Ionic liquids are of emerging interest as potential media for CO2 solubilization. This work reports on the use of biosynthesized monorhamnolipids (R,R) α-L-rhamnopyranosyl-β-hydroxyalkanoyl-β- hydroxyalkanoates (mRL), commonly obtained from strains of Pseudomonas aeruginosa, as anions in a new class of protic ionic liquids when coupled with various amine cations. These materials, termed glyonic liquids, exhibit excellent thermal stability and good conductivity, are biodegradable and of low toxicity, which allows them to be of potential use in applications wherein more toxic conventional ionic liquids may not be appropriate. Glyonic liquids based on the mRL anion and simple amine cations, such as tert-butyl amine, n-butyl amine, ammonium and octyl amine, were synthesized and their general properties characterized using NMR spectroscopy, mass spectrometry, FTIR, conductivity, thermal analysis (DSC and TGA) and rheology. The CO2 solubility properties of these glyonic liquids from 15-45 °C at pressures from 1-3 bar were investigated using a quartz crystal microbalance (QCM) system. CO2 solubilities of up to 0.5 mol CO2/mol glyonic liquid were observed under these limited conditions. Density functional theory (DFT) calculations of CO2-glyonic liquid binding energy were used to support the experimental observations and to provide better predictive abilities for future studies. The CO2 sorption properties of the glyonic liquids are generally comparable to or better than reported gas sorption values for conventional ionic liquids. Overall, the results obtained indicate that glyonic liquids may be suitable for CO2 harvesting and sensing, as they demonstrate good CO2 solubility with a fast, reversible response that can be tuned by cation choice.

Glyonic liquids based on rhamnolipids for CO2 sorption

ACS Spring 2022

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