Gasoline and Additives
GASOLINE AND ADDITIVES
Gasoline is the primary product made from petroleum. There are a number of distinct classes or grades of gasoline. Straight-run gasoline is that part of the gasoline pool obtained purely through distillation of crude oil. The major portion of the gasoline used in automotive and aviation is cracked gasoline obtained through the thermal or catalytic cracking of the heavier oil fractions (e.g., gas oil). A wide variety of gasoline types are made by mixing straight-run gasoline, cracked gasoline, reformed and synthesized gasolines, and additives.
Motor fuels account for about one-quarter of all energy use in the United States. The energy content of gasoline varies seasonally. The average energy content of regular gasoline stands at 114,000 Btu/gal in the summer and about 112,500 Btu/gal in the winter. The energy content of conventional gasolines also varies widely from batch to batch and station to station by as much as 3 to 5 percent between the minimum and maximum energy values.
Gasoline can be made from coal as well as petroleum. In the 1930s and 1940s, Germany and other European countries produced significant quantities of gasoline from the high-pressure hydrogenation of coal. But to convert the solid coal into liquid motor fuels is a much more complex and expensive process. It could not compete with the widely available and easily refined petroleum-based motor fuels.
In the United States, all gasoline is produced by private commercial companies. In many cases, they are vertically integrated so that they drill for, find, and transport oil, process the oil into gasoline and other products and then sell the gasoline to a network of retailers who specialize in certain brand name gasolines and gasoline blends. These large refiners may also market these products to other refiners, wholesalers, and selected service stations.
GROWING DEMAND FOR GASOLINE
At the end of the nineteenth century, virtually all of the gasoline produced (around 6 million barrels) was used as a solvent by industry, including chemical and metallurgical plants and dry cleaning establishments, and as kerosene for domestic stoves and space heaters. But by 1919, when the United States produced 87.5 million barrels of gasoline, 85 percent was consumed by the internal combustion engine (in automobiles, trucks, tractors, and motorboats).
Between 1899 and 1919, as demand for gasoline grew, the price increased more than 135 percent, from 10.8 cents/gal to 25.4 cents/gal. From 1929 to 1941, gasoline use by passenger cars increased from 256.7 million barrels to 291.5 million barrels. Consumption of aviation fuel went from only 753,000 barrels in 1929 to over 6.4 million barrels at the start of World War II. By 1941, gasoline accounted for over one-half of petroleum products with 90 percent of gasoline output used as fuel for automotive and aircraft engines.
Between 1948 and 1975, per capita consumption of gasoline in the United States increased from about 150 gal/yr to a little less than 500 gal/yr. A growing trend after the war was the increasing use of jet fuel for aircraft and the decline in use of aviation gasoline. After 1945, oil production increased in other parts of the world, especially the Middle East and Latin America. By the 1970s, the Middle East became a dominant oil producing region. The cartel formed by the major Middle Eastern oil producing countries, known as OPEC, became a major force in setting oil prices internationally through the control of oil production.
Since the mid-1970s, the rate of growth of per capita gasoline consumption has slowed. An important factor in causing this moderation in demand was the trend to improve automobile fuel economy that was initiated by worldwide fuel shortages. Fuel economy hovered around 14.1 mpg between 1955 and 1975; it rose sharply over the next 15 years, reaching around 28.2 mpg in 1990.
An aging population and continued improvements in engine technology and fuel economy may slow U.S. gasoline demand in the early part of the twenty-first century from the 2 percent annual growth rate of the 1990s.
KNOCKING AND OCTANE RATING
The process of knocking has been studied extensively by chemists and mechanical engineers. Knocking is rapid and premature burning (i.e., preignition) of the fuel vapors in the cylinders of the engine while the pistons are still in the compression mode. Research on knocking was carried out prior to World War I, but it was only with the increase in the size and power of automotive engines after 1920 that significant attempts were made to deal with the problem on a commercial basis.
Knocking, which has a distinctive metallic "ping," results in loss of power and efficiencies and over time causes damage to the engine. Knocking is a great energy waster because it forces the automobile to consume greater quantities of gasoline per mile than do engines that are functioning properly. The problem of engine knocking was an important factor in the U.S. push for a gasoline rating system. Around the time of World War I, there was no single standard specification or measure of gasoline performance. Many states developed their own specifications, often conflicting with those promulgated by the automotive and petroleum industries and the federal government. Even the various branches of government had their own specifications. The specifications might be based on the boiling point of the gasoline fraction, miles allowed per gallon of fuel, or the chemical composition of the gasoline.
