An exhaust gas capture treatment system applied to ethyl chloroformate synthesis

Abstract

The application relates to the technical field of tail gas treatment, in particular to a tail gas capturing and treating system applied to ethyl chloroformate synthesis, which comprises the following steps: S1, condenser pretreatment of tail gas; S2, falling film absorption, to obtain concentrated hydrochloric acid and tail gas after falling film absorption; S3, catalytic decomposition of phosgene, to obtain dilute hydrochloric acid and tail gas after catalytic decomposition; and S4, secondary series alkaline washing is carried out, and the dilute lye is used for circular spraying and is discharged through an induced draft fan. In the application, ethanol, ethyl chloroformate and other low-boiling-point substances in the tail gas are recovered through condenser pretreatment, the condensate is returned to a production system for recycling, raw material waste is reduced, and production cost is lowered. Hydrogen chloride is efficiently absorbed and converted into concentrated hydrochloric acid and dilute hydrochloric acid, which are used in the next section for recycling or external sale, resource reuse is realized, and harmful gas emission is reduced.

Description

Technical Field

[0001] This invention relates to the field of exhaust gas treatment technology, and in particular to an exhaust gas capture and treatment system applied to the synthesis of ethyl chloroformate. Background Technology

[0002] Ethyl chloroformate, with the chemical formula C3H5ClO2, is an important organic synthesis intermediate and solvent, widely used in pharmaceuticals, pesticides, herbicides, flotation agents, and chemical synthesis. Ethyl chloroformate is a colorless to pale yellow transparent liquid with a pungent odor. Its boiling point is approximately 94℃, and its specific gravity (D420) is 1.1403. It is insoluble in water but soluble in organic solvents such as ethanol, ether, benzene, and chloroform. In actual production, ethyl chloroformate is mainly prepared through the esterification reaction of ethanol with phosgene (COCl2). The reaction equation is as follows:

[0003]

[0004] In addition, ethanol can react with the generated ethyl chloroformate under certain conditions, and the equation for the side reaction is as follows:

[0005]

[0006] Phosgene is a highly reactive acylation reagent. It reacts with ethanol under mild conditions, and ethanol can further react with ethyl chloroformate to produce diethyl carbonate as a byproduct. The reaction conditions are milder than those for ethane chloroform. During the production process, the diethyl carbonate content is controlled to be below 0.5%. Therefore, in the existing synthesis system, ethanol preferentially reacts with phosgene, and a trace amount of ethanol reacts with ethyl chloroformate. The synthesis system will not produce ethane chloroform.

[0007] The exhaust gases produced by this reaction mainly include phosgene, hydrogen chloride, ethanol, and ethyl chloroformate. In existing technologies, adsorption processes using activated carbon or acid / alkali solutions are typically employed to remove pollutants from the exhaust gases. For example, patent publication number CN109663477A discloses a method for treating waste materials from the preparation of ethyl chloroformate. However, this method suffers from incomplete exhaust gas treatment, requiring multiple cycles, resulting in high energy consumption and increased exhaust gas treatment costs. Summary of the Invention

[0008] To address the problems mentioned in the background section, this invention provides a tail gas capture and treatment system for the synthesis of ethyl chloroformate.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A tail gas capture and treatment system for the synthesis of ethyl chloroformate includes:

[0011] S1. Collect the tail gas generated in each step of the ethyl chloroformate synthesis process (esterification tower, gas removal kettle, light gas removal tower), and pass it into a condenser for pretreatment to obtain recovered low-boiling-point substances and pretreated tail gas. Among them, low-boiling-point substances such as ethanol and ethyl chloroformate in the tail gas are condensed and recovered, and the condensate is returned to the production system for recycling.

[0012] S2. The pretreated tail gas enters the falling film absorption tower, where the absorbent is circulated and sprayed to absorb hydrogen chloride in the tail gas with high efficiency of ≥95%, ensuring that the concentration of hydrogen chloride in the tail gas is reduced to a safe range, and obtaining concentrated hydrochloric acid with a concentration of 30-40% and tail gas after falling film absorption. The concentrated hydrochloric acid is collected in the concentrated hydrochloric acid storage tank for recycling in the next process or for external sale.

