Tail gas trapping treatment system applied to ethyl chloroformate synthesis

Abstract

The invention relates to the technical field of tail gas treatment, in particular to a tail gas trapping treatment system applied to ethyl chloroformate synthesis, which comprises the following steps: S1, pretreating tail gas by a condenser; s2, performing falling film absorption to obtain concentrated hydrochloric acid and tail gas after falling film absorption; s3, performing catalytic decomposition on phosgene to obtain diluted hydrochloric acid and tail gas subjected to catalytic decomposition; and S4, carrying out two-stage series alkali washing, carrying out circulating spraying by using dilute alkali liquor, and discharging through an induced draft fan. Low-boiling-point substances such as ethanol and ethyl chloroformate in the tail gas are recovered through pretreatment of the condenser, and condensate is returned to a production system for cyclic utilization, so that the waste of raw materials is reduced, and the production cost is reduced. The hydrogen chloride is efficiently absorbed and converted into concentrated hydrochloric acid and diluted hydrochloric acid for recycling or selling in the next working section, so that the reutilization of resources is realized, and the emission of harmful gases is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas treatment, and in particular to a tail gas capture and treatment system applied to ethyl chloroformate synthesis. Background Art

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

[0003]

[0004] In addition, ethanol will also react with the generated ethyl chloroformate under certain conditions. The equation of the side reaction is:

[0005]

[0006] Phosgene is a highly active acylating agent, and its reaction conditions with ethanol are mild. Ethanol and ethyl chloroformate can further react to generate diethyl carbonate as a byproduct. The reaction conditions are milder than those for ethyl chloride. During the production process, the content of diethyl carbonate is controlled to be less than 0.5%. Therefore, in the existing synthesis system, ethanol reacts with phosgene first, and a trace amount of ethanol reacts with ethyl chloroformate, and the synthesis system does not generate ethyl chloride.

[0007] The tail gas produced by the reaction mainly includes phosgene, hydrogen chloride, ethanol and ethyl chloroformate. In the prior art, an adsorption process based on activated carbon or acid-base solution is usually used to remove pollutants in the exhaust gas, such as the invention patent with patent publication number CN109663477A, ​​which discloses a waste treatment method for preparing ethyl chloroformate. However, the treatment method has the problem of incomplete exhaust gas treatment and requires multiple cycles of treatment, which leads to high energy consumption and increased exhaust gas treatment costs. Summary of the invention

[0008] In order to solve the problems mentioned in the above background technology, the present invention provides a tail gas capture and treatment system applied to the synthesis of ethyl chloroformate.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A tail gas capture and treatment system for ethyl chloroformate synthesis, comprising:

[0011] S1, collect the tail gas produced by each link (esterification tower, gas-catching kettle, lightness-removing tower) of ethyl chloroformate synthesis technique, pass into condenser pretreatment, obtain the low-boiling-point substances recovered and the tail gas after pretreatment, wherein, the 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 tail gas after pretreatment enters the falling film absorption tower, and the absorption liquid is circulated and sprayed in the tower to efficiently absorb the hydrogen chloride in the tail gas, with an absorption efficiency of ≥95%, ensuring that the concentration of hydrogen chloride in the tail gas drops 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 stage or for sale;

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

[0014] S4. The tail gas after catalytic decomposition enters the alkali destruction tower. The alkali destruction tower is equipped with T38205 and T38206 for two-stage series alkali washing to neutralize the residual phosgene, hydrogen chloride and other gases in the tail gas. The alkali washing tower is equipped with corrosion-resistant fillers and circulated spraying with dilute alkali solution with a concentration of less than 10%. After the tail gas is tested and treated to meet the standards, it is sent to the original high-discharge tower and high-discharge air through the induced draft fan.

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

[0016] Furthermore, the exhaust gas pretreated in S2 is 5-10m 3 / s into the falling film absorption tower, the absorption liquid is 20-30% by mass of dilute hydrochloric acid, and the spray flow rate is 2-4m 3 / h, the operating temperature of the absorption tower is 20-40℃.

