Currently, approximately 84% of the world biodiesel production is met by rapeseed oil. The remaining portions are from sunflower oil (13%), palm oil (1%), soybean oil and others (2%) (Gui et al., 2008). More than 95% of biodiesel is still made from edible oils. To overcome this undesirable situation, biodiesel is increasingly being produced from non-edible oils and waste cooking oil (WCO). Non-edible oils offer the advantage that they do not compete with edible oils on the food market.

Used cooking oil is a waste product, and for that reason, it is cheaper than virgin plant oil. The higher initial investment required by the acid-catalyzed process (stainless-steel reactors and methanol-distillation columns) is compensated for by low feedstock cost (Zhang et al., 2003). Reusing WCO esters provides an elegant form of recycling, given that waste oils are prohibited for use in animal feed, are harmful to the environment, and human health and disrupt normal operations at wastewater treatment plants (increasing the costs of both maintenance and water purification). The production of biodiesel from WCO is still marginal, but it is increasing worldwide. The USA and China are leaders in WCO use, with 10 and 4.5 Mt/yr, respectively. Other countries and regions, such as the EU, Canada, Malaysia, Taiwan and Japan, produce approximately 0.5-1 Mt/yr (Gui et al., 2008). The potential use of WCO as a primary source for biodiesel fuel is important because such use would negate most of the actual concerns regarding the competition of food and biodiesel crops for land (Bindraban et al., 2009; Odling-Smee 2007). By converting edible oils into biodiesel fuel, food resources are actually being converted into automotive fuels. It is believed that large-scale production of biodiesel fuels from edible oils may bring global imbalance to the food supply-and-demand market, even if such a trend has been contested (Ajanovic, 2010). However, nothing prevents the use of edible oils first for cooking and then for biodiesel fuel.