The world of cellulosic ethanol is a hot business. GM has already backed two cellulosic ethanol companies, Coskata and Mascoma Corp., and many others are taking a serious look at the new type of fuel. Essentially with the same advantages and disadvantages from a fuel perspective as normal ethanol, which it shares virtually the same chemical character with, the big bonus is that cellulosic ethanol can be made from plant waste of all times, reducing the price pressure produced by food-crop ethanol.
Using technology to produce cellulosic ethanol, the fruits and vegetables of food crops can ship to the market and the leftovers -- leaves, stalks, stems, and husks -- can be ground up and made into ethanol. One of the first targets is corn stover, the leftovers from the corn harvest, somewhat of an ironic source as sugarcorn (the food) became one of the two main controversial sources of food-crop ethanol.
Unfortunately, the processes to make cellulosic ethanol are still very inefficient. And while there are acid pretreatments that can improve the performance, freeing up more sugars from the cellulose and hemicellulose in plants to be used in fermentation, these treatments are costly. Typically the acidic product is toxic, so it must undergo intensive washing and detoxifying, leaching nutrients that could have been used in fermentation and raising the costs.
That's where Michigan State University comes in with a new patented process. Bruce Dale, University Distinguished Professor of chemical engineering and materials science at the university, has invented a cheap pretreatment process using ammonia, called AFEX (ammonia fiber expansion).
Its 75 percent more efficient than with traditional enzyme treatments says Professor Dale, and is easier and more affordable than acid pretreatments. The process frees up a lot of sugar to be used in the fermentation to produce more ethanol.
Professor Dale states, "Doctoral student Ming Lau and I have shown that it's possible to use AFEX to pretreat corn stover (cobs, stalks and leaves) and then hydrolyze and ferment it to commercially relevant levels of ethanol without adding nutrients to the stover. It's always been assumed that agricultural residues such as corn stover didn't have enough nutrients to support fermentation. We have shown this isn't so."
He states, "Washing, detoxifying and adding nutrients back into the pretreated cellulose are three separate steps. Each step is expensive and adds to the cost of the biofuel. Breaking down cellulose into fermentable sugars cost effectively has been a major issue slowing cellulosic ethanol production. Using AFEX as the pretreatment process can dramatically reduce the cost of making biofuels from cellulose."
Ming Lau, a coauthor of the project who shares the patent with Professor Dale adds, "The research also shows that the chemical compounds created when the stover goes through the AFEX process can improve the overall fermentation process. This is at odds with the general perception that these compounds are detrimental and should be removed."
The pair is looking to set up a pilot plant at MBI International, a subsidiary of the MSU Foundation. However, they already are also attracting commercial interest. States Professor Dale, "There are several companies – including the Mascoma Corp., which plans to open one of the nation's first cellulosic ethanol plants here in Michigan – that may be interested in using this technology. We are working to make the AFEX technology fit these companies' needs."
The new research is published in the current issue of Proceedings of the National Academy of Sciences (PNAS).
The work was funded by the GLBRC, the MSU Research Foundation, and the Michigan Agricultural Experiment Station.