Title
Kraft lignin depolymerization in near-critical water: efect of changing co-solvent
Authors
TALLAL BELKHEIRI LENNART VAMLING THI DIEU HUYEN NGUYEN MARCO MASCHIETTI LARS OLAUSSON SVEN-INGVAR ANDERSSON LARS-ERIK AMAND and HANS THELIANDER

Published Volume 48 Issue 9-10 November-December
Keywords LignoBoost, lignin conversion, hydrogen donors, char formation, phenolic compound, near-critical water

Abstract
As part of developing a process to valorize lignin in a pulp mill with lignin separation, the depolymerisation of lignin to valuable chemicals was investigated in near-critical water. This was done by using methanol as co-solvent and hydrogen donor, phenol to suppress repolymerization (e.g. formation of char), and ZrO2 as a heterogeneous catalyst, with potassium carbonate as a co-catalyst. The reaction was carried out in a continuous flow fixed-bed reactor (500 cm3), at 280-350 °C and 25MPa. An important aspect is to suppress char formation. Therefore, the char formation was studied by using different concentrations of methanol and phenol. The char yield varied between 14% and 26%. When using methanol as the only co-solvent, the char yield decreased with increasing methanol concentration. Adding phenol resulted in a further decrease. The reactor outlet consisted mainly of two liquid phases, an aqueous and an oil phase, mixed together. The chemical analysis of the aqueous phase showed the presence of mainly phenolic compounds, for instance guaiacol, catechol, phenol and cresol.