Production and characterization of hydrochar produced from hydrothermal liquefaction of pipeline-transported softwood biomass

This study investigates hydrochar production from hydrothermal liquefaction (HTL) of pipeline-transported softwood biomass. Pipelining biomass using water as a carrier fluid offers a cost-effective alternative to truck transport, and its integration with HTL for hydrochar production is relatively unexplored. The objective of this study was to evaluate the effect of process parameters on HTL of pipelined biomass and characterize the resulting hydrochar for various applications. The yield of hydrochar produced from pipelined biomass, at the optimal process conditions, was 13.22 % (oven-dry mass basis), with 19.31 % of energy recovered in hydrochar. The hydrochar was characterized as a black, fragile, mildly acidic carbon material with a dry bulk density of 0.142 g/cm³, improved carbon content, increased surface area (9.27 m²/g), altered pore morphology, and a graphitized, amorphous structure, reflecting structural and compositional changes from the HTL process. Pipelining was found to have minimal impact on the lignocellulosic composition and particle size of the softwood biomass, but it resulted in the leaching of inorganic elements, leading to a reduction in ash content in the hydrochar. The characterization results suggest the hydrochar is suitable for soil amendment and solid fuel applications; its low surface area hinders its use as an adsorbent or for energy storage. This study thus demonstrates the potential of integrating hydro-transportation with HTL, offering a pathway to recover, manage, and use hydrochar for various applications.