Process for absorbing and treating a light tail gas containing ethyl chloroformate

Abstract

The present application relates to tail gas treatment technical field, especially to a kind of ethyl chloroformate production containing light tail gas absorption treatment process, comprising the following steps: S1, pretreatment: collecting each workshop tail gas is filtered into bag filter, and pretreatment tail gas is obtained;S2, falling film absorption treatment: pretreatment tail gas temperature is reduced to ≤40 ℃, then it is imported into falling film absorption tower, and packing layer is equipped with the light gas absorbent with concentration of 20-30%, and falling film absorption tail gas is obtained;S3, three-stage destruction tower treatment: falling film absorption tail gas is imported into three-stage destruction tower in series, and by-product salt solution and destruction tail gas are obtained, and the salt generated is collected to storage tank, and destruction tail gas is discharged after detection reaches standard.The light gas absorbent prepared by the present application shows higher light gas and ethyl chloroformate decomposition efficiency in the absorption treatment of ethyl chloroformate production containing light tail gas.

Description

Technical Field

[0001] This invention relates to the field of exhaust gas treatment technology, and in particular to a process for absorbing and treating light-emitting exhaust gas from the production of ethyl chloroformate. Background Technology

[0002] In industrial production, ethyl chloroformate is mainly produced through the esterification reaction of ethanol and phosgene. The treatment of phosgene-containing waste gas generated during this process is a crucial step in ensuring production safety and environmental protection. Due to the extremely high toxicity of phosgene, all phosgene-containing waste gas, regardless of its origin—whether from the phosgene synthesis workshop, esterification workshop, safety pressure relief systems (such as pressure relief valves and rupture membranes), or safety suction systems—must undergo rigorous treatment before being safely released into the atmosphere through high-altitude discharge stacks. The tail gas from ethyl chloroformate production not only contains highly toxic phosgene but may also contain carbon monoxide, chlorine, methanol, liquid ammonia, ammonia water, methyl chloroformate, o-phenylenediamine, calcium cyanamide, liquid alkali, oxygen, nitrogen, hydrogen chloride, hydrochloric acid, carbon dioxide, and hydrogen sulfide, among other components. Phosgene itself has extremely low melting and boiling points, high-density vapor, and exhibits strong corrosiveness upon contact with water. Combined with its non-flammability and high chemical reactivity, its treatment process is exceptionally complex and requires extreme caution.

[0003] In current practice, SN7501 catalysts are commonly used to remove phosgene from ethyl chloroformate tail gas. However, SN7501 catalysts can produce high concentrations of hydrochloric acid during hydrolysis, causing corrosion to equipment and increasing maintenance costs. Secondly, the catalytic efficiency of SN7501 catalysts is significantly affected by operating conditions, such as temperature, pressure, and tail gas composition. Furthermore, SN7501 catalysts have specific requirements regarding the impurity content in the tail gas. Excessive impurities in the tail gas may affect the catalyst's activity and lifespan, leading to catalyst poisoning and impacting tail gas treatment efficiency. Summary of the Invention

[0004] To address the problems mentioned in the background section, this invention provides a process for absorbing and treating the tail gas from the production of ethyl chloroformate.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A process for absorbing and treating the tail gas from the production of ethyl chloroformate includes the following steps:

[0007] S1. Pretreatment: Collect the exhaust gas from each workshop and pass it into a bag filter for filtration to remove dust and particulate matter from the exhaust gas. Use a tubular cooler with circulating water as the cooling medium to obtain pretreated exhaust gas.

[0008] S2. Falling film absorption treatment: After the temperature of the pretreated tail gas is reduced to ≤40℃, it is introduced into the falling film absorption tower with a diameter of DN1200mm and a height of 20m. The packing layer is filled with phosgene absorber with a concentration of 20-30% to obtain the tail gas after falling film absorption.

[0009] S3. Three-stage destruction tower treatment: The tail gas after falling film absorption is passed into a three-stage series destruction tower to completely destroy the trace amounts of phosgene and hydrogen chloride remaining in the tail gas, and obtain the by-product salt solution and the destroyed tail gas. The generated salt is collected in a storage tank, and the destroyed tail gas is discharged after testing and meeting the standards.

