Epoxidation of propylene to propylene oxide catalyzed by large-grain TS-1 in supercritical CO2

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 H2O2 as the oxidant in a supercritical CO2 (scCO2) medium was then investigated. The effects of the CO2 pressure, reaction temperature, propylene pressure, cosolvent (methanol) concentration, and reaction time on the epoxidation reaction in scCO2 were investigated and compared with those of the reaction in methanol. The use of scCO2 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, NaHCO3, urea, and (NH4)2CO3] on the epoxidation reaction in scCO2 was also investigated. The addition of alkaline components had a positive effect on the selectivity to PO as well as to H2O2 utilization. The addition of (NH4)2CO3 yielded the best results, with the H2O2 conversion, PO selectivity, H2O2 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.

The synthesis of PO from propylene, catalyzed by large grain size TS-1 (low cost, easy separation of product from the catalyst, and efficient catalyst recovery) with H2O2 as oxidant was carried out in scCO2 for the first time. The results showed the conversation and yield were 98.7% and 88.6% with scCO2 as medium and (NH4)2CO3 as additive, improved by 15.2% and 17.7% respectively compared with small grain size TS-1 in methanol.Figure optionsDownload high-quality image (123 K)Download as PowerPoint slideHighlights
► Large grain size TS-1 was introduced to propylene epoxidation.
► It is concluded that the large grain size TS-1 has important roles on propylene epoxidation in scCO2.
► Environmental-friendly scCO2 substituted for MeOH as reaction medium and increased the catalytic activity of large grain size TS-1.
► (NH4)2CO3 as additive improved the selectivity and yield of propylene oxide in scCO2.
► The maximum conversion of H2O2, selectivity of PO, utilization of H2O2, and yield of PO were 98.7%, 95.2%, 94.3% and 88.6% respectively in scCO2 with alkaline component as additives.