A process for treating exhaust gas in the production of methyl ethyl carbonate

Abstract

The application discloses a kind of waste gas treatment process in methyl ethyl carbonate production, belong to waste gas treatment technical field in carbonate production;First, waste gas is passed into adsorption tower, and is treated by adsorption in the composite adsorbent in adsorption tower;Afterwards, the composite adsorbent in adsorption tower is heated and is desorbed;Finally, the gas after desorption is treated by catalytic combustion;Wherein, composite adsorbent includes modified activated carbon-PVDF composite material, modified silica gel-PVDF composite material, modified activated carbon fiber, and modified graphene oxide.The modified activated carbon-PVDF composite material is made of activated carbon-PVDF composite material surface grafting hydrophilic monomer;Modified silica gel-PVDF composite material is made of silica gel-PVDF composite material surface grafting hydrophilic monomer;Modified activated carbon fiber is obtained by grafting polyvinyl alcohol to activated carbon fiber first, then introducing disulfide bond;Modified graphene oxide is obtained by grafting polyvinyl alcohol to graphene oxide.The composite adsorbent provided by the application has an adsorption rate of not less than 95.1%, and the concentration of organic matter after purification is less than 9mg / m 3 .

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste gas treatment in carbonate production, in particular to a waste gas treatment process in methyl ethyl carbonate production. BACKGROUND

[0002] Methyl ethyl carbonate (MEC) is a colorless transparent liquid, insoluble in water, and can be used for organic synthesis, which is an excellent solvent for lithium ion battery electrolyte. It can be synthesized by transesterification of dimethyl carbonate and ethanol under the catalysis of acid or base catalyst.

[0003] In the production process of methyl ethyl carbonate, some waste gas will be produced, which is mainly organic compounds such as methanol, ethanol and other by-products. In order to ensure environmental protection and plant safety, these waste gases need to be effectively treated.

[0004] The treatment methods that can be used for these waste gases at present include combustion treatment method, adsorption treatment method, condensation and liquid absorption method, biodegradation method and chemical absorption method, etc.

[0005] Among the above methods, the adsorption treatment method is the most common. In the prior art, activated carbon is often used to adsorb the waste gas in the synthesis process of methyl ethyl carbonate, which can effectively absorb organic compounds. However, it is found that the adsorption capacity of single granular activated carbon to waste gas is limited, and the adsorption rate of waste gas is generally less than 90%, more often 75%-85%, it is difficult to reach 90% or even higher adsorption rate. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a waste gas treatment process in methyl ethyl carbonate production, which can make the treatment efficiency (i.e. the absorption rate of volatile organic compounds) of organic waste gas reach 95.1% and above.

[0007] The technical purpose of the present application is realized by the following technical scheme:

[0008] A waste gas treatment process in methyl ethyl carbonate production, first, the waste gas is introduced into the adsorption tower, and the composite adsorbent in the adsorption tower is subjected to adsorption treatment; then the composite adsorbent in the adsorption tower is subjected to hot gas desorption; finally, the gas after desorption is subjected to catalytic combustion treatment.

[0009] Among them, the composite adsorbent includes modified activated carbon-PVDF composite material, modified silica gel-PVDF composite material, modified activated carbon fiber, and modified graphene oxide.

[0010] Among them, the modified activated carbon-PVDF composite material is formed by grafting hydrophilic monomers on the surface of activated carbon-PVDF composite material;

[0011] The modified silica gel-PVDF composite material is obtained by grafting a hydrophilic monomer on the surface of a silica gel-PVDF composite material;

[0012] The modified activated carbon fiber is obtained by grafting polyvinyl alcohol on an activated carbon fiber and then introducing a disulfide bond.

[0013] The modified graphene oxide is obtained by grafting polyvinyl alcohol on graphene oxide.