[0013] S3. The tail gas after falling film absorption enters the hydrolysis tower, which is equipped with T38202, T38203 and T38204. Phosgene is added and catalysts are used to carry out three-stage series catalytic decomposition of phosgene to obtain dilute hydrochloric acid with a concentration of 10-15% and the tail gas after catalytic decomposition. The catalytic decomposition efficiency is ≥98%, ensuring that the concentration of phosgene in the tail gas is reduced to a safe range. The dilute hydrochloric acid is used for recycling or sold externally.

[0014] S4. The tail gas after catalytic decomposition enters the alkali destruction tower, which is equipped with T38205 and T38206 for two-stage series alkali washing to neutralize residual phosgene, hydrogen chloride and other gases in the tail gas. The alkali washing tower is equipped with corrosion-resistant packing and is sprayed with dilute alkali solution with a concentration of <10%. After the tail gas is tested and found to meet the standards, it is sent to the original high-pressure exhaust tower for high-pressure exhaust to the atmosphere by an induced draft fan.

[0015] Furthermore, the operating temperature of the condenser in S1 is (-10)-5℃, the pressure is 0.1-0.5MPa, and the pretreatment time is 10-30min.

[0016] Furthermore, the pretreated exhaust gas in S2 is at a speed of 5-10m³. 3 The absorbent enters the falling film absorption tower at a rate of / s, and the absorbent is dilute hydrochloric acid with a mass fraction of 20-30%. The spray flow rate is 2-4 m³ / s. 3 / h, the operating temperature of the absorption tower is 20-40℃.

[0017] Furthermore, the exhaust gas after falling film absorption in S3 is at a concentration of 3-6m³. 3 The catalyst enters the hydrolysis tower at a rate of / s, with each stage of catalytic decomposition at 50-70℃ and a pressure of 0.2-0.4MPa. The catalytic decomposition time is 15-25min, and the catalyst loading is 0.5-1.5kg per stage.

[0018] Furthermore, the catalyst for phosgene in S3 is prepared using the following steps:

[0019] Add 0.5 mol / L sodium silicate solution and 5% polyethylene glycol solution to a reaction vessel, control the reaction temperature at 40-50℃, adjust the pH of the system to 7-9 with 1 mol / L hydrochloric acid solution, stir the reaction for 1 hour, filter, disperse the white solid in ethanol, add potassium niobate powder, stir the reaction vigorously for 30-60 minutes, and then place it in a curing oven to cure for 1-2 hours to obtain a phosgene catalyst.

[0020] Furthermore, the exhaust gas after catalytic decomposition in S4 is emitted at a rate of 2-4 m³ / h. 3 The packing material enters the alkali destruction tower at a rate of / s, and the corrosion-resistant packing includes either polypropylene or fiberglass.

[0021] Furthermore, the dilute alkaline solution in S4 is a sodium hydroxide solution, and the spray flow rate is 1-2 m³ / h. 3 / h, the operating temperature of the alkali washing tower is 25-45℃.

[0022] Furthermore, the mass ratio of sodium silicate solution, polyethylene glycol solution, ethanol and potassium niobate is (6-8):(4-5):20:(0.5-1).

[0023] Furthermore, the first stirring speed is 50-100 rpm, the second vigorous stirring speed is 200-300 rpm, and the curing temperature is 100-200℃.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention recovers low-boiling-point substances such as ethanol and ethyl chloroformate from the exhaust gas through condenser pretreatment, and returns the condensate to the production system for recycling, reducing raw material waste and lowering production costs. Hydrogen chloride is efficiently absorbed and converted into concentrated and dilute hydrochloric acid for recycling in the next process stage or for sale, realizing resource reuse while reducing the emission of harmful gases.

[0026] 2. In the hydrolysis tower, phosgene molecules undergo decomposition under the action of a catalyst. Phosgene molecules are first adsorbed onto the active sites (silanol groups and niobium ions) on the catalyst surface, forming adsorbed phosgene molecules, which lowers the activation energy of the phosgene decomposition reaction. Under the action of the self-made catalyst, the chemical bonds in the phosgene molecules break and rearrange, electrons transfer from the phosgene molecules to the catalyst surface or adjacent molecules, and chloride ions and carbon dioxide produced during decomposition desorb from the catalyst surface and are released into the gas phase, thus completing the entire catalytic decomposition process. Compared with traditional adsorbents such as activated carbon, this method can more effectively reduce the concentration of phosgene and improve treatment efficiency. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of the process for synthesizing ethyl chloroformate. Detailed Implementation

[0029] 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.

