CN1282637C - Method for producing chloroacetic acid by photochlorination of acetic acid - Google Patents

Abstract

The invention provides a method for producing chloroacetic acid by coupling a photochlorination reactor and a rectifying tower with acetic acid and chlorine as raw materials and carrying out photochlorination of the acetic acid under the photoinitiation condition. In the method of using photoinitiated chlorine gas to generate chlorine radicals and reacting the chlorine radicals with acetic acid to generate chloroacetic acid, a photochlorination reactor is a key device, and the acetic acid chlorination reaction is carried out in the photochlorination reactor. The photochlorination reactor may be a bubble column made of glass or an enamel with sight glass or a teflon-lined bubble column. The light source can be provided by a fluorescent lamp or a blue light lamp, and the fluorescent lamp or the blue light lamp is arranged at the periphery of the glass bubble tower, or irradiates the inside of the glass bubble tower through a viewing mirror of the enamel or the polytetrafluoroethylene-lined bubble tower, or is arranged in a quartz glass sleeve inside the enamel or the polytetrafluoroethylene-lined bubble tower. When acetic acid exists in a photochlorination reactor, under the irradiation of sunlight or blue light, the reaction temperature is controlled to be 80-120 ℃, preferably 100-105 ℃, and chlorine gas introduced can perform chlorination reaction with the acetic acid to generate chloroacetic acid.

Description

Method for producing chloroacetic acid by photochlorination of acetic acid

technical field

The invention relates to the synthesis of organic compounds, more specifically, using acetic acid and chlorine as raw materials, under the condition of photoinitiation, coupling a photochlorination reactor and a rectification tower to carry out photochlorination of acetic acid to produce chloroacetic acid.

Background technique

Chloroacetic acid molecules contain both halogen and hydroxyl functional groups, and have the comprehensive performance of halogenated hydrocarbons and carboxylic acids. Its acidity is stronger than that of acetic acid, and it is rich in reactivity. Paper chemicals, oil field chemicals, textile auxiliaries, surfactants, fragrances and flavors and other industries. According to survey statistics and market forecasts, industries such as pesticides, pharmaceuticals, and CMC using chloroacetic acid as raw materials have developed rapidly in recent years, and the demand for chloroacetic acid will rise steadily.

There are more than 10 synthetic methods of chloroacetic acid, such as acetic acid chlorination, trichlorethylene hydrolysis, chloroethanol oxidation, tetrachloroethane hydrolysis, glycolic acid chlorination, acetic anhydride chlorination, acetic acid chlorine oxidation method, sulfuryl chloride chlorination method, alkanol chlorination method, dichloroethane photocatalytic oxidation method, polyhalogenated acetic acid reduction method and chloroacetyl chloride hydrolysis method. However, most of these methods belong to laboratory preparation methods or are in the experimental stage, and only the direct chlorination method of acetic acid is of real industrial significance, which is widely used by domestic and foreign manufacturers.

The production technology (CN1063677A) that adopts sulfur as catalyst is relatively low in cost, but the yield is low. Sulfur powder itself is solid, which easily causes equipment blockage, is unfavorable to operation and equipment maintenance, and easily pollutes chloroacetic acid products and by-product hydrochloric acid. , reduce the grade of the product, and limit the scope of application of the product.

Adopt the technique (US3152174) that acetic anhydride is used as catalyst to produce chloroacetic acid, the selectivity of chloroacetic acid is good, the content of dichloride is relatively low, the product quality is good, and pollution is little. But acetic anhydride is expensive, and consumption is bigger, and consumption in the reaction process is bigger, can cause the rise of production cost.

In addition, in order to solve the problem of acetyl chloride loss, both catalysts need to adopt low-temperature condensation recovery equipment, resulting in high equipment investment and energy consumption. Although the catalyst research on the chlorination of acetic acid is still going on, no catalyst suitable for industrialization and better than acetic anhydride has been found yet.