[0014] As some embodiments of the present application, the weight fractions of the components in the composite adsorbent are as follows:

[0015] 100-120 parts of the modified activated carbon-PVDF composite material, 20-40 parts of the modified silica gel-PVDF composite material, 10-25 parts of the modified activated carbon fiber, and 10-25 parts of the modified graphene oxide.

[0016] As some embodiments of the present application, the weight fractions of the components in the composite adsorbent are as follows:

[0017] 105-118 parts of the modified activated carbon-PVDF composite material, 25-30 parts of the modified silica gel-PVDF composite material, 13-22 parts of the modified activated carbon fiber, and 12-20 parts of the modified graphene oxide.

[0018] As some embodiments of the present application, the weight fractions of the components in the composite adsorbent are as follows:

[0019] 115 parts of the modified activated carbon-PVDF composite material, 27 parts of the modified silica gel-PVDF composite material, 20 parts of the modified activated carbon fiber, and 18 parts of the modified graphene oxide.

[0020] As some embodiments of the present application, the PVDF material in the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material comprises PVDF powder and PTFE powder.

[0021] As some embodiments of the present application, the mass ratio of the PVDF powder and the PTFE powder is 10:1-3.

[0022] As some embodiments of the present application, the hydrophilic monomer is any one of methacrylic acid, acrylic acid, acrylamide, and methacrylamide.

[0023] As some embodiments of the present application, the mesh number of the activated carbon and the silica gel is 4-30 mesh.

[0024] As some embodiments of the present application, the preparation method of the modified activated carbon-PVDF composite material is as follows:

[0025] S1. First, the PVDF material is added to N, N-dimethylacetamide and mixed thoroughly to prepare a PVDF dispersion liquid, then activated carbon is added to the PVDF dispersion liquid and ultrasonically dispersed for 20-50 min, then the organic solvent is removed and dried at 100-150℃ under a nitrogen atmosphere for 2-5h to obtain an activated carbon-PVDF composite material;

[0026] S2. The hydrophilic monomer is uniformly sprayed onto the surface of the activated carbon-PVDF composite material, then it is placed in a stoppered glass bottle and irradiated with 60Co-γ rays to obtain a modified activated carbon-PVDF composite material.

[0027] As some embodiments of the present application, the mass ratio of the PVDF material, N, N-dimethylacetamide and activated carbon is 18: (300-350): (80-100).

[0028] Compared with the prior art, the present application has the following advantages:

[0029] 1. The present application provides a composite adsorbent comprising a modified activated carbon-PVDF composite material, a modified silica gel-PVDF composite material, a modified activated carbon fiber, and a modified graphene oxide, which can effectively adsorb waste gas in the production of ethyl methyl carbonate. Tests show that the adsorption rate of the composite adsorbent provided by the present application for volatile organic compounds in waste gas is not less than 95.1%, and the concentration of organic compounds after purification is less than 9mg / m 3 , meeting the emission standard.

[0030] 2. By adding PTFE powder to the PVDF material, the present application can effectively improve the high temperature resistance and high temperature deformation resistance of the PVDF material, ensuring that the PVDF material does not deform significantly during the thermal desorption stage, and effectively avoiding the swelling of the PVDF material due to the presence of carbonate substances in the waste gas, thereby effectively preventing the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material from deforming at high temperatures, and effectively improving the service life of the composite adsorbent.

[0031] 3. The composite adsorbent provided by the present application still has an adsorption rate higher than 80% after the 7th thermal desorption treatment, and the degree of fragmentation is less than 10%. This shows that the composite adsorbent provided by the present application can maintain high adsorption capacity for waste gas for a long time, and has extremely strong mechanical properties, which can significantly reduce the degree of fragmentation during the adsorption and thermal desorption process, effectively prolonging the service life. DETAILED DESCRIPTION

[0032] At present, the single activated carbon particles are usually used to adsorb the waste gas in the synthesis process of methyl ethyl carbonate, however, the adsorption rate of the waste gas is generally less than 90%, and in more cases, it is 75%-85%, it is difficult to reach 90% or even higher adsorption rate.

