Alternative crops for biodiesel feedstock

Biodiesel, the name popularly given to fatty acid alkyl esters, has become an attractive option for the replacement of petroleum diesel (‘petrodiesel’). While its overall impact on the greenhouse effect continues to be debated, other qualities of biodiesel are unquestioned. Biodiesel is biodegradable, generally non-toxic and has superior lubricity to petrodiesel. Overall emissions are greatly reduced. The bulk of the feedstock for its production comes from renewable resources and when biodiesel is used as a blend (up to 20%); no changes are required for existing diesel engines. However, it is still too costly and about 60–80% of the cost for biodiesel comes from the feedstock. Concerns have been raised about the propriety of using food for fuel. Proposed alternative feedstock such as Jatropha curcas address some of these concerns but have their own disadvantages. This paper is a comprehensive review of recent progress on alternative crops for feedstock and addresses the issues that may ultimately lead to their success or failure: engine performance, yield, fatty acid profile, unique minor components, unique fatty acids, toxicity and harvestability. The use of agricultural wastes, used or waste oil and microbial fats is also discussed. The conclusion is reached that a blend of oils and used oils may be the best approach for the immediate future while genetically modified plants and microalgae may provide a longer term solution.