Adsorptive separation of high purity tetramethylsilane on zeolites from low-boiling residues of dimethyldichlorosilane synthesis

Abstract

Tetramethylsilane (TMS) can be used as an appropriate precursor of fabricating low-k SiCNH barrier layer for ultra large-scale integrated circuits manufacturing. In this work, an efficient and cost-effective method was developed to prepare high valued TMS with more than 99.99 wt% purity via adsorptive separation on zeolite ZSM-5 and 13X adsorbents from the low boiling residues (LBR) of the industrial direct synthesis of dimethyldichlorosilane. The main impurities in LBR mixtures relative to TMS are isopentane and isopentenes (2-methyl-1-butene and 2-methyl-2-butene). The interaction between the molecules and zeolite framework was investigated by breakthrough experiment to understand the adsorption behavior. The adsorption capacity was also determined to evaluate the suitability of the zeolite adsorbents. It was manifested that ZSM-5 zeolite preferentially adsorbed isopentane due to the confinement effect between gas molecule and the zeolite (van der Waals interaction) since the molecular kinetic diameter of isopentane fits well with the pore size of ZSM-5. The selective adsorption of unsaturated isopentenes on zeolite 13X was also observed, which can be explained by the cation-π interaction between the CC double bond and the exchangeable cations of the Al-rich 13X with Brønsted acid sites. Furthermore, the influence of the temperature on the adsorption performance was investigated at various temperatures of 303 K, 313 K and 323 K. An increase in the temperature decreased the time to reach the breakthrough point and the corresponding adsorption capacity. An adsorptive separation experiment was carried out on a binary-adsorbent bed with ZSM-5 and 13X zeolites that can significantly increase the separation of TMS from the LBR mixtures. Finally, high valued TMS with the purity of 99.998 wt% was obtained successfully. The reusability of the zeolite adsorbents was also performed on the binary-adsorbent bed, showing the adsorbents can be fully regenerated for adsorption-regeneration cycling use. Thus, it offers an efficient and great potential route for the separation of high purity TMS from the LBR mixtures for industrial applications.