[0033] Based on this, the application provides a waste gas treatment process in the production of methyl ethyl carbonate, comprising the following steps:

[0034] A waste gas treatment process in the production of methyl ethyl carbonate, first, the waste gas is introduced into the adsorption tower and treated by the composite adsorbent in the adsorption tower; then, the composite adsorbent in the adsorption tower is desorbed by hot gas; finally, the gas after desorption is treated by catalytic combustion.

[0035] The composite adsorbent comprises modified activated carbon-PVDF composite material, modified silica gel-PVDF composite material, modified activated carbon fiber and modified graphene oxide.

[0036] The modified activated carbon-PVDF composite material is obtained by grafting hydrophilic monomers on the surface of activated carbon-PVDF composite material.

[0037] The modified silica gel-PVDF composite material is obtained by grafting hydrophilic monomers on the surface of silica gel-PVDF composite material.

[0038] The modified activated carbon fiber is obtained by grafting polyvinyl alcohol on the activated carbon fiber and then introducing disulfide bond.

[0039] The modified graphene oxide is obtained by grafting polyvinyl alcohol on the graphene oxide.

[0040] In the above scheme, the volatile organic compounds in the waste gas are first adsorbed by the composite adsorbent, and then the adsorbed volatile organic compounds are catalytically combusted by desorption, so as to achieve the purpose of purifying the waste gas.

[0041] In the above scheme, the research and development idea of the composite adsorbent is as follows:

[0042] The activated carbon is easily caked during long-time adsorption of waste gas, and the caked activated carbon is difficult to continue effective adsorption operation, so the service life of the activated carbon is generally short (not more than 3 months), in addition, due to the poor mechanical strength of the activated carbon and the problem of slight caking, the activated carbon is easily broken during the heat desorption treatment, which causes serious damage to the pores, and the adsorption effect of the activated carbon after heat desorption is greatly reduced.

[0043] In addition, in the production process of methyl ethyl carbonate, in addition to methanol or ethanol, there are also carbonate substances, and the adsorption capacity of activated carbon for the carbonate substances is relatively poor because the carbonate substances are usually polar molecules. Therefore, in addition to using activated carbon as the main adsorbent, silica gel is also added in the present application. The silica gel has a large number of siloxane bonds on the surface and a pore structure, so it is easy to adsorb organic compounds, including carbonate compounds. However, the silica gel itself has poor mechanical properties such as tensile strength and tear strength, so it is easy to deform due to mutual extrusion during the adsorption process, and it will also burst due to improper temperature control during thermal desorption, which seriously affects the adsorption effect.

[0044] Therefore, the activated carbon and silica gel need to be modified, as follows:

[0045] In the present application, the activated carbon and silica gel are mixed with PVDF material respectively to prepare activated carbon-PVDF composite material and silica gel-PVDF composite material. The introduction of PVDF material can effectively improve the mechanical strength of activated carbon and silica gel, improve the anti-caking performance of activated carbon and the high-temperature crack resistance of silica gel, so that the composite adsorbent can greatly reduce the degree of crushing during regeneration treatment and effectively prolong the service life.

[0046] However, in the activated carbon-PVDF composite material and the silica gel-PVDF composite material, the PVDF material occupies part of the pore channels and surface structures inside the activated carbon and silica gel, resulting in a decrease in the adsorption sites on the surface and inside the activated carbon and silica gel, and further leading to a decrease in the overall adsorption capacity of the composite adsorbent.

[0047] Therefore, in the present application, a hydrophilic monomer is grafted onto the surface of the PVDF material to prepare modified activated carbon-PVDF composite material and modified silica gel-PVDF composite material. The grafted hydrophilic monomer contains hydrophilic groups such as hydroxyl groups, which can effectively improve the adsorption effect of hydrophilic organic substances such as methanol and ethanol.

