二甲苯在分子筛孔道中扩散特性的分子模拟研究(英文)

Molecular simulation studies on the diffusion characteristics of xylene in various zeolites

应用分子模拟技术研究了甲苯歧化反应中的产物二甲苯各同分异构体在MFI、MEL和CAN分子筛孔道中的扩散特性,得到二甲苯各同分异构体与不同分子筛之间的相互作用能,以及吸附位和扩散特性等相关信息。计算结果表明,吸附质分子扩散的难易程度受到孔径和孔道结构的共同影响。MFI分子筛对于p-xylene有很好的选择性,不论是直孔还是弯孔,均有此特性,但弯孔中的扩散能垒较直孔中高,因此吸附质分子更倾向于在MFI分子筛直孔中进行扩散；MEL分子筛的孔径略小于MFI分子筛,各吸附质的扩散能垒较在MFI分子筛孔道中高,二甲苯各同分异构体中p-xylene的扩散能垒远小于m-xylene和o-xylene,因此,MEL分子筛也表现出对于p-xylene的选择性；在CAN分子筛的孔道中,二甲苯各种同分异构体的扩散能垒按p-xylene＜m-xylene＜o-xylene的顺序依次升高,但由于数值整体偏低,所以CAN分子筛不能够表现出对于p-xylene的择形性。

Molecular simulation methods were applied to investigate the diffusion characteristics of xylene isomers in various zeolites, such as MFI, MEL and CAN zeolites, and to rank the predicted shape-selectivity of potential zeolite catalysts for toluene disproportionation. The periodic variations of interaction energy between the molecules and the zeolite framework in the calculated diffusion energy profiles were used to predict the diffusion energy barrier. The calculations of the diffusion energy profiles for molecules in zeolites show that the diffusion characteristics of the molecules inside zeolites are sensitive to their pore architectures. The zeolites with channels whose diameters are close to the dimensions of the molecules are better shape selective catalysts. The efficiency of shape selective production of p-xylene in these zeolites are in the order MFI≈MEL〉CAN as predicted from their diffusion energy barriers. The results are also useful in understanding the interaction mode of the molecules with the zeolite framework.