Liquefaction of Kraft lignin using polyhydric alcohols and organic acids as catalysts for sustainable polyols production

[EN]In this work, three different organic acid catalysts, (acetic acid, lactic acid and citric acid), are proposed as an alternative to common catalysts used in the liquefaction process of Kraft lignin. These organic acids can easily be obtained from renewable resources and their application as a catalyst could allow the development of more environmentally friendly process in the production of biopolyols. The main objective of the present work was to study the influence of these organic acids catalysts and their concentration (3%, 6% and 9%, w/w) on the yield and properties of the obtained liquefied products. The results demonstrated that the type of the organic catalysts (85–88%) has not influenced the liquefaction yield of Kraft lignin. The highest hydroxyl number was obtained with lactic acid at 3% (660.08 mg KOH.g−1), whereas acetic acid provided the lowest acid number (0.80 mg KOH.g−1). The viscosity varied with catalysts (114.5–345.8-mPa.s) and the molecular weights of the liquefied products were in the range of 1459-1990 g.mol−1, lower than Kraft lignin (3866 g.mol−1). Moreover, volatile compounds showed traces of lignin derivatives and a few intermediate products from solvents. The low lignin signals observed by ATR-IR in the solid residue as well as the obtained liquefaction yields, suggested that most of the Kraft lignin has reacted during liquefaction process. The obtained results showed the potential value of these organic compounds to be used as renewable and more environmentally friendly catalysts in the liquefaction of Kraft lignin.