According to the principle of free radical reaction, the method of photoinitiation can dissociate chlorine molecules into chlorine free radicals, and then react with acetic acid to generate chloroacetic acid. Compared with catalysts such as sulfur and acetic anhydride, light is easy to obtain, clean and pollution-free. It should be a very ideal way to produce chloroacetic acid by direct chlorination of acetic acid through light. However, experimental studies have shown that the selectivity of direct photochlorination of acetic acid to produce chloroacetic acid is not good. When the content of chloroacetic acid reaches 20%, dichloroacetic acid is obviously formed, and it is mainly caused by the deep chlorination reaction of chloroacetic acid. Acetic acid and chloroacetic acid have a boiling point difference of about 70°C, which can be easily separated by rectification. Therefore, under the premise of using photoinitiation, it is considered to couple the acetic acid chlorination reactor with the rectification tower and use the technology of reactive distillation To curb the occurrence of a series of reactions, so that highly selective chloroacetic acid can be obtained.

Contents of the invention

The object of the present invention is to provide a method for producing chloroacetic acid by photochlorination of acetic acid by coupling a photochlorination reactor and a rectification tower with acetic acid and chlorine as raw materials under photoinitiated conditions. The method uses photoinitiation to replace catalysts such as sulfur and acetic anhydride, and has the characteristics of cleanness, no pollution, low production cost, good product quality, and easy control of production operations.

The object of the present invention can be achieved through the following measures:

In the method of using light to trigger chlorine to generate chlorine free radicals and react with acetic acid to generate chloroacetic acid, the photochlorination reactor is the key equipment, and the acetic acid chlorination reaction is carried out in such a photochlorination reactor. The photochlorination reactor can be a bubble column made of glass, or an enamelled or Teflon-lined bubble column with a sight glass. The light source can be provided by fluorescent lamps or blue light lamps. The fluorescent or blue light tubes are placed on the periphery of the glass bubble tower, or irradiated into the tower through the sight glass of the enamel or polytetrafluoroethylene-lined bubble tower, or placed on the enamel or polytetrafluoroethylene-lined bubble tower. In a quartz glass sleeve inside the tetrafluoroethylene bubble column. When acetic acid exists in the photochlorination reactor, under the irradiation of sunlight or blue light, the reaction temperature is controlled at 80-120°C, preferably between 100-105°C, and the chlorine gas introduced can undergo chlorination reaction with acetic acid to form Chloroacetic acid.

Since the chloroacetic acid produced by the chlorination of acetic acid is easily further chlorinated into dichloroacetic acid under the condition of photoinitiation, it is necessary to couple 1 to N sets of photochlorination reactors and rectification towers to form a reactive distillation device for acetic acid photochlorination. The chlorination reaction rectification operation is used to remove the chloroacetic acid generated by the chlorination reaction from the photochlorination reactor in time to avoid its deep chlorination. The reactive distillation unit includes a reactive distillation coupling zone and a separation zone, and the number of photochlorination reactors is generally less than 10, preferably 3 to 5. The rectification tower can be a plate tower or a packed tower, and the upper part of the rectification tower is connected with several photochlorination reactors to form a reactive distillation coupling area. The chlorination reaction material in the photochlorination reactor enters the coupling area of the rectification tower for separation, and the material in the coupling area of the rectification tower enters the photochlorination reactor after separation to react, thus forming a coupling operation of reaction and separation . The number of trays in the coupling zone can be 3 to 20, preferably 5 to 10, and a certain number of trays can be spaced between photochlorination reactors, or they can be closely adjacent to each other. The lower part of the rectification tower is a rectification separation zone, where the chloroacetic acid separated from the coupling zone is purified, and the material from the tower tank is the crude chloroacetic acid obtained from the chlorination reaction. The number of trays in the separation zone can also be 3-20, preferably between 6-12.

The total amount of acetic acid and chlorine is continuously fed into the reactive distillation coupling zone at a molar ratio of 0.9 to 1.5:1 (preferably 0.95 to 1.1:1), wherein the acetic acid enters the top of the tower, each tray of the coupling zone or each light In the chlorination reactor, chlorine gas is passed into each photochlorination reactor according to the ratio of 1 to 100% (generally 10 to 90%) of the total chlorine flow. Under the condition of stable operation, the temperature of the tower tank is between 150 and 190°C, the temperature at the top of the tower is between 90-100°C, the top of the tower is fully refluxed, and the material is discharged at the bottom of the tower. This is the crude product of chloroacetic acid, and the mass percentage of chloroacetic acid can reach 90-95%.

The invention has the advantages of clean and pollution-free acetic acid chlorination by photoinitiation, easy control of production operation, high yield of chloroacetic acid, low production cost and high economic benefit.

