A nitrogen recovery and utilization system in a cryogenic system

Abstract

The present invention relates to the technical field of nitrogen recovery and utilization, and discloses a nitrogen recovery and utilization system in a cryogenic system, comprising a pressure swing adsorption device and a nitrogen buffer device; the pressure swing adsorption device comprises an air inlet and an air outlet; the air outlet is connected to the inlet of the nitrogen buffer device; the outlet of the nitrogen buffer device is connected to the cryogenic system; the pressure swing adsorption device is loaded with a modified activated carbon adsorbent; after the gas in the pressure swing adsorption device is pressure-swing adsorbed by the modified activated carbon adsorbent, the unadsorbed gas is passed into the nitrogen buffer device for compression and then directly used in the reaction system. The present invention improves the recovery and utilization efficiency of nitrogen by removing impurities through adsorption by the adsorbent, obtains high-yield and high-purity nitrogen, is simple to operate, and can directly reuse the nitrogen as a nitrogen shielding gas for the reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrogen recovery and utilization, and in particular to a nitrogen recovery and utilization system in a cryogenic system. Background Art

[0002] Part of the process of drug substance synthesis involves deep-cold reaction (-80°C). Currently, conventional refrigerants, such as ethylene glycol solution, can only reach a minimum temperature of about -60°C, which still does not meet the process requirements. Liquid nitrogen is used as a refrigerant to directly pass into the jacket of the reactor or liquid nitrogen and isohexane are heat exchanged to prepare -80°C isohexane refrigerant. After heat exchange, liquid nitrogen becomes nitrogen at room temperature or low temperature. Direct discharge will lead to nitrogen waste or a low-oxygen environment will be formed in the discharge area. If people pass through or work in this area, there is a risk of asphyxiation due to lack of oxygen. The regulations stipulate that nitrogen protection measures should be taken for process systems that are intermittently operated and have flammable and explosive hazards. The comprehensive utilization of nitrogen after heat exchange can greatly reduce regional nitrogen pollution and reduce product costs.

[0003] Publication number CN103332660B Chinese invention patent discloses a kind of nitrogen recovery and reuse device, including a cartridge filter, the air inlet side of the cartridge filter is connected to the pulverized coal injection tank by a pressure relief pneumatic valve, the discharge side of the cartridge filter is connected to the pulverized coal bunker by a pneumatic powder discharge ball valve, the air outlet side of the cartridge filter is connected to the air inlet of the equalized pressure gas storage tank by a pneumatic equalizing valve, the air outlet of the equalized pressure gas storage tank is connected to the air inlet of the nitrogen buffer tank by a pneumatic diaphragm regulating valve, the tank body upper part of the nitrogen buffer tank is connected to a pressure transmitter, the air outlet of the nitrogen buffer tank is connected to the air inlet side of the nitrogen booster by an air inlet shut-off valve, and the air outlet side of the nitrogen booster is connected to the air inlet of the nitrogen gas storage tank. However, the device is mainly used in the recycling after the nitrogen blast furnace pulverized coal injection, and it is not suitable for the present invention, and can cause the recovery and utilization efficiency of nitrogen to be lower. Summary of the Invention

[0004] In order to solve the problem of how to improve the recovery and utilization efficiency of nitrogen in a cryogenic system, the present invention provides a nitrogen recovery and utilization system in a cryogenic system. The system removes impurities through adsorption by an adsorbent, is simple to operate and has low energy consumption, and can obtain high-yield and high-purity nitrogen. The system can be directly used as a protective gas in a conventional reaction system, thereby improving the recovery and utilization efficiency of nitrogen.

[0005] The specific technical solution of the present invention is as follows: the present invention provides a nitrogen recovery and utilization system in a cryogenic system, comprising a pressure swing adsorption device and a nitrogen buffer device; the pressure swing adsorption device comprises an air inlet and an air outlet; the air inlet is connected to the inlet of the nitrogen buffer device; the outlet of the nitrogen buffer device is connected to the reaction system; the pressure swing adsorption device is loaded with a modified activated carbon adsorbent; after the gas in the pressure swing adsorption device is subjected to pressure swing adsorption by the modified activated carbon adsorbent, the unadsorbed gas is passed into the nitrogen buffer device and directly used in the reaction system.

