Absorption treatment system for phosgene-containing tail gas

Abstract

The invention relates to the technical field of tail gas treatment, in particular to an absorption treatment system for phosgene-containing tail gas, which comprises the following steps: S1, introducing the phosgene-containing tail gas into a falling film absorption tower, adding a sodium hydroxide solution with the concentration of 10-20% as an absorbent, and maintaining the operation temperature for absorption treatment to obtain absorbed tail gas and salt-containing wastewater; s2, the absorbed tail gas is introduced into a three-stage catalytic destruction tower, the destruction tower is internally provided with a catalyst in advance, the operation temperature is maintained for catalytic destruction treatment, and the tail gas subjected to catalytic treatment is obtained; s3, the tail gas subjected to catalytic treatment is introduced into an alkali absorption tower, a sodium hydroxide solution with the concentration being 5% serves as an absorbent, the operation temperature is maintained for absorption treatment, and completely-treated tail gas and salt-containing wastewater are obtained. The prepared catalyst has a rich porous structure, so that reactant molecules are easier to approach to an active center on the surface of the catalyst, the catalytic reaction is accelerated, and the catalytic efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas treatment, and in particular to an absorption treatment system for tail gas containing phosgene. Background Art

[0002] As an important organic compound, methyl chloroformate is widely used in the fields of pesticides, medicine, organic synthesis, etc., especially in the pesticide industry, as a key raw material for preparing herbicides such as chloramphenicol and fungicide carbendazim. In the production process of methyl chloroformate, the phosgene method is one of the main preparation methods at present, which synthesizes methyl chloroformate by esterification reaction of methanol and phosgene. However, as a highly toxic gas, the use and emission of phosgene pose a serious threat to the environment and human health. In the production process of methyl chloroformate, unreacted phosgene will be discharged with the tail gas to form tail gas containing phosgene. These tail gases not only contain phosgene, but also may contain other harmful components such as hydrogen chloride, carbon dioxide, carbon monoxide, etc. The emission of phosgene not only violates national environmental protection laws and regulations, but also may pollute the surrounding environment and cause harm to human health. In particular, phosgene is extremely toxic and can cause severe symptoms such as respiratory irritation and pulmonary edema after inhalation, and even endanger life. Phosgene and hydrogen chloride, as the main harmful components in tail gas, have great harm to the environment. Therefore, before being discharged, it must go through a strict treatment system to meet national emission standards. For tail gas systems with high phosgene content, most of the phosgene is usually recovered first, and then the remaining phosgene is destroyed; while for systems with less phosgene content, destruction may be carried out directly.

[0003] In the prior art, although the traditional alkaline solution absorption method can absorb part of the phosgene, it is difficult to treat due to the limited solubility of phosgene in water and the large amount of acidic wastewater that may be produced during the absorption process. In addition, in addition to phosgene, the phosgene-containing tail gas may also contain multiple components such as hydrogen chloride, carbon dioxide, and carbon monoxide, which increases the complexity of tail gas treatment and may lead to low treatment efficiency. Summary of the invention

[0004] In order to solve the problems mentioned in the above background technology, the present invention provides an absorption treatment system for phosgene-containing tail gas.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A system for absorbing and treating tail gas containing phosgene comprises the following steps:

[0007] S1. Pass the phosgene-containing tail gas into a falling film absorption tower, add a sodium hydroxide solution with a concentration of 10-20% as an absorbent, maintain the operating temperature at 20-30° C., and absorb for 1-2 hours to obtain the absorbed tail gas and saline wastewater, wherein the phosgene concentration in the tail gas is less than 5 ppm;

[0008] S2, passing the tail gas after absorption into a three-stage catalytic destruction tower, in which a catalyst is pre-installed, maintaining an operating temperature of 250-350°C, and catalytic destruction treatment for 2-4 hours to obtain tail gas after catalytic treatment, in which the phosgene concentration is less than 1ppm;

[0009] S3. The tail gas after catalytic treatment is passed into an alkali absorption tower, and a 5% sodium hydroxide solution is used as an absorbent. The operating temperature is maintained at 20-40°C, and the absorption treatment is performed for 30-60 minutes to obtain completely treated tail gas and saline wastewater, and the phosgene concentration in the tail gas is less than 0.1ppm.

