A reaction system for improving the conversion rate of direct synthesis of dimethyl carbonate from carbon dioxide and methanol

Abstract

The present invention discloses a reaction system for improving the conversion rate of dimethyl carbonate (DMCO) directly synthesized from carbon dioxide and methanol, comprising a membrane catalytic reaction system and an extractant recovery system. The membrane catalytic reaction system comprises a feed system, a mixing, heating, and pressurizing system, a mesoporous membrane-extractor assembly for separating DMC from the product, a 3A molecular sieve membrane assembly for separating water from the product, a material circulation system, a heat preservation system, and a storage system. This invention provides a novel reaction system for the direct synthesis of dimethyl carbonate from carbon dioxide and methanol, which has the advantages of improving carbon dioxide conversion and increasing DMC yield.

Description

Technical Field

[0001] The invention belongs to the technical field of dimethyl carbonate synthesis, and particularly relates to a reaction system for improving the conversion rate of directly synthesizing dimethyl carbonate from carbon dioxide and methanol. Background Art

[0002] In recent years, excessive carbon dioxide emissions have become a global hot environmental issue, seriously threatening the human living environment. However, while carbon dioxide is a greenhouse gas, it is also a sustainable and renewable carbon resource. The carbon dioxide content in the atmosphere is about 0.03%. Converting carbon dioxide into valuable chemical raw materials has become a current research hotspot.

[0003] Dimethyl carbonate, with its multiple functional groups, is an important intermediate. With the help of a catalyst, carbon dioxide and methanol can be directly synthesized into dimethyl carbonate. This can effectively alleviate or even curb global environmental issues caused by carbon dioxide, while also enabling value-added chemical production that promotes carbon recycling.

[0004] At present, the main methods for synthesizing DMC are: CO2 direct synthesis method, phosgene method, ester exchange method, and methanol oxidative carbonylation method. Phosgene method is a traditional DMC synthesis method. PPG Company in the United States and BASF Company in Germany have used this process technology to produce dimethyl carbonate. Jiangsu Wuxian Pesticide Factory, Chongqing Dongfeng Chemical Plant, and Shanghai Wusong Chemical Plant in China have also used this process. However, this process uses highly toxic substance COCl2, and its by-product hydrogen chloride will cause serious corrosion to equipment, so it has gradually been eliminated from the market. In 1986, DOW Chemical Company in the United States developed a gas phase oxidative carbonylation method (Li Guisheng. Research Progress on Dimethyl Carbonate Synthesis Technology [J]. Industrial Catalysis, 2023, 31(03):31-38.), using methanol, oxygen, carbon monoxide and nitrogen monoxide as raw materials. However, in this process, water, DMC and methanol easily form azeotropes, and the simultaneous introduction of CO and O2 has explosion hazards. In 1992, Texaco reported that DMC could be obtained through the transesterification reaction of methanol and ethylene carbonate (EC) (Zhou Junjie. Application of Zeolite Membrane Catalytic Reactors in the Preparation of Dimethyl Carbonate [D]. University of the Chinese Academy of Sciences (Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences), 2021.). This process is now relatively mature, but the raw materials used in this process mainly rely on the petroleum industry, resulting in high raw material costs and serious environmental pollution caused by byproducts. Furthermore, the process involves many steps, which makes the subsequent separation of the products difficult.

[0005] Among numerous methods, direct synthesis of dimethyl carbonate from methanol and CO₂ effectively avoids the shortcomings of the aforementioned methods and offers significant advantages in terms of raw material availability and improved "atom utilization," contributing to the carbon crisis and being the greenest and most environmentally friendly technology. However, due to the stable nature of CO₂, this method cannot proceed spontaneously due to thermodynamic constraints. Improving DMC yield requires research on kinetics and breaking thermodynamic equilibrium. Therefore, research on this route focuses on catalyst application and the development of novel reaction systems. Summary of the Invention

[0006] The present invention aims to provide a method that can achieve macromolecular permeation and small molecule retention in the direct synthesis of carbon dioxide and methanol, promptly separates the product DMC and water in the system from the system, combines membrane separation with a catalytic reaction process, achieves product separation during the catalytic reaction, and strengthens the reaction while separating the products, thereby breaking the original reaction equilibrium limitation, increasing the rate in the forward reaction direction, solving the existing problems of low yield of dimethyl carbonate generated by the reaction of carbon dioxide and methanol and low carbon dioxide conversion rate, and achieving efficient carbon dioxide conversion.

