Deoxygenation of Waste Chicken Fats to Green Diesel over Ni/Al₂O₃: Effect of Water and Free Fatty Acid Content

Abstract

The deoxygenation of waste chicken fat containing a high degree of free fatty acids (FFAs) and water has been implemented to produce a green diesel, known as biohydrogenated diesel (BHD). The effect of the water and free fatty acid content in the chicken fat on the conversion, BHD yield, and liquid/gas product distribution was investigated over a Ni/γ-Al2O3 catalyst in a trickle-bed reactor. The major reaction pathway was decarbonylation/decarboxylation (DCO/DCO2), whereas hydrodeoxygenation was minor. Methane from methanation of the resultant CO/CO2 and propane cracking was a major gaseous product. The FFA and water content improved the BHD yield and the overall contribution of the DCO/DCO2. The presence of water accelerated the breakdown of the triglyceride molecules into FFAs. Therefore, waste chicken fat from food industries containing a high degree of FFAs and water content can be used as a low-cost feedstock for renewable diesel production without requirement of a pretreatment process.