Can Switchgrass Biofuel Replace Corn-based Ethanol?


Home / Can Switchgrass Biofuel Replace Corn-based Ethanol?

This a Blender fuel pump in East Lansing, Michigan combines gasoline with ethanol. Image by 127driver.

A congressional push to end an ethanol mandate, led by Senator Tom Coburn of Oklahoma, appears to be gaining steam. The Renewable Fuel Standard  Act of 2005 is quickly losing support from both Republicans and Democrats alike due to concerns over rising costs for livestock producers and farmers.

Scientists have also questioned the viability of corn-based ethanol; many companies have a higher energy input than output from the ethanol produced. These reasons point to the fact that it may be time for corn-based ethanol producers to begin looking elsewhere for an economical alternative to gasoline.

Some researchers believe that one particular prairie grass, indigenous to most of North America, may hold the key.

So Why Switchgrass?

Panicum virgatum, known commonly as switchgrass, may provide the answer to the problem at hand. One 5-year study conducted by researchers at the University of Nebraska-Lincoln found that switchgrass based ethanol can provide as much as 540 percent more energy, in contrast to ethanol from corn,  than it takes to completely process  it from the planting  stage to cellulosic ethanol. With everyone realizing that producing corn-based ethanol is a net negative energy process it seems a turn toward switchgrass may be in order.

So why is switchgrass able to provide these advantages over corn? One only has to look at the potential yield to see the answer. A team at the University of Auburn concluded that switchgrass, which can be grown in practically every corner of the United States, can produce yields of up to 15 tons an acre per year, which is enough to make around 300 gallons of cellulosic ethanol. For comparison, an acre of corn can produce around 350 gallons – but requires an energy input three times greater than is necessary for switchgrass.

Biofuels: A Need for New Technology

Now we see that switchgrass can theoretically produce ethanol at high enough levels to be implemented into the energy grid. So why has switchgrass not been seen on the large scale? The study from the University of Nebraska was concluded in 2008. Unlike corn-based fermentation, the process to form biofuel from switchgrass is only in the infant stage.

Many universities across the world are now looking for the best technology to utilize this feedstock. Some are beginning to realize maybe cellulosic ethanol isn’t the answer at all.

Ethanol Production: Latest Developments

One of the newer developments of the last few years is treating the switchgrass through a process known as fast pyrolysis. Simply put, this method heats the grass under anaerobic conditions in a matter of seconds. The cellulose, hemicelluloses and lignin of the switchgrass is degraded into smaller molecules forming a liquid mixture known as pyrolysis oil, which is a mixture of numerous compounds including acids, ketones, furans, and phenolics among other things.

The goal is to upgrade this oil into diesel and gasoline grade products that can be directly implemented into our current transportation fuel infrastructure. Unlike ethanol, these fuels could be added in amounts far greater than the 10% in gasoline that is seen today.

Converting the Bio-Oil

Pyrolysis oil is a mixture of more than 200 different, mostly oxygenated compounds. Gasoline on the other hand is made up of mostly hydrocarbons between four and six carbon atoms known as alkanes.

To bridge the gap from pyrolysis oil to gasoline many scientists are turning towards a common catalyst known as a zeolite. Using this catalyst under the right conditions it is possible to break down these large oxygenated compounds into more useful products such as ketones, phenolics and alkyl benzene compounds that can be further upgraded into the fuel grade products.

What Needs to Happen Next

For now this is where the progress has slowed considerably. Each part of the puzzle still needs to be refined, from the pyrolysis conditions to choosing the right catalyst. With help from the Obama administration in Green Energy there has been a major push among universities and private labs to solve some of these problems relating to switchgrass biofuel.

Every researcher in the field seems to have a different opinion on the best way to produce the fuel. But one thing seems to be evident; corn is out and switchgrass is in.

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