The Research Of Synthesizing Zeolite Membrane And Gas Permeation Performeance

Because of the splendid features,such as thermal stability,high pressure resistant,resistance to acid and alkali corrosion,excellent mechanical strength and so on,zeolite membranes have attractive applications in the field of gas separation.Among various zeolite membranes,NaA and ZSM-5 membranes,which also possess additional characteristics of small and uniform pore sizes,the cation in the pores can modify by ion-exchange,adjustable silica-alumina ratio and the silicon or aluminum atoms in the zeolite framework can be replaced by other atoms,making scientist be capable of synthesizing zeolite membranes with different structures and surface properties based on different kinds of gas mixtures.However,it is a pity that there are no commercial applications employing the two types of membranes for gas separation so far,due to the fact that the membranes usually are not dense and the gas selectivities will significantly reduce causing by those small pinholes or cracks existed in the membranes.For this reason,new modification material was proposed and synthesis methods were optimized in this paper to obtain defects-free and high-performance zeolite membranes.First,an innovation method for synthesizing NaA/ZSM-5 composite membrane using kaolin as buffer layer was proposed,for the first time.In this process,kaolin was modified on the surface of the support or the NaA membrane layer by filtrating as buffer layer to promote the interface interlinkage among support,NaA membrane and ZSM membrane layer and enhance the gas separation performance.The NaA and ZSM-5 membrane were synthesized under hydrothermal conditions at 60? for 24h and 180?for 12h,respectively.Through XRD and SEM characterizations,a pure-phase,dense bilayer membrane structure had obtained with the a 1 5.67?m NaA bottom layer and a 4.67?m ZSM-5 top layer.Single gas permeation measurement indicated the composite membrane can provide the permselectivity of H2 over N2 was 4.65 with the H2 permeance of 2.39×10-6 mol m-2·s-1·Pa-1 an N2 permeance of 5.13×10-7 mol·s-1· m-2· Pa-1.In addition,the NaA zeolite membrane with excellent performance was synthesized by employing APTES grafted kaolin as modified layer on the surface of support,which combined the individual advantage of APTES and kaolin.The effects of synthetic liquid composition,temperature,the numbers of modification and seeds on zeolite membrane growth were analyzed in detail.XRD and SEM results demonstrated that a uniform and defect-free NaA zeolite membrane was formed on the surface of alumina ceramic tube.Permeation measurement showed the NaA zeolite membrane can provide the permselectivity of H2 over N2 was 4.97 with the H2 permeance of 5.72×10-7 mol·n-2· s-1· Pa-1 an N2 permeance of 1.15×10-7 mol·s-1·m-2·Pa-1.At the same time,in order to deeply understand the mechanism of gas molecule transferred in zeolite pores,the permeance of H2,CH4,CO,N2,CO2 through NaA membrane,as well as the effects of temperature and pressure on gas permeance and permselectivity were conducted.The consequences proved that the separation mechanism of gas molecules in the zeolite membrane was molecular sieving.