The octane numbering system was developed in the late 1920s and was closely linked to the federal government's program of measurement standards, designed jointly by the Department of the Army and the National Bureau of Standards.
The octane number of a fuel is a measure of the tendency of the fuel to knock. The octane scale has a minimum and maximum based on the performance of reference fuels. In the laboratory, these are burned under specific and preset conditions. One reference fuel is normal heptane. This is a very poor fuel and is given an octane rating of zero. On the opposite end of the scale is iso-octane (2,2,4 trimethyl pentane). Iso-octane is a superior fuel and is given a rating of 100.
The octane rating of fuels is derived by simple laboratory procedures. The fuel being tested is burned to determine and measure its degree of "knocking." Then the two reference fuels are blended together until a reference gasoline is formed that knocks to the same degree as the tested fuel. The proportion of iso-octane present in the reference fuel is then the octane number of the tested gasoline. Some compounds, like methanol and toluene, perform better than iso-octane and, by extrapolation, their octane numbers are over 100. A higher octane number is important from a very practical consideration: it gives better engine performance in the form of more miles per gallon of gasoline.
From the 1920s to the 1940s, catalytic cracking processes were developed that not only increased processing efficiencies, but progressively raised the octane number of gasoline. In 1913, prior to the devising of the octane scale, the commercialization of the Burton Process, a noncontinuous thermal technology, produced gasoline with an estimated octane number of between 50 and 60. Continuous thermal cracking, first operated in the early 1920s, produced gasoline with an octane number of close to 75. With the first catalytic process in the form of the Houdry technology (1938), cracked gasoline reached the unprecedented octane level in the high 80s. Fluid catalytic cracking, the culmination of the cracking art that came on line in 1943, pushed the quality of gasoline to an octane level of 95.
While octane rating provided an objective and verifiable measure of performance across all grades of gasoline, it did not immediately lead to unified standards. It was not until the 1930s, when both the octane rating and new types of octane-boosting additives entered the industry, that automotive fuel began to center around two major types of gasoline—regular and premium—each operating within its own octane range. Over the next 60 years, octane rating of gasoline increased due to improved refining practices and the use of additives. In the 1970s and 1980s, the use of additives became increasingly tied to environmental concerns (i.e., clean air), as well as higher octane ratings. Gasoline has come a long way since the Model T, and it is important to note that, in terms of constant dollars, it is cheaper today than it was in 1920.
Table 1 shows the major gasoline additives that were introduced from the 1920s through the 1980s. The increase in octane number of gasoline with use of these additives is shown.
TETRAETHYLEAD: THE FIRST GASOLINE ADDITIVE
One source of knocking was related to the vehicle engine. All else being equal, an automobile engine with a higher compression ratio, advanced spark schedule, or inefficient combustion is more likely to experience knocking. Within the United States, research into knocking has focused on the chemical aspects of gasoline, which is a complex hydrocarbon mixture of paraffins, naphthenes, and aromatics.
Chemical additives first entered the industry in the first decade of the century. These additives served a number of uses. For example, they lessened the capacity of gasoline to vaporize out of the gas tank or to polymerize (i.e., produce gummy residues) in the engine. In the early 1920s, the most important application for these substances was to eliminate knocking. Tetraethylead (TEL) was the first major gasoline additive to be commercialized for this purpose.
Charles F. Kettering, the inventor of the self starter, the Delco battery, and other major components of modern automotive engineering, started to work on the problem in 1916 at his Dayton Engineering Laboratories Company (DELCO). Kettering was induced into this research not by the problems faced by the automobile but by gasoline-powered electric lighting systems for farms. These systems employed generators utilizing internal combustion engines. These engines, which burned kerosene and not gasoline, knocked badly. Kettering and his team addressed this nonautomotive concern as a profitable research project and one of potentially great benefit to the agricultural sector.
