Study On The Synthesis Of The Titanium Silicalites Catalyst And Catalytic Performance Of Isobutene Epoxidation

Isobutene is an important chemical raw material,but there are few ways to utilize isobutylene in China.In addition,alkene epoxides have broad market prospects.As a down-stream product of ethylene oxide and propylene oxide,polyurethane has been widely used.The traditional epoxide production process is chlorohydrin process that have many disadvantages.The hydrogen peroxide process for epoxides is worthy of researching from both environmental and economic points of view.This paper introduces the direct epoxidation of isobutene with hydrogen peroxide and titanium silicalite zeolite to efficiently and environmentally product a more promising methyl propylene oxide.Firstly,three kinds of widely used titanium silicalite zeolite were used as catalysts for the epoxidation reaction,including TS-1,Ti-MCM-41 and Ti-β.TS-1 has the best reaction performance among them.The epoxidation reaction had the highest BO selectivity of 95%,and the conversion and utilization of hydrogen peroxide were 38%and 76%,respectively in batch reactor with TS-1.Compare with TS-1,the BO selectivity could reach 98%,the conversion of hydrogen peroxide was less than 5%besides the reactivity was low in epoxidation reaction with Ti-MCM-41.In the reaction using Ti-β,almost all the products were hydrolyzed,and the conversion of hydrogen peroxide was less than 12%.Therefore,the TS-1 was selected as catalyst for further study.Secondly,the effect of TS-1 with different Si/Ti ratios and existence form of Ti species on the reaction performance was investigated.With the increase of Si/Ti ratio,the relative content of extraframework titanium decreases,so the selectivity of BO gradually increases.However,the absolute content of titanium in the zeolite will decrease,so the reactivity of epoxidation reaction decreases gradually.Therefore,it is the key to improving performance how to increase the framework titanium in low Si/Ti ratio.Furthermore,the TS-1 zeolite with high framework titanium content was synthesized by adding starch additives in the process of synthesis.The selectivity of BO was 65%and the conversion and utilization of hydrogen peroxide were 64%and 43%respectively in i-butene epoxidation over this TS-1 zeolites.The effects of different reaction conditions on the reaction performance were investigated.The results showed that the optimum reaction conditions were feeding the synthesized TS-1（0.3 g）and H₂O₂/methanol solution（0.5 mol/L,25 ml）,and heated material at 45 ^oC for 1 h.Finally,the preformed catalyst was produced and applied to fixed bed reaction.The performance of the TS-1 catalyst was optimized in the iso-butene epoxidation reaction and transition and amplification were accomplished from batch process to continuous process.The optimum reaction conditions were as follows:loading catalyst of 4 g;H₂O₂/methanol solution of 0.5 mol/L;temperature of 40 ^oC;pressure,1 MPa;WHSV of 1-butene of 2 h^-1;molar ratio of i-butene:H₂O₂ of 2:1.The conversion of isobutene was 40%,the selectivity of isobutylene oxide was 95%,and the conversion and utilization of hydrogen peroxide were 90%and 95%,respectively on this condition.Then,the reaction performance is basically stable in the 72 hours of continuous reaction.