CN1128127C

CN1128127C - Process for preparing benzylchlorine

Info

Publication number: CN1128127C
Application number: CN 01108198
Authority: CN
Inventors: 张跃; 严生虎; 范正明; 邱滔; 沈介发
Original assignee: JIANGSU PETROLEUM-CHEMICAL COLLEGE; China Petrochemical Corp
Current assignee: JIANGSU PETROLEUM-CHEMICAL COLLEGE; China Petrochemical Corp
Priority date: 2001-04-09
Filing date: 2001-04-09
Publication date: 2003-11-19
Anticipated expiration: 2021-04-09
Also published as: CN1316409A

Abstract

The present invention provides a method for preparing benzyl chlorine, which relates to fine chemical engineering. Under the condition of photocatalysis for toluene and chlorine gas, the benzyl chloride is produced by a technological process of chlorinating rectification, and raw materials of the toluene and the chlorine gas are continuous fed; products the benzyl chloride are continuous discharged. A main device is a chlorinating rectifying tower composed of a tower kettle, a stripping section and an illumination reaction section, and a toluene feeding pipe is positioned on the upper part of the illumination reaction section; a benzyl chloride discharging pipe is positioned in the tower kettle, and a chlorine gas feeding pipe is positioned in the stripping section; fillers in the chlorinating rectifying tower is transparent materials. The present invention has the advantages of stabilizing production processes, greatly enlarging production scales, reducing production cost by about 15% and improving the purity and the quality of products, and the content of products of the benzyl chloride reaches above 99%; therefore, the present invention is high-purity benzyl chloride which is a product desired by medicine industry, pesticide industry, dyeing industry, etc.

Description

Production method of benzyl chloride

The present invention relates to fine chemical technology, and is especially the production process of benzyl chloride.

Benzyl chloride (formula C)₆H₅CH₂Cl) is an intermediate required by medicines, dyes, pesticides and organic synthesis, is used for synthesizing phenylacetic acid in medicine and finally synthesizing penicillin, and can also be used for synthesizing diphenhydramine hydrochloride, benzalkonium bromide, econazole, prednisone, phentermine, phenylacetamide and other medicines with large consumption; the pesticide is used for producing the rice blast, and the dye is used for producing products such as a dispersant CNF, a dissolved salt B, a disperse yellow S-RFL, a high-temperature leveling agent A-10 and the like; the synthesis of other organic products such as surfactant benzalkonium chloride and the production of benzyl ester plasticizer all need benzyl chloride as raw material intermediate. However, the benzyl chloride is produced by using toluene and chlorine as raw materials, generating a mixture containing the benzyl chloride and other reaction products under a catalytic condition, and then performing rectification separation, wherein the production process is batch production or semi-continuous production. Due to the backward production technology, a large amount of mixture consisting of dichlorobenzyl, trichlorobenzyl and tar is generated in the process of producing benzyl chloride, which brings difficulty to the separation of the benzyl chloride, and leads the production process to be complex, the unit consumption of raw materials to be high, and the content of the benzyl chloride to be low, which is generally only 97 percent. The production scale is small, and the production cost is high.

The invention aims to provide a method for producing benzyl chloride, which has the advantages of continuous production process, high benzyl chloride content and low production cost.

The technical scheme for achieving the aim of the invention is that toluene and chlorine are subjected to chlorination reaction in a light irradiation reaction section under a photocatalysis condition, benzyl chloride is produced by a chlorination rectification process of rectification and purification in a stripping section, the toluene and chlorine as raw materials are continuously fed, the benzyl chloride as a product is continuously discharged, and the volume ratio of the feeding amount of the toluene and the chlorine to the discharging amount of the benzyl chloride is 1: 200-220: 1.02-1.23.

The main device for realizing the purpose of the invention is a chlorination and rectification tower consisting of a tower kettle, a stripping section and a light reaction section, wherein a toluene inlet pipe is positioned at the upper part of the light reaction section, a benzyl chloride outlet pipe is positioned at the tower kettle, a chlorine gas inlet pipe is positioned at the stripping section, and a filler in the chlorination and rectification tower is made of transparent materials.