[0010] Furthermore, in step S2, the falling film absorption tower is equipped with three layers of packing material, each layer being 2-3m high, with a total packing material height of 6-9m.

[0011] Furthermore, the phosgene absorber in step S2 is prepared by the following steps:

[0012] Sodium p-styrene sulfonate was added to water, along with 2-mercaptoethylamine and ethylene glycol. The mixture was ultrasonically treated in an ice-water bath for 10-20 minutes to obtain a monomer solution. A 20-50% polyethyleneimine aqueous solution was prepared using water. Under anaerobic conditions, the monomer solution was added dropwise to the polyethyleneimine aqueous solution at a rate of 10-15 drops per minute. A constant temperature water bath was turned on to control the reaction temperature. Potassium persulfate and sodium dodecyl sulfate were added, and the mixture was stirred. After the reaction was completed, the heating source was turned off, and ethanolamine was added to the reaction system to neutralize the remaining initiator and terminate the reaction. The reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. Dialysis was performed using water as the dialysis solution for 24-48 hours. The solution was then concentrated using a rotary evaporator at a concentration temperature ≤40℃ to obtain the phosgene absorber.

[0013] Furthermore, in step S3, the temperature inside the destruction tower is 200-250℃, the pressure is a slight negative pressure of 0.1-0.5MPa, and the tower is filled with a 30-40% sodium hydroxide solution.

[0014] Furthermore, the mass ratio of sodium styrene sulfonate, water, 2-mercaptoethylamine and ethylene glycol is (4-5)::100:(10-15):(6-7).

[0015] Furthermore, the mass ratio of the polyethyleneimine aqueous solution, the monomer solution, potassium persulfate, and sodium dodecyl sulfate is 10:(5-6):(0.08-0.3):(0.01-0.02).

[0016] Furthermore, the temperature of the constant temperature water bath is 70-80℃, the stirring speed is 200-300rpm, and the reaction time is 6-8h.

[0017] The beneficial effects of this invention are:

[0018] 1. In the technical solution of this invention, the main chain of the phosgene absorber is composed of polyethyleneimine. Through graft polymerization of 2-mercaptoethylamine and sodium p-styrenesulfonate monomer, a bifunctional side chain containing sulfonic acid groups (-SO3H) and mercapto groups is formed. The presence of sulfonic acid groups not only increases the water solubility of the polymer but also enhances the polymer's adsorption capacity for phosgene through electrostatic interactions or hydrogen bonding. Mercapto groups have a strong affinity for phosgene. During the polymerization reaction, due to the gradual grafting and polymerization of monomers, the polymer has a network structure or microporous structure, providing more adsorption sites and diffusion channels for phosgene molecules. Phosgene molecules can rapidly diffuse into the interior of the polymer through the pores and be fixed, further increasing the polymer's adsorption capacity and adsorption rate for phosgene.

[0019] 2. In the technical solution of this invention, the amino and sulfonic acid groups in the phosgene absorber can chemically react with phosgene (COCl2). In particular, the lone pair electrons on the nitrogen atom of the amino group can form covalent bonds with the carbon atoms in phosgene, thereby undergoing a substitution reaction to generate amide bonds or chlorinated hydrocarbons. The network structure of the polymer chain and the polar groups on its surface (such as sulfonic acid groups) capture phosgene molecules through physical forces such as van der Waals forces and hydrogen bonds. With a large number of adsorption sites, a significant adsorption effect on phosgene molecules can be achieved.

[0020] 3. In the technical solution of the present invention, the phosgene absorber also has stability and recyclability. After absorbing phosgene, the phosgene absorber can maintain a stable form and performance, which is convenient for subsequent recycling and treatment. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0023] Preparation Example 1

[0024] Phosgene absorbers are prepared by the following steps:

[0025] 4 kg of sodium p-styrene sulfonate was added to 100 kg of water, along with 10 kg of 2-mercaptoethylamine and 6 kg of ethylene glycol. The mixture was sonicated in an ice-water bath for 10 min to obtain a monomer solution. A 20% polyethyleneimine aqueous solution was prepared using water. Under anaerobic conditions, 5 kg of the monomer solution was added dropwise to 10 kg of the polyethyleneimine aqueous solution at a rate of 10 drops per minute. A constant temperature water bath was turned on, and the reaction temperature was controlled at 70 °C. 0.08 kg of potassium persulfate and 0.01 kg of sodium dodecyl sulfate were added, and the mixture was stirred at 200 rpm for 6 h. After the reaction was completed, the heating source was turned off, and ethanolamine was added to the reaction system. The reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. Water was used as the dialysis solution for dialysis for 24 h. The solution was then concentrated using a rotary evaporator at a concentration temperature of 40 °C to obtain the phosgene absorber.

