Research On Extractive Distillation Of Dimethyldichlorosilane And Methyltrichlorosilane

Dimethyldichlorosilane is the most extensively used methylchlorosilane monomer inthe organosilicon industry.Commonly used industrial process for dimethyldichlorosilaneproduction is the direct synthesis in which methyl chloride react with silicon and amixture of chlorosilanes including methyltrichlorosilane is produced.Dimethyldichlorosilane has a close boiling point with methyltrichlorosilane with thedifference being3.8℃.Conventional distillation requires large equipment investment andenergy consumption to achieve the desired purity which takes up a large part in theoverall cost of organosilicon production.This paper studies the separation and purificationof dimethyldichlorosilane using extractive distillation.This paper combined UNIFAC method and vapor-liquid equilibrium experiments toselect the extractant for methyltrichlorosilane and dimethyldichlorosilane,overcoming theshortcomings of theoretical prediction and experimental selection,which is low accuracyand high workload with relatively narrow solvent range respectively.According to thecharacteristics of extractant selection, multi-index and fuzziness,comprehensiveevaluation method was employed to estimate the overall properties of extractant usingselection, solubility, boiling point, viscosity, toxicity, specific heat capacity and molecularweight as indexes.The final result turned out to be tripropylamine as the best extractant.Under atmospheric pressure this paper carried out vapor-liquid equilibriumexperiments for methyltrichlorosilane,dimethyldichlorosilane and tripropylamine.The equilibrium data was then used for the parameter regression of Wilson model.Thecalculated results of Wilson model fit well with the experimental data and acted as thebasic data for the design and simulation of extractive distillation.Aspen plus was employed to simulate the conventional distillation and extractivedistillation of methyltrichlorosilane and dimethyldichlorosilane using tripropylamine asextractant.For identical separation specification,extractive distillation required lesstheoretical plates and lower reflux ratio, which was of industrial necessity and feasibility.The impact of parameters for the separation effect of extractive distillation wereanalyzed,with the optimization results as followed:the number of theoretical plates was126,the reflux ratio was24,the solvent ratio was1.6,the feed position of extractant andraw material were3and66respectively,the feed temperature of extractant and rawmaterial were70℃and65℃respectively.Batch extractive distillation experiments were carried out using tripropylamine asextractant for methyltrichlorosilane and dimethyldichlorosilane.The experimental datashowed the alteration rules of the temperature and component concentration in the towerwhich summarized the characteristics of batch extractive distillation.Based on theprevious work, sulfolane was added as cosolvent and the impact of solvent proportionbetween sulfolane and tripropylamine was studied.The final results showed that mixedsolvent gave better performance than single solvent in terms of separation property in acertain proportion range and the optimal proportion range was:1~1.2.