A system and method for methanol recovery in photocatalytic reduction of CO2 to methanol

Abstract

The present invention discloses a system and method for methanol recovery in photocatalytic reduction of CO2 to methanol. The products generated by the photocatalytic reaction of ions and methanol first enter the raw liquid circulation subsystem after the ions in the aqueous solution are removed in the raw liquid ion filtration subsystem; the solution containing methanol is heated to a certain temperature in a water bath heater and then transported to the membrane separation subsystem by a circulation pump; in the membrane separation subsystem, a large number of methanol molecules and a small amount of water molecules pass through the pervaporation membrane with high affinity for methanol under the action of osmotic pressure, and are vaporized into gas on the other side of the membrane and enter the permeate collection subsystem; in the permeate collection subsystem, the vacuum pressure provided by a vacuum pump generates osmotic pressure and circulation power to transport the gaseous permeate to a liquid nitrogen cold trap, and the gaseous permeate is condensed into liquid in the liquid nitrogen cold trap and collected as a high-concentration methanol aqueous solution.

Description

Technical Field

[0001] The present invention relates to the technical fields of clean energy preparation, ion membrane separation and pervaporation membrane separation, and particularly relates to a system and method for methanol recovery in photocatalytic reduction of CO2 to methanol. Background Art

[0002] Methanol, as a fuel with a high energy combustion value and high environmental protection value due to its combustion products being hydrocarbons, has now been widely used as a clean and highly renewable energy source. Photocatalytic reduction of CO2 to methanol in an alkaline solution has been proven to be a simple and energy-saving method, and the product composition is a solution of methanol, trace other products and ions. When extracting methanol from the product solution of the photocatalytic reduction of CO2 to methanol reaction, the distillation process is often used to achieve the recovery requirement of methanol concentration in the distillation column. However, using a distillation column for purification requires increasing equipment investment and energy consumption. At the same time, the distillation equipment is complex and the operation process is cumbersome, which cannot meet the requirements for methanol extraction in photocatalytic reduction of CO2 to methanol.

[0003] As a new separation technology, pervaporation membrane separation technology has the characteristics of high separation efficiency, simple operation process, low energy consumption and high economic benefits, and is very suitable for separating alcohols from aqueous solutions. The working life of the pervaporation membrane will be shortened in an alkaline environment and the extraction efficiency will also be reduced due to the presence of ions. Therefore, it is necessary to filter out the ions in the product solution before extracting methanol. Summary of the Invention

[0004] In order to solve the problems of methanol extraction and recovery in photocatalytic reduction of CO2 to methanol, the object of the present invention is to propose a system and method for methanol recovery in photocatalytic reduction of CO2 to methanol, which is a system and method for first filtering the ions in the product solution and then extracting and recovering methanol from the methanol aqueous solution through pervaporation membrane separation technology. The system uses an ion filtration membrane to filter the ions in the photocatalytic product solution to avoid damage to the pervaporation membrane caused by alkaline ions; the methanol aqueous solution without ions is heated to a certain temperature in the system and then purified by methanol under the action of the pervaporation membrane. The high-concentration methanol permeates out in the form of gas on the vacuum side of the membrane and is condensed into liquid and collected in a low-temperature collection bottle driven by a vacuum pump. Therefore, the object of the present invention is to use the convenient and energy-saving pervaporation membrane separation technology to separate and extract methanol. While recovering and being able to utilize methanol, it can also reduce the methanol concentration in the photocatalytic reaction product, enable the photocatalytic reaction product solution to be recycled, improve energy utilization and avoid waste of raw materials.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] A system suitable for methanol recovery in photocatalytic reduction of CO2 to methanol, which consists of an ion filtration reactor 1, an ion filtration membrane 2, a power pump 3, a first flowmeter 4, a thermometer 5, an electric stirrer 6, a water bath heater 7, a raw material bottle 8, a circulation pump 9, a second flowmeter 10, a one-way ball valve 11, a pervaporation membrane 12, a membrane reactor 13, a buffer chamber 14, a vacuum gauge 15, a first three-way valve 16, a liquid nitrogen cold trap 17, a second three-way valve 18, a drying tube 19, and a vacuum pump 20;

