Base-catalysed depolymerization of lignins in supercritical water: Influence of lignin nature and valorisation of pulping and biorefinery by-products

Different lignins from different sources (hardwoods, softwoods and crop residues) and obtained as by-products of different processes such pulping or biorefining were depolymerized in alkaline supercritical water (SCW: 386 °C and 260 bar) in an intensified continuous process to produce high value-added compounds with low-molecular-weight in only 300 ms of reaction time. The products obtained were analysed to determine the yield, selectivity to monomers, chemical structure and molecular weight distribution. The char formation was low in most cases, but the proportion of heavy and light oils were variable upon the starting material used. The monoaromatics yield depends mostly on the type of lignin utilized being the non-wood biorefinery lignins less suitable for monomers production than the technical wood ones (13-8%). The monomer distribution depends on the biomass of origin and the pulping method. This technology is equally effective when directly treating a black liquor and better results are obtained if compared to the corresponding isolated lignin.