Hydrothermal Liquefaction Process to Obtain Sludge-Derived Bio-Fuels: Setup of the Experimental Apparatus and Preliminary Tests

The increasing interest in renewable energies sources, alternative to traditional fossil fuels, is justified by both the growing energy demand and the necessity to reduce greenhouse gases emissions related to the power sector. In this context, the production of bio-oil (or bio-crude) as liquid fuel through the innovative hydrothermal liquefaction (HTL) process is of particular interest, especially when applied to biomass with high water content. In fact, water is in sub-critical state under typical HTL conditions and acts as solvent, catalyst, and reaction medium. Therefore, HTL allows to exploit the water content of biomass, thus avoiding the high energy demand of the dewatering step associated with other thermo-chemical processes (e.g., gasification, pyrolysis, etc.). For the HTL process performed in batch reactors, the minimisation of thermal transients is crucial to both obtain a high-yield bio-crude with more attractive energy properties and limit the formation of undesirable products. In this work, the setup of a lab-scale HTL apparatus was performed so to limit thermal transients, and some preliminary tests were carried out on a municipal sludge in order to evaluate the yield of the obtained bio-crude.