A VOCs tail gas treatment system

Abstract

The present invention discloses a VOCs tail gas treatment system, which belongs to the technical field of waste gas treatment. A VOCs tail gas treatment system comprises the following steps: (1) pretreatment: condensing the collected VOCs tail gas; (2) filtering: the VOCs tail gas after condensation treatment is filtered through a filter for primary filtration; (3) adsorption: the VOCs tail gas after primary filtration treatment is adsorbed by a modified molecular sieve adsorbent; (4) catalysis: the VOCs tail gas after adsorption treatment is degraded by a photocatalytic system; (5) re-adsorption: the VOCs tail gas after degradation treatment is adsorbed by modified activated carbon, and discharged after qualified detection. The VOCs tail gas treatment system of the present invention is sequentially provided with a condensation pretreatment step, a filtering step, a molecular sieve adsorption step, a photocatalytic step and an activated carbon re-adsorption step, combining the adsorption method and the catalytic method, and the two methods act synergistically to improve the efficiency of VOCs waste gas treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of waste gas treatment, and specifically relates to a VOCs tail gas treatment system. Background Art

[0002] Volatile organic chemicals, abbreviated as VOCs, refer to organic compounds with a boiling point below 260 degrees Celsius at normal pressure or a saturated vapor pressure greater than 71 Pa at room temperature. Their main components are fluorinated aromatic hydrocarbons, alcohols, ethers and esters. In addition, they also contain some inorganic substances such as hydrogen chloride, hydrogen sulfide and nitrides. They are characterized by high concentration, complex composition and strong toxicity.

[0003] There are two main sources of VOCs: fixed sources and mobile sources. Mobile sources mainly include the exhaust gas from vehicles such as cars, ships and airplanes that use petroleum products as fuel; there are many types of fixed sources, mainly the discharge from petrochemical processes and storage equipment, and various occasions where organic solvents are used, such as painting, printing, metal degreasing and degreasing, adhesives, pharmaceuticals, plastics and rubber processing. In addition to these large pollution sources, there are also small pollution sources that can be seen everywhere in daily life, such as paints, floor waxes, etc. In terms of the current technical level, the emission of these gaseous pollutants cannot be avoided, so there is an urgent need for effective VOCs control technology.

[0004] At present, the treatment of VOCs mainly includes combustion, catalytic and adsorption methods. The combustion method is to directly pass VOCs into the incinerator for combustion and convert them into CO2 and H2O. This method is simple to operate and has high treatment efficiency, but the equipment investment is high. In addition, when other inorganic pollutants such as sulfide and nitrogen oxides exist in VOCs, SO2 and NO will be produced after combustion. x Volatile pollutants such as VOCs can be removed, resulting in secondary air pollution. The catalytic method is to degrade VOCs into CO2 and H2O through a catalyst and an ultraviolet lamp. Compared with combustion and adsorption, it not only has a high treatment efficiency, but also can efficiently degrade VOCs with high concentrations and complex components, including various inorganic pollutants therein, to ensure that the tail gas can meet the emission standards. However, this method requires large equipment investment, and the catalyst needs to be replaced frequently, making its operating cost higher. The adsorption method is to pass VOCs through adsorption materials such as activated carbon, molecular sieves, and resins to adsorb the pollutants in the pores of the adsorption materials, thereby achieving the purpose of purifying the air. This method requires low investment and is simple to operate. It can also remove inorganic pollutants, but the adsorption capacity and efficiency of molecular sieves and activated carbon are limited, so they are not suitable for treating high-concentration VOCs.

[0005] In summary, the current use of catalytic and adsorption methods to treat high-concentration VOCs exhaust gas still has the problems of limited adsorption capacity and efficiency, and the need for frequent replacement of photocatalysts. Summary of the invention

[0006] The purpose of the present invention is to provide a VOCs tail gas treatment system to solve the above-mentioned problem that the photocatalyst for treating VOCs tail gas by catalysis needs to be frequently replaced and the adsorption amount and adsorption efficiency of high-concentration VOCs tail gas by adsorption are limited. The VOCs tail gas treatment system of the present invention is sequentially provided with a condensation pretreatment step, a filtration step, a molecular sieve adsorption step, a photocatalysis step and an activated carbon re-adsorption step, combining the adsorption method and the catalysis method, and the two methods work synergistically to improve the efficiency of VOCs waste gas treatment.

