Influence of long-term heat treatment of kraft black liquor on lignin precipitation and material properties

In the present study, the influence of long-term heat treatment of black liquor with focus on a subsequent lignin precipitation process was investigated. The well-known CO2 approach to precipitate a certain amount of lignin from heat-treated black liquor was studied within defined thermal conditions. Several important characteristics of lignin such as molar mass and functional groups were analysed. Viscosity and buffer capacity of black liquor were also studied. Results showed a reduction in lignin yield as a result of a decrease in molar mass and lignin demethylation after the heat treatment. The acid consumption during precipitation was found to be higher after the heat treatment.