The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics(MD) and grand canonical Monte Carlo(GCMC) simulations. The diffusion coefficients of benzene and propylene in MFI, MWW and BEA zeolites were calculated by simulating the mean-square displacements(MSD) at 298 and 600 K. Benzene and propylene showed the different adsorption rules in the channels of the three zeolites. For propylene, the molecular loadings decreased in the order: BEA(linear channel)>BEA (tortuous channel)>MFI(linear channel)>MWW(12-membered rings, 12MR channel)>MFI(tortuous channel)>MWW (10-membered rings, 10MR channel); for benzene, the molecular loadings decreased in the order: BEA(linear chan-nel)>BEA(tortuous channel)>MWW(12MR channel)>MFI(linear channel)>MFI(tortuous channel)>MWW(10MR channel). Besides, the adsorption isotherms of benzene and propylene in the three zeolites at 298 and 443 K were simulated. The results show that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the different rules for the adsorption of benzene and propylene molecules in the zeolites. At a low pressure, the unfavorable energy would make the loadings of propylene lower than those of benzene. When pressure was higher than 0.25 kPa, the adsorption of benzene in MFI would nearly reach saturation.
以六亚甲基亚胺为模板剂,乙醇为有机辅助剂,采用动态水热法合成了一系列 MCM-22分子筛,利用 X 射线衍射(XRD)、氨程序升温脱附(NH_3-TPD)、傅里叶变换红外光谱(FT-IR)和电子扫描显微镜(SEM)等表征手段考察了乙醇辅助剂对 MCM-22分子筛的结构及酸性的影响。结果表明,添加适量的乙醇可以有效调控分子筛结构性能和结晶度,分子筛的强酸位的强度适度增强,弱酸位的强度减弱,总酸量和 B 酸中心数增大,而L酸中心数减少,且晶粒尺寸减小,比表面积增加,但过量的乙醇会导致ZSM-5分子筛的生成。以苯和丙烯烷基化合成异丙苯为模型反应,评价对所制备的分子筛催化性能,发现添加合适的乙醇得到的 MCM-22分子筛具有更高的催化活性和选择性。