[0007] To achieve the above object, the present invention provides a VOCs tail gas treatment system, comprising the following steps:

[0008] (1) Pretreatment: condensing the collected VOCs tail gas;

[0009] (2) Filtration: The VOCs tail gas after condensation treatment is filtered through a filter for primary filtration;

[0010] (3) Adsorption: The VOCs tail gas after primary filtration treatment is adsorbed by modified molecular sieve adsorbent;

[0011] (4) Catalysis: The VOCs tail gas after adsorption treatment is degraded through a photocatalytic system;

[0012] (5) Re-adsorption: The VOCs tail gas after degradation treatment is adsorbed by modified activated carbon and discharged after passing the test;

[0013] The preparation method of the modified molecular sieve adsorbent is:

[0014] (31) mixing the mesoporous alumina molecular sieve with a mixed aqueous solution of ammonia and sodium carbonate, hydrothermally treating, filtering, washing and drying to obtain a precursor;

[0015] (32) In a nitrogen atmosphere, the precursor is mixed with aluminum trichloride vapor, copper chloride vapor, and titanium tetrachloride vapor for heating treatment to obtain a modified molecular sieve adsorbent;

[0016] The preparation method of modified activated carbon is:

[0017] (51) adding activated carbon to a mixed aqueous solution of melamine and triethyl phosphate for immersion for 5 to 8 hours, filtering, drying and sintering to obtain nitrogen-phosphorus-doped activated carbon;

[0018] (52) Mix 20 to 25 parts of polyvinyl alcohol, 2 to 4 parts of a surfactant, 0.5 to 3 parts of a crosslinking agent, and 90 to 100 parts of water in parts by weight and stir to obtain an adhesive;

[0019] (53) 100 parts of nitrogen-phosphorus-doped activated carbon and 120-140 parts of an adhesive are added to a reaction kettle according to weight proportions, and stirred for 6-8 hours to obtain a mixture;

[0020] (54) feeding the mixed material into a granulation device, extruding the granular carbon, and baking the granular carbon until the moisture content is less than 5%;

[0021] (55) The baked granular carbon is crushed and sieved to obtain modified activated carbon.

[0022] Preferably, the sintering temperature in step (51) is 500-800°C and the sintering time is 1-5 hours.

[0023] Preferably, the condensation treatment comprises the following steps: subjecting the collected VOCs tail gas to primary condensation and secondary condensation in sequence, the temperature of the primary condensation being 40-50°C, and the temperature of the secondary condensation being 10-15°C.

[0024] At present, the treatment methods for VOCs tail gas are mainly based on combustion, catalysis and adsorption. Using a single method to treat low-concentration VOCs tail gas can achieve good results, but when the VOCs tail gas is at a higher concentration, a single treatment method can no longer completely adsorb or degrade it. In response to the above problems, the present invention specifically combines the catalysis method and the adsorption method, and sequentially sets the steps of adsorption-photocatalysis-re-adsorption to treat high-concentration VOCs tail gas, thereby making the tail gas emissions meet national standards. The present invention continues to study and find that due to the increase in the concentration of VOCs tail gas, the molecular sieve or activated carbon used in the adsorption step and the re-adsorption step is prone to adsorption saturation, and the adsorption efficiency decreases. In response to this problem, the molecular sieve and activated carbon are modified.

[0025] For the modification of molecular sieve, the present invention first mixes the molecular sieve with a mixed solution of ammonia water and sodium carbonate. During the mixing process, ammonia water is an alkaline substance. The introduction of alkaline sites on the molecular sieve can enhance the adsorption capacity of the molecular sieve to certain acidic VOCs, which usually increases the surface polarity of the molecular sieve, so that the molecular sieve can better attract and retain VOCs molecules; the use of sodium carbonate may help adjust the pore structure of the molecular sieve to make it more suitable for adsorbing VOCs molecules of a specific size or shape. The optimization of this pore structure helps to improve the selectivity and capacity of adsorption. The present invention uses the molecular sieve treated with ammonia water and sodium carbonate as a precursor and mixes and heats it with aluminum chloride steam, copper chloride steam and titanium tetrachloride steam. During the heating process, the use of aluminum chloride, copper chloride and titanium tetrachloride steam can introduce metal ions into the molecular sieve structure. These metal ions can provide additional adsorption sites to enhance the adsorption performance of the molecular sieve to specific VOCs. In addition, these metal ions can also participate in the subsequent catalytic process as active centers to improve the decomposition efficiency of VOCs.

