| Methyl propylene oxide(MPO)is an important organic intermediate,which has a large application market in the synthesis and production of polyether and medicine.At present,there is no report of large-scale industrial production of MPO.It can only be synthesized in small batches by chlorohydrin method.However,the chlorohydrin process is polluted greatly,has many by-products and poor atomic economy,which does not meet the requirements of modern green chemical industry.So it is necessary to find a feasible green synthesis process of MPO.One-step epoxidation of olefins with H2O2 to obtain epoxides has the advantages of short process,less pollution,green economy and environmental protection,which is the focus of research in the field of olefin epoxidation.In this paper,the green process of preparing MPO by direct epoxidation of isobutene with H2O2 as oxygen source was studied.The representative heteropoly acid catalytic system and TS-1 catalytic system in homogeneous and heterogeneous catalysts were explored,and the epoxidation effect of isobutene was also studied.The modification and optimization of titanium silicate molecular sieves with different particle sizes were studied,and the possibility of substituting nano TS-1 for micro TS-1 was discussed to reduce the cost of catalyst.In the study of Heteropoly acid/H2O2 catalytic system,heteropoly acids such as phosphotungstic acid,phospho molybdic acid,silicotungstic acid and phosphotungstic acid with various phase transfer catalysts were prepared.The best heteropoly acid catalyst was confirmed by systematic experiments as peroxyphosphotungstic acid/hexadecyltrimethylammonium chloride composite catalyst.The technological conditions of epoxidation reaction were determined by single factor,variable and orthogonal experiment.Under the optimum conditions,the molar ratio of C4H8 to H2O2 is 4:1,the amount of catalyst is 0.35 g,Na2HPO4 is 0.4 g,methyl tert-butyl ether is 1.0 g,DMF20 g,temperature is 85℃,reaction time is 2.5 h,the yield of methyl propylene oxide is 51.23%,the selectivity of reaction is 86.33%,the conversion rate of H2O2 is 97.12%,and the effective utilization rate of H2O2 is 61.10%.The results showed that the heteropoly acid/H2O2/phase transfer catalyst system had a certain catalytic effect on the epoxidation reaction,but the reaction temperature was high,H2O2 and methyl propylene oxide decomposed easily at high temperature,and the catalyst was acidic,which further made the hydrolysis of methyl propylene oxide;at the same time,the catalyst was dissolved or suspended in solvents,so it was difficult to recycle.Catalytic epoxidation of isobutene with TS-1/H2O2 was studied.Two different sieves TS-1:nano-TS-1(a)and micro-TS-1(b)were selected to catalyze the epoxidation of isobutene.Two kinds of TS-1 were characterized by infrared spectroscopy,scanning electron microscopy,ICP element analysis,specific surface area and porosity analysis(BET).It was found that nano-TS-1(a)was higher than micro-TS-1(b)in skeleton titanium content,relative crystallinity,mesoporous specific surface area and pore size.The bulk catalytic properties of these two different sizes of Ti-Si zeolites were also systematically studied.The results showed that the optimum reaction conditions were as follows:the molar ratio of C4H8 to H2O2 was 3:1,the amount of catalyst was 0.35g,NaHCO3 was 0.25g,methyl tert-butyl ether was 2.0 g,CH3OH2O g,temperature was 55℃,and reaction time was 2.5 h.The yield of methyl propylene oxide in TS-1(a)catalytic epoxidation reaction was 96.2%,and TS-1 catalyst was easy to be recycled and reused.The recovery rate was over 89%.The catalytic activity of TS-1 remained basically unchanged when reused.The yield of methyl propylene oxide catalyzed by TS-1(b)was only 24.18%.The preparation of nano-sized titanium-silicon molecular sieves is expensive and requires high production technology,while micron-sized titanium-silicon molecular sieves can be prepared by cheap raw materials,and the production process requirements are relatively low.If the catalytic performance of micron TS-1(b)is improved and nano TS-1(a)is replaced,the cost of catalyst will be greatly reduced.Therefore,the optimization of TS-1(b)modification in micron scale was studied experimentally and compared with TS-1(a).TS-1(a)and TS-1(b)were modified by silane reagent,acid and organic base,and characterized by infrared spectroscopy,UV-vis,SEM,specific surface area and porosity analysis(BET).The optimum modification conditions were found by comparing the changes of catalytic performance through epoxidation experiments.It was found that TS-1(b)was modified by ethanolamine after 48 hours in oven at 230℃and the concentration of ethanolamine solution was 0.1 mol/L.The yield,selectivity,conversion and effective utilization of H2O2 were 91.56%,97.96%,98.04%and 95.34%respectively.Compared with the untreated TS-1(b)epoxy product,the yield and selectivity of the reaction were increased by 67%and 3%.Compared with nanometer TS-1(a),the yield of epoxy product is only 4.7%,and other indicators are close.Experiments show that nano-TS-1(a)with excellent performance is difficult to continuously improve its catalytic performance through modification optimization,while micro-TS-1(b)with poor performance can greatly improve its catalytic performance by appropriate modification methods such as organic alkali modification. |
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