The resurgence of environmental awareness in the U.S. could present a refining challenge during the 1990s as great as that of World War 11 or of unleaded gasoline.
In particular, tougher environmental regulations targeting vehicle emissions will change the nature of the fuels produced by refiners and the processing schemes used to produce the fuels.
By the end of the 1990s, refiners will be formulating gasoline and diesel fuel as much to meet environmental considerations as to meet quality requirements.
That could mean some substantial changes in refinery process configurations by the end of the decade.
Present and proposed U.S. Environmental Protection Agency (EPA) rules and pending legislation in the U.S. Congress to reauthorize the Clean Air Act of 1970, call for specific fuel formulas and fuel specifications to improve air quality in the U.S. They may also call for alternate fuels to be marketed in urban areas with the most severe air-quality problems.
Important features of the fuels for the 1990s will include mandated oxygen content and lower aromatics content of gasoline, lower gasoline vapor pressure, and perhaps lower olefins content. Diesel fuels will have low sulfur and aromatics contents.
These are the so-called reformulated fuels.
Alternate-fuel mandates could require the use of methanol, either neat (100%) or with some gasoline in it, liquefied petroleum gases (LPG's), compressed natural gas (CNG), and gasolines blended with ethanol (gasohol).
Each of the reformulated fuels and alternate fuels is claimed to provide certain environmental benefits. There are, however, conflicting arguments on the actual environmental benefits of the fuels and on their benefits when used in newer vehicles equipped with modern emission-control systems.
The reality is that gasoline, albeit environmental formulations of it, will remain the dominant liquid fuel for most U.S. transportation needs through the 1990s and well into the next century.
Methanol, gasohol, LPG, and CNG will likely find increased use, however, in specific-use circumstances, such as fleet vehicles where their environmental benefits can best be realized.
Unfortunately, little hard, scientific data are available on how some of these reformulations and alternatives actually perform in vehicles, either from emissions or performance standpoints.
To get the hard data, a task force of oil industry and auto industry members is now running tests and analyses on several reformulated gasolines and alternatives in modern and older vehicles to ascertain the emission levels generated by these fuels. Refiners and auto makers hope that Congress will take the task force findings into account in its work on the Clean Air Act.
The auto industry has a big stake in the fuels issues. That's because any new fuels, reformulated gasolines, diesel, or alternatives, will have to work in concert with modern emission-control systems.
They will have to provide the same level of driveability as current fuels. And the new fuels must not significantly change the fuel economy of current and future vehicle designs because the Corporate Average Fuel Economy (CAFE) regulations mandate steadily increasing fuel economy from all vehicles sold in the U.S. through the 1990s.
This first article of a three-part special report on fuels for tomorrow highlights the emissions and regulatory issues surrounding reformulated and alternate fuels, along with some of the controversy over the actual environmental benefits of the fuels. Details of the work in progress by the auto/oil industry task force and automakers' thoughts about new fuels are also cove red.
The second article in this report will examine the properties of reformulated and alternate fuels and will look at some of the reformulated gasolines that some companies have already introduced into specific markets.
Finally, the third article will look at some of the processes and refinery configurations that will be required to produce the fuels for tomorrow. Included are some new processes that may prove effective, even though these processes have yet to be commercially proven.
TARGETED EMISSIONS
Reduced ozone and carbon monoxide levels and reduced airborne toxic compounds are the main goals to be achieved by lower emissions from vehicles. Motor vehicles are said to account for almost all of the carbon monoxide emissions, and about 40% of the ozone in urban areas of the U.S. They are also a significant source of toxic compound emissions.
Specific vehicle emissions that have been targeted for reduction because they either contribute to or cause formation of these pollutants include: hydrocarbons (evaporative and exhaust), benzene, carbon monoxide (CO), and oxides of nitrogen (NOx).
Although carbon dioxide emissions are not yet targeted, they have been included in environmental discussions because of the global warming issue. But reducing CO2 emissions from vehicles that burn hydrocarbon fuels may be next to impossible, mainly because as CO emissions are reduced through better combustion, more CO2 is formed.
Hydrocarbon emissions are targeted because they combine with Nox in the air, and in the presence of sunlight form ozone (03), a significant problem in several U.S. cities. Ozone is a lung irritant and causes respiratory problems.
