Synthesis Of Dimethyldichlorosilane By Catalytic Disproportionation Of Methyltrichlorosilane Over Acid Activated Bentonites

With the rapid development of the organosilicone industry, the organosilicone materials are praised as "monosodium glutamate in the industry" with their kinds of products and widely application. However, methylchlorosilanes are the foundation of the organosilicone industry. And during the Rochow direct process, which technique of production of dimethyldichlorosilane ((CH3)2SiCl2), about 3-15% by-products of methyltrichlorosilane (CH3SiCl3) were produced. For solving the accumulated problem of methyltrichlorosilane, catalytic disproportionation it to produce dimethyldichlorosilane was considered to be the optimum solution. It not only solves the accumulated problem of by-products in dimethyldichlorosilane producing process, but also achieves the cycling of resources.In this master thesis, bentonites which were treated by different concentration of HCl and H2SO4 solution were selected as catalysts. Acid activation treatment could improve their acidic properties, surface areas and porosities. All of the catalysts were characterized by ICP-AES, XRD, N2 Adsorption-desorption and FTIR. It revealed that the chemical composition, textural properties and structure of bentonite changed a lot after acid treatment. With the increasing of acid concentration, the surface areas of bentonites increasing first and decreasing at the end, and the bentonite which treated by 30% H2SO4 exhibited the largest surface areas at 341 m2·g-1. The layer structure of bentonite was collapsed under the high acid concentrations. The acidic properties of bentonites were studied by NH3-TPD and in situ FTIR spectra of pyridine adsorption. The results showed that the acid properties and the amount of acidic sites were depended on the acid concentration in treating. Furthermore, the Bronsted acidic sites could transform into Lewis acidic sites with the thermal pretreatment.The catalytic behaviors of acid activated bentonites were studied in the disproportionation reaction under atmospheric. The effects of acid concentrations and the reaction temperatures on catalytic behavior were investigated. The results demonstrated that the bentonite activated with 30 wt% H2SO4 solution exhibited the excellent activity with 92% conversion of methyltrichlorosilane,45% selectivity toward dimethyldichlorosilane and 41% yield of dimethyldichlorosilane at 673 K under atmospheric pressure. For more investigated, it revealed that the Bronsted acidic sites facilitated the formation of dimethyldichlorosilane, while the coexistence of Lewis and Bronsted acidic sites facilitated the yield to dimethyldichlorosilane.