Research Of Trichlorosilane Disproportionation And Silane Pyrolysis Process In Polysiliocn Production

Recently, more and more attentions are paid to the process of producing polysiliconthrough silane method for its low-energy consumption，high conversion ratio of silaneand non-environmental pollution characteristics. Because the improved Siemensprocess contains a lot of defect like high energy consumption, low utilization ratio oftrichlorosilane and serious environmental pollution, a research of trichlorosilanedisproportionation and silane pyrolysis process in polysiliocn production is studied inthis paper.Two processes employing reactive distillation are proposed, simulated, optimizedand economic evaluated using process simulation software Aspen Plus in study ofsilane production via redistribution of trichlorosilane. Chemical kinetics andequilibrium are taken into account in an equilibrium chemical reaction model inAspen Plus. In the single column process,99.9%purity silane is produced at the topof the column and the top temperature is-87.02℃. The energy consumption is lowbut special cryogenic coolant under-100℃is needed which is very difficult inindustrial production. The optimal results are: overhead pressure of350kPa,rectifying section stage number of10, reactive section stage number of30, strippingsection stage number of15, feed location of12th stage, reflux ratio of39. In thedouble columns process which mainly includes a reactive distillation column and adistillation column,99.9%purity silane is produced at the top of the distillationcolumn. Top temperature of both two columns could achieved to about-32℃byvarying distillation column reflux rate and distillation column overhead pressure, soordinary cryogenic coolant could be used. The duty of two columns process is verylarge because of large recycle rate.For the polysilicon production of silane pyrolysis, a CVD model coupling the silanethermal deposition reaction with the transfer of momentum, mass and energy in thesilane-hydrogen system is established. For a simplified single tube model, CFDsoftware Fluent is firstly used to analyze the influence of inlet-gas velocity, reactiontemperature and reaction pressure on deposition characteristics. Secondly, the profileof flow and temperature in three different whole reactor (12pairs of tubes reactor,24pairs of tubes reactor and novel reactor) models are simulated on the base of single tube model. When the inlet-gas velocity is0.08m/s, the reaction temperature is800℃,reaction pressure is100kPa, deposition rate is uniform with a low energyconsumption and appropriate silane conversion ratio. At upper part of reactors, thereare vortexes. Average velocity distribution in vortex area and vortex area ratio is themost uneven and the greatest in the12pairs of tubes reactor, while in24pairs oftubes reactor, the average velocity distribution in vortex area is the most even. Thetemperature distribution in novel reactor is the most inhomogeneous. There are fourhigh temperature zones near four silicon rods dense areas.