Factors Influencing the Use of Various Low-Value Oils in Biodiesel Production

Abstract

Various low-value oils, namely, crude palm oil (CPO), crude jatropha oil (CJO), and used frying oil (UFO), were investigated by comparing them as feed oils used in biodiesel (BD) production, with the objective of clarifying the effects of various factors that influence the feed oil characteristics on the required feed pretreatment (FP), operating conditions in transesterification, and the obtained biodiesel yield and purity. First, the low-value oils were characterized in terms of fatty acid compositions and the contents of undesirable impurities. All the feed oils contained mainly C16 and C18 fatty acid chains, and the content of C16 in CPO was higher than the contents of C16 in the other feed oils. The highest contents of impurities, namely, a phospholipid, free fatty acid (FFA), and water were found in CJO. Then, the feed oils were pretreated under various conditions and subsequently transesterified to convert triglycerides to BD in the methyl ester form. The BD productivity and quality could be improved by proper feed pretreatment; deacidification and dehydration were particularly effective. Alkali deacidification is not appropriate for treating CJO since significant oil loss was observed during neutralization of FFA in deacidification. Lastly, the pretreated oils whose impurity contents were sufficiently low were transesterified under varying operating conditions. CPO gave a relatively lower yield but higher purity than the other oils because of the higher C16 content in the feed oil, which had a negative effect on yield but increased the purity in the BD product. For all feed oils, the purity of the obtained BD met the standard for BD purity, and the transesterification yields were improved by carrying out the appropriate FP, as well as adjusting the amounts of alcohol and catalyst in transesterification according to the type of feed oil. The obtained results can be applied to select the appropriate feed oils and maximize BD productivity in the BD production from various low-value oils.