Fuel Quality Assessment of Green Diesel Produced from Waste Cooking Oil

Waste cooking oil can be converted into fuel for internal combustion (IC) engine applications by transesterification or pyrolysis. Transesterification results in the production of fatty acid methyl esters called biodiesel. The variability in biodiesel composition and properties from diesel fuel leads to engine re-calibration that requires significant time and effort. Diesel-like hydrocarbons can be produced by catalytic pyrolysis of used cooking oil. Such fuel can be used as a drop-in fuel in IC engine applications. Hydrogen at high pressures and a catalyst generally promote deoxygenation during pyrolysis. Recently, novel heterogenous acid catalysts such as Ni-impregnated activated carbon (AC) and Ag-Co-impregnated AC catalysts were developed to produce deoxygenated fuel by pyrolysis at atmospheric pressure without using hydrogen. Homogenous base catalysts such as sodium hydroxide can also be used in pyrolysis to produce diesel-like fuel. The present work compares the suitability of pyrolysis oils produced from waste cooking oil using these catalysts with those produced without a catalyst. The reaction temperature was optimized for the yield and quality of the fuel. The composition of the diesel-like fuel thus produced is measured using GC-MS. Physicochemical properties such as cetane index, viscosity, density, flash point, and caloric value were measured following the ASTM standard test procedure. The results show that the reaction temperature significantly influences the kinematic viscosity of the pyrolysis oil. It is found that compared to the pyrolysis oil produced without a catalyst, the oil produced using acid catalysts had a higher calorific value. The increase in calorific value is because of the deoxygenation reactions promoted by the catalysts. The pyrolysis oils had physicochemical properties in the range of petroleum diesel. The present study shows that pyrolysis of used cooking oil without hydrogen using acid and base catalysts can produce high-quality diesel-like fuel for IC engine applications.