I have written a few posts in the past about Jatropha curcas, a tropical shrub with the potential to make an important contribution to our fuel supplies. (See here and here for previous essays concerning jatropha). While I believe that the present status of jatropha has been exaggerated, I believe the potential is enormous. I want to devote the next couple of essays to why I believe this.
In this essay, I want to provide a synopsis of jatropha by supplying an excerpt from the chapter on renewable diesel that I wrote for Biofuels, Solar and Wind as Renewable Energy Systems: Benefits and Risks. I will fill in some details in the next essay.
Jatropha curcas is a non-edible shrub native to tropical America, but now found throughout tropical and subtropical regions of Africa and Asia (Augustus et al. 2002). Jatropha is well-suited for growing in arid conditions, has low moisture requirements (Sirisomboon et al. 2007), and may be used to reclaim marginal, desert, or degraded land (Wood 2005). The oil content of the seeds ranges from 30% to 50%, and the unmodified oil has been shown to perform adequately as a 50/50 blend with petroleum diesel (Pramanik 2003). However, as is the case with other bio-oils, the viscosity of the unmodified oil is much higher than for petroleum diesel. The heating value and cetane number for jatropha oil are also lower than for petroleum diesel. This means it is preferable to process the raw oil into biodiesel or green diesel.
Jatropha appears to have several advantages as a renewable diesel feedstock. Because it is both non-edible and can be grown on marginal lands, it is potentially a sustainable biofuel that will not compete with food crops. This is not the case with biofuels derived from soybeans, rapeseed, or palm.
Jatropha seed yields can vary over a very large range – from 0.5 tons per hectare under arid conditions to 12 tons per hectare under optimum conditions (Francis et al. 2005). However, if marginal land is to be used, then yields in the lower range will probably by typical. Makkar et al. determined that the kernel represents 61.3% of the seed weight, and that the lipid concentration represented 53.0% of the kernel weight (Makkar et al. 1997). Therefore, one might conservatively estimate that the average oil yield per hectare of jatropha on marginal, non-irrigated land may be 0.5 tons times 61.3% times 53.0%, or 0.162 tons of oil per hectare. Jatropha oil contains about 90% of the energy density of petroleum diesel, so the energy equivalent yield is reduced by an additional 10% to 0.146 tons per hectare. While this is substantially less than the oil production of soybeans, rapeseed, or palm oil, the potential for production on marginal land may give jatropha a distinct advantage over the higher-producing oil crops.
A commercial venture was announced in June 2007 between BP and D1 Oils to develop jatropha biodiesel (BP 2007). The companies announced that they will invest $160 million with the stated intent of becoming the largest jatropha biodiesel producer in the world. The venture intends to produce volumes of up to 2 million tons of biodiesel per year.
Jatropha has one significant downside. Jatropha seeds and leaves are toxic to humans and livestock. This led the Australian government to ban the plant in 2006. It was declared an invasive species, and ‘too risky for Western Australian agriculture and the environment here’ (DAFWA 2006).
While jatropha has intriguing potential, a number of research challenges remain. Because of the toxicity issues, the potential for detoxification should be studied (Heller 1996). Furthermore, a systematic study of the factors influencing oil yields should be undertaken, because higher yields are probably needed before jatropha can contribute significantly to world distillate supplies (see Calculation 1). Finally, it may be worthwhile to study the potential for jatropha varieties that thrive in more temperate climates, as jatropha is presently limited to tropical climates.
Calculation 1: Consider the potential for displacing 10% of the world’s distillate demand of 1.1 billion tons per year with jatropha oil. To replace 10% of the world’s distillate demand will require 110 million tons of distillate to be replaced. Jatropha, with about 10% less energy than petroleum distillates, will require 122 million tons on a gross replacement basis (i.e., not considering energy inputs). On marginal, non-irrigated land the yields will likely be at the bottom of the range of observed yields. At a yield of 0.146 tons per hectare (the lower range of yields), this would require 836 million hectares, which is greater than the 700 million hectares currently occupied by permanent crops.
An estimated 2 billion hectares of land is considered to be degraded and perhaps suitable for jatropha cultivation (Oldeman et al. 1991). There are also an estimated 1.66 billion hectares in Africa that are deemed suitable for jatropha production (Parsons 2005). This could provide a valuable cash crop for African farmers. But, until an estimate is made of the energy inputs required to process and distribute the jatropha-derived fuel on a widespread basis – especially on marginal land – the real potential for adding to the world’s net distillate supply is unknown.
Augustus, G.S., Jayabalan, M., & Seiler, G.J. (2002). Evaluation and bioinduction of energy components of Jatropha curcas. Biomass and Bioenergy., 23, 161-164. BP. (2007). BP and D1 Oils Form Joint Venture to Develop Jatropha Biodiesel Feedstock. Retrieved July 14, 2007 from the BP corporate web site: http://www.bp.com/genericarticle.do?categoryId=2012968&contentId=7034453 DAFWA, Department of Agriculture and Food, Western Australia. (2006). Jatropha Banned in WA. Retrieved August 3, 2007 from http://www.agric.wa.gov.au/content/sust/biofuel/191006jatrophe.pdf Francis, G., Edinger, R. & Becker, K. (2005). A concept for simultaneous wasteland reclamation, fuel production, and socio-economic development in degraded areas in India: Need, potential and perspectives of Jatropha plantations Natural Resources Forum 29 (1), 12–24. Heller, J. (1996). Physic nut Jatropha Curcas L. Promoting the conservation and use of underutilized and neglected crops. Institute of Plant Genetics and Crop Plant Research (Gartersleben) and International Plant Genetic Resources Institute: Rome Vol. 1. Makkar H., Becker K., Sporer F., & Wink M. (1997). Studies on the nutritive potential and toxic constituents of different provenances of Jatropha curcas. Journal of Agricultural Food Chemistry 45, 3152–3157. Oldeman, L. R.,. Hakkeling R. T. A., & Sombroek, W. G. (1991). World Map of the Status of Human-induced Soil Degradation: An explanatory note. Wageningen, International Soil Reference and Information Centre, Nairobi, United Nations Environment Programme. Parsons, K. (2005). Jatropha in Africa: Fighting the Desert & Creating Wealth. EcoWorld. Retrieved July 14, 2007, from http://www.ecoworld.com/home/articles2.cfm?tid=367 Pramanik, K. (2003). Properties and use of Jatropha curcas oil and diesel fuel blends in compression ignition engine. Renewable Energy Journal, 28, (2), 239–248. Sirisomboon, P., Kitchaiya, P., Pholpho, T., & Mahuttanyavanitch, W. (2007). Physical and mechanical properties of Jatropha curcas L. fruits, nuts and kernels, Biosystems Engineering, 97, (2), 201-207. Wood, P. (2005). Out of Africa: Could Jatropha vegetable oil be Europe’s biodiesel feedstock?, Refocus, 6 (4), 40-44.