Cellulosic Ethanol Technically Comes of Age

by Emil Morhardt

Making liquid fuel out of crop waste is, in principal, an extremely good idea. But the ethyl alcohol (ethanol) we add to gasoline—and also drink in vodka, wine and beer—has been made out of edible fruits and grains. Corn ethanol, the main gasoline substitute is made out of the corn kernels which otherwise might become corn meal or tortillas, cutting into the food supply and encouraging conversion of more land into cropland. There have been many studies on the effect of this land conversion on atmospheric CO2 levels, and it appears that it will often be a decade or more before the CO2 released from land conversion will be offset by the substitution of ethanol for fossil fuels.

On the other hand, if inedible crop waste could be economically converted to ethanol, neither of these problems would occur. The operable word, though, is “economically”. Engineers have long known how to convert cellulose, the main constituent of the non-edible parts of plants, into fermentable sugar, but it takes the expenditure of energy, adding too much to the cost of the final fuel. What has been needed is a process that gets the energy use down to a practical level.

That finally has happened; on September 3, the first commercial-scale cellulosic ethanol plant, making the fuel out of corn stover (corn cobs, leaves, husks and stalks) opened in Iowa, planning to produce 20 million gallons of ethanol a year. It isn’t clear from the press release from the plant’s operators, or from a nice writeup in Science Magazine, exactly what has made this plant commercially possible, but the wholesale cost of a gallon of cellulosic ethanol has dropped to around $2 per gallon. Now the question is whether there will be sufficient regulatory incentives to overcome the reluctance of oil companies to share the fuel business with farmers.

Since you have to pay to read more than the summary of the Science article, even though it’s just a commentary, I’ll try to encapsulate its main points here. Since 2005, oil refiners and importers in the US have been required to sell increasing amounts of cellulosic ethanol, 6.6 billion liters this year, but they couldn’t produce anything like that much–just 1.1 million liters. So the EPA backed off, but basically fined the industry $1 for each mandated gallon of cellulosic ethanol they didn’t produce. That’s $6.5 billion dollars this year. That should be a big incentive to cellulosic ethanol producers. The problem is that the ethanol market is saturated with non-cellulosic corn ethanol. EPA could solve the problem by mandating more than the current 10% ethanol in the fuel mix, but it didn’t; it lowered the requirement instead. This makes oil companies happy, but gets us further away from a renewable energy economy. It’s all politics, but we’ll find out later this year what EPA plans to do.

Service, R., 2014. Renewable Energy. Cellulosic ethanol at last? Science (New York, NY) 345, 1111. Summary only: http://www.sciencemag.org/content/345/6201/1111.summary


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