Daira Aragon, Collins Kimbeng, Shyue Lu, Donal F. Day and Benjamin Legendre

Interest in biofuel production from nonfood sources has prompted the development of high-yielding, dedicated energy crops such as energycane. Energycane varieties are high fiber sugarcane varieties that can potentially grow in more northerly climes and in marginal lands with minimal inputs. Fermentable sugars in energycane are as high as 78 percent of the sugar available in commercial sugarcane. There is an opportunity to extract these readily available fermentable sugars using roller mills or diffusers – similar to the processing of commercial sugarcane – and to use the fiber byproduct, or bagasse, as lignocellulosic biomass for release of additional fermentable sugars or for conversion into electricity. The southeastern United States can serve as the location for new biorefineries that use energycane as the primary feedstock, taking advantage of the knowledge base created by the well-established sugarcane industry.

To adopt energycane as a commercial feedstock for the production of biofuels and bio-based chemicals, it is necessary to determine planting area, crop yields, fermentable sugar yields and product yields that would make a biomass plant operation economically feasible. Researchers at the LSU AgCenter, in partnership with other academic institutions and industries, are investigating these aspects as part of the Sustainable Bioproducts Initiative, a multi-year project funded by the U.S. Department of Agriculture. The initiative evaluates production scenarios incorporating energycane and sweet sorghum as feedstocks into biorefinery schemes for the production of biofuels and other products such as butanol. Butanol is a fuel with a higher energy content than ethanol that does not require extensive modification to vehicle engines because of its similarities with gasoline.

Simulations of a biorefinery using an energycane feedstock were performed to project butanol yields and power generation. Simulation is a low-cost, lowrisk method for determining feasibility requirements and yields of a process before physical implementation. The simulation in this study was developed using the software named SUGARS. It follows Daira Aragon, the same principles as a sugar factory, where cane is pressed in roller mills and the juice is evaporated to obtain syrup. The bagasse remaining after pressing is either burned in boilers to generate electrical power or pretreated and hydrolyzed to obtain lignocellulosic sugars in a conversion plant that is included in the simulation model.

The simulation program was used to determine the potential for the production of butanol and the generation of electrical power from three energycane varieties – Ho 02-113, HoCP 72-114 and Ho 01-007. Table 1 shows input values used in the simulation. Crop yields for mechanically harvested material were taken from values previously reported in literature, while other data were obtained from the juice and bagasse of whole-stalk samples collected at the Sugar Research Station in St. Gabriel. The samples were analyzed at the Audubon Sugar Institute, also in St. Gabriel, for fermentable sugars (sucrose, glucose and fructose) in the juice and complex sugars (cellulose and hemicellulose) in the bagasse.

The juice extracted during milling would be used for the production of biofuels regardless of how the bagasse is used. Simulations show that up to 328 gallons per acre of butanol solvent – which is a mixture of butanol, isopropanol and ethanol – could be produced from the sugars in juice. Additional fuel can be produced from the lignocellulosic sugars released from the bagasse. In this case, potential butanol yields obtained from simulation reached 739 gallons per acre. Figure 1 shows the potential butanol solvent yields by variety using sugars from juice and lignocellulosic sugars from bagasse. Variety Ho 02-113 could produce 1,046 gallons per acre of butanol, between 19-26 percent more than the other varieties tested. Figure 2 shows the export power that can be potentially generated if the bagasse is burned in high-pressure boilers. A facility milling 10,000 tons per day of variety HoCP 72-114 during 120 days has the potential to generate enough power to supply more than 22,000 homes in Louisiana for an entire year (average household consumption of 1,253 kilowatt hours per month).

Variety Ho 02-113 gives the best total butanol production. In terms of power generation, HoCP 72-114 presents the best performance for power generation per ton of cane. However, processing the same acreage of each variety will place Ho 02-113 at the top of the list because of its higher crop yield, producing 22 percent more electricity than HoCP 72-114 and 36 percent more than Ho 01-007. Overall, variety Ho 02-113, with production of more than 1,000 gallons per acre of butanol and 110 megawatts of power for export, has the greatest potential to become a feedstock in commercial production of biofuels and power. Energycane yields may vary by location and year. Nonetheless, these production figures are a good indication of what could potentially be obtained. Because energycane would have a longer harvesting season than sugarcane, October through March, sugar factories in Louisiana could complement their season by processing variety Ho 02-113 and exporting electricity to the grid or producing fermentable sugar syrup and bagasse to supply a biorefinery.

Daira Aragon is an assistant professor at the Audubon Sugar Institute, St. Gabriel. Her co-authors are Collins Kimbeng, an associate professor, Sugar Research Station, St. Gabriel; and Shyue Lu, research associate, Donal F. Day, professor, and Benjamin Legendre, professor and department head, Audubon Sugar Institute.

(This article was published in the spring 2015 issue of Louisiana Agriculture.)

Daira Aragon, assistant professor at the Audubon Sugar Institute, stands next to an evaporator where juice extracted from energycane and sweet sorghum can be processed into biofuel. Photo by A. Denise Attaway

Figure 1. Potential butanol solvent yields by variety using sugars from juice and lignocellulosic sugars from bagasse (gallons per acre).

Figure 2. Potential export power that can be generated if the bagasse is burned in high-pressure boilers (killowatts per ton).