Extraction of phenolic compounds from sulfur-free black liquor thanks to hydrothermal treatment before the production of syngas for biofuels

Abstract

Nowadays, black liquor, the liquid residue from cooking step in pulp industry is burnt to produce energy for the plant. But as the pulp mills have energy in excess, higher added values applications for black liquor may be looked for. Hydrothermal treatment offers a good opportunity as it is well suited for this kind of wet feedstock. It may be used to depolymerize organic compounds or produce syngas for biofuels applications. The objective of this study is to combine phenols and biofuel production by extracting the small organic molecules formed at moderate temperature prior to complete gasification of black liquor. Hydrothermal experiments from 225 °C to 600 °C have been performed on sulfur-free black liquor in batch reactor. At 280 °C phenol, guaiacol and syringol were found in their highest quantity: 5% of the initial lignin (which represented 6 wt% of the liquid black liquor) could be converted into these three compounds.