[0006] Liquid nitrogen is used to cool isohexane to prepare isohexane refrigerant for use in a cryogenic system. The nitrogen is then recycled to avoid direct discharge, which may result in nitrogen waste or a low-oxygen environment in the discharge port area. If a person passes through or works in this area, there is a risk of suffocation due to lack of oxygen, as well as the risk of flammability and explosion. In addition to the temperature increase caused by heat exchange, nitrogen also introduces ambient air, water vapor, etc. during the process, which requires adsorption and removal by an adsorbent. The nitrogen protective gas can then be used for conventional reactions to achieve effective recycling of nitrogen. The adsorbent used is a modified activated carbon adsorbent. The activated carbon itself has abundant micropores and is a porous amorphous carbon with strong adsorption capacity. In addition, its surface also has abundant active groups that can be mixed and modified with a variety of organic substances. The resulting modified activated carbon adsorbent can enhance adsorption, thereby improving the separation efficiency of nitrogen. The present invention can obtain nitrogen with high yield and purity, and will not introduce other impurities during secondary use. The whole process is simple to operate and has low energy consumption, thereby improving the recycling efficiency of nitrogen.

[0007] Preferably, the processing pressure of the pressure swing adsorption device is 0.3-0.8 MPa, and the processing temperature is 20-30°C.

[0008] The adsorbent at the treatment pressure and treatment temperature has better adsorption effect.

[0009] Preferably, the pressure swing adsorption device further comprises an exhaust port and a hot air inlet; the air inlet and exhaust port are arranged at the upper end of the pressure swing adsorption device; the air outlet and hot air inlet are arranged at the lower end of the pressure swing adsorption device.

[0010] Preferably, the system further comprises a heating and heat exchange device; the inlet of the heating and heat exchange device is connected to the exhaust port of the pressure swing adsorption device; the outlet of the heating and heat exchange device is connected to the hot air inlet of the pressure swing adsorption device.

[0011] Preferably, the processing temperature of the heating and heat exchanging device is 80-100°C.

[0012] Preferably, the modified activated carbon adsorbent is regenerated by reversely purging the gas introduced through the hot air inlet at normal pressure, and the gas generated after desorption is discharged from the exhaust port.

[0013] Preferably, the preparation method of the modified activated carbon adsorbent comprises the following steps:

[0014] (1) Ethyltrichlorosilane, phenyltrichlorosilane and vinyltriethoxysilane are added dropwise to a mixed solution of water and toluene, and the mixture is heated to 55-75° C. to react for 30-80 minutes. After the reaction is completed, the aqueous layer is allowed to stand and separated to obtain a vinyl silicone resin prepolymer; (2) Activated carbon and g-C3N4 nanosheets are added to the vinyl silicone resin prepolymer and stirred to mix, wherein the pore size of the activated carbon is not greater than 2 nm; fumaric acid, azobisisobutyronitrile, chloroform and N,N-dimethylformamide are then added and mixed. The method comprises the following steps: performing reduced pressure distillation at 75 to 85° C. for 2 to 4 hours; adding chitosan and chloroform to mix, and then dropping a sodium tripolyphosphate solution, and crosslinking for 20 to 30 minutes after the dropwise addition is completed; the mass volume ratio of the g-C3N4 nanosheets, chitosan, chloroform and sodium tripolyphosphate solution is 0.1 to 0.3 g: 4 to 7 g: 10 to 20 mL: 1 to 3 mL; and the concentration of the sodium tripolyphosphate solution is 2 to 4 mg / mL; placing the nanosheets into a mold after the reaction is completed, and calcining the mixture after curing to obtain a modified activated carbon adsorbent.

[0015] Activated carbon inherently possesses a well-developed pore structure. When mixed with silicone resin and calcined, the silica serves as the external structural framework, forming a micro-mesoporous structure that effectively fixes adsorbed gases. The surface of g-C3N4 nanosheets is rich in amino groups, which increase the adsorbent's basic centers. Furthermore, the partially exposed micropores after calcination increase the specific surface area and enhance gas adsorption. Fumarene cross-links with activated carbon, g-C3N4 nanosheets, and vinyl silicone resin prepolymer, improving the adsorbent's binding and stability. Added chitosan forms a gel after cross-linking with sodium tripolyphosphate. It also cross-links with some of the active amino groups on the g-C3N4 nanosheets, enhancing cohesion between the adsorbents. After calcination, it also forms an amorphous porous carbon structure, increasing the specific surface area and complicating the pore structure. Because the molecules and content of impurity gases in the cryogenic system are relatively small, the modification of the functional groups on the surface of activated carbon and the complexity of the pore structure are conducive to the adsorption of small molecules such as carbon dioxide, oxygen, and free water in the air, thereby improving the recovery and utilization efficiency of nitrogen.