[0007] The interior of the ion filtration reactor 1 is divided into two parts by the ion filtration membrane 2. The upper part is the photocatalytic product area, and the lower part is the filtration area. The outlet of the filtration area is connected to the inlet of the power pump 3. The outlet of the power pump 3 is connected to the inlet of the first flowmeter 4. The outlet of the first flowmeter 4 is connected to the inlet of the raw material bottle 8. The outlet of the raw material bottle 8 is connected to the inlet of the circulation pump 9. The outlet of the circulation pump 9 is connected to the inlet of the second flowmeter 10. The outlet of the second flowmeter 10 is connected to the upper part of the membrane reactor 13. The membrane reactor 13 is divided into two parts by the pervaporation membrane 12. The upper part is the raw material liquid chamber. The outlet of the raw material liquid chamber is connected to the inlet of the one-way ball valve 11. The outlet of the one-way ball valve 11 is connected to the upper outlet of the ion filtration reactor 1. The lower part of the membrane reactor 13 is the permeate liquid chamber. The outlet of the permeate liquid chamber is connected to the inlet of the buffer chamber 14. The outlet of the buffer chamber 14 is connected to the inlet of the first three-way valve 16. One side outlet of the first three-way valve 16 is connected to the inlet of the liquid nitrogen cold trap 17. The outlet of the liquid nitrogen cold trap 17 is connected to one side inlet of the second three-way valve 18. The other side outlet of the second three-way valve 16 is connected to the other side inlet of the second three-way valve 18. The outlet of the second three-way valve 18 is connected to the inlet of the drying tube 19. The outlet of the drying tube 19 is connected to the inlet of the vacuum pump 20.

[0008] The ions in the photocatalytic reaction product solution are filtered through the ion filtration membrane 2. The filtered solution is driven by the power pump 3 into the raw material bottle 8, heated to a preset temperature by the water bath heater 7, and then driven by the circulation pump 9 into the membrane reactor 13. Under the action of the osmotic pressure difference and the pervaporation membrane 12, the high-concentration methanol aqueous solution vaporizes into a gas in the permeate liquid chamber of the pervaporation membrane. The gaseous permeating substance is driven by the vacuum pump 20 into the liquid nitrogen cold trap 17 to be condensed into a liquid and collected.

[0009] The ion filtration reactor 1 is made of alkali-resistant plexiglass, divided into two hollow upper and lower parts. The middle part is isolated from the upper and lower parts by a rubber O-ring and the ion filtration membrane 2, and is fixed and clamped by bolts on the outside;

[0010] The ion filtration membrane 2 is assembled by three layers of membranes, namely the primary ion filtration membrane on the top layer, the high-level ion filtration membrane in the middle layer, and the porous support membrane at the bottom layer. The ion filtration membrane 2 isolates the ionic products in the product in the upper part of the ion filtration reactor 1, and methanol and water molecules pass through the ion filtration membrane into the lower part of the ion filtration reactor 1;

[0011] The power pump 3 is used to provide the power for the product solution after filtering ions to enter the raw material bottle 8 and control the flow rate.

[0012] The first flowmeter 4 is used to monitor the flow rate of the product solution.

[0013] The ion filtration reactor 1, the ion filtration membrane 2, the power pump 3, and the first flowmeter 4 constitute an ion filtration subsystem.

[0014] The water bath heater 7 is used to heat the temperature of the raw material liquid so that the raw material liquid reaches a suitable temperature for extraction, increasing the extraction ability and flux of methanol.

[0015] The raw material bottle 8 is used to store the methanol aqueous solution, equipped with a thermometer 5 to monitor the temperature of the solution in the raw material bottle and an electric stirrer 6 to stir the solution in the raw material bottle to make the temperature distribution in the raw material bottle uniform.

[0016] The circulation pump 9 is used to provide the power for the circulation of the raw material liquid and control the flow rate of the raw material liquid.

[0017] The second flowmeter 10 is used to monitor the flow rate of the circulation of the raw material liquid.

[0018] The single-phase ball valve 11 is used to control the opening and closing of the circulation of the raw material liquid, remaining closed when loading and preheating the raw material bottle 8 and remaining open when the raw material liquid is circulating.

[0019] The water bath heater 7, the raw material bottle 8, the circulation pump 9, the second flowmeter 10, and the single-phase ball valve 11 together constitute a raw material liquid circulation subsystem. The circulation pump 9 drives the low-concentration methanol aqueous solution to flow through the upper part of the membrane reactor 13. Part of the methanol in the raw material liquid is extracted and then flows back to the upper outlet of the ion filtration reactor 1 as a lower-concentration methanol aqueous solution to be mixed with the rich ion solution after ion barrier.

