Production of phenolic monomers from lignin in hydrothermal medium: Effect of rapid heating and short residence time

This study investigates the influence of heating rate and short residence time (1-15 min) on the hydrothermal liquefaction (HTL) of alkali lignin, as a function of reaction temperature (280-320 degrees C). A novel induction-heating reactor system (IHRS) was designed and was used for rapid heating rate (similar to 100 degrees C/min), while a resistive-heating reactor system (RHRS) was used for slow heating rate (similar to 5.3 degrees C/min). The experiment using IHRS with a short residence time (1 min) resulted in the highest yield of carbon recovery in biocrude (52.2 +/- 0.63 wt%) at 320 degrees C under autogenous pressure. In contrast, the experiments using RHRS or longer residence time (8-15 min) with IHRS showed lower biocrude yield due to the promotion of gasification and undesired secondary reactions. The detailed characterization of biocrude revealed that rapid heating rate improves the selectivity of compound in biocrude, such as phenol, while slow heating rate produced a broader distribution of compounds, including anisole and alkyl phenols at 320 degrees C for 1 min residence time. Furthermore, the usefulness of phenol as capping agent during IHRS of lignin was demonstrated in suppressing char formation and increasing biocrude yield.