Many research efforts have been made to improve the hydrothermal/subcritical water liquefaction (HTL) process for producing biocrude from biomass and lignin. All these studies applied conventional electric resistance heating methods which takes pre-heating times in the range of 30-60 minutes to raise to the desired reaction temperature in laboratory experiments. It leads uncertainties in interpretation of the depolymerization chemistry and reaction time due to its slow heating rate. To overcome this limitation, rapid heating HTL batch reactor equipped with induction heating system is used. It is capable of handling up to 200 mL biomass slurry, with fast heating rate (up to 70°C/min), and fast cooling that allows reactions to take place in a well-defined reaction environment. Lignin, which readily available as a byproduct from pulping and bioethanol industry was chosen as the feedstock representative for this study. The objective is to obtain aromatic monomeric compounds which can be valuable precursor for high value products. HTL of lignin was carried out in the absence and presence of K<sub>2</sub>CO<sub>3</sub> in the temperature range of 250-350°C using the induction heating batch reactor as a function of short residence time (2-15 min). To compare with induction heating batch system with a conventional resistance heating system, a 500 mL HTL reactor from Parr instrument company with heating rate up to 5°C/min was used to produce biocrude. After the reaction, biocrude, biochar, and aqueous organic phase were obtained and subjected to the GC-MS, elemental composition, FTIR, and total organic carbon analysis. The produced biocrude contained broad spectrum of aromatic monomeric compounds including anisol, phenol, cresol, guaiacol and catechol. Biocrude will be used in the production of sustainable high-value lubricant improver. The influence of heating rate and short residence time to the product yield and its chemical composition is discussed.

Lignin depolymerization in subcritical water : Effect of rapid heating and short residence time

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