Although criticism of ethanol ranges from it requiring more energy to produce than what is available in the final product, being too expensive, and producing only negligible carbon reductions, technology on the horizon and the use of cellulosic feedstocks may quiet the opposition. New and developing conversion methods that take advantage of cellulose, the main component of plant cell walls and the most common organic compound on earth, should make production of ethanol more cost effective and less energy intensive than gasoline.

Ethanol, usually made from corn or sugarcane feedstock, can also be produced from a variety of cellulosic feedstocks. These include agricultural waste (wheat and rice straw or corn leaves, stalks, and cobs), forest residue (dead wood, logging residue), municipal solid waste, and energy crops (switchgrass, hybrid poplars). Not only are many of these sources practically free, but they are plentiful and have a positive energy balance when used to produce ethanol, meaning more ethanol energy is produced than was needed to make the ethanol.

Cellulosic feedstocks

Cellulosic feedstocks, such as wood chips, can be used to produce ethanol. Photo Credit: DOE/NREL, Warren Gretz

Cellulosic ethanol is an important biofuel for many reasons. According to Nathan Glasgow and Lena Hansen of the Rocky Mountain Institute, it will produce twice the ethanol yield of corn-based ethanol at a lower cost and a better net energy equation. The pair also says that while corn-based ethanol reduces carbon emissions by about 20 percent below gasoline, cellulosic ethanol is predicted to be carbon neutral or even net-carbon-negative. The U.S. Department of Energy (DOE) estimates that based on units of energy at the gas pump, 1.23 units of fossil fuel is used to produce gasoline, .74 units of fossil energy is used to produce corn-based ethanol, and .2 units of fossil energy is used to make cellulosic ethanol.

In addition to the benefits of using cellulosic feedstock, new conversion technologies are being developed to produce ethanol from this material. One method, thermal gasification, converts biomass into a synthesis gas composed of carbon oxides and hydrogen. A biological process using microorganisms or a catalytic reactor then converts the gas into ethanol. Enzymatic reduction hydrolysis is another conversion technology. It uses enzymes and “smart bugs” to turn biomass into sugar, which is then converted into ethanol. The first commercial scale plant using this method is scheduled to be built and operational in about two years and is estimated to produce cellulosic ethanol at an estimated price of $1.30/gallon.

gasification plant

Gasification plants convert cellulosic feedstocks into ethanol. Photo Credit: DOE/NREL, Warren Gretz

Although these technologies are expensive, the DOE predicts their further development will reduce the cost of producing cellulosic ethanol by as much as sixty cents per gallon by 2015.




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