, the gas is cooled to 80°C by an air cooler, then to 40°C by a water cooler, and finally to 25°C by a chilled water system. The electrostatic precipitator adopts a honeycomb structure with an electric field strength of [insert value here]. It can effectively capture submicron-sized tar droplets, thereby removing tar from exhaust gas.

[0028] During the regeneration of the composite catalyst, the regeneration unit includes a purging unit, a carbon burning unit, and a reduction unit. Each unit is controlled and switched through a program. The purging unit uses hot nitrogen circulation and is equipped with a gas heater and a circulating fan. The carbon burning unit achieves safe removal of carbon deposits by controlling the oxygen concentration and heating rate. The reduction unit uses a gas distribution device to adjust the hydrogen-nitrogen ratio.

[0029] Nitrogen purging: The nitrogen flow rate is 3-5 times the volume of the composite catalyst per hour. The purging temperature is gradually increased from room temperature to 220℃, with a heating rate of... This ensures complete desorption of physically adsorbed substances (such as methanol and unreacted gases); carbon deposit removal: the oxygen concentration in the oxygen-containing nitrogen gas is precisely controlled within... heating rate To prevent catalyst sintering due to excessively rapid heating, the carbon dioxide content in the exhaust gas is monitored in real time during the heat preservation stage. When the carbon dioxide concentration drops to a certain level... The carbon deposit removal is considered complete when the following conditions are met; reduction treatment: the hydrogen concentration in the hydrogen-containing nitrogen gas is... The reduction temperature is 230℃. During the reduction process, the activity of the composite catalyst is monitored online. When the activity recovers to more than 95% of the initial value, the reduction is stopped, and a reusable composite catalyst can be obtained.

[0030] Example 3 The multi-stage fixed-bed reactor is divided into two temperature control zones. The reaction temperature of the first reaction zone of the multi-stage fixed-bed reactor is 200-250℃, and the reaction temperature of the second reaction zone is 250-300℃. The pressure of the multi-stage fixed-bed reactor is 5-10MPa.

[0031] The composite catalyst is specifically... The composite catalyst was prepared by co-precipitation method, and the precipitant was... The solution and precipitate have a pH of 8-9, and the hydrothermal aging temperature is [temperature missing]. The aging time is 10-14 hours.

[0032] In this embodiment, the multi-stage fixed-bed reactor adopts a vertical pressure vessel design with a shell made of stainless steel composite plate material. Multiple composite catalyst beds are set inside the multi-stage fixed-bed reactor, and cooling units are set between the beds to control the reaction temperature of each stage. The multi-stage fixed-bed reactor is equipped with multi-point temperature sensors to monitor the bed temperature distribution in real time. The pressure control adopts multi-stage adjustment to ensure that the reaction pressure is stable within the set range.

[0033] The catalyst adopts a composite formulation design, with the main active components including oxides of copper, zinc and aluminum, and cerium oxide added as an auxiliary agent. The catalyst is prepared by a co-precipitation process. By controlling the pH value, temperature and aging time of the precipitation process, the crystal structure and pore characteristics of the catalyst are regulated. The formed catalyst is graded and screened to ensure uniform particle size distribution. The catalyst is loaded using dense phase conveying to ensure uniform bed packing.

[0034] The reaction temperature control adopts a multi-stage heat transfer oil circulation, with each stage having its temperature controlled independently. The heat transfer oil is equipped with a heater and a cooler, and the oil temperature can be adjusted to the required temperature according to the reaction exothermic situation. The gas distribution adopts a multi-stage orifice plate design to ensure that the reaction gas is evenly distributed in the bed cross section.

[0035] Multi-stage fixed-bed reactors with temperature zone control adapt to the different stages of the catalytic reaction (low-temperature stages favor methanol production, while high-temperature stages increase the reaction rate). Compared to single-stage reactors, carbon dioxide conversion is improved. Composite catalysts are optimized through formulation and preparation processes. The addition of [a specific ingredient] enhances the oxygen storage capacity and stability of the catalyst compared to traditional [methods / technology]. The catalyst has an extended service life, improved methanol selectivity, a simple and low-cost preparation process, and is reusable, making it suitable for large-scale industrial production and providing a stable and efficient catalytic system for green methanol production.

