Wood/plastic copyrolysis in an auger reactor: Chemical and physical analysis of the products

Previous studies observed that slow copyrolysis of wood and plastic in enclosed autoclaves produced an upgraded raw bio-oil with increased hydrogen content. We now demonstrate that fast simultaneous pyrolyses of 50:50, w/w, pine wood/waste plastics in a 2 kg/h lab scale auger-fed reactor at 1 atm, with a short vapor residence time, generates higher heating value upgraded bio-oils. Three plastics: polystyrene (PS), high density polyethylene (HDPE) and polypropylene (PP) were individually copyrolyzed with southern yellow pine wood at 525, 450 and 450 °C, respectively, to generate modified bio-oils upon condensation. These liquids exhibited higher carbon and hydrogen contents, significantly lower oxygen contents, higher heats of combustion and lower water contents, acid values and viscosities than pine bio-oil. The formation of cross-over wood/plastic reaction products was negligible in the oils. Simultaneous pyrolysis process design requires using a temperature at which the plastic’s thermal decomposition kinetics produce vapors rapidly enough to prevent vaporized plastic from condensing on wood chars and exiting the reactor.