Chemical Technology February 2015

Life Cycle Assessment (LCA) of biodiesel

by T Sebitso, M Kharidzha and KG Harding, all of the School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa Although biodiesel is seen as an eco-friendly alternative to fossil fuels, the processing methods can vary its environmental impact.

B iodiesel may be defined as a monoalkyl ester of long chain fatty acids derived from a renewable lipid feedstock, such as vegetable oil or animal fat (Basheer et al , 2012). Biodiesel production has received considerable interest in the recent years as an alternative to the diesel produced from fossil fuels. This is because not only is biodiesel biodegradable and non-toxic, it also has a higher flash point (about 423 K) making it less volatile, safe to handle and to transport (Morais et al , 2010). It is compatible with currently existing technology of diesel production, eliminating the need to reconstruct and redesign equipment. Biodiesel has lower carbon mon- oxide, NO x , SO x and particulates emissions as compared to conventional diesel. Carbon dioxide emissions are not considered important because they can be absorbed by terrestrial plants through photosynthesis provided the highly productive ecosystems are not replaced by the less photo- synthetically active biodiesel crop (Kiwjaroun et al , 2008). Biodiesel, however, has its disadvantages: its production rate accounts for only 15 % of the transportation demands. The reason why the conventional diesel cannot be replaced completely by biodiesel is because its production competes with the food crop; the only solution is to use more land for biodiesel agriculture which leads to high costs. The costs of vegetable oil can be up to 75 % of the whole process and thus leading to the biodiesel process being 1,5 times more expensive than conventional diesel (Morais et al , 2010). Biodiesel utilises various feed-stocks, including waste

cooking oil, clean vegetable oil and animal fat. The advantage of using waste cooking oil is that it serves as a waste treat- ment process, thus solving waste disposal problems. Waste cooking oil also leads to the reduction in the production costs as compared to the vegetable oil. The trans-esterification process is used in the production of biodiesel. It involves a catalysed chemical reaction with oil or fat (triglyceride) and alcohol as reactant. The reaction products are biodiesel and glycerol. Life Cycle Assessment (LCA) A Life Cycle Assessment is a tool that is used to determine or assess the impact of a product or a process on the en- vironment. It evaluates the use of energy and raw material consumption, wastes and emissions of a product's life cycle (Navigant Consulting, Inc, 2012). An LCA assesses a material or a product from 'cradle to grave', meaning that a material is assessed from the mo- ment raw materials are extracted from the environment, its production, use, to the time the material is returned to earth as waste (SAIC, 2006). An LCA is used to evaluate the amount of energy, rawmaterials consumed, emissions to the atmosphere as well as the amount of waste generated during a product’s entire life cycle (Navigant Consulting, Inc, 2012). Showing the environmental impacts of a product’s life cycle using an LCA is helpful to decision makers when choosing themost feasible process or whenmaking improvements. An LCA is carried out using a method that has four stages which

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Chemical Technology • February 2015