Reaction mechanism of styrene monomer recovery from waste polystyrene by supercritical solvents

The degradation of polystyrene in supercritical benzene, toluene, ethylbenzene and p-xylene was studied at 310-370 °C, 4.0-6.0 MPa using a novel fast process. Supercritical degradation has unique properties such as excellent heat and mass transfer. By using this technique, polystyrene has been successfully depolymerised into monomer, dimer and other products in a very short reaction time with high conversion. Toluene used as supercritical solvent was more effective than other solvents such as benzene, ethylbenzene and p-xylene for the recovery of styrene from polystyrene, though the conversions of polystyrene were similar in all the above solvents. The highest yield of styrene obtained from polystyrene in supercritical toluene at 360 °C for 20 min reached 77 wt.%. The reaction mechanism consists of depolymerisation of polystyrene and secondary reactions due to closed system. This study indicated that different supercritical solvents affected these two processes differently.