Effect of temperature and time on oil yield and quality during co-liquefaction between empty fruit bunch (EFB) and high-density polyethylene (HDPE) using methanol as solvent

Energy production from waste such as empty fruit bunches (EFB) and high-density polyethylene (HDPE) is gaining interest due to declining petroleum resources. However, single liquefaction of EFB or HDPE typically produces low oil yields with high solid residues, and only limited studies have explored their co-liquefaction. In addition, most liquefaction studies use water as a solvent, but it requires supercritical conditions with high temperature and pressure which is energy-intensive. This study investigates the effects of temperature and reaction time on oil yield and quality during co-liquefaction of EFB and HDPE using methanol as a solvent, which has lower critical points than water. A feedstock ratio EFB:HDPE of 1:3 was selected on its high heating value and volatile matter content, with low moisture and ash contents. Co-liquefaction was performed in a batch reactor at 220 – 320 °C for 0 – 30 minutes. Results showed that both parameters strongly influenced oil yield. Increasing temperature and reaction time initially enhanced oil production, but excessive values led to secondary cracking and gas formation. The optimum condition (240 °C, 20 minutes) yielded the highest oil selectivity, which was 97.31%. Under this condition, co-liquefaction outperformed single liquefaction of EFB or HDPE in terms of oil yield and quality. FTIR analysis revealed that the co-liquefaction oil contained lower O-H, C=C, and C-O groups and higher C-H content, indicating greater energy density. These findings demonstrate the potential of EFB – HDPE co-liquefaction as an efficient method for producing high-quality oil.