双阳离子体系高通量丝光沸石膜的合成及其乙酸脱水应用

Synthesis of High-Flux Mordenite Membranes by Binary Cations System for Pervaporation Dehydration of Acetic Acid

采用多种表征技术详细研究了碱金属阳离子对丝光沸石分子筛膜生长和渗透汽化性能的影响。结果表明,Li^(+)、Na^(+)、K^(+)和Cs^(+)以及Na^(+)-Li^(+)、Na^(+)-K^(+)和Na^(+)-Cs^(+)的不同离子组合对丝光沸石分子筛膜的形貌和性能有很大影响。研究发现,碱金属阳离子通过促进硅在初始凝胶中的溶解,在硅铝酸盐的重排过程中起到结构导向作用,进而起到构筑丝光沸石晶体骨架结构的作用。Na^(+)对丝光沸石晶体的结晶有明显的促进作用,而Li^(+)、K^(+)和Cs^(+)在相同的结晶时间内表现出较慢的结晶速率。在合成凝胶中用K^(+)代替少量Na^(+)可以显著改善膜表面的亲水性。特别是合成凝胶中Na^(+)/K^(+)比(nNa^(+)/nK^(+))为2时,形成了更致密、更亲水的丝光沸石分子筛膜,显示出更高的渗透汽化性能。对于90℃下HAc质量分数为90%的HAc/H_(2)O混合物的分离,该膜显示出2.67 kg·m^(-2)·h^(-1)的高渗透通量和约为4000的分离因子。此外,最优条件下合成的丝光沸石分子筛膜在90℃下长达240 h渗透汽化分离90%的HAc/H_(2)O混合物依然显示优越的酸稳定性。

The influences of alkali-metal cations on growth and pervaporation(PV)performance of mordenite membranes were investigated in detail with multiple characterization techniques.The results show that the morphology and quality of mordenite membrane are greatly influenced by Li^(+),Na^(+),K^(+)and Cs^(+)as well as the mixed Na^(+)-Li^(+),Na^(+)-K^(+)and Na^(+)-Cs^(+).It is found that alkali-metal cations play a structure-directing role on the nucleation when aluminosilicate is rearranged by facilitating the dissolution of silicon in initial gel,and then play the structure formation effect for constructing mordenite framework.Na^(+)has a significant acceleration effect on mordenite crystallization while Li^(+),K^(+)and Cs^(+)exhibit a slower crystallization rate in the equal crystallization time.The replacement of a small amount of Na^(+)with K^(+)in synthesis gel can improve the hydrophilicity of membrane surface.Especially,the Na^(+)/K^(+)ratio(nNa^(+)/nK^(+))of 2 in synthesis gel resulted in the formation of denser and more hydrophilic mordenite membranes with higher PV performances.For separation of a HAc/H_(2)O mixture containing mass fraction of 90%HAc at 90℃,the membrane showed a high permeation flux of 2.67 kg·m^(-2)·h^(-1) and a high separation factor of about 4000.Moreover,the mordenite membrane displayed a long-term acid stability in pervaporation of a 90%HAc/H_(2)O mixture at 90℃for 240 h.