Separation of CO2/CH4 mixture through carbonized membrane prepared by gel modification

The carbonized hollow fiber membranes were prepared through gelation of polyamic acid solution, imidization and carbonization of polyamic acid (PAA) gel by mainly controlling the gelation conditions. The microstructure of the carbonized membranes was evaluated by micropore volume, which was measured by molecular probe method. The permeation properties of pure CO2, pure CH4 and CO2/CH4 mixture through the carbonized membranes were measured and analyzed. High CO2/CH4 permselectivity was achieved by the carbonized membrane which was prepared under a specific condition (gelation condition: temperature 275 K, pH of coagulant 9.4; carbonization condition: temperature 1023 K, time 3 h). The permeance of CO2 at 298 K and the activation energy for CO2 permeation for mixed gas system were almost equal to those for pure gas system in this carbonized membrane. On the other hand, the permeance of CH4 for mixed gas system decreased in comparison to that for pure gas system due to the hindrance of CH4 permeation by CO2 molecules existing inside the micropores, so that the activation energy for CH4 permeation increased and the CO2/CH4 permselectivity for mixed gas system was greater in comparison to results from pure gas permeation. It was found that the micropores of 0.43-0.50 nm played a very important role to create high CO2/CH4 permselectivity. (C) 2000 Elsevier Science B.V. All rights reserved.