Kettering hired Thomas Midgley Jr., a mechanical engineer from Cornell, to work with him on the
|Tetraethyl lead (TEL)||100|
|Methyl-t-butyl ether (MTBE)||116|
|Ethyl-t-butyl ether (ETBE)||118|
project. Studying the combustion process in more detail, Kettering and Midgley determined that low volatility in the fuel caused knocking to occur. This conclusion led them to search for metallic and chemical agents to blend with the gasoline to increase volatility and reduce knocking.
A promising line of research led Midgley to the halogen group of chemicals and specifically iodine and its compounds. General Motors purchased DELCO Labs in 1919 and the search for an anti-knock agent came under GM management, with Kettering and Midgley remaining on board to continue the work, but with the focus now on automotive application.
Using iodine as their starting point, they experimented with a series of compounds including the anilines and a series of metals near the bottom of the periodic table. Lead turned out to be the most effective of the additives tested. But lead alone caused a number of problems, including the accumulation of its oxide in engine components, and particularly the cylinders, valves, and spark plugs.
Experiments continued to find an appropriate form of lead that could at the same time prevent the formation of oxide deposits. Ethylene was found to combine with lead to form tetraethyllead (TEL), a stable compound that satisfied this requirement.
Kettering and Midgley were the first to identify it as a prime antiknock agent, though the compound had been known since 1852. They estimated that only a very small amount of TEL—a few parts per thousand—would result in a 25 percent increase in horsepower as well as fuel efficiency.
The next stage of development was to design a production process to link the ethyl group to lead. GM attempted to make TEL from ethyl iodide. They built an experimental plant, but the process proved too expensive to commercialize.
An alternative source of the ethyl component was ethyl bromide, a less expensive material. It was at this point that GM called upon DuPont to take over process development. DuPont was the largest U.S. chemical company at the time. It had extensive experience in the scale-up of complex chemical operations, including explosives and high-pressure synthesis. The manufacturing process was undertaken by DuPont's premier department, the Organic Chemical section. GM contracted with DuPont to build a 1,300 pound per day plant. The first commercial quantities of TEL were sold in February 1923 in the form of ethyl premium gasoline.
In 1923, GM set up a special chemical division, the GM Chemical Co., to market the new additive. However, GM became dissatisfied with DuPont's progress at the plant. In order to augment its TEL supply, and to push DuPont into accelerating its pace of production, GM called upon the Standard Oil Company of New Jersey (later Esso/Exxon) to set up its own process independently of DuPont. In fact, Jersey Standard had obtained the rights to an ethyl chloride route to TEL. This turned out to be a far cheaper process than the bromide technology. By the mid-1920s, both DuPont and Jersey were producing TEL.
GM brought Jersey in as a partner in the TEL process through the formation of the Ethyl Corporation, each party receiving a 50 percent share in the new company. All operations related to the production, licensing, and selling of TEL from both DuPont and Jersey were centralized in this company.
Soon after production began, TEL was held responsible for a high incidence of illness and deaths among production workers at both the DuPont and Jersey Standard plants. The substance penetrated the skin to cause lead poisoning. Starting in late 1924, there were forty-five cases of lead poisoning and four fatalities at Jersey Standard's Bayway production plant. Additional deaths occurred at the DuPont Plant and at the Dayton Laboratory. This forced the suspension of the sale of TEL in 1925 and the first half of 1926.
These incidents compelled the U.S. Surgeon General to investigate the health effects of TEL. The industry itself moved rapidly to deal with the crisis by instituting a series of safety measures. Now, ethyl fluid was blended at distribution centers and not at service stations (it had been done on the spot and increased the chances of lead poisoning to service station attendants). Also, ethyl gasoline was dyed red to distinguish it from regular grade gasoline. DuPont and Jersey placed tighter controls over the production process. The federal government placed its own set of restrictions on TEL. It set the maximum limit of 3 cc of TEL per gallon of gasoline. By 1926, TEL was once again being sold commercially.
Ironically, this episode proved beneficial to DuPont. DuPont became the dominant source of TEL after the mid-1920s because they perfected the chloride process and were far more experienced than Jersey Standard in producing and handling toxic substances.
The Ethyl Corp. and DuPont held the TEL patent, and controlled the TEL monopoly. The company held the sole right to the only known material that could eliminate automotive knocking. And it used its influence in the gasoline market to manipulate prices. Over the next few years, the company wielded its monopoly power to maintain a 3–5 cent differential between its "ethyl" gasoline and the regular, unleaded gasoline sold by the rest of the industry.