[0010] Furthermore, the saline wastewater produced by the falling film absorber and the alkali absorber is collected into the wastewater collection pool through a pipeline and initially filtered to remove suspended solids. The filtration flow rate is 2-5m 3 / h, pump the filtered wastewater into the sedimentation tank, add aluminum sulfate, the dosage is 1-3‰ of the wastewater volume, stir and mix, the stirring speed is 50-100rpm, the stirring time is 15-30min, the static sedimentation tank, the sedimentation time is not less than 2h, the supernatant is pumped into the biochemical treatment tank, the precipitate is collected as sludge and sent to the sludge treatment system, the dissolved oxygen (DO) in the biochemical treatment tank is controlled to 2-4mg / L, the temperature is 20-35℃, the pH value is 6.5-8.5, add activated sludge, the dosage is 1-3% of the tank volume, the biochemical treatment time is not less than 12h, pump it out through the outlet, conduct final inspection on the effluent, and discharge it after meeting the standards.

[0011] Furthermore, the flow rate of the phosgene-containing tail gas in step S1 is 1000-1100m 3 / h.

[0012] Furthermore, the flow rate of the tail gas after absorption in step S2 is 950-1000m 3 / h.

[0013] Furthermore, the dosage of the catalyst in step S2 is 5-10 kg.

[0014] Further, the catalyst in step S2 is prepared by the following steps:

[0015] A1. Slowly add polyetherimide and polyethylene glycol into a reactor containing dimethyl sulfoxide, stir at room temperature until completely dissolved, add azobisisobutyronitrile, heat to 70-80°C under nitrogen protection, keep warm and stir to react for 12-24 hours. After the reaction is completed, pour the solution into a dialysis bag, dialyze with distilled water, replace the dialysate every 4 hours, dialyze for a total of 20-24 hours, and freeze-dry the solution to obtain a copolymer substrate;

[0016] A2. Add the copolymer base and 4-aminobenzoic acid into a reactor containing N,N-dimethylformamide, stir at room temperature until completely dissolved, add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide, stir at room temperature for 6-12 hours, centrifuge, wash the precipitate obtained by centrifugation with ethanol 2-3 times, place in a vacuum drying oven, and dry at 40°C to constant weight to obtain a catalyst.

[0017] Furthermore, the flow rate of the tail gas after catalytic treatment in step S3 is 800-850m 3 / h.

[0018] Furthermore, in step A1, the mass ratio of polyetherimide, polyethylene glycol, dimethyl sulfoxide and azobisisobutyronitrile is (1-2): (2-4): 8: (0.01-0.03).

[0019] Furthermore, in step A2, the mass ratio of the copolymer substrate, 4-aminobenzoic acid, N,N-dimethylformamide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide is (1-1.5):(2.2-2.8):10:(0.05-0.08):(0.02-0.06).

[0020] Beneficial effects of the present invention:

[0021] 1. In the technical solution of the present invention, the copolymer substrate is formed by free radical polymerization of polyetherimide (PEI) and polyethylene glycol (PEG), has a three-dimensional network structure, and is rich in active functional groups such as amino and ether bonds, which enhances the hydrophilicity and adsorption properties of the catalyst. In step A2, 4-aminobenzoic acid forms an amide bond with the amino group on the copolymer substrate through a condensation reaction, further enhancing the stability of the catalyst and giving it a specific catalytic activity. The carbonyl and amino groups in the amide bond act as active centers and can interact with phosgene molecules to promote the adsorption and activation of phosgene molecules. In addition, through steps such as dialysis and freeze drying, the porous structure of the catalyst is retained, greatly increasing the specific surface area of ​​the catalyst, and further improving its adsorption properties and catalytic activity.

[0022] 2. In the technical solution of the present invention, the porous structure and rich active functional groups of the catalyst significantly improve its adsorption performance for phosgene molecules, and tightly bind to phosgene molecules through interactions such as hydrogen bonds or van der Waals forces, making phosgene molecules more easily adsorbed on the catalyst surface.

[0023] 3. In the technical solution of the present invention, during the activation process of phosgene molecules, the active centers such as amide bonds on the catalyst surface transform the phosgene molecules from a stable adsorbed state to a highly active intermediate species through reactions such as electron transfer and bond breaking, thereby providing favorable conditions for subsequent decomposition reactions.

[0024] 4. In the technical solution of the present invention, the porous structure of the catalyst makes it easier for the reactant molecules to approach the active centers on its surface, thereby accelerating the catalytic reaction and improving the catalytic efficiency.

[0025] 5. In the technical solution of the present invention, the prepared catalyst has good thermal stability and chemical stability, which effectively prevents the catalyst from decomposing or deactivating during the catalytic process and prolongs its service life. In summary, the microstructure and preparation mechanism of the catalyst jointly determine its high efficiency and stability in the treatment of phosgene-containing tail gas, providing a strong guarantee for environmentally friendly emissions. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the raw materials used in the present invention are all conventional products purchased from the market.

