n e w s of t h e w e e k dure uses hydrogen under conditions that are generally regarded as explosive. The Minnesota researchers prepare catalysts by coating porous, one-piece alumina supports (monoliths) with 1 to 5% platinum and tin by weight. The group flows ethane, oxygen, University of Minnesota researchers prepare catalysts for and hydrogen in a ethylene production by coating centimeter-scale alumina 2:1:2 ratio over a catamonoliths (left) with a platinum-tin film. With use, the metal aggregates Into micrometer-sized platinum-tin particles (right). lyst heated to near 950 °C, then analyzes ethane—to make ethylene. The process the products with gas chromatography typically runs near 85% selectivity (to and mass spectrometry. form a single product) at roughly 60% A number of features of the new cataethane conversion. And while these lytic process are surprising, the group plants are cleverly designed to derive notes. First, as Stair points out, the reacmuch of the heat they require from tion ought to be dangerous because of the burning unwanted by-products, that en- hydrogen-to-oxygen ratio—especially in ergy-saving feature helps convert more the presence of platinum. Yet the researchthan 10% of the ethane into carbon diox- ersfindthat the two equivalents of ethane ide—a greenhouse gas. The units also in the mixture make it nonflammable. emit harmful nitrogen oxides. Also unexpected is the high olefin seBut now a group of chemical engi- lectivity. High temperatures usually lead neers from the U.S. and Italy have dem- to many products, they explain, because onstrated that with a certain platinum- entropy effects cause all reaction chantin catalyst and large amounts of hydro- nels to open. Yet at 950 °C, the reaction gen they can produce ethylene by proceeds toward a single product partial oxidation of ethane at greater "Another surprising aspect of this rethan 85% selectivity and 70% conversion action," Schmidt remarks, "is that it [Science, 2 8 5 , 712 (1999)]. The devel- yields as much hydrogen in the prodopment may lead to much smaller and ucts as is fed into the reactor." That simpler chemical plants that produce means that an external source of hydroless C0 2 and other pollutants. gen may be unnecessary if a reactor is The research team includes chemi- designed with a recycle feature. cal engineering professor Lanny D. The team proposes that the reaction Schmidt and graduate students Ashish occurs by way of mechanisms that are S. Bodke and David A. Olschki of the very different from conventional homoUniversity of Minnesota, Minneapolis, geneous and heterogeneous catalytic and chemical engineering professor processes. The group examined catalytEliseo Ranzi of Polytechnic University ic surface-only mechanisms, purely gasof Milan, Italy. phase (homogeneous) mechanisms, "Production of ethylene by steam re- and catalytic hydrogen oxidation folforming is believed to be the petro- lowed by homogeneous ethane decomchemical industry's biggest contributor position. But the researchers note that With about 55 billion lb of ethylene pro- to greenhouse gases," comments Peter none of the scenarios agrees satisfactoduced in the U.S. each year, commodity C. Stair, a professor of chemistry at rily with their observations. chemical reaction engineering would Northwestern University, Evanston, 111. Schmidt and coworkers say that addiseem to be set in its ways. But thanks to re- "If one were able to find a way around tional experiments and simulations are cent developments, that mature technolo- that problem, that would certainly be a required before a comprehensive mechagy may learn a thing or two yet Research- significant contribution." nistic model can be developed. In the ers have come up with a catalyst and proceStair emphasizes, however, that be- meantime, the group asserts that exdure to convert ethane to ethylene in a fore the new technology can be commer- treme conditions such as these "may prohighly efficient manner thafs friendlier to cialized, several issues—especially in the vide the environments to carry out simithe environment than the process most area of process safety—need to be thor- lar reactions to produce chemicals with manufacturers currently use. oughly addressed. Although the re- high efficiency, improved energy use, Today's chemical plants generally searchers report that they never observe and less pollution." use steam cracking of alkanes—mainly flames during experiments, the proceMitch Jacoby ly shut down because of low prices and oversupply, and Canada's Methanex Corp., the world's largest methanol producer, has reported losses for the past several quarters. Losing MTBE, the outlet for 40% of methanol production, would only compound the producers' troubles. MTBE producers, of course, are in even worse shape. They fall into three categories: oil companies that make small amounts at their refineries, propylene oxide makers for whom MTBE is a coproduct, and merchant market suppliers that make the oxygenate by reacting isobutylene with methanol. Bill Richard, vice president of oxygenates for the Houston-based consulting firm DeWitt & Co., notes that companies in the third category will suffer the most from a ban. Many of them got into the business in the early 1990s to meet MTBE demand spurred by the 1990 Clean Air Act Amendments' 2% oxygenate requirement. Richard says these firms could stay afloat by converting MTBE plants to other octane-enhancing additives, such as isooctane. But at today's octane prices, he says, these operations wouldn't provide an adequate return. MTBE and methanol makers have some breathing room because the EPA advisory panel is recommending substantial lead time—up to four years if MTBE is eliminated, less if use is merely cut back. Meanwhile, producers of ethanol, the only other significant gasoline oxygenate, are already lobbying for their product in a post-MTBE marketplace. Richard cautions, however, that substantially increased ethanol use in gasoline would likely mean sharply higher prices for consumers. Michael McCoy
New ethylene process is environment-friendly
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AUGUST 2,1999 C&EN
