Ionic liquid solvent properties as predictors of lignocellulose pretreatment efficacy

TLDR

Effective pretreatment of lignocellulosic biomass is essential for biofuel production, and while room‑temperature ionic liquids (RTILs) are increasingly used for this purpose, the physicochemical parameters that drive their effectiveness remain poorly understood. This study investigates how the Kamlet–Taft α, β, and π* solvent polarity parameters of selected RTILs predict their pretreatment efficacy on lignocellulosic biomass. The authors assessed pretreatment by varying RTIL composition and water content, noting that decreasing the β parameter through acetate dilution or water addition reduces lignin removal, cellulose crystallinity reduction, and sugar yields. The β parameter proved to be an excellent predictor of pretreatment efficacy; RTILs with β > 1.0 removed over 32 % of lignin and achieved >65 % glucose yields, whereas a β = 0.60 RTIL removed only 19 % of lignin and did not improve sugar yield.

Abstract

Effective pretreatment of lignocellulosic biomass is vital to its bioconversion to a usable liquid fuel. A growing body of work has focused on using room temperature ionic liquids (RTILs) to pretreat lignocellulose for subsequent fermentation. However, little is known about the physicochemical parameters of RTILs that promote effective pretreatment. In this work we examine the relationship between the Kamlet–Taft α, β, and π* solvent polarity parameters of different RTILs ([Emim][OAc], [Bmim][OAc], and [Bmim][MeSO4]) and effective pretreatment of lignocellulosic biomass. We find the β parameter is an excellent predictor of pretreatment efficacy. Acetate containing RTILs (β > 1.0) remove >32% of lignin from maple wood flour and significantly reduce cellulose crystallinity, resulting in >65% glucose yields after 12 h cellulase hydrolysis. Pretreatment in [Bmim][MeSO4] (β = 0.60) results in the removal of only 19% of the wood flour's lignin with no decrease in crystallinity, and no improvement in sugar yield over untreated wood flour. The addition of water and the dilution of the acetate anion with the methyl sulfate anion decrease the β value and subsequently have a negative impact on lignin extraction, cellulose crystallinity, and sugar yields.