[0028] Preparation Example 1

[0029] The catalyst is prepared by the following steps:

[0030] A1. Slowly add 10 kg of polyetherimide and 20 kg of polyethylene glycol into a reactor containing 80 kg of dimethyl sulfoxide, stir at room temperature until completely dissolved, add 0.1 kg of azobisisobutyronitrile, heat to 70 ° C under nitrogen protection, keep warm and stir for 12 hours, after the reaction is completed, pour the solution into a dialysis bag, dialyze with distilled water, replace the dialysate every 4 hours, dialyze for 20 hours in total, and freeze-dry the solution to obtain a copolymer substrate;

[0031] A2. Add 10 kg of the copolymer base and 22 kg of 4-aminobenzoic acid into a reactor containing 100 kg of N,N-dimethylformamide, stir at room temperature until completely dissolved, add 0.5 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.2 kg of N-hydroxysuccinimide, stir at room temperature to react for 6 hours, centrifuge, wash and dry to obtain a catalyst.

[0032] Preparation Example 2

[0033] The catalyst is prepared by the following steps:

[0034] A1. Slowly add 15 kg of polyetherimide and 30 kg of polyethylene glycol into a reactor containing 80 kg of dimethyl sulfoxide, stir at room temperature until completely dissolved, add 0.2 kg of azobisisobutyronitrile, heat to 75 ° C under nitrogen protection, keep warm and stir for 18 hours, after the reaction is completed, pour the solution into a dialysis bag, dialyze with distilled water, replace the dialysate every 4 hours, dialyze for 20 hours in total, and freeze-dry the solution to obtain a copolymer substrate;

[0035] A2. Add 12.5 kg of the copolymer base and 25 kg of 4-aminobenzoic acid into a reactor containing 100 kg of N,N-dimethylformamide, stir at room temperature until completely dissolved, add 0.6 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.4 kg of N-hydroxysuccinimide, stir at room temperature to react for 10 hours, centrifuge, wash and dry to obtain a catalyst.

[0036] Preparation Example 3

[0037] The catalyst is prepared by the following steps:

[0038] A1. Slowly add 20 kg of polyetherimide and 40 kg of polyethylene glycol into a reactor containing 80 kg of dimethyl sulfoxide, stir at room temperature until completely dissolved, add 0.3 kg of azobisisobutyronitrile, heat to 80 ° C under nitrogen protection, keep warm and stir for 24 hours, after the reaction is completed, pour the solution into a dialysis bag, dialyze with distilled water, replace the dialysate every 4 hours, dialyze for a total of 24 hours, and freeze-dry the solution to obtain a copolymer substrate;

[0039] A2. Add 15 kg of the copolymer base and 28 kg of 4-aminobenzoic acid into a reactor containing 100 kg of N,N-dimethylformamide, stir at room temperature until completely dissolved, add 0.8 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 0.6 kg of N-hydroxysuccinimide, stir at room temperature to react for 12 h, centrifuge, wash and dry to obtain a catalyst.

[0040] Example 1

[0041] A system for absorbing and treating tail gas containing phosgene comprises the following steps:

[0042] S1, pass the phosgene-containing tail gas into the falling film absorption tower, the flow rate is 1000m 3 / h, adding 10% sodium hydroxide solution as absorbent, maintaining the operating temperature at 20°C, absorbing for 1h, obtaining tail gas and saline wastewater after absorption, and measuring the phosgene concentration in the tail gas to be 4.6ppm;

[0043] S2, the tail gas after absorption is passed into the three-stage catalytic destruction tower, and the flow rate is 950m 3 / h, the catalyst prepared in Preparation Example 1 was pre-installed in the destruction tower, the dosage was 5kg, the operating temperature was maintained at 250°C, the catalytic destruction treatment was performed for 2h, and the tail gas after catalytic treatment was obtained. The phosgene concentration in the tail gas was measured to be 0.8ppm;

[0044] S3, the tail gas after catalytic treatment is passed into the alkali absorption tower with a flow rate of 8000m 3 / h, using 5% sodium hydroxide solution as absorbent, maintaining the operating temperature at 20°C, and absorbing for 30 minutes to obtain completely treated tail gas and saline wastewater. The phosgene concentration in the tail gas was measured to be 0.05ppm.

