Enzymatic transesterification of Jatropha oil
© Kumari et al; licensee BioMed Central Ltd. 2009
Received: 17 July 2008
Accepted: 14 January 2009
Published:
Enzymatic transesterification of Jatropha oil
© Kumari et al; licensee BioMed Central Ltd. 2009
Received: 17 July 2008
Accepted: 14 January 2009
Published: 14 January 2009
Transesterification of Jatropha oil was carried out in t-butanol solvent using immobilized lipase from Enterobacter aerogenes. The presence of t-butanol significantly reduced the negative effects caused by both methanol and glycerol. The effects of various reaction parameters on transesterification of Jatropha oil were studied.
The maximum yield of biodiesel was 94% (of which 68% conversion was achieved with respect to methyl oleate) with an oil:methanol molar ratio of 1:4, 50 U of immobilized lipase/g of oil, and a t-butanol:oil volume ratio of 0.8:1 at 55°C after 48 h of reaction time. There was negligible loss in lipase activity even after repeated use for seven cycles.
To the best of our knowledge this is the first report on biodiesel synthesis using immobilized E. aerogenes lipase.
Biodiesel is a renewable fuel that can be synthesized from edible, non-edible and waste oils. Due to diminishing petroleum reserves, vegetable oils have attracted attention as a potential renewable source for the production of alternatives to petroleum-based diesel fuel. A number of processes have been developed for biodiesel production involving chemical or enzyme catalysis or supercritical alcohol treatment [1–4]. Enzymatic transesterification of triglycerides is a good alternative to chemical processes due to its eco-friendly, selective nature and low temperature requirements [5–9].
Many starting materials such as soybean oil [10, 11], sunflower oil [12, 13], cotton seed oil, rapeseed oil, palm oil [16, 17] and restaurant kitchen wastes  have been evaluated for preparation of biodiesel by the enzymatic route. In many countries, like India, where edible oils are not in surplus supply, there is a need to search for alternative starting materials, such as from non-edible oils. Oil of Jatropha curcas (Euphorbiaceae), a non-edible oil, has been chosen for the present investigation. The seeds and oil are toxic due to the presence of toxic phorbol esters. The oil content of Jatropha seed ranges from 30 to 50% by weight, whereas in kernel the oil content ranges from 45 to 60%. The fatty acid composition of Jatropha oil consists of oleic acid 43.1%, linoleic acid 34.3%, stearic acid 6.9%, palmitic acid 4.2% and other acids 1.4%. Jatropha curcas is a low-growing tree, generally planted as a hedge for protecting crops from animals. It can be grown on barren land under harsh conditions and can be cultivated as a part of the strategy for reclaiming degraded lands. Keeping all this in view, the Indian Government has announced a 'National Mission on Biodiesel' for Jatropha plantations in wasteland regions that is to be implemented on an area of 400,000 ha over the next five years.
There are many reports on biodiesel production using enzyme catalysis by free or immobilized lipases [7, 8, 10, 15, 18, 21–23]. Immobilized lipase in particular is suitable for continuous biodiesel production because of the ease of its recovery from the reaction mixture. There are two major limitations of lipase-catalyzed biodiesel synthesis. One is higher cost (which can be reduced up to a certain extent by immobilization) and another is its inactivation by methanol and glycerol. It has been reported that as methanol is insoluble in vegetable oils, it inhibits the immobilized lipases and thereby decreases the catalytic activity of the transesterification reaction. Further, the hydrophilic by-product glycerol is also insoluble in the oil, so it is easily adsorbed onto the surface of the immobilized lipase leading to a negative effect on lipase activity and operational stability. Use of several solvents such as n-hexane and petroleum ether in the reaction medium has been reported  but the problem persisted since the inhibition of lipases still occurred due to poor solubility of methanol and glycerol in the hydrophobic solvents. There are some reports on enhanced biodiesel synthesis in presence of t-butanol as a solvent [27–29]. As both methanol and glycerol are soluble in t-butanol, the inhibitory effect of methanol and glycerol on lipase activity is reduced. Moreover, t-butanol is not a substrate for the lipases because it does not act on tertiary alcohols.
Biodiesel synthesis from Jatropha oil has been reported by Chromobacterium viscosum and Pseudomonas cepacia lipases. In both the cases the ethanolysis of Jatropha oil for biodiesel synthesis has been carried out [20–30]. In the present investigation, methano