[0026] For the modification of activated carbon, the present invention first uses melamine and triethyl phosphate as raw materials to introduce nitrogen and phosphorus elements into activated carbon. During the doping process, nitrogen and phosphorus elements can change the electronic structure of activated carbon, forming more π-electron orbits, thereby enhancing the adsorption capacity of activated carbon to polar gas molecules (such as some VOCs). Nitrogen and phosphorus doping can also introduce new active sites, which can enhance the chemical adsorption capacity of the activated carbon surface. Nitrogen and phosphorus doping can also introduce alkaline or acidic sites, which helps to enhance the interaction between the activated carbon surface and certain VOCs, especially those organic substances with specific functional groups, thereby improving adsorption selectivity and adsorption capacity. Therefore, nitrogen and phosphorus doping can adjust the hydrophobicity or hydrophilicity of the activated carbon surface, making it more suitable for adsorbing target pollutants. For example, if the target pollutant is hydrophobic, the adsorption effect can be increased by improving the hydrophobicity of activated carbon. The present invention mixes nitrogen and phosphorus doped activated carbon with an adhesive. The addition of the adhesive will affect the porosity and pore size distribution of the activated carbon, thereby optimizing the diffusion path of the gas inside the activated carbon and improving the adsorption rate.

[0027] Preferably, a plate-type photocatalyst is provided in the photocatalytic system, and the main components of the plate-type photocatalyst are TiO2, zinc oxide and graphene oxide, and the mass ratio of TiO2, zinc oxide and graphene oxide is (8-12):(3-5):1.

[0028] In order to improve the photocatalytic efficiency, the present invention also defines the main components of the plate-type photocatalyst, with titanium dioxide as the main material, and zinc oxide and graphene oxide as auxiliary additions, wherein TiO2 is a common photocatalyst, but it is mainly effective under ultraviolet light, ZnO is also an effective photocatalyst, and it also has a certain response in the visible light range, and graphene oxide has a large specific surface area and good conductivity, which can promote the separation of photogenerated carriers and reduce electron-hole recombination. The combination of the three can broaden the light response range, thereby improving the photocatalytic efficiency. The introduction of ZnO and GO can also enhance the physical and chemical stability of TiO2, prevent TiO2 from aggregating or degrading during long-term use, thereby ensuring its long-term photocatalytic activity. Due to the presence of GO, it can improve the stability and mechanical strength of the composite material, thereby extending the service life of the photocatalyst and reducing the replacement frequency. The presence of GO may also help to improve the anti-pollution property of the composite material, making the photocatalyst not easily blocked or covered by pollutants, thereby maintaining a high activity.

[0029] The present invention further studies and finds that although adding zinc oxide and graphene oxide to titanium dioxide can improve the photocatalytic performance, the photocatalyst will still degrade and change its structure during long-term use, resulting in a decrease in photocatalytic performance. In view of this, the present invention finds that the physical stability of the photocatalyst can be improved by changing the ratio of titanium dioxide, zinc oxide and graphene oxide. The mass ratio of TiO2, zinc oxide and graphene oxide in the present invention is (8-12): (3-5): 1. If the ratio of ZnO or GO is not appropriate, the physical stability of the composite material may be insufficient, and it may be easily degraded or structurally changed when encountering an acidic or alkaline environment, thereby affecting its long-term performance. The present invention also limits the particle size and morphology of titanium dioxide, zinc oxide and graphene oxide, which can also enhance the mechanical strength of the material, making it more durable in practical applications and reducing the frequency of replacement. Appropriate particle size can also improve the physical stability and environmental resistance of the material, reduce aggregation or precipitation during use, and thus extend the service life of the catalyst.

[0030] Preferably, the particle size of titanium dioxide is 200 nm, and it is anatase. The microscopic morphology of titanium dioxide is irregular. It is purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., and the model is XT-TiO2-03.

[0031] Preferably, the zinc oxide has a particle size of 400 nm and an irregular microscopic morphology, and is purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-ZNO-04.

[0032] Preferably, graphene oxide is less than 10 μm and is purchased from Shanghai Xiangtian Nanomaterials Co., Ltd. with model number XT-GO-01.

[0033] Preferably, the mass concentration of ammonia water in the mixed aqueous solution is 3-5%, the mass concentration of sodium carbonate is 10-20%, the solid-liquid mass ratio of the mesoporous alumina molecular sieve and the mixed aqueous solution is 1:(30-50); the temperature of the hydrothermal treatment is 100-120°C, and the time is 8-10h.

[0034] Preferably, the mesoporous alumina molecular sieve is at least one of MCM-41, KIT-1, SBA-1, SBA-2, SBA-6, SBA-11, FDU-2, FDU-5, AMS-8 and TUD-1.

[0035] Preferably, the flow rate of aluminum trichloride vapor is 5-10 mL / min, the flow rate of cupric chloride vapor is 3-5 mL / min, and the flow rate of titanium tetrachloride vapor is 1-3 mL / min; the heating temperature is 500-800° C., and the time is 3-6 h.

[0036] Preferably, the mass concentration of melamine in the second mixed aqueous solution is 40-45%, the mass concentration of triethyl phosphate is 20-25%, and the solid-liquid mass ratio of activated carbon to the second mixed aqueous solution is 1:(25-35).

[0037] Preferably, the baking temperature is 80-120° C. and the baking time is 2-8 hours.