[0007] The technical solution of the present invention:

[0008] A reaction system for improving the conversion rate of direct synthesis of dimethyl carbonate from carbon dioxide and methanol, the reaction system comprising a membrane catalytic reaction system and an extractant recovery system;

[0009] Membrane catalytic reaction subsystem, including feeding system, mixing temperature and pressure system, separation DMC membrane assembly, water separation membrane assembly, material circulation system, insulation system and storage system;

[0010] The feeding system includes a carbon dioxide feeding system and a methanol feeding system; the carbon dioxide feeding system includes a CO2 storage tank 13, a CO2 flow regulating valve 14 and a CO2 flow meter 15, the CO2 storage tank 13 provides CO2 raw material, and the flow rate of CO2 is accurately controlled by the CO2 flow regulating valve 14 and the CO2 flow meter 15; the methanol feeding system includes a methanol storage tank 16, a methanol feed pump 17, a methanol flow regulating valve 18, a methanol vaporizer 19 and a methanol flow meter 20, the methanol storage tank 16, the methanol feed pump 17, the methanol vaporizer 19 and the methanol flow meter 20 are connected in sequence, the methanol flow regulating valve 18 adopts a bypass regulation form, and the opening of the methanol flow regulating valve 18 is controlled by the parameters set by the methanol flow meter 20, thereby accurately controlling the feed amount of methanol;

[0011] The mixing, heating, and pressurizing system primarily consists of a feed gas preheater 21, a steam regulating valve 42, and a steam trap 43. A thermocouple is installed on the outlet pipe of the feed gas preheater 21. By controlling the temperature on the pipe, the opening of the steam regulating valve 42 is adjusted, thereby regulating the temperature of the mixed gas. After steam heating, the gas is discharged from the system through the steam trap 43. Carbon dioxide from the carbon dioxide feed system, methanol vapor from the methanol feed system, and the recycled material from the water separation membrane assembly, from which water has been completely or partially removed, are all fed into the pipe side of the feed gas preheater 21, where they are mixed, heated, and pressurized before being fed into the inert membrane catalytic reactor.

[0012] The separation DMC membrane assembly 26 is an inert membrane catalytic reactor, in which a mesoporous membrane with a pore size of 2-4 nm is used as a separation membrane; fillers 3 are installed between the shell 4 and the membrane tube 7 and at both ends of the inert membrane catalytic reactor to promote uniform distribution of materials; a catalyst 8 is filled in the middle to catalyze the direct reaction of carbon dioxide and methanol to produce DMC and water; the mixed gas from the raw gas preheater 21 enters the separation DMC membrane assembly 26 through the air inlet 2 and reacts in the catalyst bed. The raw materials and The product contacts the membrane tube 7; the discharge port 12 and feed port 10 of the DMC separation membrane assembly 26 are respectively connected to the extractant storage tank 22 through pipelines, and an extractant feed pump 23 is provided on the pipeline of the feed port 10, through which the extractant is fed into the tube side of the inert membrane catalytic reactor; a pipeline is connected between the discharge port 12 and the feed port 10, and an extractant flow meter 25 and an extractant flow regulating valve 24 are provided on the pipeline for regulating the DMC-containing extract flowing out of the inert membrane catalytic reactor;

[0013] The membrane assembly for separating water is a dehydration membrane reactor 35, in which a 3A molecular sieve membrane with a pore size of no more than 0.3 nm is selected. The raw materials, water, and a small amount of DMC that has not permeated through the separation membrane in the inert membrane catalytic reactor flow out from the outlet 11 of the separation DMC membrane assembly 26 and are fed into the dehydration membrane reactor 35 via a compressor 34. The difference between the dehydration membrane reactor 35 and the separation DMC membrane assembly 26 is that there is no catalyst between the shell and the membrane tube. One end of the tube side of the dehydration membrane reactor 35 is closed, and the other end is connected in sequence to a second condenser 37, a vacuum buffer tank 38, and a vacuum pump 39. The second condenser 37 is also connected to a water storage tank 40.

