The manufacture of silicon crystals generates a vent gas comprised primarily of Hydrogen, Chlorosilanes, and Hydrogen Chloride. By combining compression, cryogenic condensation, catalytic reaction, distillation, ambient adsorption and cryogenic adsorption, Chemical Design, Inc. has developed a process that separates the vent stream into components that are readily recycled. Mixed Chlorosilanes are recovered as a liquid stream suitable for distillation to Trichlorosilane for reuse, and Silicon Tetrachloride which can be converted to Trichlorosilane. Anhydrous Hydrogen Chloride is recovered with high purity, suitable for use in Trichlorosilane production. Recovered Hydrogen typically contains <10 ppm total contaminants and can be recycled to the Trichlorosilane vaporizer without further treatment. For some applications, CDI has achieved <1ppm total contaminants (99.9999% pure Hydrogen). This process is also attractive environmentally because there are no waste streams to dispose of and the opportunity to introduce contamination is minimized because no outside streams such as water and caustic solution are brought into contact with the gas stream. The use of this process with CDI's special grade activated carbon and properly selected materials of construction result in the production of a very high quality electronic grade polycrystalline silicon.