Ammonium-based eutectic solvents for the fractionation of woody biomass

Abstract

The sustainability of bioproducts hinges on the sustainable sourcing of their raw materials, such as lignocellulosic components—cellulose, hemicellulose, and lignin. In this context, lignocellulosic biomass (LCB) is a promising renewable resource that requires an effective pretreatment process to liberate its components for subsequent valorization. However, traditional fractionation methods are resource-intensive and do not align with current decarbonization goals and the shift toward a circular economy. Deep eutectic solvents have been explored in recent years for their potential as pulping agents. This study systematically evaluated 1:2 choline chloride–levulinic acid (ChCl-Lev, DES2) and 1:2 betaine–levulinic acid (Bet-Lev, DES1) DESs for Eucalyptus wood fractionation, assessing other process parameters (DES type, temperature, time, and biomass-to-DES ratio (S/L ratio)) as well as DES recoverability and recyclability. Through Experimental Design and Analysis of Variance (ɑ=0.05), the significant effects of DES type, Temperature, and Time, as well as their interactions, on the lignin, glucan, and hemicellulose content of the DES-treated residues were determined. The research demonstrated the superior fractionation performance of ChCl-Lev over Bet-Lev, especially under higher treatment conditions. Under these conditions, ChCl-Lev treatments produced solid residues with moderate yield (68-69%), with 67-68% glucan content, 13-15% hemicellulose content, and 19-20% lignin content. The DESs facilitated the extraction of lignin and hemicellulose while largely preserving cellulose fibers, with glucan removal remaining low (<5%), as confirmed by compositional analysis and FTIR spectroscopy. Optimal conditions for ChCl-Lev fractionation were determined to be 130 °C for 6 hours using a 1:5 w/w biomass-to-DES ratio, which will produce a solid residue containing 66.58% glucan, 15.36% hemicellulose, and 20.50% lignin. The recovery and reuse of DESs were successfully evaluated for three and two cycles, respectively, and revealed interesting findings, such as sustained pulping performance of recovered Bet-Lev but improved pulping performance of recovered ChCl-Lev compared to neat DES2 (yield of 47.12% and glucan content of 92.50%). A hydrated DES2 was also tested based on the recycling studies and showed comparable results. The work demonstrates the potential of the proposed DES-based fractionation process as an alternative pulping method for Eucalyptus wood.