Absorption treatment process for light-containing tail gas in ethyl chloroformate production

Abstract

The invention relates to the technical field of tail gas treatment, in particular to an ethyl chloroformate production light-containing tail gas absorption treatment process which comprises the following steps: S1, pretreatment: collecting tail gas of each workshop, and introducing the tail gas into a bag-type dust collector for filtering to obtain pretreated tail gas; s2, falling film absorption treatment: reducing the temperature of the pretreated tail gas to be less than or equal to 40 DEG C, introducing the pretreated tail gas into a falling film absorption tower, and filling a filler layer with a phosgene absorbent with the concentration of 20-30% to obtain tail gas after falling film absorption; and S3, third-stage destroying tower treatment: introducing the tail gas subjected to falling film absorption into a third-stage series-connection destroying tower to obtain a byproduct salt solution and destroyed tail gas, collecting generated salt into a storage tank, and discharging the destroyed tail gas after the tail gas is detected to reach the standard. The phosgene absorbent prepared by the preparation method disclosed by the invention shows relatively high phosgene and ethyl chloroformate decomposition efficiency in absorption treatment of light-containing tail gas produced by ethyl chloroformate.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas treatment, in particular to an absorption treatment process for light-containing tail gas from ethyl chloroformate production. Background Art

[0002] In industrial production, ethyl chloroformate is mainly prepared by the esterification reaction of ethanol and phosgene, and the treatment of phosgene-containing waste gas generated in the process is a key step to ensure production safety and environmental protection. Due to the extremely high toxicity of phosgene, all waste gases containing phosgene, whether from the exhaust of the phosgene synthesis workshop, esterification workshop, the safety pressure relief system of the device (such as pressure relief valve, bursting membrane, etc.), or the suction gas of the safety suction system of the device, must undergo strict destruction treatment before they can be safely discharged into the atmosphere through the high-altitude discharge cylinder. The tail gas of ethyl chloroformate production contains not only highly toxic phosgene, but also carbon monoxide, chlorine, methanol, liquid ammonia, ammonia water, methyl chloroformate, o-phenylenediamine, lime nitrogen, liquid alkali, oxygen, nitrogen, hydrogen chloride, hydrochloric acid, carbon dioxide and hydrogen sulfide. Phosgene itself has extremely low melting and boiling points, high-density vapor, and strong corrosiveness when it comes into contact with water. In addition, its non-flammability and high chemical reactivity make its treatment process particularly complicated and require high caution.

[0003] In current practice, SN7501 catalyst is often used to remove phosgene from ethyl chloroformate tail gas, but SN7501 catalyst can produce high concentration of hydrochloric acid during the hydrolysis process, which causes corrosion to the equipment and increases the equipment maintenance cost. Secondly, the catalytic effect of SN7501 catalyst is greatly affected by operating conditions, such as temperature, pressure, tail gas composition, etc. In addition, SN7501 catalyst has certain requirements for the impurity content in the tail gas. If the tail gas contains too many impurities, it may affect the activity and service life of the catalyst, cause catalyst poisoning, and affect the efficiency of tail gas treatment. Summary of the invention

[0004] In order to solve the problems mentioned in the above background technology, the present invention provides a light-containing tail gas absorption treatment process for the production of ethyl chloroformate.

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

[0006] A light-containing tail gas absorption treatment process for ethyl chloroformate production comprises the following steps:

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

[0008] S2, falling film absorption treatment: after the temperature of the pre-treated tail gas is reduced to ≤40°C, it is passed into a falling film absorption tower with a tower diameter of DN1200mm and a tower height of 20m. The packing layer is filled with a phosgene absorbent with a concentration of 20-30%, and the tail gas after falling film absorption is obtained;

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

[0010] Furthermore, in step S2, three packing layers are arranged in the falling film absorption tower, each layer is 2-3m high, and the total packing height is 6-9m.

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

[0012] Sodium p-styrene sulfonate is added to water, 2-mercaptoethylamine and ethylene glycol are added, and ultrasonic treatment is performed in an ice water bath for 10-20 minutes to obtain a monomer solution, and a polyethyleneimine aqueous solution with a concentration of 20-50% is prepared with water. In an oxygen-free environment, the monomer solution is added dropwise to the polyethyleneimine aqueous solution at a dropping speed of 10-15 drops per minute, a constant temperature water bath is turned on, the reaction temperature is controlled, potassium persulfate and sodium dodecyl sulfate are added, and the reaction is stirred. After the reaction is completed, the heating source is turned off, ethanolamine is added to the reaction system to neutralize the remaining initiator and terminate the reaction, and the reaction solution is transferred to a dialysis bag with a molecular weight cutoff of 5000Da, and dialyzed for 24-48 hours using water as a dialysis fluid, and concentrated by a rotary evaporator at a concentration temperature of ≤40°C to obtain a phosgene absorbent.