The reaction principle of the present invention is as follows;

the reaction equation for toluene and chlorine is:

in the above-mentioned series of chlorination reactions, there are three reactions, and only the benzyl chloride, which is the reaction product of the first-stage reaction (1), is the desired product of the present invention. Therefore, if the reaction process is not controlled, the reaction of toluene and chlorine continues to generate the reaction product benzyl dichloride of the second-stage reaction (2) and the reaction product benzyl trichloride of the third-stage reaction (3) to form a complex mixture containing various components such as toluene, benzyl chloride, benzyl dichloride, benzyl trichloride and the like, which brings great difficulty for subsequent separation and purification of benzyl chloride. The existing industrial technology is a process combining batch chlorination reaction and batch rectification separation, when the reaction of toluene and chlorine is stopped until the conversion rate reaches about 60%, the reaction mixture is rectified for many times, and benzyl chloride is separated out. However, when the conversion rate reaches 60%, the content of benzyl dichloride and benzyl trichloride is high, and the content of benzyl chloride in the rectified benzyl chloride product is also high, so that the content of benzyl chloride in the product can only reach about 97%, and if further purification is carried out, equipment needs to be added, the operation cost and the raw material consumption are increased, and the product cost is greatly increased. If the conversion rate is controlled to be lower, the generation of benzyl dichloride and benzyl trichloride can be controlled, but the load of rectifying and separating benzyl chloride is increased, so that the production capacity is influenced, and the production cost is greatly improved. In order to improve the purity of the product and reduce the production cost, the invention adopts the modern reactive distillation technology to be applied to the production of benzyl chloride, namely, benzyl chloride is produced by a chlorination distillation synthesis method, the second-stage reaction and the third-stage reaction in the reaction of toluene and chlorine are strictly controlled, the concentration of the product benzyl chloride of the first-stage reaction is controlled, the higher the concentration of the benzyl chloride is, the higher the concentrations of the second-stage reaction product benzyl dichloride and the third-stage reaction product benzyl trichloride are, and the lower the concentration of the benzyl chloride is, the lower the concentrations of the benzyl dichloride and the benzyl trichloride are, and in order to ensure that the content of the benzyl chloride in a tower kettle is more than 99 percent, through calculation and specific practice of reaction kinetics, the result shows that the content of the benzyl chloride in a light irradiation reaction section is required to be controlled to be less than. Inthe process of technological operation, the volume ratio of the feeding amount of the toluene and the chlorine to the discharging amount of the benzyl chloride is kept to be 1: 200-220: 1.02-1.23, and meanwhile, the total content of impurity iron in the fed toluene and chlorine is less than 0.01%. Because the chlorination and rectification tower is adopted to synthesize the benzyl chloride, continuous feeding and discharging can be carried out, and continuous production in the whole process is realized, and the continuous production process is convenient to adopt automatic control, so that the production process is stable, the production scale can be greatly improved, the production cost is reduced by about 15 percent, and the purity and the quality of the product are improved.

Different from the common reactive distillation technology applied to the processes of esterification reaction, etherification reaction and the like, in the process of synthesizing benzyl chloride by the chlorination distillation synthesis method, the product is a component which is difficult to volatilize, and the product benzyl chloride can only be discharged from a tower kettle, which brings more difficulty to the design and process control of the reactive distillation tower. The chlorination and rectification tower as the main apparatus for chlorination and rectification combines two unit operations of chlorination reaction and rectification together and consists of tower kettle, stripping section, illumination reaction section, etc. benzyl chloride is discharged from the tower kettle, chlorine gas is fed to the stripping section below the illumination reaction section, and toluene is fed to the upper part of the illumination reaction section.

As the chlorination reaction of the toluene and the chlorine is a gas-liquid heterogeneous reaction, in order to obtain a better gas phase distribution effect and a larger gas-liquid contact area and promotethe reaction, a packed reaction rectifying tower is adopted, and in order to obtain better illumination depth and uniformity of a reaction area, a packing is made of transparent materials, such as glass, transparent plastic, quartz and the like. In order to effectively control the reaction process of chlorination rectification, the position of a reaction section in the tower can be controlled by adjusting the position of a light source and the position of a chlorine gas feeding pipe, and the number of the chlorine gas feeding pipes is 1-6.

The high-purity benzyl chloride with the benzyl chloride content of more than 99 percent is an urgent product in the industries of medicine, pesticide, dye and the like, and lays a foundation for reducing import and providing export.

The invention is further illustrated by the following examples and figures.

FIG. 1 is a schematic diagram of a chlorination rectification column.

FIG. 2 is a schematic diagram of a process flow for synthesizing benzyl chloride by chlorination and rectification.

