Waste valorization: harnessing biogas plant residues for fuel production

Abstract

Hydrothermal liquefaction (HTL) represents a transformative technology in the quest for net-zero emissions and the establishment of a circular bio-economy. This study investigates an innovative approach to waste valorization by converting digestate fibers from biogas plants into renewable fuels using HTL and catalytic upgrading. The HTL process yielded biocrude with 37 wt% and achieved 70 wt% energy recovery from the dry ash-free biomass, demonstrating HTL's efficiency in capturing energy from biowaste. Catalytic upgrading of the biocrude, including hydrotreatment (HDT) and other refining steps, reduced the oxygen content by 98% to 0.16 wt%, and boosted energy density to 45.8 MJ kg⁻¹, aligning with ASTM D975 standards for diesel and ISO 8217 for marine fuels. The feasibility of co-processing biocrude with conventional heavy oil was also explored. Blending trials with 10 wt% partially upgraded biocrude showed stable performance over 200 hours in an HDT reactor, indicating compatibility and a viable pathway for integrating renewable biocrude with traditional heavy distillates, enhancing fuel production sustainability. This approach provides a promising route to incorporate renewable sources into conventional fuel production, supporting sustainable fuel technologies.