[0038] Preferably, the iodine adsorption value of the activated carbon is 1000 mg / g and the specific surface area is 1000-1100 m 2 / g;

[0039] The surfactant is sodium dodecyl sulfate and the cross-linking agent is starch.

[0040] Preferably, the particle size of the modified activated carbon is 1-3 mm.

[0041] Therefore, the present invention adopts the above-mentioned VOCs tail gas treatment system, which has the following beneficial effects:

[0042] 1. The VOCs tail gas treatment system of the present invention is sequentially provided with a condensation pretreatment step, a filtration step, a molecular sieve adsorption step, a photocatalyst step and an activated carbon re-adsorption step, and combines the adsorption method with the catalytic method. The two methods work synergistically, which can not only improve the efficiency of VOCs waste gas treatment, but also improve the effect of waste gas treatment.

[0043] 2. The present invention introduces specific chemical groups or elements, such as AlCl3, CuCl2 and TiCl4, on the surface of the mesoporous alumina molecular sieve. These components can enhance the polarity and lipophilicity of the molecular sieve surface, thereby improving its selective adsorption capacity for VOCs. In addition, the modification process may form more adsorption sites inside the molecular sieve, thereby increasing the adsorption amount.

[0044] 3. The nitrogen and phosphorus doping in the present invention can change the electronic structure of activated carbon, improve the chemical activity of its surface, and make the activated carbon have a higher affinity for certain VOCs. This doping can also enhance the stability of activated carbon and prevent deactivation caused by chemical reactions during the adsorption process.

[0045] 4. The plate-type catalyst of the present invention uses TiO2 as the main photocatalytic component, and its synergistic effect with zinc oxide and graphene oxide can improve the photocatalytic efficiency. The photogenerated electron-hole pairs of TiO2 are easy to recombine, while zinc oxide and graphene oxide can play a role in separating electron holes, reducing recombination losses, thereby improving photocatalytic activity. In addition, the presence of graphene oxide can also improve the conductivity of the catalyst, reduce resistance, make it easier to transmit photogenerated electrons, improve photocatalytic efficiency and extend the service life of the catalyst.

[0046] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0047] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and a specific operation process, but the present invention is not limited to this embodiment.

[0048] Example 1

[0049] This embodiment provides a VOCs tail gas treatment system, comprising the following steps:

[0050] (1) Pretreatment: The collected VOCs tail gas is subjected to condensation treatment; the collected VOCs tail gas is subjected to primary condensation and secondary condensation in sequence, the primary condensation temperature is 45°C, and the secondary condensation temperature is 12°C;

[0051] (2) Filtration: The VOCs tail gas after condensation treatment is filtered through a filter for primary filtration;

[0052] The filter used in this step is a conventional filter in the art, such as a cartridge filter;

[0053] (3) Adsorption: The VOCs tail gas after primary filtration treatment is adsorbed by modified molecular sieve adsorbent;

[0054] (4) Catalysis: The VOCs tail gas after adsorption treatment is degraded by a photocatalytic system; a plate-type photocatalyst is provided in the photocatalytic system, and the main components of the plate-type photocatalyst are TiO2, zinc oxide and graphene oxide, and the mass ratio of TiO2, zinc oxide and graphene oxide is 10:4:1;

[0055] The particle size of titanium dioxide is 200 nm, anatase, and the microscopic morphology of titanium dioxide is irregular. It was purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-TiO2-03;

[0056] The particle size of zinc oxide is 400 nm, the microscopic morphology is irregular, and it was purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-ZNO-04;

[0057] Graphene oxide <10 μm, purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-GO-01;

[0058] (5) Re-adsorption: The VOCs exhaust gas after degradation treatment is adsorbed by modified activated carbon and discharged after passing the test.

[0059] The preparation method of the modified molecular sieve adsorbent is:

[0060] (31) The mesoporous alumina molecular sieve is mixed with a mixed aqueous solution of ammonia and sodium carbonate, subjected to hydrothermal treatment, filtered, washed and dried to obtain a precursor; the mass concentration of ammonia in the mixed aqueous solution is 4%, the mass concentration of sodium carbonate is 10%, and the solid-liquid mass ratio of the mesoporous alumina molecular sieve to the mixed aqueous solution is 1:40; the temperature of the hydrothermal treatment is 110°C and the time is 8 hours; the mesoporous alumina molecular sieve is MCM-41;

[0061] (32) In a nitrogen atmosphere, the precursor was mixed with aluminum trichloride vapor, copper chloride vapor, and titanium tetrachloride vapor and heated to obtain a modified molecular sieve adsorbent; the flow rate of aluminum trichloride vapor was 8 mL / min, the flow rate of copper chloride vapor was 4 mL / min, and the flow rate of titanium tetrachloride vapor was 2 mL / min; the heating temperature was 600 °C, and the time was 4 h.

