Preparation of CO2-philic polymeric membranes by blending poly(ether-b-amide-6) and PEG/PPG-containing copolymer

Abstract

In the present work, membranes from block copolymer poly(ether-b-amide-6) (Pebax® MH 1657) and its blends with poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-block-PPG-block-PEG) and poly(ethylene glycol)-ran-poly(propylene glycol) (PEG-ran-PPG) copolymers were prepared by a solution casting and solvent evaporation method. In fact, the beneficial properties of PEG (high selectivity) with those of PPG (high permeability, amorphous) have been combined. The fabricated membranes were characterized by DSC, FTIR-ATR, AFM and SEM. According to DSC analysis, T_m for both soft and hard segments, T_g and crystallinity of blended membranes were decreased which was beneficial for the gas transport through the membranes. Effects of additive mass content (10 to 50 wt%), operating temperature (−10 to 30 °C) and feed pressure (3 to 15 bar) on gas transport properties were studied for CO₂ and CH₄ gases. The use of PPG randomly distributed in the PEG, was more effective to enhance the membrane separation properties. CO₂ permeability was increased eight-fold (from 84 to 677 Barrer), while the CO₂/CH₄ selectivity nearly remained constant. The mixed gas results of the blended membrane showed that the plasticizing effect of CO₂ increased the permeability of CH₄ with no significant change in the CO₂ permeability which resulted in lower mixed gas selectivity. Also, it was found that the CO₂ permeability remained high at sub-ambient conditions (down to −10 °C) as soft phase crystallization did not occur.