[0014] The material circulation system includes an extractant recycling system and a reaction material circulation system. The extractant recycling system uses a pump to return the extractant obtained from the extractant recovery system to the inert membrane catalytic reactor. The reaction material circulation system uses a compressor to return the material on the retentate side of the water separation membrane module after water removal to the feed gas preheater 21 for reaction.

[0015] The insulation system is designed to keep the circulating materials and the heated reaction raw material pipelines warm or heat them to maintain the reaction temperature of the reaction system and ensure the smooth progress of the reaction;

[0016] The storage system includes raw material tanks and product storage tanks, wherein the raw material tanks include a CO2 storage tank 14, a methanol storage tank 16 and an extractant storage tank 22; the product storage tanks include a dimethyl carbonate storage tank 41 and a water storage tank 40;

[0017] The extractant recovery system includes a heat exchanger 33, a condensate flowmeter 28, a condensate flow regulating valve 29, a first condenser 30, a distillation tower 31, and a reboiler 32. The DMC-dissolved extractant flowing out of the inert membrane catalytic reactor is heat exchanged with the high-temperature extractant obtained from the bottom of the distillation tower 31 through the heat exchanger 33. After preheating, it enters the distillation tower 31 and undergoes distillation separation within the distillation tower 31. The overhead product is DMC. After condensation in the first condenser 30, the DMC is divided into two streams. One stream is returned to the distillation tower 31 as reflux, and the reflux ratio of the distillation tower 31 is controlled by the condensate flowmeter 28 and the condensate regulating valve 29. The other stream is sent to the DMC storage tank 41 as the product for storage. The extractant exchanges heat with the raw material of the distillation tower 31 in the heat exchanger 33. After heat exchange, the extractant is sent to the extractant storage tank 22 for reuse.

[0018] The catalyst used in the catalytic reaction is a supported catalyst or a metal oxide catalyst.

[0019] The supported catalyst includes a carrier and a transition metal supported on the carrier, wherein the transition metal is at least one of Fe, Co, Ni, Cu, and Zn, and the carrier is at least one of Cs2O, La2O3, ZrO2, Al2O3, SiO2, TiO2, nitrogen-doped hierarchical porous carbon (NHPC), and activated carbon, and the loading amount of the transition metal is 0 to 20 wt% calculated as its corresponding oxide.

[0020] The metal oxide catalyst is an oxide composed of Ce and another transition metal, wherein the transition metal is one of Mn, Ti, Zr, Zn, and Fe.

[0021] Beneficial effects of the present invention:

[0022] 1. The reaction system of the present invention directly removes the product by passing large molecules through the membrane reaction system and intercepting small molecules, thereby breaking the kinetic limitations of the reaction and achieving a high product yield.

[0023] 2. The experimental device of the present invention can use any solid catalyst that can catalyze the reaction, thereby reducing industrialization costs.

[0024] 3. The reactor of the present invention combines a membrane system with a catalytic reaction and a process flow, and the reaction conditions are mild.

[0025] 4. The process flow of the present invention realizes heat recovery and raw material circulation, reducing industrialization costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The reactor of the present invention;

[0027] Figure 2 1 is a process flow chart of the reaction system of the present invention;

[0028] Among them, 1-upper flange, 2-air inlet, 3-packing, 4-housing, 5-external threaded pipe joint, 6-internal threaded pipe joint, 7-membrane tube, 8-catalyst, 9-lower flange, 10-feed port, 11-air outlet, 12-discharge port, 13-CO2 storage tank, 14-CO2 flow regulating valve, 15-CO2 flow meter, 16-methanol storage tank, 17-methanol feed pump, 18-methanol flow regulating valve, 19-methanol vaporizer, 20-methanol flow meter, 21-raw gas preheater, 22-extractant storage tank, 23-extractant Feed pump, 24-extractant flow regulating valve, 25-extractant flow meter, 26-separation DMC membrane assembly, 27-first heating furnace, 28-condensate flow meter, 29-condensate flow regulating valve, 30-first condenser, 31-distillation tower, 32-reboiler, 33-heat exchanger, 34-compressor, 35-dehydration membrane reactor, 36-second heating furnace, 37-second condenser, 38-vacuum buffer tank, 39-vacuum pump, 40-water storage tank, 41-dimethyl carbonate storage tank, 42-steam regulating valve, 43-drain valve. DETAILED DESCRIPTION

[0029] In order to clearly illustrate the technical features of this solution, this solution is described below through specific implementation methods.

