JPS6058215B2 - Manufacturing method of monochloroacetic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved process for producing monochloroacetic acid by liquid phase chlorination of acetic acid.

More specifically, when producing monochloroacetic acid by reacting acetic acid and chlorine in the presence of a catalyst, some (or all) of the raw material chlorine gas is added to the reaction liquid that has substantially completed the chlorination reaction.
Chlorine gas containing acetyl chloride is blown into the reaction solution by adjusting the residence time of the solution to about 0.3 to 5 minutes and the liquid/gas weight ratio to about 2 to 10 to diffuse and discharge acetyl chloride from the reaction solution. The present invention relates to a method for producing monochloroacetic acid, which is characterized in that it is used as a raw material gas to a reaction tower. Many methods have been proposed to obtain monochloroacetic acid by chlorination of acetic acid (for example, see US Pat. No. 2,539,238 and US Pat. No. 2,688,634).

Catalysts used include acetyl chloride, acetic anhydride, sulfur, and phosphorus. Even in the case of sulfur, phosphorus, etc., acetyl chloride and acetic anhydride are produced during the reaction, and it is known that these act as true catalysts. . Therefore, the reaction process is thought to proceed mainly with acetyl chloride and acetic anhydride as follows.
C+Cl2→ ClCH2COOH+CHaCOCl/
CH3C0Cl+CH3C00H-C+HCl Therefore, the reaction liquid obtained from the above reaction, which has substantially completed the chlorination reaction, consists of monochloroacetic acid, acetic acid and acetyl chloride, and in the next step distillation column, acetic acid, acetyl chloride,
Monochloroacetic acid is separated from the bottom of the column.

At this time, acetyl chloride has an extremely high vapor pressure (vapor pressure l
50TmHg/10°C), economical condensation recovery is almost impossible under reduced pressure distillation. However, in these conventional methods, there have been almost no reports of attempts to recover acetyl chloride from the reaction solution and reduce the amount of catalyst. As a result of extensive research, the inventors of the present invention discovered that acetyl chloride in the reaction solution is diffused by blowing in chlorine gas, which is a raw material, and is recycled to the reaction tower along with the chlorine gas, and then sent to the distillation tower for the next step. It has been discovered that the above-mentioned problem can be solved by drastically reducing the amount of acetyl chloride introduced, and the present invention has been completed.

The advantages and effects of the present invention are as follows.

That is, (1) since the recovery rate of acetyl chloride is improved, the usage rate of acetic anhydride as a catalyst can be reduced. (2) Since the carrier gas for dispersion is the raw material chlorine gas, no extra energy is required. (3) Since not only acetyl chloride but also acetic acid is dissipated and recycled to the reaction column (at the same time, the chlorination reaction of unreacted acetic acid also progresses slightly), the energy cost in the distillation column in the next step is reduced. (4) Unnecessary side reactions due to the coexistence of highly reactive acetyl chloride in the distillation column are avoided. (5) Wastewater treatment costs based on pollution laws and regulations due to unrecovered acetyl chloride can be reduced. Therefore, the method for producing monochloroacetic acid according to the present invention as described above is industrially extremely excellent. By the way, it is conventionally known to strip and recover acetyl chloride in a reaction solution by flowing it countercurrently with hydrogen chloride gas (Japanese Patent Publication No. 33-875).

However, in this disclosed method, the used hydrogen chloride and the collected acetyl chloride must be separated and recovered again, and cannot be directly recycled to the reaction column. In addition, since hydrogen chloride gas has a higher solubility in the dispersion liquid than chlorine gas, it has disadvantages such as having a large influence on the next process, and is a method inferior in effectiveness compared to the method of the present invention. As the target liquid to which the method of the present invention can be applied, a reaction liquid that has substantially completed the chlorination reaction for producing monochloroacetic acid is suitably used.

Originally, carrying out the chlorination reaction in the presence of acetyl chloride (catalyst) and dissipating (recovering) acetyl chloride from the reaction solution have contradictory purposes, and side reactions occur simultaneously in the production of monochloroacetic acid. In order to solve this big problem, it is necessary to ensure that both of these requirements are satisfied, and the present invention has achieved this. In the method of the present invention, the temperature of the stripping tower used in the step of dissipating acetyl chloride from the reaction solution after blowing chlorine gas into the reaction solution is approximately 8.
A temperature of 0 to 140°C is suitable.

This temperature control ensures that the reaction liquid sent to the stripping tower is approximately 90 to 1
Since the temperature is maintained at 20° C., the temperature can be controlled within the above range by adjusting the temperature of one of the chlorine gases. If this temperature is lower than about 80° C., diffusion will not be carried out smoothly and chlorine gas will dissolve in the diffusion liquid (reaction liquid) after diffusion, resulting in loss. On the other hand, if the temperature is higher than about 140° C., side reactions may occur, resulting in coloring of the emitted liquid and lowering the purity, which is not preferable. The residence time of the chlorine gas blown into the reaction solution for dispersion is usually about 0.3 to 9 minutes, and the reaction solution/chlorine gas ratio (weight ratio) is usually selected from about 2 to 10.

