Magazine article Science News

Surreptitiously Converting Dead Matter into Oil and Coal

Magazine article Science News

Surreptitiously Converting Dead Matter into Oil and Coal

Article excerpt

Just as everyone knows that oil and water don't mix, scientists know that organic reactions don't work well in aqueous solutions.

But to a small group of scientists studying how oil and coal form from carbon-rich decayed plants and algae, aqueous organic chemistry- reactions of carbon-based compounds in hot water - represents a better way of thinking about how the Earth created those vast underground energy reserves.

"We're promoting the idea that water is important in natural organic reactions," says Michael D. Lewan, a geochemist with the U.S. Geological Survey (USGS) in Denver.

In addition, sustained investigation into how hot water affects organic materials may lead to more efficient and environmentally friendly processes. Someday, water may aid in making -- and recycling or cleaning up -- plastics and other petroleum-based products.

Once again, this commonplace substance turns out to have some uncommon attributes. "We just take water for granted:' says Theodore P. Goldstein, an organic chemist at Mobile Research & Development Corp. in Princeton, N.J. "We don't think its properties can change."

Little did he and others realize how mutable water can be.

Until now, scientists thought that coal forms when dying plants in soggy marshes get buried, creating a peat that simmers in this soupy environment. If no oxygen is present, chemical events slowly change peat, first into lignite and then, millions of years later, into bituminous coal. If temperatures climb high enough, anthracite coal forms.

Oil formation was viewed similarly, Dead marine microorganisms sink to the seafloor, then become buried by silt washing out of a river. If enough silt piles up, it creates a geologic Dutch oven, in which high temperature and pressure cause the organic debris to condense. A source rock -- oil shale -- forms. In its pores, chemical processes continue until oil oozes forth. The key requirement is getting this "oven" hot enough for a long enough time - or so everyone thought.

These explanations did not satisfy Andrew Kaldor, a researcher at Exxon Research and Engineering Co. in Annandale, N.J. He realized that ideas about oil and coal formation had evolved many years ago and had not really been updated to include new chemical and biological knowledge.

So Kaldor and Exxon organic chemist Michael Siskin decided to reexamine these ideas by first determining the chemical composition of organic materials in source-rock shales - an awesome job given the complex and highly variable nature of this starting material and the cascade of molecular transformations that occurs in forming oil and coal.

In both, plant matter decays into a potpourri of molecules that, depending on the conditions at hand, break up and clump in any number of ways. Carbon atoms get rearranged into assorted rings and chains to create a complex, interlocking network. Hydrogen atoms join, leave, and sometimes rejoin this network. as do other elements such as oxygen, nitrogen, or sulfur, eventually forming giant, insoluble macromolecules. "It's everything that winds up in the sediments," notes Goldstein.

Few chemists would even know how to begin teasing out the right combination of hydrocarbons to create oil or coal, but somehow nature manages to break these giant molecules in just the right places.

To understand this process better, the Exxon group collected samples of oil shale from different parts of the world. The samples included a series from oil shale under the North Sea, where rocks in different locations exhibit different degrees of transformation. Siskin then placed the samples into a pressurized reaction vessel and heated them individually to temperatures ranging from 570[degree]C to 750[degree]C. These hotter-thannatural conditions sped up the transformation from a geologic time frame of millions of years to one measured in days and hours.

Over the course of about two years, these and other tests helped the scientists piece together the locations of various atoms and side groups in representative molecular structures and in the intermediate products created in the transformation from molecular glob to oil. …

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