Synergistic interactions during hydrothermal liquefaction of plastics and biomolecules

We performed co-liquefaction of plastics and biomolecules, in ratios that mimic their abundance in municipal solid waste (MSW), in both subcritical (300, 350 °C) and supercritical (400, 425 °C) water. Hydrothermal liquefaction (HTL) of this simulated MSW mixture produces an oil product, and the highest energy recovery (45%) in the oil occurred at the lowest temperature examined (300 °C). This energy recovery was more than twice that expected, based on energy recovery from HTL of each component individually at the same condition. Interactions between biomolecules and plastics increase the oil yield from HTL and enable the processing of plastics at lower HTL operating temperatures (e.g., 300 ˚C) than would be possible for processing the plastics alone. Cellulose, starch, and lignin interact synergistically with mixtures of polypropylene, polycarbonate, polystyrene and polyethylene terephthalate to increase the oil yield. These interactions form new products and accelerate the depolymerization of the plastics.