[0030] Example

[0031] A reaction system for improving the conversion rate of direct synthesis of dimethyl carbonate from carbon dioxide and methanol, comprising a membrane catalytic reaction subsystem and an extractant recovery system;

[0032] Membrane catalytic reaction subsystem, including feed system, mixed temperature and pressure system, separation DMC membrane components (see attached Figure 1 ), water separation membrane components, material circulation system, insulation system and storage system;

[0033] The feeding system includes a carbon dioxide feeding system and a methanol feeding system; the carbon dioxide feeding system includes a CO2 storage tank 13, a CO2 flow regulating valve 14 and a CO2 flow meter 15. The CO2 storage tank 13 provides CO2 raw materials and accurately controls the flow of carbon dioxide through the CO2 flow regulating valve 14 and the CO2 flow meter 15; the methanol feeding system includes a methanol storage tank 16, a methanol feed pump 17, a methanol flow regulating valve 18, a methanol vaporizer 19 and a methanol flow meter 20. The methanol storage tank 16, the methanol feed pump 17, the methanol vaporizer 19 and the methanol flow meter 20 are connected in sequence. The methanol flow regulating valve 18 adopts a bypass regulation form. The opening of the methanol circulation regulating valve 18 is controlled by the parameters set by the methanol flow meter 20, thereby accurately controlling the feed amount of methanol.

[0034] The mixed temperature-raising and pressurizing system mainly consists of a raw gas preheater 21, a steam regulating valve 42 and a steam trap 43. A thermocouple is set on the outlet pipe of the raw gas preheater 21. The opening of the steam regulating valve 42 is adjusted by controlling the temperature on the pipe, thereby adjusting the temperature of the mixed gas. After steam heating, it is discharged from the system through the steam trap 43. The carbon dioxide from the carbon dioxide feed system, the methanol vapor from the methanol feed system and the circulating material from the water separation membrane assembly that has been completely or partially dehydrated are all fed into the pipe side of the raw gas preheater 21, where they are mixed, heated and pressurized, and then fed into the inert membrane catalytic reactor.

[0035] The separation DMC membrane assembly 26 is an inert membrane catalytic reactor, and its structure is as shown in the attached Figure 1As shown. Fillers 3 are installed between the outer shell 4 and the membrane tube 7, and at both ends, to promote uniform material distribution. A catalyst is placed in the middle to catalyze the direct reaction of carbon dioxide and methanol to produce DMC and water. The mixed gas from the feed gas preheater 21 enters the DMC separation membrane assembly 26 through the air inlet 2, where a reaction occurs in the catalyst bed. The raw materials and products in the reaction system come into contact with the membrane tube 7. Because this system uses a mesoporous membrane (2-4 nm) as the separation membrane, all components can permeate from one side of the membrane to the other. To isolate only DMC from the system, an extractant is introduced into the membrane tube 7. This extractant dissolves only DMC, while other components are largely insoluble in the extractant and are trapped in the reaction system to continue the catalytic reaction. In specific operation, the outlet 12 and feed port 10 of the DMC separation membrane assembly 26 are connected to the extractant storage tank 22 via a pipeline. An extractant feed pump 23 is provided in the pipeline of the feed port 10. The extractant feed pump 23 feeds the extractant into the tube side of the inert membrane catalytic reactor, eluting the DMC that permeates the membrane from the inner surface of the membrane tube, while also retaining water, carbon dioxide, and methanol. During this process, the extractant feed pump 23 controls the pressure in the membrane tube side to maintain a pressure balance on the inner surface of the membrane and prevent the permeation of water, methanol, and carbon dioxide. The extractant flowmeter 25 and the extractant regulating valve 24 regulate the extractant (containing DMC) flowing out of the inert membrane catalytic reactor. On the one hand, a portion of the extractant is fed to the extractant recovery system at a stable flow rate for extractant recovery. On the other hand, the extractant is self-circulated to balance the flow fluctuations caused by pressure regulation. At the same time, the extractant can be fully utilized to extract DMC. To minimize the impact of water on the reaction, a dual-membrane system was employed: one membrane module for DMC separation and one for water separation. The water generated during the reaction was then pumped through a compressor into the water separation module for separation.

