Hydro- and solvothermolysis of kraft lignin for maximizing production of monomeric aromatic chemicals

The hydro-/solvothermolysis of kraft lignin using water and ethanol as a solvent were investigated in this study. The effect of the water-to-ethanol ratio on the yields of monomeric aromatic chemicals (MACs) and the kinetic behavior of MACs was studied in a series of batch experiments. The yields of MACs other than catechol increased as the ratio of ethanol increased, and the content of the total MACs in bio-crude oil (BCO) reached 35% when the ratio of ethanol was 100% at a reaction temperature of 300 °C. The formation of phenol, guaiacol, and alkylguaiacols was enhanced in ethanol, while the formation of catechol was dominant in water. The formation of more substituted MACs such as vanillin, acetoguaiacone, and homovanillic acid was not affected by the solvent. The role of reaction parameters on the yields of MACs was elucidated, and the main reaction pathways in water and in ethanol were proposed.