Utilization of waste automotive landfill engine oil for fatty acid methyl ester synthesis using microwave irradiation: an intensified approach

With increasing automotive vehicles, disposal of waste automotive landfill engine oil (WALEO) is foremost challenge. Present work investigated synthesis of fatty acid methyl esters (FAMEs) from WALEO using first stage of orthophosphoric-catalyzed acid esterification followed by subsequent stage of potassium hydroxide-catalyzed alkaline transesterification using conventional and intensified microwave methods. Process parameters for study were molar ratio of oil–methanol, and catalyst concentration. The optimize parameters of acid esterification for reducing acid value from 33.72 to 1.71 mg of KOH/g of oil were catalyst concentration: 12% weight/weight, reaction temperature: 60 \(^\circ{\rm C} \) and molar ratio: 1:2 using conventional method. Nearly same results were obtained using microwave-assisted esterification but there was considerable decrease in process time requirement using intensified approach of microwave irradiations. Time required for processing was 210 and 30 min for conventional and microwave methods, respectively. Microwave accelerated the rate of reaction by 7.5 times. There was substantial decrease in energy requirement for esterification process and energy utilization was 14.2–26.4 mg/kJ for conventional and microwave methods, respectively. Transesterification of esterified oil were performed using microwave method. The optimized parameters for transesterification process were molar ratio: 1:6, catalyst concentration: 1% weight/weight, reaction time: 15 min and yield: 92.3%.