钛硅分子筛在环己酮肟气相贝克曼重排反应中的失活

Deactivation of Titanosilicalite (TS-1, Ti-MCM-41) in the Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime

对比了不同孔径的钛硅分子筛催化剂Ti MCM 4 1 (Si/Ti摩尔比 =2 7)和TS 1 (Si/Ti摩尔比 =2 5 )对环己酮肟气相贝克曼重排反应的催化性能 ,分析了它们在重排反应中的积碳量和孔体积的变化 .结果表明 ,这些钛硅分子筛催化剂的失活主要是由积碳引起的 ,且积碳速率受催化剂孔径的制约 .在重排反应过程中 ,TS 1催化剂微孔孔道内的积碳量随反应时间线性增加 ,微孔体积随反应时间线性下降 ;而二次孔内的积碳量随反应时间呈指数增加 。

TS 1 (Si/Ti molar ratio=25) and Ti MCM 41 (Si/Ti molar ratio=27) molecular sieves were tested at 330 ℃ for the synthesis of caprolactam by the vapor phase Beckmann rearrangement of cyclohexanone oxime (CHO). TS 1 showed higher activity, caprolactam selectivity and stability than Ti MCM 41, indicating that the pore size of the molecular sieves is an important factor influencing the catalytic performance. The deactivation of the titanosilicalite molecular sieves was a result of coke deposition. The coke deposition on Ti MCM 41 was much more rapid and heavier than that on TS 1, which suggests that the larger pore size is beneficial to the formation of coke or coke precursors. The coke amount and pore volume of TS 1 were measured after it reacted with CHO at 370 ℃ and WHSV(CHO)=4 5 h -1 for different times. The results showed that the micropore volume of the TS 1 catalyst decreased linearly with the reaction time while the mesopore volume declined exponentially. The amount of the coke inside the pores of the used TS 1 catalyst was in proportion to the reaction time. However, the amount of the coke outside the micropores or in the mesopores of the TS 1 catalyst increased exponentially with the reaction time. Thus, the deactivation of the TS 1 catalyst was mainly caused by the coke formation outside the micropores of the zeolite crystals.