Dimethyl carbonate (DMC) is an important raw material for the production of chemicals, which is widely used in synthetic fibers, plastics, pesticides, pharmaceuticals, fuels and other fields. In this paper, we will introduce the manufacturing methods of dimethyl carbonate, including phosgene gas method, ester exchange method, and methanol oxidation carbonylation method.
1. Phosgene method
Phosgene method is a method of generating dimethyl carbonate by reacting phosgene and methanol as raw materials at low temperature. The reaction principle of this method is as follows:
COCl2 + 2CH3OH → (COOCH3)2 + 2HCl
This method has the advantages of simple production process, easy to obtain raw materials, high yield, etc. However, the phosgene produced in the production process is highly toxic, flammable and explosive, which requires high requirements for the production equipments and operation conditions, and makes it difficult to produce safely and the environmental protection and treatment costs are high.
2. Ester exchange method
Ester exchange method is a method that takes diethyl carbonate and methanol as raw materials and carries out ester exchange reaction under the action of catalyst to generate dimethyl carbonate and ethanol. The reaction principle of this method is as follows:
(COOC2H5)2 + 2CH3OH → (COOCH3)2 + 2C2H5OH
The ester exchange method has the advantages of easy availability of raw materials, mild reaction conditions, and less difficulty in safe production, etc. However, the selection and use of catalysts have a large impact on the reaction yield and product quality, and the process conditions need to be strictly controlled.
3. Methanol oxidative carbonylation method
Methanol oxidative carbonylation method is a method of generating dimethyl carbonate by oxidative carbonylation reaction with methanol, carbon monoxide and oxygen as raw materials under the action of catalyst. The reaction principle of this method is as follows:
2CH3OH + CO + 1/2O2 → (COOCH3)2 + H2O
The methanol oxidative carbonylation method has the advantages of easy availability of raw materials, mild reaction conditions, and environmental friendliness, and it is one of the methods that have been researched more at home and abroad. However, the method needs to solve the problems of catalyst activity, selectivity and lifetime, as well as the problems of removing the by-products and water produced during the reaction.
Besides the above three methods, some other methods such as urea method and propylene carbonate method can also be used to manufacture dimethyl carbonate, but due to the limitations of yield, cost and other factors, it is less applied at present.
No matter which method is used to manufacture dimethyl carbonate, the reaction conditions and raw material quality need to be strictly controlled to ensure product quality and production safety. Meanwhile, since dimethyl carbonate is a toxic and harmful chemical, the production process needs to strengthen environmental protection control and the treatment of waste gas and water to protect the environment and the health of personnel.
