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

Abstract

Cellulose acetate (CA) is an attractive membrane polymer for CO2 capture market. However, its low CO2 pe1meability hampers its application as part of a membrane for most relevant types of CO 2 containing feeds. This work investigates the enhancement of CA separation performance by incorporating ionic liquid-like pendants (1methylimidazol, 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, FfIR, DSC/TGA, and processed into thin-film composite membranes. The membrane performance in C0 2 /N 2 mixed-gas permeation experiments shows a decrease in CO 2 and N 2 permeability and an initial decrease and then gradual increase in C0 2 /N 2 selectivity with increasing HEDMA conrenr. The an1otmt 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.

A Review on Ionic Liquid Gas Separation Membranes

“…This term later spread in the community of groups working on ILs polymerization and was facilitated by works of Mecerreyes et al [116][117][118]. Eventually, the term 'PIL' also started to be associated with the polymers post-modified chemically to mimic the structure of polymerized ILs [119][120][121][122][123][124]. Currently, the term poly(ionic liquids) refers to several variations, such as "polymerized ionic liquids", "polymeric ionic liquids", and "polyionic liquids", that are used interchangeably, and it is widely applied to the broad range of polymeric materials, comprising a similar structure of repeated electrolyte units bound to a shared polymer backbone.…”

“…Similar stability can be achieved by the incorporation of hydroxide, carbonate, phosphate, and phosphonate The majority of cationic PILs are synthesized in two steps: Quaternization (includes imidization) followed by anion exchange. The possibility to incorporate quaternary ammonium groups combined with interchangeable anions opens plenty of opportunities for customization [119,124,204]. Even broader PILs customization can be achieved by incorporating other hetero-ions, such as phosphonium, sulphonium, boronium, etc.…”

Molecular Engineering of Copoly(ionic liquids)-Based Membranes for CO2 Separation

“…Hu et al synthesized PILs by grafting PEG onto the two ionic polymers to make more flexible membranes by using PEG as a plasticizer because of its low glass transition temperature. Moreover, modifying CA with pyrrolidinium cations to form CA-based PILs provided a promising method to promote gas permeability and selectivity of the CA-derived membranes for CO 2 separation. , In addition, poly­(norbornene)­s, emerging as a promising materials class, have been synthesized and prepared as membranes for gas separation due to its tunability of thermal properties as well as structural scaffolds, also including easily polymerized by various polymerization mechanisms. Ravula et al incorporated the poly­(norbornene)­s into PILs to fabricate membranes for CO 2 separation with enhanced CO 2 /N 2 and CO 2 /CH 4 selectivities .…”