Fractionation of woodmeal by prehydrolysis and thermal organosolv. Process strategy, recovery of constituents, and solvent fractionation of lignins so produced

A prototype hardwood Populus deltoids has been fractionated in kg quantities into its primary constitutive polymers, namely, cellulose, hemicelluloses, and lignin, under optimal recovery conditions for each fraction. Our approach is targeted at processing sawdust or finally divided wood ( d p ≤ 0.5 mm) and involves a thermomechano‐solvolytic treatment of medium consistency suspensions in two process development units operated sequentially. Firstly, the hemicellulose fraction is removed from the initial wood by a aqueous‐steam pretreatment (auto‐hydrolysis) at conditions where nearly 90% of the hemicelluloses are solubilized. Secondly, the treated wood (lignocellulose) is separated into cellulose and lignin rich fractions by subjecting it to an organosolvolytic treatment using ethylene glycol as solvent. An experimental unit which can be operated in semi‐continuous or continuous modes is described and was employed for this step. The recovery of each fraction via appropriate mass balances is presented. Also, a comparative characterization of the lignins isolated via (a) the direct solvolysis route and (b) the sequential aqueous‐steam pretreatment followed by solvolysis approach is made using solvent fractionation, molar mass distribution, and 13 C NMR spectroscopy methods.