Throughout the 1930s TEL proved itself a profitable product for DuPont, which remained virtually the only TEL producer into the post–World War II period. With no advantage to be gained in further collaboration, DuPont severed its ties with Ethyl Corp. in 1948 and continued to manufacture TEL independently.
COMPETING AGAINST TEL: ALTERNATIVE ANTIKNOCK TECHNOLOGY
As the automotive industry continued to introduce higher compression engines during the 1920s and 1930s, refiners increasingly relied on TEL to meet gasoline quality. By 1929, fifty refiners in the United States had contracted with the Ethyl Corp. to incorporate TEL in their high test gasoline.
TEL was not the only way to increase octane number. Those few companies who did not wish to do business with Jersey Standard, sought other means to produce a viable premium gasoline. TEL represented the most serious threat to the traditional gasoline product. It was cheap, very effective, and only 0.1 percent of TEL was required to increase the octane number 10 to 15 points. In contrast, between 50 to 100 times this concentration was required of alternative octane enhancers to achieve the same effect.
Benzol and other alcohol-based additives improved octane number, up to a point. Experiments using alcohol (ethanol, methanol) as a replacement for gasoline began as early as 1906. In 1915, Henry Ford announced a plan to extract alcohol from grain to power his new Fordson tractor, an idea that never achieved commercial success.
The shortage of petroleum after World War I induced an intense search for a gasoline substitute in the form of alcohol. The trade press felt alcohol would definitely replace gasoline as a fuel at some point. The advantages of alcohol cited in the technical press included greater power and elimination of knocking.
The push to use alcohol as a fuel surfaced at various times coinciding with real or perceived gasoline shortages and often directed by the farm lobby during periods of low grain prices. The great discoveries of oil in the Mid-Continental fields in the1920s reduced the incentive for the use of alcohol as a fuel. But in the 1930s the severe agricultural crisis brought back interest in alcohol. Alcohol distillers, farmers, and Midwest legislators unsuccessfully attempted to regulate the blending into gasoline of between 5–25 percent ethanol. It took the oil supply disruptions of the 1970s for farm state legislators to pass legislation to highly subsidize ethanol. The subsidies, which remain in effect today, are the reason ethanol continues to play a notable role as a fuel additive.
As experiments at Sun Oil Co. in the early 1930s indicated, there were serious disadvantages associated with alcohol. While alcohol did in fact appear to increase the octane number, it left large amounts of deposits in the engine. Alcohol also vaporized out of the gas tank and engine at rapid rates. And the combustion temperature of the alcohol group is lower than for hydrocarbons because it is already partially oxidized.
The most effective competitive approach for the more independent refiners was in developing new types of cracking technologies. Companies like Sun Oil, one of the few companies who remained independent of Jersey and Ethyl, continued to expand the limits of thermal cracking, notably by employing higher pressures and temperatures. Sun's gasoline reached octane levels close to those achieved by gasolines spiked with TEL (i.e., between 73 and 75). Sun Oil continued to compete with additives purely through advanced cracking technology, a path that would lead by the late 1930s to the first catalytic cracking process (i.e., the Houdry Process). But by this time, more advanced refining processes were coming on line and competing with the Houdry Process. By the early 1940s, Jersey Standard developed fluidized bed catalytic cracking technology. Fluidized cracking proved superior to Houdry's fixed bed process with respect to both production economies and the quality of the product (i.e., octane rating of the gasoline). Fluidized cracking quickly displaced Houdry's catalytic cracking technology as the process of choice.
Competition did not center on quality alone. Price and packaging were called into play as weapons against the onslaught of TEL. For example, as a marketing tool, Sun Oil dyed its gasoline blue to more easily identify it as a high premium fuel (customers actually saw the gasoline being pumped in a large clear glass reservoir on top of the gas pump). Sun then competed aggressively on price. Whereas TEL-using refiners sold two grades of gasoline, regular and premium, Sun marketed only its premium "blue Sunoco" at regular grade prices. Sun could do this because it was not burdened, as TEL was, with such additional costs as blending and distribution expenses that cut into profit margins.
