Hydrothermal processing of Kraft lignin for carboxylic acid production

Abstract

The present study describes, for the first time ever, the production of organic acids by hydrothermal treatments using Kraft lignin from black liquor as feedstock, analysing the effect of the temperature and the type of atmosphere. The presence of oxygen had a positive impact on the total amount of acids, particularly, at 70 bar and 210 °C, being formed 172.8 g of acids per kg of Chemical Oxygen Demand consumed after 120 min of treatment. Moreover, it generated a final reaction medium mainly composed of acids, which represented 81.8% of the remaining total organic load. On the contrary, the maximum generation under an inert atmosphere was 17% lower, being reached after 120 min at 70 bar and 190 °C. Furthermore, selecting the operating conditions could be a tool to obtain a certain distribution of acids, increasing the proportions of lactic and acetic acid in the final mix compared to malic and formic acid during the wet oxidation process, while the latter prevailed during the thermal hydrolysis.