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RESEARCH NOTES Lubricity-Enhancing Properties of Soy Oil When Used as a Blending Stock for Middle Distillate Fuels Janet M. Hughes,*,† George W. Mushrush,‡,§ and Dennis R. Hardy‡ Geo-Centers, Inc., 4640 Forbes Boulevard, Suite 130, Lanham, Maryland 20706, Materials Chemistry, Code 6121, Naval Research Laboratory, 4555 Overlook Avenue, SW, Washington, D.C. 20375, and Chemistry Department, George Mason University, Fairfax, Virginia 22030
As the price of middle distillate fuels continues to rise, the use of bioderived materials as fuel blending stocks becomes attractive. In the present research, a severely hydrotreated diesel fuel was blended in concentrations of 10-20% and was shown to have significantly better lubricity as measured by ASTM D6078/BOCLE, ASTM D6079/SLBOCLE, and BOTD. The current ASTM methods showed a wide differentiation between the hydrotreated fuel and the soy blends. The differences in the BOTD measurements were not as large. Introduction Low-sulfur diesel fuel has been required in the United States since 1993.1,2 In 1999, the Environmental Protection Agency proposed “Tier 2” standards that would require the same emission standards for gasoline and diesel engines. These “fuel neutral” standards are expected to be phased in between 2004 and 2009.3 With these ever-tighter restrictions placed on diesel fuel exhaust emissions, refiners will have to treat crudes more severely than ever before in order to reduce the amount of sulfur and aromatics present in the fuel. This is all happening at a time when the production of petroleum fuels in the United States is declining while the civilian and military consumption is increasing.4 Increased refining severity is known to remove the trace surface-active species responsible for a fuel’s lubricity.5,6 Because many components within an engine rely on the fuel for sufficient lubrication, any reduction in the natural lubricating capabilities of the fuel would bring about excessive wear and untimely loss of engine performance. Lubricity additives have been added to fuels in order to protect the engine from excessive wear.7,8 The notion that a renewable blending stock could be used to increase the fuel supply as well as have other positive effects on the fuel is promising. The possibility of using a soybean-derived diesel fuel as a blending stock has been studied previously.4 At that time the potential stability problems that could be encountered with blending commercial soy fuel with both a stable and unstable middle distillate fuel were investigated. ASTM stability tests were conducted on fuel blends of 10-20 vol %, and it was found that the soy-fuel mixtures improved the stability of both the * Corresponding author. Phone: 202-404-2546. Fax: 202404-3719. E-mail:
[email protected]. † Geo-Centers, Inc. ‡ Materials Chemistry, Code 6121, Naval Research Laboratory. § George Mason University.
stable and unstable fuels. We are now interested in the lubricating properties of this soy-derived fuel when blended with a poor-lubricity fuel. Biodiesel fuels have been studied not only as a BTU source and low-emission component but also for their lubrication properties.9-11 Past studies have looked at the lubricating properties of biodiesels produced from canola, corn, sunflower, and olive oils as well as used cooking oil.10 One study involved the blending of soybean oil with two fuels. It was found that the lubricity improved upon blending; however, both of the fuels studied already had acceptable lubricity. This study did mention the exceptional scuffing load capacity of the neat biodiesel.9 A second study showed an improvement in lubricity for two conventional low-sulfur diesel fuels, but this study used specific soy methyl esters.11 The purpose of this study was to determine the lubricity effects of the blending of a finished, commercially available soybean-derived fuel with a poor-lubricity diesel fuel. Experimental Section Reagents. (i) Soy Diesel Fuel. The soy-derived diesel fuel, SoyGold, was supplied by Ag Environmental Products, Lenexa, KS. This fuel was a pale yellow color and had a boiling point greater than 200 °C. It had negligible water solubility, a specific gravity of 0.88, and a flash point of 218 °C. (ii) Middle Distillate Fuel. The petroleum middle distillate fuel was severely hydrotreated and had a specific gravity of 0.83, a sulfur content, as measured by ASTM D 5453,12 of 30 1 75 50 200
24 35 40
wear scar
wear scar
45 2500 60
