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, CO 2, 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 CO 2 and H 2 gases, respectively, whereas that of N 2 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 CO 2 /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 CO 2 from N 2 in power plants, H 2 recycle from ammonia purge gas, O 2 enrichment from air for medical applications, and CO 2 removal from water-gas shift reaction to improve H 2 yield.