Distillation of Grass Clippings

Distillation cooks the grass and releases plant sugars that ferment to alcohol.

The shear volume of grass clippings generated every spring is staggering. If you have a lawn, you can probably envision the mass of the biological waste. Some people recycle clippings as nitrogen sources in their compost bins or as mulch, but much of the debris goes in landfills where local recycling services don't exist. This green waste could potentially be a source of fuel much like other crops such as soybeans and corn. The key is the method of harvesting that fuel, and distillation offers a clue.

Ethanol

Ethanol is a natural, renewable energy source that is essentially pure grain alcohol. It may be distilled from many botanical sources but the production process is expensive. In addition, some of the commonly used crops like corn are also human food and raise concerns about reduced cropland for food use. Ethanol's power comes from sugars that are released during a fermenting process. This is fueled by bacteria and results in a potential replacement for gasoline.

Potential

The dream of energy independence would be realized if we could free ourselves from our reliance upon fossil fuels. It is not an easily recognized goal, as the process is not yet refined and the yield doesn't match the usefulness of gasoline. According to the Department of Energy, you would need 1.5 gallons of ethanol to go the same distance as 1 gallon of gasoline. The National Resource Defense Council, however, reports that the production of cellulose biofuel will soon cost less than 50 cents per gallon. The cost versus effectiveness of the product might be a non-issue if the fuel is made from items that would have been discarded in the past.

Theory

To make alcohol, which can be used as a fuel, you need sugar. Many fruits and other plant materials contain sugar and woody items contain starch, which easily converts to sugar. Grasses are composed of cellulose. To convert cellulose you need an acid or enzyme to break it down. Currently, a pretreatment of sulfuric acid is applied to release the sugars and then the grass is fermented. Then the resulting ethanol must be distilled to purify it enough for use. The process is lengthy and not cost effective, at the time of publication.

Method

Grass must be subjected to 300 to 400 lbs. per square inch of pressure at temperatures of up to 400 degrees F to begin breaking apart. Once acid is added, the cellulose breaks into two different kinds of sugar. The fermenting process is enhanced with yeast and then the resulting product is filtered. The distillation process involves a still that keeps the liquid just below 200 F. During the cooking, the alcohol vaporizes and moves through copper tubing to be collected. This is a rudimentary fermenting and distilling process which is similar to that used to make liquors and other types of alcoholic beverages.

References

• Rowan University: RuGreen -- Save the Grass Clippings, Save the World.
• California State Science Fair; Biofuel -- A Home Run for the Environment; Kyle A. Douglas
• The University of York; Grass Clippings -- The Fuel of Tomorrow?; March 2010
• Metrofarm; Gas from Grass -- New Possibilities; Michael Olson; September 2007