[0036] The membrane tube 7 is the core part of the reaction system. It is necessary to separate the DMC with a larger kinetic diameter (between 0.47 and 0.63 nm) in the reaction system from the water molecules (0.28 nm), carbon dioxide molecules (0.33 nm) and methanol molecules (0.38 nm) with smaller kinetic diameters. Under normal circumstances, small molecules are more likely to penetrate the molecular sieve membrane. In order to ensure that the macromolecular DMC can preferentially permeate through the membrane, this system combines membrane separation with extraction technology, and selects a mesoporous membrane with a porous alumina tube or a porous stainless steel tube as a carrier and a synthetic pore size between 2 and 4 nm to ensure that the macromolecular DMC can permeate. In order to avoid the small molecule components also permeating through, vacuum and inert gas purge are not used on the other side of the membrane to desorb the permeated components, but an extractant is selected to elute the permeated components because the extractant can only dissolve DMC. Therefore, only DMC can enter the extractant and be separated from the system, while other components are retained in the system and continue to react. The mesoporous membrane is preferably an MCM-48 mesoporous membrane. The extractant can be selected from o-xylene, butyl acetate, methylphenol, phenol, aniline, isoamyl acetate, etc., preferably o-xylene.

[0037] The water separation membrane assembly 35 selectively permeates the water produced in the inert membrane catalytic reactor. For this system, a hydrophilic molecular sieve membrane is used. Considering that the kinetic diameter of water molecules is less than 0.3 nm, while the diameter of other components is greater than 0.3 nm, a small-pore molecular sieve is selected for the membrane, with a pore size of 0.3 nm or less, preferably 3A molecular sieve. The raw materials, water and a small amount of DMC that has not permeated through the membrane in time in the inert membrane reactor flow out from the air outlet 11 of the membrane assembly 26 and are sent to the dehydration membrane reactor 35 for separating water through the compressor 34. The difference between the dehydration membrane reactor 35 and the DMC separation membrane assembly 26 is that there is no catalyst between the shell and the membrane tube. The membrane tube of the dehydration membrane reactor 35 is closed at one end and connected to the vacuum pump 39 at one end. The permeated water is separated from the dehydration membrane reactor 35 by vacuum desorption. That is, the material from the compressor 34 contacts the membrane in the assembly, and the hydrophilic membrane set selectively transmits the water in the material. After vacuum desorption on the other side, it enters the condenser 37. The condensed water enters the water storage tank 40 for storage. A vacuum buffer tank is set between the condenser 37 and the vacuum pump 39. On the one hand, it maintains the pressure stability of the system. At the same time, it can separate the entrained water to prevent the water from entering the vacuum pump 39 and affecting the operation of the vacuum pump 39. The unpermeated components flow out of the shell-side gas outlet and enter the feed gas preheater 21, where they are mixed with methanol or carbon dioxide and then enter the reaction system as feedstock for a repeat reaction. This recirculating material acts as a disturbance in the catalytic process, enhancing the uniform distribution of material concentration in the reaction system and improving reaction efficiency.

[0038] The material circulation system includes an extractant recycling system and a reaction material circulation system; the extractant recycling system uses a pump to send the extractant obtained from the extractant recovery system back to the inert membrane catalytic reactor for repeated use, thereby reducing the consumption of the extractant; the reaction material circulation system is a membrane component for separating water. After removing water, the material on the retentate side is returned to the raw gas preheater (21) for reaction by a compressor, which removes the product water in the reaction on the one hand, and on the other hand, plays a stirring role in the reaction material during the material circulation process, so that the material in the reaction system is evenly distributed, the concentration gradient and temperature gradient are reduced, and the reaction is promoted.

