Preparation Of Ti-doped Phenyl-bridged Ordered Mesoporous Organosilicon And Its Application In Alkene Epoxidation

Propylene oxide is an important organic intermediate,which is widely used in petrochemical,pharmaceutical,electronics and polymer materials and other fields.Olefin epoxidation is an important way to prepare epoxy compounds.The existing production methods include chlorohydrin process,co-oxidation method and hydrogen peroxide oxidation method.The development of highly selective and easy recovery catalysts is still the key issue to the establishment of efficient epoxidation systems for olefins.This thesis is based on the previous work of our research group,the preparation conditions of titanium-doped phenyl-bridged ordered mesoporous organosilicon(Ti-PMOs)were further optimized.The performance and reusability of these catalysts were investigated in the epoxidation of cyclohexene,and then Ti-PMOs were applied to the propylene epoxidation reaction with t-butyl hydroperoxide as oxygen source.The reaction conditions were optimized and the structure-activity relationship was explored to provide research accumulation in the development of new catalytic system for propylene epoxidation.Primarily,Ti-PMOs catalysts were prepared by one-step hydrothermal synthesis method under acidic conditions.Silane modification of Ti-PMOs was carried out in the following steps.In order to match the hydrolysis rate of titanium source tetrabutyl titanate(TBOT)and silicon source,the effects of the type and amount of hydrolysis inhibitor on the structure of Ti-PMOs were investigated.The catalysts were characterized by the techniques of FT-IR,UV-Vis,N2 physical adsorption and so on.The results showed that the highest Ti content of Ti-PMOs catalyst was obtained when we used H2O2 as hydrolysis inhibitor with the amount of n(TBOT): n(H2O2)=0.02:12 relative to acetylacetone.The catalyst was applied to epoxidation of cyclohexene with TBHP as oxidant.And the reaction was carried out at 80°C for 5 hours with molar ratio of cyclohexene to TBHP 2:1.The 37.4% of cyclohexene conversion was obtained,and the selectivity of cyclohexene oxide reched 100%.Secondly,in order to explore the reusability of Ti-PMOs catalyst,the catalyst was recovered twice by solvent washing and filtration.The results showed that the content of active titanium in the skeleton after the first recovery was lost significantly,but the content of active titanium after the second recovery was almost unchanged.The recovered catalyst was applied to the cyclohexene epoxy reaction.As a result,the conversion rate of cyclohexene after two recycling was decreased to 25.9% and 24.8%,respectively,and the selectivity of cyclohexane oxide was separately decreased to 97.7% and 93.0%.The reaction produced few amount of by-products of cyclohexanone and cyclohexanedione simultaneously.Finally,in order to further clarify the structural characteristics of the catalyst,NH3-TPD and micro-raman spectra were used to compare the forms and distribution of titanium in Ti-SBA-15,Ti-PMOs and Ti-PMOs-S(silanization).At the same time,the above catalysts were used in the epoxidation reaction of propylene with TBHP as the oxygen source.The results showed that the addition of the organosilicon source and futher silanization were beneficial to the formation of the active tetra-coordinated titanium,thus improving the activity of the catalyst.The effects of solvent type,reaction temperature,olefin ratio and reaction time on the epoxidation of propylene were investigated by using Ti-PMOs-S as catalyst.The results showed that Ti-PMOs-S catalyzed the epoxidation of propylene with acetonitrile as solvent and molar ratio of propylene to TBHP 6.5: 1 at 120 ? for 2h,the conversion of TBHP was 95.8%,the selectivity of propylene oxide and tertiary butanol(based on TBHP)were 78.8% and 95.9%,respectively.