固定床反应器上挤条小晶粒TS-1催化丙烯环氧化反应

摘要

采用纳米TS-1母液作为晶种,在四丙基溴化铵(TPABr)-乙胺廉价水热体系中,合成出晶粒尺寸为600 nm×400 nm×250 nm的小晶粒钛硅分子筛(TS-1),用挤条法将其成型,得到的挤条小晶粒TS-1被用于催化固定床反应器中的丙烯环氧化反应.采用X射线衍射(XRD)光谱,傅里叶变换红外(FTIR)光谱,紫外-可见(UV-Vis)漫反射光谱及氮气物理吸附对挤条成型的小晶粒TS-1进行表征,并对丙烯环氧化的最优反应条件进行考察.其中所考察的条件包括：反应温度,压力,丙烯/H2O2摩尔比(n(C3H6)/n(H2O2)),丙烯、甲醇及H2O2的质量空速(WHSV)以及NH3·H2O浓度.在所考察的范围内,温度对环氧丙烷(PO)收率的影响较小,当反应压力为2.0 MPa, n(C3H6)/n(H2O2)为4时,可以得到最高的PO收率.当丙烯、甲醇及H2O2的空速分别为0.93、2.5及0.25 h-1时, PO在产物中的含量最高.较低的NH3·H2O浓度对高PO收率更有利.在优化的反应条件下,对比不同晶粒大小TS-1的催化性能,并考察了挤条小晶粒TS-1的长期运转性能,连续反应1000 h, H2O2转化率及PO选择性仍能维持在95%以上.%A smal-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 systematical y studied to identify ideal conditions for propylene epoxidation over smal-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 smal-crystal TS-1. The tests indicated that H2O2 conversion and PO selectivity could both reach 95%, even after 1000 h on stream.