Dimethyl carbonate is an environmentally friendly raw material, which can meet the requirements of current clean process, conform to the strategic trend of sustainable development, and has many excellent properties, so its synthesis process has attracted more and more attention. There are four existing DMC production processes, among which oxidative carbonylation is an earlier and more mature process, and its product price is also lower, while transesterification is a higher product price, which was once considered to be an uneconomical process. In recent years, with the enhancement of environmental awareness, there are more and more researches on transesterification process, and big companies such as Shell even regard it as a typical example of sustainable development planning and developing green environmental protection technology. It is said that the newly developed transesterification process can obviously reduce investment and cost. According to economic analysis, the price of DMC products in the process of oxidative carbonylation is restricted by the prices of methanol and carbon monoxide, and the prices of ethylene oxide, ethylene glycol and steam are restricted by the price of DMC products in the process of transesterification. Therefore, the joint construction of ethylene oxide and dimethyl carbonate production bases has potential economic benefits. At present, the demand for dimethyl carbonate in China is still in short supply, which is a good opportunity for development and construction.
The initial production method of DMC was phosgene method, and 19 18 was successfully developed. However, the toxicity and corrosiveness of phosgene limit the application of this method, especially with the increasing attention to environmental protection all over the world, phosgene method has been eliminated. Since 1980s, the research on the production technology of dimethyl carbonate has attracted wide attention. According to the statistics of Michael A.Pacheco and Christopher L.Marshall, since 1980- 1996, there have been more than 200 patents on DMC production technology [2]. In the early 1980s, Italian EniChem Company realized the industrialization of oxidative carbonylation of methanol to DMC with CuCl as catalyst, which was the first industrialized non-phosgene synthesis process and the most widely used process. The disadvantage of this process is that the catalyst deactivation is serious at high conversion rate, so its one-way conversion rate is only 20%. In 1990s, the research of DMC synthesis technology developed rapidly: Ube in Japan improved the oxidative carbonylation process of methanol of EniChem Company, and chose NO as the catalyst, thus avoiding the deactivation of the catalyst, making the conversion rate almost reach 100%, and it has been industrialized; Texaco Company of the United States has developed a process in which ethylene oxide reacts with carbon dioxide to produce ethylene carbonate, and then transesterification with methanol to produce DMC. Ethylene glycol was co-produced by this process, and 1992 was industrialized. This method is considered to have low yield and high production cost. The annual output of DMC must be higher than 55 kt, and its investment and cost can compete with other methods. In addition, there is a new process, namely methanolysis of urea, which can reduce the cost if combined with urea production, and this process is expected to be commercialized [7~ 1 1]. Table 3 gives the composition of the operating procedures of the above four processes to compare their complexity. Table 3 DMC process complexity comparison process methanol oxidative carbonylation copper chloride nitric oxide transesterification (ethylene carbonate) urea methanol decomposition detailed steps feed gas compression feed gas compression methanol evaporation urea dissolution oxidative carbonylation oxidation carbonylation transesterification methanol decomposition reaction gas recovery * * * Boiling neptunium * * * Using carbon dioxide to remove methyl nitrous acid from boiling distillate to generate methanol, recover ammonia gas, recover catalyst, treat methanol, recover methanol, recover DMC, recover DMC and purify DMC. In recent years, the key technologies of DMC research and development are still oxidative carbonylation and transesterification. Typical oxidative carbonylation methods include ENI liquid phase method, Dow gas phase method and UBE atmospheric gas phase method, while the usual transesterification process is the transesterification of ethylene carbonate or propylene carbonate with methanol to obtain DMC. It is reported that Shell Company has recently developed a new process to produce dimethyl carbonate from propylene oxide and dimethyl carbonate to produce dimethyl carbonate, which can obviously reduce investment and operating costs. Compared with the oxidative carbonylation process, the production cost per ton of carbonate is reduced by 300 dollars. The process uses greenhouse gas carbon dioxide, which is an environment-friendly process and can reduce the carbide emission of 10%. China has also invested a lot of energy in the research of transesterification process, but most of them are concentrated in the laboratory and pilot stage. Only by further simplifying the process and optimizing the catalyst can industrialization be realized [12~ 17].