Benzene emissions are targeted because benzene is a known carcinogen. Benzene is found in finished gasoline (Table 1), and it is also generated as a result of gasoline combustion in a vehicle's engine.
CO emissions are on the list as a toxic substance. CO emissions are a problem in cold weather, particularly in regions where there are frequent temperature inversions (warm air overlays cold air, trapping pollutants in the surface atmosphere).
NOx is a target because it is one of the reactants in the formation of ozone. NOx levels are affected more by combustion temperatures in an engine than they are by components in the fuel.
Fuel composition plays a variable role in emission reduction, depending on the emittant and the vehicle it is used in.
Reduced gasoline vapor pressure results in probably the most significant reduction of evaporative, hydrocarbon emissions while an auto is running (Fig. 1). The hydrocarbon emission reductions provided by low-volatility gasoline during the summer months should substantially reduce ozone levels in urban areas.
CO emissions from older vehicles without modern emission controls can be reduced by blending gasoline with an oxygenated compound, such as methyl-tertiary-butyl-ether (MTBE), ethyl-tertiary-butyl-ether (ETBE), tertiary-amyl-methyl-ether (TAME), methanol, ethanol, or other alcohols. But there may be little or no reduction in CO emissions from newer vehicles.
Lower emissions could be provided by a narrower gasoline boiling range. The present gasoline boiling range is C5 to about 430 F.
If the gasoline 90% distillation temperature were limited to 300-350 F., some of the heavier hydrocarbon compounds in gasoline would be eliminated. Fewer heavy compounds would reduce engine deposits, allowing optimum combustion conditions and minimum exhaust emissions. Emission-control systems also could operate at peak efficiency for longer periods of time.
Alternate fuels, such as methanol and methanol blends, ethanol blends, LPG'S, and CNG, are claimed to provide substantial reductions of some of the targeted emissions. But they may increase emissions of other compounds whose pollution contributions are not yet well documented (formaldehyde from methanol, for instance).
REGULATORY ACTIVITIES
Even though renewed environmental concern is spurring regulatory agencies and the U.S. Congress to quickly pass new rules, regulatory action designed to improve air quality by mandating fuel specifications is not new. Refiners had to cope with rules requiring unleaded gasoline for cars with catalytic converters as far back as the mid-1970s.
In 1985, EPA rules limited gasoline lead content to 0.1 g/gal. And on June 1, 1989, rules that limit gasoline vapor pressure during the summer in much of the U.S. went into effect (OGJ, May 27, 1989, p. 79).
Those rules reduce gasoline volatility from about 11.5 psi Rvp to 9 psi Rvp. (Rvp, Reid vapor pressure, is the standard unit of measure for gasoline volatility.) Emissions limits for gasoline vehicles are shown in Table 2.
The EPA proposes further Rvp limits. Rvp is likely to be limited to 7.0-7.5 psi Rvp after 1992 in many areas of the U.S.
EPA is also considering rules to reformulate highway diesel fuels. EPA wants to limit diesel sulfur content to 0.05 wt % and aromatics content to as low as 10 vol % (OGJ, Apr. 6, 1987, p. 19). The aromatics limit may be replaced by a minimum cetane specification because cetane level may be a better control over exhaust particulate emissions from diesel vehicles.
Myriad rules governing fuel type and composition have been proposed for the reauthorization of the Clean Air Act.
These rules are designed to reduce air pollution in U.S. cities that do not consistently meet the National Ambient Air Quality Standards (NAAQS) set by the 1970 Clean Air Act.
More than 100 U.S. cities fail to consistently meet NAAQS, and nine cities are considered to be in the worst shape.
The Bush administration and Congress, last fall, were considering legislation that would require a minimum of 1 million vehicles that could run on alternate fuels in those cities.
The fuel of choice at that time was methanol, but LPG and CNG would also have qualified.
Some refiners chose to take a leading position in the attack on air-quality problems.
They began marketing reformulated gasolines that have been shown to reduce emissions of some pollutants in several areas of the U.S.
It is likely that, as a result of those moves, alternate-fuel vehicle requirements were not included in the Senate's version of the Clean Air Act that was sent to the House of Representatives in April. But reformulated gasoline is.
