Structural and morphological changes in kraft lignin during hydrothermal carbonization

In this paper we have investigated the changes in kraft lignin structure and morphology upon hydrothermal carbonization (HTC) at 240 °C with and without the presence of carbonization catalysts. The main conclusion of this study is that the structure of kraft lignin was altered only slightly during the hydrothermal carbonization. The main changes in the kraft lignin's structure were demethylation and dealkylation as well as cleavage of ß-O-4 bonds. The final product had a more thermally stable and complex cross-linked structure. More pronounced changes occurred in the material structure and morphology upon the addition of catalysts. The energy density of the resulting materials was not significantly different from the energy density of the original kraft lignin.