By KEVIN WALKER
Michigan Correspondent EAST LANSING, Mich. — A recently published study may help to make cellulosic ethanol a more commercially attractive enterprise.
The study, published in the proceedings of the National Academy of Sciences on Jan. 22, is about cellulosic ethanol production using a process called AFEX, or ammonia fiber expansion.
“I think it has to be called a breakthrough. That is the most fair, accurate description, I believe,” said Bruce Dale, a professor in the chemical engineering and materials science department at Michigan State University (MSU) and a co-author of the study.
AFEX has certain benefits over other methods of pretreating cellulosic materials, according to Ming Lau, a doctorate student in chemical engineering and materials science at MSU and the first author of the paper.
“The choice of the pretreatment method is crucial in determining the viability of this technology due to pretreatment’s pervasive impact on ethanol fermentation,” Lau said. “This pretreatment is unique to this process. We do not need to detoxify the sugar solution or add nutrients with AFEX. Detoxification and adding nutrients add significant costs to the ethanol making process.”
Pretreatment of cellulosic materials is necessary using conventional methods because lignin, a material that gives plants their strength, has to be broken down before the sugars in the material can be made accessible.
Lau said that “detoxification” adds 20 percent to the cost of making ethanol. While toxins that inhibit fermentation aren’t there in the material to begin with, the pretreatment process, such as acid pretreatment, releases fermentation inhibitors, he said. Unfortunately, nutrients are also washed away during pretreatment and must be replaced.
“AFEX breaks down the structure without producing fermentation inhibitors,” Lau said.
The other aspect of the research that’s unique, according to Lau, is the use of a brewer’s yeast called saccharomyces cerevisiae 424A (LNH-ST). The numbers at the end of the name of this yeast indicate that it’s been genetically modified. Researchers at Purdue University developed it. The unmodified version of the yeast is commonly used in ethanol production since it can ferment various sugars, including glucose; it can’t ferment xylose, however, without modification. This is important because xylose is a plant sugar that consists of 30 percent of the plant sugars in cellulosic materials.
“My research shows that xylose can be used almost completely, but it is used more slowly than glucose,” Lau said. “In any chemical process, the most important factor is how much product can you get per ton of feedstock.”
Lau said they are currently able to get about 65 gallons of ethanol per ton of biomass using the AFEX process. He described this as “fulfilling the minimal requirement for commercial production.”
“85 gallons per ton is something that is achievable in the near future,” Lau added. “This is the benchmark that would signify the technological maturity of this new enterprise.”
According to the report, “the straightforward cellulosic ethanol technology reported here, which converts sugars from lignocellulosic materials to ethanol without washing, detoxification and nutrient supplementation, is significant in the search for a highly competitive cellulosic ethanol production strategy.”
But, Lau said, more research needs to be done to increase the amount and concentrations of available fermentable sugars, which is most essential in the effort to increase ethanol yield per ton of biomass.
For more on this research, go online at www.everythingbiomass.org |
