What are the main process steps for the production of propylene oxide by the chlorohydrin method?

Propylene oxide (Epichlorohydrin) is an important basic chemical raw material, which is widely used in the production of epoxy resin, polyurethane, foam plastic and coating. The chlorohydrin method is one of the main processes for the production of propylene oxide, which is favored by the industry because of its mature process, simple equipment and high conversion rate. In this paper, the main process steps of producing propylene oxide by chlorohydrin method will be analyzed in detail, and its key technology and process advantages will be discussed.

Chlorohydrin production of propylene oxide process overview

Chlorohydrin method is a classic method of propylene oxide production, the core reaction is through the oxidation of propylene chloride in acidic conditions, the formation of propylene oxide. Compared with other methods, the chlorohydrin method has the advantages of simple process, low equipment investment and low production cost. With the advancement of technology and the improvement of environmental protection requirements, the chlorohydrin method still occupies an important position in industrial applications.

Synthesis of allyl chloride

Allyl chloride (Chloroprene) is a key intermediate in the production of propylene oxide by chlorohydrin method. The synthesis process usually uses the addition reaction of propylene and chlorine under specific conditions to generate allyl chloride and by-products. The following are the main steps in the synthesis of allyl chloride:

1. Raw material ratio and reaction conditions: Propylene and chlorine are mixed in a certain proportion, usually under liquid or gas phase conditions. The reaction temperature is controlled at 40-60 ° C., and the pressure is normal or pressurized to improve the reaction efficiency.

2. Use of a catalyst: In order to accelerate the reaction rate, a catalyst such as hydrogen peroxide or manganese dioxide is usually added. The catalyst can promote the addition reaction of chlorine and propylene and increase the production rate of chloropropene.

3. Separation and purification: The mixture after the reaction needs to be separated to remove unreacted propylene and chlorine, as well as by-products such as hydrochloric acid. Through distillation or other separation techniques, high purity chloropropene is obtained in preparation for subsequent reactions.

oxidative cyclization reaction

Oxidative cyclization of chloropropene under acidic conditions is the core step in the production of propylene oxide. This reaction usually uses concentrated sulfuric acid as a catalyst, chloropropene in an acidic environment cyclization reaction, the formation of propylene oxide. Specific steps are as follows:

1. Reaction medium and conditions: Chloropropene reacts with hydrogen peroxide or oxygen under the catalysis of concentrated sulfuric acid. The reaction temperature is controlled at 0-50 ° C., and the pressure is normal pressure or slight positive pressure to ensure efficient reaction.

2. The role of catalyst: concentrated sulfuric acid is not only used as a catalyst, but also can absorb the water generated during the reaction, and promote the reaction to the direction of propylene oxide. The presence of sulfuric acid helps to maintain the acidic environment of the reaction and promotes completion of the cyclization reaction.

3. The mechanism of the cyclization reaction: under acidic conditions, the electrophilic addition and elimination reaction of chloropropene occurs to form an epoxy ring. The reaction mechanism involves the generation and capture of the carbon positive ion intermediate, ensuring the efficient generation of propylene oxide.

Post-processing and distillation

After the oxidative cyclization reaction is completed, subsequent processing is required to obtain high-purity propylene oxide:

1. Neutralization and Separation: The reaction mixture needs to be neutralized to remove excess acid, followed by separation of propylene oxide and other by-products by distillation or extraction.

2. Distillation purification: through multiple distillation, further removal of impurities and low boiling point components, to obtain high purity propylene oxide products.

3. Disposal of impurities: Small amounts of by-products such as water and salts may be formed during the reaction. These impurities need to be removed by filtration, distillation and other methods to ensure the quality of the product.

Process Advantages and Challenges

The main process steps for the production of propylene oxide by chlorohydrin include the synthesis of chloropropene, oxidative cyclization reaction, post-treatment and distillation. The biggest advantage of this process is simple process, low equipment investment and low production cost. The chlorohydrin process also faces environmental pressure, such as how to treat chlorine-containing by-products and wastewater. In the future, with the improvement of environmental protection requirements, the process optimization and green development of chlorohydrin method will be particularly important.

Conclusion

The production of propylene oxide by chlorohydrin has become an important industrial production method because of its unique process characteristics and high production efficiency. From the synthesis of chloropropene to oxidative cyclization, to post-treatment and distillation, each step is essential. In the future, with the advancement of technology and the improvement of environmental protection requirements, the chlorohydrin method will be continuously optimized to provide more efficient and environmentally friendly solutions for the production of propylene oxide.