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You know how combustion works, right? Strike a match on a rough surface, or shoot a spark at a volatile gas. Pfft! You have flame.
But with flame comes soot and other carbon compounds. That’s understandable if the flame is at the tip of a wooden match, because the flame turns the wood into ash. But even burning gas leaves soot. So where does the soot come from?
Researchers at the U.S. Department of Energy’s Lawrence Berkeley National Lab and the University of Hawaii report that they’ve figured out the first step that changes what are known as “gas-phase molecules” into solids.
This knowledge could lead to the development of more efficient fuels of the future, and even more efficient use of traditional fossil fuels with less waste. Their research was published June 20 online in the journal Angewandte Chemie (Applied Chemistry), a weekly, peer-reviewed scientific journal published on behalf of the German Chemical Society.
Musahid Ahmed, scientist in the Chemical Sciences Division at Berkeley Lab, says that for more than three decades, researchers have been constructing computer models in an effort to explain how gas molecules form soot.
Molecules can combine in many different ways to create soot and other carbon emissions. Ahmed’s team focused on one promising theory called hydrogen abstraction-acetylene addition, of HACA, which was developed more than 20 years ago at the University of California-Berkeley.
According to this theory, if a benzene molecule, a ring of six carbon and six hydrogen atoms, is put in a high-temperature, high-pressure environment, it loses one of its hydrogen atoms. This altered ring then attracts acetylene, a two-hydrogen, two-carbon molecule, to link up with the altered benzene molecule like a kind of tail.
This acetylene tail would then lose one of its hydrogen atoms. This increasingly changing molecule then attracts a second acetylene molecule, bringing to four the number of carbon atoms in the tail. Next, the tail curls so that its end connects with the original molecular ring, thereby creating the double-ring structure of naphthalene.
As the rings link up and propagate during combustion, they grow virtually unchecked to become the huge, carbon-heavy “macromolecules” of simple soot.
That’s the theory, anyway. To see if it’s correct, Ahmed’s team used a device called a “hot nozzle,” which recreates the pressure and temperature of the combustion environment. It pumped two chemicals, nitrosobenzene and acetylene, through the nozzle at a pressure of about 5.8 pounds per square inch and at a temperature of more than 1,300 degrees Fahrenheit.
The result: Naphthalene, just as the researchers had expected.
Ahmed’s work isn’t done, however. The research still must “unravel the pathways to more complex systems” of carbon residue, said co-researcher Ralf Kaiser, professor of physical chemistry at the University of Hawaii at Manoa. So far, the plan is to use infrared spectroscopy to examine more of the different kinds of molecules generated in later stages of combustion.
By Andy Tully of Oilprice.com
Andy Tully is a veteran news reporter who is now the news editor for Oilprice.com