The Study On Synthesis Of Hexamethyldisilazane

Hexamethyldisilazane(HMDS) is an important reagent of organic silicon,it has been widely used in medicine,semiconductor and rubber,etc.In this paper,many process conditions have been improved on the base of present method,which using hexane as solvent,trimethylchlorosilane(TMS) was ammoniated to HMDS.Many factors that affect the experiment were investigated,the appropriate operating conditions were chosen.Hydrolysis kinetics law of HMDS was studied,the vapor-liquid equilibrium(VLE) data were measured and correlated for relative solution including HMDS.The study has a great direction significance for industrial production and basic research on the synthesis technology of HMDS.The reaction solution of synthesis HMDS contains product HMDS,solvent hexane and byproduct hexamethyldisiloxane(MM),which come from the hydrolysis of TMS and HMDS.A gas chromatogram method was established for the quantitative analysis of HMDS.This method simple,rapid and accurate,and is suitable for the process control.In this study,by using mono-factor experiment and orthogonal design,the optimum technological conditions were found as follows:The molar rata of TMS to hexane 1:1.5,NH₃ rate 0.36L.min^-1,feeding raw speed 15min,reaction temperature 30℃and reaction solution treated with 5℃water.After the reaction finished, continue to NH₃ 30min,ventilation amount 0.12L.min^-1,hold on temperature 40℃. Under the optimum technological conditions,the five times repeat experiments were tested,the results show that the yield of HMDS is 90%or more.Hydrolysis kinetics of HMDS was researched at various pH and temperatures and hydrolysis equation was established.The results showed that HMDS hydrolysis followed the first-order reaction law,the equation is lnK=(-3.466×10³/T) +9.979, which describes the relationship between the reaction coefficient and the reaction temperature.In the rang of 208K-308K,the hydrolysis rate increased with the rise of temperature,the reaction activation energy was 28.81 kJ·mol^-1 when pH=7.The pH was a critical factor for HMDS hydrolysis,HMDS was stably when pH＞11,while the hydrolysis rate accelerated obvious when pH＜9,the results provided basis base for industrial production and farther research.Hexane-HMDS,MM-HMDS and binary systems isobaric(101.30kPa) vapor-liquid equilibrium(VLE) data were measured with a modified Rose still.The saturated vapor pressures of HMDS and hexane at experimental temperatures were measured by static method,and have attained the Antoine parameters of HMDS by regression.The experimental date were tested by area test method and showed the VLE data conform to the demand of thermodynamic consistency.Margules,Van Laar, Wilson and NRTL models were used to correlation the experimental data,the results showed that the system of hexane-MM has higher average relative deviations,and the calculated data from four models accorded well with the experimental data of hexane-HMDS and MM-HMDS systems.This study provide basic base for distillation and purification of HMDS.