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

[0018] Further, the phosgene catalyst in S3 is prepared by the following steps:

[0019] Add 0.5 mol / L sodium silicate solution and 5% polyethylene glycol solution into the reaction kettle, control the reaction temperature to 40-50°C, adjust the pH value of the system to 7-9 with 1 mol / L hydrochloric acid solution, stir and react for 1 hour for the first time, filter, disperse the white solid in ethanol, add potassium niobate powder, stir and react vigorously for 30-60 minutes for the second time, put into a curing furnace for curing for 1-2 hours, and obtain a catalyst for phosgene.

[0020] Furthermore, the tail gas after catalytic decomposition in S4 is 2-4m 3 / s into the alkali destruction tower, and the corrosion-resistant filler includes one of polypropylene or fiberglass.

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

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

[0023] Furthermore, the speed of the first stirring is 50-100 rpm, the speed of the second intense stirring is 200-300 rpm, and the curing temperature is 100-200°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention recovers low-boiling-point substances such as ethanol and ethyl chloroformate in the tail gas through condenser pretreatment, and returns the condensate to the production system for recycling, thereby reducing the waste of raw materials and reducing production costs. Hydrogen chloride is efficiently absorbed and converted into concentrated hydrochloric acid and dilute hydrochloric acid, which are used for recycling in the next stage or sold externally, realizing the reuse of resources and reducing the emission of harmful gases.

[0026] 2. In the hydrolysis tower, phosgene molecules undergo decomposition reaction under the action of the catalyst. The phosgene molecules are first adsorbed by the active sites (silanol and niobium ions) on the catalyst surface to form adsorbed phosgene molecules, which reduces the activation energy of the phosgene molecule decomposition reaction. Under the action of the homemade catalyst, the chemical bonds in the phosgene molecules are broken and rearranged, and electrons are transferred from the phosgene molecules to the catalyst surface or adjacent molecules. The chloride ions and carbon dioxide produced by the decomposition are desorbed from the catalyst surface and released into the gas phase, thereby completing the entire catalytic decomposition process. Compared with traditional adsorbents such as activated carbon, it can more effectively reduce the concentration of phosgene and improve the treatment efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 This is a flowchart of the synthesis process of ethyl chloroformate. DETAILED DESCRIPTION

[0029] 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.

[0030] Unless otherwise specified, the raw materials used in the present invention are all conventional products purchased from the market.

[0031] Preparation Example 1

[0032] The catalyst for phosgene comprises the following steps:

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

[0034] Preparation Example 2

[0035] The catalyst for phosgene comprises the following steps:

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

[0037] Preparation Example 3

[0038] The catalyst for phosgene comprises the following steps:

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

[0040] Example 1

[0041] A tail gas capture and treatment system for ethyl chloroformate synthesis, comprising:

[0042] S1, collecting the tail gas generated in each link of the ethyl chloroformate synthesis process, passing it into a condenser for pretreatment for 10 minutes, the operating temperature of the condenser is -10°C, and the pressure is 0.1MPa, to obtain the recovered low-boiling point substances and the pretreated tail gas;

[0043] S2, the exhaust gas after pretreatment is 5m 3 / s into the falling film absorption tower, and 20% dilute hydrochloric acid is circulated and sprayed in the tower, with a spray flow rate of 2m 3 / h, the operating temperature of the absorption tower is 20°C, concentrated hydrochloric acid and tail gas after falling film absorption are obtained, and the concentrated hydrochloric acid is collected in a concentrated hydrochloric acid storage tank;

[0044] S3, tail gas after falling film absorption at 3m 3 / s into the hydrolysis tower, adding 0.5kg

[0045] The phosgene prepared in Example 1 was subjected to three-stage series catalytic decomposition of phosgene using a catalyst for 15 minutes, with each stage of catalytic decomposition at 50° C. and a pressure of 0.2 MPa to obtain dilute hydrochloric acid and tail gas after catalytic decomposition;

[0046] S4, the exhaust gas after catalytic decomposition enters 2m 3 / s alkali destruction tower, two-stage series alkali washing, alkali washing tower is equipped with polypropylene filler, and 5% sodium hydroxide solution is used for circulation spraying, the spray flow rate is 1m 3 / h, the operating temperature of the alkali washing tower is 25℃, and the tail gas is detected and treated.

