Hydrochars derived from co-hydrothermal carbonization of polyvinyl chloride and biomass as fuels

• Co-hydrothermal carbonization of PVC with walnut shells was investigated at different reaction times. • Biomass addition suppressed PVC agglomeration and improved hydrochar morphology. • Co-HTC enhanced chlorine removal at short reaction times. • Extended HTC favored aromatization and higher thermal char stability. The waste management of polyvinyl chloride (PVC) is an important environmental challenge. Due to the high chlorine content, incineration causes serious environmental and technical problems. Hydrothermal carbonization (HTC) offers a promising pathway to convert PVC wastes that are not suitable for mechanical recycling into a valuable chlorine-depleted hydrochar. Adding biomass to the hydrothermal process has the potential to improve the fuel properties of the resulting hydrochar. Therefore, co-HTC of PVC and walnut shells was performed with different reaction times. HTC was also applied to the pure materials to distinguish between the effect of HTC and synergistic effects due to the interaction of PVC with biomass. Results showed that co-HTC suppressed PVC agglomeration and produced smaller, more uniform particles, especially at shorter reaction times. The chemical structure of the co-HTC fuel was analyzed using ATR-IR spectroscopy showing a complete breakdown of the biomass matrix and the elimination of C-Cl bonds. To investigate the potential application of PVC-biomass hydrochar as fuel, conversion tests were performed including TG analysis in 20 % O 2 in He. Further, pyrolysis was investigated using a high-temperature setup with industrially relevant heating rates of about 10 3 K s −1 showing that the HTC treatment led to the formation of more condensed aromatic structures increasing the thermal stability of the hydrochar.