A continuous process for the preparation of chloroformates

Abstract

This invention belongs to the field of chloroformate synthesis technology, and particularly relates to a continuous preparation method of chloroformates, comprising the following steps: 1) feeding the reactant raw material alcohol and phosgene together into a synthesis tower via an absorption tower for reaction, generating crude chloroformate and byproduct hydrogen chloride; 2) sending the crude chloroformate formed in step 1) to a degassing tower, returning the phosgene removed from the degassing tower to the synthesis tower for further reaction, and then distilling the chloroformate after phosgene removal into a purification system to obtain the target product chloroformate; 3) sending the byproduct hydrogen chloride formed in step 1) into an absorption tower for washing with the raw material alcohol and then into the tail gas system. The beneficial effects of this invention are: it realizes continuous production of chloroformate products through synthesis and deacidification, improves the synthesis reaction rate, and shortens the deacidification time; simultaneously, through the recovery and recycling of phosgene, it reduces raw material consumption and forms a clean, inherently safe, automated production process.

Description

Technical Field

[0001] This invention belongs to the field of chloroformate synthesis technology, and particularly relates to a continuous preparation method of chloroformate. Background Technology

[0002] The most widely used chloroformate processes currently include batch and semi-continuous methods. The synthesis and deacidification of chloroformate products are time-consuming, and continuous synthesis and deacidification have not been achieved. Furthermore, the degree of automation is low, and the raw material consumption cost is high.

[0003] The batch process mainly involves adding a fixed amount of alcohol and phosgene to the synthesis reactor for reaction. After the reaction is completed, the material is sent to the deacidification reactor for deacidification by purging with nitrogen until the product meets the specifications. The single reactor reaction time is 24 hours, and the deacidification time is also about 24 hours. The single reactor production efficiency is low and the reaction selectivity is low.

[0004] The semi-continuous method uses a reaction tower, where phosgene and alcohol are continuously introduced from the bottom of the synthesis tower, and semi-finished products are continuously overflowed from the top of the tower. The esters produced are piped into deacidification kettles. When the amount of esters in each deacidification kettle reaches a certain level, nitrogen gas is introduced to deacidify the product. The deacidification time for a single kettle is about 24 hours, resulting in low production efficiency.

[0005] Existing batch and semi-continuous processes involve phosgene-containing tail gases generated during the reaction and degassing processes, which are directly fed into the tail gas treatment system. These require catalytic removal of phosgene, followed by hydrochloric acid absorption and alkaline washing. Excess phosgene present in the tail gas from the feedstock necessitates removal via catalytic reaction, increasing production costs and posing significant safety risks.

[0006] Currently, the production processes used for chloroformate products include batch and semi-continuous methods. The disadvantages of these two processes include:

[0007] 1. The single-reactor reaction time is about 24 hours, the reaction rate is slow and the reaction selectivity is low.

[0008] 2. The deacidification time is about 24 hours, resulting in low single-reactor production efficiency.

[0009] 3. In order to increase production capacity, a large number of deacidification reactors need to be installed, resulting in high fixed asset investment.

[0010] 4. A large amount of nitrogen is required during deacidification, resulting in high energy consumption and high waste gas treatment costs.

[0011] 5. Most operations require manual on-site switching, resulting in low automation, high labor intensity, and adverse effects on occupational health.

[0012] 6. Phosgene raw materials require large quantities and excessive amounts, resulting in high phosgene consumption and high waste gas treatment costs. Summary of the Invention

[0013] To overcome the shortcomings of the prior art, this invention provides a continuous preparation method for chloroformates, thereby realizing the continuous production of chloroformate products through synthesis and deacidification, improving the synthesis reaction rate and shortening the deacidification time; at the same time, by recovering and recycling phosgene, the consumption of raw materials is reduced; equipment investment is reduced, the level of automation control is improved, labor intensity is reduced, and a clean and inherently safe automated production is formed.

[0014] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0015] A continuous preparation method for chloroformate specifically includes the following steps:

[0016] 1) The reactant alcohol is fed into the synthesis tower through the absorption tower and reacts with phosgene fed into the synthesis tower to produce crude chloroformate and byproduct hydrogen chloride;

[0017] 2) The crude product chloroformate formed in step 1) is sent to the degassing tower. The phosgene removed from the degassing tower is returned to the synthesis tower to continue the reaction. The remaining chloroformate and chloroformate diester after the phosgene is removed are sent to the purification system for distillation to obtain the target product chloroformate.

[0018] 3) The byproduct hydrogen chloride formed in step 1) is sent to the absorption tower, washed with raw material alcohol and then enters the tail gas system. The alcohol after absorbing phosgene enters the synthesis tower for reaction.

