New chemical recycling methodologies: hydrous pyrolysis to recover monomer from polyolefins

Thermal degradation of polystyrene has been investigated in the presence of water under subcritical conditions (hydrous pyrolysis). The experiments were carried out in closed systems under inert atmosphere, in the temperature range 300-350 °C, at pressures up to 180 atm, for 1-120 h. The results showed that the presence of water increases the yields of volatile products, mainly in the first steps of the pyrolytic process, with a high selectivity in the monomer. In order to improve the phase contact between water and polymer during the pyrolysis, some runs have been carried out on silica-supported polystyrene and using a stirred reactor. Under these conditions, the above effects appeared to be greatly enhanced. The best recovery of styrene, close to 71%, has been achieved at 320 °C and 8 h.