[0030] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0031] Preparation Example 1

[0032] The catalyst for phosgene is prepared by the following steps:

[0033] 6 kg of 0.5 mol / L sodium silicate solution and 4 kg of 5% polyethylene glycol solution were added to a reactor. The reaction temperature was controlled at 40 °C. The pH of the system was adjusted to 7 with 1 mol / L hydrochloric acid solution. The reaction was stirred for the first time at 50 rpm for 1 h. After filtration, the white solid was dispersed in 20 kg of ethanol. 0.5 kg of potassium niobate powder was added. The reaction was stirred vigorously for the second time at 200 rpm for 30 min. The mixture was then placed in a curing oven and cured at 100 °C for 1 h to obtain a phosgene catalyst.

[0034] Preparation Example 2

[0035] The catalyst for phosgene is prepared by the following steps:

[0036] 7 kg of 0.5 mol / L sodium silicate solution and 4.75 kg of 5% polyethylene glycol solution were added to a reactor. The reaction temperature was controlled at 45 °C. The pH of the system was adjusted to 8 with 1 mol / L hydrochloric acid solution. The mixture was stirred for the first time at 60 rpm for 1 h. After filtration, the white solid was dispersed in 20 kg of ethanol. 0.75 kg of potassium niobate powder was added, and the mixture was stirred vigorously for the second time at 250 rpm for 45 min. The mixture was then placed in a curing oven and cured at 150 °C for 1.5 h to obtain a phosgene catalyst.

[0037] Preparation Example 3

[0038] The catalyst for phosgene is prepared by the following steps:

[0039] 8 kg of 0.5 mol / L sodium silicate solution and 5 kg of 5% polyethylene glycol solution were added to a reactor. The reaction temperature was controlled at 50 °C. The pH of the system was adjusted to 9 with 1 mol / L hydrochloric acid solution. The reaction was stirred for the first time at 100 rpm for 1 h. After filtration, the white solid was dispersed in 20 kg of ethanol. 1 kg of potassium niobate powder was added. The reaction was stirred vigorously for the second time at 300 rpm for 60 min. The mixture was then placed in a curing oven and cured at 200 °C for 2 h to obtain a phosgene catalyst.

[0040] Example 1

[0041] A tail gas capture and treatment system for the synthesis of ethyl chloroformate includes:

[0042] S1. Collect the tail gas generated in each step of the ethyl chloroformate synthesis process, and pre-treat it in a condenser for 10 minutes. The operating temperature of the condenser is -10℃ and the pressure is 0.1MPa. The recovered low-boiling-point substances and the pre-treated tail gas are obtained.

[0043] S2, the pre-treated exhaust gas at 5m 3 The solution enters the falling film absorber at a rate of / s, and is circulated and sprayed with 20% dilute hydrochloric acid at a flow rate of 2m³ / s. 3 / h, the operating temperature of the absorption tower is 20℃, and concentrated hydrochloric acid and tail gas after falling film absorption are obtained. The concentrated hydrochloric acid is collected into the concentrated hydrochloric acid storage tank.

[0044] S3, the exhaust gas after falling film absorption is at 3m 3 0.5 kg of the solution enters the hydrolysis tower at a rate of / s.

[0045] The phosgene prepared in Example 1 was subjected to a three-stage catalytic decomposition of phosgene for 15 min using a catalyst. Each stage of catalytic decomposition was carried out at 50°C and 0.2 MPa, yielding dilute hydrochloric acid and tail gas after catalytic decomposition.

[0046] S4, the exhaust gas after catalytic decomposition enters a 2m... 3 The alkali washing tower, with its two-stage series alkali washing process, is equipped with polypropylene packing and circulated with a 5% sodium hydroxide solution at a flow rate of 1 m³ / s. 3 / h, the operating temperature of the alkali washing tower is 25℃, and the treated exhaust gas is monitored.

[0047] Example 2

[0048] A tail gas capture and treatment system for the synthesis of ethyl chloroformate includes:

[0049] S1. Collect the tail gas generated in each step of the ethyl chloroformate synthesis process, and pre-treat it in a condenser for 20 minutes. The operating temperature of the condenser is 0℃ and the pressure is 0.3MPa. The recovered low-boiling-point substances and the pre-treated tail gas are obtained.

