(569dl) Investigating the Application of Stimuli-Responsive Ionic Liquids in Biomass Pretreatment for Selective Fractionation.

This study presents a novel approach to synthesize pH-responsive surface-active ionic liquids (ILs) for the selective fractionation of lignocellulosic biomass, with a focus on lignin. Utilizing the synthesis of N-hexadecyl-N-methylpyrrolidinium acetate (C16MPAc), a pH-sensitive IL, in pretreatment processes, we demonstrate its efficacy in fractionating cellulose, lignin, and hemicellulose components. Through a noncovalent bonding method, C16MPAc is combined with potassium phthalic acid (PPA) to form mixed cationic surfactants. The resulting IL exhibits selective distillation properties crucial for the fractionation process. Rheological analysis, cryogenic-transmission electron microscopy, and dynamic light scattering techniques elucidate the microstructural transitions from spherical to wormlike micelles, highlighting the pH-sensitive rheological properties essential for efficient pretreatment. Nuclear magnetic resonance and UV–vis spectroscopy investigations reveal the distinct binding affinities of hydrotropes to C16MPAc at varying pH levels, with PPA demonstrating superior binding capability. These findings underscore the versatility and economic viability of the noncovalent bonding method for fabricating pH-responsive surface-active ILs tailored for lignocellulosic biomass pretreatment, particularly in a lignin-first approach. Analytical methods including rheological analysis, cryogenic-transmission electron microscopy, dynamic light scattering, nuclear magnetic resonance spectroscopy, and UV–vis spectroscopy were employed to characterize the ILs and elucidate their behavior in the fractionation process.