Hydrothermal Co-Liquefaction of Synthetic Polymers and Miscanthus giganteus: Synergistic and Antagonistic Effects

Synthetic polymers constitute one of the main carbon-containing wastes generated nowadays. In this study, combined hydrothermal liquefaction (co-HTL) is evaluated for 1:1 mixtures of Miscanthus Giganteus and different synthetic polymers including poly-acrylonitrile-butadiene-styrene (ABS), Bisphenol-A based Epoxy resin, high density polyethylene (HDPE), low density polyethylene (LDPE), polyamide 6 (PA6), polyamide 6/6 (PA66), polyethylene terephthalate (PET), polycarbonate (PC), polypropylene (PP), polystyrene (PS) and polyurethane foam (PUR), using batch HTL reactors at 350 {\deg}C. Based on mass balances and oil composition, a comprehensive discussion of observed interactions is presented. The results show that even though polyolefins do not depolymerize under these conditions, the oil products depicts that these materials interact with miscanthus oil changing its composition. Bisphenol-A based polymers as PC and epoxy resins both contribute for the formation of monomer-like structures in the oil. PET increases the presence of carboxyl groups, while polyamides and PUR increase significantly the oil yield, modifying oil composition towards nitrogen-containing molecules. PUR co-HTL was found to increase both oil carbon and energy yields, leading to process improvement when compared to pure miscanthus processing.