[0039] The purpose of the insulation system is to avoid heat loss. Insulation or heating is designed in the circulating material and heated reaction raw material pipelines to maintain the reaction system near the designed reaction temperature and ensure smooth reaction.

[0040] The storage system includes raw material tanks and product storage tanks, wherein the raw material tanks include a CO2 storage tank 14, a methanol storage tank 16 and an extractant storage tank 22; the product storage tanks include a dimethyl carbonate storage tank 41 and a water storage tank 40;

[0041] The extractant recovery system includes a heat exchanger 33, a condensate flowmeter 28, a condensate flow regulating valve 29, a condenser 30, a distillation tower 31, and a reboiler 32. The DMC-dissolved extractant flowing out of the membrane catalytic reactor is heat-exchanged with the high-temperature extractant obtained from the bottom of the tower via heat exchanger 33. After preheating, it enters the distillation tower 31, where it undergoes distillation separation. The overhead product is DMC, which is condensed in condenser 30 and split into two streams. One stream is returned to the distillation tower as reflux, with the reflux ratio of the distillation tower controlled by the condensate flowmeter 28 and condensate regulating valve 29. The other stream is sent to the DMC storage tank 41 as the product for storage. The bottom product is a high-temperature, high-purity extractant. To recover the extractant's heat, the extractant is heat-exchanged with the distillation tower's feedstock in the heat exchanger 30. After heat exchange, the extractant is sent to the extractant storage tank 22 for reuse.

[0042] The designed reaction system can greatly improve the conversion rate of carbon dioxide and the yield of DMC, solving the problem of low carbon dioxide conversion rate in other reaction systems.

[0043] A reaction system for directly synthesizing dimethyl carbonate from methanol and carbon dioxide comprises a shell 4 and a membrane tube 7. The two ends of the shell 4 are respectively connected to an upper flange 1 and a lower flange 9. The upper flange 1 and the lower flange 9 are tightly connected to the outer tube 4.

[0044] The upper flange 1 and the lower flange 9 are respectively provided with a feed port 10 and a discharge port 12;

[0045] The housing 4 is provided with an air inlet 2 and an air outlet 11 at both ends;

[0046] The feed port 10 and the discharge port 12 are respectively connected to the external threaded pipe joint 5;

[0047] Both ends of the membrane tube 7 are fixed by internal threaded pipe joints 6;

[0048] The internal and external threaded pipe joints are sealed by gaskets;

[0049] A packing layer 3 is provided in the annular gap between the housing 4 and the feed port 10 and the discharge port 12;

[0050] A catalyst bed 8 is provided in the annular gap between the membrane tube 7 and the membrane tube 4 .

[0051] The CO2 storage tank 13 is connected to the raw gas preheater 21 through the CO2 flow regulating valve 14 and the CO2 flow meter 15;

[0052] The methanol storage tank 16 is connected to the methanol vaporizer 19 through a pipeline, and after partial reflux through the methanol flow meter 20 and the methanol flow control valve 18, it is connected to the raw gas preheater 21;

[0053] The raw gas preheater is connected to the air inlet 2 of the membrane reactor through an insulation pipeline, and the temperature of the preheater is accurately controlled by the temperature control steam regulating valve 42 of the material in the outlet pipeline;

[0054] The extractant storage tank 22 is connected to the membrane reactor feed port 10 via an extractant feed pump 23;

[0055] The membrane reactor 26 is externally provided with a first heating furnace 27 for heating;

[0056] The membrane reactor outlet 12 is provided with an extract flow controller 24 and an extract flow meter 25, which control a portion of the extract to circulate through the extract feed pump to extract DMC, and another portion of the extract is regulated by the extract flow meter 25 and the extract regulating valve to flow into the heat exchanger 33 at a set flow rate for heat exchange and then enter the distillation tower for extractant recovery;

[0057] The membrane component for separating DMC uses MCM-48 membrane as the separation membrane and o-xylene as the extractant to separate DMC;

[0058] The extracted liquid from the heat exchanger 33 is connected to the distillation tower 31 through an insulated pipeline. The product dimethyl carbonate passes through the condenser 30 at the top of the tower. After partial reflux is controlled by the condensate flowmeter 28 and the condensate flow regulating valve 29, the rest of the condensate flows out of the distillation tower 31 and enters the dimethyl carbonate storage tank 41.

