Fractionation of ‘water-soluble lignocellulose’ into C5/C6 sugars and sulfur-free lignins†
Recently, we demonstrated the mechanocatalytic depolymerization of lignocellulosic substrates as a powerful methodology that fully converts lignocellulosic substrates into ‘water-soluble lignocellulose’. We now show that the saccharification of the aqueous solution of depolymerized beechwood, pinewood and sugarcane bagasse (at 140 °C for 1 h) produces a high yield of sugars (e.g. 88–92% glucose, 3.5–8% glucose dimers and 93–98% xylose relative to the glucan and xylan fractions, respectively) and leads to precipitation of sulfur-free lignins. Noteworthy, the formation of furfurals is suppressed because the ‘water-soluble lignocelluloses’ undergo hydrolysis at relatively low temperatures. At 140 °C, 5-hydroxymethylfurfural and furfural are formed in yields not exceeding 1.4 and 5.7%, respectively. The separation of the carbohydrate fraction (as C5 and C6 sugars) from the lignin fraction is thus feasible by simple filtration.