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Ethanol As Fuel

April 23, 2007 | A version of this story appeared in Volume 85, Issue 17

I read with interest the article about Diversa and Celunol and the first-ever integrated cellulose to ethanol plant (C&EN, Feb. 19, page 11). I have also seen the recent announcements from Iogen. The first plant to make ethanol from cellulose enzymatically was operated by Gulf Oil Chemicals in Military, Kan., from 1976-79. That plant used the process developed, dubbed the "Gulf Process," to make cellulase enzymes and then used a patented simultaneous saccharification fermentation process to convert the sugar to alcohol.

In total, there were 17 patents on the process. In the late 1970s when biofuels were all the buzz, several papers were given at ACS meetings by Gulf employees and grad students from Virginia Polytechnic Institute. The Gulf pilot plant was capable of processing 1 ton per day of cellulose to alcohol and was operated on a continuous basis. A special stripper column, also patented, was developed to remove the alcohol from the high-solids-containing process stream.

Gulf later donated the technology to the University of Arkansas, where extensive work was done to classify feedstocks and pretreatments of feedstocks for the enzyme production and saccharification. At that time, a 50-ton-per-day plant was designed and was the next step in the demonstration of the technology. That was when the furor for alcohol fuels cooled down.

The Gulf technology is still a valid process. The best source of cellulosic feedstock that is routinely gathered is municipal solid waste. A city of 140,000 people generates enough cellulose in its waste stream to support a 25 million-gal-per-year alcohol plant. This does not impact the food chain and greatly reduces the amount of trash going to landfills. What a wonderful idea!

Paul J. Blotkamp
Lincoln, Neb.

J. C. Jones's letter, which appears to support corn ethanol as a viable fuel, is distressing (C&EN, March 12, page 3). It is a classic example of the flexibility of facts and figures that Milton Maciel's analysis—cited by Jones for supporting corn ethanol's "positive" energy return on energy invested (EROEI)—was actually written to argue for corn ethanol's inviability as a fuel. Jones further implies by citation that the EROEI cited by Maciel should be trusted, although we have nothing other than Maciel's self-description as an ethanol expert from Brazil within the citation itself.

Finally, it appears to me that while Maciel and Jones refer to the EROEI in a manner that implies some standard usage in the field, I have no personal evidence to support this supposition. Most illuminating of all, for me, is that the laws of thermodynamics would seem to preclude any value for an ERORI greater than 1, yet Maciel offers ERORI values of 9 for ethanol from sugarcane and 1.3 for ethanol from corn (and Jones celebrates the latter). Some energy input has to be omitted from these ERORI calculations to achieve any value greater than 1. It is my suspicion that vested interests breed differing omissions.

Might I suggest a "back-of-the-envelope" exercise for my colleagues to estimate the economic viability of corn ethanol? Independent corn farmers were operating right on the margin before the price of corn was driven up by the political hoopla for ethanol fuel. This fact offers a baseline breakeven cost that is essentially all fuel in nature: the diesel to run the equipment, the coal to generate the electricity used to make the fertilizers, the gasoline for the farmer's personal vehicles, and so on. This number is perfect for estimation in that, while definitely imperfect, it is also likely to be close enough: The cost of this corn can be taken to be the cost of the fuel to produce it.

Now calculate the theoretical yield of ethanol from the average sugar content and add the energy to distill the concentrate, and we have a pretty good final figure to compare to the energy yielded by burning the same fuel. If this ratio is near 1:1, then corn ethanol is not likely viable as anything other than a tool to lobby the Iowa caucuses.

Steve Griffin
Peoria, Ariz.


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