Sustainable valorization of wood residue for the production of biofuel materials via continuous flow hydrothermal liquefaction

Abstract Almost half of the wood resulted from mass deforestation for infrastructure and agricultural developments is declared waste. To mitigate the impact and exploit renewable sources of energy sustainably it is paramount to explore their further utilizations. Hydrothermal liquefaction (HTL) technology holds the promise to convert biomass into biofuels. In this study, conversion of wood residue under continuous flow, subcritical HTL was investigated under two conditions; untreated and alkaline pretreated. Results show that 4% NaOH pretreatment increased the production of fermentation sugar, glucose, by 1.8-fold (equivalent to 90 g/L) and facilitated faster recovery times compared to raw wood. Also, at 0.2 MPa HTL, the alkaline pretreatment shifted the hydrolysis of arabinose and cellobiose to rhamnose and increased the fluid's acidity from pH of 6.1 to pH of 3.5. Under the pretreatment, the energy output from glucose reached 246 kJ and the average Net Energy Ratio for glucose during liquefaction reached values as high as 63%. These results will usher in new waste conversion methods into sustainable biofuels via continuous flow HTL, thereby supporting the green energy transition towards net zero.