Chapter 6 - Sustainable Waste-to-Energy Technologies: Transesterification

Abstract

Global demand for petroleum has been increasing due to rising populations, expanding industrialization, and urbanization. There is an urgent need to search for alternative fuels due to growing environmental concerns about greenhouse gas (GHG) emissions from fossil fuels and the volatility of fuel price. Transesterified vegetable oil (i.e., biodiesel) is one of the promising alternative fuels that may replace conventional petroleum diesel, because it is renewable, biodegradable, and nontoxic, with relatively low aromatic and sulfur content, while providing relatively low net CO2 emissions, high fuel efficiency, and high conversion rate. Biodiesel can be synthesized from a wide range of feedstocks (e.g., edible vegetable oils, animal fats, and waste cooking oil) through the reaction of triglycerides with a monohydric alcohol in the presence of a base or an acid catalyst to form fatty acid methyl ester (FAME) and glycerol. A major economic challenge of commercializing biodiesel from edible oils is the high feedstock cost and conflict with feedstocks that could be used as food resources. Low-grade oil, mostly waste cooking oil (WCO), could be a potential substitute as an alternative to edible feedstocks, despite the generally high free fatty acid (FFA) and water content of WCO. Repurposing waste cooking oil into biodiesel not only eliminates the discharge of this material to treatment facilities but also provides the benefit of reduced water and soil pollution. This chapter focuses on the production of biodiesel by homogeneous base-catalyzed transesterification of waste cooking oil obtained from food service businesses and institutions. In addition, the purification and potential valorization of crude glycerol generated as a by-product of the transesterification reaction is also presented.