[0026] Preparation Example 2

[0027] Phosgene absorbers are prepared by the following steps:

[0028] 4.5 kg of sodium p-styrene sulfonate was added to 100 kg of water, along with 12.5 kg of 2-mercaptoethylamine and 6.5 kg of ethylene glycol. The mixture was sonicated in an ice-water bath for 15 min to obtain a monomer solution. A 35% polyethyleneimine aqueous solution was prepared using water. Under anaerobic conditions, 5.5 kg of the monomer solution was added dropwise to 10 kg of polyethyleneimine aqueous solution at a rate of 10 drops per minute. A constant temperature water bath was turned on, and the reaction temperature was controlled at 75 °C. 0.12 kg of potassium persulfate and 0.015 kg of sodium dodecyl sulfate were added, and the mixture was stirred at 250 rpm for 7 h. After the reaction was completed, the heating source was turned off, and ethanolamine was added to the reaction system. The reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. The solution was dialyzed for 36 h using water as the dialysate. The solution was then concentrated using a rotary evaporator at a concentration temperature of 35 °C to obtain a phosgene absorber.

[0029] Preparation Example 3

[0030] Phosgene absorbers are prepared by the following steps:

[0031] 5 kg of sodium p-styrene sulfonate was added to 100 kg of water, along with 15 kg of 2-mercaptoethylamine and 7 kg of ethylene glycol. The mixture was sonicated in an ice-water bath for 20 min to obtain a monomer solution. A 50% polyethyleneimine aqueous solution was prepared using water. Under anaerobic conditions, 6 kg of the monomer solution was added dropwise to 10 kg of the polyethyleneimine aqueous solution at a rate of 15 drops per minute. A constant temperature water bath was turned on, and the reaction temperature was controlled at 80 °C. 0.3 kg of potassium persulfate and 0.02 kg of sodium dodecyl sulfate were added, and the mixture was stirred at 300 rpm for 8 h. After the reaction was completed, the heating source was turned off, and ethanolamine was added to the reaction system. The reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. The solution was dialyzed with water as the dialysate for 48 h and then concentrated using a rotary evaporator at 30 °C to obtain a phosgene absorber.

[0032] Example 1

[0033] A process for absorbing and treating the tail gas from the production of ethyl chloroformate includes the following steps:

[0034] S1. Pretreatment: Collect the exhaust gas from each workshop and pass it into a bag filter for filtration to obtain pretreated exhaust gas;

[0035] S2. Falling film absorption treatment: After the temperature of the pretreated tail gas is reduced to 40°C, it is introduced into the falling film absorption tower. The tower is equipped with three layers of packing, each layer is 2m high, and the total packing height is 6m. The packing layer is filled with 1kg of phosgene absorber prepared in Preparation Example 1 with a concentration of 20%, and the tail gas after falling film absorption is obtained.

[0036] S3. Three-stage crushing tower treatment: The tail gas after falling film absorption is passed into a three-stage crushing tower connected in series. The temperature inside the tower is 200℃ and the pressure is a slight negative pressure of 0.1MPa. The tower is filled with 30% sodium hydroxide solution to obtain by-product salt solution and crushed tail gas. The generated salt is collected in a storage tank. The crushed tail gas is discharged after testing and meeting the standards.

[0037] Example 2

[0038] A process for absorbing and treating the tail gas from the production of ethyl chloroformate includes the following steps:

[0039] S1. Pretreatment: Collect the exhaust gas from each workshop and pass it into a bag filter for filtration to obtain pretreated exhaust gas;

[0040] S2. Falling film absorption treatment: After the temperature of the pretreated tail gas is reduced to 30°C, it is introduced into the falling film absorption tower. The tower is equipped with three layers of packing, each layer is 2.5m high, and the total packing height is 7.5m. The packing layer is filled with 1kg of phosgene absorber prepared in Preparation Example 2 with a concentration of 25%, and the tail gas after falling film absorption is obtained.

