Acetic anhydride, also known as acetic anhydride, is an important chemical raw material and acetylating agent, which has a wide range of uses in medicine, dyes, spices, pesticides and other fields. At present, the industrial production of acetic anhydride in China mainly includes carbonyl synthesis and acetic acid cracking, with a total market circulation capacity of about 700,000 tons, of which carbonyl synthesis process capacity is 150,000 tons, and the others are acetic acid cracking process.
In the carbonyl synthesis process, methyl acetate is formed by methanol and acetic acid under the action of catalyst, and then methyl acetate is carbonylated with methanol and carbon monoxide in the presence of iodomethane and rhodium catalyst to form acetic anhydride and co-produce acetic acid. The reaction equation is:
Carbonyl synthesis process has the advantages of low energy consumption, less waste discharge, stable operation and excellent comprehensive cost, but the process is relatively complex, high operation technical requirements, large investment in production equipment, so there are few devices using this production process in China.
Acetic acid cracking method, also known as ketene method, first acetic acid in 700-750℃, 10-20kPa pressure and triethyl phosphate as a catalyst under the condition of cracking dehydration to produce ketene, and then liquid acetic acid absorption of ketene to generate acetic anhydride, after distillation purification to obtain finished acetic anhydride. The reaction equation is:
Acetic acid cracking process consumes relatively high energy and discharges more three wastes. However, due to mature technology and relatively small equipment investment, all new installations in China have adopted this process in recent years.
At present, the production capacity of acetic anhydride cracking method accounts for 79% of the total production capacity in China, and the new production capacity planned in the later stage is basically this process. In the fully competitive market environment, the industry price basically fluctuates around the cost line of cracking process. The raw material of this process is acetic acid, and its production cost is directly linked to the price of acetic acid. In recent years, due to the great fluctuation of acetic acid price, the cost of cracking method also fluctuates greatly. By comparing the price trend of acetic anhydride and acetic acid in the past two years, it can be seen that the price trend of domestic acetic anhydride is basically consistent with the price of acetic acid.