[0062] The preparation method of modified activated carbon is:

[0063] (51) The activated carbon was added to a mixed aqueous solution of melamine and triethyl phosphate and soaked for 6 h, then filtered, dried and sintered at a temperature of 600 °C for 2 h to obtain nitrogen-phosphorus doped activated carbon;

[0064] The mass concentration of melamine in the mixed solution is 42%, the mass concentration of triethyl phosphate is 22%, and the solid-liquid mass ratio of the activated carbon to the mixed aqueous solution II is 1:30;

[0065] The iodine adsorption value of activated carbon is 1000 mg / g, and the specific surface area is 1000-1100 m 2 / g; activated carbon was purchased from Shandong Yuyang Activated Carbon Co., Ltd., model number is YK100;

[0066] (52) Mix 22 parts of polyvinyl alcohol, 3 parts of a surfactant, 1 part of a cross-linking agent, and 95 parts of water in parts by weight and stir to obtain an adhesive;

[0067] The surfactant is sodium dodecyl sulfate, and the cross-linking agent is starch;

[0068] Polyvinyl alcohol was purchased from Guangzhou Ligou New Materials Co., Ltd., model PVA103, CAS: 9002-89-5;

[0069] Starch was purchased from Shanghai Yuanye Biotechnology Co., Ltd., CAS: 9005-84-9;

[0070] (53) 100 parts of nitrogen and phosphorus-doped activated carbon and 125 parts of an adhesive were added to a reaction kettle according to their weight ratios and stirred for 7 hours to obtain a mixture;

[0071] (54) The mixed material is fed into a granulation device, extruded into granular carbon, and the granular carbon is baked until the moisture content is less than 5%; the baking temperature is 90° C. and the time is 3 h;

[0072] (55) crushing the baked granular carbon, and sieving it after crushing to obtain modified activated carbon;

[0073] The particle size of the modified activated carbon is 1 mm.

[0074] Example 2

[0075] This embodiment provides a VOCs tail gas treatment system, including the following steps:

[0076] (1) Pretreatment: The collected VOCs tail gas is subjected to condensation treatment; the collected VOCs tail gas is subjected to primary condensation and secondary condensation in sequence, the primary condensation temperature is 40°C, and the secondary condensation temperature is 10°C;

[0077] (2) Filtration: The VOCs tail gas after condensation treatment is filtered through a filter for primary filtration;

[0078] (3) Adsorption: The VOCs tail gas after primary filtration treatment is adsorbed by modified molecular sieve adsorbent;

[0079] (4) Catalysis: The VOCs tail gas after adsorption treatment is degraded by a photocatalytic system; a plate-type photocatalyst is provided in the photocatalytic system, and the main components of the plate-type photocatalyst are TiO2, zinc oxide and graphene oxide, and the mass ratio of TiO2, zinc oxide and graphene oxide is 8:3:1;

[0080] The particle size of titanium dioxide is 200 nm, anatase, and the microscopic morphology of titanium dioxide is irregular. It was purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-TiO2-03;

[0081] The particle size of zinc oxide is 400 nm, the microscopic morphology is irregular, and it was purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-ZNO-04;

[0082] Graphene oxide <10 μm, purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-GO-01;

[0083] (5) Re-adsorption: The VOCs exhaust gas after degradation treatment is adsorbed by modified activated carbon and discharged after passing the test.

[0084] The preparation method of the modified molecular sieve adsorbent is:

[0085] (31) The mesoporous alumina molecular sieve is mixed with a mixed aqueous solution of ammonia and sodium carbonate, subjected to hydrothermal treatment, filtered, washed and dried to obtain a precursor; the mass concentration of ammonia in the mixed aqueous solution is 5%, the mass concentration of sodium carbonate is 18%, and the solid-liquid mass ratio of the mesoporous alumina molecular sieve to the mixed aqueous solution is 1:35; the temperature of the hydrothermal treatment is 120°C and the time is 8 hours; the mesoporous alumina molecular sieve is SBA-1;

[0086] (32) In a nitrogen atmosphere, the precursor was mixed with aluminum chloride vapor, copper chloride vapor, and titanium tetrachloride vapor and heated to obtain a modified molecular sieve adsorbent; the flow rate of aluminum chloride vapor was 6 mL / min, the flow rate of copper chloride vapor was 3 mL / min, and the flow rate of titanium tetrachloride vapor was 1 mL / min; the heating temperature was 750 °C, and the time was 5 h.

