Research Of Inner Skin Hollow Fiber Polyion Complex Membrane And Its Pervaporation Performance

Electrostatic layer-by-layer (LBL) adsorption of oppositely charged polyelectrolytes has proven to be a promising method for the preparation of polyion complex membranes. But now this method is mainly used to assemble flat sheet and tubular membranes. Since hollow fiber membrane has some advantages such as high-packing density, self-contained mechanical support, this study therefore seeked to assemble inner skin hollow fiber polyion complex membranes by using a dynamic LBL adsorption technique. Subsequently, polyion complex membranes were applied to the pervaporation dehydration of organic solvents. The assembly process was successfully accomplished by alternatively dynamically filtrating polyacrylic acid (PAA) and polyethyleneimine (PEI) on a hydrolyzed hollow fiber polyacrylonitrile (PAN) membrane under a negative pressure condition.In this paper, the effects of dynamic assembly conditions on pervaporation performance of hollow fiber polyion complex membranes were investigated. It was found that the lower MWCO of PAN support membrane or the higher polyion bilayers numbers could improve pervaporation performances of polyion complex membranes. Meanwhile, the results showed that the higher negative pressure or the lower flow velocity could benefit for the formation of a defect-free selective layer. Then, the effects of operation conditions on the pervaporation separation behavior of various alcohol/water mixtures were subsequently investigated. It was found that the higher feed temperature and the larger molecular weight of alcohol could facilitate the pervaporation separation. In the case of pervaporation of 95wt% ethanol/water mixtures, under the temperature of 50℃, the separation factor and the permeate flux of hollow fiber polyion complex membranes with only 2.5 bilayers were about 821.7 and 132.8g/ (m2·h), respectively.In order to improve the permeate flux and mechanical properties of polyion complex membrane, single-side surface hydrolysis of PAN hollow fiber membrane by liquid transpositional method were also studied. The experimental results of IR and EDX proved that the carboxyl group only formed on the inner surface of PAN hollow fiber membrane by surface hydrolysis, but not on the outer surface and cross-section. It was found that the mechanical properties of single-side surface hydrolyzed PAN membranes were improved compared with entirely hydrolyzed PAN membrane. The pervaporation flux highly increased while the selectivity was still kept at a relatively high level.