Introduction

The consumption and demand for the petroleum products are increasing every year due to increase in population, standard of living and urbanization. Diesel consumption pattern in India has  not varied much  and is around 36x106 tonnes as reported by the Ministry of Petroleum and Natural Gas (Table 1). The increase in crude oil import affects the country’s economy and its development. The diesel vehicles were banned in New Delhi for serious problem of  air pollution due to higher emissions  of polluted  gases. The acid rain, global warming and health hazards are the results of ill effects of increased polluted gases like SOx, COand particulate matter in atmosphere.  

Today’s diesel engines  require a clean burning, stable fuel that performs well under the variety of operating conditions. Biodiesel is the only alternative fuel that can be used directly in any existing unmodified diesel engine. Because it has similar properties to diesel fuel, biodiesel can be blended at any ratio with diesel fuel.  In most of  the developed countries, biodiesel is produced from soybean, rapeseed, sunflower, peanut, etc., which are essentially edible in Indian context. Among the various vegetable oil sources, non-edible oils are suitable for  biodiesel production.  Because edible oils  are already in demand and too expensive than diesel fuel. Among the non-edible oil sources, Jatropha curcas is identified as potential biodiesel source and comparing with other sources, which has added advantages as rapid growth, higher seed productivity, suitable  for tropical and subtropical regions of the world. 

Biodiesel 

Biodiesel is a variety of ester-based oxygenated fuels derived from natural, renewable biological sources such as vegetable oils.  It’s name indicates, use of this fuel in diesel engine alternate to diesel fuel. Biodiesel operates in compression ignition engines like petroleum diesel thereby requiring no essential engine modifications. Moreover it can maintain the payload capacity and range of conventional diesel. Biodiesel fuel can be made from new or used vegetable oils and animal fats. Unlike fossil diesel, pure biodiesel is biodegradable, nontoxic and essentially free of sulphur and aromatics.

Chemistry of biodiesel production 

Biodiesel is produced by transesterification  of large, branched triglycerides in to smaller,  straight chain molecules of  methyl esters, using an alkali or acid or enzyme  as catalyst. There are three stepwise reactions with intermediate formation of diglycerides and  monoglycerides  resulting in the production of three moles of methyl esters and one mole of glycerol from triglycerides. Alcohols such as methanol, ethanol, propanol, butanol and amyl alcohol are used in the transesterification process.  Methanol and  ethanol are used most frequently, especially methanol because of its low cost, and physical and chemical advantages. They can quickly react with triglycerides and sodium  hydroxide is easily dissolved in these alcohols.Stoichiometric molar ratio of alcohol to triglycerides required for transesterification reaction is 3:1. In practice, the ratio needs to be higher to drive the equilibrium to a maximum ester yield.