n e w s of t h e w e e k

CUTTING BACK MTBE EPA panel says additive, while leading to cleaner air, is polluting water...

An Environmental Protection Agency advisory panel last week called for a substantial reduction in the use

of methyl tert-butyl ether (MTBE) as a gasoline additive. The group also recom­mended that Congress remove the cur­rent requirement that 2% of reformulated gasoline by weight consist of oxygen—a mandate of the 1990 Clean Air Act Amendments. MTBE is by far the most common oxygenate em­ployed to meet that mandate.

The panel was appointed by EPA Administrator Carol M. Browner in November 1998 to address the growing problem of MTBE from leaking gasoline tanks and from spills contami­nating water supplies. The addi­tive has been used in gasoline since 1979 to raise octane levels, but in recent years has been add­ed in much larger amounts as a clean-burning oxygenate in gas­oline that is reformulated to im­prove air quality in polluted areas.

The federal reformulated gasoline program "has been a tremendous help to air quality," according to Daniel S. Green-baum, chairman of the 13-member panel and president of Cambridge, Mass.-based Health Effects Institute, a nonprofit group supported by EPA and industry. "We urge all parties to take quick action to pre­serve these benefits while minimizing current and future contamination of the nation's drinking water supplies." Other members of the panel represent state, in­dustry, and environmental groups.

At a press conference to announce the report, Greenbaum said the prob­lem of MTBE in the water supply is not a health and safety issue, but an envi­ronmental one. Although 5 to 10% of drinking water supplies in areas where high-oxygenate gasoline is being used have detectable amounts of MTBE, the majority are "well below levels of public health concern," the panel said.

MTBE is a known carcinogen in ani­mals, but a link to human carcinogenici­ty has not been made. Greenbaum not­ed that MTBE is, in fact, less toxic than other gasoline components. EPA does not have a standard for MTBE in water.

However, problems with taste and odor in contaminated areas have caused some communities to stop using their water supplies, Greenbaum said.

The panel made several recommenda­tions for balancing clean air and clean wa­ter issues. In addition to calling for a sub­stantial, but as yet unspecified, re-

Browner (left) and Greenbaum

duction in MTBE use, it said that water protection programs should be strength­ened, that EPA should continue to seek mechanisms to maintain air quality, and that future additives or products should be fully tested before widespread use— so that similar problems don't occur in the future, Greenbaum said.

"The recommendations I received from the panel," Browner said in a state­ment, "confirm EPA's belief that we must begin to significantly reduce the use of MTBE in gasoline as quickly as possible without sacrificing the gains weVe made in achieving cleaner air."

Part of the panel's proposal to reduce

MTBE use would require legislation: The panel said removing the 2% oxygen requirement would "ensure that ade­quate fuel supplies can be blended in a cost-effective manner."

"EPA is committed to working with Congress to provide a targeted legisla­tive solution that maintains our air qual­ity gains and allows for the reduction of MTBE," Browner said.

At the press conference, Robert Per-ciasepe, EPA's assistant administra­tor for the Office of Air & Radiation, stressed that such legislation must pre­serve the role of renewable fuels in the

gasoline supply. Not all of the panel's recom­

mendations were unanimous. In a dissenting opinion, panel mem­ber Todd C. Sneller, adminis­trator of the Nebraska Ethanol Board, criticized the proposal to remove the 2% oxygen standard, saying it did not take into account all public policy objectives related to the standard. EPA's insistence on maintaining the role of renew­able fuels likely would address these concerns.

And Lyondell Chemical, the largest North American MTBE producer, which also had a repre­sentative on the panel, said there

had been "an emotional rush to judgment" in condemning MTBE. The company says continuing to address problems with leak­ing underground storage tanks will greatly reduce the release of gasoline, and there­fore MTBE. The Oxygenated Fuels Asso­ciation, an industry group, has expressed a similar sentiment, saying once water pro­tection problems are addressed, there will be no need to restrict clean-fuel options."

A summary of the panel's recommen­dations is available on the Internet (http: //www.epa.gov/oms/consumer/fuels/ oxypanel/blueribb.htm). The full report is expected later this month.

