Transportation fuel composition has been targeted as a major factor in the type and quantity of vehicle emissions.
Gasoline vapor pressure and its benzene, aromatics, olefins, and oxygen contents, and diesel fuel sulfur and aromatics contents can all be factors in overall air quality in the U.S.
The issues surrounding these and other factors were introduced in the first article of this report.
In addition to reformulated gasolines and diesel fuels, alternatives have also been considered by state and federal legislative bodies because they are claimed to provide substantial emissions benefits.
The present Clean Air Act reauthorization includes provisions that mandate that a minimum number of alternate fuel vehicles be available, along with alternate fuels for them. Currently the mandate applies only to the Los Angeles metropolitan area.
U.S. refiners have joined the efforts to improve air quality in the U.S. Some have already introduced reformulated gasolines and diesel fuels to various areas of the country and, as mentioned, are participants in the Auto/Oil Air Quality Improvement R&D Program.
Reformulated gasolines will likely contain advanced additive packages that may contribute to lower emissions by keeping engines and fuel systems clean and operating at peak efficiency. One additive, MMT, designed primarily as an octane booster, has been shown to also help reduce vehicle emissions. The producer has, in fact, just applied for an EPA waiver for it in unleaded gasoline.
This second part of a three-part special report on fuels for tomorrow examines the properties of some of the new reformulated gasolines and diesel fuels. Also examined are the properties of the fuels that are being used in the first phase of the auto/oil test program, and the properties and potential of some of the alternate fuels and gasoline additives.
NEW FORMULATIONS
Several companies have already introduced reformulated gasolines and diesel fuels to U.S. markets where air-quality is the poorest. Although none of the current reformulations is the complete answer to the nation's overall air-quality problems, these new gasolines are designed to make incremental improvements in the air quality of the regions in which they are sold.
ARCO'S EC-1
The first reformulation to hit the market, and probably the catalyst for the appearance of other reformulations, was ARCO Products Co.'s EC-1 emission-control gasoline. EC-1 was first introduced to the South Coast basin in California on Sept. 1, 1989.
The reformulated gasoline is targeted at older vehicles that do not have catalytic converters and sophisticated emission control equipment. According to ARCO, these vehicles comprise about 15% of the vehicle population in the South Coast basin, but they contribute more than 30% of the vehicle emissions in the area.'
EC-1 resulted from extensive testing done by ARCO on older vehicles to measure the gasoline's effect on hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emissions. Fleet testing was done at Southwest Research Institute in San Antonio and at the National Institute for Petroleum & Energy Research in Bartlesville, Okla. EPA emission-test procedures were strictly adhered to.
The test fleet consisted of 20 vehicles selected to match the model-year distribution of cars and light-duty trucks in the Los Angeles basin that don't have catalytic converters. Each vehicle was tested in duplicate on EC-1 and a fuel representative of the leaded regular gasoline sold in Southern California.
In addition to measuring HC, CO, and NOx, emission levels generated by EC-1, analysis of the type and quantity of hydrocarbon species in the HC samples was done. In total, some 75,000 data points were generated from the tests.
EC-1 gasoline has the specifications shown in Table 1. Table 2 shows a comparison of EC-1 with available leaded regular gasoline.
Fleet test results showed statistically significant reductions of the regulated emissions: exhaust HC's, 5% less; CO, 10% less; NOx, 6% less; and evaporative HC's, 22% less. Benzene emissions in the exhaust were down 43%. A summary of actual emissions is shown in Table 3.
Vehicle performance tests, consisting of driveability and road octane measurements, were also conducted on the fleet. Results indicated that EC-1 was incrementally better than regular leaded gasoline.
ARCO also had the emissions data analyzed in urban air-quality models to determine the effect EC-1 could have on overall air quality. Systems Applications Inc. was contracted to use its Urban Airshed Model on EC-1 emissions data and base-case data to project the effects on 1990 air quality in the Los Angeles basin.
The modeling showed that EC-1 could result in 350 to 600 tons/day less pollutants from vehicles, depending on the definition and extent of misfueling that is assumed. (Misfueling means using leaded gasoline grades in vehicles restricted to unleaded grades.)
The 350-tons/day value is equivalent to removing up to 20% of the nonconverter-equipped vehicles from the road, or 320,000 vehicles. Peak and average ozone levels were also reduced.
All of the model results are based on the assumption that EC-1 replaced all leaded regular gasoline in Southern California, and that off-road as well as on-road vehicles used the reformulation.
