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CO2's Future Is In Nature's Hands

June 11, 2007 | A version of this story appeared in Volume 85, Issue 24

The future of carbon dioxide is in the hands of nature, not man (C&EN, April 30, page 11). Anything that man tries to convert into some useful chemical will take up more energy than can be gotten back. But nature can easily convert it into plant chemicals using sunlight for energy, and we are letting huge amounts of already harvested biofuel crops go to waste.

But how? It's occurring in the massive mess of our organic waste-handling system, which has embarked on a composting frenzy. That just speeds the recycling of trapped carbon back to carbon dioxide via accelerated biodegradation. Nature was smarter than man in burying large amounts of dead biota to make coal and oil, thereby reducing levels of that gas on the globe to allow year-round ice packs and so on.

But man can imitate nature by taking those wastes and pyrolyzing them to get charcoal and fuel distillate. Some of the charcoal would be buried, slowly reducing our carbon footprint, while some charcoal and some fuel distillate would be used to fire the pyrolysis process. Heat in the exhaust from the firing and heat from the hot charcoal would be converted into steam for power generation using heat exchangers. The fuel distillate is refined to get water out and produce a vehicle fuel.

The pyrolysis process could also be applied to biofuel crops and crop discards, as well as to solids separated from fecal wastes in sewage and at animal farms. The process would leave no cellulose or lignin to become a problem, as occurs with bioethanol, and would eliminate any toxins and germs that might spread from dumps to contaminate groundwater. The process would usurp no land or water from food production, which may become a major problem with big-time bioethanol production. It could easily turn our costly waste-handling messes into profits while kicking our oil addiction.

So let nature take up carbon dioxide and then let us take advantage of its bioproducts to generate energy while reducing the size of our carbon footprint.

James A. Singmaster III
Fremont, Calif.

I read the article about the future of CO2 with great interest. I would like to point out that the article's author mentioned supercritical fluid chromatography (SFC) technology as one way to utilize CO2. The story suggested that this technology is only suitable for limited use.

Since the 1980s, SFC has evolved into a powerful and efficient technique that today is widely used in the food, microelectronics, agriculture, and pharmaceutical industries worldwide. As a chromatographer working in the pharmaceutical industry, I have used this technology extensively every day to solve complicated chemical problems such as the separation and purification of drugs.

It is highly efficient and can be applied in separations of almost all of the druglike compounds that I know of. Every major pharmaceutical company in the world has enough bulk CO2 available to implement this technology. My peers around the world and I are working together to push this green technology to make a greener world.

I believe the progress of SFC itself is worth a cover story.

Ziqiang Wang
West Point, Pa.

"What Can We Do with CO2?" I don't know. But I do know that we should not store it underground and create a threat that it could escape in a release that would be catastrophic for a future generation.

Albert S. Hester
Ormand Beach, Fla.

Eric J. Beckman accurately describes the 1980s' "rush to develop supercritical fluid technology." But as he and others know, many of the applications "developed" were ill-advised and ill-fated and resulted in the loss of bloom of supercritical fluids. He accurately related that supercritical fluids turned out to be "a solution in search of a problem." Continuing, he says correctly that supercritical CO2's solvent power is "feeble for polar compounds ... and that its feeble solvent power makes it suitable only for niche applications."

Fortunately, in my company there are many niche applications that have sustained us for 26 years. We do have solutions for a wide range of industrial (and academic) problems, in fractionation of lubricants, purification of reactive monomers, and separation of impurities from medical polymers and polymeric medical devices (and still many others). It is exactly the feeble solvent power of supercritical CO2 that allows for discrimination and selectivity among soluble components in a mixture and that allows for the development of so many processes in so many industries.

Beckman says that using CO2 as a solvent "seems to have hit a wall." Again, in my company, that statement is wrong. Use of CO2 has not hit a wall. Supercritical CO2 is alive and well and increasing in application and importance.

Val Krukonis, Phasex Corp.
Lawrence, Mass.



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