Pebax membrane for CO2/CH4 separation: Effects of various solvents on morphology and performance

In this study, the effects of different solvents on the morphology and permeation of poly(ether-block-amide) (Pebax-1657) membranes were investigated. Pebax membranes were fabricated via a solution casting method with five different solvents, that is, N,N-dimethyl formamide (DMF), N, N-dimethyl acetamide (DMAc), N-methyl-2-pyrrolidone (NMP), formic acid, and a mixture of ethanol (EtOH) with water (H2O). Cross-sectional scanning electron microscopy analysis of the membranes was performed to investigate the morphology of the prepared membranes. X-ray diffraction and Fourier transform infrared analysis were also carried out to characterize the membranes. The interactions of the polymer and various solvents were evaluated with Hansen solubility parameters. Permeation experiments for CO2 and CH4 gases were performed to study the effects of the solvents on the permeation properties of the membranes. The solvent properties, such as the molar volume, boiling point, and solubility parameters, were investigated as were the membranes characteristics, such as the crystallinity, d-spacing, and fractional free volume. The results obtained from the experiments show that the CO2 permeability for the membranes prepared with different solvents followed this order: NMP > DMF > Formic acid > DMAc > H2O/EtOH mixture. With increasing molar volume, the gas permeability increased for all of the membranes, except for DMAc, which showed a lower permeability because of its highly crystalline structure. DMF showed a higher CO2/CH4 ideal selectivity compared to the other membranes and, consequently, could be introduced as the best solvent from all aspects for the Pebax-1657 membrane. (C) 2016 Wiley Periodicals, Inc.