[0016] Preferably, in step (1), the mass ratio of ethyltrichlorosilane, phenyltrichlorosilane and vinyltriethoxysilane is 35-50:25-35:10-15; the volume ratio of water and toluene is 1-1.5:1;

[0017] Preferably, in step (2), the mass volume ratio of the activated carbon, g-C3N4 nanosheets, vinyl silicone resin prepolymer, fumaric acid, azobisisobutyronitrile, chloroform and N,N-dimethylformamide is 0.5-1g:0.1-0.3g:50-60g:5-10g:0.5-1g:50mL:10-30mL; the molecular weight of the chitosan is 10,000-50,000; the curing is heated and pressurized curing, the temperature is 90-100°C, and the pressure is 3-5MPa; the calcination temperature is 300-400°C, and the time is 2-4h.

[0018] The pore size and addition amount of activated carbon are particularly critical for forming a good micro-mesoporous structure. In addition, the added chitosan is also part of the skeleton that ultimately forms the pore structure. Its molecular weight and cross-linking degree also affect the distribution of the pore structure. The adsorbent formed under the ratio of the present invention has a larger specific surface area, and the micro-mesoporous structure is more conducive to the adsorption and fixation of gases, and the separation and recovery rate of nitrogen is higher.

[0019] Preferably, the processing pressure of the nitrogen buffer device is 1 to 5 KPa.

[0020] Preferably, the system further comprises a liquid seal tank and a circulation pump; the inlet of the liquid seal tank is connected to the nitrogen buffer device; the inlet of the circulation pump is connected to the outlet of the nitrogen buffer device; and the outlet of the circulation pump is connected to the reaction system.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The adsorbent is used to remove impurities, thereby improving the recovery efficiency of nitrogen. The operation is simple, and the nitrogen can be directly reused as nitrogen protective gas for conventional reactions;

[0023] (2) The modification of the functional groups on the surface of activated carbon and the complexity of the pore structure increase the specific surface area, which is conducive to selective adsorption and improves the yield and purity of nitrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the nitrogen recovery and utilization system in the cryogenic system of the present invention.

[0025] The reference numerals are: tail gas 1, pressure swing adsorption device 2, air inlet 201, air outlet 202, exhaust port 203, hot air inlet 204, nitrogen buffer device 3, heating and heat exchange device 4, liquid seal tank 5, circulation pump 6, reaction system 7. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the embodiments.

[0027] Overall embodiment

[0028] A nitrogen recovery and utilization system in a cryogenic system includes a pressure swing adsorption unit 2, a nitrogen buffer unit 3, a heating and heat exchange device 4, a liquid seal tank 5, and a circulation pump 6. The pressure swing adsorption unit 2 includes an air inlet 201, an air outlet 202, an exhaust port 203, and a hot air inlet 204. The air inlet 201 and exhaust port 203 are located at the upper end of the pressure swing adsorption unit 2, while the air outlet 202 and hot air inlet 204 are located at the lower end of the pressure swing adsorption unit 2. Furthermore, the pressure swing adsorption unit 2 is loaded with a modified activated carbon adsorbent. Tail gas 1 enters through the air inlet 201 and is adsorbed by the modified activated carbon adsorbent. The unadsorbed gas is then passed into the nitrogen buffer unit 3. The air outlet 202 of the pressure swing adsorption unit 2 is connected to the inlet of the nitrogen buffer unit 3. The inlet of the liquid seal tank 5 is connected to the upper end of the nitrogen buffer unit 3, thereby sealing the nitrogen buffer unit 3. The processing pressure of the nitrogen buffer device 3 is 1-5KPa. After being compressed by the nitrogen buffer device 3, the gas enters the reaction system 7 through the circulation pump 6 connected to the outlet of the nitrogen buffer device 3 and is reused as nitrogen protection gas for the reaction.

