May 30 2005
Understanding fire is one of the oldest challenges in chemistry. Even after 150 years of flame chemistry research, scientists are making new findings. An international research consortium, including CAS researchers, discovered for the first time in their experiments a class of important intermediates of hydrocarbon oxidation -- enols --that apparently is common is flames.
The discovery was made through a cooperation among researchers from the US, China and Germany. Qi Fei, Sheng Liusi and Zhang Yunwu from the CAS-affiliated University of Science and Technology of China (USTC) are key players of the team. The experiments were conduced at the Advanced Light Source facility at the Lawrence Berkeley National Laboratory and the National Synchrotron Radiation Laboratory (NSRL) at USTC. Their findings were published online by the Science magazine on May 12.
Hundreds of chemical species form and turn into other products when fires burn. carbonyl compounds are well-established intermediates, but their less stable enol isomers that have a hydroxyl group attached to a doubly bonded carbon atom are not.
Enols have a structure that includes properties of both alkenes and alcohols, hence the name. The simplest alkene is ethylene (C2H4), a gas that is produced in nature as a plant hormone and is also a major chemical feedstock. The primary commercial use of ethylene is the production of polyethylene, a common plastic. When a hydroxyl group (OH) replaces a hydrogen atom in ethylene, it becomes an enol called ethenol (CH2CHOH). Ethenol exists only as a transient or fleeting species in chemical reactions, but altered, stable forms of ethenol are main ingredients in latex paints, hair sprays, shampoos and glues.
Enols were first predicted as possibilities in 1880. One enol, i.e. ethenol, was observed in a non-flame environment in 1973 and its reaction in liquids is well known. Their presence in flames, however, had been little suspected until scientists applied a new technique that use synchrotron radiation for photoionization mass spectrometry to reveal both its structure and its mass.
Using research facilities in the U.S. and China, researchers collected oxidation products and intermediates from the combustion of various fuels from different locations in the burner flame and collimated the samples into a molecular beam. Then they used a tunable synchrotron-generated vacuum UV beam to ionize the molecular beam, and analyzed the resulting ions with mass spectrometry. They observed a class of enols: ethenol, propenol, and butenol.
To study fire chemistry, researchers use computer models to simulate chemical reactions during combustion. Previous research has never dealt with enols. The result of the latest experiment will correct the existing oxidation model of hydrocarbon, providing new strategies for the simulation of the incomplete oxidation in fuel cells and in supercritical water, as well as for controlling pollutants produced in combustion.
While the researchers don't know where the discovery will lead, it offers new directions in efforts to reduce soot and other pollutants in flames, improve fuel cells, and model planetary atmospheres and interstellar chemistry, according CAS experts.
As a winner of the prestigious CAS Bairen Award, Prof. Qi Fei rejoined the NSRL in 2003 after spending two-year as a post-doc at the Advanced Light Source facility in Lawrence Berkeley National Laboratory. With the support from CAS and National Natural Science Foundation of China, Prof. Qi has set up during a very short time a facility to study of combustion and flame with synchrotron radiation photoionization molecular beam mass spectrometer. It is now considered the most sensitive research facility with widest wave-length coverage in the world.
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