Development of crosslinked poly(ether-block-amide) membrane for CO2/CH4 separation

Thin film composite membranes of poly(ether-block-amide) (PEBAX-1657) were prepared on PVDF ultra-porous substrate by solution casting and solvent evaporation method. The membrane was crosslinked by a novel method using 2% (v/v) 2,4-toluylene diisocyanate (TDI) in hexane medium. Sorption studies were carried out in pure water to confirm crosslinking. Both the unmodified and modified membranes were characterized by scanning electron microscopy (SEM) to study the morphologies of the surface and cross-section. X-ray diffraction (XRD) experiments were carried out to understand the intermolecular interactions and separation mechanisms. Thermal stability of the membrane was assessed by differential scanning calorimetry (DSC). Single gas permeabilities of CO2 and CH4 and the resultant ideal selectivities were determined for unmodified PEBAX-1657 membrane using an indigenously built high-pressure gas separation manifold. A comparison was made with PEBAX-2533 membrane, also prepared in this study, to evaluate the effect of rigid block content in the polymers. As the pressure was varied from 10 to 40 kg/cm2, the permeance and ideal selectivity for the unmodified PEBAX-1657 were found to range from 3.0 to 4.8 GPU and 18 to 25, respectively. On the other hand PEBAX-1657 membrane crosslinked for 5 min exhibited only one-fifth the permeance (0.6–0.9 GPU) but almost twice the selectivity (38–47). The effect of crosslinking time (0–60 min) and binary feed mixture composition (5–20% CO2) on performance of membrane was studied at a constant pressure. PEBAX-1657 was found to be promising for the separation of CO2 from CH4.