The Synthesis Of NaX Zeolite Hollow Fiber Membranes For Their Gas Permeances

Zeolite membrane is one kind of important inorganic membranes. Inorganicmembrane has many advantages: resistance to high tenperature, high pressure andcorrosion resistance and so on. At the same time，zeolite membarnes aJso possessmany advantages of zeolite: zeolite pore is on molecular scale, therefore differentmolecules can be effectively separated by the molecular sieving role of zeolite; Thediversity of zeolite type and structure determine the diversity of the zeolite nature.Experiment and industrial production can choose the suitable zeolite as the membranemateral according to their requirements of the separation; The channels of zeolite andtheir surefce can be modiifed and improved, which make the pore and adsorptionperofrmance of zeolite adjustable. NaX-type zeolite has a pore diameter of about0.74nm and three-dimensional pore structure. Compared with other zeolites, NaX-typezeolite has a larger pore size. So NaX zeolite membranes have great devebpmentspace in a separation of large molecule mixed system, pervaporation and membranereactor and so on. NaX-type zeolite membrane has gradually become a promisingmembrane materialHerein, the preparation of NaX-type zeolites was firstly investigated by directcrystallization without seed geL Based on the research of conventional hydro thermalsynthesis, the method of membrane synthesis was improved. The synthetic formulaand excellent performance of zeolite membranes were obtained on aluminium holbwfiber supports optimizing some factors of hydro thermal synthesis. Lastly, theas-prepared NaX-type zeolite membranes were applied to separation for N2/CO2gasmixture. Moreover, a better separation performance ofr N2/CO2mixture is obtained.The results achieved were as follows:(1) The hydrothermal synthesis conditions such as aging time, synthesis temperature and time，alkalinity and water content in the system were investigated indetail. The results indicated that increasing aging time was helpful to generate morecrystal nucleus, but overbng aging time could cause the generation of NaP-typezeolite. Prolonging synthesis time and rising synthesis tenperature were favorable forthe ofrmation of zeolite crystals, but trans-crystalliziation phenomena was easy tooccur and led to mixed-crystal. The Si/Al ratio had no significant effect on the zeolitesynthesis. The effect of Na/Si ratio and water content on the crystal!inity of theproduct was larger.(2) The alumina hollow ifber membrane was prepared by dry-wet spinningprocess combined with sintering process, then dense and continuous NaX zeolitelayers were synthesized by a secondary growth method on these substrates. Theeffects of gel conposition, hydrothermal treatment process and the quality of NaXmembranes were investigated. The results indicated that increasing aging timeaccelerated the crystal growth rate, but overlong aging time could cause thegeneration of NaP-type zeolite; If synthesis time was too short, there were no layerswith good integrity grown on the surefce of the s import. Overlong synthesis time mayresult in polycrystalline accumulation phenomenon, which made the zeolite layerthicken and the layer surefce was not smooth; Synthesis temperature affected thegrowth rate of zeolite crystal layers. In a certain temperature range, with the increaseof synthesis temperature, the crystals growth rate became faster; The Na/Si ratioshould be kept moderate, otherwise there would be no crystal formation on the surfaceof the simport or the layer was flawed. The Si/Al ratio did not play a signiifcant rolein the tested range. When the water content was too low, the crystals size wereuniform, the layer was thick and rough. When the water content was too high, thezeolite crystallization was incomplete, there was still some amorphous phase on thelayer. Under the optimum hydrothermal synthesis, NaX-type zeolites growed onsurefce of the hollow ifber support, the layer thickness was about30um. For theN2/CO2gas mixture N2was prior to CO2through NaX-type zeolite membarne and aseparation efe tor of4.96was found.(3) The NaX-type zeolite hollow fiber membranes were organic functionalLzed by grafting. The eiffciency of the membrane separation was improved significantly,because organic amine possessed strong CO2binding ability.