Utilization of black-liquor by hydrothermal liquefaction

Abstract

Black liquor (BL) was utilized by acidification and hydrothermal liquefaction (HTL). The acidified BL, lignin-like powder, had its higher heating value (HHV) increased to 23.55 kJ/g. It was hydrothermal liquefied under two atmospheric conditions of H2 and N2. The obtained product was characterized by Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), and Gas chromatography-mass spectrometry (GC–MS). The highest biocrude yield (38 wt%) was observed at 300 °C under N2 atmosphere, whereas 41 wt% at 300 °C under H2 atmosphere. The components of the liquid product were classified in the range of C6-C8 with phenolic-rich compounds. The solid product under N2 atmosphere, biochar, contained higher heating values (HHV) from 30 to 33 kJ/g along with a C/H ratio from 15.89 to 23.52, corresponding to good quality coal. The presence of hydrogen led to more remarkable amounts of phenolic compounds than the nitrogen atmosphere. This might be due to the bond cleavage by the hydrogenation and hydrogenolysis reaction under the H2-based condition.