Heroes: Grow Jatropha, Save the World?

Jatropha is a tough, shrubby weed with golf-ball-size fruit that yields a refinable oil. The plant can grow in unfavorable conditions, with little fertilizer or water, and cannot be used for food, avoiding the problem of competition between food and fuel supplies that corn now faces. Until recently, jatropha was best-known in India and elsewhere as a hedge to keep wild animals from wandering onto farms.

The jatropha oil is subjected to a process called transesterification. Plant oils - those derived from jatropha as well as the oilseed rape and soya beans from which biodiesel is produced in Europe and the U.S. - consist mainly of triglycerides, the fatty acid esters of glycerin. They are extremely viscous and tend to resinification - qualities that are not desirable inside a fuel tank.

Transesterification, in which the glycerin is replaced by methanol, makes it possible to use the processed plant oil as fuels. However, that’s only the first step in the transformation of plant oil into biodiesel. After transesterification, the resulting raw product is centrifuged and washed with water to cleanse it of impurities, such as glycerin and excess methanol. Only at the end of this process is the biodiesel of usable quality.

In a 2004 Daimler study it was revealed that jatropha-based biofuel can be used without any problems in modern CDI engines adapted for biodiesel. What’s more, this fuel produces only half of the unburned hydrocarbon emissions and one-third of the particulate emissions produced by diesel fuel derived from crude petroleum.

Furthing jatropha's stock is some Goldman Sachs data on the estimated cost per barrel of fuel made from a variety of sources:

• Cellulose: $305


• Wheat: $125


• Rapeseed: $125


• Soybean: $122


• Sugar Beets: $100


• Corn: $83


• Sugar Cane: $45


• Jatropha: $43

Just like everything in life, there are downsides. The plant has never been domesticated. Jatropha's oil output is unpredictable and often lower than expected. Although it can grow without water, it tends to do much better when water is added, raising its cost of production and mitigating some of the perceived benefits.

For now the question remains: "Can a scrappy weed truly help to save the world?"

Sources:
Popular Science
The Wall Street Journal
Daimler
Biopact
Institute of Science in Society