Hydrous pyrolysis of polystyrene

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 18 MPa, for 1-120 h. The products obtained, separated as gases, volatiles, and heavy compounds, were analyzed qualitatively and quantitatively by gas-chromatography, gas-chromatography/mass spectrometry and size exclusion chromatography. The results showed that the presence of water increases the yields of the volatile products, mainly in the first steps of the pyrolytic process, and leads to higher yields of monomer. This latter observation suggests a lowering of the secondary reactions extent.