Preparation And Pervaporation Performance Of Microstructure Controlled CHA-type Zeolite Membrane

Zeolite chabazite（CHA）with the Si/Al ratio of 2-∞in the framwork has3-dimentional and 8-membered ring window,and an effective pore diameter of 0.38nm.These properties（superior pore structure,moderate pore diameter and adjustable Si/Al ratio）allow CHA-type zeolite membranes to have the wide potential industrial applications for pervaporation（PV）performance,gas separation and shape selective catalytic reactions.Keeping in mind that high quality of zeolite layer is curcial to the PV performances,manipulating the microstructure of zeolite layers is an effective way to the fabrication of high performance membranes.In this paper,CHA-type zeolite membranes with the medium Si/Al ratio were prepared by the introduction of ionic liquids（ILs）and cesium ions,which can be expected to solve the current problems for industrial separation such as unstablity and low separation efficiency,The content is mainly divided into the following two parts:1.Pure zeolite chabazite（CHA）crystals were successfully synthesized with the addition of imidazolium-based ionic liquids（ILs）.The use of ionic liquid is played the role of structure-directing agent,and also improved the Si/Al ratio（Si/Al=2.8）in the framework.ILs could be used repetitively at least 3 times for synthesis high-crystallinity zeolites.Under the optimized synthetic conditions,a continued zeolite CHA membrane obtained from the initial gel containing1-buthyl-3-methylimidazolium bromide（[Bmim]Br）on the mullite tubular supports showed high water flux of 6.3 kg m^-2 h^-1 with high ion rejection（100%）for pervaporation（PV）separation of 3.5 wt.%Na Cl aqueous solution at 75 ^oC.The effect of temperature and feed concentration on the desalination performance of ILs-CHA membranes were also investigated.With increasing the operating PV temperature at90 ^oC,the water flux increase to 10.3 kg m^-2 h^-1,their salt rejections are always 100%.Note that the zeolite CHA membranes show excellent separation performances even for desalination of 10 wt.%Na Cl aqueous solution.Furthermore,this ILs-CHA zeolite membrane keep stable separation performance with stable water flux as well as high salt rejection within the investigated period of 4 d for 3.5 wt.%Na Cl aqueous solution at 75 ^oC,demonstrating the ILs-CHA zeolite membranes would be potential candidates for desalination.2.Zeolite CHA crystals with high crystallinity were firstly synthesized via ultrasonic-assisted aging at the low synthesis temperature,and their size is 1-2μm.Through these zeolite seeds,pure CHA-type zeolite membranes were synthesized from organic template-free aluminosilicate gel containing cesium ion on the tubular supports.The dense gel containing cesium ion lead to the formation of the CHA zeolite with a higher Si/Al ratio of 3.0 and a shorter synthesis time of 6 h.The effects of synthesis parameters such as crystallization temperature and time,precursor composition（i.e.aluminium,water,and alkali content）on the growth and pervaporation performance of zeolite crystals and membranes were investigated.Meanwhile,zeolite chabazite membrane under the optimal conditions shows a high flux of 2.9 kg m^-2h^-1together with separation factor of 1500 for water/ethanol（10/90wt.%）aqueous mixture at 75 ^oC.Then,the as-synthesized zeolite CHA membranes were affected by operating temperatures and feed concentration,and their pervaporation performance before and after acid treatment were discussed.These Cs-CHA membranes can be extended to organic dedydration in an acid environment.