[0059] The bottom product obtained after the bottom liquid of the distillation tower 31 is refluxed through the reboiler 32 is connected to the heat exchanger 33 through a pipeline, and then flows back to the extractant storage tank 22 after heat exchange with the extraction liquid.

[0060] The membrane reactor gas outlet 11 is connected to the water separation membrane assembly 35 through a compressor 34 via an insulation pipeline;

[0061] The membrane assembly 35 for separating water is externally provided with a second heating furnace 36 for heating;

[0062] The membrane assembly for separating water uses 3A molecular sieve membrane as the separation membrane, vacuum is used for desorption on the permeate side, and water is recovered by condensation. The material on the retentate side is sent to the raw gas heater 21 through a compressor for circulation and catalytic reaction.

[0063] The water separated by the water separation membrane assembly is condensed by the condenser 37 and enters the water storage tank 40. The non-condensable gas in the condenser is pumped out by the vacuum pump 39 through the vacuum buffer tank 38.

Claims

1. A reaction system for improving the conversion rate of direct synthesis of dimethyl carbonate from carbon dioxide and methanol, characterized in that: The reaction system includes a membrane catalytic reaction system and an extractant recovery system; A membrane catalytic reaction system, comprising a feed system, a mixing temperature-increasing and pressurizing system, a separation DMC membrane assembly (26), a water separation membrane assembly, a material circulation system, a heat preservation system and a storage system; The feeding system includes a carbon dioxide feeding system and a methanol feeding system; the carbon dioxide feeding system includes a CO2 storage tank (13), a CO2 flow regulating valve (14) and a CO2 flow meter (15); the CO2 storage tank (13) provides CO2 raw materials, and the flow of CO2 is accurately controlled by the CO2 flow regulating valve (14) and the CO2 flow meter (15); the methanol feeding system includes a methanol storage tank (16), a methanol feeding pump (17), a methanol flow regulating valve (18), a methanol vaporizer (19) and a methanol flow meter (20); the methanol storage tank (16), the methanol feeding pump (17), the methanol vaporizer (19) and the methanol flow meter (20) are connected in sequence, and the methanol flow regulating valve (18) adopts a bypass regulation form, and the opening of the methanol flow regulating valve (18) is controlled by the parameters set by the methanol flow meter (20), thereby accurately controlling the feeding amount of methanol; The mixed temperature-raising and pressurizing system mainly consists of a raw gas preheater (21), a steam regulating valve (42) and a steam trap (43). A thermocouple is set on the outlet pipe of the raw gas preheater (21). The opening of the steam regulating valve (42) is adjusted by controlling the temperature on the pipe, thereby adjusting the temperature of the mixed gas. After steam heating, it is discharged from the system through the steam trap (43). Carbon dioxide from the carbon dioxide feed system, methanol vapor from the methanol feed system and the circulating material from the water separation membrane assembly that has been completely or partially dehydrated are all fed into the pipe side of the raw gas preheater (21), where they are mixed, heated and pressurized, and then fed into the inert membrane catalytic reactor. The separation DMC membrane assembly (26) is an inert membrane catalytic reactor, wherein a mesoporous membrane with a pore size of 2-4 nm is used as a separation membrane; fillers (3) are installed between the shell (4) and the membrane tube (7) and at both ends of the inert membrane catalytic reactor to promote uniform distribution of materials; a catalyst (8) is installed in the middle to catalyze the direct reaction of carbon dioxide and methanol to produce DMC and water; the mixed gas from the raw gas preheater (21) enters the separation DMC membrane assembly (26) through the air inlet (2) and reacts in the catalyst bed. The raw materials and products in the reaction system react with the membrane. The discharge port (12) and feed port (10) of the separation DMC membrane assembly (26) are respectively connected to the extractant storage tank (22) through pipelines, and an extractant feed pump (23) is provided on the pipeline of the feed port (10), and the extractant is fed into the pipe side of the inert membrane catalytic reactor through the extractant feed pump (23); a pipeline is