In the past few decades, fossil fuels mainly petroleum, natural gas and coal have been playing an important role as the major energy resources worldwide. However, these energy resources are non-renewable and are projected to be exhausted in the near future. The situation has worsened with the escalating energy consumption worldwide due to rapid population growth and economic development. This has caused the price of crude petroleum to hit a record high of USD (US dollar) 90 per barrel in October 2007 and still rising. Therefore, there is an urgent need to find a new energy resource that is renewable, clean, reliable and yet economically feasible as a substitution to the current fossil fuels. In this context, recently, biodiesel derived from vegetable oil has been shown to be a potential alternative replacing petroleum-derived diesel oil for diesel engine.
Biodiesel is mono alkyl ester derived from oils (plant or animal) which have characteristics similar to petroleum-derived diesel oil. Currently, about 84% the world biodiesel production is met by rapeseed oil. The remaining portion is from sunflower oil (13%), palm oil (1%) and soybean oil and others (2%) [1]. Since more than 95% of the biodiesel is made from edible oil, there are many claims that a lot of problems may arise. By converting edible oils into biodiesel, food resources are actually being converted into automotive fuels. It is believed that large-scale production of biodiesel from edible oils may bring global imbalance to the food supply and demand market. Recently, environmentalists have started to debate on the negative impact of biodiesel production from edible oil on our planet especially deforestation and destruction of ecosystem [2]. They claimed that the expansion of oil crop plantations for biodiesel production on a large scale has caused deforestation in countries such as Malaysia, Indonesia and Brazil since more and more forest has been cleared for plantation purposes. Furthermore, the line between food and fuel economies is blurred as both of the fields are competing for the same oil resources. In other words, biodiesel is competing limited land availability with food industry for plantation of oil crop. Arable land that would otherwise have been used to grow food would instead be used to grow fuel [3]. In fact, this trend is already being observed in certain part of this world. There has been significant expansion in the plantation of oil crops for biodiesel in the past few years in order to fulfill the continuous increasing demand of biodiesel. Fig. 1 shows the trend in global vegetable oil ending stocks due to the production of biodiesel in the years 1991–2005 [4]. Although there is continuous increase in the production of vegetable oil; however, the ending stocks of vegetable oils are continuously decreasing due to increasing production of biodiesel. Eventually, with the implementation of biodiesel as a substitute fuel for petroleum-derived diesel oil, this may lead to the depletion of edible-oil supply worldwide.