[0045] Example 2

[0046] A system for absorbing and treating tail gas containing phosgene comprises the following steps:

[0047] S1, pass the phosgene-containing tail gas into the falling film absorption tower, the flow rate is 1050m 3 / h, adding 15% sodium hydroxide solution as absorbent, maintaining the operating temperature at 25°C, absorbing for 1.5h, obtaining tail gas and saline wastewater after absorption, and measuring the phosgene concentration in the tail gas to be 4.2ppm;

[0048] S2, the tail gas after absorption is passed into the three-stage catalytic destruction tower, and the flow rate is 980m 3 / h, the catalyst prepared in Preparation Example 2 was pre-installed in the destruction tower, the dosage was 8kg, the operating temperature was maintained at 300°C, the catalytic destruction treatment was performed for 3h, and the tail gas after catalytic treatment was obtained. The phosgene concentration in the tail gas was measured to be 0.7ppm;

[0049] S3, the tail gas after catalytic treatment is passed into the alkali absorption tower with a flow rate of 830m 3 / h, using 5% sodium hydroxide solution as absorbent, maintaining the operating temperature at 30°C, and absorbing for 45 minutes to obtain completely treated tail gas and saline wastewater. The phosgene concentration in the tail gas was measured to be 0.04ppm.

[0050] Example 3

[0051] A system for absorbing and treating tail gas containing phosgene comprises the following steps:

[0052] S1, pass the phosgene-containing tail gas into the falling film absorption tower, the flow rate is 1100m 3 / h, adding 20% ​​sodium hydroxide solution as absorbent, maintaining the operating temperature at 30°C, absorbing for 2h, obtaining tail gas and saline wastewater after absorption, and measuring the phosgene concentration in the tail gas to be 4.1ppm;

[0053] S2, the tail gas after absorption is passed into the three-stage catalytic destruction tower, and the flow rate is 1000m 3 / h, the catalyst prepared in Preparation Example 3 was pre-installed in the destruction tower, the dosage was 10kg, the operating temperature was maintained at 350°C, the catalytic destruction treatment was performed for 4h, and the tail gas after catalytic treatment was obtained. The phosgene concentration in the tail gas was measured to be 0.5ppm;

[0054] S3, the tail gas after catalytic treatment is passed into the alkali absorption tower with a flow rate of 850m 3 / h, using 5% sodium hydroxide solution as absorbent, maintaining the operating temperature at 40°C, and absorbing for 60 minutes to obtain completely treated tail gas and saline wastewater. The phosgene concentration in the tail gas was measured to be 0.04ppm.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that polyetherimide is used instead of the catalyst prepared in Preparation Example 1, and the remaining steps are the same as those in Example 1. The phosgene concentration in the final tail gas is measured to be 3.6 ppm.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 2 is that polyethylene glycol is used instead of the catalyst prepared in Preparation Example 2, and the remaining steps are the same as those in Example 2. The phosgene concentration in the final tail gas is measured to be 2.9 ppm.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 3 is that 4-aminobenzoic acid is used instead of the catalyst prepared in Preparation Example 3, and the remaining steps are the same as those in Example 3. The phosgene concentration in the final tail gas is measured to be 4.5 ppm.

[0061] According to GB 37823-2019 "Pharmaceutical Industry Air Pollutant Emission Standard" and GB 31572-2015 "Synthetic Resin Industry Pollutant Emission Standard", the emission limits for phosgene are 1 mg / m 3 and 0.5 mg / m 3 .

[0062] In Example 1-3, the phosgene concentration in the tail gas was effectively reduced by three steps: a falling film absorption tower, a three-stage catalytic destruction tower, and an alkali absorption tower. The final phosgene concentrations in the tail gas were 0.05 ppm, 0.04 ppm, and 0.04 ppm, respectively, which were far lower than the emission limits (1 mg / m 3 and 0.5 mg / m 3 ). The treatment system in the embodiment showed extremely high treatment efficiency, especially the catalyst in the three-stage catalytic destruction tower, which significantly reduced the phosgene concentration in the tail gas.

[0063] Comparative Examples 1-3 used polyetherimide, polyethylene glycol and 4-aminobenzoic acid to replace the catalyst used in the example, and the other steps remained unchanged. The phosgene concentrations in the final tail gas of Comparative Examples 1-3 were 3.6ppm, 2.9ppm and 4.5ppm, respectively, which were much higher than the concentrations in the example, and partly exceeded the limit of the emission standard. When a single component was used as a catalyst substitute, the treatment efficiency was significantly reduced, indicating that these single components could not provide sufficient catalytic activity to effectively decompose phosgene.