[0029] The processing pressure of the pressure swing adsorption unit 2 is 0.3-0.8 MPa, and the processing temperature is 20-30°C. The recycling system also includes a heating and heat exchange unit 4, the inlet of which is connected to the exhaust port 203 of the pressure swing adsorption unit 2, and the outlet of which is connected to the hot air inlet 204 of the pressure swing adsorption unit 2. The processing temperature of the heating and heat exchange unit 4 is 80-100°C. The treated modified activated carbon adsorbent is regenerated by reverse purging at atmospheric pressure with gas introduced through the hot air inlet 204. The gas generated after desorption is discharged through the exhaust port 203 for recycling. The heating and heat exchange unit 4 discharges the gas when the gas reaches the dischargeable gas requirement.

[0030] The preparation method of the modified activated carbon adsorbent comprises the following steps:

[0031] (1) adding ethyltrichlorosilane, phenyltrichlorosilane and vinyltriethoxysilane in a mass ratio of 35-50:25-35:10-15 dropwise to a mixed solution of water and toluene in a volume ratio of 1-1.5:1, heating to 55-75° C. to react for 30-80 minutes, and after the reaction is completed, standing to separate the water layer to obtain a vinyl silicone resin prepolymer;

[0032] (2) Add activated carbon and g-C3N4 nanosheets to vinyl silicone resin prepolymer and stir to mix, wherein the pore size of the activated carbon is not greater than 2 nm; then add fumaric acid, azobisisobutyronitrile, chloroform and N,N-dimethylformamide and mix, and distill under reduced pressure at 75-85°C for 2-4 hours, wherein the mass volume ratio of the activated carbon, g-C3N4 nanosheets, vinyl silicone resin prepolymer, fumaric acid, azobisisobutyronitrile, chloroform and N,N-dimethylformamide is 0.5-1g: 0.1-0.3g: 50-60g: 5-10g: 0.5-1g: 50mL: 10-30mL; then add the separated Chitosan with a molecular weight of 10,000 to 50,000 is mixed with chloroform, and then a sodium tripolyphosphate solution is added dropwise, and cross-linking is carried out for 20 to 30 minutes after the addition is completed; the mass volume ratio of the g-C3N4 nanosheets, chitosan, chloroform and sodium tripolyphosphate solution is 0.1 to 0.3 g: 4 to 7 g: 10 to 20 mL: 1 to 3 mL; the concentration of the sodium tripolyphosphate solution is 2 to 4 mg / mL; after the reaction is completed, the mixture is placed in a mold, heated and pressurized to solidify at a temperature of 90 to 100° C. and a pressure of 3 to 5 MPa, and then calcined at a temperature of 300 to 400° C. for 2 to 4 hours to obtain a modified activated carbon adsorbent.

[0033] Example 1

[0034] A nitrogen recovery and utilization system in a cryogenic system, such as Figure 1 As shown, the pressure swing adsorption system includes a pressure swing adsorption unit 2, a nitrogen buffer unit 3, a heating and heat exchange device 4, a liquid seal tank 5, and a circulation pump 6. The pressure swing adsorption unit 2 includes an air inlet 201, an air outlet 202, an exhaust port 203, and a hot air inlet 204. The air inlet 201 and exhaust port 203 are located at the upper end of the pressure swing adsorption unit 2, while the air outlet 202 and hot air inlet 204 are located at the lower end of the pressure swing adsorption unit 2. Furthermore, the pressure swing adsorption unit 2 is loaded with a modified activated carbon adsorbent. Tail gas 1 enters through the air inlet 201 and is adsorbed by the modified activated carbon adsorbent. The unadsorbed gas is then passed into the nitrogen buffer unit 3. The air outlet 202 of the pressure swing adsorption unit 2 is connected to the inlet of the nitrogen buffer unit 3. The inlet of the liquid seal tank 5 is connected to the upper end of the nitrogen buffer unit 3, thereby sealing the nitrogen buffer unit 3. The processing pressure of the nitrogen buffer device 3 is 3KPa. After being compressed by the nitrogen buffer device 3, the gas re-enters the reaction system 7 through the circulation pump 6 connected to the outlet of the nitrogen buffer device 3 and is reused as nitrogen protective gas for the reaction.