[0020] The membrane reactor 13 is made of plexiglass, divided into two hollow upper and lower cavities, separated into a raw material liquid cavity and a permeate liquid cavity in the middle by a pervaporation membrane 12, fixed and clamped externally with screws and equipped with a rubber O-ring for sealing.

[0021] The pervaporation membrane 12 is a composite membrane, consisting of three layers. The surface layer material is polydimethyl diethoxysilane with high affinity for methanol and high hydrophobic performance and no pores. The middle layer material is polyvinylidene fluoride with porous material and good hydrophobic performance. The bottom layer is a non-woven fabric support layer with high mechanical strength. The pervaporation membrane 12 is fixed in the middle of the upper and lower cavities of the membrane reactor 13 through a rubber O-ring and screws and supported by a metal porous mesh.

[0022] The described membrane reactor 13 and the pervaporation membrane 12 together constitute a membrane reaction subsystem. The methanol aqueous solution undergoes a pervaporation process within the pervaporation membrane 12 under the driving force of the pressure difference on both sides of the pervaporation membrane 12 and permeates out as a high-concentration methanol-water gas in the permeate chamber of the membrane reactor 13.

[0023] The described buffer chamber 14 is connected to the atmosphere through a micro-regulating valve to adjust the vacuum pressure in the permeate chamber and is equipped with a vacuum gauge 15 to monitor the vacuum pressure in the permeate chamber.

[0024] The described first three-way valve 16 and second three-way valve 18 are used to control the gas flow route in the permeate chamber. When the permeate chamber is in the collection stage, the first three-way valve 16 and the second three-way valve 18 are adjusted to make the gas path lead to the liquid nitrogen cold trap 17. When the collection bottle in the liquid nitrogen cold trap 17 is full or when the collection bottle needs to be replaced after reaching the collection time, the first three-way valve 16 and the second three-way valve 18 are adjusted to make the gas path lead to the side without the liquid nitrogen cold trap 17.

[0025] The described liquid nitrogen cold trap 17 consists of a Dewar flask with good heat insulation performance, a collection bottle, and low-temperature liquid nitrogen. The collection bottle is inserted into the Dewar flask filled with low-temperature liquid nitrogen, and the gas in the permeate chamber is condensed into a liquid in the collection bottle and collected.

[0026] The described drying tube 19 is used to absorb the uncondensed gas in the permeate chamber to prevent the gas from entering the vacuum pump 20 and affecting its performance.

[0027] The described vacuum pump 20 is used to provide the driving force for the gas flow in the permeate chamber and to provide the vacuum pressure for the permeate chamber of the membrane reactor 13, so as to generate a pressure difference on both sides of the pervaporation membrane 12, enabling the methanol and water molecules to undergo a pervaporation process within the pervaporation membrane and permeate out in a gaseous state in the permeate chamber.

[0028] The described buffer chamber 14, first three-way valve 16, liquid nitrogen cold trap 17, second three-way valve 18, drying tube 19, and vacuum pump 20 together constitute a permeate collection subsystem.

[0029] The working method of the described system suitable for methanol recovery in photocatalytic reduction of CO2 to methanol includes the following steps:

[0030] The product solution of photocatalytic reduction of CO2 to methanol containing ions undergoes a filtration effect through the ion filtration membrane 2 in the ion filtration reactor 1, forming a rich-ion solution at the upper outlet, and is mixed with the solution with a low methanol concentration after methanol extraction and continues to be recycled back to the photocatalytic system for use; the product solution without ions after filtration at the lower part flows into the raw material bottle 8 under the drive of the power pump 3.

[0031] After the raw material liquid filtered by the ion filtration subsystem is heated to a preset temperature in the raw material bottle 8 by the water bath heater 7, it enters the raw material liquid chamber of the membrane reactor 13 driven by the circulation pump 9. In the membrane reactor 13, a large number of methanol molecules are selectively permeated through the pervaporation membrane 12 into the permeate chamber, and a methanol aqueous solution with a lower concentration is formed at the outlet of the raw material liquid chamber, flowing to the upper outlet of the ion filtration reactor 1 to be mixed with the ion-rich product solution for continuous use in the photocatalytic reaction;

[0032] Through the action of the pervaporation membrane 12, methanol-water gas with a high methanol concentration is generated in the permeate chamber of the membrane reactor 13, and flows to the liquid nitrogen cold trap 17 driven by the vacuum pump 20 to be condensed into a liquid state and collected.