[0041] S3. Three-stage crushing tower treatment: The tail gas after falling film absorption is passed into a three-stage crushing tower connected in series. The temperature inside the tower is 220℃ and the pressure is a slight negative pressure of 0.3MPa. The tower is filled with 35% sodium hydroxide solution to obtain by-product salt solution and crushed tail gas. The generated salt is collected in a storage tank. The crushed tail gas is discharged after testing and meeting the standards.

[0042] Example 3

[0043] A process for absorbing and treating the tail gas from the production of ethyl chloroformate includes the following steps:

[0044] S1. Pretreatment: Collect the exhaust gas from each workshop and pass it into a bag filter for filtration to obtain pretreated exhaust gas;

[0045] S2. Falling film absorption treatment: After the temperature of the pretreated tail gas is reduced to 40°C, it is introduced into the falling film absorption tower. The tower is equipped with three layers of packing, each layer is 3m high, and the total packing height is 9m. The packing layer is filled with 1kg of phosgene absorber prepared in Preparation Example 3 with a concentration of 30%, and the tail gas after falling film absorption is obtained.

[0046] S3. Three-stage crushing tower treatment: The tail gas after falling film absorption is passed into a three-stage crushing tower connected in series. The temperature inside the tower is 250℃ and the pressure is a slight negative pressure of 0.5MPa. The tower is filled with 40% sodium hydroxide solution to obtain by-product salt solution and crushed tail gas. The generated salt is collected in a storage tank. The crushed tail gas is discharged after testing and meeting the standards.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that polyethyleneimine is used instead of the phosgene absorber prepared in the preparation example; the remaining steps are the same as in Example 1.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 2 is that sodium p-styrene sulfonate is used instead of the phosgene absorber prepared in the preparation example; the remaining steps are the same as in Example 2.

[0051] Comparative Example 3

[0052] The difference between this comparative example and Example 3 is that 2-mercaptoethylamine is used instead of the phosgene absorber prepared in the preparation example; the remaining steps are the same as in Example 3.

[0053] Comparative Example 4

[0054] The difference between this comparative example and Example 1 is that the SN7501 catalyst is used instead of the phosgene absorber prepared in the preparation example, while the remaining steps are the same as in Example 1.

[0055] Referring to GB 19041-2024 "Safety Specifications for the Production of Phosgene and Phosgene Products", the phosgene concentration in the final exhaust gas of Examples 1-3 and Comparative Examples 1-4 was tested. The phosgene concentration before and after exhaust gas treatment in each example and comparative example was recorded, and the phosgene decomposition efficiency was calculated as follows: Decomposition efficiency = (phosgene concentration before treatment - phosgene concentration after treatment) / phosgene concentration before treatment. The results are shown in Table 1.

[0056] Table 1. Phosgene treatment results of Examples 1-3 and Comparative Examples 1-4

[0057]

[0058]

[0059] Simultaneously, the concentration of ethyl chloroformate in the final exhaust gas of Examples 1-3 and Comparative Examples 1-4 was detected, and the concentration of ethyl chloroformate before and after exhaust gas treatment in each example and comparative example was recorded. The decomposition efficiency of ethyl chloroformate was calculated as follows: Decomposition efficiency = (Ethyl chloroformate concentration before treatment - Ethyl chloroformate concentration after treatment) / Ethyl chloroformate concentration before treatment. The results are shown in Table 2.

[0060] Table 2. Results of ethyl chloroformate treatment in Examples 1-3 and Comparative Examples 1-4

[0061]

[0062] Table 1 shows that the phosgene decomposition efficiency of Examples 1-3 was 99.98%, indicating that the self-made phosgene absorbent could effectively capture and decompose phosgene in the falling film absorber. The phosgene decomposition efficiency of Comparative Examples 1-4 was significantly lower than that of the Examples, especially Comparative Examples 1-3, whose decomposition efficiencies ranged from 76.03% to 85.24%. Comparative Example 1 used polyethyleneimine instead of the absorbent, possibly because polyethyleneimine itself does not have the ability to react efficiently with phosgene, or the reaction conditions were not compatible. Comparative Examples 2 and 3 used sodium p-styrene sulfonate and 2-mercaptoethylamine instead of the absorbent, respectively. These two substances, when used alone, may not form an effective phosgene decomposition mechanism. Comparative Example 4 used SN7501 catalyst, which, although having some catalytic effect, had a lower catalytic efficiency than the self-made absorbent.