[0035] The processing pressure of the pressure swing adsorption unit 2 is 0.6 MPa, and the processing temperature is 30°C. The recycling system also includes a heating and heat exchange unit 4, the inlet of which is connected to the exhaust port 203 of the pressure swing adsorption unit 2, and the outlet of which is connected to the hot air inlet 204 of the pressure swing adsorption unit 2. The processing temperature of the heating and heat exchange unit 4 is 95°C. The treated modified activated carbon adsorbent is regenerated by reverse purging at atmospheric pressure with gas introduced through the hot air inlet 204. The gas generated after desorption is discharged through the exhaust port 203 for recycling. The heating and heat exchange unit 4 discharges the gas when it reaches the required dischargeable gas.

[0036] The preparation method of the modified activated carbon adsorbent comprises the following steps:

[0037] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0038] (2) Add 0.6 g of activated carbon (pore size of 2 nm) and 0.2 g of g-C3N4 nanosheets to 55 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 °C for 3 h; then add 5 g of chitosan with a molecular weight of 30,000 and 15 mL of chloroform, and then add 1.5 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 °C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 400 °C for 3 h to obtain a modified activated carbon adsorbent.

[0039] Example 2

[0040] A nitrogen recovery and utilization system in a cryogenic system includes a pressure swing adsorption unit 2, a nitrogen buffer unit 3, a heating and heat exchange device 4, a liquid seal tank 5, and a circulation pump 6. The pressure swing adsorption unit 2 includes an air inlet 201, an air outlet 202, an exhaust port 203, and a hot air inlet 204. The air inlet 201 and exhaust port 203 are located at the upper end of the pressure swing adsorption unit 2, while the air outlet 202 and hot air inlet 204 are located at the lower end of the pressure swing adsorption unit 2. Furthermore, the pressure swing adsorption unit 2 is loaded with a modified activated carbon adsorbent. Tail gas 1 enters through the air inlet 201 and is adsorbed by the modified activated carbon adsorbent. The unadsorbed gas is then passed into the nitrogen buffer unit 3. The air outlet 202 of the pressure swing adsorption unit 2 is connected to the inlet of the nitrogen buffer unit 3. The inlet of the liquid seal tank 5 is connected to the upper end of the nitrogen buffer unit 3, thereby sealing the nitrogen buffer unit 3. The processing pressure of the nitrogen buffer device 3 is 3KPa. After being compressed by the nitrogen buffer device 3, the gas re-enters the reaction system 7 through the circulation pump 6 connected to the outlet of the nitrogen buffer device 3 and is reused as nitrogen protective gas for the reaction.

[0041] The processing pressure of the pressure swing adsorption unit 2 is 0.8 MPa, and the processing temperature is 25°C. The recycling system also includes a heating and heat exchange unit 4, the inlet of which is connected to the exhaust port 203 of the pressure swing adsorption unit 2, and the outlet of which is connected to the hot air inlet 204 of the pressure swing adsorption unit 2. The processing temperature of the heating and heat exchange unit 4 is 95°C. The treated modified activated carbon adsorbent is regenerated by reverse purging at atmospheric pressure with gas introduced through the hot air inlet 204. The gas generated after desorption is discharged through the exhaust port 203 for recycling. The heating and heat exchange unit 4 discharges the gas when it reaches the required dischargeable gas.

[0042] The preparation method of the modified activated carbon adsorbent comprises the following steps:

[0043] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0044] (2) Add 0.8 g of activated carbon (pore size of 1 nm) and 0.2 g of g-C3N4 nanosheets to 50 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 85 °C for 3 h; then add 6 g of chitosan with a molecular weight of 20,000 and 15 mL of chloroform, and then add 2 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 °C and a pressure of 4 MPa to cure it, and then calcine it at a temperature of 400 °C for 3 h to obtain a modified activated carbon adsorbent.

