Many sugarcane biorefineries operate for only seven months each year, turning freshly harvested crops into ethanol and biodiesel. When feedstock supplies run out, biorefineries shut down for the other five months. However, according to recent research in the US, dual-purpose crops could produce both ethanol and biodiesel for nine months of the year—increasing profits by as much as 30 percent.
A paper recently published in Industrial Biotechnology is the result of recent research in the US into dual-purpose biofuel crops. The paper “Techno-Economic Analysis of Biodiesel and Ethanol Production from Lipid-Producing Sugarcane and Sweet Sorghum” is authored by Stephen Long, Gutgsell, Endowed Professor of Plant Biology and Crop Sciences at the Carl R. Woese Institute for Genomic Biology at the University of Illinois along with Vijay Singh, Director of the Integrated Bioprocessing Research Laboratory at Illinois, Haibo Huang, Virginia Polytechnic Institute and State University, and Tom Clemente, University of Nebraska.
The researchers simulated the profitability of Plants Engineered to Replace Oil in Sugarcane and Sweet Sorghum (PETROSS) with 0 percent, 5 percent, 10 percent and 20 percent oil and found that growing sorghum in addition to sugarcane could keep biorefineries running for an additional two months, increasing production and revenue in the region of by 20 to 30 percent.
– Currently, sugarcane and sweet sorghum produce sugar that may be converted to ethanol. Our goal is to alter the plants’ metabolism so that it converts this sugar in the stem to oil—raising the levels in current cultivars from 0.05 percent oil, not enough to convert to biodiesel, to the theoretical maximum of 20 percent oil. With 20 percent oil, the plant’s sugar stores used for ethanol production would be replaced with more valuable and energy dense oil used to produce biodiesel or jet fuel, explained co-lead author Stephen Long.
Decrease capital utilisation costs with additional feedstock
This work and the PETROSS project are currently funded by the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E), which supports initial research for high-impact energy technologies to show proof of concept before private-sector investment. Today, PETROSS sugarcane produces 13 percent oil by dry weight, 8 percent of which is the kind of oil used to make biodiesel. At 20 percent oil, sugarcane would produce 13 times more oil—and six times more profit—per acre than soybeans.
A biorefinery plant processing PETROSS sugarcane with 20 percent oil would have a 24 percent internal rate of return (IRR) —a metric used to measure the profitability of potential investments—which increases to 29 percent when PETROSS sorghum with 20 percent oil is processed for an additional two months during the sugarcane offseason.
– When a sugarcane plant has to shut down, the company is still paying for capital utilisation; they have spent millions of dollars on equipment that isn’t used for five months. We propose bringing in another crop, sweet sorghum, to put that equipment to use and decrease capital utilisation costs, said co-lead author Vijay Singh.
By decreasing capital utilisation costs, the cost to produce ethanol and biodiesel drops by several cents per litre. Processing lipid-sorghum during the lipid-cane off-season increased annual biofuel production by 20 to 30 percent, thereby increasing total revenue without any additional investment in equipment.
The simulations in this paper accounted for the equipment required to retrofit ethanol plants to produce biodiesel. In the US, about 90 percent of ethanol plants are already retrofitted to produce biodiesel. According to Singh, the study suggests that it is cost effective in places like Brazil where they produce a large amount of sugarcane, it makes sense to retrofit ethanol plants.