Enhancement of Shelf-Life and Oxidative stability of Jatropha curcas Biodiesel in Zimbabwe

Abstract

Biodiesel is an environment friendly liquid biofuel similar to petro-diesel in terms of fuel quality and combustion characteristics. Increasing environmental concerns, fast depleting petroleum reserves and agriculture based economy of Zimbabwe are the driving forces to promote biodiesel as an alternative renewable fuel. Biodiesel, derived from Jatropha curcas seed oil has great potential to be used as a diesel engine fuel in Zimbabwe to reduce air pollution and to reduce dependence on limited fossil fuel.

Under normal storage conditions diesel fuel can be expected to stay for 12 months or more at 20oC. The research carried out showed that the Jatropha biodiesel has a storage life of 3 months. Beyond this period, the diesel reacts with oxygen from the atmosphere that forms fine sediments and gums, which block the fuel filters leading to poor performance of the engine. This is attributed to the presence of double bonds in the J. curcas oil mainly oleic, linoleic or linolenic acids. J. curcas biodiesels have different amounts of esters (which vary from different geographical location) and the trend of increasing stability is linolenic < linoleic < oleic. These esters undergo auto-oxidation with different rates depending upon the numbers and positions of the double bonds and result in the formation of a series of by-products like acids, esters, aldehydes, ketones, lactones among others. Therefore the aim of the current work is to study the oxidation stability of J. curcas biodiesel and also the effectiveness of various antioxidants which enhance its shelf life. Five antioxidants namely tertiary Butylhydroquinone (TBHQ), Butylated hydroxytoluene (BHT), Butylated hydoxanisole (BHA), Pyrogallol (PY) and Gallic Acid (GA) have been used in this work. PY was found to be the best antioxidants among all 5 antioxidants used. The optimum amount of antioxidant (PY) for pure biodiesel was 3000 ppm.