[0064] In an embodiment, the catalyst is prepared by copolymerization of polyetherimide and polyethylene glycol, combined with compounds such as 4-aminobenzoic acid, and may provide multiple active sites, which can efficiently catalyze the decomposition reaction of phosgene. The copolymerization of polyetherimide and polyethylene glycol forms a copolymer substrate with a specific structure and properties, which provides a good support platform for subsequent catalytic reactions. By adding compounds such as 4-aminobenzoic acid, active sites that can catalyze the decomposition of phosgene are formed in the catalyst. These active sites can reduce the activation energy of the reaction and promote the decomposition of phosgene. As single components, polyetherimide, polyethylene glycol and 4-aminobenzoic acid lack specific active sites formed by copolymerization in the catalyst, and may not be able to effectively catalyze the decomposition reaction of phosgene. Although these single components may have certain physical absorption effects, their effects are far less than the chemical catalysis in the catalyst. In addition to the catalyst, the operating conditions also have a significant effect on the treatment efficiency. In an embodiment, by optimizing these conditions, the treatment efficiency is further improved.

[0065] In summary, the catalysts prepared in Preparation Examples 1-3 achieved efficient treatment of phosgene-containing tail gas in Examples 1-3.

[0066] In the description of the specification, the description with reference to the terms "embodiment", "various embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or preparation example are included in at least one embodiment or preparation example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or preparation example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or preparation examples in a suitable manner.

[0067] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A system for absorbing and treating phosgene-containing tail gas, characterized in that: The following steps are involved: S1. Pass the phosgene-containing tail gas into a falling film absorption tower, add a sodium hydroxide solution with a concentration of 10-20% as an absorbent, maintain the operating temperature at 20-30° C., and absorb for 1-2 hours to obtain the absorbed tail gas and saline wastewater; S2, passing the absorbed tail gas into a three-stage catalytic destruction tower, in which a catalyst is pre-installed, maintaining an operating temperature of 250-350°C, and catalytically destroying the tail gas for 2-4 hours to obtain the catalytically treated tail gas; S3. The tail gas after catalytic treatment is passed into an alkali absorption tower, and a 5% sodium hydroxide solution is used as an absorbent. The operating temperature is maintained at 20-40° C. and the absorption treatment is performed for 30-60 minutes to obtain completely treated tail gas and saline wastewater.

2. The absorption treatment system for phosgene-containing tail gas according to claim 1, characterized in that: The flow rate of the phosgene-containing tail gas in step S1 is 1000-1100m 3 / h.

3. The absorption treatment system for phosgene-containing tail gas according to claim 1, characterized in that: The flow rate of the tail gas after absorption in step S2 is 950-1000m 3 / h.

4. The absorption treatment system for phosgene-containing tail gas according to claim 1, characterized in that: The dosage of the catalyst in step S2 is 5-10 kg.

5. The absorption treatment system for phosgene-containing tail gas according to claim 1, characterized in that: The catalyst in step S2 is prepared by the following steps: A1. Slowly add polyetherimide and polyethylene glycol into a reactor containing dimethyl sulfoxide, stir at room temperature until completely dissolved, add azobisisobutyronitrile, heat to 70-80°C under nitrogen protection, keep warm and stir for 12-24 hours, after the reaction is completed, pour the solution into a dialysis bag, dialyze with distilled water, replace the dialysate every 4 hours, dialyze for a total of 20-24 hours, and freeze-dry the solution to obtain a copolymer substrate; A2. Add the copolymer base and 4-aminobenzoic acid into a reactor filled with N,N-dimethylformamide, stir at room temperature until completely dissolved, add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide, stir at room temperature for 6-12 hours, centrifuge, wash and dry to obtain a catalyst.

6. The absorption treatment system for phosgene-containing tail gas according to claim 1, characterized in that: The flow rate of the tail gas after catalytic treatment in step S3 is 800-850m 3 / h.

7. The absorption treatment system for phosgene-containing tail gas according to claim 5, characterized in that: In step A1, the mass ratio of polyetherimide, polyethylene glycol, dimethyl sulfoxide and azobisisobutyronitrile is (1-2): (2-4): 8: (0.01-0.03).

8. The absorption treatment system for phosgene-containing tail gas according to claim 5, characterized in that: In step A2, the mass ratio of the copolymer substrate, 4-aminobenzoic acid, N,N-dimethylformamide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide is (1-1.5):(2.2-2.8):10:(0.05-0.08):(0.02-0.06).