[0047] Example 2

[0048] A tail gas capture and treatment system for ethyl chloroformate synthesis, comprising:

[0049] S1. Collect tail gas generated in each link of the ethyl chloroformate synthesis process, pass it into a condenser for pretreatment for 20 minutes, the operating temperature of the condenser is 0° C., and the pressure is 0.3 MPa, to obtain recovered low-boiling point substances and pretreated tail gas;

[0050] S2, the exhaust gas after pretreatment is 8m 3 / s into the falling film absorption tower, and 25% dilute hydrochloric acid is circulated and sprayed in the tower, with a spray flow rate of 3m 3 / h, the operating temperature of the absorption tower is 30°C, concentrated hydrochloric acid and tail gas after falling film absorption are obtained, and the concentrated hydrochloric acid is collected in a concentrated hydrochloric acid storage tank;

[0051] S3, tail gas after falling film absorption at 5m 3 / s into the hydrolysis tower, add 1kg of the phosgene catalyst prepared in Example 2 to carry out three-stage series catalytic decomposition of phosgene for 20min, each stage of catalytic decomposition is 60°C, the pressure is 0.3MPa, and dilute hydrochloric acid and tail gas after catalytic decomposition are obtained;

[0052] S4, the exhaust gas after catalytic decomposition enters 3m 3 / s alkali destruction tower, two-stage series alkali washing, alkali washing tower is equipped with polypropylene filler, and 5% sodium hydroxide solution is used for circulating spraying, the spray flow rate is 1.5m 3 / h, the operating temperature of the alkali washing tower is 35℃, and the tail gas is detected and treated.

[0053] Example 3

[0054] A tail gas capture and treatment system for ethyl chloroformate synthesis, comprising:

[0055] S1. Collect tail gas generated in each link of the ethyl chloroformate synthesis process, pass it into a condenser for pretreatment for 30 minutes, the operating temperature of the condenser is 5° C., and the pressure is 0.5 MPa, to obtain recovered low-boiling point substances and pretreated tail gas;

[0056] S2, pre-treated exhaust gas at 10m 3 / s into the falling film absorption tower, and 30% dilute hydrochloric acid is circulated and sprayed in the tower, with a spray flow rate of 4m 3 / h, the operating temperature of the absorption tower is 40°C, concentrated hydrochloric acid and tail gas after falling film absorption are obtained, and the concentrated hydrochloric acid is collected in a concentrated hydrochloric acid storage tank;

[0057] S3, tail gas after falling film absorption at 6m 3 / s into the hydrolysis tower, add 1.5kg of the phosgene catalyst prepared in Example 3 to carry out three-stage series catalytic decomposition of phosgene for 25min, each stage of catalytic decomposition is 70°C, the pressure is 0.4MPa, and dilute hydrochloric acid and tail gas after catalytic decomposition are obtained;

[0058] S4, the exhaust gas after catalytic decomposition enters 4m 3 / s alkali destruction tower, two-stage series alkali washing, alkali washing tower is equipped with polypropylene filler, and 5% sodium hydroxide solution is used for circulation spraying, the spray flow rate is 2m 3 / h, the operating temperature of the alkali washing tower is 45℃, and the tail gas is detected and treated.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that sodium silicate is used instead of the phosgene catalyst, and the remaining steps are the same as those 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 the phosgene catalyst, and the remaining steps are the same as those 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 the phosgene catalyst, and the remaining steps are the same as those in Example 3.