[0048] However, in the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material, the hydrophilic monomers are aggregated on the surface of the activated carbon or silica gel, which can greatly improve the adsorption effect of organic substances, but the hydrophilic monomers will hinder the transport of volatile organic substances to the activated carbon and silica gel, resulting in a decrease in the contact opportunity between the volatile organic substances and the activated carbon and silica gel, and further leading to a decrease in the adsorption efficiency.

[0049] Based on this, the application adds activated carbon fibers, which not only have very high adsorption performance on organic matters such as methanol and ethanol, but also can be inserted between the modified activated carbon-PVDF composite material, the modified silica gel-PVDF composite material, and the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material, that is, the activated carbon fibers can pass through the hydrophilic monomer and be connected with the activated carbon or the silica gel, and then build a transmission channel between the activated carbon, the silica gel or the activated carbon and the silica gel, so that the volatile organic matter can be transmitted to the inside of the activated carbon and the silica gel along the transmission channel, the contact opportunity of the waste gas with the activated carbon and the silica gel is improved, and then the adsorption effect is improved.

[0050] However, because the activated carbon fiber itself is relatively soft, under the pressure of the particle components such as the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material, the activated carbon fiber will be gradually compressed, so that the pore in the activated carbon fiber becomes smaller, which seriously affects the adsorption effect.

[0051] Based on this, polyvinyl alcohol is introduced on the surface of the activated carbon fiber, which can form a network structure on the surface of the activated carbon fiber, and then play a certain buffering effect on the pressure of the particle components, and then reduce the degree of compression of the activated carbon fiber; and the hydroxyl structure in the polyvinyl alcohol can also improve the adsorption effect on hydrophilic organic matters such as methanol and ethanol.

[0052] Because of the above-mentioned methacrylamide monomer and polyvinyl alcohol, although the adsorption capacity of the organic matter can be improved, at the same time, a plurality of layers of obstacles are formed outside the activated carbon and the silica gel, which adversely affects the adsorption performance of the activated carbon and the silica gel.

[0053] Based on this, the application further introduces a disulfide bond on the activated carbon fiber, which can not only further improve the compression resistance and buffering capacity of the activated carbon fiber to further solve the compression problem of the activated carbon fiber and improve the adsorption effect of the activated carbon fiber, but also can be inserted between the polyvinyl alcohol group or the hydrophilic group, thereby increasing the distance between adjacent polyvinyl alcohol groups and adjacent hydrophilic monomers, and thereby reducing the hindering degree of the polyvinyl alcohol group and the hydrophilic monomer to the activated carbon and the silica gel, and significantly improving the contact opportunity of the volatile organic matter with the activated carbon and the silica gel.

[0054] Finally, on the basis of the above components, modified graphene oxide is added, which has a layered structure that can form a waste gas transport channel, and has strong adsorption performance for waste gas, and can also fill the gaps between the above-mentioned particle components, effectively improving the capture of the composite adsorbent for waste gas, and further improving the adsorption capacity. At the same time, the polyvinyl alcohol groups in the modified graphene can form hydrogen bonds between the same groups between other components, thereby effectively improving the binding capacity between other components, and at the same time, effectively solving the problem of its own agglomeration, and further solving the problem of the hardening of the composite adsorbent.

[0055] Through the synergistic effect of the above components, the composite adsorbent prepared can effectively adsorb the waste gas in the production of methyl ethyl carbonate. Tests show that the adsorption rate of the composite adsorbent provided by the present application for waste gas is not less than 95.1%, and the concentration of organic matter after purification is less than 9mg / m 3 , meeting the emission standard.

