Development of polyion complex hollow fiber membrane for separation of water-ethanol mixtures

Abstract

For the purpose of separating water-ethanol mixtures by the use of the pervaporation technique, a new hollow fiber membrane composed of the polyion complex (PIC) consisting of polyacrylic acid and polycation was developed. To obtain this a new technique was developed instead of coating. That is, polyacrylonitrile membrane was partially hydrolysed to introduce carboxylic groups and then converted to the polyion complex. The hydrolysis reaction and the formation of a separating layer were analyzed by the use of IR, SEM and EDS. Through these observations it was found that carboxylic groups were uniformly formed by immersing the membrane into a NaOH aqueous solution. Moreover, the pores of less than 0.1 μm in diameter on the inner surface of the membrane disappeared with the proceeding of a hydrolysis reaction. The carboxylic layer was changed into the separating layer by immersing the membrane into an ionene aqueous solution. By varying the hydrolysis conditions and optimizing the post-treatment, the preparation of a hollow fiber having PIC as a separating layer became possible. An excellent module with an effective membrane area of 6 m 2 showed more than a 5,000 separation factor and approximately 400 g/m 2·h in permeation rate for 95 wt% ethanol solution at 60°C.