Nylon 4, which possesses high mechanical strength and good affinity for water, can be considered as a liquid separation membrane. To improve the hydrophilicity of a Nylon 4 membrane for pervaporation and evapomeation processes, and to overcome the hydrolysis of polyvinyl alcohol (PVA), this study attempts to prepare a PVA-g-Nylon 4 membrane by y-ray irradiation grafting of vinyl acetate (VAc) onto Nylon 4 membrane, followed by hydrolysis treatment. The effects of downstream pressure, irradiation dose, VAc monomer concentration, degree of grafting, feed composition, and size of alcohols on the separation of water-alcohol mixtures were studied. The surface properties of the prepared membrane were characterized by FTIR, ESCA, and a contact angle meter. A separation factor of 13.8 and a permeation rate of 0.352 kg/m'.h can be obtained for a PVA-g-Nylon 4 membrane with a degree of grafting of 21.2% for a 90-wt% ethanol feed concentration. Compared to the pervaporation process, the evapomeation process has a significantly increased separation factor with a decreased permeation rate for the same PVA-g-Nylon 4 membrane.

SYNOPSISThe ethanol-water separation by pervaporation with y-ray irradiation-modified nylon 4 membrane was investigated. The membrane was prepared by homografting y-ray irradiation of vinyl acetate (VAc) monomer onto nylon 4, poly(viny1 acetate) (PVAc) -homo-g-nylon 4 followed by hydrolysis treatment, poly (vinyl alcohol) (PVA) -homo-g-nylon 4. The homografting method shows significant improvement in the degree of grafting of ( VAc) onto nylon 4 over the heterografting method. For example, the degrees of grafting of the VAc with 30 vol % and total dose of 2 Mrad for the heterografkd method and for the homografted method are 14.1 and 42.2%, respectively. The effects of irradiation with or without oxygen in solution, irradiation time, VAc content, degree of grafting, crystallinity, feed concentration, and operating temperature on performances of the PVA-homo-g-nylon 4 membrane were carried out. Comparison of the separation factor of sorption in membrane ( C Y , ,~) and that of pervaporation ( a p e w ) was made. A separation factor of 7.3 and a 0.691 kg/m2 h permeation rate can be obtained by the PVA-homo-g-nylon 4 membrane with a degree of grafting of 42.2% for 90 wt % ethanol feed concentration. Compared with the unmodified nylon 4 membrane, which has the separation factor of 4 and permeation rate of 0.350 kg/ m2 h, the PVA-homo-g-nylon 4 membrane shows improved a separation factor and permeation rate. 0 1993 John Wiley & Sons, Inc. INTRODUCTIONThe separation process by pervaporation through graft polymerization of some vinyl monomers onto the polymeric substrate has been The various modified methods included were blending, cross-linking, 7-10 and This process is potentially useful in fields where pervaporation techniques are appropriate, such as fractionation of close-boiling components, azeotropic mixtures, isomeric mixtures, and heat-sensitive mixtures.The mechanism of the separation process of binary mixtures is complicated because of the difference in affinities of the permeating mixture for the polymer membrane. The diffusion coefficients of the components are used principally to separate them, thus resulting in nonlinear transport with respect ~~~ ~ * To whom correspondence should be addressed. Nylon 4 membrane has been regarded as a promising membrane material for separation purposes because of its excellent strength and inherent affinity to water. Use of Co60 y-ray irradiation, chemical grafting, and plasma deposition methods to improve the performance of nylon 4 for reverse osmosis,26 ultrafiltration, 27 dialysis, 28 and hemodialysis 29 have been reported by our laboratory. To improve the hydrophilicity of nylon 4 membranes for pervaporation purposes and to overcome the dissolution of PVA in water, this study attempts to obtain PVA-homog-nylon 4 membrane by y-ray irradiation homografting of vinyl acetate ( VAc) onto nylon 4 membrane, followed by hydrolysis treatment. The effects of VAc content, irradiation time, irradiation with or without oxygen, degree of grafting, crystallinity, feed concentration, a...

No abstract