[0056] In order to further improve the high temperature resistance and high temperature resistance of the composite adsorbent, as some embodiments of the present application, the components of the PVDF material are further limited, and the PVDF material in the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material includes PVDF powder and PTFE powder. Because the melting point of PVDF material is 172℃, the heat distortion temperature is 112~145℃, and it is easy to swell under the action of carbonate, although the melting point and heat distortion temperature are changed after grafting hydrophilic monomers, in order to ensure that the subsequent multiple thermal desorption can be carried out smoothly, some PTFE powder is added in the PVDF material, which can significantly improve the high temperature resistance and melting point of the PVDF material, and then ensure that the subsequent thermal desorption is carried out smoothly, and at the same time, after multiple thermal desorption, the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material will not be obviously deformed by heat.

[0057] The carbon dioxide production in the production of methyl ethyl carbonate is further described in detail in combination with the specific embodiments.

[0058] Example 1

[0059] The waste gas in the production of methyl ethyl carbonate is introduced into the adsorption tower filled with gas flow distributor and composite adsorbent for purification, and the purified gas is discharged; then the organic matter adsorbed in the composite adsorbent is subjected to hot air desorption, and the desorbed gas is subjected to catalytic combustion treatment, and is discharged.

[0060] Among them, the temperature of the waste gas entering the adsorption tower is 20-30℃, and the gas flow rate is 0.8m 3 / s.

[0061] The composite adsorbent comprises the following components by weight:

[0062] 119 parts of modified activated carbon-PVDF composite material, 22 parts of modified silica gel-PVDF composite material, 19 parts of modified activated carbon fiber, and 15 parts of modified graphene oxide.

[0063] The preparation methods of the above components are as follows:

[0064] ① The preparation method of the modified activated carbon-PVDF composite material is as follows:

[0065] S1. First, the PVDF material is added to N, N-dimethylacetamide and mixed thoroughly to prepare a PVDF dispersion liquid. Then, 4-10 mesh activated carbon is added to the PVDF dispersion liquid and dispersed at 35-45°C under ultrasonic waves (ultrasonic frequency of 40 KHz, power of 200 W) for 30 min. After that, the organic solvent is removed and dried at 125°C under a nitrogen atmosphere for 3.5 h to obtain an activated carbon-PVDF composite material. The mass ratio of the PVDF material, N, N-dimethylacetamide, and activated carbon is 18:320:95.

[0066] S2. 8% of a hydrophilic monomer by total mass of PVDF is uniformly sprayed onto the activated carbon-PVDF composite material. Then, they are put together in a glass bottle with a stopper and irradiated with 60Co-γ rays (irradiation dose rate of 25 Gy / h, irradiation dose of 50 kGy) to obtain the modified activated carbon-PVDF composite material.

[0067] ② The preparation method of the modified silica gel-PVDF composite material is as follows:

[0068] S1. First, the PVDF material is added to N, N-dimethylacetamide and mixed thoroughly to prepare a PVDF dispersion liquid. Then, 8-20 mesh silica gel is added to the PVDF dispersion liquid and dispersed at 35-45°C under ultrasonic waves (ultrasonic frequency of 40 KHz, power of 200 W) for 30 min. After that, the organic solvent is removed and dried at 125°C under a nitrogen atmosphere for 3.5 h to obtain a silica gel-PVDF composite material. The mass ratio of the PVDF material, N, N-dimethylacetamide, and silica gel is 18:320:95.

[0069] S2. 8% of an acrylic acid monomer by total mass of PVDF is uniformly sprayed onto the silica gel-PVDF composite material. Then, they are put together in a glass bottle with a stopper and irradiated with 60Co-γ rays to obtain the modified silica gel-PVDF composite material.

