Researchers at the LSU AgCenter’s Audubon Sugar Institute
in St. Gabriel, La., are combining their knowledge of sugarcane processing with chemical engineering to develop a synergy between sugar production and ethanol. Some of the same process technology industry uses for producing ethanol from corn can be used to produce it from many other raw materials, including sugarcane and similar plants.
"The knowledge base is here," said Donal Day
, a researcher at the Audubon Sugar Institute.
Ethanol, which can replace a portion of the gasoline consumers pump into their cars, is produced by fermenting sugars. In the United States, these sugars typically come from corn starch. Ethanol from corn is made by treating the cornstarch with enzymes to create sugar. Then the sugar is fermented with a yeast to produce ethanol – an alcohol.
"It’s just like making beer," Day said. But AgCenter researchers are looking at nonfood sources of sugar as alternatives. Some of these sources include cellulosic materials, such as a plant called energy cane, sweet sorghum, a grass called miscanthus and bagasse – the fibrous portion of a sugarcane stalk that remains after the juice is squeezed out. To make ethanol from cellulose, the plant fibers first have to be treated so enzymes can reach the main sugar structures in cellulose.
Various forms of cellulose contain several types of sugars, particularly glucose and xylose. Giovanna DeQueiroz
, a researcher at the Audubon Sugar Institute, is looking for ways to treat various cellulosic materials to extract the sugars that can be turned into ethanol and other valuable chemicals.
"Developing enzymes is an important step in coming up with an economical process for producing ethanol from cellulose," DeQueiroz said. "We have many ways to make ethanol from cellulosic crops, but we have to be concerned with costs and environmental considerations. We convert feedstocks into sugars, primarily glucose but also xylose. We pre-treat the fibers to open the structure so enzymes can get to the cellulose and release these sugars. Our goal is to identify and optimize the process so it can be used with various cellulosic materials."
The LSU AgCenter has patents on the technology DeQueiroz is working with, but the process still needs to be refined.
"Xylose is difficult to work with because we can’t get high yields of ethanol," she said.
Conversion from cellulose to sugars and then to ethanol depends not only on the pre-treatment technology but also on the enzymes – bacteria or yeasts – and microorganisms that can transform the material from one compound to another. But researchers say one of the challenges is to find the right organisms that will work on both glucose and xylose simultaneously.
"Most of these bugs prefer only one sugar," Day said. "If one converts glucose, it doesn’t particularly like xylose."
Many other plant materials can be turned into ethanol, but the technology needs to be economical to be practical. "The process of producing ethanol from cellulose is not inexpensive," Day said.
Researchers from the LSU AgCenter’s Sugar Research Station and from the U.S. Department of Agriculture’s research station in Houma have developed several varieties of energy cane that can be used as feedstock for producing ethanol. This cousin of sugarcane yields more biomass – the total mass of the plant – but less sugar than sugarcane. Still, it offers a longer growing season because it can withstand colder temperatures.
"Energy cane could be grown farther north in Louisiana than sugarcane is now," Day said.
LSU AgCenter researchers looking for other plants to fill out the growing seasons are evaluating sweet sorghum and miscanthus. Other Audubon Sugar Institute researchers are working to develop economical methods for producing cellulosic ethanol because it could be a boon to Louisiana agriculture.
Louisiana sugar mills operate only three to four months a year, and they have much of the machinery that would be necessary for gathering, crushing and milling plants that are similar to sugarcane and could be converted into ethanol, researchers said. The systems for harvesting and delivering sugarcane and related plant materials systems also are in place.
"They only need to add chemical and bioreactors and distilleries to complete the process," DeQueiroz said. "And the energy to operate the process would come from the same source as sugarcane processing – burning biomass to run the boilers already in place."
To be efficient, an ethanol plant has to work year-round, whether it’s an existing sugar mill or a new biomass plant. Many feedstocks such as sugarcane, sweet sorghum and similar plants deteriorate over time, so they can’t be stockpiled for too long for ethanol production.
"We need a way to assure continuous delivery," Day said. "We can start with sugarcane in the fall, then move to energy cane later in the winter, then change to sweet sorghum and finally to miscanthus as the year goes on. If there’s money in converting cellulose into ethanol, it will come."
(This article was published in the winter 2009 issue of Louisiana Agriculture.)