Solubility parameters of enzymatic hydrolysis lignin: a comparative study of inverse gas chromatography and Hansen...

Enzymatic hydrolysis lignin (EHL), a major byproduct of second-generation bioethanol production, is a promising renewable feedstock but remains challenging, in part because systematic solvent screening for EHL processing is largely absent from the literature. In this work, we combine inverse gas chromatography (IGC) with gravimetric solubility measurements to establish a practical, experimentally validated framework for solvent selection in EHL processing. Infinite dilution activity coefficients were measured for 31 probe solvents across 408.15-438.15 K. The IGC data were used to determine Hansen solubility parameters (HSPs): δ _D = 19.15, δ _P = 13.01, δ _H = 8.30 and δ _t = 24.58 MPa^0.5 while the interaction radius R ₀ = 8.98 MPa^0.5 was fitted using the gravimetric solubility experiments. Surface properties were also evaluated using the Snyder-Karger model. Polar and hydrogen-bonding interactions were identified as the dominant drivers of EHL-solvent affinity. The resulting HSP solubility sphere was validated against gravimetric solubility measurements for 22 solvents, where bio-based solvents such as γ-valerolactone was located within the EHL solubility sphere, highlighting their potential as promising bio-based solvent candidates for further evaluation in lignin processing. This work supports the development of an experimental basis for selecting alternative solvents for EHL processing and contributes to more sustainable routes for lignin valorization in lignocellulosic biorefineries.