Preparation And Study Of NaA Zeolite Membrane For Dehydration Of Organics

Pervaporation (PV) is a new-type membrane separation process with high separation efficiency, low energy consumption, low pollution and convenience in operation, and it has been widely applied in dehydration of organic solvents in recent years. NaA zeolite membranes with high hydrophilicity and micro-aperture (0.41nm) which ranges between the diameters of the most organic solvents and water molecules have become ideal materials in dehydration of organics by pervaporation. Therefor, it is of significance to conduct preparation and application studies of NaA zeolite membranes.In this thesis, the preparation conditions of sub micron-size NaA seeds by the ball-milling method were firstly investigated. Then we used the submicron-size ball-milled seeds to prepare NaA zeolite membrane on the supports with length of8cm by secondary growth method. Based on this, industrial scale-up productions of NaA zeolite membrane were conducted. NaA zeolite membranes were prepared on the supports with length of80cm. The as-synthesized NaA zeolite membranes were characterized by SEM, XRD and PV. The main research results obtained in the work were as follows:(1) NaA zeolite membranes were prepared on the small pore α-Al2O3supports with length of8cm by secondary growth method with submicron-size NaA seeds. The preparation conditions of submicron-size NaA seeds and the effects of seeding concentration and crystal morphology on microstructure and performance of membranes were researched. Pervaporation experiments were carried out at feed temperature of75℃and permeate pressure of100-200Pa for dehydration of90wt.%ethanol/water mixtures with a laboratory scale apparatus to test the performance of as-synthesized membranes. The NaA zeolite membrane prepared using ball-milled seeds showed the high reproducibility and the high performance with the maximum water flux of1.48kg·m-2·h-1and the separation factor of5380.(2) It was investigated that the8cm macroporous α-Al2O3supports with some flaws were modified by different methods. Well-intergrown and continuous NaA zeolite membranes were prepared on the well-modified macroporous support coated with ball-milled seeds. Under the condition of75℃and100～200Pa, the separation performance of as-synthesized membrane for dehydration of90wt.%ethanol/water mixtures was tested by PV. The result was that the separation factor was more than5000and the water flux reached2.07kg·m-2·h-1.(3) NaA zeolite membranes of industrial specifications were successfully prepared in batches on the80cm lengh and small pore a-Al2O3supports. The as-synthesized membranes were tested by PV using a pilot scale apparatus. Maintaining200L-h"1of the feed flow rate, when the feed temperature was75℃, the maximum permeation flux for dehydration of90wt.%ethanol/water mixtures could reach2.53kg·m-2·h-1and the separation factor was7702among all of tested membranes. The reproducibility of as-synthesized membranes was high.(4) The effects of feed temperature and concentration of ethanol/water mixtures and methanol/water mixtures on pervaporation performance of membranes were researched. In the two systems mentioned above, the water flux of NaA zeolite membranes was increasing with the rising of feed temperature and decreasing with the increase of feed concentration, but the water concentration of permeation sides was slightly affected by feed temperature or concentration and keeped essentially unchanged, closing to100%.