Gas permeation and pervaporation of water/alcohols through the microporous carbon membranes prepared from resorcinol/formaldehyde/quaternary ammonium compounds

Microporous carbon membranes were prepared on an α-alumina support by a pyrolysis of composites of a resorcinol/formaldehyde (RF) polymer and a quaternary ammonium compound (QAC). Tetramethylammonium bromide (TMAB) and tetrapropylammonium bromide (TPAB) were used as cationic surfactant. The results of N2 adsorption, H2 permeation and thermogravimetric measurements suggested that micropores appeared at 250 °C due to the decomposed gases from QAC in the RF/QAC composite resins, and the micropore volume increased at elevated temperature to 500 °C due to the gasification of QAC/RF resins. The pore sizes of the carbon membranes prepared using TMAB and TPAB were estimated to be about 0.4 and 0.5 nm based on the molecular size of the gases (H2, CH4, CF4 and i-C4H10) used in single gas permeations. The carbon membrane prepared using TMAB showed high selectivities to water in the pervaporation of H2O/ethanol and H2O/isopropanol mixtures. The carbon membrane prepared using TPAB showed a separation factor of 1155 for the H2O/IPA mixture at 30 °C. The high selectivity to H2O for the carbon membrane can be explained by not only the hydrophilic nature of the pore surface but also the molecular sieving effect.