Thermodynamic Study on SiCl₄ Hydrogenation System in Siemens Process

Abstract

The study of fifteen possible chemical reaction in the SiCl₄ hydrogenation system in Siemens process based on the thermodynamic data for related pure compositions are reported in this paper. Curves of ΔG_m^θ-T for the 15 chemical reactions in the system have been fitted. The five independent reactions in the process have also been obtained and the relations of Κ_p^θ and temperature have been fitted. Furthermore, diagrams of the equilibrium gas phase composition versus temperature under pressures of 1 atm, 3 atm, and 5 atm and feed mole ratios (χ_H2 / χ_SiCl4) of 2 : 1, 3 : 1, and 4 : 1 are present herein. Finally, the influencing factors (such as temperature, pressure and the feeding molar ratio) on the conversion ratio from SiCl₄ to SiHCl₃ have been studied. Diagrams of the η-conversion ratio are presented as a function of temperature, pressure and feed mole ratio, respectively. The optimum operation parameters in the actual production are determined by thermodynamic and kinetic studies. The results show that the conditions of 1100°C, 3 atm and feed mole ratio (χH₂ / xSiCl₄) of 4 : 1 are most preferable. Under these conditions, the conversion ratio from SiCl₄ to SiHCl₃ is 24.81%, contrary to the less than 20% in actual production.