Measurements Of Defect/Pore Size Distribution And Modelling For Zeolite Membranes

Zeolite membranes have regular pores of molecular dimension, and have been widely applied as separation membranes and membrane catalysts. As a hot topic in microporous materials, zeolite membranes have gained comprehensive attention, which have potential applications in energy and environment fields. A defect-free zeolite membrane has molecular sieve pores with no defects such as pinholes, cracks or grain boundary defects. However, on account of the faultiness on the synthetic technology, it is difficult to prepare the zeolite membranes with no defects, which greatly impede their industrial applications on a large scale.Defect/pore size distribution is an important and effective parameter to evaluate the quality of zeolite membranes. Permporometry experiments combined with a suitable mathematical model can decide the defect/pore size distribution of zeolite membranes accurately.In the permporometry experiment, the permeance of a non-condensable gas, such as helium, is measured as a function of a certain relative vapor pressure of a condensable gas, such as n-hexane. Within the scope of the micropore, the adsorption of n-hexane is based on the micropore filling mechanism and the Horváth-Kawazoe equation has been used to describe the micropore size; the n-hexane is condensed in mespores and macropores, and the pore size is obtained by using the Kelvin equation. By comparing the two different methods to calculate the thickness of adsorption layer, Harkins-Jura equation and t-Curves, the latter one is more accurate. Gas permeation experiments to separate CO2/CH4 and CH4/i-C4H10 gas mixtures are conducted for CrAPSO-34 and TS-1 membranes. Pervaporation experiments to separate ethanol/water and TIPB/ethanol are conducted for silicate-1 and beta membranes. It is demonstrated that separation factor drops quickly with the increasing of the maximal defect size. Comparison with the pore size distribution and separation factor, it has been proved that permporometry is an accurate and effective method to evaluate the quality and separation performance of zeolite membranes.