The Hindu Business Line : Transesterification — The magic solution for bio-diesel

THE recent press report regarding the automobile giant DaimlerChrysler and the Council of Scientific and Industrial Research (CSIR) joining hands for a five-year partnership project to develop bio-diesel from the seeds of the jatropha plant must gladden many researchers working on engine studies using different vegetable oils, including jatropha.

Though the use of vegetable oil in engines is as old as Dr Rudolf Diesel himself, sustained interest in plant oils was not evinced in Europe or the US, as the fossil fuels were available from petroleum sources in spite of frequent "petro quakes" from West Asia.

In India, however, continuing research work on renewable energy sources, including vegetable oils, is underway in various laboratories starting from the classic work of, Prof H. A. Havemann, and his associates at the Indian Institute of Science from the early 1940s.

Compared to diesel oil, many vegetable oils have acceptable heat value and ignition quality, designated by the "cetane number" to qualify, with minor engine adjustments, as a fuel for diesel engines. But the major problem with the direct use of untreated (neat) vegetable oil is its higher viscosity. This clogs the nozzle-orifice, affects fuel injection and atomisation of the fuel, and results in incomplete combustion.

Besides this, longer engine trials have resulted in injector choking, more engine deposits, ring-sticking and thickening of the engine lubricant, polymerisation and partial oxidation during storage of the oil, causing an increase in viscosity.

This experience lead to the use of modified vegetable oil by preconditioning the fuel. Among the many ways of adapting the fuel to the engine, transesterification is the most viable process that is used in commercial practice today.

Bio-diesel is the generic name for the family of diesel fuel alternatives produced by transesterification of oils from agricultural feedstock.

Vegetable oils are triglycerides, which are esters derived from long chain fatty acids and polyalcohol glycerol. R1, R2 and R3 in the equation are the hydrocarbon chains (CnHm) of the fatty acid and could be the same depending on the type of vegetable oil.

The normal chain length for plant oils is from 12 to 22 carbon atoms, with 0 to 3 double bonds that are responsible for the physico-chemical properties of the oil.

Transesterification is the magic trick that brings the physico-chemical properties of the neat oil close to that of diesel fuel. It refers to the conversion of an organic ester into another ester of the same acid.

The schematic shows the reactions taking place where one molecule of triglyceride (a plant oil, say, jatropha) reacts with three molecules of methanol to produce three molecules of methyl ester (bio-diesel), while one molecule of glycerol separates.

The reaction takes place at proper mixture ratios of reactants with a suitable catalyst at designated temperature (from 32{+0}C to 83{+0}C) in reaction vessels, with vigorous stirring. This is a batch process for small-scale production and is time-consuming.

In commercial practice, large-scale production is only feasible in continuous processes. Ethanol and butanol are also used to produce bio-diesel. Pure bio-diesel is biodegradable, non-toxic and essentially free from sulphur and aromatics.

It can significantly reduce emissions from diesel engines and could help improve air quality and mitigate environmental damage caused by combustion of fossil fuels. Home-grown vegetable-based fuels and lubricants could significantly reduce dependence on imported petroleum products.

The bio-diesel can be used without major modification of the engine. The transition from diesel fuel to bio-diesel can be smooth, as the engine can be switched to diesel fuel in case of disruption in the supply of bio-diesel. A 20 per cent blend of bio-diesel with regular diesel (called B20) can also be used as the first step in the transition.

In the US, a low-level bio-diesel blend, known as premium diesel, was sold in high volumes. Bio-diesel has a high flash- point and low volatility, providing a high degree of handling safety. Although testing of bio-diesel has been successful, much work remains to be done. This work includes improving production efficiency through reductions in production time, greater consistency of fuel quality across all bio-diesel products, and studies of long-term performance.

Transportation, storage and dispensing systems are the same. But bio-diesel's solvent effect requires attention while storing in concrete tanks.

The king-size question is whether there is enough agricultural feedstock to meet the complete diesel oil replacement demand. Requirement of land, fertilisers, pesticides, farm equipment and water are to be studied with care. Cultivating the oil-producing plants can also decrease the biodiversity in a particular area.

Fortunately, India is a tropical country with diverse evergreen plants natural to our environment. These are lost because of deforestation caused, largely, by unplanned industrial growth. These trees must be saved and new plantations must be created with the dual purpose of environmental preservation and as a source for biofuels.

Besides relying on jatropha alone, oils from other plant sources such as karanji (Pongamia pinnata) trees, must be considered. There is also good potential in rice bran oil. With a suitable transesterification process, all these can be upgraded to diesel quality and mixed to standard diesel grade and marketed.

Tropical regions of the world with evergreen trees are best suited to study the development of bio-diesel technology. With great enthusiasm, experienced researchers in India look forward to a rewarding experience in this project.

(The author is a former professor of mechanical engineering at IIT Madras.)

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