The degradation of kraft lignin during hydrothermal treatment for phenolics

Kraft lignin was hydrothermally depolymerized at low temperature/short time in water for producing value-added phenolics. The effects of residence time (15, 60 min) and reaction temperature (130, 180, 230ºC) on yields of oils and phenolic compounds were studied in detail. Total oil yield was found to range between 7% and 10%. The compositions of oils were analyzed by GC-MS to confirm the main compound to be guaiacol (2-methoxy phenol) in the range of 12–55% of oil depending on different reaction conditions. The most interesting was the finding that maximum value of total oil yield (10% of kraft lignin) and guaiacol amount (55% of oil) was obtained at 130ºC/15, 60 min which is a low reaction temperature/short time, while the residual kraft lignins were analyzed by FTIR with respect to the conversion mechanism of kraft lignin by this process.