[0065] Comparative Example 4

[0066] The difference between this comparative example and Example 1 is that nano-silicon dioxide is used instead of the phosgene catalyst, and the remaining steps are the same as those 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 the phosgene catalyst, and the remaining steps are the same as those in Example 2.

[0069] Comparative Example 6

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

[0071] 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 1-6 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, and 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 can be seen from Table 1, Examples 1-3 used the phosgene catalyst prepared according to Preparation Examples 1-3, and the decomposition efficiency reached more than 99.8%. Comparative Examples 1-6 used sodium silicate, polyethylene glycol, potassium niobate, nano-silicon dioxide, activated carbon or no catalyst to treat phosgene, and their phosgene decomposition efficiency was much lower than that of Examples 1-3. This indicates that the phosgene decomposition efficiency may be reduced if no or inappropriate catalyst is used in the comparative examples. Sodium silicate, polyethylene glycol, potassium niobate, etc., when used alone, may not form a substance with high catalytic activity.

[0076] In summary, the phosgene catalysts prepared in Examples 1-3 showed extremely high efficiency in the catalytic decomposition of phosgene, which may be due to the combined effects of the composition, preparation process and catalytic mechanism of the catalyst. However, in Comparative Examples 1-6, the phosgene decomposition efficiency was reduced due to the lack or inappropriateness of the catalyst, insufficient catalytic activity, differences in the preparation process and the influence of reaction conditions.

[0077] 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.

[0078] 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 tail gas capture and treatment system for ethyl chloroformate synthesis, characterized in that: include: S1, collecting the tail gas generated in each link of the ethyl chloroformate synthesis process, passing it into a condenser for pretreatment, and obtaining recovered low-boiling point substances and pretreated tail gas; S2, the tail gas after pretreatment enters the falling film absorption tower, and the absorption liquid is circulated and sprayed in the tower to obtain concentrated hydrochloric acid and tail gas after falling film absorption, and the concentrated hydrochloric acid is collected in the concentrated hydrochloric acid storage tank; S3, the tail gas after falling film absorption enters the hydrolysis tower, and a phosgene catalyst is added to carry out three-stage series catalytic decomposition of phosgene to obtain dilute hydrochloric acid and tail gas after catalytic decomposition; S4. The tail gas after catalytic decomposition enters the alkali destruction tower for two-stage series alkali washing. The alkali washing tower is equipped with corrosion-resistant fillers and is circulated and sprayed with dilute alkali solution with a concentration of less than 10%. After the tail gas is tested and treated to meet the standards, it is discharged through the induced draft fan.

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

3. The tail gas capture and treatment system for ethyl chloroformate synthesis according to claim 1, characterized in that: The exhaust gas pre-treated in S2 is 5-10m 3 / s into the falling film absorption tower, the absorption liquid is 20-30% by mass of dilute hydrochloric acid, and the spray flow rate is 2-4m 3 / h, the operating temperature of the absorption tower is 20-40℃.

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

5. The tail gas capture and treatment system for ethyl chloroformate synthesis according to claim 1, characterized in that: 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 into the reaction kettle, control the reaction temperature to 40-50°C, adjust the pH value of the system to 7-9 with 1 mol / L hydrochloric acid solution, stir and react for 1 hour for the first time, filter, disperse the white solid in ethanol, add potassium niobate powder, stir and react vigorously for 30-60 minutes for the second time, put into a curing furnace for curing for 1-2 hours, and obtain a catalyst for phosgene.

6. The tail gas capture and treatment system for ethyl chloroformate synthesis according to claim 1, characterized in that: The tail gas after catalytic decomposition in S4 is 2-4m 3 / s into the alkali destruction tower, and the corrosion-resistant filler includes one of polypropylene or fiberglass.

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

8. The tail gas capture and treatment system for ethyl chloroformate synthesis according to claim 5, 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).

9. The tail gas capture and treatment system for ethyl chloroformate synthesis according to claim 5, characterized in that: The speed of the first stirring is 50-100 rpm, the speed of the second intense stirring is 200-300 rpm, and the curing temperature is 100-200°C.

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