[0045] Example 3

[0046] A nitrogen recovery and utilization system in a cryogenic system includes a pressure swing adsorption unit 2, a nitrogen buffer unit 3, a heating and heat exchange device 4, a liquid seal tank 5, and a circulation pump 6. The pressure swing adsorption unit 2 includes an air inlet 201, an air outlet 202, an exhaust port 203, and a hot air inlet 204. The air inlet 201 and exhaust port 203 are located at the upper end of the pressure swing adsorption unit 2, while the air outlet 202 and hot air inlet 204 are located at the lower end of the pressure swing adsorption unit 2. Furthermore, the pressure swing adsorption unit 2 is loaded with a modified activated carbon adsorbent. Tail gas 1 enters through the air inlet 201 and is adsorbed by the modified activated carbon adsorbent. The unadsorbed gas is then passed into the nitrogen buffer unit 3. The air outlet 202 of the pressure swing adsorption unit 2 is connected to the inlet of the nitrogen buffer unit 3. The inlet of the liquid seal tank 5 is connected to the upper end of the nitrogen buffer unit 3, thereby sealing the nitrogen buffer unit 3. The processing pressure of the nitrogen buffer device 3 is 3KPa. After being compressed by the nitrogen buffer device 3, the gas re-enters the reaction system 7 through the circulation pump 6 connected to the outlet of the nitrogen buffer device 3 and is reused as nitrogen protective gas for the reaction.

[0047] The processing pressure of the pressure swing adsorption unit 2 is 0.6 MPa, and the processing temperature is 30°C. The recycling system also includes a heating and heat exchange unit 4, the inlet of which is connected to the exhaust port 203 of the pressure swing adsorption unit 2, and the outlet of which is connected to the hot air inlet 204 of the pressure swing adsorption unit 2. The processing temperature of the heating and heat exchange unit 4 is 95°C. The treated modified activated carbon adsorbent is regenerated by reverse purging at atmospheric pressure with gas introduced through the hot air inlet 204. The gas generated after desorption is discharged through the exhaust port 203 for recycling. The heating and heat exchange unit 4 discharges the gas when it reaches the required dischargeable gas.

[0048] The preparation method of the modified activated carbon adsorbent comprises the following steps:

[0049] (1) 45 g of ethyltrichlorosilane, 30 g of phenyltrichlorosilane, and 15 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.5:1, and the mixture was heated to 75° C. for 70 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0050] (2) Add 0.6 g of activated carbon (pore size of 2 nm) and 0.3 g of g-C3N4 nanosheets to 60 g of vinyl silicone resin prepolymer and stir to mix; then add 0.8 g of fumaric acid, 0.6 g of azobisisobutyronitrile, 50 mL of chloroform and 15 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 ° C for 3 h; then add 5 g of chitosan with a molecular weight of 30,000 and 20 mL of chloroform, and then add 1 mL of 3 mg / mL sodium tripolyphosphate solution dropwise. After the addition is completed, cross-link for 30 minutes; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 100 ° C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 350 ° C for 4 h to obtain a modified activated carbon adsorbent.

[0051] Comparative Example 1

[0052] The difference from Example 1 is that g-C3N4 nanosheets are not added in the preparation method of the modified activated carbon adsorbent.

[0053] The steps include:

[0054] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0055] (2) Add 0.6 g of activated carbon (pore size of 2 nm) to 55 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 ° C for 3 h; then add 5 g of chitosan with a molecular weight of 30,000 and 15 mL of chloroform, and then add 1.5 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 ° C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 400 ° C for 3 h to obtain a modified activated carbon adsorbent.

[0056] Comparative Example 2

[0057] The difference from Example 1 is that chitosan is not added in the preparation method of the modified activated carbon adsorbent.

[0058] The steps include:

[0059] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0060] (2) Add 0.2 g of g-C3N4 nanosheets to 55 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 °C for 3 h; then add 5 g of chitosan with a molecular weight of 30,000 and 15 mL of chloroform, and then add 1.5 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 °C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 400 °C for 3 h to obtain a modified activated carbon adsorbent.

[0061] Comparative Example 3

[0062] The difference from Example 1 is that in the preparation method of the modified activated carbon adsorbent, the pore size of the activated carbon is 10 nm.

[0063] The steps include:

[0064] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0065] (2) Add 0.6 g of activated carbon (pore size of 10 nm) and 0.2 g of g-C3N4 nanosheets to 55 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 ° C for 3 h; then add 5 g of chitosan with a molecular weight of 30,000 and 15 mL of chloroform, and then add 1.5 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 ° C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 400 ° C for 3 h to obtain a modified activated carbon adsorbent.