NEXT-GENERATION DIESEL
Diesel fuels have also been targeted for reformulation. EPA has proposed rules to limit highway diesel sulfur content to 0.05 wt % and aromatics content to 20 vol %, or possibly as low as 10 vol %. Rather than an aromatics limit, the cetane number of diesel may be specified at 45 minimum.
These rules are expected to go into effect in 1993 unless EPA moves faster on them. Southern California already requires a maximum 0.05 wt % sulfur content in diesel sold there.
Some companies are not waiting for EPA, however. Coastal New England Inc. recently introduced its "next generation" diesel fuel to jobbers and fleet users in the New England area.
Although the diesel fuel will not be a low-sulfur diesel fuel until EPA's rules go into effect, its high cetane quality and additive package are said to result in lower emissions of hydrocarbons, carbon monoxide, and particulates, according to Paul J. Nazzaro, Coastal's commercial marketing manager (Fig. 1).
The fuel's high cetane number is maintained by selecting only those crude oils and diesel feedstocks that have high cetane quality. The proprietary additive package includes a cold-flow improver that eliminates kerosine blending in winter, thus keeping the fuel's heating value up.
The additive package also contains a deicer and a biocide to reduce bacteria growth in fuel storage systems.
The high cetane and additive package keep vehicle fuel systems clean and provide cleaner fuel burning in an engine, according to the company.
Coastal intends to produce its next-generation diesel fuel at Coastal Corp.'s Aruba, Netherlands Antilles, refinery. The 450,000-b/d crude capacity refinery will have about 150,000-b/d capacity to produce the new diesel fuel.
OTHER REFORMULATIONS
Shortly after ARCO's introduction of EC-1, several other refining and marketing companies began hitting the market with their reformulated gasolines. Among those companies are: Diamond Shamrock Refining & Marketing Co., Conoco Inc., Sun Refining & Marketing Co., Marathon Petroleum Co., Phillips 66 Co., Amoco Corp., Shell Oil Co., and Exxon U.S.A. Diamond Shamrock Refining & Marketing Co.'s RG-87 reformulated gasoline, marketed in the Denver area, will replace its regular unleaded gasoline, and it will be dispensed at pumps with large nozzles. The fuel hits the older car population with the worst emissions.
RG-87 limits aromatics content to 20 vol %, has an Rvp 1 psi below Colorado requirements, and has an octane rating of 87 (R+M)/2 compared to 86.5 for its leaded regular. The gasoline contains MTBE.
Phillips 66 Co. introduced its Super-Clean brands of reformulated gasoline into the St. Louis metropolitan area in April.
The reformulated gasoline, with 20-30% fewer aromatics and olefins, 33% less sulfur, and 35% less benzene, will be offered in all three gasoline grades.
All of the gasolines will meet EPA Rvp rules and they will contain MTBE. The gasolines will be made at Phillips 66 Co.'s Sweeney, Tex., refinery at the rate of 6,000 b/d. Phillips also announced in April it will market LPG in the Denver area.
Conoco Inc. introduced a reformulated, unleaded gasoline in the Denver area and stopped producing leaded regular gasoline at its Commerce City, Colo., refinery on Mar. 1. Conoco will also offer a diesel fuel at several Denver locations that is lower in sulfur than diesel presently available.
Marathon Petroleum Co. began offering its reformulated Amaraclean gasoline in three gasoline grades in 161 Detroit-area stations at the end of March. The reformulation, made at Marathon's 68,500 b/d Detroit refinery, has reduced vapor pressure and aromatics content, and it includes MTBE similar to ARCO's EC-1.
Amoco Corp. will sell a low-vapor-pressure gasoline beginning July and August this year in Northern Illinois and Indiana, including the Chicago metropolitan area (OGJ, Dec. 4, 1989, pi 31). The gasoline, manufactured at Amoco's Whiting, Ind., refinery, will have an Rvp of 9.5 psi, 1 psi below specified rules for the area.
Others include Shell Oil Co. with its introduction of SU2000E into its markets in the Gulf and East Coasts. Shell's gasoline is a premium, unleaded gasoline with lower vapor pressure and 1 Wt % oxygen content through the addition of MTBE.
Exxon will also begin supplying a lower-vapor-pressure gasoline along the Gulf and East Coasts. Exxon's reformulation will be sold as unleaded premium and unleaded midgrade gasoline. The gasoline will not contain oxygen in most of the area, but will contain 1 wt % oxygen through the addition of MTBE in the New York metropolitan area. MTBE is added in this region because, according to Exxon, New York has a particularly severe CO level problem.
