Issue Date: August 10, 2009
Your welcomed article "Cellulosic Scale-Up" was in error when it stated that "there has never been commercial production of cellulosic ethanol" (C&EN, April 27, page 10). Ethanol has been produced from cellulose for almost 100 years. The technology progressed most rapidly around World War II, when shipments of oil across oceans were severely limited and highly risky. Germany, Russia, and the U.S. were leaders in the construction of pilot and production facilities for cellulosic ethanol. The practice continued well into the 1990s in the U.S. when Georgia-Pacific was listed as one of the major contributors to the domestic ethanol market. It continues today in several European and Asian countries.
What is different between the existing cellulosic ethanol schemes and the Energy Department projects described in the article is the method of cellulose-to-glucose conversion. In contrast to cornstarch (also a "polyglucose," like cellulose), cellulose virtually never occurs in pure form, and its depolymerization to glucose is highly complex. In practical terms, this means that cellulosic ethanol in commercially existing and economically viable processes is always a coproduct of the manufacture of pulp for paper products and such cellulose derivatives as cellulose acetate.
It is the lesson of end-product multiplicity that the renewable fuels industry has to learn from paper producers and oil refiners. A 30-cent-per-lb single end product, ethanol, produced in less than 30% yield from an agricultural or forest resource through technologically challenging process technology (based on isolated enzymes) remains an invitation for fiscal disaster.
The solution to cellulosic ethanol must lie in product multiplicity. Glucose from cellulosic resources will continue to be viable only if it draws advantage from its associated natural polymeric constituents, amorphous heteropolysaccharides and polyaromatic lignin. The latter have seen much attention recently, and there have been numerous demonstrations of utility in various chemicals and materials.
A shift is required from the most recent practice of producing cellulosic pulp alongside some coproducts (of which cellulose may be one) to glucose production with a greater emphasis on coproducts. But cellulosic ethanol has been around for a long time and is likely to be around much longer.
Wolfgang G. Glasser
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