Gas Permeation Behavior of Pebax-1657 Nanocomposite Membrane Incorporated with Multiwalled Carbon Nanotubes

Incorporation of multiwalled carbon nanotubes (MWNT) on the gas permeation properties of H-2, CO2, O-2, and N-2 gases in poly(ether-block-amide) (Pebax-1657) membrane has been investigated. Pebax-1657 was dissolved in the ethanol water mixture and cast on an ultraporous polyethersulfone substrate followed by complete solvent evaporation. Nanocomposite membranes were prepared by dispersion of MWNT in concentrations of 0-5% of polymer weight in the Pebax solutions with sonication for 2 h to ensure uniformity. Cross-linking was carried out in hexane medium using 2,4-toluylene diisocyanate (TDI). The permeabilities of pure gases were measured at room temperature, and the ideal selectivities were determined at pressures varying from 1-3 MPa using an indigenously built high-pressure gas separation manifold. For neat Pebax membrane, high permeabilities of 55.8 and 32.1 barrers were observed for CO2 and H-2 gases, respectively, whereas that of N2 was as low as 1.4 barrers. The selectivity of cross-linked 2% MWNT Pebax membrane was enhanced from 83.2 to 162 with increasing feed pressure (1-3 MPa) for the CO2/N-2 gas pair, whereas the corresponding values for H-2/N-2 and O-2/N-2 systems were found to be in the range 82.5-90 and 7.1-6.8, respectively. The membranes were characterized by scanning electron microscopy (SEM) to study surface and cross-sectional morphologies. Fourier transform infrared (FT-IR), wide-angle X-ray diffraction (WAXD), and ion exchange capacity (IEC) studies were carried out to determine the effect of MWNT incorporation on intermolecular interactions, degree of crystallinity, and extent of cross-linking, respectively. Fractional free volume (FFV) calculations based on density measurements were conducted along with water sorption studies to explain permeation behavior. The use of modified block copolymer membranes provides a means for separation of CO2 from N-2 in power plants, H-2 recycle from ammonia purge gas, O-2 enrichment from air for medical applications, and CO2 removal from water-gas shift reaction to improve H-2 yield.