[0019] As a preferred embodiment of the present invention, in step 1), the raw material alcohol enters from the top of the synthesis tower, and phosgene enters from the bottom of the tower to carry out a countercurrent contact reaction.

[0020] As a preferred embodiment of the present invention, in step 2), chloroformate flows out from the top of the refining system and dichloroformate flows out from the bottom of the refining system.

[0021] As a preferred embodiment of the present invention, in step 1), the raw material alcohol first absorbs a small amount of phosgene in the reaction tail gas in an absorption tower, and then enters the synthesis tower for reaction. The alcohol after phosgene absorption is the ester produced by the reaction, and the ester produced enters the synthesis tower together with the raw material alcohol.

[0022] As a preferred embodiment of the present invention, in step 2), the reaction product coming out of the bottom of the synthesis tower enters the degassing tower to remove phosgene and hydrogen chloride gas contained in the material by distillation. The removed gas is returned to the synthesis tower and mixed with the raw material phosgene for reaction.

[0023] In step 3), the phosgene carried in the byproduct hydrogen chloride is washed with raw material alcohol in the absorption tower to form an alcohol solution of the product ester, which then enters the synthesis tower for reaction; the purified hydrogen chloride gas enters the tail gas tower for subsequent preparation of hydrochloric acid.

[0024] As a preferred embodiment of the present invention, in step 1), the molar ratio of the raw material alcohol and phosgene is 1:1 to 1:1.5.

[0025] As a preferred embodiment of the present invention, in step 1), the molar ratio of the raw material alcohol and phosgene is 1:1 to 1:1.1.

[0026] As a preferred embodiment of the present invention, the raw material alcohol has the structural formula R-OH, wherein R is an aliphatic compound or an aromatic compound.

[0027] As a preferred embodiment of the present invention, R in R-OH is either benzyl or C1-C4 aliphatic group.

[0028] As a preferred embodiment of the present invention, the temperature of the distillation column is 10-90℃, and more preferably, the top temperature is 10-50℃, the bottom temperature is 50-90℃, and the top pressure is -0.1~0.1MPa.

[0029] As a preferred embodiment of the present invention, the temperature of the degassing tower is 10-90℃, preferably, the top temperature of the tower is 10-40℃, the bottom temperature of the tower is 50-90℃, and the pressure is -0.1-0.1MPa.

[0030] As a preferred embodiment of the present invention, the temperature of the absorption tower is 0-40℃ and the pressure is 0-0.1MPa.

[0031] As a preferred embodiment of the present invention, the temperature in the synthesis tower is 5-50°C, preferably 10-25°C.

[0032] The synthesis tower of the present invention may be a tubular reactor, but is not limited to this structure.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. The continuous countercurrent phosgenation synthesis and continuous distillation deacidification and purification are adopted to improve the selectivity of the reaction and the production efficiency. The formation rate of chloroformate is over 95%, while reducing the equipment size and the feed holding capacity of the reaction system.

[0035] 2. The gas exiting from the top of the degassing tower is returned to the synthesis tower to continue participating in the reaction, reducing raw material consumption.

[0036] 3. The byproduct hydrogen chloride in the gas phase at the top of the synthesis tower is washed with raw material alcohol to remove phosgene, and the hydrogen chloride directly enters the tail gas tower for treatment; the unreacted phosgene in the gas phase is absorbed by the raw material alcohol to form an alcohol solution containing esters, and the phosgene is recovered and recycled. The conversion rate of phosgene can reach 85-95%, which improves the utilization rate of raw materials and reduces the waste gas treatment load.

[0037] 4. The raw material alcohol enters from the top of the synthesis tower, and phosgene enters from the bottom of the synthesis tower. The two phases flow countercurrently and come into full contact to react, which is conducive to heat transfer and improves reaction selectivity. At the same time, the conversion rate of the raw material alcohol reaches more than 99%, and the reaction is basically complete.

[0038] 5. Deacidification is carried out by heated distillation, achieving continuous distillation deacidification, reducing auxiliary production time, improving equipment utilization, and eliminating nitrogen stripping, thus eliminating nitrogen consumption (using the same molar ratio of alcohol and phosgene, batch or semi-continuous methods consume 20 Nm³ of nitrogen). 3 (The nitrogen gas carries away hydrogen chloride at a temperature of 80°C, consuming a large amount of heat, resulting in energy waste and increased costs).