[0070] ③ The preparation method of the modified activated carbon fiber is as follows:

[0071] S1: 175 g of N,N-dimethylformamide, 5 g of activated carbon fiber, 100 g of polyvinyl alcohol and 1.5 of toluene diisocyanate were added into a reaction bottle and reacted at 45°C for 10 h, after which the first modified activated carbon fiber was obtained by filtering, washing and drying;

[0072] S2: 150 g / L of (3-mercaptopropyl)triethoxysilane was added into a 90% volume fraction of ethanol solution, after which it was shaken at 30°C for 60 min, and then the first modified activated carbon fiber was put into the solution, and after padding, it was baked at 120°C for 2 min to obtain the second modified activated carbon fiber;

[0073] A 100 g / L solution of α-lipoic acid was prepared, 100 g / L of anhydrous sodium sulfite was added to reduce and dissolve the α-lipoic acid, 3 g / L of penetrant JFC was then added to obtain a finishing liquor, and the second modified activated carbon fiber was immersed in the finishing liquor, and after padding, it was put into a steamer, the steaming temperature was 120°C, and the time was 20 min. After steaming, it was subjected to constant tension air permeation oxidation for 6 h to obtain the modified activated carbon fiber.

[0074] (4) The preparation method of the modified graphene oxide is as follows:

[0075] 175 g of N,N-dimethylformamide, 5 g of graphene oxide (with a sheet size of 50 nm-200 nm), 80 g of polyvinyl alcohol and 1.5 of toluene diisocyanate were added into a reaction bottle and reacted at 45°C for 10 h, after which the first modified activated carbon fiber was obtained by filtering, washing and drying.

[0076] Example 2

[0077] Compared with Example 1, only the amount of each component in the composite adsorbent was changed, and the rest of the process and process parameters were the same. The amount of each component after the change is as follows:

[0078] 118 parts of modified activated carbon-PVDF composite material, 25 parts of modified silica gel-PVDF composite material, 20 parts of modified activated carbon fiber, and 15 parts of modified graphene oxide.

[0079] Example 3

[0080] Compared with Example 1, only the amount of each component in the composite adsorbent was changed, and the rest of the process and process parameters were the same. The amount of each component after the change is as follows:

[0081] 115 parts of modified activated carbon-PVDF composite material, 27 parts of modified silica gel-PVDF composite material, 20 parts of modified activated carbon fiber, and 18 parts of modified graphene oxide.

[0082] Example 4

[0083] Comparative Example 1, only the PVDF material in the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material is replaced by a mixed material of PVDF powder and PTFE powder, and the mass ratio of the two is 10:1.5. The rest of the process and process parameters are the same as in Example 1.

[0084] Comparative Example 1

[0085] The composite adsorbent is only 4-10 mesh activated carbon.

[0086] Comparative Example 2

[0087] The composite adsorbent is a mixture of 4-10 mesh activated carbon and 8-20 mesh silica gel, and the mass ratio of the two is 120:22.

[0088] Comparative Example 3

[0089] Comparative to Example 1, only the types of each component in the composite adsorbent are changed, and the rest of the process and process parameters are the same. The changed components are as follows:

[0090] 120 parts of activated carbon-PVDF composite material, 22 parts of silica gel-PVDF composite material, 19 parts of activated carbon fiber, and 15 parts of graphene oxide.

[0091] Comparative Example 4

[0092] Comparative to Example 1, only the types of each component in the composite adsorbent are changed, and the rest of the process and process parameters are the same. The changed components are as follows:

[0093] 144 parts of modified activated carbon-PVDF composite material and 19 parts of modified activated carbon fiber.

[0094] Experimental Example 1: The adsorption rate of the composite adsorbent to waste gas when first used.

[0095] The VOCs concentration of the waste gas entering the adsorption tank and the VOCs concentration in the gas purified by the adsorption tank are tested respectively to measure the adsorption rate of the composite adsorbent to waste gas when first used. The adsorption rate (%) = [(VOCs concentration before purification - VOCs concentration after purification) / VOCs concentration before purification] x 100%.

[0096] In this experimental example, except for the slight difference in volatile organic compound concentration when the waste gas enters the tower, the other conditions such as the adsorption time of the waste gas, the inlet gas velocity, the inlet gas temperature, the inlet gas velocity, the shape and size of the adsorption tower and other external conditions are the same. The test results are shown in Table 1.

