Dimethyl Carbonate (DMC) is an environmentally friendly chemical intermediate, widely used in methylation, carbonylation, carbonyl methylation and ethoxylation reactions, known as the "new cornerstone" of organic synthesis today. Dimethyl Carbonate is usually produced by transesterification in industry. In the production process, dimethyl carbonate and methanol form azeotrope, which is difficult to be separated by ordinary distillation method.

In recent years, extractive distillation, pressurized distillation, azeotropic distillation and membrane separation have been used to produce high purity Dimethyl Carbonate. Compared with the latter three processes, extractive distillation has the advantages of low energy consumption, simple process and wide selection of solvents, and is the technical trend of energy saving and low consumption separation of Dimethyl carbonate and methanol azeotrope.

Patent CN103159586A discloses a continuous extractive distillation separation method of Dimethyl Carbonate - methanol azeotropic mixture. Under normal pressure, using ethylene glycol as extraction agent, solvent ratio is 1 ~ 3, the separation of Dimethyl Carbonate - methanol mixture in the central tower of the feed, extracting agent on top of the tower feed, reflux ratio is 2, the extraction of the rectifying column of high purity methanol at the top of the column can bottom and dimethyl carbonate and extraction agent, the bottom fraction into solvent recovery tower, reflux ratio is 3, Dimethyl Carbonate is extracted from the top of the tower, and the extractant extracted from the bottom of the tower can be recycled. There is a phase separation zone between ethylene glycol, dimethyl carbonate and methanol, which results in lower separation efficiency and higher energy consumption.

Patent CN105037162A discloses a continuous extractive distillation separation method for Dimethyl Carbonate - methanol azeotropic mixture. N, N - diethylamide, N - formyl morpholine or the mixture of the two in any proportion as the extractant.

Patent CN1367772A discloses a method for the separation of methanol and Dimethyl Carbonate in a distillation column by extractive distillation, and the steam is taken away from the distillation column by side-line distillation. Phenol is used as extraction agent, but the melting point of phenol is high, and it is easy to crystallize at room temperature, resulting in pipe blockage.

To sum up, the existing technology uses traditional organic solvents as extractant to separate Dimethyl Carbonate and methanol by extractive distillation, which has problems of high energy consumption and environmental pollution.

Ionic liquids are composed of anion and anion, and have excellent properties such as non-volatilization, excellent thermal stability, designable structure and low melting point. They are considered as a new kind of green solvent, and have been widely used and studied in chemical reaction, chemical separation and gas treatment in recent years.