[0087] The preparation method of modified activated carbon is:

[0088] (51) The activated carbon was added to a mixed aqueous solution of melamine and triethyl phosphate and soaked for 7 h, then filtered, dried and sintered at a temperature of 650 °C for 1 h to obtain nitrogen-phosphorus doped activated carbon;

[0089] The mass concentration of melamine in the mixed solution is 40%, the mass concentration of triethyl phosphate is 20%, and the solid-liquid mass ratio of the activated carbon to the mixed aqueous solution is 1:30;

[0090] The iodine adsorption value of activated carbon is 1000 mg / g, and the specific surface area is 1000-1100 m 2 / g; activated carbon was purchased from Shandong Yuyang Activated Carbon Co., Ltd., model number is YK100;

[0091] (52) Mix 24 parts of polyvinyl alcohol, 4 parts of a surfactant, 2 parts of a cross-linking agent, and 100 parts of water in parts by weight and stir to obtain an adhesive;

[0092] The surfactant is sodium dodecyl sulfate, and the cross-linking agent is starch;

[0093] Polyvinyl alcohol was purchased from Guangzhou Ligou New Materials Co., Ltd., model PVA103, CAS: 9002-89-5;

[0094] Starch was purchased from Shanghai Yuanye Biotechnology Co., Ltd., CAS: 9005-84-9;

[0095] (53) 100 parts of nitrogen and phosphorus-doped activated carbon and 120 parts of an adhesive were added to a reaction kettle according to their weight ratios and stirred for 8 hours to obtain a mixture;

[0096] (54) feeding the mixed material into a granulation device, extruding the granular carbon, and baking the granular carbon until the moisture content is less than 5%;

[0097] (55) crushing the baked granular carbon, and sieving it after crushing to obtain modified activated carbon;

[0098] The baking temperature is 115°C and the time is 6h;

[0099] The particle size of the modified activated carbon is 3 mm.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 1 is that in step (3), no modified molecular sieve is used as the adsorbent, but mesoporous alumina molecular sieve MCM-41 is directly used as the adsorbent.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that sodium carbonate is not added to the mixed aqueous solution 1 in the modified molecular sieve adsorbent, and ammonia water of equal mass concentration is used instead.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 1 is that during the preparation of the modified molecular sieve adsorbent, the precursor is only mixed with aluminum chloride vapor for heating treatment, and aluminum chloride vapor with an equal flow rate is used to replace copper chloride vapor and titanium tetrachloride vapor.

[0106] Comparative Example 4

[0107] The difference between this comparative example and Example 1 is that the mass ratio of TiO2, zinc oxide and graphene oxide in step (4) is 10:4:5.

[0108] Comparative Example 5

[0109] The difference between this comparative example and Example 1 is that the zinc oxide in step (4) has a particle size of 1 μm and an irregular micromorphology, and is purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., model XT-ZNO-05.

[0110] Comparative Example 6

[0111] The difference between this comparative example and Example 1 is that in step (4), the nanostructured carbon nanotubes are <30 μm and are purchased from Shanghai Xiangtian Nanomaterials Co., Ltd. with a model number of XT-GO-03.

[0112] Comparative Example 7

[0113] The difference between this comparative example and Example 1 is that in step (5), modified activated carbon is not used as the adsorbent but pure activated carbon is directly used as the adsorbent.

[0114] Comparative Example 8

[0115] The difference between this comparative example and Example 1 is that no melamine is added in step (51), and triethyl phosphate of equal mass concentration is used to replace melamine.

[0116] Comparative Example 9

[0117] The difference between this comparative example and Example 1 is that triethyl phosphate is not added in step (51), and melamine of equal mass concentration is used to replace triethyl phosphate.

[0118] Comparative Example 10

[0119] The difference between this comparative example and Example 1 is that during the preparation of the modified activated carbon, the activated carbon is directly mixed with the mixed aqueous solution of melamine and triethyl phosphate and the adhesive to obtain a mixture.

[0120] Performance Testing

[0121] (1) VOCs tail gas treatment effect test

[0122] A VOCs tail gas treatment system is constructed, which includes a condenser, a filter, a first adsorption box (filled with modified molecular sieve), a photocatalytic device (equipped with a plate-type photocatalyst) and a second adsorption box (filled with modified activated carbon), which are connected through a ventilation pipeline.

[0123] During the test, the VOCs exhaust air intake volume was 3000cm 3 / min, the total volume of the adsorbent (modified molecular sieve and modified activated carbon) bed is 100cm 3 The volume of the catalyst is 2.5 cm 3 .

[0124] The VOCs exhaust gas concentration before treatment is 400mg / Nm 3, calculated by volume percentage, the specific components of VOCs tail gas are: 33% diethylene glycol ethyl ether acetate, 21% propylene glycol methyl ether acetate, 9% dibasic acid ester, 7% ethylene glycol butyl ether, 7% dipropylene glycol methyl ether, 5% naphtha, 5% methanol, 5% cyclohexane, 4% vinyl chloride, 2% acrylonitrile, and 2% monoethanolamine.

