Hydrothermal decomposition of alkali lignin in sub- and supercritical water

Alkali lignin as an example of waste plant biomass was subjected in a batch reactor to decomposition in sub- and supercritical water. Hydrothermolysis of alkali lignin with relatively highmolecular-weight led to the production of phenolic compounds such as guaiacol and catechol, as well as phenol, m-cresol, p-cresols and o-cresol. Both an increase growth in conversion time and an increase in reaction temperature promoted secondary reactions: degradation of alkali lignin decomposition products, leading to, their repolymerization and carbonization. The components of the liquid fractions of products were examined by GC–MS and HPLC, whereas the solid charred post-reaction residues were analyzed by elemental analysis and FTIR.

► Utilizing of alkali lignin-waste of pulp and paper industry.
► Hydrothermal decomposition of alkali lignin as a new method of its conversion.
► Low molecular phenolic compounds as a valuable products of studied reaction.
► Repolymerization of monomeric phenols resulting in biochar formation.