[0039] 6. The method of the present invention does not require solvents, reducing the steps of solvent removal and solvent recovery, and is simple to operate and low in cost. Attached Figure Description

[0040] Figure 1 This is a process flow diagram for preparing methyl chloroformate in Example 1 of the present invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] Example 1:

[0043] The process flow diagram for preparing methyl chloroformate according to this invention is as follows: Figure 1 As shown, the specific steps include the following:

[0044] 1) The reactants methanol and phosgene are placed in a synthesis tower at a molar ratio of 1:1.1 for reaction. Methanol enters the synthesis tower from the top of the tower via an absorption tower, while phosgene enters from the bottom of the tower. The reaction temperature is 25°C. The two react in a countercurrent and fully contact each other in the synthesis tower to form the crude product methyl chloroformate and the byproduct hydrogen chloride.

[0045] 2) The crude product methyl chloroformate formed in the synthesis tower flows out from the bottom of the tower and enters the degassing tower. The top temperature of the degassing tower is 40℃ / bottom temperature is 90℃, and the top pressure is 0.1MPa. Phosgene is removed in the degassing tower. The removed phosgene is combined with the raw material phosgene through a pipeline and enters the synthesis tower to complete the phosgene recovery. A small amount of hydrogen chloride gas in the degassing tower enters the synthesis tower and enters the absorption tower with the newly generated hydrogen chloride gas. At the same time, the methyl chloroformate remaining after the gas removal in the degassing tower enters the distillation tower for purification. The top temperature of the distillation tower is 32℃ / bottom temperature is 70℃, and the top pressure is -0.05MPa. The distillation yields the target product chloroformate. The by-product hydrogen chloride, unreacted phosgene, and a small amount of ester generated in the synthesis tower flow out from the top of the tower and enter the absorption tower. The absorption tower is sprayed and washed with raw material methanol. Methanol enters the absorption tower at atmospheric pressure, which operates under slight negative pressure with a top temperature of 10°C. The raw methanol reacts with unreacted phosgene flowing from the synthesis tower to form a methanol solution containing methyl chloroformate, which then enters the synthesis tower. The washed hydrogen chloride is discharged into the tail gas system. The entire process is a continuous feed and discharge operation, achieving a methyl chloroformate purity of 98.8%, a yield of 96%, and a phosgene conversion rate of 90.9%. The entire process does not use nitrogen, resulting in a short deacidification time and enabling continuous deacidification and continuous production of methyl chloroformate.

[0046] In this embodiment, the reaction tail gas is washed with methanol in the absorption tower, and the unreacted phosgene reaction products are returned to the synthesis tower, which improves the phosgene utilization rate and product yield. At the same time, hydrogen chloride can be separated and sent to the tail gas system for treatment.

[0047] It should be noted that, Figure 1 This diagram is merely an illustration of the process flow of the present invention and is not the only form of implementation of the invention. The present invention protects the process flow and method; other structures that can achieve the corresponding effects of the process of the present invention can also be used in the present invention.

[0048] Example 2:

[0049] The method for preparing ethyl chloroformate according to the present invention specifically includes the following steps:

[0050] 1) The reactants ethanol and phosgene are placed in a synthesis tower at a molar ratio of 1:1.15 for reaction. Ethanol enters the synthesis tower from the top via an absorption tower, while phosgene enters from the bottom. The reaction temperature is 20°C. The two react in a countercurrent and fully contact each other in the synthesis tower to form the crude product ethyl chloroformate and the byproduct hydrogen chloride.

[0051] 2) The crude product, ethyl chloroformate, formed in the synthesis tower flows out from the bottom of the tower and enters the degassing tower. The top temperature of the degassing tower is 40℃, the bottom temperature is 60℃, and the top pressure is -0.08MPa. Phosgene is removed in the degassing tower. The removed phosgene is combined with the raw material phosgene through a pipeline and enters the synthesis tower to complete the phosgene recovery. A small amount of hydrogen chloride gas in the degassing tower enters the synthesis tower and enters the absorption tower along with the newly generated hydrogen chloride gas. At the same time, the remaining ethyl chloroformate after gas removal in the degassing tower enters the distillation tower. The top temperature of the distillation tower is 4℃. Distillation at 5℃ / bottom temperature 70℃ and top pressure -0.09MPa yields the target product, ethyl chloroformate. The byproducts generated in the synthesis tower, including hydrogen chloride, unreacted phosgene, and a small amount of ester, flow out from the top and enter the absorption tower. The absorption tower uses ethanol as feedstock for absorption; the ethanol enters at room temperature and operates under slight negative pressure at a top temperature of 15℃. The ethanol reacts with the unreacted phosgene escaping from the synthesis tower to form an ethanol solution containing ethyl chloroformate, which then enters the synthesis tower. The washed hydrogen chloride is discharged into the tail gas system. The entire process is a continuous feed and continuous discharge, achieving ethyl chloroformate purity of 99.1%, a yield of 98%, and a phosgene conversion rate of 86.9%. The entire process does not use nitrogen, resulting in a short deacidification time and continuous deacidification and butyl chloroformate production.

