The Preparation And Application Of Inorganic Molecular Sieve Membrane For Desalination

With the rapid growth of global population and the acceleration of urbanization,the shortage of water resource is becoming one of the biggest challenges facing contemporary society.Desalination of seawater and brackish water is one of the effective ways to solve this worldwide problem.Compared with reverse osmosis and multi-stage flash evaporation,pervaporation technology has advantages of low energy consumption and low pretreatment requirements,it is a new desalination technology with great industrial application potential.Inorganic microporous molecular sieve membrane is a potential desalination membrane material due to its controllable microporous structure and suitable pore size.Focusing on the preparation of high-performance supports and inorganic microporous molecular sieve membrane for desalination,the preparation and optimization of ZSM-5 zeolite membrane,organic-inorganic hybrid silicon BTESE membrane and hollow fiber support have been investigated successively,and their applications in desalination by pervaporation were also investigated.The main contents are as follows:The synthesis method of ZSM-5 zeolite membrane and the influence of key conditions on its morphology and properties were investigated.The best ZSM-5 membrane for PV desalination is prepared by the secondary crystallization method with 175?for 48h,and its synthetic solution's molar ratio was n(Al₂O₃):n(Si O₂):n(Na₂O):n(Na F):n(H₂O)=0.05:1:0.21:1.01:55.The flux and salt rejection of the membrane for PV desalination of 3.5 wt.%H₂O/Na Cl mixtures at 75?were 8.35 kg·m^-2·h^-1 and>99.9%,and it kept stable for 60h..The synthesis method of BTESE membrane and the influence of key conditions on the morphology and properties of BTESE membrane were investigated.The results show that the best BTESE membrane for desalination was prepared by three-step sol-thermal coating method,which using 2.5wt.%BTESE precursor sol as the synthesis solution,three times 30min rapid calcination at 300?.The flux and salt rejection of the membrane for PV desalination of 3.5wt.%H₂O/Na Cl mixtures at 60?were 10.37 kg·m^-2·h^-1 and>99.9%,and it kept stable for120h.The influences of casting solution recipe,air spacing in spinning process and sintering curve on the morphology and properties of ceramic hollow fibers were investigated.It was found that the regulation of the air gap in spinning process was the most economical method to improve the morphology and properties of ceramic hollow fibers.According to the previous experience and the improvement of the parameters,the ceramic hollow fiber with excellent morphology,permeability and mechanical strength was prepared.The mass fraction ratio of casting solution was PESf:?-Al₂O₃:NMP:PVP=8.14:50:40.68:1.18(The mass ratio of amorphous 1?m to amorphous 0.2?m powder is 42.52:7.48),the spinning conditions were as follows:air spacing 6cm,nitrogen pressure 0.3MPa,inner and outer diameter of spinneret ID/OD=1mm/2mm,and both internal and external flocculants were water.The ceramic hollow fiber with excellent morphology,permeability and mechanical strength was prepared,and its bending strength was 35.22 MPa.and pure water flux is 82g·m^-2·h^-1.Organic-inorganic hybrid silicon BTESE membrane was synthesized on plate supports and ceramic hollow fiber supports by three-step sol-gel synthesis method,and the desalination effect of pervaporation was good.The flux of the plate BTESE membrane reached 23.58 kg·m^-2·h^-1,and the rejection rate was more than 99.8%with stable hydrothermal stability.Hollow fiber BTESE membrane flux reached 30.57 kg·m^-2·h^-1,and the rejection rate reached more than99.8%.Although the hydrothermal stability was poor,it shows a high potential for application of PV desalination.The influence of temperature and salt concentration on the pervaporization performance of BTESE membrane was investigated.With the increase of temperature,the pervaporization flux of BTESE membrane increased gradually,but the rejection rate remained basically unchanged.With the increase of the concentration,the flux of the membrane decreases gradually and the rejection rate remains stable.