Synergistic Co-Pyrolysis of Oil Palm Empty Fruit Bunch and Polypropylene Waste: Insights into Reaction Kinetics and Bio-Oil Upgrading Mechanisms

Abstract Oil palm empty fruit bunch and polypropylene were synergistically co-pyrolyzed in order to clarify the reaction kinetics and bio-oil upgrading mechanisms. The experiments, including the kinetic study, were conducted in a semi-batch reactor at temperatures between 400 and 600 °C using a controlled 50:50 wt % blending ratio. Based on the product distribution results. The optimal temperature for bio-oil production was determined and subsequently applied to evaluate the influence of different empty fruit bunch and polypropylene blending ratios (100:0, 75:25, 50:50, 25:75, and 0:100 wt.%) on product yield and composition. The results demonstrated that temperature significantly influenced thermal decomposition pathways and product distribution. A temperature of 550 °C was identified as the optimum condition to produce bio-oil while suppressing secondary cracking and excessive gas formation. The blending ratio strongly affected product selectivity, with the 50:50 mixture achieving the highest liquid yield (44.54%). At these operating conditions, the hydrocarbon fraction of the bio-oil increased substantially to 47.2%, indicating that hydrogen transfer from polypropylene promoted the conversion of oxygenated intermediates into hydrocarbon-rich compounds through synergistic deoxygenation reactions, thereby upgrading the bio-oil and improving its energy potential. Concurrently, an enhancement in biochar quality was also observed. The apparent activation energy was found 54.02 kJ mol−1 within the temperature interval of 400–600 °C. These findings provide mechanistic insights into the co-pyrolysis of empty fruit bunch and polypropylene and demonstrate the potential of this process to improve bio-oil quality through the valorization of biomass and plastic waste.