[0033] In the method described above, the ion filtration subsystem first filters the ions from part of the product solution and introduces it into the raw material bottle 8 for preheating. After reaching the preset temperature, the power pump 3 and the circulation pump 9 are started simultaneously, and the flow rates of the ion filtration subsystem and the raw material liquid circulation subsystem are monitored and adjusted through the first flowmeter 4 and the second flowmeter 10 to keep the flow rates of the two the same; the volume of the raw material bottle 8 is such that at the set flow rate of the product solution, the low-temperature product solution flowing into the raw material bottle 8 and the solution preheated to the preset temperature in the bottle are mixed without causing a significant drop in the temperature in the bottle; when the permeate chamber collects the high-concentration methanol aqueous solution, at a set time or when the collection bottle is full, the opening directions of the first three-way valve 16 and the second three-way valve 18 are changed so that the permeate chamber can still operate at low pressure. After quickly replacing the collection bottle, the first three-way valve 16 and the second three-way valve 18 are switched back to the original direction to continue collecting.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] (1) The system of the present invention uses an ion filtration membrane to separate and filter the ions in the product solution, which simplifies the system while saving energy.

[0036] (2) The system of the present invention uses pervaporation membrane separation technology to separate and extract methanol, which reduces equipment investment while consuming less energy and improves the economic benefits of photocatalytic methanol production.

[0037] (3) In the system of the present invention, the solution can be recycled. The ion-rich solution after membrane filtration by the ion filtration subsystem and the methanol aqueous solution with a lower concentration after the action of the membrane in the raw material liquid circulation subsystem can be mixed and used as the raw material liquid for photocatalytic preparation.

[0038] (4) Using liquid nitrogen to condense the high-concentration methanol permeate not only simplifies the equipment structure, but also the ultra-low temperature provided by liquid nitrogen can ensure that the high-concentration methanol is completely collected, improving the economic benefits of the system. Description of the Drawings

[0039] Figure 1 It is a schematic structural diagram of the system of the present invention. Specific embodiments

[0040] Please refer to Figure 1 , a system for methanol recovery in photocatalytic reduction of CO2 to methanol according to an embodiment of the present invention, which is composed of an ion filtration reactor 1, an ion filtration membrane 2, a power pump 3, a first flowmeter 4, a thermometer 5, an electric stirrer 6, a water bath heater 7, a raw material bottle 8, a circulation pump 9, a second flowmeter 10, a one-way ball valve 11, a pervaporation membrane 12, a membrane reactor 13, a buffer chamber 14, a vacuum gauge 15, a first three-way valve 16, a liquid nitrogen cold trap 17, a second three-way valve 18, a drying tube 19, and a vacuum pump 20;

[0041] The inside of the pressure ion filtration reactor 1 is divided into two parts by the ion filtration membrane 2. The upper part is the photocatalytic product area, and the lower part is the filtration area. The outlet of the filtration area is connected to the inlet of the power pump 3, the outlet of the power pump 3 is connected to the inlet of the first flowmeter 4, the outlet of the first flowmeter 4 is connected to the inlet of the raw material bottle 8, the outlet of the raw material bottle 8 is connected to the inlet of the circulation pump 9, the outlet of the circulation pump 9 is connected to the inlet of the second flowmeter 10, and the outlet of the second flowmeter 10 is connected to the upper part of the membrane reactor 13; The membrane reactor 13 is divided into two parts by the pervaporation membrane 12. The upper part is the raw material liquid chamber, and the outlet of the raw material liquid chamber is connected to the inlet of the one-way ball valve 11. The outlet of the one-way ball valve 11 is connected to the upper outlet of the ion filtration reactor 1; The lower part of the membrane reactor 13 is the permeate chamber. The outlet of the permeate chamber is connected to the inlet of the buffer chamber 14. The outlet of the buffer chamber 14 is connected to the inlet of the first three-way valve 16. One side outlet of the first three-way valve 16 is connected to the inlet of the liquid nitrogen cold trap 17. The outlet of the liquid nitrogen cold trap 17 is connected to one side inlet of the three-way valve 18. The other side outlet of the three-way valve 16 is connected to the other side inlet of the second three-way valve 18. The outlet of the second three-way valve 18 is connected to the inlet of the drying tube 19. The outlet of the drying tube 19 is connected to the inlet of the vacuum pump 20.

