蒸汽相转化和晶种二次生长法制备不对称NaA分子筛膜层

摘要

采用蒸汽相转化和晶种二次生长法，在大孔氧化铝载体上制备不对称NaA分子筛膜层。制备过程包括蒸汽相转化法在载体表面制备底层多孔NaA分子筛膜，再采用晶种二次生长法制备上层致密分子筛膜层。考察了凝胶 Na2O/Al2O3比、凝胶前处理时间、凝胶水量以及蒸汽相转化时间对于蒸汽相转化法制备多孔 NaA分子筛膜性能的影响，得到的优化条件为：凝胶组成为7.5Na2O：2SiO2：Al2O3：150H2O，前处理条件为50℃水浴加热5 h。在多孔NaA分子筛膜的表面涂覆120 nm晶种，二次生长制备得到下层带有孔洞上层致密的NaA分子筛膜。膜层的性能通过扫描电镜分析以及在质量分数为90%乙醇水溶液75℃条件下的渗透汽化表征，其通量为3.43 kg/(m2·h)，分离因子为3685。%Asymmetric zeolite NaA membrane layers are synthesized on tubular α-Al2O3 supports by the vapor phase transfer method followed by seeded growth. The preparation of the asymmetric zeolite NaA membrane layer includes the preparation of porous zeolite NaA membrane sublayer by vapor phase transfer method and the preparation of dense top layer by seeded growth. The effects of the Na2O/Al2O3 ratio, pretreatment time and water content of the hydrogel, as well as the vapor phase transfer time on properties of porous zeolite NaA membranes are investigated. The optimal conditions of the hydrogel are as follows:pretreatment temperature 50 ℃, pretreatment time 5 h, and the composition of the hydrogel 7.5Na2O:2SiO2:Al2O3:150H2O. The seeds of 120 nm are coated on the porous zeolite NaA membrane by wetting-rubbing. Asymmetric zeolite NaA membrane layers are synthesized with the secondary growth method from the seeded membranes. Zeolite NaA membranes are characterized by SEM and pervaporation separation of 90% ethanol aqueous solution at 75 ℃. The flux of the membrane is up to 3.43 kg/(m2·h), while the separation factor is 3 685.