Hydrothermal liquefaction of sewage sludge for biofuel applications: A kinetic process model and a simulation analysis

Abstract

The present work analyzes hydrothermal liquefaction (HTL) as a sustainable and efficient method for converting sewage sludge into biocrude and other valuable products. HTL operates at moderate temperatures and pressures, allowing the direct processing of wet biomass without the need for prior drying, making it a more energy-efficient alternative to conventional waste management methods. The study includes the identification and analysis of the reaction pathways involved in the HTL process from sewage sludge, with the objective of optimizing biocrude production. A kinetic model was developed to predict the yield of biocrude, gases, and aqueous and solid phase products under different operating conditions. The model was validated with experimental data, demonstrating high accuracy and reinforcing the viability of HTL as a scalable process. A simulation of the HTL process was carried out using Aspen Plus v12, revealing that the optimal temperature to maximize biocrude yield is approximately 300 ºC, with a residence time of 25 minutes. Under these conditions, the process achieves a biocrude yield of around between 45% and 50%, which aligns reasonably well with experimental results showing a yield of around 30% yield. The research highlights the potential of HTL to reduce solid waste, recover renewable energy, and support the principles of the circular economy. By addressing discrepancies between experimental and simulated results, the project provides valuable insights for the industrial-scale implementation of HTL, promoting sustainable sewage sludge management and biofuel production.