By the late 1920s and into the 1940s, with the use of either TEL, other additives, or advanced cracking technology, a number of premium grade gasolines appeared on the market. In addition to Sun's premium, there was Gulf's "NoNox," Sinclair's premium "H.C.'s" gasoline, and Roxana Petroleum's "Super-Shell." The use of TEL has plummeted since the government's mandate in 1975 to install catalytic converters for reducing the carbon monoxide and unburned hydrocarbons in automotive exhaust gases. This is because lead poisons the noble metal (chiefly platinum) catalysts used. In addition the lead bearing particulates in the emissions from engines burning leaded fuel are toxic in their own rights.
POSTWAR DEVELOPMENTS: GASOLINE AND THE ENVIRONMENT
Additives and the blending process became an increasingly important part of gasoline manufacture after World War II. Refiners had to balance such factors as customer specifications, regulatory requirements, and probable storage (i.e., nonuse) time. The industry became more precise in how, when, and how many of components should be added to gasolines. The large, modern refinery increasingly incorporated complex computer programs to help plan and effect blending requirements. Critical factors that had to be factored into these calculations included seasonal adjustments, current and anticipated demand, regulatory levels, and supply schedules of the various components.
Since the 1950s, an increasing portion of a refiner's R&D has gone into new and improved additives. Beyond their role as antiknock agents, additives and blending agents have taken on an ever broadening range of functions to improve the performance of fuels in automotive and aircraft engines.
Sulfur and Gasoline
In recent years, there has been a greater understanding of the role of automotive emissions as environmental pollutants. Sulfur dioxide, nitrogen oxides, and carbon monoxide degrade the earth's atmosphere and are health hazards. Carbon dioxide adds to the atmospheric buildup of greenhouse gases and in turn accelerates the process of global warming.
Sulfur is a particular problem as an environmental hazard. It occurs naturally in various concentrations in petroleum, and it is difficult and costly to remove all of it. Distillation and cracking removes some, but small amounts survive the distillation and cracking processes and enter into the gasoline. The average level of sulfur in gasoline has not changed much since 1970, remaining at 300 parts per million (ppm) with a range between 30 and 1,000 ppm.
High levels of sulfur not only form dangerous oxides, but they also tend to poison the catalyst in the catalytic converter. As it flows over the catalyst in the exhaust system, the sulfur decreases conversion efficiency and limits the catalyst's oxygen storage capacity. With the converter working at less than maximum efficiency, the exhaust entering the atmosphere contains increased concentrations, not only of the sulfur oxides but also, of hydrocarbons, nitrogen oxides, carbon monoxides, toxic metals, and particulate matter.
In the 1990s, the EPA began controlling sulfur through its reformulated gasoline program. It developed regulations in 1999 that would sharply reduce the sulfur content in gasoline from 300 ppm to a maximum of 80 ppm.
The new regulations, scheduled to go into effect in 2004, are compelling certain refiners to purchase low-sulfur content ("sweet") crude oil. This is the strategy being pursued by Japanese refiners. However, the Japanese are not major oil producers but import oil from other producing countries. U.S. refiners, in contrast, consume oil from a wide range of ("sour") petroleum sources that have a high-sulfur content, including Venezuela, California, and parts of the Gulf Region. U.S. companies own and operate oil producing infrastructures (i.e., derricks, pipelines), within the United States and overseas. They are committed to working these oil fields, even if producing high-sulfur oil. U.S. refineries thus need to continue dealing with high-sulfur crude oil. Imported crude from the Middle East, while historically low in sulfur, is also becoming increasingly less sweet.
Petroleum refiners will have to reduce sulfur content at the refineries. This will require the costly retooling of some of their plant operations in order to achieve a suitable fuel mix. Removing additional amounts of sulfur at the refinery will entail installation of separate catalyst-based process such as hydro-sulfurization. Another possible approach is the removal of sulfur in liquid oil or gasoline by the use of both organic and inorganic scavenger agents added to the oil or gasoline to seek out, combine with, and precipitate out sulfur and its compounds.
Reformulated Gasoline and MTBE
Prior to the Clean Air Act of 1990, environmental regulations were aimed at reducing emissions as they left the exhaust system. The catalytic converter has been the primary means of attacking air pollution in this way. After 1990, regulations for the first time undertook to alter the composition of the fuel itself. Reformulated gasoline applies to gasoline that is sold in the nine metropolitan areas designated by the EPA with the highest level of ozone pollution. About 48 million people reside in areas where ozone concentrations exceed federal standards.
