From experimental data to thermophysical insight: characterizing choline-based ionic liquids using advanced data...

Extracting valuable compounds from biomass requires the use of efficient dissolution processes, preferably at mild conditions. In the present study we examine the impact of hydration on the thermophysical properties of four choline-based ionic liquids (CHILs) that were shown to dissolve lignin efficiently in our previous work. Density and isobaric heat capacity across various temperatures and levels of hydration was measured. Due to the hygroscopic nature of these ionic liquids, careful control of the water content and extrapolation to zero water content were performed to derive their pure-phase properties. The extrapolation as well as the measurement uncertainty and outlier detection was carried out by means of a robust non-statistical approach based on mathematical gnostics. Derived apparent molar properties reveal distinct ion-water interactions, underpinning the role of hydration in modulating CHIL performance. These insights advance the fundamental understanding of CHIL-water mixtures and support their development for sustainable biomass processing and other green chemical technologies.