Plasticization behavior of crown-ether containing polyimide membranes for the separation of CO2

This paper describes the influence of crown-ether ring size and rigidity on the gas separation performance of CO2/N-2 and plasticization behavior of crown-ether containing Matrimid (R) 5218 polyimide membranes. The crown-ethers provide the membrane material with good affinity for CO2 due to the polar ether segments. Three different crown-ethers were used that differ in ring size and in rigidity (DB21C7, DB18C6 and 18C6). The gas separation performance of the crown-ether containing membranes was evaluated using pure gas and mixed gas conditions at pressures up to 40 bar. Thermal analysis (TGA and DSC) shows that the incorporation of the crownethers in the polyimide matrix was successful and that the crown-ethers have good compatibility with the polymer matrix. Gas sorption in the crown-ether containing membranes shows an enhanced solubility selectivity due to the enhanced interaction with CO2 compared to the pristine Matrimid (R). However, both solubility and permeability of CO2 and N-2 are decreased in these crown-ether containing membranes over the whole pressure range. When the molecular size of the crown-ether decreases (DB21C7 > DB18C6 > 18C6) the permeability increases. In addition, the incorporation of the more rigid crown-ethers (DB18C6 and DB21C7) causes rigidification of the polymer matrix contributing to the lower permeability of DB18C6 and DB21C7-based membranes. Pure gas CO2 permeation measurements show a typical plasticization behavior for pristine Matrimid (R), while for the crown-ether containing membranes the extent of plasticization is significantly reduced. Next to that the plasticization pressure is shifted to higher CO2 feed pressures. No plasticization was observed for the crown-ether containing membranes in the mixed gas conditions, as a result of the lower solubility of the crown-ether containing membranes and competition effects of CO2 and N-2. The differences in size and rigidity of the different crown-ethers showed no significant influence on the plasticization resistance of crown-ether containing membranes. Altogether, the operating window of these crown-ether containing membranes is increased with respect to Matrimid (R) showing their potential to operate at higher CO2 partial pressure without compromising selectivity.

Automated summary

This study investigates the impact of crown-ether ring size and rigidity on the gas separation performance and plasticization behavior of Matrimid (R) 5218 polyimide membranes. The crown-ether containing membranes exhibit enhanced solubility selectivity for CO2 but reduced solubility and permeability for both CO2 and N-2. The variation in crown-ether size and rigidity does not significantly affect the plasticization resistance of the membranes.