[0042] The system of the present invention includes an ion filtration subsystem, a raw material liquid circulation subsystem, a membrane reaction subsystem, and a permeate collection subsystem. The membrane reaction subsystem and the permeate collection subsystem operate in a mutually bound manner, and can operate independently or simultaneously with the other two subsystems. The steps of the system specifically applicable to methanol recovery in photocatalytic reduction of CO2 to methanol are described as follows:

[0043] Containing Na 2+ , OH - , The product solution of the photocatalytic reduction of CO2 by plasma is filtered through the ion filtration membrane 2 in the ion filtration reactor 1, and a rich ion solution is formed at the upper outlet, which is mixed with the low-concentration methanol-water solution after methanol extraction and then recycled back to the photocatalytic system as the feed liquid. The product methanol-water solution without ions after filtration at the lower part flows into the feed bottle 8 driven by the power pump 3;

[0044] The feed liquid filtered by the ion filtration subsystem is heated to a preset temperature in the feed bottle 8 by the water bath heater 7, and then enters the feed liquid chamber of the membrane reactor 13 driven by the circulation pump 9. In the membrane reactor 13, a large number of methanol molecules are selectively permeated through the pervaporation membrane 12 into the permeate chamber, and a methanol-water solution with a lower concentration is formed at the outlet of the feed liquid chamber, which flows to the upper outlet of the ion filtration reactor 1 to be mixed with the rich ion product solution for continuous use in the photocatalytic reaction;

[0045] Through the action of the pervaporation membrane 12, a methanol-water gas with a high methanol concentration is generated in the permeate chamber of the membrane reactor 13, and flows to the liquid nitrogen cold trap 17 driven by the vacuum pump 20 to be condensed into a liquid and collected.

[0046] The present invention combines the use of an ion filtration membrane and a pervaporation membrane. After filtering out the ions in the product solution through the ion filtration membrane, it enters the pervaporation membrane for methanol extraction. It can not only achieve the effects of energy conservation, convenient operation and improved economic benefits, but also extend the service life of the pervaporation membrane, further reduce the input and increase the output. Therefore, the present invention can well meet the requirements and be applied to the production process of photocatalytic reduction of CO2 to prepare methanol.

[0047] The above are only the preferred embodiments 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, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A system for methanol recovery in photocatalytic reduction of CO2 to methanol, characterized in that: It consists of an ion filtration reactor (1), an ion filtration membrane (2), a power pump (3), a first flowmeter (4), a thermometer (5), an electric stirrer (6), a water bath heater (7), a raw material bottle (8), a circulation pump (9), a second flowmeter (10), a one-way ball valve (11), a pervaporation membrane (12), a membrane reactor (13), a buffer chamber (14), a vacuum gauge (15), a first three-way valve (16), a liquid nitrogen cold trap (17), a second three-way valve (18), a drying tube (19), and a vacuum pump (20). The interior of the ion filtration reactor (1) is divided into two parts by the ion filtration membrane (2). The upper part is the photocatalytic product area, and the lower part is the filtration area. The outlet of the filtration area is connected to the inlet of the power pump (3). The outlet of the power pump (3) is connected to the inlet of the first flowmeter (4). The outlet of the first flowmeter (4) is connected to the inlet of the raw material bottle (8). The outlet of the raw material bottle (8) is connected to the inlet of the circulation pump (9). The outlet of the circulation pump (9) is connected to the inlet of the second flowmeter (10). The outlet of the second flowmeter (10) is connected to the upper part of the membrane reactor (13). The membrane reactor (13) is divided into two parts by the pervaporation membrane (12). The upper part is the raw material liquid chamber. The outlet of the raw material liquid chamber is connected to the inlet of the one-way ball valve (11). The outlet of the one-way ball valve (11) is connected to the upper outlet of the ion filtration reactor (1). The lower part of the membrane reactor (13) is the permeate liquid chamber. The outlet of the permeate liquid chamber is connected to the inlet of the buffer chamber (14). The outlet of the buffer chamber (14) is connected to the inlet of the first three-way valve (16). One side outlet of the first three-way valve (16) is connected to the inlet of the liquid nitrogen cold trap (17). The outlet of the liquid nitrogen cold trap (17) is connected to one side inlet of the second three-way valve (18). The other side outlet of the first three-way valve (16) is connected to the other side inlet of the second three-way valve (18). The outlet of the second three-way valve (18) is connected to the inlet of the drying tube (19). The outlet of the drying tube (19) is connected to the inlet of the vacuum pump (20). The ion filtration reactor (1) is made of alkali-resistant plexiglass and is divided into two hollow upper and lower parts. The middle part is isolated from the upper and lower parts by a rubber O-ring and the ion filtration membrane (2), and the outside is fixed and clamped by bolts. The ion filtration membrane (2) is assembled by three layers of membranes, namely the primary ion filtration membrane on the uppermost layer, the high-level ion filtration membrane in the middle layer, and the porous support membrane at the bottom layer. The ion filtration membrane (2) isolates the ionic products in the product in the upper part of the ion filtration reactor (1), and methanol and water molecules pass through the ion filtration membrane and enter the lower part of the ion filtration reactor (1). The power pump (3) is used to provide the power for the product solution after filtering ions to enter the raw material bottle (8) and control the flow rate. The first flowmeter (4) is used to monitor the flow rate of the product solution. The ion filtration reactor (1), the ion filtration membrane (2), the power pump (3), and the first flowmeter (4) constitute an ion filtration subsystem.

