Gas permeation through carbonized hollow fiber membranes prepared by gel modification of polyamic acid

Polyamic acid (PAA) hollow fiber membrane was formed through gelation process. The gelation conditions, such as time, temperature and pH of coagulant were controlled. Subsequently PAA membrane was imidized at 473 K for 0.5 h and 673 K for 1 h, followed by carbonizing at 1023 K for 3 h in nitrogen atmosphere. The carbonization conditions were fixed to investigate the effect of gelation conditions on the properties of the carbonized membrane. The microstructure of the carbonized membrane was evaluated by the micropore volumes, which were measured using CO2, n-C4H10 and iso-C4H10. The micropore volumes depended on gelation temperature and pH of coagulant. The permeances of single component gas such as CO2 and CH4 through the carbonized membrane were measured using a volumetric membrane apparatus, and were in the order CO2, H-2 > He, O-2 > N-2 > CH4. The gelation process was important to control microstructure, permeance and permselectivity of the carbonized membrane. High permeance of CO2 and high CO2/CH4 permselectivity through the carbonized membrane were obtained under specific conditions of the gelation: time 6 h, temperature 275 K and pH 9.4. It was found that the performance of the carbonized membrane was superior to that of polyimide membrane developed so far. It was found that the transport of CO2 was mainly governed by adsorption effect and that of CH4 was restricted by molecular sieving effect in the carbonized membrane. (C) 1999 Elsevier Science B.V. All rights reserved.