Reformulation refers to the transformation of gasoline to make it cleaner with respect to emissions. Beginning in 1995, specifications for reformulated gasoline included a 2 percent minimum oxygen content and a maximum content of various organic and inorganic pollutants. In addition, heavy metal additives in gasoline are prohibited. A disadvantage of reformulated gasoline is that it contains 1 to 3 percent less energy per gallon than traditional gasoline.
Many reformulated gasolines use oxygenated compounds as additives. Clean Air regulations specify the need for oxygenated fuel in 39 metropolitan areas with high carbon monoxide concentrations. The regulations for oxygenated fuel are seasonal: during the winter season, gasoline must contain a minimum of 27 percent oxygen. The oxygen helps engines to burn the fuel more completely which, in turn, reduces monoxide emissions. The major additive to supply the additional oxygen to reformulate gasoline to satisfy these requirements is the methanol derivative, methyl tertiary butyl ether (MTBE). Currently, this additive is used in over 30 percent of U.S. gasoline.
MTBE was first used as a fuel additive in the 1940s and was a popular additive in Europe in the 1970s and 1980s. In the late 1970s, MTBE began replacing lead in this country to enhance octane number. In the late 1980s, California led the way in the United States for its use as an oxygenate for cleaner burning fuel. The consumption of MTBE in the United States increased rapidly between 1990 and 1995 with the passage of the Clean Air Act and, a few years later the implementation of the federal reformulated gasoline program. Currently, MTBE is produced at 50 U.S. plants located in 14 states. About 3.3 billion gallons of MTBE, requiring 1.3 billion gallons of methanol feedstock, are blended annually into reformulated gasoline.
In the late 1990s, MTBE came under serious attack on grounds of both efficacy and safety. A report by the National Research Council (1999) stated that the addition of oxygen additives in gasoline, including MTBE and ethanol, are far less important in controlling pollution than emission control equipment and technical improvement to vehicle engines and exhaust systems.
Moreover, MTBE has been found in groundwater, lakes and reservoirs used for drinking water, and it has been linked to possible serious disease. The probable occurrence of cancerous tumors in laboratory rats injected with MTBE alerted federal agencies as to its possible health hazards. In 1999, the EPA reversed itself, recommending the phasing out of MTBE as an additive to gasoline.
During the first half of 2000, MBTE production in the Unites States averaged 215,000 barrels per day. In the same six-month period, the average production offuel ethanol was 106,000 barrels per day. In light of the EPA's 1999 recommendation, ethanol will most likely replace MTBE as an effective oxygenate additive. In addition to its use as an oxygenate, ethanol enhances octane ratings and dilutes contaminants found in regular gasoline.
New and Emerging Gasoline Additives
The development and blending of additives is undertaken for the most part by the petroleum refining industry. Additives are essential to the economic well-being of the industry because they tend to boost sales for gasoline and diesel fuel. In most cases, additives do not differ in price by more than three to four cents a gallon. The recently developed additives do not necessarily sacrifice fuel efficiency for higher octane numbers. They are multifunctional. In addition to boosting octane ratings they may also clean the engine, which, in turn, leads to greater fuel efficiency.
Beyond their role in enhancing octane numbers and reducing emissions, the group of more recent fuel additives performs a growing range of functions: antioxidants extend the storage life of gasoline by increasing its chemical stability; corrosion inhibitors prevent damage to tanks, pipes, and vessels by hindering the growth of deposits in the engine and dissolving existing deposits; demulsifiers or surface active compounds prevent the formation of emulsions and the dirt and rust entrained in them that can foul the engine and its components.
Beginning in the 1970s, gasoline additives increasingly took on the role of antipollutant agent in the face of government attempts to reduce automotive emissions into the atmosphere. Despite the advances made in cracking and reforming technologies and in the development and blending of additives (not to mention enhancements in the engine itself), the use of automotive gasoline has increased the level of air pollution. This is so because modern distillates, blends of straight run and cracked or chemically transformed product, tend to have a higher aromatic content. The result is longer ignition delays and an incomplete combustion process that fouls the engine and its components and increases particulate and oxide emissions.
