Effect of Metal Oxide Catalysts on Degradation of Waste Polystyrene in Hydrogen at Elevated Temperature and Pressure in Benzene Solution

Degradation of waste polystyrene is carried out in presence of hydrogen using several metal oxide catalysts at elevated temperature and pressure for recycling. Benzene is used as a solvent for degradation. Initial hydrogen pressure in the autoclave is kept at 7.0 kg/cm² (g) and polystyrene degradation is carried out at 240 °C. After degradation, degraded polystyrene residue is separated and analyzed by Fourier transform infra red (FTIR) spectroscopy whereas filtrate is analyzed by gas chromatography (GC) for finding the degradation mechanism of polystyrene. Degradation rate is enhanced in presence of hydrogen and time dependent weight average molecular weight of degraded polystyrene is determined using viscosity method. Degradation rate constants for the different catalysts are calculated based on the proposed degradation mechanism. Alkali metal oxide catalyst shows higher reactivity towards polystyrene degradation as compare to the transition metal oxide catalyst i.e., degradation rate constant decreases with the increase in electro negativity of metal element of the catalyst. Though manganese (IV) oxide is a transition metal catalyst, but shows higher reactivity due to its reduction towards stable manganese (II) oxide under degradation environment. Finally, degradation rate constant of polystyrene is correlated with the catalyst activity i.e., electro negativity of metal element in the catalyst.