The two have a close correlation, and can be appropriately determined within the above range based on experiments, depending on the type and specifications of the stripping tower, the composition of the reaction solution, or the extent to which acetyl chloride is to be recovered. Ru. Incidentally, part (or all) of the raw material chlorine gas is provided as the blown chlorine gas, but as in the case of temperature, harsh conditions are not preferable because side reactions may occur.
In other words, it is important to choose mild conditions suitable only for dissipating acetyl chloride, and the above-mentioned liquid residence time and reaction liquid/chlorine gas ratio ranges are suitable for this purpose. As for the type of the stripping tower, any type conventionally used in the stripping unit process can be used, such as a packed column or a falling liquid film type.

Other conditions for carrying out the method of the present invention are selected from the range conventionally used in industrial production methods using monochloroacetic acid, and are, for example, as follows. That is, in the reaction column stage, the reaction temperature is about 80-120°C (pressure is about 0-2.5k).
acetic acid and acetic anhydride at a ratio of about 10:2 under gIcT1G)
When continuous reactions are carried out by charging 10 to 12 parts (by weight) of chlorine gas to 10 parts of acetic acid, a reaction solution (composition: about 75 to 85% of monochloroacetic acid and dichloroacetic acid) is produced. , about 15-25% of acetic acid and about 3-5% of acetyl chloride). Next, the reaction solution passes through a stripping tower to diffuse acetyl chloride, and in the product production stage, the stripped liquid of acetyl chloride is distilled to recover unreacted acetic acid, and then crystallized in a crystallization tank to produce purified monochloroacetic acid. obtain. Next, a first example of a continuous embodiment of the method of the present invention will be described.
This will be explained based on the diagram.

That is, raw material acetic acid and acetic anhydride are charged into the reaction tower 3 through conduits 1 and 2, and raw chlorine gas is blown into the reaction tower 3 from the lower part through conduits 4 and 5. The reaction exhaust gas is extracted through a conduit 10, passed through a cooler 11, and removed to the outside of the system. Acetic acid, acetyl chloride, etc. condensed in the condenser are collected and recycled to the reaction column via conduit 12. The reaction liquid extracted from the middle of the reaction tower 3 is passed through the conduit 13 to the pump 1.
4 and is sent to the upper part of the diffusion tower 8.

At the same time, part or all of the raw material chlorine gas passes through the conduits 4 and 6, passes through the preheater 7, enters the lower part of the stripping tower 8, and flows countercurrently with the reaction liquid from the upper part. The stripping liquid from which volatile substances have been removed from the lower part of the stripping tower 8 is extracted through the conduit 15 and sent to the next step (distillation), where the desired product of monochloroacetic acid is obtained. On the other hand, chlorine gas accompanied by acetyl chloride and the like is extracted from the upper part of the stripping tower 8 through a conduit 9, and this purge gas is directly blown into the reaction tower as part or all of the reaction raw material. Next, the present invention will be specifically explained with reference to comparative examples and examples.

Comparative Example A chlorination reaction was carried out using a reaction tower (made of glass, 12', CSTR type) according to the following data.

That is, 1161yIH of acetic acid and 33% of acetic anhydride were placed in a reaction column.
Prepare at 32y1H and add chlorine gas to this at 1540y1H.
The mixture was blown in and reacted at 100 to 105°C for 7.5 hours.

At this time, exhaust gas 1021yIH is discharged, and reaction liquid 201
2y river is obtained. The composition of the reaction solution was as follows.
---. Then, when the obtained reaction solution was subjected to vacuum distillation (pressure 100wrfnHgabs, condenser temperature 20'C), acetic acid 369yIH and acetyl chloride 45y were extracted from the top of the column.
y river was recovered.

That is, it can be seen that the components 22y1H and 44y were lost. Example 1 Diffusion tower (made of glass, 40mm φ x 600w0nH11h/
Using 10W1 porcelain Raschig ring packing, packed tower type),
The reaction solution obtained in the comparative example was diffused using the following data.

That is, the above reaction liquid (107C) was poured into 201
Charge 2y river, blow 220yIH chlorine gas from the bottom of the tower, react the reaction liquid and liquid residence time 4 mark 2, liquid/gas weight ratio =
9.2, the emitted liquid 1873y1 flows from the bottom of the column.
Purge gas 359y1H was obtained from the top of the H1 column, and its composition was as follows.

That is, the acetyl chloride recovery rate was 47.2%.Then, the obtained dispersion liquid was distilled in the same manner as in the comparative example, and acetic acid 301y1H and acetyl chloride 24yIH were recovered from the top of the column, and the loss of each component was only 22yIH and 23yIH. Nakatsuta.

Examples 2 to 4 Next, the reaction liquid shown in the comparative example was treated in a stripping tower in the same manner as in Example 1 except for the data shown in Table 1, and the results were as shown in Table 1.

That is, the recovery rate of each acetyl chloride was about 50 to 70%.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of a continuous embodiment of the method of the present invention. 3... Reaction tower, 7... Preheater, 8...
...Radiation tower, 11...Cooler, 14...
...Pump, 1, 2, 4, 5, 6, 9, 10, 12,
13,15... Conduit.

Claims (1)

[Claims] 1. When producing monochloroacetic acid by reacting acetic acid and chlorine in the presence of a catalyst, a part (or all) of the raw material chlorine gas is added to the reaction liquid that has substantially completed the chlorination reaction, and the liquid residence time is approximately 0.3. The acetyl chloride is diffused from the reaction solution by blowing it in for ~5 minutes and adjusting the liquid/gas weight ratio to about 2 to 10, and the discharged chlorine gas containing acetyl chloride is used as a raw material gas to the reaction tower. A method for producing monochloroacetic acid, characterized in that it is used.