[0097] Table 1:

[0098]

[0099] From Table 1, it can be seen that the composite adsorbents in Examples 1-3 have very strong adsorption effect on the waste gas in the production of methyl ethyl carbonate, specifically, the adsorption rate is not less than 95.1%, and the volatile organic compound concentration after adsorption by the composite adsorbent is <9 mg / m 3 , meeting the emission requirements.

[0100] In Comparative Examples 1 and 2, single activated carbon or a mixture of activated carbon and silica gel is used as the adsorbent, and the adsorption effect is poorer than that of the present application, and the adsorption rate does not reach 90%.

[0101] In Comparative Example 3, the components are not modified, and the final adsorption effect is not much different from that of Comparative Example 2, and does not reach 90%.

[0102] The composite adsorbent in Comparative Example 4 has improved adsorption effect compared with Comparative Examples 1-3, and the adsorption rate is greater than 90%, but the adsorption rate is still lower compared with Examples 1-4.

[0103] From Comparative Examples 3 and 4, it can be seen that the adsorption effect of the composite adsorbent prepared without strictly following the component amount or component type provided in the present application is reduced.

[0104] Experimental Example 2: Test the adsorption rate of the adsorbent after multiple thermal desorption.

[0105] The adsorbents in Examples 1-4 and Comparative Examples 1-4 have the same thermal desorption time point each time, and the thermal desorption is performed by using the prior art.

[0106] Among them, the adsorption rate of the composite adsorbent in Examples 1-3 is >80% after 7 times of thermal desorption, and the breakage rate of the activated carbon-PVDF composite material and the silica gel-PVDF composite material in the composite adsorbent is not more than 15%.

[0107] The adsorption rate of the composite adsorbent in Example 4 is >80% after 7 times of thermal desorption, and the breakage rate of the activated carbon-PVDF composite material and the silica gel-PVDF composite material in the composite adsorbent is not more than 10%. It can be seen that the composite adsorbent in Example 4 can greatly reduce the breakage degree of the composite adsorbent due to the addition of PTFE powder, which specifically manifests in effectively improving the deformation degree of the two composite materials during the thermal desorption stage, and effectively improving the bursting degree of the silica gel, and at the same time, due to the improvement of the mechanical strength of the composite adsorbent, the degree of breakage between components caused by heavy pressure during the adsorption process can be significantly improved.

[0108] Among them, the composite adsorbents in Examples 1-4 do not appear to be hardened from the first adsorption to the entire process of 7 times of thermal desorption.

[0109] The adsorbent in Comparative Example 1 has an adsorption rate less than 60% and a broken rate of activated carbon > 40% after 3 times of thermal desorption. The adsorbent cannot continue to adsorb after 3 times of thermal desorption and needs to be replaced. The activated carbon in Comparative Example 1 has already appeared the problem of hardening before the third thermal desorption.

[0110] The adsorbent in Comparative Example 2 has an adsorption rate less than 60% and a broken rate of the whole adsorbent > 40% after 3 times of thermal desorption. The adsorbent cannot continue to adsorb after 3 times of thermal desorption and needs to be replaced.

[0111] The adsorbent in Comparative Example 3 has an adsorption rate less than 65% and a broken rate of the whole adsorbent < 10% after 4 times of thermal desorption. The reason for the low broken rate is that PVDF protects activated carbon and silica gel, which greatly reduces the broken rate of the two composite materials. However, the pore structure of activated carbon and silica gel is blocked by PVDF, which reduces the adsorption sites. In addition, the structure of activated carbon fibers with high adsorption capacity collapses and compresses during long-term high pressure, which further damages the pore structure and reduces the overall adsorption capacity of the composite adsorbent.

[0112] The adsorbent in Comparative Example 4 has an adsorption rate less than 70% and a broken rate of the whole adsorbent < 10% after 7 times of thermal desorption. In this comparative example, the adsorption effect is not as good as Examples 1-4 because silica gel-PVDF composite material and modified graphite oxide are not used. However, the broken rate of the material is greatly reduced due to the protection of PVDF on activated carbon.

