Understanding the effect of zeolite crystal expansion/contraction on separation performance of NaA zeolite membrane: A combined experimental and molecular simulation study
Understanding the effect of zeolite crystal expansion/contraction on separation performance of NaA zeolite membrane: A combined experimental and molecular simulation study
复制标题
DOI：
10.1016/j.memsci.2017.05.057
复制
发表时间：
2017-10-01
影响因子：
9.5
通讯作者：
Murad, Sohail
中科院分区：
文献类型：
--
作者：
Qu, Fanyu;Shi, Rui;Murad, Sohail
通过实验测量和分子模拟研究了吸附引起的沸石晶体尺寸变化对 NaA 沸石膜用于醇脱水的分离性能的影响。水/IPA 的蒸气渗透 (VP) 分离显示，由于随着进水浓度降低，IPA 通量增加，选择性急剧下降。然而，在水/甲醇和水/乙醇混合物的情况下，醇通量几乎与给水浓度无关。渗透孔隙率测量和分子模拟表明，在低水负载量下，NaA 晶体轻微收缩，而在较高水负载量下膨胀，这显着影响晶间缺陷。此外，在低水负载下，晶间缺陷不会被缺陷位点吸附的水所阻挡。甲醇和乙醇均可进入沸石，减少晶体收缩。然而，异丙醇无法进入 NaA 晶体，因此无法减轻低水负载量的影响。基于这一知识，低含水量的水/异丙醇混合物中甲醇或乙醇的存在有望提高NaA沸石膜的脱水性能。对于水/其他大分子混合物的脱水也观察到该结果。我们的研究加深了对 NaA 沸石膜渗透和分离的理解。
Experimental measurements and molecular simulations were used to investigate the effect of adsorption-induced changes in zeolite crystal size on the separation performance of NaA zeolite membrane for dehydration of alcohols. The vapor permeation (VP) separations of water/IPA showed a dramatic decrease in selectivity due to increase of IPA flux as the feed water concentration decreased. However, in the case of water/methanol and water/ethanol mixtures, the alcohol fluxes were almost independent of the feed water concentration. Permporosimetry measurements as well as molecular simulations show that at low loading of water, NaA crystals contract slightly, while they expand at higher loadings, which significantly affects the intercrystalline defects. In addition, at low water loadings intercrystalline defects are not blocked by water adsorbed at the defect sites. Both methanol and ethanol can enter the zeolite to reduce the crystal contraction. However, isopropanol cannot enter the NaA crystal and is thus unable to mitigate the effects of low water loadings. Based on this knowledge, the presence of methanol or ethanol in the water/isopropanol mixtures with low water content was expected to improve the dehydration performance of NaA zeolite membrane. This result was also observed for the dehydration of water/other large molecular mixture. Our studies here provide an improved understanding of the permeation and separations for NaA zeolite membrane.