An amendment sponsored by Senator Thomas Daschel (D-N.D.) requires reformulated gasoline to be available in the nine worst noncompliance cities by as early as 1994.
Specifications for the reformulation in the Daschel amendment include: vapor pressure limited to 8.5 psi Rvp, aromatics content limited to 25 vol %, benzene content limited to 1.0 vol %, and that the reformulation have a minimum 2.7 wt % oxygen content.
Reductions of CO levels have been achieved in Denver, Phoenix, and Tucson, where winter gasoline must contain as much as 2 wt % oxygen.
The Senate bill originally called for 3.1 wt % oxygen, but it was later reduced 2.7 wt % because that would allow the reformulation to remain fuel-neutral (other blendstocks besides ethanol could be used to meet the requirement).
The House of Representatives late last month passed House Bill 3030 that mandates similar reformulated gasoline for nonattainment areas. An amendment, sponsored by Rep. Bill Richardson (D-N.M.) calls for an oxygen content of 3.1 wt %.
MTBE could not fulfill all of the oxygen requirements because EPA limits MTBE in gasoline to 15 vol % (1 4.8 vol % MTBE yields 2.7 wt % oxygen). The latest house bill includes a requirement for a minimum number of alternate fuel vehicles in the Los Angeles area. Congress is now working to merge the House and Senate bills for passage by September.
EMISSIONS BENEFITS CONTROVERSY
Controversy abounds over the environmental benefits provided by many of the fuels that are being considered in proposed legislation. Much of the controversy stems from the lack of good data on how these fuels behave in various engine and fuel-system designs.
Despite the controversy, each may be able to make a contribution to U.S. transportation-fuel needs during the 1990S.
METHANOL QUESTIONED
Methanol's benefits have been questioned because of a suspected, but not yet fully documented, increase in formaldehyde emissions when it is burned, and because there is limited capacity in the U.S. to produce the quantities of the alcohol needed for motor-fuel use.
Limited capacity means that much of the methanol would likely have to come from areas with substantial reserves of natural gas that can't be economically or easily sent to market. Supply from those areas would mean further reliance on foreign sources to meet U.S. transportation needs.
Despite those negative circumstances, methanol has had use in motor vehicles, particularly in fleet operations.
For example, the Bank of America in California ran an extensive fleet test on methanol vehicles during the early 1980s.
Of course, that study was concerned more with security of supply of motor fuel than with environmental concerns. But that experience could justify the use of methanol 'in some dedicated fleet operations. And the U.S. auto industry has been developing flexible-fuel vehicles since the mid-1980s for the specific purpose of operation on methanol and its blends.
OXYGEN BENEFITS QUESTIONED
The oxygen content specified in the Clean Air Act for reformulated gasoline is questioned because of doubts about its CO-reducing effects in modern automobiles with advanced emission-control systems.
Opponents claim that the oxygen will reduce CO emissions only from older cars that don't have modern computer controls with fuel-management and emissions-control systems.
As older cars are scrapped, oxygen in gasoline will have a diminishing effect on CO emissions.
Modern car computers contain a feature called adaptive learning.
The feature is part of the system in the car computer that senses oxygen in the exhaust.
Based on the level of oxygen detected in the automobile exhaust, the computer makes engine adjustments to maintain optimum combustion of the fuel.
The adaptive learning feature stores information about the engine's emission-control settings during operation of the car, and then maintains those settings the next time the car is operated.
Because these advanced-control systems maintain tight control over an engine's combustion conditions, oxygen in the gasoline would provide little, if any, CO emission reduction over what the emission-control system can accomplish.
Still, oxygen in the gasoline can provide some interim CO reductions in areas that have high winter CO levels until most of the older cars on the road are replaced with newer models.
Much of the oxygen content in gasoline will be provided by blending ethers, such as MTBE, into gasoline and using ethanol-gasoline blends.
And because ethers also have high octane and low blending vapor pressure values, oxygen will likely be in gasoline whether mandated or not.
HIGHER GASOHOL EMISSIONS SUSPECTED
Ethanol-gasoline blends are opposed because some argue they might increase emissions.
Other arguments against ethanol blends are the federal tax credit ethanol gets when it is used in motor fuel, and EPA proposals that allow gasohol to have an Rvp 1 psi higher than gasoline.
