Synthesis And Catalytic Properties In Propylene Epoxidation Of Titanium Silicalites

Titanium silicalite-1(TS-1) was synthesized by using industrial silica sol as Si source, titanium tetrachloride as Ti source and the colloid of nano-sized TS-1as seeds. The synthesized samples were characterized by XRD、FT-IR、 UV-Vis and SEM. Catalytic performances of TS-1were evaluated by the reaction of propylene epoxidation. Results are as follows.1. Small-crystal TS-1was synthesized in a TPABr-ethylamine hydrothermal system using the colloid of nano-sized TS-1as seeds. The influences of seeds aged at different temperatures, crystallization time and amount of alkaline additives on synthesis of TS-1were investigated. Using colloid seeds aged at80℃or100℃, small-crystal TS-1with a crystal size of about400nm×400nm×200nm can be synthesized. Adding colloidal seed can short the crystallization time of TS-1. When crystallization time was36h, TS-1can be synthesized with good catalytic performance. Alkaline additives can effectively neutralize the acidity introduced by the silica sol, this can improve selectivity of PO in propylene epoxidation reaction. Under the optimal conditions (45℃,3.0MPa, n(C3H6,)/n(H2O2)=3.5, WHSVs of propylene was0.7h-1), conversion of H2O2and selectivity of PO were92.0%and98.5%, respectively.2. TS-1could be synthesized without TPABr. The influences of organic amines, amount of seeds and alkaline additives on synthesis of TS-1were investigated. Organic amines can influence the crystallization of TS-1, form of titanium species and the catalytic activity of TS-1. Among ethylamine, ethylenediamine, n-butylamine, triethylamine and tri-n-propylamine, the catalytic activity of TS-1synthesized by n-butylamine was highest. When the molar ratio of TPA+/SiO2was0.020, conversion of H2O2was88.7%. This shows that the synthesis method reduced the amount of TPA+effectively. Alkaline additives can improve selectivity of PO in propylene epoxidation reaction.