Towards ionic liquid fractionation of lignocellulosics for fermentable sugars

The present study investigates wood fractionation through ionic liquid (IL) mediated pretreatment, for obtaining simple fermentable sugars, namely oligo-and monosaccharides, and in particular hexoses (and pentoses). The study focuses on softwood, Scots Pine (Pinus sylvestris) and Norway Spruce (Picea abies), exposed to ionic liquid 1-ethyl-3-methylimidazolium chloride (EmimCl). Since both EmimCl and the monosaccharides are water-soluble and dissolve readily in similar solvents, the separation of this hydrophilic IL from sugars is difficult. Moreover, the analytics of monosaccharides released from lignocellulosics with the help of EmimCl is challenging. Sufficiently diluted samples, with low enough EmimCl concentrations, tolerated by GC sugar columns, can be also analyzed by GC. The results obtained suggest that some IL-tolerating HPLC columns can be utilized for a quantitative determination of monosaccharides. However, frequently, these columns have low separation ability for monosaccharides and, consequently, the retention time values are very close to each other. So far, the best results on HPLC utilization were obtained with isocratic elution, using a refractive index detector and a diode array UV detector in series.