[0050] S2, the pre-treated exhaust gas at 8m 3 The solution enters the falling film absorber at a rate of / s, and is sprayed with 25% dilute hydrochloric acid at a flow rate of 3m³ / s. 3 / h, the operating temperature of the absorption tower is 30℃, and concentrated hydrochloric acid and tail gas after falling film absorption are obtained. The concentrated hydrochloric acid is collected into the concentrated hydrochloric acid storage tank.

[0051] S3, the exhaust gas after falling film absorption is at 5m 3 The phosgene was fed into the hydrolysis tower at a rate of / s. 1kg of the phosgene prepared in Example 2 was added and the phosgene was subjected to a three-stage catalytic decomposition for 20min. Each stage of catalytic decomposition was carried out at 60℃ and 0.3MPa, yielding dilute hydrochloric acid and tail gas after catalytic decomposition.

[0052] S4, the exhaust gas after catalytic decomposition enters a 3m... 3 The alkali washing tower, equipped with polypropylene packing, performs a two-stage series alkali washing process. A 5% sodium hydroxide solution is circulated and sprayed at a flow rate of 1.5 m³ / s. 3 / h, the alkaline scrubbing tower operates at a temperature of 35℃, and the treated exhaust gas is monitored.

[0053] Example 3

[0054] A tail gas capture and treatment system for the synthesis of ethyl chloroformate includes:

[0055] S1. Collect the tail gas generated in each step of the ethyl chloroformate synthesis process, and pre-treat it in a condenser for 30 minutes. The operating temperature of the condenser is 5℃ and the pressure is 0.5MPa. The recovered low-boiling-point substances and the pre-treated tail gas are obtained.

[0056] S2, the pretreated exhaust gas at 10m 3 The solution enters the falling film absorber at a rate of / s, and is circulated and sprayed with 30% dilute hydrochloric acid at a flow rate of 4m³ / s. 3 / h, the operating temperature of the absorption tower is 40℃, and concentrated hydrochloric acid and tail gas after falling film absorption are obtained. The concentrated hydrochloric acid is collected into the concentrated hydrochloric acid storage tank.

[0057] S3, the exhaust gas after falling film absorption is at 6m 3 The phosgene was fed into the hydrolysis tower at a rate of / s, and 1.5kg of the phosgene prepared in Example 3 was added. The phosgene was then subjected to a three-stage catalytic decomposition for 25min. Each stage of catalytic decomposition was carried out at 70℃ and 0.4MPa, yielding dilute hydrochloric acid and tail gas after catalytic decomposition.

[0058] S4, the exhaust gas after catalytic decomposition enters a 4m... 3 The alkali washing tower, with its two-stage series alkali washing process, is equipped with polypropylene packing and circulated with a 5% sodium hydroxide solution at a flow rate of 2 m³ / s. 3 / h, the operating temperature of the alkali scrubbing tower is 45℃, and the treated exhaust gas is monitored.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that sodium silicate is used instead of phosgene catalyst; the remaining steps are the same as in Example 1.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 2 is that polyethylene glycol is used instead of phosgene catalyst; the remaining steps are the same as in Example 2.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 3 is that potassium niobate is used instead of phosgene catalyst; the remaining steps are the same as in Example 3.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 1 is that nano-silica is used instead of phosgene catalyst, while the other steps are the same as in Example 1.

[0067] Comparative Example 5

[0068] The difference between this comparative example and Example 2 is that activated carbon is used instead of phosgene catalyst; the remaining steps are the same as in Example 2.

[0069] Comparative Example 6

[0070] The difference between this comparative example and Example 3 is that no phosgene catalyst is added; the remaining steps are the same as in Example 3.

[0071] 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 1-6 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.

[0072] Table 1. Phosgene treatment results of Examples 1-3 and Comparative Examples 1-6

[0073]

[0074]

[0075] As shown in Table 1, Examples 1-3 used the phosgene catalysts prepared according to Examples 1-3, and the decomposition efficiency all reached over 99.8%. However, Comparative Examples 1-6 used sodium silicate, polyethylene glycol, potassium niobate, nano-silica, activated carbon, or no catalyst for phosgene treatment, respectively, and their phosgene decomposition efficiencies were much lower than those of Examples 1-3. This indicates that the absence or use of unsuitable catalysts in the comparative examples may lead to a decrease in phosgene decomposition efficiency. Sodium silicate, polyethylene glycol, potassium niobate, etc., when used alone, may not be able to form substances with highly efficient catalytic activity.

