Toshimune Yoshinaga

Gas Permeation Properties and Characterization of Asymmetric Carbon Membranes Prepared by Pyrolyzing Asymmetric Polyimide Hollow Fiber Membrane

Abstract Carbon membranes were continuously prepared by pyrolyzing an asymmetric polyimide hollow fiber membrane at temperatures ranging from 600 to 1000°C under nitrogen for 3.6 min. The asymmetric polyimide hollow fiber membrane was treated under atmospheric air at 400°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°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°C.

Relation of gas permeability with structure of aromatic polyimides II

Abstract We investigated relations between diffusivities on polyimides and physical parameters with mobilities of segments and examined viscoelasticity of polyimides on introducing the parameter as an index of mobilities of polymer chains. Each relaxation temperature of viscoelasticities on polyimide films having ordered regions was almost the same as that on the amorphous states. The CF 3 group as a substituent showed the similar effect to that of CH 3 group in elastic relaxation. The storage modulus was correlated well with the gas diffusivity. And in the case that relations between the diffusion coefficients and cohesive energy densities (CED) which were introduced as an index of cohesiveness of segments, the relation between CED and the gas diffusivities showed a good correlation. Mobilities of segments affected strongly the gas diffusivities even in the glassy polymers such as polyimides.