2. The system for methanol recovery in photocatalytic reduction of CO2 to methanol according to claim 1, characterized in that: The ions in the photocatalytic reaction product solution are filtered through the ion filtration membrane (2). The filtered solution enters the raw material bottle (8) driven by the power pump (3), is heated to a preset temperature by the water bath heater (7), and then enters the membrane reactor (13) driven by the circulation pump (9). Under the action of the osmotic pressure difference and the pervaporation membrane (12), the high-concentration methanol aqueous solution vaporizes into a gas in the permeate chamber of the pervaporation membrane. The gaseous permeating substance is driven by the vacuum pump (20) into the liquid nitrogen cold trap (17) to be condensed into a liquid and collected.

3. The system for methanol recovery in photocatalytic reduction of CO2 to methanol according to claim 1, characterized in that: The water bath heater (7) is used to heat the temperature of the raw material liquid, so that the raw material liquid reaches a suitable temperature for extraction, increasing the extraction ability and flux of methanol. The raw material bottle (8) is used to store the methanol aqueous solution, equipped with a thermometer (5) to monitor the temperature of the solution in the raw material bottle and an electric stirrer (6) to stir the solution in the raw material bottle to make the temperature distribution in the raw material bottle uniform. The circulation pump (9) is used to provide the circulation power of the raw material liquid and control the flow rate of the raw material liquid. The second flowmeter (10) is used to monitor the flow rate of the raw material liquid circulation. The one-way ball valve (11) is used to control the opening and closing of the raw material liquid circulation, remaining closed when loading and preheating the raw material bottle (8), and remaining open during the raw material liquid circulation. The water bath heater (7), the raw material bottle (8), the circulation pump (9), the second flowmeter (10), and the one-way ball valve (11) together constitute the raw material liquid circulation subsystem. The low-concentration methanol aqueous solution is driven by the circulation pump (9) to flow through the upper part of the membrane reactor (13). Part of the methanol in the raw material liquid is extracted and then flows back to the upper outlet of the ion filtration reactor (1) as a lower-concentration methanol aqueous solution to be mixed with the ion-rich solution after ion barrier.

4. The system for methanol recovery in photocatalytic reduction of CO2 to methanol according to claim 1, characterized in that: The membrane reactor (13) is made of plexiglass, divided into two hollow upper and lower cavities, separated into a raw material liquid chamber and a permeate chamber in the middle by the pervaporation membrane (12), fixed and clamped externally with screws and equipped with a rubber O-ring for sealing. The pervaporation membrane (12) is a composite membrane, consisting of three layers. The surface layer material is polydimethyldiethoxysilane with high affinity for methanol and high hydrophobic performance and no pores. The middle layer material is polyvinylidene fluoride with porous material and good hydrophobic performance. The bottom layer is a non-woven fabric support layer with high mechanical strength. The pervaporation membrane (12) is fixed in the middle of the upper and lower cavities of the membrane reactor (13) by a rubber O-ring and screws and supported by a metal porous mesh. The membrane reactor (13) and the pervaporation membrane (12) together constitute the membrane reaction subsystem. The methanol aqueous solution undergoes a pervaporation process in the pervaporation membrane (12) under the push of the pressure difference on both sides of the pervaporation membrane (12) and permeates out as a high-concentration methanol water gas in the permeate chamber of the membrane reactor (13).

