Resourceful Treatment And Utilization Of Chlorosilane Residue From Polysilicon Production

During the production process of domestic polysilicon industry, a portion ofchlorosilane residue will be formed inevitably from the quench and distillationprocess of low-temperature hydrogenation exhaust, the distillation process ofsynthesis exhaust，the distillation process of reducing exhaust. The chlorosilaneresidue is mainly composed of chlorosilanes mostly referring to silicon tetrachloride,silicon-based solid impurities and high value-added component such ashexachlorodisilane. At present, most of the domestic polysilicon enterprises use thehydrolysis method to deal with the residue, which will result in a serious waste of rawmaterials, cause a harsh operating environment and require high cost equipment.Some illegal enterprises even discharge the residue directly to the environment, whichwill cause great damage to the environment. Dealing with the chlorosilane residue ofdomestic polysilicon production process effectively has become one of thebottlenecks for the development of polysilicon industry. Foreign research on therecovery of high value-added components such as hexachlorodisilane in chlorosilaneresidue has begun, but domestic research in this area is still in a blank stage. For those,this paper aim to establish a green recovering and purifing process for chlorosilaneresidue, which can recover the high value-added components effectively.The main research work and results are as follows:(1) Problems of chlorosilane residue disposing processes are introduced. Thegeneral composition of chlorosilane residue are analyzed and discussed. A recoveringand purifying process for chlorosilane residue is established by Aspen Plus simulationsoftware. The simulation results show high product recovery, which the purity ofsilicon tetrachloride can reach99.6%and the purity of hexachlorodisilane99.59%. Inaddition, the economic performance evaluation for the process is conducted by usingtotal annual cost and the result show a surprising economic benefits.(2) The optimal operating parameters of the process are determined by using thesensitivity analysis module of Aspen Plus software, and the optimal results are: refluxratio of0.5, feed location of20th plate, distillate rate of2300kg/h for T1; mass refluxrate of2000kg/h, feed location of20th plate, distillate rate of75kg/h for T2; refluxratio of8, feed location of52th plate, bottom rate of130kg/h for T3; mass reflux rate of3500kg/h, feed location of45th plate, distillate rate of20kg/h for T4; reflux ratio of8, feed position of42th stage, bottom rate of100kg/h for T5.(3) The process for recovering and purifying chlorosilane residue is improvingby applying the different pressure thermally coupled distillation. Componentsdistribution, energy consumption and product purity for both conventional distillationprocess and different pressure thermally coupled distillation process are compared.The results showed the seperation effect of differential thermal coupling distillationprocess is close to the conventional distillation process, but the improved process cansave energy by20%and purity of hexachlorodisilane and silicon tetrachloride canreach98.1wt%and99.5wt%respectively.(4) Two kinds of processes for dealing with low-temperature hydrogenationslurry, spray drying method and spin flash drying method, are compared. Advantagesand disadvantages of each process are discussed. The results show that investment andcost of each process are close to each other. The biggest advantage for the spraydrying method is to facilitate continuous production and for the spin flash dryingmethod is the resolution of aluminum chloride volatile.