Hydrocarbon biofuel from hydrotreating of palm oil over unsupported Ni–Mo sulfide catalysts

Abstract

Research on the production of bio-hydrogenated diesel as a green second-generation biodiesel is increasingly attractive for renewable energy utilization in engines, and has potentially been produced from the hydrotreating of vegetable oils. The present work investigated the hydrodeoxygenation of palm oil catalyzed by unsupported nickel-molybdenum (Ni–Mo) sulfide synthesized by a hydrothermal method. The effects of the operating parameters, such as the reaction time (0.5–3 h), temperature (280–320 °C), oil concentration (5–15%) on the n-alkane yield were evaluated. A longer reaction time and higher temperature promoted the reaction via decarboxylation and decarbonylation pathways. Under the appropriate condition (300 °C, 2 h, and initial H2 pressure of 30 bar), the yield of C14–18 alkanes was 75.3 wt%, while the selectivity of n-C15, n-C16, n-C17, and n-C18 alkanes was 21.8, 19.7, 29.6, and 28.1%, respectively. Gas chromatography-mass spectrometry analysis revealed n-alkenes, alcohols, and esters as byproducts. Characterization of catalyst revealed it had a sandwich structure consisting of weakly coupled layers, rim sites and Ni edges, which catalyzed the reaction efficiently. The catalyst could be reused for at least four cycles of palm oil hydrodeoxygenation with retention of a good performance with the decreased 17–25% alkane yield (2nd to 4th cycle with 50.8–57.3% n-C14–18 yield).