[0113] In summary, the composite adsorbent in Examples 1-4 not only has a strong adsorption effect on volatile organic compounds in waste gas during the first run, but also has good adsorption effect after 7 times of thermal desorption, effectively improving the service life.

Claims

1. A waste gas treatment process in the production of methyl ethyl carbonate, characterized in that, First, the waste gas is introduced into the adsorption tower and adsorbed by the composite adsorbent inside the tower; then, the composite adsorbent in the adsorption tower is desorbed by hot gas; finally, the desorbed gas is subjected to catalytic combustion treatment. The composite adsorbent comprises the following components by weight: 100-120 parts of modified activated carbon-PVDF composite material, 20-40 parts of modified silica gel-PVDF composite material, 10-25 parts of modified activated carbon fiber, and 10-25 parts of modified graphene oxide. The modified activated carbon-PVDF composite material is formed by grafting hydrophilic monomers onto the surface of the activated carbon-PVDF composite material. The modified silicone-PVDF composite material is formed by grafting hydrophilic monomers onto the surface of a silicone-PVDF composite material; The modified activated carbon fiber is obtained by first grafting polyvinyl alcohol onto activated carbon fiber and then introducing disulfide bonds. The modified graphene oxide is obtained by grafting polyvinyl alcohol onto graphene oxide.

2. The waste gas treatment process in the production of methyl ethyl carbonate according to claim 1, characterized in that, The weight proportions of each component in the composite adsorbent are as follows: 105-118 parts modified activated carbon-PVDF composite material, 25-30 parts modified silica gel-PVDF composite material, 13-22 parts modified activated carbon fiber, and 12-20 parts modified graphene oxide.

3. The waste gas treatment process in the production of methyl ethyl carbonate according to claim 1, characterized in that, The weight proportions of each component in the composite adsorbent are as follows: 115 parts of modified activated carbon-PVDF composite material, 27 parts of modified silica gel-PVDF composite material, 20 parts of modified activated carbon fiber, and 18 parts of modified graphene oxide.

4. The waste gas treatment process in the production of methyl ethyl carbonate according to claim 1, characterized in that, The PVDF material in the modified activated carbon-PVDF composite material and the modified silica gel-PVDF composite material includes PVDF powder and PTFE powder.

5. The waste gas treatment process in the production of ethyl methyl carbonate according to claim 4, characterized in that, The mass ratio of PVDF powder to PTFE powder is 10:1~3.

6. The waste gas treatment process in the production of ethyl methyl carbonate according to claim 1, characterized in that, The hydrophilic monomer is any one of methacrylic acid, acrylic acid, acrylamide, and methacrylamide.

7. The waste gas treatment process in the production of methyl ethyl carbonate according to claim 1, characterized in that, The activated carbon and silica gel have a mesh size of 4-30.

8. The waste gas treatment process in the production of methyl ethyl carbonate according to claim 1, characterized in that, The preparation method of the modified activated carbon-PVDF composite material is as follows: S1. First, add PVDF material to N,N-dimethylacetamide and mix thoroughly to prepare PVDF dispersion. Then, add activated carbon to the PVDF dispersion and ultrasonically disperse for 20-50 min. After removing the organic solvent, dry at 100-150℃ under nitrogen atmosphere for 2-5 h to obtain activated carbon-PVDF composite material. S2. The hydrophilic monomer is uniformly sprayed onto the surface of the activated carbon-PVDF composite material, then placed in a stoppered glass bottle and irradiated with 60Co-γ rays to obtain the modified activated carbon-PVDF composite material.

9. The waste gas treatment process in the production of methyl ethyl carbonate according to claim 8, characterized in that, The mass ratio of the PVDF material, N,N-dimethylacetamide and activated carbon is 18:(300-350):(80-100).

Images