Unlike simple sugars or even starches in the grains of plants, such as corn kernels, cellulose doesn’t dissolve in water. This is good for keeping plants healthy, but it's a problem for making biofuels.
Before the complex sugars in cellulose and hemicellulose (from woody plants) can be converted into ethanol or other biofuels and chemicals, they must be broken down into simple sugars. Because the process is difficult to do efficiently, it can significantly raise production costs.
Bruce Dale, professor of chemical engineering and materials science at MSU, developed a method to turn agricultural waste like corn stover or rice straw and nonfood plants into material easily processed into biofuel and chemicals. The Michigan Biotechnology Institute is MSU’s bio-based technology “de-risking” enterprise and helps step up Dale’s process. MBI works both with MSU researchers and with external organizations to develop their technologies.
Dale developed a process — ammonia fiber expansion, or AFEX — to pretreat cellulosic biomass with ammonia. MSU and MBI have received several patents on the process, and the research has been funded by the Great Lakes Bioenergy Research Center.
“As the pioneering land grant institution, we’re working to solve problems in a real-world way,” said Aaryn Richard, communications manager for MBI. “The beauty of Dr. Dale’s AFEX technology is it’s sustainability: it’s repurposing things we already have in abundance.”
AFEX uses ammonia and water under moderate pressure and heat to break plant material down into an intermediate form. Sugars can then be easily extracted and converted into fuels and chemicals, replacing oil and natural gas. Nearly all the ammonia is recycled and the rest goes into the intermediate product – which could alternatively be turned into cattle feed.
The process could add a broad range of affordable, sustainable and local fuel sources to America’s energy assets. It promises new economic opportunities for rural communities and solutions to concerns over cost and food-versus-fuel tradeoffs.
“The AFEX process makes the breakdown of cellulose and hemicellulose more efficient,” Dale said. “Using enzymes alone, about 15 percent of cellulose and hemicellulose is broken down into simple sugars; when AFEX is used before adding the enzymes, more than 90 percent of the cellulose and hemicellulose is broken down into fermentable sugars.”
The AFEX pretreatment process also increases the value of some cellulosic materials for other uses, such as feed for dairy and beef cows. Dale is collaborating with MSU AgBio Research animal scientist Michael Allen to evaluate the feed potential of several types of pretreated cellulosic plant materials.
Cellulosic materials that have been treated with the AFEX process are also easier and less expensive than raw, untreated materials to turn into pellets. Combined with regional biomass processing centers, pretreatment and pelletizing could solve a major logistical issue in the cellulosic biofuels industry.
"Because cellulosic materials are bulky, it's expensive to ship them very far," Dale said. "Getting enough of these materials together in one place is a challenge that the regional biomass processing centers would address. If we 'densify' the cellulosic materials into pellets, it's likely that the traditional corn grain handling equipment will work to load and unload the materials, further simplifying the logistical and transport issues."