The competitive advantage that may be gained by offering environmentally better fuels will probably spur other companies to introduce new fuels.
AUTO/OIL PROGRAM'S TEST FUELS
Phase 1 of the Auto/Oil Air Quality Improvement R&D program will be testing several different gasoline reformulations and alternate fuels to determine their effectiveness as emissions reducers, and to identify and quantify the individual species of compounds emitted when the various fuels are burned. (See the first article of this report for details on the goals and procedures of this program.)
Each of the various fuels will be tested in various vehicles-new, old, and prototype flexible fuel vehicles. Emission test results will then be used in air-quality models to determine the overall effects on air quality these fuels will have.
PHASE 1 TEST FUELS
Test fuels, supplied by Phillips 66 Co., Sweeney, Tex., in Phase 1 of the auto/oil program will include average gasoline on the market today, 23 different gasoline reformulations, and two blends of methanol and gasoline (M10 and M85). Industry average gasoline specifications include: 32 vol % aromatics, 12 vol % olefins, no MTBE, and the gasoline will blended to a 90%-off distillation temperature of 335 F.
Some of the industry-average gasoline will contain 10 vol % ethanol. In the case of the ethanol blends, Rvp will be limited 1 psi higher at 10 psi.
Reformulated gasoline specifications will include 20 vol % aromatics, 5 vol % olefins, an Rvp of 8 psi, and a 90%-off temperature of 280 F. One reformulated blend will contain 17 vol % ETBE, with aromatics at 20 vol %, olefins at 5 vol %, and a 90%off temperature of 2801 F.
M10 will be a blend of 10 vol % methanol and 90 vol % industrial-average gasoline. M85 will contain 85 vol % methanol and 15 vol % industry-average gasoline, with the blend Rvp adjusted to 9 psi by adding butane.
PRESENT AVERAGE GASOLINE
Reformulated and alternate fuels used in the test program will be examined along with average gasolines on the market today. To determine the specifications and quantities of average gasoline currently produced in the U.S., the National Petroleum Refiners Association completed a survey of U.S. refineries in April.
The survey examined processes and blend-component specifications of refinery-manufactured and acquired blendstocks for the period Apr. 1 to Sept. 30, 1989. Manufactured stocks totaled 6,524,127 b/cd, and acquired stocks totaled 264,562 b/cd (Table 4). Note that imported finished gasoline stocks are not included in the totals.
Those stocks, blended into finished gasoline, were combined for a total 6,788,689 b/cd of finished gasoline (Table 5).
The 90%-boiling point distillation temperature of the various gasoline grades was in the 330-340 F. range for motor gasoline. And due to EPA rules in effect last summer, Rvp ranged from 9.210.5 psi.
Note also that aromatics content of the various grades ranged from a high of 38 vol % for premium unleaded grades to a low of 27.8 vol % for leaded regular. Olefins content ranged from a high of 14.3 for regular unleaded to a low of 7.0 vol % for unleaded premium.
Note that unleaded regular also contained a significant amount of oxygenated blendstock at 2.7 vol %. (Table 5 data do not show the level of ethanol blended into gasoline because ethanol is blended at distribution terminals and not refineries.) Little oxygenated material was used in the unleaded and leaded regular grades, with both containing 0.2 vol %.
Aromatics and olefins contents of the various blendstocks are given in Table 6. Note the aromatics level of 31.8 vol % compared to some of the reformulated gasolines available at 20 vol %, and the reformulated gasoline specified in the Senate version of the Clean Air Act at 25 vol %.
One of the test fuels will be used to test emissions affected by gasoline sulfur content. That fuel will be EPA's certification-test fuel (indolene clear), spiked with 500 ppm tertiary butyl disulfide, to obtain a 40 ppm sulfur level.
OTHER ALTERNATIVES
Compressed natural gas and LPG are two other alternate fuels that have gained interest in the clean-air debate. Several demonstration and test programs are under way for CNG-fueled vehicles, and LPG has been used for many years to power industrial and agricultural vehicles.
These fuels, because they are composed of only light hydrocarbons, eliminate a substantial portion of the reactive components that form ozone. But dispensing and storage of the fuels is more complicated.
Compressed natural gas, to achieve reasonable range from a vehicle, requires a vehicle fuel tank designed for pressures above 3,000 psig, and LPG requires a pressure vessel designed for at least 250 psig. And both require special fittings for refueling.
But because the vehicle fuel system must handle a pressurized fluid, the fuel system is totally sealed from ambient. This means that evaporative emissions from vehicles are virtually eliminated, substantially reducing evaporative hydrocarbon emissions.
