Modification Of NaY Zeolite Membrane,and Pervaporation Of Heteroatoms On Its

NaY zeolite membrane has medium channel system,low Si/Al ratio and good hydrophilicity,which is an alternative membrane for separation of alcohol aqueous solution and other liquid mixtures.However,there are many difficulties for preparation of high-quality NaY zeolite membranes.Cracks and impure phase are easy to produce during membrane forming process,it is difficult to control thickness of zeolite layer and orientation of crystalline growth.NaY zeolite membrane has a large ion exchange capacity,heteroatom modification is a direct and effective method for improving separation performance of NaY zeolite membrane.Processes of heteroatom modification are divided into two types:ion-exchange post treatment and direct hydrothermal synthesis.Therefore,the main research content of this work is divided into the following two aspects:（1）Ion-exchange post treatment of NaY zeolite membranes.Different nitrate salts,including Co（NO₃）₂,Mg（NO₃）₂,Zn（NO₃）₂,Ca（NO₃）₂,Cu（NO₃）₂,KNO₃,and Ag NO₃,have great effects on the channel structure and water affinity of the NaY zeolite membrane in this work.When the concentration of nitrate salt,ion-exchange temperature and time are 0.1 mol·L^-1,50°C and 2 h,the ion-exchange degree order of NaY zeolites is Ag⁺>K⁺>Ca²⁺>Zn²⁺>>Co²⁺>Mg²+.Especially,Ag⁺and K⁺cation exchange degree of NaY zeolites are achieved to 96.54%and 82.77%in this work.BET surface,total pore capacity,pore size distribution and water contact angle of the ion-exchanged NaY zeolites are all disordered by mono-and di-valent cations.Di-valent nitrate salt is favor for increasing the dehydration performance of NaY zeolite membranes by ion-exchange.When the ion-exchange solution is Zn（NO₃）₂,the total flux variation and separation factor variation of the NaY membrane are-45%and 230%for separation of 10 wt%H₂O/Et OH mixture by pervaporation,and the ion-exchanged membranes showed good reproducibility.（2）Preparation and performance of heteroatom NaY zeolite membrane.Because the separation performance NaY zeolite membrane is increased by ion-exchange with Zn（NO₃）₂ solution,mono-and di-valent nitrate are added in the precursor synthesis gel for preparing heteroatom NaY zeolite membrane in this study,including Co（NO₃）₂、Mg（NO₃）₂、Zn（NO₃）₂、Ca（NO₃）₂、Cu（NO₃）₂、KNO₃and Ag NO₃.Influences of kinds and content of nitrate,crystallization time and temperature,crystallization methodon the growth and performance of heteroatom NaY zeolite membrane are investigated.Monovalent nitrate could not prepare NaY zeolite membrane,while the divalent nitrate are favor for preparing heteroatom NaY zeolite membranes.In addition,the characterization results of XPS,infrared spectroscopy,and ultraviolet spectroscopy indicate that the Zn-NaY zeolite membranes are successfully prepared with Zn（NO₃）₂solution,which is conducive to the preparation of dense and reproducible heteroatomic Zn-NaY zeolite membranes.When the ratio of initial synthesis gel is 2525 Si O₂:1 Al₂O₃:22 Na₂O:990 H₂O:7.5 NH₄F:0.4 Zn（NO₃）₂,the crystallization time and temperature are 7 h and 100℃,the pure phase and ca.7-8μm Zn-NaY zeolite membrane layer are formed on the tubular support.