[0125] Adsorption catalytic removal rate = (VOCs tail gas concentration before adsorption catalysis - concentration after adsorption catalysis) / VOCs tail gas concentration before adsorption catalysis × 100%.

[0126] Table 1 Performance test results

[0127]

[0128]

[0129] (2) Acid resistance test and alkali resistance test

[0130] Acid resistance: The modified activated carbon, modified molecular sieve and photocatalyst prepared in the examples and comparative examples were introduced into a carbon disulfide saturated gas at normal pressure for 7 days, and then the changes in the experimental samples were observed. The test results are shown in Table 2.

[0131] Alkali resistance: The modified activated carbon, modified molecular sieve and photocatalyst prepared in the examples and comparative examples were introduced into a saturated ammonia gas at normal pressure for 7 days, and then the changes in the experimental samples were observed. The test results are shown in Table 2.

[0132] The test results are divided into three situations. No dusting means that the structure of the molecular sieve and activated carbon has not changed significantly. Slight dusting means that powdery substances begin to float on the surface of the molecular sieve and activated carbon, and a small amount has fallen to the outside. Dust loss means that a certain amount of powder has appeared on the outside of the molecular sieve and activated carbon, and its structure has become loose.

[0133] Table 2 Acid and alkali resistance test results

[0134] Group Molecular sieve surface state Surface state of activated carbon Catalyst surface state Example 1 No dust No dust No dust Example 2 No dust No dust No dust Comparative Example 1 Dust No dust No dust Comparative Example 2 Slightly dusty No dust No dust Comparative Example 3 Slightly dusty No dust No dust Comparative Example 4 No dust No dust Slightly dusty Comparative Example 5 No dust No dust Slightly dusty Comparative Example 6 No dust No dust Slightly dusty Comparative Example 7 No dust Dust No dust Comparative Example 8 No dust Slightly dusty No dust Comparative Example 9 No dust Slightly dusty No dust Comparative Example 10 No dust Slightly dusty No dust

[0135] It can be seen from the above performance test results that Examples 1-2 have a good adsorption catalytic removal rate for VOCs tail gas, especially Example 1 has the most outstanding comprehensive performance, which is mainly because the present invention uses modified molecular sieves and modified activated carbon.

