Spend a buck and get 30 cents worth of food to make it through ’till lunch. That is synonymous to the energy balance for ethanol production from corn; = 1.3. Let’s just think outside the barrel for a moment, ethanol we can make today from corn kernels is just a sub-mediocre fuel source; the low energy return, the crop’s intensive fertilization/herbicide/pest control for cultivation pollutes waterways, and increased demand drives up food costs (corn prices doubled last year). And anyway, the corn ethanol industry is projected to produce, at most, the equivalent of only 15 billion gallons of fuel by 2017.

Cellulosic ethanol, in theory, is a much better bet. Most of the plant species suitable for producing this kind of ethanol — like switchgrass, a fast- growing plant found throughout the Great Plains — aren’t food crops. And according to a joint study by the US Departments of Agriculture and Energy, we can sustainably grow more than 1 billion tons of such biomass on available farmland. Cellulosic ethanol yields roughly 80 percent more energy than is required to grow and convert it.

But lets look a little closer; traditional monoculture farming practiced on the leading cellulosic ethanol crop, switchgrass, was found by University of Minnesota research last year to under-produce the bioenergy found in mixed grasses of dry soil by 238%.

To date, all biofuels, including cutting-edge nonfood energy crops such as switchgrass, elephant grass, hybrid poplar and hybrid willow, are produced as monocultures grown primarily in fertile soils.
The researchers estimate that growing mixed prairie grasses on all of the world’s degraded land could produce enough bioenergy to replace 13 percent of global petroleum consumption and 19 percent of global electricity consumption.

According to the study, the practice of using degraded land to grow mixed prairie grasses for biofuels could provide stable production of energy and have additional benefits, such as renewed soil fertility, cleaner ground and surface waters, preservation of wildlife habitats, and recreational opportunities.

In addition, fuels made from prairie biomass are “carbon negative,” which means that producing and using them actually reduces the amount of carbon dioxide in the atmosphere. In contrast, corn ethanol and soybean biodiesel are “carbon positive,” meaning they add carbon dioxide to the atmosphere, although less than fossil fuels.

O.K. That seems like a more sustainable way to produce ethanol than from corn kernels, and surprisingly even cellulosic monocultures. But making fuel from cellulosic plant material is more complicated and costly than producing ethanol from corn, and an ongoing wave of discovery and innovation is changing that. A multitude of study centers are currently focused on enzymes to economically break down the cellulose into fermentable sugars. For instance, genomic sequencing and analysis of termite gut microbes is being carried out by the U.S. Department of Energy Joint Genome Institute (DOE JGI), the California Institute of Technology, Verenium Corporation, INBio, the National Biodiversity Institute of Costa Rica, and the IBM Thomas J. Watson Research Center. All this in an effort to determine the correct cocktail of enzymes which nature uses to digest plant materials. A little more on this later.

But wait! Let’s not just stop there. I’ve heard that ethanol itself does not have as much energy output as gasoline. There are other alcohols that can be made from biomass and can burn in car engines as well. What about butanol? Butanol is the longest chain of carbons in alcohols having four, which is more similar to gasoline than ethanol with two carbons. Butanol has been demonstrated to work in some vehicles designed for use with gasoline without any modification. Hmmm… But to match the combustion characteristics of gasoline, utilization of butanol fuel as a substitute requires fuel-flow increases (though butanol has only slightly less energy than gasoline, so the fuel-flow increase required is only minimal, maybe 10%, compared to 40% for ethanol). Butanol tolerates water contamination better than ethanol, and is less corrosive and more suitable for distribution through existing gasoline pipelines. It blends with diesel or gasoline, and is less likely to separate from this fuel than ethanol if the fuel is contaminated with water. There is also a vapor pressure co-blend synergy with butanol and gasoline containing ethanol, which facilitates ethanol blending. This facilitates storage and distribution of blended fuels.

The feedstocks of butanol are the same as for ethanol — energy crops such as sugar beets, sugar cane, corn grain, wheat and cassava as well as agricultural byproducts such as straw and corn stalks. Cellulosic materials would also fill this category. Recent biotechnology co-developed by Environmental Energy Inc. and Ohio State University utilizes a fibrous bed bioreactor to produce the alcohol butanol as its primary output. The patented process using C. tyrobutyricum produces mainly butyric acid and hydrogen which is then pumped into another fibrous bed bioreactor where C. acetobutylicum converts the butyric acid into butanol, thus optimizing butanol production. Essentially, the new process makes butanol production competitive with other biofuels both economically and in energy production.

But, as you can see, it still takes a lot of energy to produce butanol from prairie grass. It is still getting better though, because it is more sustainable and because it will take less to convert vehicles and systems over to run on this alcohol. It can still be tweaked a little more. The Mixalco process is right in line with further sustainable development of alcohol fuels. With all of this, it will still not completely replace oil, due to constraints on our system and lack of enough arable land to deliver sheer replaceable volumes of this alternative fuel. What is also needed in this equation is fuel efficiency standards of everything (vehicles at least) that consumes fuel for energy.

UPDATE 12/11/08: Physicist Searches for Alternative Fuel Technologies

Nobel Prize-winning physicist, and now Obama’s Energy Secretary, Steven Chu, confirms that using cellulosic material to produce biofuels makes sense. I’m excited with hope that the US government shows promise of returning to science-based decision-making, where applicable.