[0076] In summary, the phosgene catalysts prepared in Examples 1-3 exhibited extremely high efficiency in the catalytic decomposition of phosgene, likely due to the combined effects of catalyst composition, preparation process, and catalytic mechanism. In contrast, the phosgene decomposition efficiency in Comparative Examples 1-6 was reduced, possibly due to the absence or inappropriateness of the catalyst, insufficient catalytic activity, differences in preparation processes, and the influence of reaction conditions.

[0077] 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.

[0078] 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 tail gas capture and treatment system for the synthesis of ethyl chloroformate, characterized in that, include: S1. Collect the tail gas generated in each step of the ethyl chloroformate synthesis process, and pass it into a condenser for pretreatment to obtain the recovered low-boiling-point substances and the pretreated tail gas. S2. The pretreated tail gas enters the falling film absorption tower, and the absorption liquid is circulated and sprayed inside the tower to obtain concentrated hydrochloric acid and tail gas after falling film absorption. The concentrated hydrochloric acid is collected into the concentrated hydrochloric acid storage tank. S3. The tail gas after falling film absorption enters the hydrolysis tower, where phosgene is added and a catalyst is used to perform a three-stage series catalytic decomposition of phosgene to obtain dilute hydrochloric acid and the catalytic decomposition tail gas. S4. The tail gas after catalytic decomposition enters the alkaline destruction tower for two-stage series alkaline washing. The alkaline washing tower is equipped with corrosion-resistant packing and is sprayed with dilute alkaline solution with a concentration of <10%. After the tail gas meets the standards, it is discharged through an induced draft fan. The catalyst for phosgene in S3 is prepared by the following steps: Add 0.5 mol / L sodium silicate solution and 5% polyethylene glycol solution to a reaction vessel, control the reaction temperature at 40-50℃, adjust the pH of the system to 7-9 with 1 mol / L hydrochloric acid solution, stir the reaction for 1 hour, filter, disperse the white solid in ethanol, add potassium niobate powder, stir the reaction vigorously for 30-60 minutes, and then place it in a curing oven to cure for 1-2 hours to obtain a phosgene catalyst.

2. The tail gas capture and treatment system for the synthesis of ethyl chloroformate according to claim 1, characterized in that, The operating temperature of the condenser in S1 is (-10)-5℃, the pressure is 0.1-0.5MPa, and the pretreatment time is 10-30min.

3. The tail gas capture and treatment system for the synthesis of ethyl chloroformate according to claim 1, characterized in that, The pretreated exhaust gas in S2 is discharged at 5-10m 3 The absorbent enters the falling film absorption tower at a rate of / s, and the absorbent is dilute hydrochloric acid with a mass fraction of 20-30%. The spray flow rate is 2-4 m³ / s. 3 / h, the operating temperature of the absorption tower is 20-40℃.

4. The tail gas capture and treatment system for the synthesis of ethyl chloroformate according to claim 1, characterized in that, The exhaust gas after falling film absorption in S3 has a velocity of 3-6m³. 3 The catalyst enters the hydrolysis tower at a rate of / s, with each stage of catalytic decomposition at 50-70℃ and a pressure of 0.2-0.4MPa. The catalytic decomposition time is 15-25min, and the catalyst loading is 0.5-1.5kg per stage.

5. The tail gas capture and treatment system for the synthesis of ethyl chloroformate according to claim 1, characterized in that, The exhaust gas after catalytic decomposition in S4 is released at a rate of 2-4m. 3 The packing material enters the alkali destruction tower at a rate of / s, and the corrosion-resistant packing includes either polypropylene or fiberglass.

6. The tail gas capture and treatment system for the synthesis of ethyl chloroformate according to claim 1, characterized in that, The dilute alkaline solution in S4 is a sodium hydroxide solution, and the spray flow rate is 1-2 m³ / h. 3 / h, the operating temperature of the alkali washing tower is 25-45℃.

7. The tail gas capture and treatment system for the synthesis of ethyl chloroformate according to claim 1, characterized in that, The mass ratio of sodium silicate solution, polyethylene glycol solution, ethanol and potassium niobate is (6-8):(4-5):20:(0.5-1).

8. The tail gas capture and treatment system for the synthesis of ethyl chloroformate according to claim 1, characterized in that, The first stirring speed is 50-100 rpm, the second vigorous stirring speed is 200-300 rpm, and the curing temperature is 100-200℃.

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