[0066] Comparative Example 4

[0067] The difference from Example 1 is that in the preparation method of the modified activated carbon adsorbent, the amount of activated carbon added is too much.

[0068] The steps include:

[0069] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0070] (2) Add 2 g of activated carbon (pore size of 2 nm) and 0.2 g of g-C3N4 nanosheets to 55 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 ° C for 3 h; then add 5 g of chitosan with a molecular weight of 30,000 and 15 mL of chloroform, and then add 1.5 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 ° C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 400 ° C for 3 h to obtain a modified activated carbon adsorbent.

[0071] Comparative Example 5

[0072] The difference from Example 1 is that in the preparation method of the modified activated carbon adsorbent, the molecular weight of chitosan is 100,000.

[0073] The steps include:

[0074] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0075] (2) Add 0.6 g of activated carbon (pore size of 2 nm) and 0.2 g of g-C3N4 nanosheets to 55 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 °C for 3 h; then add 5 g of chitosan with a molecular weight of 100,000 and 15 mL of chloroform, and then add 1.5 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 °C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 400 °C for 3 h to obtain a modified activated carbon adsorbent.

[0076] Comparative Example 6

[0077] The difference from Example 1 is that in the preparation method of the modified activated carbon adsorbent, too much chitosan is added.

[0078] The steps include:

[0079] (1) 40 g of ethyltrichlorosilane, 35 g of phenyltrichlorosilane, and 13 g of vinyltriethoxysilane were added dropwise to 400 mL of a mixed solution of water and toluene in a volume ratio of 1.2:1, and the mixture was heated to 70° C. for 65 min. After the reaction was completed, the aqueous layer was allowed to stand and separated to obtain a vinyl silicone resin prepolymer;

[0080] (2) Add 0.6 g of activated carbon (pore size of 2 nm) and 0.2 g of g-C3N4 nanosheets to 55 g of vinyl silicone resin prepolymer and stir to mix; then add 7 g of fumaric acid, 0.5 g of azobisisobutyronitrile, 50 mL of chloroform and 20 mL of N,N-dimethylformamide, and distill under reduced pressure at 80 °C for 3 h; then add 12 g of chitosan with a molecular weight of 30,000 and 15 mL of chloroform, and then add 1.5 mL of sodium tripolyphosphate solution with a concentration of 2 mg / mL, and cross-link for 25 minutes after the addition is completed; after the reaction is completed, put it into a mold, heat and pressurize it at a temperature of 95 °C and a pressure of 3 MPa to cure it, and then calcine it at a temperature of 400 °C for 3 h to obtain a modified activated carbon adsorbent.

[0081] Table 1 Yield and purity of nitrogen in the recycling system

[0082]

[0083]

[0084] In Table 1, nitrogen yield is the percentage of nitrogen in the output gas; nitrogen purity is the percentage of nitrogen in the output gas in the feed gas.

[0085] As shown in Table 1, the present invention improves the recovery and utilization efficiency of nitrogen by adsorbent adsorption and impurity removal, obtains high yield and high purity, is simple to operate, and can directly reuse nitrogen as a nitrogen shielding gas for the reaction. Comparative Example 1 shows that the addition of g-C3N4 nanosheets is conducive to improving the yield and purity of nitrogen. This is because g-C3N4 nanosheets can provide abundant alkaline centers and surface functional groups for activated carbon adsorbents, which contribute to selective adsorption. Comparative Example 2 shows that chitosan helps to form a micro-mesoporous structure. The porous carbon skeleton and silica skeleton formed by it jointly promote the complexity of the pore structure, which is conducive to the fixation of the gas after adsorption to improve the nitrogen yield. Comparative Examples 3-4 show that activated carbon pore size, addition amount, etc. are particularly critical for forming a good micro-mesoporous structure. Activated carbon pore size is too large to balance the ratio of micro-mesoporous pores. Too much addition of activated carbon is not conducive to uniform dispersion. Nitrogen molecules are larger, and the complex micro-mesoporous structure in the present invention is conducive to the adsorption and fixation of small molecules. Comparative Examples 5-6 show that too large a molecular weight of chitosan and too much addition will make it difficult to form a uniform dispersion in the polymer, and the pore size of the porous skeleton formed by calcination tends to be larger, which is easy to adsorb some nitrogen and has a low separation efficiency.

