Evaluation of Waste Process Grease as Feedstock for Biodiesel Production

Awareness of the depletion of fossil energy reserves, the rising demand for energy in the world and the problems associated with the burning of fossil fuel encourage researchers to find alternative energy sources, such as biodiesel. The use of inedible and waste oils as feedstock for biodiesel production is an important way of converting waste into valuable energy products. In this study, waste process grease (WPG) was used to produce biodiesel via two processing routes. The traditional two-step alkaline catalyzed transesterification method (route 1) produced biodiesel that did not conform to the SANS1935 biodiesel standard of South Africa with regard to sulfur and phosphorous levels. The WPG in the second process route was modified by saponification with aqueous sodium hydroxide followed by acidulation with hydrochloric acid to be purified by means of column chromatography. A hydrophobic resin with methanol as the mobile phase was used to reduce the non-polar sulfur from the grease. The crude biodiesel produced by means of acid esterification using sulfuric acid as catalyst was purified using silica gel with hexane as the mobile phase. The sulfur level in the biodiesel was reduced to a low enough level to conform to the SANS1935 standard for biodiesel production. It was shown with this study that waste process grease from the metal working industry can be used to produce biodiesel that conforms to the SANS 1935 specification for sulfur and is suitable to be used in biodiesel blending. A preliminary economic assessment shows that owed to the complexity of the second process route, biodiesel produced by this process is not economically viable given the current petroleum diesel prices. With the rising trend in crude oil prices and the limited supply of feedstock for biodiesel, WPG is anticipated to become a viable feedstock for biodiesel production in future.