Black liquor is a side stream from pulp and paper industry containing lignin and other organic and inorganic materials. Catalytic alkaline oxidation of black liquor was carried out employing CuO/TiO2 catalyst in a trickle bed reactor employing mild reaction conditions (150-200°C, 80 bar) and short contact times (4-9 minutes). The effects of temperature, contact time, and presence of catalyst were investigated. In our best operating conditions, i.e. 200°C, 4 min contact time, lignin conversion was complete and phenolic monomers were obtained (maximum total yield 6.2 wt.%), among which vanillin (maximum yield 3.3 wt.%). Vanillin represented 53 wt.% of phenolic monomers. At longer contact times, the degradation of phenolic compounds was observed. The application of a continuous trickle bed reactor, allowing short reaction times and limiting degradation reactions, is particularly appropriate for this reaction. Vanillin productivity in this reactor is 936 g.m 3 .h -1 .

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.

Industrial Kraft black liquor from maritime pine was oxidised in aqueous, alkaline medium, under air, at 150°C, with or without CuO/TiO2 catalyst. The oxidation products were analysed 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 main phenolic compound, and the formation of aliphatic compounds in higher yields, with formic, succinic and tartronic acids being the main identified aliphatic compounds. The presence of the catalyst favoured the formation of phenolic and aliphatic compounds. Replacing Kraft black liquor by pure Kraft lignin as a starting material did not improve the performances of the catalytic oxidation, indicating that lignin purification may not be necessary under our conditions. Switching from a batch reactor to a fixed bed reactor, operating under similar conditions, did not increase the yields of oxidation products but did increase the productivity. This work demonstrates the potential of Kraft black liquor to produce a large panel of compounds, including phenolics, aliphatic acids and oxidised lignin, all of which valuable in chemical industry. For the first time, a catalytic process for the chemical valorisation of Kraft black liquor is presented.