[0086] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0087] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. Application of a modified activated carbon adsorbent in a nitrogen recovery and utilization system in a cryogenic system, characterized in that: The invention comprises a pressure swing adsorption device and a nitrogen buffer device; the pressure swing adsorption device comprises an air inlet and an air outlet; the air outlet is connected to the inlet of the nitrogen buffer device; the pressure swing adsorption device is loaded with a modified activated carbon adsorbent; The preparation of modified activated carbon adsorbent includes: (1) Ethyltrichlorosilane, phenyltrichlorosilane and vinyltriethoxysilane are added dropwise to a mixed solution of water and toluene, and the mixture is reacted at 55-75°C for 30-80 minutes. After the reaction is completed, the mixture is allowed to stand and the aqueous layer is separated to obtain a vinyl silicone resin prepolymer; (2) Add activated carbon and g-C3N4 nanosheets to vinyl silicone resin prepolymer and stir to mix. The pore size of the activated carbon is not greater than 2 nm. Then add fumaric acid, azobisisobutyronitrile, chloroform and N,N-dimethylformamide and mix them. Distill under reduced pressure at 75-85 °C for 2-4 h. Then add chitosan and chloroform and mix them. Then dropwise add sodium tripolyphosphate solution with a concentration of 2-4 mg / mL. Based on the amount of chloroform added for the second time, the ratio of g-C3N4 nanosheets, chitosan, chloroform and sodium tripolyphosphate solution is 0.1-0.3 g: 4-7 g: 10-20 mL: 1-3 mL. After the addition is complete, cross-link for 20-30 min. After the reaction is completed, put it into a mold and bake it after curing.

2. The use according to claim 1, characterized in that The outlet of the nitrogen buffer device is connected to the reaction system; after the gas in the pressure swing adsorption device is subjected to pressure swing adsorption by the modified activated carbon adsorbent, the unadsorbed gas is passed into the nitrogen buffer device and directly used in the reaction system.

3. The use according to claim 1, characterized in that The processing pressure of the pressure swing adsorption device is 0.3~0.8MPa, and the processing temperature is 20~30℃.

4. The use according to claim 1, wherein The pressure swing adsorption device further comprises an exhaust port and a hot air inlet; the air inlet and exhaust port are arranged at the upper end of the pressure swing adsorption device; the air outlet and hot air inlet are arranged at the lower end of the pressure swing adsorption device.

5. The use according to claim 2, characterized in that It also includes a heating and heat exchange device; the inlet of the heating and heat exchange device is connected to the exhaust port of the pressure swing adsorption device; the outlet of the heating and heat exchange device is connected to the hot air inlet of the pressure swing adsorption device.

6. The use according to claim 5, characterized in that The processing temperature of the heating and heat exchanging device is 80-100°C.

7. The use according to claim 5 or 6, characterized in that The modified activated carbon adsorbent is regenerated by reversely sweeping the gas introduced through the hot air inlet under normal pressure, and the gas generated after desorption is discharged from the exhaust port.

8. The use according to claim 1, characterized in that In step (1), the mass ratio of ethyltrichlorosilane, phenyltrichlorosilane and vinyltriethoxysilane is 35-50:25-35:10-15; the volume ratio of water and toluene is 1-1.5:1; In step (2), when chloroform is added for the first time, the mass volume ratio of the activated carbon, g-C3N4 nanosheets, vinyl silicone resin prepolymer, fumaric acid, azobisisobutyronitrile, chloroform and N,N-dimethylformamide is 0.5~1g:0.1~0.3g:50~60g:5~10g:0.5~1g:50mL:10~30 mL; the molecular weight of the chitosan is 10000~50000; the curing is heated and pressurized curing, the temperature is 90~100℃, and the pressure is 3~5MPa; the calcination temperature is 300~400℃, and the time is 2~4h.

9. The use according to claim 1, characterized in that The processing pressure of the nitrogen buffer device is 1~5KPa.

10. The use according to claim 2, characterized in that It also includes a liquid seal tank and a circulation pump; the inlet of the liquid seal tank is connected to the nitrogen buffer device; the inlet of the circulation pump is connected to the outlet of the nitrogen buffer device; and the outlet of the circulation pump is connected to the reaction system.

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