There are currently, however, some CNG vehicles that are designed to run on both CNG and gasoline. These, of course, have some evaporative HC emissions from the gasoline system.
American Gas Association (AGA) reported the findings of 12 recent studies on CNG-fueled vehicles. Studies reported include those conducted by the California Air Resources Board (CARB), Sierra Research Inc., Argonne National Laboratory, the Society of Automotive Engineers (SAE), Radian Corp., Inform, and others, and compared to published EPA estimates.
The studies covered emissions of hydrocarbons, CO, and NOx, from both duel-fueled (CNG and gasoline) vehicles and advanced vehicles where CNG was the only fuel used. When compared to gasoline, CNG showed a positive reduction in reactive HC (RHC) emissions, compared to gasoline, in several of the studies (Fig. 2). Reductions were also scored for CO emissions, and NOx, emissions were slightly reduced.
FUEL ADDITIVES MAY LOWER EMISSIONS
Gasoline additives originally designed to keep fuel systems and engines clean and to boost octane have been found to aid in emissions reduction when blended into gasoline.
It has always been somewhat of a given that if an engine's fuel system (carburetor, injection system, and intake) and combustion chamber were kept free of deposits, the engine operates more efficiently.
Efficient operation, it was assumed, should equate to minimum emissions. With that in mind, tests have been conducted on gasolines with additive packages in them to validate the assumption,
Polybutene and polyether amines developed by Chevron Research & Technology Co., and used in additives made by Chevron's Oronite division, have been shown to reduce emissions.2
A recent 10-car, 50,000-mile test, comparing unleaded gasoline with and without an additive package, showed reductions of all targeted emissions, HC's, CO, and NOx, (Fig. 3).The additives become more effective as vehicle mileage increases.
The study was an EPA durability test on five 1979 and five 1980 model cars.
For a more than 35 years, Ethyl Corp. has made the octane-boosting additive, methylcyclopentadienyl manganese tricarbonyl (MMT), now branded Hitech 3000. It is still being used in some leaded U.S. gasoline and all gasoline in Canada, but EPA does not allow its use in unleaded grades in the U.S.
Ethyl Corp. ran several tests on MMT to show that it reduces vehicle CO emissions by 0.22 g/mile, and NO), emissions by an average of 0.11 g/mile.3
The test results showed a small, but detectable increase in hydrocarbon emissions (an average of 0.0100.018 g/mile over 75,000 miles), but MMT raised the octane number of the gasoline 0.9 number. That result would be negated if other octane-boosting gasoline blendstocks were reduced to maintain specification octane in an MMT blend. And reduction of those blendstocks would also lower gasoline volatility and its associated evaporative HC emissions.
The program consisted of a 48-car test fleet designed in consultation with EPA and the auto industry. Exhaust emissions were compared at 5,000-mile intervals up to 75,000 miles from paired sets of vehicles fueled on clear fuel (no MMT) and fuel containing MMT.
Ethyl also conducted a 100,000-mile test on four 1988 Chevrolet Corsicas with 2.01. engines, two with MMT and two without.
The tests were done to determine the effects of MMT on the cars' emission-control systems.
Results showed that engine emissions systems were not harmed by MMT and that catalytic converters exhibited equal or slightly better HC conversion, equal CO conversion, and good improvement in NOx conversion.
Oxygen sensors were compared at 50,000 miles, and no difference was found. And driveability was not affected for any of the test vehicles.
Ethyl Corp. reapplied for a fuel additive waiver under Section 21 1 (f)(4) of the 1970 Clean Air Act on May 9. George Unzelman, president of HyOx Inc., Fallbrook, Calif., says that using MMT could allow a 28 vol % aromatics limit in the U.S. gasoline pool, (OGJ, Apr. 9, p. 43).
But he also says there is only a 50:50 chance that EPA will approve the waiver.
REFERENCES
- Cohu, Linda K., Rapp, Larry A., and Segal, Jack S., "EC-1 Emission Control Gasoline," ARCO Products Co., Anaheim, Calif., September 1989.
- Gibbs, Lewis M., and Peyla, R.J., "A New Era for Gasoline Additives," Chevron Research and Technology Co., Oronite Technology Group, Richmond, Calif., May 1990.
- Ethyl Corp.'s reapplication before the U.S. Environmental Protection Agency for a fuel additive waiver, Ethyl Corp., P.O. Box 2189, Richmond, Va., May 9, 1990.
Copyright 1990 Oil & Gas Journal. All Rights Reserved.