Effect of polypropylene pyrolyzate as the solvent on hydrodeoxygenation of palm oil using Ni-Cu/ZrO2 catalyst

Abstract

Green diesel is a biofuel that can be used directly in diesel engines and can be synthesized by hydrodeoxygenation (HDO) reaction of triglyceride (TG). Generally, this reaction requires a high hydrogen pressure (40–150 bar) and a high composition of organic solvent to facilitate a higher hydrogen solubility in the liquid phase. In many cases, long carbon-chain alkanes, mostly n-dodecane, have been used as solvents. The present work aims to investigate the potential of hydrogenated and non-hydrogenated polypropylene (PP) pyrolyzate as solvents in an effort to utilize plastic wastes in HDO reaction of palm oil. The reaction was carried out using bimetallic catalyst Ni-Cu/ZrO2 in a reactor with a hydrogen gas self-inducing impeller to facilitate a higher load-up hydrogen gas in the liquid phase. The effect of reaction time in HDO involving two solvents, i.e., PP pyrolyzate and hydrogenated PP pyrolyzate, was elucidated in this work. The results showed that hydrogenated PP pyrolyzate facilitates a higher deoxygenation activity than PP pyrolyzate. In addition, the synthesized bimetallic catalyst promoted the decarbonylation/decarboxylation route over the hydrodeoxygenation route at reaction temperatures of 280–350 °C. The conversion of TG increased from 51 % to 93 % by increasing the reaction temperature from 280 °C to 350 °C, with the corresponding highest yield of green diesel was 82 %. Therefore, the hydrogenated PP pyrolyzate can substitute the usual long carbon-chain alkanes.