Epoxidation of Propylene over Small-Crystal TS-1 Extrudate in a Fixed-Bed Reactor

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 velocities (WHSVs) of propylene,methanol and H2O2,and the concentration of NH3·H2O,were systematically studied to identify ideal conditions for 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 were 0.93,2.5,and 0.25 h-1,respectively.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.