New process could double ethanol production

A new processing technique may double ethanol yields by shielding a key processing ingredient, according to scientists at the U.S. Department of Energy’s Ames Laboratory.

Emily A. Smith, Ames Laboratory research scientist and Iowa State University assistant professor of chemistry, and Jason Lupoi, Ames Lab research assistant, have taken the existing technique of enzyme mobilization and applied it to renewable energy by better protecting the enzymes necessary for ethanol production.  Enzymes are responsible for chopping up large chemical chains of cellulose into small, useable sugar molecules.  The sugar is then consumed by yeasts to produce ethanol, through a process called fermentation.  With current techniques, the enzymes are damaged during the chopping process, which prevents them from turning all the cellulose into useable sugar.

Using enzyme immobilization, yields are improved because the new technique better protects the fragile enzymes. The benefits are similar to wrapping a delicate package in bubble wrap.  The technique fixes the enzymes on a silica nanoparticle, which protects them from deforming during reaction conditions. The protection of enzymes allows them to turn cellulose into sugar more effectively, leading to higher ethanol yields. The main benefit is that “enzyme immobilization produces more [sugar] at lower temperatures,” said Lupoi.  The current process requires different temperatures for the chopping of cellulose and fermentation of sugar. During the chopping process, enzymes require warm conditions, around 122oF, but at that temperature, yeasts do not work well; yeasts prefer temperatures around 95oF.  Enzyme immobilization allows both steps to be conducted at the same temperature. “Now the two conditions jive” explained Lupoi, “the enzymes and yeasts work at the same optimal temperature,” reducing a temperature-lowering step from the production process.

The prices of ethanol could be reduced by the discovery of a new technique that could double ethanol yields. Photo by Melanie Snyder

Eliminating a production step by using the enzymes and yeast simultaneously also helps reduce the cost of production because less time and energy is required to adjust temperatures.

Besides enzyme protection, the silica particles can be collected at the end of the production process and reused.  Smith and Lupoi’s research can still produce sugar from cellulose even after three uses of the same enzyme-coated silica particles.

 “The next step would be to scale up our work,” said Smith, “to see if this type of strategy is suitable for commercial ventures. This is the realm of engineers, and this is a challenge for them to take on.” 

The scaling challenge is to weigh the costs and benefits of the research by determining if a large volume of initial materials would still double the ethanol produced and how much the new material and equipment would cost industry. 

If the benefits outweigh the cost, enzyme immobilization has the possibility of greatly impacting the ethanol industry.