HZSM-5分子筛上甲醇制烯烃典型产物的传质行为研究

分子筛催化甲醇制烯烃反应(MTO)是典型的扩散主导反应过程,运用频率响应技术系统研究了几种典型产物分子(乙烯/乙烷、丙烯/丙烷、苯)在HZSM-5分子筛上的扩散行为。结果表明,频率响应法成功辨析了不同产物分子的传质规律,证实C2和C3烃分子在HZSM-5微孔孔道内具有相近的扩散速率,但由于受晶体表面阻碍效应影响不同,乙烷分子可自由进出HZSM-5分子筛孔道,而丙烷分子则受到较显著的微孔孔道扩散限制。另外,苯分子的扩散速率显著小于C2和C3分子,且苯分子受晶体表面阻抗效应的影响较小。本研究结果可用于解释HZSM-5分子筛在MTO反应中产物选择性的特点及表面结焦原因,进而从传质角度为高活性、选择性以及稳定性的高效甲醇转化制烃催化剂的定向开发提供理论指导。

Determination of mass transfer behavior of typical products of MTO (methanol to olefins) reactions over HZSM-5 zeolite

Methanol conversion to olefins (MTO) catalyzed by zeolite catalysts is a typical diffusion dominated reaction process. In this paper, the diffusion behavior of several typical product molecules (ethylene/ethane, propylene/propane, benzene) on a HZSM-5 zeolite was systematically studied by using Frequency Response method. The results show that the mass transfer regularity of the product molecules have been successfully determined by the Frequency Response method. It is confirmed that the diffusion rates of C2 and C3 hydrocarbon molecules within the HZSM -5 micropores are similar, but the effects of the surface resistance are different. So, the C2 molecules can freely go in and out of the channels of the HZSM-5 zeolite, while the diffusion of C3 molecules is significantly affected by the channel diffusion limitation. In addition, the diffusion rate of benzene molecules is observably lower than that of C2 and C3 molecules, and the resistant effects of benzene molecules caused by the zeolite crystal surface are not serious. The conclusions obtained in this study can be used to explain the product selectivity of MTO reaction over HZSM-5 zeolites and the coking mechanism of the catalyst, and provide the mass transfer theoretical guidance for the preparation of the MTO catalysts with excellent performance.