Study of Effect of pressure and temperature on the gas separation properties of a novel copolyimide membrane with flexible moieties

Abstract

In this research a novel copolyimide was synthesized with aliphatic diamine, which composed of 3,3ʹ4,4ʹ-Benzophenonetetracarboxylic dianhydride (BTDA), 4,4ʹ-Oxydianyline (ODA) and 4,9-dioxa-1,12-dodecacanediamine monomers. Synthesis was performed by thermal imidization in a two-pot procedure that carried out by unique block copolymerization method. The physical properties of the copolyimide were characterized by FT-IR and XRD. The permeability properties of O2, N2, CH4, and CO2 gases of synthesized copolyimide at different pressures and temperatures has been evaluated. The permeability coefficients of O2, N2, CH4, and CO2 decrease slightly with increasing pressure but for CO2 was more intense. The percentages of permeability decay increase exactly in the order of CO2 (3.30 Å), O2 (3.46 Å), N2 (3.64 Å), and CH4 (3.80 Å). Increasing temperature promoted permeability and diffusion coefficients which demonstrated reverse behavior with increasing pressure. Also, selectivity was observed to show the same trend for temperature as pressure effect. Compared with fully aromatic BTDA-ODA structure, the gas permeability and diffusion coefficients increased with adding aliphatic diamine because of flexible moieties in this monomer; however, the permselectivity of gas pairs such as O2/N2, CO2/CH4 and CO2/N2 was slightly decreased.