MTBE's misconception
Your editorial," MTBE's slide continues," makes a number of very good points on the absurdity (and possibly the inevitability) of the loss of methyl tertiary butyl ether (MTBE) as a component in U.S. gasoline (OGJ, Aug. 2, 1999, p. 17).
Your paragraph on the (weak) benefits of oxygenates in fighting ozone, however, repeats the common misconception that MTBE detracts from the aim of gasoline reformulation more than it helps. In both the federal and California Air Resources Board (CARB) formulations, the effectiveness of reformulated gasoline (RFG) in reducing ozone (or other contaminants) depends on reducing the olefins, aromatics, benzene, and sulfur in the blend. MTBE contains none of these objectionable compounds.
By dilution alone, the 11% or so of MTBE in the mix reduces all of these bad actors by a significant degree. In addition, the high octane of MTBE permits the refiners to reduce the severity of catalytic reformer operations. At lower severity, the reformers make less aromatics, so that the aromatic content of the blend is further reduced. In this context the oxygen content of MTBE has only a minor role.
While it is possible that gasoline with no MTBE can meet a minimum set of standards under some circumstances, the air pollution will inevitably be worse than it would have been if MTBE were to be used as before.
Dexter Miller
Vice President
DeWitt & Co. Inc.
Houston
Fuel cells
I read the articles on "Future Transport Fuels" in your July 12 issue with interest, having been directly involved with several major oil companies in assessments of what kinds of engines and related fuels they should plan for. The articles were well-prepared and provide an important base point for considering future energy requirements (OGJ, July 12, 1999, p. 37-60).
However, some factors were not addressed, including development of a new kind of power plant that, if commercialized, could make much of the effort described unnecessary. The new external combustion, or "near carnot," engines developed by STM Corp., Ann Arbor, Mich., can meet the federal and state vehicle environmental regulations and can use essentially any kind of fuel-almost interchangeably-independent of cetane, octane, sulfur level, or even energy content. They are as efficient as the best diesel engines.
It is generally recognized that internal combustion engines, (gasoline and diesel) are approaching their practical limits in terms of efficiency and emissions. Improvements in emissions will compromise their efficiency, probably increase costs, and reduce reliability, as well as require tailored fuels. External combustion engines provide an alternative approach. They were overlooked in most energy planning because previous attempts to develop a practical embodiment have failed (they were complex, expensive, and had unacceptable response and life characteristics). A new concept (the STM engine) has overcome those problems.
The STM engines are simpler than internal combustion engines, they should cost less to produce, and they have longer lives than comparable internal combustion engines. They can meet the proposed California vehicle emission (and noise) standards without any after-treatment (no catalytic converters, mufflers, etc.). Their efficiency is comparable to the proton-exchange membrane (PEM) fuel cell systems.
From the viewpoint of the oil and gas industries, their most important characteristic is that they can use essentially any fuel (gasoline, diesel, natural gas, biomass, landfill gas, stored thermal energy, solar, etc.) with little or no preparation. Fuel composition could be based on environmental, not engine performance, requirements. Their commercialization could reduce the need to spend billions of dollars on modifications to refineries to produce reformulated gasoline or diesel fuels.
Likewise, there are reasons to doubt whether the PEM fuel cells will meet the goals that have been set for them. Fuel cells are promising but are at an early state of development comparable with that of internal combustion engines decades ago. They have difficulty in achieving competitive performance and costs (complicated by the need for special fuels). The efficiency levels quoted usually ignore the energy consumed in producing the fuel (methanol or hydrogen).
The process of producing the methanol and reforming it on the vehicle to produce hydrogen will consume half the energy in the original resource (natural gas or petroleum). Thus, a fuel cell that requires a manufactured fuel (methanol, hydrogen, etc.) is at a disadvantage in terms of resource consumption with an engine that only requires nominal fuel preparation. Measured against the STM engines (which have efficiencies in the high 40% range) the on-vehicle efficiency of PEM fuel cells is not high enough to offset the processing losses. If we want to extend the life of existing resources, it is the combination of the fuel consumed during processing and distribution as well as on the vehicle, that counts.
The emphasis on PEM fuel cells may have diverted research efforts away from other cell types, such as alkaline cells, that are inherently less costly and can provide higher efficiencies. (I have to take part of the blame, having initiated GM's fuel cell program).
Other fuel cells can be more efficient and less expensive. They can provide significantly higher efficiencies than PEMs (60% or greater) and can use low-cost materials (no platinum, etc.). Alkaline cells have been neglected because their performance is rapidly degraded by the presence of carbon in the fuel (or carbon dioxide in the air-oxygen side). There has been essentially no research directed at resolving the poisoning problem, although there are interesting possibilities.
I have been an advocate of fuel cells and believe that they will eventually supersede internal combustion engines in many-but not all-applications. Even if successful, fuel cells will not have a significant impact on vehicle energy consumption for decades. Transportation needs a near-term solution-a product that can be available sooner and achieve the majority of the energy and environmental benefits that fuel cells can, in theory, provide. The STM external combustion engine provides that opportunity.
Albert J. Sobey,
President
Albert Sobey & Associates
Oxygenates in transport fuels
The May 24th issue of Oil and Gas Journal contains a summary of recent work by the National Research Council (NRC) in Canada in which oxygenated organic compounds-ethanol or methyl tertiary butyl ether-were evaluated as additives for reformulated gasoline (OGJ, May 24, 1999, p. 39). One of the findings was that neither compound had a major effect in reducing ozone formation. When studying the article I was reminded of a pilot study carried out in California in the '80s. About 500 Ford Escort cars were run on methanol alone instead of gasoline up to a total mileage of about 50,000. One of the conclusions was that significant-around 17%-reductions in the ambient ozone levels would accrue from nationwide use of methanol instead of gasoline.
Methanol is traditionally made from synthesis gas that can be made from natural gas (as in the plant near New
Plymouth, New Zealand). Methanol production via synthesis gas is energetically less favorable than direct conversion of methane to methanol, an area in which a good deal of research and development is currently taking place. This is particularly useful where natural gas occurs, or is brought onshore, in remote places lacking a pipeline connection to centers of population. Once methanol is made in this way, its distribution is relatively straightforward, certainly more so than distribution of liquefied natural gas (LNG), which is an alternative natural gas product where pipeline reticulation is not possible. When (if) the direct conversion technology becomes a reality-yielding methanol for use as an automotive fuel, we can perhaps expect ozone reductions as a bonus.
J.C. Jones
Department of Engineering
University of Aberdeen
Scotland
