Aerosol-assisted Synthesis Of TS-1 Zeolites And Its Catalytic Performance In Gas-phase Propylene Epoxidation

Titanium silicate-1（TS-1）exhibits excellent catalytic performance in propylene epoxidation.The liquid-phase propylene epoxidation technology（HPPO）has been commercialized with hydrogen peroxide as the oxidant,but there are still some problems such as large separation energy consumption and long process flow.Therefore,the study on the gas-phase epoxidation of propylene using gaseous H₂O₂ directly synthesize from H₂/O₂ has attracted extensive attention.The synthesis of the efficient TS-1 catalysts for gas-phase epoxidation of propylene is highly required.In this thesis,TS-1 zeolite was synthesized by an aerosol-assisted hydrothermal crystallization method.By optimizing the synthesis conditions,the obtained TS-1 zeolite exhibited good catalytic performance in the gas-phase propylene epoxidation.Then the TS-1zeolite was treated with a mixed solution of sodium hydroxide and triton X-100.The post treatment further improved the catalytic performance of the TS-1 zeolite.Firstly,TS-1 zeolite was synthesized by an aerosol-assisted hydrothermal crystallization.The synthesis conditions were optimized systematically by studying the effects of silicon-titanium ratio,crystallization time,crystallization temperature,crystallization mode and template concentration.The optimal synthesis conditions were:=60,TPAOH（25%）/Si=0.05,and rolling crystallization at 170℃for 48h.The obtained TS-1 zeolite displays good titanium distribution,high crystallinity,micrometer-size size which is suitable for gas-phase propylene epoxidation.Secondly,the modification method has been applied to the TS-1 zeolite synthesized by the aerosol-assisted hydrothermal crystallization method.To avoid the severe damage to zeolite structure by NaOH,the mixed solution of NaOH and different organic solvents,such as Polyvinylpyrrolidone,disodium ethylenediaminetetraacetic acid（EDTA disodium）,tetrapropylammonium bromide（TPABr）,β-cyclodextrin,cetyltrimethylammonium bromide（CTAB）and triton X-100,was used as the modification solution.The effects of different organic solvents and solution concentrations on the structure and catalytic performance of TS-1 have been studied.The best modification solution is 0.1mol/L NaOH-0.06 mol/L Triton X-100.Although some non-framework titanium species appeared on the treated TS-1,the present of the mesoporous structure and the increased exterior surface area improved the diffusion property.As a result,the catalysts exhibited excellent catalytic performances.The propylene conversion was increased from 8.8%to 14.3%and the selectivity of PO was increased from 61.7%to 93.6%;H₂O₂ utility was increased from 41.5%to 67.3%.