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Friendlier Gases Through Ethylene Research
Two recent developments in catalysis, one in replacing ethylene with an alternative material and the other in improving processes for making ethylene, hold out hope for cheaper, more environmentally friendly gases in industrial processes. These two independent projects illustrate the variety of innovative approaches of research to managing the pollution and high costs of hydrocarbon processing. Both research projects are supported by the Office of Basic Energy Science's Chemical Sciences Division.
When ethylene is used to make alpha-olefins, the immediate result is a complex mixture of alpha-olefins of various lengths. This mixture typically does not match the required quantities of specific carbon chain-lengths and so requires costly recycling processes. However, Alan Goldman of Rutgers University has devised a way to obtain alpha-olefins using n-alkanes instead of ethylene and results in a single alpha-olefin of a desired length. N-alkanes (CnH2n+2), also known as paraffins, are hydrocarbons consisting of simple unbranched chains of carbon and hydrogen atoms. In addition to yielding a single-component product, the n-alkanes are much less costly than ethylene. The method developed by the Rutgers team uses an iridium catalyst.
This catalyst cleaves the strongest carbon-hydrogen bond of the n-alkane, leaving an alpha-olefin. Although the process leaves behind an iridium-hydrogen complex, an olefin, such as low-cost propylene, is then added, which reacts with the remaining complex to regenerate the original iridium complex, thus creating an efficient catalytic cycle. This method could eventually save considerable processing, capital, and energy costs. (Other accounts of this work can be found in the Journal of the American Chemical Society [vol.121, p. 4086 (1999)], Chemical Communications [p. 655 (1999)], and Chemical and Engineering News [July 5, 1999]). Making It Better Steam-cracking in a tube furnace is currently the most common method of producing ethylene from ethane. The new reaction process uses a platinum-tin catalyst in a reactor where the total residence time over the catalyst is 1 millisecond, compared to the much longer time required for steam-cracking. The method is also unusual in that oxygen and hydrogen are fed into the reactor along with ethane. Moreover, because the reaction produces hydrogen, it may be possible to incorporate a hydrogen recycle process so that no hydrogen needs to be added.
The reaction modeling and analyses done in Schmidt's laboratory was supported by DOE's Office of Basic Energy Sciences, Chemical Sciences Division, and the experimental equipment was supported by the National Science Foundation. This work was reported in the July 30, 1999, issue of Science. Contact: Lanny Schmidt, University of Minnesota, (612) 625-9391, schmi001@tc.umn.edu |
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