Deeper insights into the fate of key elements and prediction of products yields along the hydrothermal liquefaction of civil sludge via dynamic modelling and mass balances

Hydrothermal liquefaction (HTL) stands out as a highly promising thermochemical route for transforming wet biomass, such as sewage sludge, into valuable bio-crude oil. HTL offers several benefits, including waste volume reduction, recovery of energy and resources, and a decrease in GHG emissions. Understanding the reaction kinetics of HTL is crucial for process optimization and efficient resource recovery. In this work, a lumped kinetic model based on experimental data for HTL of sewage sludge in a 500 mL batch apparatus, at a heating rate of ~8°C/min and temperatures of 150–370°C, was developed to predict the yields of bio-crude, solid residue, aqueous phase and gas, as a function of reaction time and temperature. The inclusion of a first-order ash dissolution dynamic model allowed to predict the ash distribution in the solid residue and aqueous phase.