Julie Grisham

... which makes things go from bad to worse for MTBE makers

P roducers of methyl tert-buty\ ether (MTBE) and its main feed­stock, methanol, thought things

couldn't get any worse—but they did. Three months ago, these firms learned

of a ban on MTBE in California that, if im­plemented, would take 25% of the global MTBE market off the map. Now, they are

faced with a recommendation by an Envi­ronmental Protection Agency advisory panel that use of the fuel additive be re­duced or eliminated in the rest of the coun­try—another 40% of the global market

Methanol producers are doing poorly today, even without bans and cutbacks. Several U.S. methanol plants are current-

AUGUST2,1999C&EN 5

New ethylene process is environment-friendly With about 55 billion lb of ethylene pro­duced in the U.S. each year, commodity chemical reaction engineering would seem to be set in its ways. But thanks to re­cent developments, that mature technolo­gy may learn a thing or two yet Research­ers have come up with a catalyst and proce­dure to convert ethane to ethylene in a highly efficient manner thaf s friendlier to the environment than the process most manufacturers currently use.

Today's chemical plants generally use steam cracking of alkanes—mainly

University of Minnesota researchers prepare catalysts for ethylene production by coating centimeter-scale alumina monoliths (left) with a platinum-tin film. With use, the metal aggregates Into micrometer-sized platinum-tin particles (right).

ethane—to make ethylene. The process typically runs near 85% selectivity (to form a single product) at roughly 60% ethane conversion. And while these plants are cleverly designed to derive much of the heat they require from burning unwanted by-products, that en­ergy-saving feature helps convert more than 10% of the ethane into carbon diox­ide—a greenhouse gas. The units also emit harmful nitrogen oxides.

But now a group of chemical engi­neers from the U.S. and Italy have dem­onstrated that with a certain platinum-tin catalyst and large amounts of hydro­gen they can produce ethylene by partial oxidation of ethane at greater than 85% selectivity and 70% conversion [Science, 285 , 712 (1999)]. The devel­opment may lead to much smaller and simpler chemical plants that produce less C02 and other pollutants.

The research team includes chemi­cal engineering professor Lanny D. Schmidt and graduate students Ashish S. Bodke and David A. Olschki of the University of Minnesota, Minneapolis, and chemical engineering professor Eliseo Ranzi of Polytechnic University of Milan, Italy.

"Production of ethylene by steam re­forming is believed to be the petro­chemical industry's biggest contributor to greenhouse gases," comments Peter C. Stair, a professor of chemistry at Northwestern University, Evanston, 111. "If one were able to find a way around that problem, that would certainly be a significant contribution."

Stair emphasizes, however, that be­fore the new technology can be commer­cialized, several issues—especially in the area of process safety—need to be thor­oughly addressed. Although the re­searchers report that they never observe flames during experiments, the proce­

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, and hydrogen in a 2:1:2 ratio over a cata­lyst heated to near 950 °C, then analyzes

the products with gas chromatography and mass spectrometry.

A number of features of the new cata­lytic process are surprising, the group notes. First, as Stair points out, the reac­tion ought to be dangerous because of the hydrogen-to-oxygen ratio—especially in the presence of platinum. Yet the research­ers find that the two equivalents of ethane in the mixture make it nonflammable.

Also unexpected is the high olefin se­lectivity. High temperatures usually lead to many products, they explain, because entropy effects cause all reaction chan­nels to open. Yet at 950 °C, the reaction proceeds toward a single product

"Another surprising aspect of this re­action," Schmidt remarks, "is that it yields as much hydrogen in the prod­ucts as is fed into the reactor." That means that an external source of hydro­gen may be unnecessary if a reactor is designed with a recycle feature.

The team proposes that the reaction occurs by way of mechanisms that are very different from conventional homo­geneous and heterogeneous catalytic processes. The group examined catalyt­ic surface-only mechanisms, purely gas-phase (homogeneous) mechanisms, and catalytic hydrogen oxidation fol­lowed by homogeneous ethane decom­position. But the researchers note that none of the scenarios agrees satisfacto­rily with their observations.

Schmidt and coworkers say that addi­tional experiments and simulations are required before a comprehensive mecha­nistic model can be developed. In the meantime, the group asserts that ex­treme conditions such as these "may pro­vide the environments to carry out simi­lar reactions to produce chemicals with high efficiency, improved energy use, and less pollution."

Mitch Jacoby

6 AUGUST 2,1999 C&EN

n e w s of t h e w e e k

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