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

[0014] Furthermore, the mass ratio of sodium p-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° C., the stirring speed is 200-300 rpm, and the reaction time is 6-8 h.

[0017] Beneficial effects of the present invention:

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

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

[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 shape and performance, which is convenient for subsequent recovery and treatment. DETAILED DESCRIPTION

[0021] 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.

[0022] Unless otherwise specified, the raw materials used in the present invention are all conventional products purchased from the market.

[0023] Preparation Example 1

[0024] The phosgene absorbent comprises the following steps to prepare:

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

[0026] Preparation Example 2

[0027] The phosgene absorbent comprises the following steps to prepare:

[0028] 4.5 kg of sodium p-styrene sulfonate was added to 100 kg of water, 12.5 kg of 2-mercaptoethylamine and 6.5 kg of ethylene glycol were added, and the mixture was ultrasonically treated for 15 min in an ice-water bath to obtain a monomer solution. A 35% polyethyleneimine aqueous solution was prepared with water. In an anaerobic environment, 5.5 kg of the monomer solution was added dropwise to 10 kg of polyethyleneimine aqueous solution at a dropping speed of 10 drops per minute. A constant temperature water bath was turned on to control the reaction temperature to 75°C. 0.12 kg of potassium persulfate and 0.015 kg of sodium dodecyl sulfate were added, and the reaction was stirred at 250 rpm for 7 hours. After the reaction was completed, the heating source was turned off, ethanolamine was added to the reaction system, and the reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. Water was used as a dialysate for 36 hours of dialysis treatment, and the solution was concentrated by a rotary evaporator at a concentration temperature of 35°C to obtain a phosgene absorbent.

[0029] Preparation Example 3

[0030] The phosgene absorbent comprises the following steps to prepare:

[0031] 5 kg of sodium p-styrene sulfonate was added to 100 kg of water, 15 kg of 2-mercaptoethylamine and 7 kg of ethylene glycol were added, and the mixture was ultrasonically treated for 20 min in an ice-water bath to obtain a monomer solution. A 50% polyethyleneimine aqueous solution was prepared with water. In an anaerobic environment, 6 kg of the monomer solution was added dropwise to 10 kg of polyethyleneimine aqueous solution at a dropping speed of 15 drops per minute. A constant temperature water bath was turned on to control the reaction temperature to 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, ethanolamine was added to the reaction system, and the reaction solution was transferred to a dialysis bag with a molecular weight cutoff of 5000 Da. The reaction solution was dialyzed for 48 h using water as a dialysis fluid, and concentrated by a rotary evaporator at a concentration temperature of 30° C. to obtain a phosgene absorbent.

[0032] Example 1

[0033] A light-containing tail gas absorption treatment process for ethyl chloroformate production comprises the following steps:

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

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

[0036] S3. Three-stage destruction tower treatment: The tail gas after falling film absorption is passed into a three-stage destruction tower in series. The temperature in the tower is 200°C 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 tail gas after destruction. The generated salt is collected in a storage tank, and the tail gas after destruction is discharged after being tested and meeting the standards.

[0037] Example 2

[0038] A light-containing tail gas absorption treatment process for ethyl chloroformate production comprises the following steps:

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

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

[0041] S3. Three-stage destruction tower treatment: The tail gas after falling film absorption is passed into a three-stage destruction tower in series. The temperature in the tower is 220°C and the pressure is a slightly negative pressure of 0.3MPa. The tower is filled with 35% sodium hydroxide solution to obtain by-product salt solution and tail gas after destruction. The generated salt is collected in a storage tank, and the tail gas after destruction is discharged after being tested and meeting the standards.

[0042] Example 3

[0043] A light-containing tail gas absorption treatment process for ethyl chloroformate production comprises the following steps:

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

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

[0046] S3. Three-stage destruction tower treatment: The tail gas after falling film absorption is passed into a three-stage destruction tower in series. The temperature in the tower is 250°C and the pressure is a slight negative pressure of 0.5 MPa. The tower is filled with 40% sodium hydroxide solution to obtain by-product salt solution and tail gas after destruction. The generated salt is collected in a storage tank, and the tail gas after destruction is discharged after being tested 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, and the remaining steps are the same as those 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, and the remaining steps are the same as those 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, and the remaining steps are the same as those in Example 3.