[0063] As shown in Table 2, the decomposition efficiency of ethyl chloroformate in Examples 1-3 was also as high as 99.92% to 99.93%, indicating that the self-made phosgene absorber also has a certain degradation ability for ethyl chloroformate. The decomposition efficiency of ethyl chloroformate in Comparative Examples 1-4 was significantly lower than that in the Examples. Similar to the results of phosgene treatment, the substitute substances also showed obvious limitations in the decomposition of ethyl chloroformate.

[0064] In summary, the phosgene absorbers prepared in Examples 1-3 exhibited high phosgene and ethyl chloroformate decomposition efficiency in the absorption and treatment of phosgene-containing tail gas from ethyl chloroformate production.

[0065] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0066] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for absorbing and treating the tail gas containing light during the production of ethyl chloroformate, characterized in that, Includes the following steps: S1. Pretreatment: Collect the exhaust gas from each workshop and pass it into a bag filter for filtration to obtain pretreated exhaust gas; S2. Falling film absorption treatment: After the temperature of the pretreated tail gas is reduced to ≤40℃, it is introduced into the falling film absorption tower. The packing layer is filled with phosgene absorber with a concentration of 20-30% to obtain the tail gas after falling film absorption. S3. Three-stage crushing tower treatment: The tail gas after falling film absorption is passed into a three-stage crushing tower connected in series to obtain the by-product salt solution and the crushed tail gas. The generated salt is collected in a storage tank, and the crushed tail gas is discharged after testing and meeting the standards. The phosgene absorber in step S2 is prepared by the following steps: Sodium p-styrene sulfonate was added to water, along with 2-mercaptoethylamine and ethylene glycol. The mixture was ultrasonically treated in an ice-water bath for 10-20 minutes to obtain a monomer solution. A 20-50% polyethyleneimine aqueous solution was prepared using water. Under anaerobic conditions, the monomer solution was added dropwise to the polyethyleneimine aqueous solution at a rate of 10-15 drops per minute. A constant temperature water bath was turned on to control the reaction temperature. Potassium persulfate and sodium dodecyl sulfate were added, and the mixture was stirred. After the reaction was completed, the heating source was turned off, and ethanolamine was added to the reaction system. The reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. Water was used as the dialysis solution for dialysis treatment for 24-48 hours. The solution was then concentrated using a rotary evaporator at a concentration temperature ≤40℃ to obtain the phosgene absorber.

2. The process for absorbing and treating the tail gas from the production of ethyl chloroformate according to claim 1, characterized in that, In step S2, the falling film absorption tower is equipped with three layers of packing material, each layer being 2-3m high, with a total packing height of 6-9m.

3. The process for absorbing and treating the tail gas from the production of ethyl chloroformate according to claim 1, characterized in that, In step S3, the temperature inside the destruction tower is 200-250℃, the pressure is a slight negative pressure of 0.1-0.5MPa, and the tower is filled with a 30-40% sodium hydroxide solution.

4. The process for absorbing and treating the tail gas from the production of ethyl chloroformate according to claim 1, characterized in that, The mass ratio of sodium styrene sulfonate, water, 2-mercaptoethylamine and ethylene glycol is (4-5):100:(10-15):(6-7).

5. The process for absorbing and treating the tail gas from the production of ethyl chloroformate according to claim 1, characterized in that, The mass ratio of polyethyleneimine aqueous solution, monomer solution, potassium persulfate and sodium dodecyl sulfate is 10:(5-6):(0.08-0.3):(0.01-0.02).

6. The process for absorbing and treating the tail gas from the production of ethyl chloroformate according to claim 1, characterized in that, The temperature of the constant temperature water bath is 70-80℃, the stirring speed is 200-300rpm, and the reaction time is 6-8h.

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