The American Petroleum Institute sponsored a research study conducted by Sierra Research Inc., Sacramento, Calif., that shows ethanol-gasoline blends increase pollution levels.'
The study shows that exhaust hydrocarbon emissions from ethanol-gasoline blends are about the same as gasoline, CO emissions are 25% lower (at least in older cars), exhaust NOx emissions increase by 8-15%, and evaporative hydrocarbon emissions increase by 50% (Fig. 2). The emission increases are said to increase ozone formation by about 6%.
The higher evaporative-hydrocarbon emissions result from the higher volatility of ethanol-gasoline blends, according to the study. Higher NOx emissions result from combustion of a leaner fuel-air mixture.
The study's conclusions are based on normalized emission profiles from a Ford Crown Victoria, flexible-fuel vehicle, and on EPA estimates on how ethanol affects the composition of both exhaust and evaporative emissions from gasoline-fueled vehicles.
The ozone-forming potential of ethanol blends was determined by using the incremental reactivity approach of W.P.L. Carter of the University of California at Riverside, and proposed for use by the California Air Resources Board (CARB), according to Sierra.
Those findings were challenged by the Renewable Fuels Association, Washington, D.C., claiming that the study considered a worst-case scenario for ethanol-gasoline blends.
Eric Vaugh, Renewable Fuels president, said the incremental reactivity approach has not been adopted by CARB and has recently been declared obsolete and inaccurate by W.P.L. Carter.
Vaugh also said the study had compared emissions of ethanol-gasoline blends to a fuel that is not available on the market (EPA's certification test fuel, indolene clear). And it only looked at emissions from one prototype vehicle, not from a vehicle representative of the current fleet.
Despite the controversy over the emission-reducing benefits of ethanol-gasoline blends, they too have had several years of experience in normal vehicles.
And there are some plants operating in the U.S. that produce ethanol from corn and similar grains for use in gasoline blending.
For those reasons, and because of strong support from the agricultural community, ethanol-gasoline blends will likely continue to be used in areas of high CO levels, particularly in agricultural areas of the U.S. where adequate grain feedstocks are available.
OTHER FUELS
There is little controversy over other alternate fuels,
such as LPG and CNG. There are also few data on their emission benefits.
Most of the limits to use of LPG and CNG are related to the lack of an adequate infrastructure for dispensing the fuels and because special vehicle fuel tanks are required,
Both fuels require special refueling systems and pressure vessels for vehicle fuel tanks.
Vehicle operating range is a problem with CNG. That's why it must be compressed to more than 3,000 psi in the vehicle fuel tank to obtain reasonable range.
But both fuels have the potential to burn cleaner in an engine because they don't contain heavier hydrocarbon components. They also don't contain the more-reactive components found in gasoline.
LPG has had significant experience as a motor fuel, and CNG has had some success in test fleets. As a result, both of these fuels will see some growth in use in dedicated fleet vehicles.
AUTOMAKERS' POSITIONS
Automakers are watching the fuels issues as closely as refiners because any new fuel formulations or alternatives must perform properly in their vehicles, from both performance and emissions standpoints.
General Motors Corp. would like refiners to eliminate gasolines that are formulated at the upper extremes of aromatic and olefins content, and at high 90% distillation temperature (T90).2 Wide variations in properties of commercial gasolines can strain the calibration limits designed into engines to provide good fuel economy, emission control, and drive-ability, according to GM.
GM also says that refiners must include emission control as a consideration in fuel formulations, as some have already done.
And reformulation composition should vary seasonally to achieve optimum emission reductions.
GM also says that gasoline vapor pressure should be no higher than 9 psi Rvp in summer in most areas of the country.
A lower Rvp may be needed in high-ozone, high-temperature areas, such as Los Angeles.
GM calls for an initial cap on aromatics at 25 vol % to reduce the reactivity of vehicle emissions and reduce engine deposits. A 0.8 wt % cap on benzene should be incorporated into the aromatics cap.
GM would also like to see a 5 vol % cap on gasoline olefins content to minimize emissions of reactive hydrocarbons. And to improve catalytic converter operation, GM wants a 300 ppm cap on sulfur content, lower if further converter improvements warrant it.