[0053] Comparative Example 4

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

[0055] With reference to GB 19041-2024 "Safety Specification for the Production of Phosgene and Phosgenation Products", the phosgene concentration in the final tail gas of Examples 1-3 and Comparative Examples 1-4 was detected, the phosgene concentration before and after the tail gas treatment in each example and comparative example was recorded, and the decomposition efficiency of phosgene was calculated, 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] The concentration of ethyl chloroformate in the final tail gas of Examples 1-3 and Comparative Examples 1-4 was detected at the same time, and the concentration of ethyl chloroformate before and after the tail gas treatment in each Example and Comparative Example was recorded, and the decomposition efficiency of ethyl chloroformate was calculated, 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. Ethyl chloroformate treatment results of Examples 1-3 and Comparative Examples 1-4

[0061]

[0062] As can be seen from Table 1, the phosgene decomposition efficiency of Examples 1-3 is 99.98%, indicating that the homemade phosgene absorbent can capture and decompose phosgene very effectively in the falling film absorption tower. The phosgene decomposition efficiency of Comparative Examples 1-4 is significantly lower than that of the embodiments, especially Comparative Examples 1-3, whose decomposition efficiency is between 76.03% and 85.24%. Comparative Example 1 uses polyethyleneimine instead of the absorbent, which may be because polyethyleneimine itself does not have the ability to react efficiently with phosgene, or the reaction conditions do not match. Comparative Examples 2 and 3 use sodium p-styrene sulfonate and 2-mercaptoethylamine instead of the absorbent, respectively. These two substances may not form an effective phosgene decomposition mechanism when used alone. Comparative Example 4 uses SN7501 catalyst. Although it has a certain catalytic effect, its catalytic efficiency is lower than that of the homemade absorbent.

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

[0064] In summary, the phosgene absorbents of Preparation Examples 1-3 showed high phosgene and ethyl chloroformate decomposition efficiency in the absorption treatment of phosgene-containing tail gas in the production of ethyl chloroformate.

[0065] In the description of the specification, the description with reference to the terms "preparation example", "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.

[0066] 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 light-containing tail gas absorption treatment process for the production of ethyl chloroformate, characterized in that: The following steps are involved: S1. Pretreatment: Collect tail gas from each workshop and pass it into a bag filter for filtration to obtain pretreated tail gas; S2, falling film absorption treatment: after the temperature of the pre-treated tail gas is reduced to ≤40°C, it is passed into a falling film absorption tower, in which a phosgene absorbent with a concentration of 20-30% is contained in the packing layer, and tail gas after falling film absorption is obtained; S3, three-stage destruction tower treatment: the tail gas after falling film absorption is passed into three-stage destruction towers in series to obtain by-product salt solution and tail gas after destruction. The generated salt is collected in a storage tank, and the tail gas after destruction is discharged after being tested and meeting the standards.

2. A light-containing tail gas absorption treatment process for ethyl chloroformate production according to claim 1, characterized in that: In step S2, three packing layers are arranged in the falling film absorption tower, each layer is 2-3m high, and the total packing height is 6-9m.

3. A light-containing tail gas absorption treatment process for ethyl chloroformate production according to claim 1, characterized in that: The phosgene absorber in step S2 is prepared by the following steps: Sodium p-styrene sulfonate is added into water, 2-mercaptoethylamine and ethylene glycol are added, and the mixture is ultrasonically treated for 10-20 minutes in an ice water bath to obtain a monomer solution, a polyethyleneimine aqueous solution with a concentration of 20-50% is prepared with water, and the monomer solution is added dropwise into the polyethyleneimine aqueous solution in an oxygen-free environment at a dropping speed of 10-15 drops per minute, a constant temperature water bath is turned on, the reaction temperature is controlled, potassium persulfate and sodium dodecyl sulfate are added, and the reaction is stirred. After the reaction is completed, the heating source is turned off, ethanolamine is added into the reaction system, and the reaction solution is transferred into a dialysis bag with a molecular weight cutoff of 5000Da, and the dialysis treatment is performed for 24-48 hours using water as a dialysis fluid, and the phosgene absorbent is obtained by concentrating the mixture through a rotary evaporator at a concentration temperature of ≤40°C.

4. A light-containing tail gas absorption treatment process for ethyl chloroformate production according to claim 1, characterized in that: In step S3, the temperature in the destruction tower is 200-250° C., the pressure is a slight negative pressure of 0.1-0.5 MPa, and 30-40% sodium hydroxide solution is contained in the tower.

5. A light-containing tail gas absorption treatment process for ethyl chloroformate production according to claim 3, characterized in that: The mass ratio of sodium p-styrene sulfonate, water, 2-mercaptoethylamine and ethylene glycol is (4-5)::100:(10-15):(6-7).

6. A light-containing tail gas absorption treatment process for ethyl chloroformate production according to claim 3, characterized in that: 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).

7. A light-containing tail gas absorption treatment process for ethyl chloroformate production according to claim 3, characterized in that: The temperature of the constant temperature water bath is 70-80°C, the stirring speed is 200-300rpm, and the reaction time is 6-8h.

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