Epoxidation of propylene to propylene oxide catalyzed by large-grain TS-1 in supercritical CO 2

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Large-grain titanium silicalite (TS-1, 3.0 μm long), which is a low-cost catalyst that can easily be separated from the product and exhibits an efficient catalyst recovery, was synthesized using tetrapropylammonium bromide (TPABr) as the template. However, it exhibited very poor catalytic activity in the traditional organic solvent compared with small-grain TS-1. The epoxidation of propylene to propylene oxide (PO) using the large-grain TS-1 as the catalyst and H 2O 2 as the oxidant in a supercritical CO 2 (scCO 2) medium was then investigated. The effects of the CO 2 pressure, reaction temperature, propylene pressure, cosolvent (methanol) concentration, and reaction time on the epoxidation reaction in scCO 2 were investigated and compared with those of the reaction in methanol. The use of scCO 2 as the reaction medium significantly improved the catalytic activity of the large-grain TS-1 and increased the PO yield from 50.1 to 83.5%. The effect of alkaline components [NaOH, NaHCO 3, urea, and (NH 4) 2CO 3] on the epoxidation reaction in scCO 2 was also investigated. The addition of alkaline components had a positive effect on the selectivity to PO as well as to H 2O 2 utilization. The addition of (NH 4) 2CO 3 yielded the best results, with the H 2O 2 conversion, PO selectivity, H 2O 2 utilization, and PO yield reaching 98.7%, 95.2%, 94.3%, and 88.6%, respectively. Therefore, a novel approach to PO production is introduced, which provides a basis as well as technical parameters for its further industrialization.