[0136] The comparative example is obviously inferior to the embodiment in the corresponding performance test because it does not adopt the necessary technical solution. In comparative example 1, unmodified molecular sieve is directly used for tail gas treatment. It can be seen from the results that the acid and alkali resistance of the molecular sieve decreases, which also affects the effect of tail gas treatment, proving that the modification of the molecular sieve has an important influence on its own structure and the effect of tail gas treatment. In comparative example 2, sodium carbonate is not added when the molecular sieve is activated. It can be seen from the results that the structure of the molecular sieve and its effect on tail gas treatment are affected, proving the importance of using ammonia and sodium carbonate to treat the molecular sieve at the same time. In comparative example 3, when the molecular sieve is metal-modified, only aluminum chloride is used as a metal. It can be seen from the results that the environmental resistance and tail gas treatment effect of the molecular sieve are reduced, which explains the necessity of using three metals to modify the molecular sieve at the same time in this application. Comparative example 4 changes the ratio of the three materials in the photocatalyst and increases the ratio of graphene oxide. It can be seen from the results that the structure of the photocatalyst and the treatment effect of tail gas are both deteriorated, affecting the treatment effect of the entire system. Comparative Examples 5 and 6 respectively changed the particle size of zinc oxide and the particle size of graphene oxide. It can be seen from the results that the effect of tail gas treatment is deteriorated, indicating that the parameters of zinc oxide and the parameters of graphene oxide have a very important influence on the tail gas treatment effect of the overall system. In Comparative Example 7, activated carbon is directly used as an adsorbent without modifying the activated carbon. It can be seen from the results that the physical structure of the activated carbon and the tail gas treatment effect are affected, and declines occur to varying degrees, indicating the necessity of modifying the activated carbon for the overall system to treat the tail gas. In Comparative Examples 8 and 9, melamine and triethyl phosphate were not added during the activated carbon modification process, and only one doping was performed on the activated carbon. It can be seen from the results that the activated carbon doped with only one element is compared with the activated carbon doped with two elements in Example 1-2. The physical structure stability and the tail gas treatment effect of the overall system are both deteriorated, indicating the necessity of using two elements to dope the activated carbon at the same time in the present invention. In Comparative Example 10, melamine and triethyl phosphate are directly mixed with activated carbon, and then an adhesive is added. From the results, it can be seen that the physical structure of the activated carbon obtained by this preparation method is easily affected by the external environment, and the effect of the overall system in treating exhaust gas is also deteriorated, indicating the necessity of first doping the activated carbon with two elements and then mixing it with the adhesive in the present invention, which can further optimize the adsorption effect of the activated carbon, thereby improving the adsorption catalytic effect of the entire exhaust gas treatment system. The above experimental results further prove the importance of the technical solution defined in the present invention for its technical effect.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A VOCs tail gas treatment system, characterized in that: The following steps are involved: (1) Pretreatment: condensing the collected VOCs tail gas; (2) Filtration: The VOCs tail gas after condensation treatment passes through the filter for primary filtration; (3) Adsorption: The VOCs tail gas after primary filtration treatment is adsorbed by modified molecular sieve adsorbent; (4) Catalysis: The VOCs tail gas after adsorption treatment is degraded through a photocatalytic system; (5) Re-adsorption: The VOCs tail gas after degradation treatment is adsorbed by modified activated carbon and discharged after passing the test; The preparation method of the modified molecular sieve adsorbent is: (31) mixing the mesoporous alumina molecular sieve with a mixed aqueous solution of ammonia and sodium carbonate, hydrothermally treating, filtering, washing and drying to obtain a precursor; (32) In a nitrogen atmosphere, the precursor is mixed with aluminum trichloride vapor, copper chloride vapor, and titanium tetrachloride vapor and heated to obtain a modified molecular sieve adsorbent; The preparation method of modified activated carbon is: (51) adding activated carbon to a mixed aqueous solution of melamine and triethyl phosphate for immersion for 5 to 8 hours, filtering, drying and sintering to obtain nitrogen-phosphorus doped activated carbon; (52) Mix 20-25 parts of polyvinyl alcohol, 2-4 parts of a surfactant, 0.5-3 parts of a cross-linking agent, and 90-100 parts of water in parts by weight and stir them uniformly to obtain an adhesive; (53) 100 parts of nitrogen-phosphorus-doped activated carbon and 120-140 parts of an adhesive were added to a reaction kettle according to their weight ratios and stirred for 6-8 hours to obtain a mixture; (54) feeding the mixed material into a granulation device, extruding the granular carbon, and baking the granular carbon until the moisture content is less than 5%; (55) crushing the baked granular carbon, and sieving after crushing to obtain modified activated carbon; The photocatalytic system is provided with a plate-type photocatalyst, the main components of which are TiO2, zinc oxide and graphene oxide, and the mass ratio of TiO2, zinc oxide and graphene oxide is (8~12):(3~5):

1.

2. A VOCs tail gas treatment system according to claim 1, characterized in that: The condensation treatment includes the following steps: the collected VOCs tail gas is subjected to primary condensation and secondary condensation in sequence, the temperature of the primary condensation is 40~50℃, and the temperature of the secondary condensation is 10~15℃.

3. A VOCs tail gas treatment system according to claim 1, characterized in that: The mass concentration of ammonia water in the mixed aqueous solution is 3-5%, the mass concentration of sodium carbonate is 10-20%, and the solid-liquid mass ratio of the mesoporous alumina molecular sieve to the mixed aqueous solution is 1:(30-50); the temperature of the hydrothermal treatment is 100-120°C, and the time is 8-10h.

4. A VOCs tail gas treatment system according to claim 1, characterized in that: The mesoporous alumina molecular sieve is at least one of MCM-41, KIT-1, SBA-1, SBA-2, SBA-6, SBA-11, FDU-2, FDU-5, AMS-8 and TUD-1.

5. A VOCs tail gas treatment system according to claim 1, characterized in that: The flow rate of aluminum trichloride vapor is 5-10 mL / min, the flow rate of copper chloride vapor is 3-5 mL / min, and the flow rate of titanium tetrachloride vapor is 1-3 mL / min; the temperature of the heating treatment is 500-800°C, and the time is 3-6 hours.

6. A VOCs tail gas treatment system according to claim 1, characterized in that: The mass concentration of melamine in the mixed aqueous solution II is 40-45%, the mass concentration of triethyl phosphate is 20-25%, and the solid-liquid mass ratio of the activated carbon to the mixed aqueous solution II is 1:(25-35).

7. A VOCs tail gas treatment system according to claim 1, characterized in that: The baking temperature is 80~120℃ and the time is 2~8h.

8. A VOCs tail gas treatment system according to claim 1, characterized in that: The iodine adsorption value of activated carbon is 1000 mg / g, and the specific surface area is 1000~1100m 2 / g; The surfactant is sodium dodecyl sulfate and the cross-linking agent is starch.

9. A VOCs tail gas treatment system according to claim 1, characterized in that: The particle size of modified activated carbon is 1-3mm.

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