5. The system for methanol recovery in photocatalytic reduction of CO2 to methanol according to claim 1, characterized in that: The buffer chamber (14) is connected to the atmosphere through a micro-regulating valve to adjust the vacuum pressure of the permeate chamber, and is equipped with a vacuum gauge (15) to monitor the vacuum pressure of the permeate chamber. The first three-way valve (16) and the second three-way valve (18) are used to control the gas flow path in the permeate chamber. When the permeate chamber is in the collection stage, the first three-way valve (16) and the second three-way valve (18) are adjusted to make the gas path lead to the liquid nitrogen cold trap (17). When the collection bottle in the liquid nitrogen cold trap (17) is full or the collection bottle needs to be replaced when the collection time is reached, the first three-way valve (16) and the second three-way valve (18) are adjusted to make the gas path lead to the side without the liquid nitrogen cold trap (17). The liquid nitrogen cold trap (17) consists of a Dewar flask with good heat insulation performance, a collection bottle and low-temperature liquid nitrogen. The collection bottle is inserted into the Dewar flask filled with low-temperature liquid nitrogen, and the gas in the permeate chamber is condensed into a liquid in the collection bottle and collected. The drying tube (19) is used to absorb the uncondensed gas in the permeate chamber to prevent the gas from entering the vacuum pump (20) and affecting its performance. The vacuum pump (20) is used to provide the driving force for the gas flow in the permeate chamber and the vacuum pressure for the permeate chamber of the membrane reactor (13), so that a pressure difference is generated on both sides of the pervaporation membrane (12), enabling the methanol and water molecules to undergo the pervaporation process in the pervaporation membrane (12) and permeate out in the gaseous state in the permeate chamber. The buffer chamber (14), the first three-way valve (16), the liquid nitrogen cold trap (17), the second three-way valve (18), the drying tube (19) and the vacuum pump (20) together constitute the permeate collection subsystem.

6. The working method of the system for methanol recovery in photocatalytic reduction of CO2 to methanol according to any one of claims 1 to 5, characterized in that, It includes the following steps: The product solution of photocatalytic reduction of CO2 to methanol containing ions is filtered through the ion filtration membrane (2) in the ion filtration reactor (1), and a rich-ion solution is formed at the upper outlet, which is mixed with the solution with a low methanol concentration after methanol extraction and then recycled back to the photocatalytic system for use; the product solution without ions after filtration at the lower part flows into the raw material bottle (8) driven by the power pump (3). The raw material liquid filtered from the ion filtration subsystem is heated to a preset temperature in the raw material bottle (8) by the water bath heater (7), and then enters the raw material liquid chamber of the membrane reactor (13) driven by the circulation pump (9). In the membrane reactor (13), a large number of methanol molecules are selectively permeated through the pervaporation membrane (12) into the permeate chamber, and an aqueous methanol solution with a lower concentration is formed at the outlet of the raw material liquid chamber, which flows to the upper outlet of the ion filtration reactor (1) and is mixed with the rich-ion product solution for continuous use in the photocatalytic reaction. Through the action of the pervaporation membrane (12), methanol-water gas with a high methanol concentration is generated in the permeate chamber of the membrane reactor (13), and flows to the liquid nitrogen cold trap (17) driven by the vacuum pump (20) to be condensed into a liquid and collected.

7. The method according to claim 6, wherein: The ion filtration subsystem first filters the ions from a part of the product solution and then introduces it into the raw material bottle (8) for preheating. After reaching the preset temperature, the power pump (3) and the circulation pump (9) are started simultaneously, and the flow rates of the ion filtration subsystem and the raw material liquid circulation subsystem are monitored and adjusted through the first flowmeter (4) and the second flowmeter (10) to make the flow rates of the two consistent; the volume of the raw material bottle (8) is such that at the set flow rate of the product solution, the low-temperature product solution flowing into the raw material bottle (8) and the solution preheated to the preset temperature in the bottle are mixed without causing a significant drop in the temperature in the bottle; when the permeate chamber collects the high-concentration methanol aqueous solution, at a set time or when the collection bottle is full, the opening directions of the first three-way valve (16) and the second three-way valve (18) are changed so that the permeate chamber can still operate at low pressure. After quickly replacing the collection bottle, the first three-way valve (16) and the second three-way valve (18) are switched back to the original directions to continue collection.

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