Organosilicon monomer DMC (Dimethyl Cyclosiloxane Mixture) is the core intermediate in the organosilicon industrial chain, mainly composed of octamethylcyclotetrasiloxane (D4), hexamethylcyclotrisiloxane (D3) and decamethylcyclopentasiloxane (D5), among which D4 accounts for 60%–80%. As a key link connecting upstream raw materials and downstream deep-processing products, DMC is a colorless and transparent liquid at room temperature, with low viscosity, high volatility, excellent thermal stability and chemical inertness. The bond energy of Si–O bond in its molecular structure is as high as 452 kJ/mol, much higher than that of C–C bond, enabling it to maintain structural stability in extreme environments such as high temperature, strong acid and strong alkali. It is the core raw material for preparing various organosilicon products such as silicone oil, silicone rubber and silicone resin, and its synthesis process and technical level directly determine the development quality of the organosilicon industry.
The core synthesis process of DMC takes "chlorosilane hydrolysis-condensation—cracking—rectification" as the main line, mainly adopting the combined route of equilibrium method and cracking method. The core raw materials are dimethyldichlorosilane, metallic silicon and methyl chloride, among which the cost of metallic silicon and methyl chloride accounts for more than 60% of the total cost of DMC. The specific process is as follows: first, dimethyldichlorosilane is generated by the reaction of silicon powder and methyl chloride, then silanol is generated by hydrolysis reaction, and silanol further undergoes condensation and cyclization reactions to form crude DMC, which is finally purified by rectification to remove impurities to obtain high-purity finished products. The traditional process has shortcomings such as low reaction efficiency, many by-products and high energy consumption, and the content of D3/D4 cyclomers is difficult to control accurately, which is difficult to meet the needs of high-end applications.
In recent years, DMC synthesis technology has been continuously upgraded, focusing on three core directions: purity improvement, green energy saving and structural controllability. In the field of catalysts, enterprises have gradually replaced traditional acid catalysis with green alkali catalysis, reducing equipment corrosion and pollutant emissions, and increasing the reaction conversion rate to more than 99%; in the rectification process, the combination of continuous rectification and membrane separation technology is adopted to increase the purity of DMC to more than 99.95%, meeting the needs of high-end scenarios such as semiconductors and medical care. In addition, leading enterprises have realized precise control of the proportion of D3/D4/D5 cyclomers by optimizing process parameters, adapting to the polymerization needs of different downstream products, and promoted solvent-free production processes, with the comprehensive VOC removal efficiency reaching more than 95%, complying with environmental protection policy requirements.
At present, domestic DMC synthesis technology has basically achieved independent control, with the number of industry-related patents increasing by more than 12% annually, and technical barriers gradually being built. Leading enterprises have significantly improved the yield of high-purity products through technological breakthroughs such as catalyst optimization and cyclomer separation and purification, and accelerated the layout of environmentally friendly products with low D3/D4 cyclomer content to meet the requirements of EU REACH regulations and high-end customer certification. In the future, with the popularization of continuous production processes and the development of new catalysts, DMC production will move towards a more efficient, greener and more precise direction, further reducing production costs, improving product competitiveness, and providing core support for the high-end transformation of the organosilicon industry.