Catalytic co-pyrolysis of teak wood sawdust and polystyrene: Effect of process parameters on yield and properties of pyrolysis oil

The present study explores the thermo-catalytic co-pyrolysis of waste teak wood sawdust (TWS) and polystyrene (PS) using a semi-batch reactor. The experiments were performed at varying temperatures (450-550 °C), biomass-to-plastic ratios (10-50 wt.%), and catalyst loadings (5-20 wt.% of CaO and MgO). The physicochemical analysis of TWS and PS revealed HHV values of 19.50 and 43.18 MJ kg^-1, and oxygen contents of 45.40% and 0.43%, respectively. TGA results showed major biomass degradation occurring between 150-550 °C, while the FTIR analysis identified key functional groups, including C-H, C=C, -OH, and C=O. Thermal pyrolysis at 500 °C produced a 46.05% liquid yield, while the addition of 30 wt.% PS increased yield by 5.53%. The resultant pyrolytic oil exhibited an improved carbon content (81.37%) and a higher heating value (37.85 MJ kg^-1). The GC-MS analysis demonstrated a 59.69% increase in hydrocarbon yield at 30 wt.% PS while acids and ketones reduced by 4.58% and 9.74%, respectively. The addition of CaO (5 wt.%) and MgO (10 wt.%) enhanced the deoxygenation, aromatisation, and cracking reactions, resulting in selectivity towards aromatic hydrocarbons. The catalytic pyrolytic oil yielded 62% total hydrocarbons, with the aromatic fraction accounting for 56% of the total hydrocarbons. The NMR study further confirmed the shifting of the hydrogen from oxygen-containing compounds towards aromatic structures. Furthermore, blending PS at a dynamic ratio decreased the char yield, whereas adding catalysts increased it. The catalytic char showed increased ash content and demonstrated alkaline pH. Overall, the thermo-catalytic co-pyrolysis has significant potential to contribute to the circular economy by converting waste into renewable fuels and chemicals.