关键词: 丙烯环氧化, TS-1, H₂O₂, 反应条件, 表征, 固定床反应器

Abstract:

A small-crystal titanium silicalite-1 (TS-1) with a size of 600 nm×400 nm×250 nm was synthesized using a nano-sized TS-1 mother liquor as the seed in a tetrapropyl ammonium bromide (TPABr)-ethylamine hydrothermal system, and was extruded with silica sol. The obtained TS-1 extrudate was characterized by X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy, and nitrogen physisorption. The reaction conditions, including temperature, pressure, molar ratio of propylene/H₂O₂ (n(C₃H₆)/n(H₂O₂)), the weight hourly space velocity (WHSV) of propylene, methanol and H₂O₂, and the concentration of NH₃·H₂O, were systematically studied to identify ideal condition propylene epoxidation over small-crystal TS-1 extrudate. The reaction temperature had little effect on the propylene oxide (PO) yield under the conditions examined. The highest PO yield was obtained when the pressure was 2.0 MPa and the n(C₃H₆)/n(H₂O₂) was 4. The PO content in the product was maximized when the WHSVs of propylene, methanol and H₂O₂ was 0.93, 2.5 and 0.25 h^-1respectively. A low concentration of NH₃·H₂O was beneficial for a high PO yield. Under the optimized condition, we compared catalytic performances of TS-1 with different crystal sizes and performed a long-term test over the small-crystal TS-1. The tests indicated that H₂O₂ conversion and PO selectivity could both reach 95%, even after 1000 h on stream.

Key words: Epoxidation of propylene, TS-1, H₂O₂, Reaction condition, Characterization, Fixed-bed reactor