Description of drawings

Fig. 1 is a process flow diagram of producing chloroacetic acid by photochlorination of acetic acid.

Detailed ways

In order to further illustrate the present invention, illustrate by example below:

Example one:

Chlorine gas feed: 0.58mol/h, acetic acid feed: 0.56mol/h, tower top reflux flow: 19.44ml/min, light source is blue light. After rectification by acetic acid photochlorination reaction, the molar composition of the output from the tower kettle is: 1.21% acetic acid, 93.14% chloroacetic acid, and 5.65% dichloroacetic acid.

Example two:

Chlorine gas feed: 0.58mol/h, acetic acid feed: 0.56mol/h, tower top reflux flow: 23.14ml/min, light source is blue light. After rectification by acetic acid photochlorination reaction, the molar composition of the output from the tower kettle is: 1.17% acetic acid, 93.30% chloroacetic acid, and 5.53% dichloroacetic acid.

The result of comparative example one and example two, under the situation that acetic acid and chlorine feed amount are identical, change tower top reflux flow rate, improve the separation ability of tower, the mole composition of tower kettle discharge is basically the same, illustrates that the generation of dichloroacetic acid except In addition to the deep chlorination of chloroacetic acid, there is also the possibility that acetic acid can directly generate dichloroacetic acid.

Example three:

Chlorine gas feed: 0.72mol/h, acetic acid feed: 0.70mol/h, tower top reflux flow: 23.14ml/min, light source is blue light. After rectification by acetic acid photochlorination reaction, the molar composition of the discharge from the tower kettle is: 2.88% acetic acid, 91.49% chloroacetic acid, and 5.63% dichloroacetic acid.

Compared with example one, example three increased the feed rate of acetic acid and chlorine, and the results showed that the conversion rate of acetic acid and the selectivity of chloroacetic acid all decreased.

Example four:

Chlorine gas feed: 0.58mol/h, acetic acid feed: 0.56mol/h, tower top reflux flow: 23.14ml/min, light source is white light. After rectification by acetic acid photochlorination reaction, the molar composition of the output from the tower kettle is: 2.04% acetic acid, 92.14% chloroacetic acid, and 5.82% dichloroacetic acid.

Compared with Example 1, Example 4 uses white light as the light source for photoinitiation, and the results show that both light sources can play a better initiating effect, but when white light is used, it is not as good as blue light in terms of acetic acid conversion and chloroacetic acid selectivity.

Claims (6)

1. chloroacetic method of acetate light chlorination production is characterized in that the optical chlorinating reaction device is following two kinds: the 1) bubble tower of making by glass, and fluorescent lamp or blue-ray light place the periphery of glass bubble tower; 2) have the enamel of visor or the bubble tower of lining teflon, fluorescent lamp or blue-ray light pass through the visor of enamel or lining teflon bubble tower to the tower internal radiation, or place the quartz glass sleeve of enamel or lining teflon bubble tower inside; With 3～5 optical chlorinating reaction devices and the rectifying tower anabolic reaction rectifier unit that is coupled, this device comprises reactive distillation coupled zone and disengaging zone, with acetate and chlorine total amount by 0.9～1.5: 1 mole proportioning feeds the reactive distillation coupled zone continuously, wherein acetate enters cat head, in each column plate of coupled zone or each the optical chlorinating reaction device, chlorine feeds each optical chlorinating reaction device respectively in 10～90% ratios that account for total logical chlorine dose, under the condition of stable operation, the temperature of tower still is at 150～190 ℃, the temperature of cat head is at 90～100 ℃, temperature is at 80～120 ℃ in the optical chlorinating reaction device, the cat head total reflux, discharging at the bottom of the tower.

2. the chloroacetic method of acetate light chlorination production of carrying out according to claim 1 is characterized in that the coupled zone stage number is 3～20.

3. the chloroacetic method of acetate light chlorination production of carrying out according to claim 2 is characterized in that the coupled zone stage number is 5～10.

4. the chloroacetic method of acetate light chlorination production of carrying out according to claim 1 is characterized in that the disengaging zone stage number is 3～20.

5. the chloroacetic method of acetate light chlorination production of carrying out according to claim 4 is characterized in that the disengaging zone stage number is 6～12.

6. the chloroacetic method of acetate light chlorination production according to claim 1, the mole proportioning that it is characterized in that the total amount of acetate and chlorine is 0.95～1.1: 1.