Structure Regulation Of NaY Zeolite Membranes And The Study Of Their Pervaporation Performance

NaY zeolite membrane has an effective pore size of 0.74 nm and strong hydrophilicity and polarity,so it has advantages in separating macromolecular material mixtures and some special systems which have similar properties but with polar differences.As a green chemical product,DMC is prepared by using MeOH as a raw material in industrial production,after the reaction process azeotropic mixture of DMC and MeOH which is difficult to separate by traditional separation process is formed.The kinetic diameter of MeOH molecular is smaller than that of DMC,and more hydrophilic and polar than DMC.So using NaY zeolite membrane to separate MeOH/DMC mixtrues,MeOH will penetrate preferentially.In this paper,the effects of the type and size of zeolite seed,the surface properties of the supports and the composition and properties of the dispersion medium of the seed on the quality of seed layer and zeolite membrane were studied in detail.And the effects of constant temperature and variable temperature crystallization methods on the microstructure of NaY zeolite membrane were also discussed.The zeolite seed,supports,seed layers and NaY zeolite membranes were characterized by transmission electron microscopy?TEM?,scanning electron microscopy?SEM?and X-ray diffraction?XRD?.Then,we investigated the pervaporation performance of NaY membranes for the separation of MeOH/DMC mixtrues.The results are as follows:1.The quality of seed layer was affectted by the size of the zeolite seed.It aggregated seriously when the size of seed was too small,and it was difficult to be assembled when the size of seed was too large.With the size of 500–600 nm NaY zeolite as seed crystal,the support can be completely covered.2.The surface properties of the supports had some influence on the formation of seed layer and film.The zeolite seed could be completely covered on the ?-Al₂O₃ and porous stainless steel supports.But on the porous stainless steel support,the seed could not adhere tightly which led to the final membrane falling off from the substrate.3.With the water as a single dispersion medium,the seed crystal covered the supports completely which is more uniform than that using ethanol as dispersion medium.And when adding 0.6 wt% polydiene dimethyl ammonium chloride solution?PDDA?in water as a mixed dispersion medium,the seed layer could cover the supports more flatly,without any supports exposed,the zeolite membrane from this seed layer was also intact.4.Dense and continuous NaY zeolite membranes were synthesized by crystallization at 100? for 7 h with the seed layer prepared with small NaY zeolite as seed crystal,0.6 wt% PDDA solution as a mixed dispersion medium on the ?-Al₂O₃ support.And the thickness of membranes prepared under variable temperature condition?140?2 h?100?6 h?was smaller than that obtained under constant temperature condition,but more dense than the former.5.The NaY zeolite membrane which crystallized at 100? for 7 h was used for the separation of MeOH/DMC?50 wt %?mixtures at 50? by pervaporation.The total fluxes increased?0.648–0.796 Kg/?m²·h??,and separation factors decreased?24.52–3.24?as the methanol concentration increased?20–80 wt %?.The total fluxes increased?0.278–1.224 Kg/?m²·h??,and separation factors decreased?23.52–2.78?as the feed temperature increased?20–70??.