Lignin extraction from kraft black liquor and its conversion to phenol-rich oil by hydrothermal liquefaction process

This study exploited lignin from black liquor as feedstock in the hydrothermal liquefaction process. The operation conditions such as temperature, operation time, and solvent ratio (by adding ethanol) were explored, with temperature identified as the most significant parameter. The optimum condition generating the highest oil yield (58.9 %) was found at an operating temperature, time, and solvent ratio of 275 degrees C, 30 min, and 1:1 water-toethanol ratio, respectively. The extracted oil was further characterized, revealing phenolic-rich oil containing about 83.4 % phenol, which was dominated by guaiacol. The lignin-to-oil conversion was initiated by thermochemical degradation comprising a series of multiple chemical reactions. The overall process reduced sulfur, nitrogen, and oxygen content linked to reaction instability, favoring solid char yield. The resulting higher heating value of the extracted phenol-rich oil was about 27.8 kJ/g, almost twice that of the raw black liquor only having 14.1 kJ/g.