The degradation properties of polystyrene in supercritical benzene

toluene

ethylbenzene and p-xylene were studied between 340～370℃ using a quick process．Benzene hydrocarbons are the fine solvents of polystyrene．All the solvents have unique properties such as excellent heat transfer and mass transfer at supercritical conditions

and the degradation conversions of polystyrene were similar using different solvents．The conversion of polystyrene was close to thorough degradation when the temperature reached 370℃．Supercritical degradation of polystyrene in toluene improved the liquid product yield close to 97％ while reducing the gas and residue oil less than 1％ and 3％

respectively．The products are mainly composed of benzene

ethylbenzene

xylene

styrene

α-methylstyrene etc．But it is noted that the yield of styrene was quite different in different superedtical solvents．The experiments showed that the yield of styrene was much higher using supereritical toluene as solvent than that with other solvents．The yield of styrene obtained from polystyrene in superoritical toluene at 350℃ for 30 min reached a value of 75．5 wt％．The reaction mechanism consists of depolymerization of polystyrene and secondary reactions．The result showed that supercritical solvents affected the secondary reaction differently

because the styrene obtained from degradation could not separate out from the system quickly．Moreover

among the solvents employed in our work

toluene was founded to be the most effective supercritical solvent to recovery styrene from polystyrene．Based on the continuous distribution kinetics

the madel of polystyrene degradation was developed at the mechanistic level using popullation balance equations formulated via the method of moments．The activation energy of polystyrene degradation in supercritieal toluene obtained from Arrhenius equation is 138．4 kJ·mol-1．