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 .
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