MSc Chemistry 2nd semester
Due to gradual depletion of world petroleum reserves and the impact of environmental pollution, considerable attention is needed for suitable alternative fuels as a substitute of traditional fossil fuels. The esters of vegetable oils and animals fats are known as biodiesel. Biodiesel is emerging as a promising substitute of an alternative fuel and has gained significant attention due to the predicted depletion of conventional fuels availability in near future and environmental pollution concern. Biodiesel is an eco-friendly, renewable alternative fuel for diesel engine made from esters of vegetable oils and animal fats. As an alternative to petro diesel, biodiesel must be technically feasible, economically competitive, environmentally acceptable and readily available.
Direct use of vegetable oils found to be problematic due to their greater viscosity which affects piston, injector deposit and oil thickening etc. Conversion of oils to their alkyl esters reduce the viscosity and produce fuel the properties that are similar to petroleum based diesel fuel. For the countries like Nepal, utilization of biodiesel produced from Jatropha oil by trans esterification process is one of the most promising options to replace conventional fossil diesel fuel. Properties obtained for the Jatropha oil methyl ester are very closely matched with the values of conventional diesel fuel and can be used without any modification in the existing diesel engine.
About Jatropha Curcas
Jatropha curcas,locally known as Sajiyon is a small tree of about 3.0m height belonging to the family Euphorbiaceae. It has a short trunk with thick branches spreading into a crown of dark green leaves. The bark is pale brown and the leaves are attached to long petioles. It can grow on almost any site, wide range of soil and climatic conditions, mostly found in terai, chure and hilly parts of the Nepal. A litre of pure diesel can be extracted from four kilos of jatropha seeds. Jatropha tree have a productive life of 30-40 years with about 3 kg of seeds annually. It is most suitable non-edible oil seed plant due to its various favourable attributions like hardy nature, short gestation period, adaptability in wide range of agro-climatic conditions, high oil recovery and quality of oil etc. When jatropha seeds are crushed, the resulting oil can be processed to produce a high quality biodiesel that can be used in a standard diesel car, while the residue can also be processed and that can bused biomass feedstock power electricity plants or used as fertilizer.
Materials and method
Biodiesel can be produced from Edible & Non Edible Oils. There are three basic routes to biodiesel production from oils and fats:
1. Base catalysed trans esterification of the oil.
2. Direct acid catalysed trans esterification of the oil.
3. Conversion of the oil to its fatty acids and then to biodiesel.
Almost all biodiesel is produced using base catalysed trans esterification as it is the most economical process requiring only low temperatures and pressures and producing a 98% conversion yield. The Trans esterification process is the reaction of a triglyceride (fat/oil) with an alcohol to form esters and glycerol. A triglyceride has a glycerine molecule as its base with three long chain fatty acids attached. The characteristics of the fat are determined by the nature of the fatty acids attached to the glycerine. The nature of the fatty acids can in turn affect the characteristics of the biodiesel. During the esterification process, the triglyceride is reacted with alcohol in the presence of a catalyst, usually a strong alkaline like sodium hydroxide or potassium hydroxide. The alcohol reacts with the fatty acids to form the mono-alkyl ester, or biodiesel and crude glycerol. In most production methanol or ethanol is the alcohol used (methanol produces methyl esters while ethanol produces ethyl esters) and is base catalysed by either potassium or sodium hydroxide, Potassium hydroxide has been found to be more suitable for the ethyl ester biodiesel production, while either base can be used for the methyl ester. A common product of the trans esterification process Oil Methyl Ester (OME) produced from raw oil reacted with methanol. The figure below shows the chemical process for methyl ester biodiesel.
Advantages of using jatropha oil as a biodiesel
1. Biodiesel can be used as substitute or partial replacement to diesel fuel.
2. Special pumps or high pressure equipment for fuelling are not required.
3. Biodiesel being an oxygenated fuel contributes to complete combustion hence, improved emissions profile reduces public health risks.
4. Reduces the dependence on imported petroleum diesel fuel.
5. Superior lubrication capabilities of biodiesel increases engine life.
6. Easily decomposes biologically and in the case of an accident no harm is done to soil or ground water.
1. NOx emissions are higher, since biodiesel tends to increase NOx emissions.
2. Due to lower energy content of biodiesel, engine performance will be less as compared to diesel.
3. Due to more viscosity, gum formation and piston sticking would occur under long term use of biodiesel due to the presence of glycerine.
Jatropha oil has been chosen as feedstock for biodiesel production since it is no-edible and success of its cultivation in varying degrees of climatic conditions. Physical and chemical properties of produced biodiesel are found to be in close agreement with that of the petro diesel and with international standards of biodiesel.
Nepal may not have the fossil fuel deposits to meet the demand for diesel but some dependency on imports could be reduced if serious initiatives were taken to produce our own bio-fuel. There is a need to develop commercial farming of jatropha and make it a sustainable fuel source. To meet the challenges of excessive import, we have to strengthen our oil seed sector and lay special emphasis on harnessing the existing and augmenting future potential source of green fuel.