Epoxidation Of Propylene Over Titanosilicate Zeolite By Using Cumene Hydroperoxide As The Oxidant

In the epoxidation of propylene to produce propylene oxide,the choice of catalyst is highly dependent on the type of oxidant.To meet the concept of green chemistry,the commonly used oxidants are hydrogen peroxide and cumene hydroperoxide.Hydrogen peroxide oxidation method and cumene peroxide co-oxidation method have great application prospects as environment-friendly cleaner production process.Previous research demonstrates that the catalyst for propylene epoxidation needs to have tetracoordinated titanium,surface hydrophobicity and mesoporous structure with cumene hydroperoxide as the oxidant.Currently,silylated mesoporous molecular sieves and amorphous titanium-silicon composites are widely used in industrial plants for this reaction.Compared to mesoporous and amorphous materials,hierarchical TS-1 has better hydrophobicity,hydrothermal stability,thermal stability and wider pore size distribution.In this paper,different titanium-silicon materials were prepared and their catalytic activity has been tested for the epoxidation of propylene using cumene hydroperoxide as an oxidant.Besides,hierarchical TS-1 was used to investigate the influence of reaction conditions.In this paper,titanium-silicon materials such as Ti-MCM-41,Ti-HMS,Ti-SiO₂,HTS-1,uncrystallized HTS-1 precursors and amorphous titanium silicon composite have been prepared by hydrothermal synthesis method.Characterization of the titanium-silicon materials was carried out with XRD,UV-vis,FT-IR and SEM to study the effect of synthesis conditions and modification on its structure.Propylene epoxidation was used as a probe reaction to evaluate the catalytic performance of different catalysts.The hierarchical TS-1synthesized under different conditions was used for the epoxidation of propylene.It was found that Si/Ti molar ratio,polyquaternium-6 amount and the crystallization time all affect the performance of the catalyst.The optimal synthesis conditions were obtained as follows:SiO₂/TiO₂ mole ratio was 33,the mass ratio of polyquaternium-6 to SiO₂ was 3/3,the crystallization time was 4 days.The modification of catalyst includes silylation,acid treatment,alcohol treatment and salt treatment.Silylation modification and alcohol treatment increase the surface hydrophobicity of the catalyst and the metal salt modification reduces the number of acid sites,which all can improve the catalytic performance of the catalyst.The acid treatment can wash away the anatase and the non-framework titanium that covers the active sites of the catalyst,resulting in the improved catalytic performance.Combined with the characterization of the catalyst and the reaction results,it was found that the content of titanium in the catalyst framework,mesoporous volume,the connectivity of pores,surface hydrophobicity and the number of acid sites had great influence on the catalyst performance.The influence of the reaction conditions on the catalytic performance was studied in the batch reactor by using a single variable method.In addition,the mass concentration of epoxy propane in the system was used as an indicator of catalyst performance.The influences of reaction conditions including the amount of catalyst and oxidant,reaction time,temperature and solvent were systematically studied.Under the optimal conditions:reaction temperature80°C,reaction pressure 0.8 MPa,CHP concentration 7%,mass ratio of CHP to catalyst was15:1,reaction time 4 h,the utilization effective of CHP reached 72.75%and the selectivity of PO was 100%.