INTEGRALLY SKINNED POLYSULFONE HOLLOW-FIBER MEMBRANES FOR PERVAPORATION

From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process des cribed here differs from the traditional dry-wet spinning process wher e the fiber enters the coagulation bath after passing a certain air ga p. In the present process, a specially designed tripple orifice spinne ret has been used that allows spinning without contact with the air. T his spinneret makes it possible to use two different nonsolvents subse quently. During the contact time with the first nonsolvent, the polyme r concentration in the top layer is enhanced, after which the second c oagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of +/- 1 mum have been obtained, supported by a porous sublayer. The effect of spinning param eters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and p ervaporation experiments, using a mixture of 80 wt % acetic acid and 2 0 wt % water at a temperature of 70-degrees-C. Higher fluxes as a resu lt of a lower resistance in the substructure could be obtained by addi ng glycerol to the spinning dope, by decreasing the polymer concentrat ion, and by adding a certain amount of solvent to the bore liquid. Oth er parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent. (C) 1994 John Wiley & Sons, Inc .