Conversion And Utilization Of By-products In The Direct Synthesis Process Of Methylchlorosilanes

The paper is concerned with a process for the preparation of dimethyldichlorosilane from unavoidable byproducts including low-boiling components with high methyl content, high-boiling residues and methyltrichlorosilane from the direct synthesis of methylchlorosilanes.The paper consists of two parts.Part one: Converting the high-boiling residue to valuable monosilanes through cleavage reaction with HC1.The methylchlorodisilanes can be converted into monosilanes by cleaving Sii bonds in methylchlorodisilanes in the presence of hydrogen chloride. N,N-dimethylaniline is a better catalyst. The dissolvable components of high-boiling residues must be removed by distillation. The proportion of cleavage and total conversion increase with the increasing of reaction temperature and the quantity of catalyst. The flux of hydrogen chloride and length of the fractionator also influences the reaction.The optimum reaction condition was obtained: reaction temperature is 135-145, ratio of high-boiling and hydrogen chloride(wt%) is 1: 0.3-0.35 and ratio of high-boiling in the reactant is 0.75-lwt%. Generally , cleavage ratio is 70%, and for the best can reach to 80.5%. The results of analysis indicates that the produtions of reaction are methyltrichlorosilane, dimethyldichlorosilane and methyldichlorosilane.Part two: Redistributed reactions between methyltrichlorosialne, low-boiling residues and non-cleavable high-boiling components.Methyltrichlorosilane can react with the low-boiling components containing high content of methyl groups and non-cleavable high-boiling components. As a result, methyltrithlorosilane can be converted into dimethyldichlorosilane .AlCla is good as a catalyst for the reaction. The conversion of methyltrichlorosilane and content of dimethyldichlorosilane in the products increase with the increasing of the quantity of AlCla. High reaction temperature and long reaction time were prefer to obtain high conversion of methyltrichlorosilane and high content of dimethyldichlorosilane in the products.The composition of low-boiling residue was determined by GC-MS Methyl content of high-boiling and low-boiling influences the efficiency of the redistribution reaction directly. Trimethylchlorosilane and Me3SiOSiMe3 are beneficial to the redistribution reaction. The optimum reaction condition was obtained: reaction temperature is 300 癈 , reaction time is 2 hours. Reagent includes methyltrithlorosilane39%, high-boiling non-cleavable components27% and low-hoiling components 33%. Under these conditions, the conversion of methyltrichlorosilane is 66.2% and the content of dimethyldichloroislane in the production is 46.4 %.The mechanism of two type reactions were also invested validated and discussed.