The manufacture of silicon crystals generates a vent gas comprised primarily of hydrogen, chlorosilanes, and hydrogen chloride. Chemical Design, Inc.’s process combines compression, cryogenic condensation, catalytic reaction, distillation, ambient adsorption and cryogenic adsorption to purify the hydrogen gas to 99.9999% for re-use. Mixed chlorosilanes are recovered as a liquid stream suitable for distillation to trichlorosilane for reuse. Silicon tetrachloride can be converted to trichlorosilane. The hydrogen chloride is recovered with high purity. The process is attractive environmentally because there is no waste streams disposal.