Continued implementation of clean air legislation, especially within the United States, is expected to accelerate the consumption of fuel additives. In 1999, the EPA proposed wide-ranging standards that would effectively reformulate all gasoline sold in the United States and significantly reduce tailpipe emissions from trucks and sports utility vehicles. These regulations require potentially expensive sulfur-reducing initiatives from both the oil industry and the automakers. For refiners, it will require significant redesign and retooling of plant equipment and processes will be required in order to achieve suitable changes in the fuel mix because the U.S. oil industry is committed to continue development of its sour petroleum reserves. The DOE expects that the more complex processing methods will add six cents to the cost of a gallon of gasoline between 1999 and 2020.
In the United States alone, the demand for fuel additives is expected to reach over 51 billion pounds by 2002. Oxygenates are anticipated to dominate the market, both within the United States and internationally. Nonpremium gasoline and diesel fuel represent the fastest growing markets for fuel additives.
A recently marketed fuel additive is MMT (methylcyclopentadienylmanganese tricarbonyl). MMT was first developed by the Ethyl Corporation in 1957 as an octane enhancing agent and has experienced a growth in demand in the 1990s. MMT was Ethyl Corporation's first major new antiknock compound since TEL.
However, in 1997, the EPA blocked the manufacture of MMT. The Agency took this action for two reasons. It determined that MMT had the potential for being hazardous to humans, and in particular to children. The EPA is especially concerned about the toxic effects of the manganese contained in MMT. Also, the EPA discovered that MMT was likely interfering with the performance of the catalytic converters in automobiles and in turn causing an increase in exhaust emissions in the air. In 1998, the EPA decision was overturned by a federal appeals court in Washington. The court's decision allows the Ethyl Corp. to test MMT while it is selling the additive. The decision set no deadline for the completion of tests. In addition to its use in the United States, MMT is consumed as an additive in unleaded gasoline in Canada.
In addition to MTBE and MMT, other kinds of additives are being developed. Some of these are derivatives of alcohol. Variations of MTBE are also being used, especially the ether-derived ETBE (ethyl-t-butyl ether).
A new generation of additives specifically designed for aircraft gasoline are also being developed. These additives address such problems as carbon buildup, burned and warped valves, excessive cylinder head temperatures, stuck valves and piston rings, clogged injectors, rough idle, and detonation. Aviation fuel additives often act as detergents (to remove deposits), octane enhancers, and moisture eliminators.
Competition from Alternative Fuels
Most alternative fuel vehicles on the road today were originally designed for gasoline, but converted for use with an alternative fuel. Because the petroleum industry has successfully responded to the competitive threats of alternative fuels by developing reformulated gasolines that burn much cleaner, the conversions are typically performed more for economic reasons (when the alternative fuel is less expensive, which has occurred with propane) rather than environmental reasons. It is likely that technical advances will continue to permit petroleum refiners to meet the increasingly more stringent environmental regulations imposed on gasoline with only minor increases in the retail price. And since petroleum reserves will be abundant at least through 2020, gasoline promises to dominate automotive transportation for the foreseeable future.
However, fuel cell vehicles, which are designed to generate their power from hydrogen, pose a major long-term threat to the preeminence of gasoline. Automakers believe the best solution is to extract hydrogen from a liquid source because hydrogen has a low energy density and is expensive to transport and store. All the major automakers are developing fuel cell vehicles powered by hydrogen extracted from methanol because reforming gasoline into hydrogen requires additional reaction steps, and a higher operating temperature for the reformer. Both requirements are likely to make the gasoline reformer larger and more expensive than the methanol reformer. Moreover, the sulfur content of gasoline is another major reason that automakers are leery of developing gasoline reformers for fuel cell vehicles. Quantities as low as a few parts per million can be a poison to the fuel cell stack. There are no gasoline reformer fuel cell vehicles in operation, so an acceptable level of sulfur has not been determined. If it is determined that an ultralow-sulfur gasoline blend can be developed specifically for fuel cell vehicles, it would be a far less expensive solution than developing the fuel production, delivery and storage infrastructure that would be needed for methanol-powered fuel cell vehicles.
Sanford L. Moskowitz
See also: Efficiency of Energy Use, Economic Concerns and; Engines; Fuel Cells; Fuel Cell Vehicles; Hydrogen; Methanol; Synthetic Fuel.
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