Vegetable oil as a feedstock for biodiesel synthesis

Abstract

Limited reserves of fossil fuels as well as the growing concern for the environment, has led to a worldwide search for renewable energy sources, among which biodiesel, a mixture of fatty acid methyl esters (FAME), is one of the most perspective alternative fuels since it is a non-toxic and can be produced from different renewable sources through simple cost-effective alcoholysis, while being compatible with existing infrastructures. Vegetable oils, as renewable in nature and environmentally friendly, with a possibility to be produced on a large scale, represent a promising feedstock for biodiesel production. In this chapter, a comprehensive review of different vegetable oils as a feedstock for biodiesel synthesis is reported, including edible and non-edible oils, as well as waste vegetable oils. Selection of feedstock for biodiesel production mainly depends on the specific conditions and circumstances in some region (climate, presence of certain crops, the economic development of a country, etc.). Various fatty acid compositions of triacylglycerols directly determine the quality and fulfillment of the standards of biodiesel. One of the crucial points which determine technology route for biodiesel synthesis is content of free fatty acids (FFA) which might be present in vegetable oils, as well as the presence of water and other compounds. Also, many analysis performed in the past have shown that the production cost of biodiesel is mainly determined by the price of used feedstock, which represents 70-80% of total production costs of biodiesel. Currently more than 95% of feedstock comes from edible oils since they are easily accessible, consists mainly of triacylglycerols, whereby the properties of biodiesel produced from these oils are suitable to be used as diesel fuel substitute. Most commonly used edible oils for biodiesel production are rapeseed, soybean, sunflower and palm. However, for economic and social reasons, in recent years research and development of biodiesel production has focused on other sources of triacylglycerols, in order to replace edible oils by lower-cost non-edible plant oils and the waste cooking oils, feedstocks that are unsuitable for human consumption. Properties of different oils and biodiesel obtained from them as well as the technologies suitable for biodiesel synthesis are compared in this chapter. The wellknown fact is that the conventional and to-day widely applied homogeneous method of biodiesel synthesis is sensitive to the presence of impurities in the oil, primarily the presence of FFA and water. Furthermore, biodiesel synthesis is followed by creation of large amount of wastewater produced during neutralization of catalyst and purification of final product. The drawbacks of a homogeneous process can be avoided by applying technologies based on utilization of heterogeneous catalyst or by application of the noncatalytic supercritical process of biodiesel synthesis. These technologies for biodiesel production were also analyzed and compared.