[0036] Example 4 Carbon dioxide capture specifically includes: when using pressure swing adsorption (PSA), the adsorption pressure is... The desorption pressure is The adsorbent is 13X molecular sieve; when using amine absorption, the concentration is... The methyldiethanolamine aqueous solution is used as the absorbent, with an absorption temperature of 40-60℃ and a regeneration temperature of 105-120℃.

[0037] A pretreatment system is installed at the inlet of the solid oxide electrolyzer to control the resistivity of the inlet water within a certain range. The medium- and high-temperature exhaust gas from the steel plant is used to preheat the incoming water to 70-90℃ through a heat exchanger.

[0038] The current density of the solid oxide electrolytic cell is Hydrogen production power consumption The electrical energy of the solid oxide electrolyzer is generated by solar or wind power.

[0039] In this embodiment, pressure swing adsorption (PSA) employs a multi-tower setup for carbon dioxide capture, with each tower packed with 13X molecular sieve. The adsorption towers utilize pressure equalization and depressurization equipment, along with vacuum pumping, to ensure the purity of the captured carbon dioxide. Pressure swing adsorption (PSA) uses a programmed valve for automatic switching, with each adsorption cycle lasting 8 minutes. Amine absorption employs a combination of a packed absorber and a plate regeneration tower. The absorber is filled with perforated metal corrugated packing, and the regeneration tower uses 20 dual-flow trays with a condenser at the top. The absorbent is... Aqueous solution, circulation volume is The amine absorption system is equipped with a liquid heat exchanger for energy recovery.

[0040] In the preparation of green hydrogen, the solid oxide electrolyzer adopts a modular design, which is composed of multiple solid oxide electrolyzers. Each solid oxide electrolyzer module has an electrolysis power of 500kW, an operating temperature of 750℃, and a steam conversion rate of 85%. The influent water pretreatment system includes a reverse osmosis unit and a mixed bed fine treatment to ensure the quality of the influent water. The preheating of the solid oxide electrolyzer utilizes medium-low temperature industrial waste gas at 200-400℃. The influent water is heated to 80℃ through a plate heat exchanger, realizing the efficient utilization of industrial waste gas resources.

[0041] The power supply uses a thyristor rectifier, is equipped with reactive power compensation and harmonic filtering devices, and monitors parameters such as voltage, current and temperature of the electrolytic cell in real time to achieve optimized operation. The entire electrolysis unit is directly connected to photovoltaic power stations and wind power plants to achieve direct green power supply.

[0042] Two carbon dioxide capture methods are adapted to different operating conditions (pressure swing adsorption is suitable for low-concentration waste gas, and amine absorption is suitable for medium- and high-concentration waste gas), with high capture rates and stable purity of captured products, meeting the quality requirements of subsequent reactions for carbon dioxide. Optimization of influent pretreatment and preheating in solid oxide electrolyzers reduces energy consumption and corrosion risks, extends the service life of solid oxide electrolyzers, and enables truly "green" preparation of green hydrogen by relying on renewable energy sources such as solar and wind power, resulting in lower hydrogen production power consumption. Combined with the utilization of waste heat from steel plants, the overall energy consumption of the process is further reduced, resulting in significant environmental benefits.

[0043] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, and the technical solutions resulting from such changes, modifications, substitutions and alterations are within the protection scope of the present invention.

Claims

1. A method for preparing green methanol using carbon dioxide and green hydrogen from petrochemical tail gas, characterized in that: Includes the following steps: S1. Collect industrial waste gas discharged from lime kiln, converter and blast furnace coke oven of steel plant during production process, and pre-treat it according to the gas source characteristics of the industrial waste gas to obtain pre-treated waste gas. S2. The pretreated waste gas is subjected to carbon dioxide capture by pressure swing adsorption or amine absorption to obtain crude carbon dioxide gas. The crude carbon dioxide gas is then purified in three stages: primary desulfurization, secondary denitrification and tertiary dehydration, to obtain pure carbon dioxide. S3. Start the solid oxide electrolyzer to produce hydrogen through water electrolysis, and use a heat exchange system to heat the solid oxide electrolyzer by using high-temperature waste gas from the blast furnace or converter of the steel plant, so as to maintain the operating temperature of the solid oxide electrolyzer at [temperature missing]. After completion, green hydrogen is obtained; S4. The pure carbon dioxide and the green hydrogen are mixed in a molar ratio of 1:3 or 1:4 to form a composite gas; the composite gas is introduced into a multi-stage fixed-bed reactor, and then a composite catalyst is added to the multi-stage fixed-bed reactor to obtain a methanol precursor after catalytic reaction. S5. The methanol precursor is discharged from the multi-stage fixed-bed reactor and condensed, and crude methanol liquid is separated after condensation; then the crude methanol liquid is purified by azeotropic distillation with cyclohexane as an azeotropic agent to obtain the green methanol.

2. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: The gas source characteristics of the industrial waste gas are pretreated, specifically as follows: When the industrial waste gas is lime kiln tail gas, it is first passed through a coupled pretreatment system consisting of a cyclone separator and an electrostatic precipitator connected in series to reduce the dust concentration in the lime kiln tail gas to a level that is not too high. the following; When the industrial waste gas is converter gas, it is first passed through a selective catalytic oxidation tank equipped with a platinum-aluminum catalyst. At the reaction temperature, a catalytic reaction is carried out to selectively oxidize carbon monoxide in the converter gas to carbon dioxide; When the industrial waste gas is blast furnace coke oven gas, it is passed through a purifier consisting of a condenser and an electrostatic precipitator connected in series to reduce the tar content in the blast furnace coke oven gas to a minimum. The following steps are taken to remove dust at the same time.

3. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: The crude carbon dioxide gas undergoes a three-stage purification process, specifically including: Primary desulfurization: The crude carbon dioxide gas is passed through a desulfurization tower filled with zinc oxide adsorbent to remove the total sulfur content of the crude carbon dioxide gas to a certain level. A first-order gas is obtained; Secondary denitrification: The desulfurized primary gas is passed through an adsorption tower packed with molecular sieves to remove nitrogen oxides from the primary gas. A secondary gas is obtained; Three-stage dehydration: The secondary gas is passed through a drying tower filled with silica gel or the molecular sieve to remove moisture from the secondary gas to a certain level. After completion, the pure carbon dioxide is obtained.

4. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: The multi-stage fixed-bed reactor is divided into two temperature control zones. The reaction temperature of the first reaction zone of the multi-stage fixed-bed reactor is 200-250℃, and the reaction temperature of the second reaction zone is 250-300℃. The pressure of the multi-stage fixed-bed reactor is 5-10MPa.

5. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: The composite catalyst is specifically... The composite catalyst was prepared by a co-precipitation method, and the precipitant was... The solution has a precipitation pH of 8-9, the hydrothermal aging temperature is 110-130℃, and the aging time is 10-14h.

6. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: The carbon dioxide capture is performed using either the pressure swing adsorption (PSA) method or the amine absorption method. The PSA method is used for the industrial waste gas from the lime kiln, while the amine absorption method is used for the industrial waste gas from the converter and the blast furnace / coke oven.

7. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: The carbon dioxide capture process specifically includes: When the pressure swing adsorption method is used, the adsorption pressure is 0.8-1.2 MPa, the desorption pressure is -0.08 to -0.05 MPa, and the adsorbent is 13X molecular sieve; When using the amine absorption method, a concentration of [missing information] is used. The methyldiethanolamine aqueous solution is used as the absorbent, with an absorption temperature of 40-60℃ and a regeneration temperature of 105-120℃.

8. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: When the activity of the composite catalyst decreases to its initial activity The composite catalyst is then regenerated, specifically including: The composite catalyst with decreased activity was first purged with nitrogen gas at a temperature of 200-250°C for 2-4 hours to remove the physical adsorbates on the surface of the composite catalyst. The composite catalyst is then subjected to carbon deposition removal by burning. The composite catalyst is in an oxygen-containing environment... In the nitrogen atmosphere, with The temperature is increased to 350-400℃ at a certain rate and maintained for 4-8 hours to burn off the carbon deposits on the composite catalyst, thus completing the impurity removal process. After impurity removal, the composite catalyst is treated with a hydrogen-containing solution. The nitrogen gas is reduced at a temperature of 200-250℃ for 2-4 hours to obtain the regenerated composite catalyst.

9. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: A pretreatment system is installed at the water inlet of the solid oxide electrolytic cell to control the resistivity of the inlet water within a certain range. The medium- and high-temperature exhaust gas from the steel plant is used to preheat the incoming water to 70-90℃ through a heat exchanger.

10. The method for preparing green methanol from petrochemical tail gas carbon dioxide and green hydrogen according to claim 1, characterized in that: The current density of the solid oxide electrolytic cell is Hydrogen production power consumption The electrical energy of the solid oxide electrolytic cell is generated by solar or wind power.

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