Potential of catalytic oxidation of Kraft black liquor for the production of biosourced compounds

Industrial Kraft black liquor from maritime pine was oxidized in aqueous, alkaline medium, under air, at 150C, with or without CuO/TiO2 catalyst. The oxidation products were analyzed by HPLC, elemental analysis, SEC, FTIR, NMR. The results showed the depolymerisation of lignin, the formation of phenolic compounds in low yields, with vanillin being the major phenolic compound, and the formation of aliphatic compounds in higher yields, with formic, succinic and tartronic acids being the major identified aliphatic compounds. The presence of catalyst favoured the formation of phenolic and aliphatic compounds. Replacing Kraft black liquor by pure Kraft lignin as a starting material did not enhance the performances of catalytic oxidation, showing that lignin purification may not be necessary in our conditions. Switching from a batch reactor to a fixed bed reactor, working under similar conditons, did not increase the yields in oxidation products but increased the productivity. This work shows the potential of Kraft black liquor to produce a large panel of compounds, including phenolics, aliphatic acids and oxidized lignin, all being valuable in chemical industry.