Influence of ionic liquid-like cationic pendants composition in cellulose based polyelectrolytes on membrane-based CO2 separation

Cellulose acetate (CA) is an attractive membrane polymer for CO2 capture market. However, its low CO2 permeability hampers its application as part of a membrane for most relevant types of CO2 containing feeds. This work investigates the enhancement of CA separation performance by incorporating ionic liquid-like pendants (1-methylimidazol, 1-methylpyrrolidine, and 2-hydroxyethyldimethylamine (HEDMA) on the CA backbone. These CA-based polyelectrolytes (PEs), synthesised by covalent grafting of cationic pendants with anion metathesis, were characterised by NMR, FTIR, DSC/TGA, and processed into thin-film composite membranes. The membrane performance in CO2/N-2 mixed-gas permeation experiments shows a decrease in CO2 and N-2 permeability and an initial decrease and then gradual increase in CO2/N-2 selectivity with increasing HEDMA content. The amount of HEDMA attached to the CA backbone determines overall separation process in bifunctional PEs. This indicates that the hydroxy-substituted cationic pendants alter interactions between PEs network and permeating CO2 molecules, suggesting possibilities for further improvements.

Automated summary

This study investigates enhancing the separation performance of cellulose acetate (CA) by incorporating ionic liquid-like pendants. The experiments show that with increasing HEDMA content, the permeability of CO2 and N-2 decreases, while the selectivity of CO2/N-2 initially decreases and then gradually increases. This suggests potential for further improvements by altering interactions between the polymer network and permeating CO2 molecules.