Gas permeation properties and characterization of asymmetric carbon membranes prepared by pyrolyzing asymmetric polyimide hollow fiber membrane

Carbon membranes were continuously prepared by pyrolyzing an asymmetric polyimide hollow fiber membrane at temperatures ranging from 600 to 1000 degrees C under nitrogen for 3.6 min. The asymmetric polyimide hollow fiber membrane was treated under atmospheric air at 400 degrees C before pyrolysis. By scanning electron microscopy, the carbon membranes were observed to have an asymmetric structure of which a skin layer consisted of nodule aggregates. The asymmetric carbon membranes displayed high performance of gas permeability and selectivity. For example, the membranes prepared by pyrolyzing at over 700 degrees C had permeation rates of hydrogen ranging from 10(-4) to 10(-3) cm(3) (STP)/(cm(2) s cmHg) and ratios of the permeation rate of hydrogen to that of methane ranging from 100 to 630 at a feed gas composition of 50% hydrogen in methane and at 80 degrees C.