Referring to fig. 1-2, a chlorination rectification tower 2 is provided with a tower kettle 7, a heater 9 is arranged in the tower kettle 7, an oil furnace heater is adopted here, a stripping section 5 is connected above the tower kettle 7, an illumination reaction section 3 is arranged above the stripping section 5, a light source 13 is arranged on the periphery of the illumination reaction section 3, the light source adopts a mercury lamp or other light sources, the stripping section 5 and the illumination reaction section 3 are filled with a filler 6, the filler 6 is a transparent material, and the filler adopts glass or transparent plastic or quartz.

The production operation process comprises the following steps: firstly, crude distillation is carried out on raw material toluene and a certain amount of benzyl chloride are put into a tower kettle 7 of a chlorination rectification tower 2, a heater 9 is started to heat, cooling water in a condenser 11 is started, the toluene in the tower kettle is evaporated into gas, the gas flows out from a gas discharge pipe 1 at the top of the tower, enters the condenser 11 through a condenser inlet pipe 10 to be condensed into liquid, flows out from a condenser outlet pipe 12, enters an illumination reaction section 3 in the chlorination rectification tower 2 through a toluene feed pipe 14, and when the toluene content in the illumination reaction section 3 reaches over 85.5 percent and the benzyl chloride content in the tower kettle 7 reaches over 99 percent, continuous addition of toluene and chlorine is started. Toluene after crude distillation enters a condenser 11 through a condenser inlet pipe 10 to be condensed into liquid, flows out of a condenser outlet pipe 12, enters an illumination reaction section 3 in a chlorination rectification tower 2 through a toluene inlet pipe 14, chlorine enters a stripping section 5 from a chlorine inlet pipe 4, rises to the illumination reaction section 3, reacts with the toluene under the catalytic action of light to generate benzyl chloride, hydrogen chloride and trace benzyl dichloride, the benzyl chloride and the trace benzyl dichloride flow downwards to enter the stripping section 5 for rectification separation, the temperature of a tower kettle 7 is controlled to be between 175 and 185 ℃, the volume ratio of the feeding amount of the toluene and the chlorine to the discharging amount of the benzyl chloride is controlled to be between 1: chlorine and benzyl chloride and 1: 200-220: 1.02-1.23, the content of the benzyl chloride in the illumination reaction section 3 is controlled to be less than 14.5 percent, and the generated hydrogen chloride gas and unreacted toluene gas flow out from a gas outlet pipe 1 at the top of the tower, enters a condenser 11 through a condenser inlet pipe 10 for condensation, the toluene is condensed into liquid, enters the illumination reaction section 3 from a condenser outlet pipe 12 through a toluene inlet pipe 14, and the toluene at the tower top is totally refluxed. The hydrogen chloride gas is discharged out of the reaction system from an outlet pipe 12 of the condenser, a byproduct of 30% hydrochloric acid is obtained through a tail gas absorption device, the content of benzyl chloride in the product reaches 99.1-99.5%, and the result of the product is 99.3% after the product is inspected by a product quality supervision and inspection center of Jiangsu province.

Claims

1. A production method of benzyl chloride is characterized in that: the method comprises the steps of carrying out chlorination reaction on toluene and chlorine through an illumination reaction section (3) under a photocatalysis condition, and then producing benzyl chloride through a chlorination rectification process of rectification and purification of a stripping section (5), wherein the toluene and chlorine are continuously fed as raw materials, the benzyl chloride is continuously discharged, and the volume ratio of the feeding amount of the toluene and the chlorine to the discharging amount of the benzyl chloride is 1: 200-220: 1.02-1.23.

2. The process for the production of benzyl chloride according to claim 1, characterized in that: the total content of impurity iron in the fed toluene and chlorine is less than 0.01 percent.

3. The process for the production of benzyl chloride according to claim 1, characterized in that: controlling the content of benzyl chloride in the illumination reaction section (3) to be less than 14.5 percent.

4. A chlorination rectification column [ 2]for producing benzyl chloride, characterized in that: it mainly comprises a tower kettle (7), a stripping section (5) and a light reaction section (3); a toluene feeding pipe (14) is positioned at the upper part of the illumination reaction section (3), a benzyl chloride discharging pipe (8) is positioned at the tower bottom (7), and a chlorine feeding pipe (4) is positioned at the stripping section (5); the filler (6) in the chlorination rectification tower (2) is made of transparent materials.

5. The chlorination rectification column [ 2]for producing benzyl chloride according to claim 5, characterized in that: the number of the feed pipes (4) for chlorine is 1-6.

6. The chlorination rectification column [ 2]for producing benzyl chloride according to claim 5, characterized in that: the transparent material of the filler (6) is glass, transparent plastic or quartz.