Ethanol was produced as a co-product from the remaining sugar from the cane. The ethanol production costs from lipid-cane were between $0.40/L and $0.46/L. The internal rate of return (IRR) for the soybean biodiesel process was 15.0%, and the IRR for the lipid-cane process went from 13.7 to 24.0% as the lipid content increased from 2 to 20%.

Flow diagram of the lipid-cane process. Huang et al. Click to enlarge.

Because of its high productivity, lipid-cane with 20% lipid content can produce 6700 L of biodiesel from each hectare of land, whereas soybean can only produce approximately 500 L of biodiesel from each hectare of land.

The team had earlier altered sugarcane metabolism to convert sugars into lipids, or oils, which could be used to produce biodiesel. The natural makeup of sugarcane is typically only about 0.05 percent oil. Within a year of starting the project, the team was able to boost oil production 20 times, to approximately 1 percent. At the time of this analysis, the “oil-cane” plants are producing 12% oil. The ultimate goal is to achieve 20%. Oil cane has additional advantages that have been engineered by the team. These include increased cold tolerance and more efficient photosynthesis, which leads to greater biomass production and even more oil.

If all of the energy that goes into producing sugar instead goes into oil, then you could get 17 to 20 barrels of oil per acre. A crop like this could be producing biodiesel at a very competitive price, and could represent a perpetual source of oil and a very significant offset to greenhouse gas emissions, as well.

—Stephen Long, co-author

In their analysis, the team looked at the land area, technology, and costs required for processing oil-cane biomass into biodiesel under a variety of oil production scenarios, from 2 percent oil in the plant to 20 percent. These numbers were compared with normal sugarcane, which can be used to produce ethanol, and soybean.

The analysis showed that oil cane with 20 percent oil in the stem, grown on under-utilized acres in the southeastern United States, could replace more than two-thirds of the country’s use of diesel and jet fuel. This represents a much greater proportion than could be supplied by soybean, even if the entire crop went to biodiesel production. Furthermore, oil cane could achieve this level of productivity on a fraction of the land area that would be needed for crops like soybean and canola, and it could do so on land considered unusable for food crop production.

The current full production cost of biodiesel from soybean is $4.10 per gallon ($1.08 per liter). Using oil cane instead, that cost decreases to $3.30 per gallon for 2 percent oil cane and to $2.20 per gallon for 20 percent oil cane. The ethanol produced from 1-, 5- and 10 percent oil cane would add to the cost benefit.

The project received funding from the Department of Energy’s ARPA-E program.

Resources

• Huang, H., Long, S. and Singh, V. (2016) “Techno-economic analysis of biodiesel and ethanol co-production from lipid-producing sugarcane,” Biofuels, Bioprod. Bioref. doi: 10.1002/bbb.1640