(290k) Influence of Thermally Labile Polymer on Gas Separation Properties of Carbon Membranes Derived from Poly(2,6-Dimethyl-1,4-Phenylene Oxide)

Interests on inorganic membranes have been increased for the potentials in gas separation technology due to good thermal and chemical stabilities. Of inorganic membranes, carbon membranes are considered to be one of the promising materials for membrane-based gas separation because of their excellent permeation and separation properties even under high pressure and temperature. The preparation of carbon membranes involves the following consecutive steps, such as polymeric membrane preparation, pretreatment, pyrolysis, and post-treatment. Of polymers, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is considered as one of the alternative promising polymeric precursors for carbon membrane preparation. In this study, the carbon membranes were prepared by the pyrolyisis of PPO polymer coated on the surface of the macroporous alumina ceramic membrane with a thermally labile polymer, polyvinylpyrrolidone (PVP) (molecular weight: 40,000) at the heating temperature of 973 K. Also, As post-treatment method, the post-oxidation of pyrolyzed carbon membranes was carried out in air circumstance at the heating temperature of 673 K in order to investigate the oxidation curing effect on the permeation performances. The permeation results showed that gas transport through the PPO and PPO blend carbon membranes was controlled by the molecular sieving effect. In addition, the addition of thermally labile polymer decreased gas permeance compared with the results of the PPO carbon membranes. The results imply that introduction of the thermally labile polymer showed pore controlling effects during the carbonization of the PPO polymer. For the oxidized carbon membranes, permeance of gas species increased due to increase in the membrane pore diameter, pore volume and surface area. It was observed that air oxidation increased permeance especially of gas species with large molecular size (e.g., N₂, CH₄, and C₂H₆), implying that the pore size distribution moved to a higher value. In the case of the post-oxidation of PPO blend carbon membrane, the permeation results showed higher gas permeances than those of the oxidized PPO carbon membranes, indicating that the thermally labile PVP remaining in the carbon membrane structure was removed during air oxidation, thus increasing the membrane pore volume. In the permeation results for the pyrolyzed and the post-oxidized PPO blend carbon membranes, it was shown that the introduction of the thermally labile polymer led to the membrane pore structure controlling in the carbon membranes during pyrolysis and air oxidation.