Effect of oil-sludge loading on synergistic interactions and fuel quality in tri-pyrolysis of oil palm biomass and polypropylene

This study investigates the tri-pyrolysis of oil palm fresh fruit bunches (PFFB), medical waste polypropylene bottles (MWPB), and used cooking oil sludge (UCOS) in a batch pyrolysis reactor, focusing on UCOS as a hydrogen-rich co-feedstock. Experiments were conducted at a fixed PFFB:MWPB ratio of 1:1 while varying UCOS contents (0.5, 1, and 2) to evaluate product yields, thermal behavior, chemical composition, and energy characteristics of the resulting tri-pyrolysis oil (TPO). The results showed that TPO was the dominant product under all conditions, with oil yield increasing from 43.23 % to 51.87 % as UCOS content increased, while gas yield decreased and char yield remained nearly constant. Thermogravimetric analysis indicated that UCOS decomposed at lower temperatures than PFFB and MWPB, promoting early volatile release and synergistic thermal cracking. GC-MS analysis revealed a shift toward saturated hydrocarbons with increasing UCOS content, particularly enrichment of C 15 -C 17 alkanes favorable for diesel-range fuels, accompanied by reduced olefinic compounds. Oxygenated and nitrogen-containing species persisted but shifted toward heavier lipid-derived compounds at higher UCOS ratios. The TPO exhibited high energy content, with lower heating values ranging from 41.75 to 43.48 MJ kg -1 , comparable to conventional liquid fuels. Overall, UCOS-assisted tri-pyrolysis demonstrates strong potential as an efficient waste-to-energy pathway. • Liquid, gas, and char yields from tri-pyrolysis were systematically quantified. • UCOS addition enhanced oil yield and promoted synergistic thermal cracking. • Tri-pyrolysis oil exhibited high energy content and diesel-range hydrocarbons. • UCOS acted as a hydrogen-rich co-feedstock, improving oil composition and fuel quality.