Feedstock considerations in lignocellulosic biomass fractionation using low-cost ionic liquids
The IonoSolv pretreatment is a new technique employing protic low-cost ionic liquids and has previously been applied to successfully fractionate switchgrass and the grass Miscanthus giganteus. This study investigates the effect of using the protic ionic liquid solution [N2220][HSO4]80% with two different acid/base ratios (1.02 and 0.98) at 120, 150 and 170 °C on the pretreatment outcome of the hardwood willow. The ionic liquid solution was able to fractionate willow and a pulp and lignin fraction were recovered after treatment. The pretreatment success was determined via enzymatic hydrolysis of the pulp, which showed that the IonoSolv pretreatment was able to increase enzymatic glucose yields compared to untreated willow biomass. The pretreatment produced a cellulose-rich pulp with high hemicellulose and lignin removal. The pulp composition and glucose yield after saccharification were greatly influenced by the acidity of the ionic liquid solution, temperature and pretreatment time. The extracted lignin was analysed via 2-D HSQC NMR and GPC to investigate the changes in lignin structure induced by the pretreatment severity. Lignin structure (in terms of interunit linkages and S/G ratio) and molecular weight varied significantly depending on the pretreatment conditions used.