Quantifying molecular surface barriers and intracrystalline diffusion in nanoporous materials by zero‐length column

Abstract

The zero‐length column (ZLC) method has been frequently used to measure the effective diffusivity of guest molecules in nanoporous crystalline materials. Recent studies unveiled that the mass transport of guest molecules could originate from either intracrystalline diffusion and/or surface barriers. Directly quantifying the intracrystalline diffusivity and surface permeability of guest molecules. therefore, is essential for understanding the mass transfer and thus optimizing the design of nanoporous crystalline materials. In this work, we extended the ZLC method, based on a derived theoretical expression of the desorption rate, to decouple the surface barriers and intracrystalline diffusion from effective diffusion of guest molecules in nanoporous materials. The diffusivities of ethane, propane and n‐pentane in SAPO‐34 and Beta zeolites have been experimentally measured to verify the effectiveness of this method.

甲醇制烯烃过程中h-ZSM-5分子筛积碳对分子筛表面传质阻力的影响

“…扩散系数, 结果表明由于受到了积碳的阻碍, 晶内扩散 系数随反应时间的增加而下降. Gao等 [43] [45] , 可测量小粒径分子筛的表面 传质系数(表面渗透率), 且具有较广泛的适用范围 [46] .…”

“…丙烷在新鲜及积碳的分子筛样品上的表面传质系 数(表面渗透率)采用零长柱技术测定, 具体的测试细 节见网络版补充材料. 基于Xie等 [45] 提出的解析表达 式, 客体分子的表面渗透率可直接由式(2)确定:…”