Specially reformulated gasolines should be used where they can provide the highest environmental benefits, according to Gilliam Clark, head of Chrysler Corp.'s fuels and lubricants department.
He commended those refining companies that have introduced reformulated gasolines targeted at the older vehicle population.
All fuels and fuel components are valuable resources that should not be squandered where they provide little or no environmental benefit, and where they won't be used by the vehicles that can benefit most by them. He noted some of the recent reformulated gasoline introductions that replace premium and mid-grade unleaded gasolines.
"These gasolines will be purchased by people who can afford them," he said. "Those people do not drive the older cars that benefit most from reformulated gasoline, so is it wasted."
Clark also said care should be taken in specifying Rvp limits on gasoline.
He doesn't want to see a rash of driveability problems occur because of too low an Rvp at certain times during the year.
The spring and fall periods where gasolines make the transition to higher or lower Rvp could be a problem. In the spring, residual higher winter Rvp gasoline could cause problems with meeting Rvp rules. Residual summer low Rvp gasoline could cause cold starting problems in the fall.
Even though there is controversy surrounding reformulations and alternatives, vehicles designed to run on methanol fuels could comprise 15% of new vehicle sales by the year 2000, according to Clark. He also thinks 1-5% of the vehicle population could be made up of units that are fueled with LPG and CNG.
But he said that regulatory agencies should stop looking for that all-around, alternate-fuel vehicle that can do everything.
There is only one vehicle design that can do almost everything, and that vehicle runs on gasoline.
He did not think methanol would gain much favor because there are still technical problems with flexible-fuel and methanol-fuel vehicles. Cold starting is still a problem with methanol in colder climates.
When these vehicles are started from cold, a large quantity of liquid methanol can enter the cylinders. This can cause serious lubricant dilution problems that severely shorten engine life. He said that some vehicles could not endure more than 200 cold starts without engine damage from lack of lubrication.
Refiners, in addition to their effort,, to develop reformulated gasolines, will also have an opportunity to develop improved lubricants if methanol becomes prevalent as a motor fuel.
Those thoughts were echoed by Roberta Nichols, manager of the alternate fuels department Ford Motor Co., Dearborn, Mich. Even though Ford has more than 200 flexible-fuel vehicles on the road, the technology still has a way to go.
Although the technology is improving, Ford does not have long-term experience data on the reliability of the fuel-type sensor located in the fuel supply line. This sensor measures the refractive index of the fuel to determine the amount of alcohol in the fuel, and adjusts the engine parameters accordingly.
Good progress is being made on engine lube oil developments to help minimize cold-start lubricity problems, but more work is still required in the lubricants area.
Nichols also agrees that gasoline will remain the dominant motor fuel well into the next century. But the alternatives will find markets in specific locations for specific purposes.
TASK FORCE TO GET HARD DATA
Much of the controversy over the environmental benefits of reformulated and alternate fuels will be settled when Phase 1 results of the Auto/Oil Air Quality Improvement R&D Program, that started on Apr. 5, become available later this year or early next.
Three major U.S. auto companies and 14 U.S. refining companies (Table 3) are responsible for conducting a comprehensive research and testing program that will assess the relative reductions in vehicle emissions and improvements in urban air quality, especially ozone, achievable with reformulated gasolines and methanol fuels. All testing and analyses will be conducted by both industries, with the cost of the program shared equally.
The program is co-chaired by Keith W. McHenry, senior vice-president-technology, for Amoco Corp., Chicago, and Joseph M. Colucci, head of the fuels and lubricants department at General Motors Research Laboratories, Warren, Mich.
PROGRAM GOALS
The R&D program has to accomplish several tough goals so that the data gained from program studies will form an accurate, reliable data base of information for use in future U.S. air-quality studies. Major goals of the program are:
- To assure that the best possible data are available with respect to candidate alternate fuels, including reformulated gasoline and methanol, when searching for solutions to the nation's air-quality problems.
- To develop data necessary to allow informed decisions on air-quality matters affecting customers of the oil and auto industries.
- To provide these data to the Bush administration, members of the U.S. Congress, officials of the EPA, other executive-branch officials, and state regulatory agencies.
