  Hydrothermal liquefaction could potentially utilize mixed plastic wastes for
sustainable biocrude production, however the fate of plastics under HTL is
largely unexplored for the same reaction conditions. In this study, we evaluate
how synthetic waste polymers can be depolymerized to bio-crude or platform
chemicals using HTL at typical conditions expected in future commercial
applications with and without alkali catalyst (potassium hydroxide). We
evaluate different characteristics for HTL processing of
poly-acrylonitrile-butadiene-styrene (ABS), Bisphenol-A Epoxy-resin,
high-density polyethylene (HDPE), low density PE (LDPE), polyamide 6 (PA6),
polyamide 66 (PA66), polyethylene terephthalate (PET), polycarbonate (PC),
polypropylene (PP), polystyrene (PS) and polyurethane (PUR) at 350 {\deg}C and
20 minutes residence time. Polyolefins and PS showed little depolymerization
due to lack of reactive sites for hydrolysis. HTL of PC and Epoxy yielded
predominantly bisphenol-A in oil fraction and phenols in aqueous phase. PA6 and
PA66 yielded one of its monomers caprolactam and a range of platform chemicals
in the aqueous phase. PET produces both original monomers. PUR yields a complex
oil containing similar molecules to its monomers and longer hydrocarbons. Our
results show how HTL can depolymerizes several different synthetic polymers and
highlights which of those are the most attractive or are unsuitable for
subcritical processing.