connected between the discharge port (12) and the feed port (10), and an extractant flow meter (25) and an extractant flow regulating valve (24) are provided on the pipeline for regulating the DMC-containing extract flowing out of the inert membrane catalytic reactor; The membrane assembly for separating water is a dehydration membrane reactor (35), wherein a 3A molecular sieve membrane with a membrane pore size of no more than 0.3 nm is selected; the raw materials, water and a small amount of DMC that has not permeated through the separation membrane in the inert membrane catalytic reactor flow out from the gas outlet (11) of the separation DMC membrane assembly (26) and are sent to the dehydration membrane reactor (35) through a compressor (34); the difference between the dehydration membrane reactor (35) and the separation DMC membrane assembly (26) is that there is no catalyst between the shell and the membrane tube; one end of the tube side of the dehydration membrane reactor (35) is closed, and the other end is connected in sequence to a second condenser (37), a vacuum buffer tank (38), and a vacuum pump (39); the second condenser (37) is also connected to a water storage tank (40); The material circulation system includes an extractant recycling system and a reaction material circulation system; the extractant recycling system uses a pump to send the extractant obtained from the extractant recovery system back to the inert membrane catalytic reactor; the reaction material circulation system uses a compressor to send the material on the retentate side of the water separation membrane component after water removal back to the raw gas preheater (21) for reaction; The insulation system is designed to keep the circulating materials and the heated reaction raw material pipelines warm or heat them to maintain the reaction temperature of the reaction system and ensure the smooth progress of the reaction; The storage system includes a raw material tank and a product storage tank, wherein the raw material tank includes a CO2 storage tank (13), a methanol storage tank (16) and an extractant storage tank (22); the product storage tank includes a dimethyl carbonate storage tank (41) and a water storage tank (40); The extractant recovery system includes a heat exchanger (33), a condensate flow meter (28), a condensate flow regulating valve (29), a first condenser (30), a distillation tower (31) and a reboiler (32); the extractant dissolving DMC flowing out of the inert membrane catalytic reactor is heat-exchanged with the high-temperature extractant obtained from the bottom of the distillation tower (31) through the heat exchanger (33), and then enters the distillation tower (31) after preheating, and is distilled and separated in the distillation tower (31). The top product is DMC. After DMC is condensed in the first condenser (30), it is divided into two streams. One stream of material is returned to the distillation tower (31) as reflux, and the reflux ratio of the distillation tower (31) is controlled by the condensate flow meter (28) and the condensate regulating valve (29); the other stream of material is sent to the DMC storage tank (41) for storage as a product; the extractant exchanges heat with the raw material of the distillation tower (31) in the heat exchanger (33), and the extractant after heat exchange is sent to the extractant storage tank (22) for reuse.

2. The reaction system for improving the conversion rate of direct synthesis of dimethyl carbonate from carbon dioxide and methanol according to claim 1, characterized in that: The catalyst (8) used in the catalytic reaction is a supported catalyst or a metal oxide catalyst.

3. The reaction system for improving the conversion rate of direct synthesis of dimethyl carbonate from carbon dioxide and methanol according to claim 2, characterized in that: The supported catalyst includes a carrier and a transition metal supported on the carrier, wherein the transition metal is at least one of Fe, Co, Ni, Cu, and Zn, and the carrier is at least one of Cs2O, La2O3, ZrO2, Al2O3, SiO2, TiO2, nitrogen-doped graded porous carbon, and activated carbon, and the loading amount of the transition metal is 1 to 20 wt% based on its corresponding oxide.

4. The reaction system for improving the conversion rate of direct synthesis of dimethyl carbonate from carbon dioxide and methanol according to claim 2, characterized in that: The metal oxide catalyst is an oxide composed of Ce and another transition metal, wherein the transition metal is one of Mn, Ti, Zr, Zn and Fe.

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