Research will emphasize the specific chemical composition of emissions relative to potential improvements in air quality, primarily ozone. Economic studies will be conducted to determine the relative cost-effectiveness of alternatives for reducing emissions.
The program will be conducted in two phases.
Phase 1 is a $14.5-million study that will concentrate on reformulated gasolines producible in volume from existing refineries, and usable in existing vehicles that will be in the public fleet in the 1990S.
Methanol-gasoline blends that are usable in flexible fuel vehicles will also be studied. Phase 1 results are scheduled to be available by early 1991 (Table 4).
Phase 2 will study future gasoline formulations, including those requiring refinery process changes, and usable in future, prototype vehicles with advanced emission control systems.
The second phase will also study advanced methanol fuels and vehicles and consider other advanced fuel/vehicle combinations. Phase 2 costs will be determined as Phase 1 progresses.
PROGRAM EXECUTION
Phase 1 will consist of five test matrices of fuels and vehicles that will be conducted at Ford Motor Co. and General Motors Corp. facilities. Each test matrix will test specific vehicles on specific fuels (Table 5). Details of the test fuels are presented in the second article of this special report. Vehicle types will include both old and new traditional models and prototype flexible fuel vehicles (Table 6).
Effects of aromatics content, olefins content, MTBE content, and 90%-off, distillation temperature (T90) variations will be studied in the matrices that test reformulated gasolines. Results will be compared to tests on existing industrial average gasoline and the EPA certification fuel. Ethanol and ETBE content and Rvp variations will be studied in other reformulated gasolines.
Tests on 10% methanol/gasoline (M10) and 85% methanol/gasoline (M85) will also be compared to industrial average gasoline.
Another test matrix will study variations in gasoline sulfur level.
EMISSIONS TESTS
All emissions testing will be conducted in EPA-certified auto company laboratories. Exhaust and evaporative emissions and running losses will be measured.
The measurements will provide accurate hydrocarbon speciation (identification and quantification of hydrocarbon species in emissions) data with recovery and reproducibility that will allow air-quality modeling of large vehicle-emission data sets. Species identification and quantification will include detailed determination and measurement of: hydrocarbon species from C1 to C12 by gas chromatography (GC), aldehyde and ketone species using liquid chromatography (LC), and methanol, ethanol, MTBE, and ETBE species using GC measurements.
The list of the species to be identified and quantified has been finalized to include 145 components. Some specific toxic compounds to be identified are: hydrocarbons 1,3-butadiene, benzene, styrene, and naphthalene; and oxygenates acrolein, methanol, formaldehyde, and acetaldehyde.
Fuel formulations for the program will be blended by Phillips 66 Co. at its Sweeney, Tex., refinery. All test vehicles used will be purchased by the program.
Contracting of work will be done by the Coordinating Research Council (CRC), acting as agent for the participating companies.
Contractors will mainly be responsible for integrating emissions data into air-quality models.
The primary contractor for the program is Systems Applications Inc. Subcontractors include: Radian Corp., Sonoma Technology Inc., and the University of California at Riverside (UCR).
Systems Applications Inc. is responsible for development of emissions inventories, application of models, and overall coordination. Radian is responsible for selected aspects of developing emissions inventories and application of models for one city.
Sonoma Technology and UCR are responsible for implementation of the atmospheric chemical mechanism, while UCR will conduct experiments on MTBE.
An advisory council will provide peer review of the program execution. It will be made up of academic experts in the fields of air quality, combustion/emissions, and statistics.
Advice and comment will be requested of EPA, the U.S. Department of Energy, CARB, the Northeast States for Coordinated Air Use Management (Nescaum), and other regulatory agencies.
REFERENCES
- Report prepared for the American Petroleum Institute, "The Air Pollution Consequences of Using Ethanol-Gasoline Blends in Ozone Non-Attainment Areas," Report No. SR90-05-01, May 8, 1990, Sierra Research Inc., Sacramento, Calif.
- Colucci, Joseph M., "What Can the Oil Industry Do in the 1990s-An Auto Man's Perspective," Report No. GMR-7010, F&L-893, General Motors Research Laboratories, Fuels and Lubricants Dept., Warren, Mich., Apr. 25, 1990.
Copyright 1990 Oil & Gas Journal. All Rights Reserved.
