Microporous polypropylene hollow fiber membranes: Part II. Pervaporation separation of water/ethanol mixtures by the poly(acrylic acid) grafted membranes

Polypropylene hollow fiber membranes grafted with poly(acrylic acid) were used for water–ethanol separation by pervaporation. The effects of grafting degree of poly(acrylic acid) (PAA), the cross-linking degree of the grafted-PAA, the sodium counter-ions as well as the operation temperature and the ethanol concentration in feed mixtures on pervaporation properties were investigated. It was found that water-permselective pervaporation membranes could be prepared by the grafting polymerization of acrylic acid on microporous polypropylene hollow fiber membrane surface. The separation factor increased with the increase of grafting degree of PAA in the range of 20–70 wt.%. Incorporating counter-ions as well as multifunctional comonomer into the grafted chains could improve the selectivity but sacrificed the permeation flux. The separation factor of the counter-ion containing membrane decreased according to the sequence Al3+ > K+ > Ca2+ > Na+ > Li+ and the permeation flux increased following the sequence Al3+ < Ca2+ < K+ < Na+ < Li+. Remarkable increase in permeation flux without decrease in separation factor was observed for Al3+ as counter-ion in this membrane. These results might be ascribed to the increase of packing density and the decrease of swelling degree of grafted layer on the membrane surface.