Preparation of a plate-like C/C composite membrane for gas separation

Plate-like C/C composite membranes were prepared by spin-coating pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyamic acid (PAA) on membrane supports from bituminous coal and anthracite. The effects of coating time, the properties and pretreatment of the membrane supports, and modification by a blending surface modifier in PAA on the gas separation performance of the membranes were investigated. Scanning electron microscopy was used to characterize the microstructure of the membranes. Results indicate that the single gas permeation rates of the membranes decrease and selectivities increase with an increase in coating time. The gas separation performance of the bituminous coal-based membranes is better than that of anthracite-based ones. The pre-immersion treatment of anthracite supports can greatly improve the gas permeation rate of the membranes. A surface modifier improves the binding strength between the carbon plate and PAA, and membranes with the surface modifier additive exhibit molecular sieving after only one spin-coating. For the bituminous coal-based membranes, the selectivities of H₂/N₂, CO₂/N₂, O₂/N₂ are 94.3, 18.3, 10.2 respectively, and the selectivity for O₂/N₂ of air is 10.8 with the O₂ permeation rate of 4.99×10^-9 mol · m^-2 · s^-1 · Pa^-1. The O₂ concentration can reach 74.4% after one enrichment.