[0052] Example 3:

[0053] The method for preparing benzyl chloroformate according to the present invention specifically includes the following steps:

[0054] 1) The reactants benzyl alcohol and phosgene are placed in a synthesis tower at a molar ratio of 1:1.05 for reaction. Benzyl alcohol enters the synthesis tower from the top via an absorption tower, while phosgene enters from the bottom. The reaction temperature is 15℃. The two react in a countercurrent and fully contact each other in the synthesis tower to form the crude product benzyl chloroformate and the byproduct hydrogen chloride.

[0055] 2) The crude product benzyl chloroformate formed in the synthesis tower flows out from the bottom of the tower and enters the degassing tower. The top temperature of the degassing tower is 12℃ / bottom temperature is 65℃, and the top pressure is -0.09MPa. Phosgene is removed in the degassing tower. The removed phosgene is combined with the raw material phosgene through a pipeline and enters the synthesis tower to complete the phosgene recovery. A small amount of hydrogen chloride gas in the degassing tower enters the synthesis tower and enters the absorption tower with the newly generated hydrogen chloride gas. At the same time, the remaining benzyl chloroformate after the gas removal in the degassing tower enters the distillation tower. The top temperature of the distillation tower is... Distillation at 45℃ (bottom temperature 80℃, top pressure -0.095 MPa) yields the target product, benzyl chloroformate. The byproducts generated in the synthesis tower, including hydrogen chloride, unreacted phosgene, and a small amount of ester, escape from the top and enter the absorption tower. Benzyl alcohol (5℃) is used for absorption in the absorption tower, which operates under slight negative pressure at a top temperature of 20℃. The benzyl alcohol reacts with the unreacted phosgene from the synthesis tower to form a benzyl alcohol solution containing benzyl chloroformate, which enters the synthesis tower. The washed hydrogen chloride is then sent to the tail gas system. The entire process is a continuous feed and discharge process, achieving a benzyl chloroformate purity of 98.7%, a yield of 95.5%, and a phosgene conversion rate of 95.2%. The entire process does not use nitrogen, resulting in a short deacidification time and continuous deacidification and benzyl chloroformate production.

[0056] The foregoing detailed examples of the present invention are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A continuous preparation method for chloroformate, characterized in that... Includes the following steps: 1) The reactant alcohol is fed into the synthesis tower through the absorption tower and reacts with phosgene fed into the synthesis tower to produce crude chloroformate and byproduct hydrogen chloride; 2) The crude product chloroformate formed in step 1) is sent to the degassing tower. The phosgene removed from the degassing tower is returned to the synthesis tower to continue the reaction. The remaining chloroformate and chloroformate diester after the phosgene is removed are sent to the purification system for distillation to obtain the target product chloroformate. 3) The byproduct hydrogen chloride formed in step 1) is sent to the absorption tower, washed with raw material alcohol, and then enters the tail gas system. The absorbed liquid enters the synthesis tower for reaction. In step 1), the raw material alcohol from the absorption tower enters from the top of the synthesis tower, and phosgene enters from the bottom of the tower to carry out a countercurrent contact reaction. In step 1), the raw material alcohol first absorbs a small amount of phosgene in the reaction tail gas in the absorption tower, and then enters the synthesis tower. In step 2), the reaction product coming out of the bottom of the synthesis tower enters the degassing tower to remove phosgene and hydrogen chloride gas contained in the material by distillation. In step 3), the phosgene carried in the byproduct hydrogen chloride is washed with raw material alcohol in the absorption tower, and the purified hydrogen chloride gas enters the tail gas tower for subsequent preparation of hydrochloric acid; the raw material alcohol has the structural formula R-OH, where R is benzyl or C1-C4 aliphatic group; the top temperature of the degassing tower is 10~40℃, the bottom temperature is 50~90℃, and the pressure is -0.1~0.1MPa; the temperature of the absorption tower is 0~40℃, and the pressure is slightly negative.

2. The method according to claim 1, characterized in that... In step 1), the molar ratio of the raw material alcohol and phosgene is 1:1 to 1:1.

5.

3. The method according to claim 2, characterized in that... In step 1), the molar ratio of the raw material alcohol and phosgene is 1:1 to 1:1.

1.

4. The method according to claim 1, characterized in that... The temperature in the synthesis tower is 5~50℃.

5. The method according to claim 1, characterized in that... The temperature in the synthesis tower is 10~25℃.

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