Study On Analysis Of The Low-Boiling Residues Of Methylchlorosilanes And Extraction Of Tetramethylsilane

In the organic silicon industry,methylchlorosilane is the most important monomer in preparing organosilicon polymer,which accounts for more than 90%of all organicsilicon monomers.It is synthesized through the direct process in the industry,i.e.,the direct reaction of methyl chloride and silicon under heat condition through copper catalyst.Three classes of components including the important methylchlorosilanes,low-boiling residues(LBR) and high-boiling residues are distilled from the products of the direct reaction.The boiling point of LBR is less than 40℃and it accounts for 4～5%of all the products.Wide varieties of LBR and narrow range of boiling points make LBR be difficult to be applied.Heretofore, there is no an economic and effective approach to treat LBR.It adopts combustion method to yield gas phase silica aerogel abroad,while the domestic technology is immature,and the discharge of LBR will result in serious environment pollution and resource waste.At present,with the expansion of production scale of methylchlorosilane monomers,the LBR amount is considerable,reaching to about 4.8～5kt a year,which contains about 40～75%tetramethylsilane(TMS).High-purity TMS(≥99%wt) can be used as blowing agent,fuel additive agent,reference reagent of nuclear magnetic resonance and reagent gas of chemical ionization mass spectrometry.Ultrapure TMS(≥99.99%wt) can be used to manufacture semiconductor materials,low-k materials,chemical vapor deposition organosilicon materials,plasma-polymerized organosilicon layers and etc.The boiling point of TMS is close to the impurities',so it is impossible to take the rectification method to extract TMS from LBR.Therefore,it is meaningful to explore a newly economic and effective way.This paper will research the analysis of LBR and the extraction of TMS.The methods and results were as follows:1.According to the polarities and physicochemical properties of LBR,16 components of them from direct synthesis process,including the most important difficult-to-separate group of dimethylchlorosilane,2-methyl-2-butene and methyldichlorosilane,were well separated on a DB-624 capillary column.Effect of column temperature and carrier gas flow rate on resolution of LBR was investigated.It was confirmed that,low column temperature and carrier gas flow rate were favorable to the separation.Under the optimal conditions,16 LBR components were qualitatively analyzed by gas chromatography-mass spectra(GC-MS) and gas chromatography(GC) on the basis of retention time and molecular structure of LBR constituents.Then they were quantitatively analyzed by GC with the flame ionization detector(FID),using peak area normalization method.2.After the removal of components containing Si-Cl from LBR by hydrolysis distillation,VLBR was obtained,in which TMS was the dominative ingredient and small molecular olefins and alkanes were the major impurity.According to the sieving principle of molecular sieves,HZSM-5 was employed to clarify TMS by adsorption distillation approach. In this approach,HZSM-5 could adsorb the impurities completely except TMS,leaving behind high-purity TMS.Moreover,the separation condition,including feed ratio,heating rate and adsorption temperature,had great influence on the molecular sieve's refining effects.The slower the heating rate was,the better the purification was,but the worse the separation efficiency was. Different adsorption temperature made the material acting with adsorbent by the means of gas or liquid state,called gas-solid adsorption or liquid-solid adsorption respectively.The results indicated that,the gas-solid adsorption was better than the liquid-solid adsorption, and its optimized conditions were as follows:ambient temperature:≤25℃,atmospheric pressure,amount of HZSM-5:76g,HZSM-5 activation conditions:at 380℃in 4h,amount of material(TMS40.24%):15.2g,adsorption temperature:40℃,heating temperature:from 20℃to 27℃(material temperature,staying 45min),finally to 40℃.Under the optimized conditions,99.99%TMS were obtained,and its yield was 92.04%.The used molecular sieve could be regenerated at 460℃for 4h and was reused there times with the same refining effects,but the yield decreased by about 10%successively.In a word,qualitative-and-quantitative method for the LBR in this paper is simple,fast and efficient,and is suitable for rapid analysis and separation of production control for the methylchlorosilanes.The HZSM-5 adsorption method extracting TMS from LBR is economic and valid,and it provides practical technology not only for the effective use of LBR,but also for the fabrication of the high-purity TMS.3.The originality in this thesis:HZSM-5 was applied to clarify TMS using adsorption distillation approach.HZSM-5 could adsorb all the impurities but TMS,with high-purity TMS(99.99%) remained.The used molecular sieve could be recycled for many times,thus economic and environmental friendly.