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 (À10 to 30 C) and feed pressure (3 to 15 bar) on gas transport properties were studied for CO 2 and CH 4 gases. The use of PPG randomly distributed in the PEG, was more effective to enhance the membrane separation properties. CO 2 permeability was increased eight-fold (from 84 to 677 Barrer), while the CO 2 /CH 4 selectivity nearly remained constant. The mixed gas results of the blended membrane showed that the plasticizing effect of CO 2 increased the permeability of CH 4 with no significant change in the CO 2 permeability which resulted in lower mixed gas selectivity. Also, it was found that the CO 2 permeability remained high at sub-ambient conditions (down to À10 C) as soft phase crystallization did not occur.

Blending PPO‐based molecules with Pebax MH 1657 in membranes for gas separation

“…SEM pictures from pristine Pebax and blend membranes upon 50 wt % additive incorporation are shown in Figure . A defect‐free structure with no microscopic signs of phase separation is observed, in agreement with other work . Structural features (i.e., little cracks) that can be distinguished were presumably caused by sample pretreatment.…”

“…The results show that the applied additives do not act as plasticizers nor spacers on the crystalline domains inside the block copolymer. It was shown previously that PEG/PPG copolymer additives, with higher PEO/PPO ratios, did decrease crystallinity in both the polyether and polyamide domains …”

“…In the majority of studies concerning additive blending in Pebax, gas transport properties were altered through reducing crystalline effects with strong permeability enhancements . In this work, the PPO‐rich additives interacted with the amorphous parts, altering gas transport properties through a higher specific volume.…”

“…One series of additives included a random distribution of PPO within a PEO chain (PEG‐ ran ‐PPG) [where PPG is poly(propylene glycol)] whereas the other featured a block of PPO with PEO segments on both ends (PEG‐ block ‐PPG‐ block ‐PEG), a molecule from the so‐called Pluronics family. The PEG‐ ran ‐PPG additive thereby resulted in higher permeability increases (+705% for random vs. +545% for block distribution) . Also in mixed matrix membranes, addition of PEG‐ ran ‐PPG resulted in a strong synergistic effect on permeance and selectivity .…”

Amine‐functionalized CuBTC/poly(ether‐b‐amide‐6) (Pebax® MH 1657) mixed matrix membranes for CO2/CH4 separation

“…On the other hand, block copolymers containing ethylene oxide (EO) units or more generally polyether block amides (under the trademark Pebax) have been identified as outstanding materials for CO 2 separation. Pebax is a thermoplastic elastomer containing poly ethylene oxide (PEO) segments as the permeable phase and polyamide (PA) crystalline phase giving mechanical strength to the membrane …”