PEP Review 2003-11
Ethanol from Bagasse
Published: December 2003
Ethanol's biggest problem as a fuel is its high cost. The U.S. wholesale price in 2002 was around $1.10 per gallon. At this price it is not competitive with gasoline. However, tax breaks provide a stimulus for using ethanol as a fuel in the United States. A strong factor in the U.S. ethanol market is the expectation that it will replace MTBE as an oxygenate in reformulated gasoline or become the main renewable additive in gasoline, should the federal government adopt a renewable fuels requirement. As a result, U.S. ethanol capacity is growing significantly.
BC International Corp. in Dedham, MA has developed technology for converting sugar cane bagasse, rice straw, orchard slash and other waste biomass into ethanol. The company plans to build a plant in Jennings, Louisiana to produce 23.2 million gallons of ethanol per year from bagasse. BCI has been at the site since 1995 developing technology for using bacteria to convert agricultural wastes into ethanol. In 2000 BCI began seeking funding for the $90 million project, but has not yet been successful and construction will probably be delayed to 2004 or later. A recent BCI patent for producing ethanol from biomass, published in 1996, serves as the basis for this PEP Review. The core technology is dilute acid prehydrolysis of the lignocellulosic biomass with enzymatic saccharification of the remaining cellulose and fermentation of the resulting glucose and xylose to ethanol.
Organic wastes are potential low cost fermentation substrates for making ethanol. Much of this waste is crop residues. One such waste material is bagasse, which is the matted cellulosic fiber residue from sugar cane that has been processed in a sugar mill. It contains considerable quantities of cellulose, a beta-linked glucose polymer, which is difficult to break down into glucose. In addition, it contains hemicellulose, which is a more complex polymer of several sugars including xylose and arabinose. Entwined around the two sugar polymers is lignin, a polymer that does not contain sugar. In BCI's process, cellulose and hemicellulose are converted to ethanol, but lignin is not.
Our economic evaluation, based on PEP's concept of the process, indicates that significant progress must be made in the conversion of bagasse to ethanol to meet the Department of Energy's 2010 target ethanol selling price of under $1.07 per gallon. Capital-related items make up a large share of the overall economics. Yield improvements in all three major steps of the process would enable lower capital requirements. Significant improvement in the process economics could result if revenue were to be generated by sale of the residual lignin.