propriate to investigate the lubricity properties of blends containing 20% soy diesel and lower. Additionally, because the intent is to produce a blending stock to increase the fuel supply, concentrations below 10% biodiesel were not appropriate for this study. Thus, fuel blends of 10 and 20 vol % SoyGold/petroleum diesel were prepared. The neat fuels and blends were measured for lubricity by the two ASTM methods. A third test, the Falex BOTD test stand, from Falex International Ltd., Berkshire, U.K., was also used to determine the lubricity of the samples. This test is currently under review at the ASTM D-02 committee level. A summary of the test conditions for each method can be found in Table 1. The tests were designed specifically for measuring the adhesive wear associated with the high loads found in diesel engines. For this study, the incremental load test in the ASTM method D6078, SLBOCLE, was used. This test may briefly be described as follows: A 50-mL test specimen was placed in a reservoir and the temperature adjusted to 25 °C. A 500-g mass was placed on a load arm holding a nonrotating steel ball. A steel ring, rotating at 525 rpm, was partially immersed in the test fuel. The steel ball was lowered such that it made contact with the rotating steel ring. After a 30-s break-in period, the ball was kept in contact with the ring for 60 s, after which it was moved at least 0.75 mm away from the ring so that a new load could be applied. The tangential frictional force was recorded and the friction coefficient calculated. The minimum load required to give a frictional coefficient of greater than 0.175 was considered to be a measure of the lubricating properties of the fuel. The higher the load, the better the lubricity of the fuel. According to information found in the diesel fuel specification, ASTM D975, fuels with SLBOCLE values below 2000 g may cause accelerated wear in fuellubricated rotary-type injection pumps.16 ASTM D6079, HFRR, may be described briefly as follows: A 2-mL sample was placed in the test reservoir at 60 °C. A fixed steel ball was held in a vertically mounted chuck and forced against a horizontally mounted stationary steel plate with a 200-g applied load. The test ball was oscillated at 50 Hz and a stroke length of 1 mm for 75 min while in contact with the steel plate. The wear scar generated on the test ball was considered to be a measure of the lubricating property of the fuel. A large wear scar implies an unacceptable lubricity fuel. Fuels with wear scars of 450 µm or lower at 60 °C should be able to protect fuel injection equipment according to ASTM D975.16 The BOTD test method used in this study may be summarized as follows: Three disks are placed in a specimen assembly and covered with a 35-mL sample of fuel. A ceramic ball is pressed into the cavity formed
Table 2. Lubricity Test Results sample
ASTM D6078 SLBOCLE, g
ASTM D6079 HFRR, µm
BOTD, µm
neat fuel 10% SoyGold 20% SoyGold neat SoyGold
1700 5050 5300 6000
600 115 75 155
660 350 310 450
by the three disks, thus making a three-point contact. The force of the ball is 2.5 kg of force (24.5 N), and the ball is rotated at 60 rpm for 45 min. The average wear scar diameter is determined. The test is run in duplicate, and the average of these two tests is referred to as the BOTD rating. Similar to the HFRR, a low wear scar implies an acceptable lubricity fuel. Results and Discussion Previous work in our lab has shown that soy-derived diesel fuel, SoyGold, offers many advantages for use as a blending stock.4 Blends in the 10-20% concentration range produced fuels that met and/or exceeded ASTM requirements for diesel fuel specifications.16 Even though the SoyGold may contain an antioxidant, the concentration of the antioxidant in a 20% blend would be considered minimal. Thus, the results indicating that these blends yielded fuels that were storage stable for at least 1 year are important. Table 2 gives the results of the three different lubricity tests. The neat fuel that was severely hydrotreated had poor-lubricity characteristics as measured by the SLBOCLE and HFRR. The lubricity of the fuel improved dramatically when blended with the soy diesel. The neat SoyGold had the highest value for the SLBOCLE, 6000 g. The wear scars for both the HFRR and BOTD were lowest for the 20% blend, 75 µm and 0.31 mm, respectively. When viewing the test results, one needs to consider the repeatability of the test methods. Repeatability is comparing the results obtained by the same operator using the same instrument. For ASTM D6078, SLBOCLE, that value is 900 g, for ASTM D6079, HFRR, it is 80 µm. Thus, the lubricity values of the neat SoyGold and the 10% and 20% blends are essentially the same for both the SLBOCLE and HFRR. The differences between the unacceptable lubricity, neat hydrotreated fuel, and the soy blends were significant for the SLBOCLE and HFRR, even taking into consideration repeatability. For example, in the SLBOCLE tests, there was a 3600 g difference between the neat fuel and the 20% blend, while in the HFRR, there was a 525 µm difference for the same sample set. In the BOTD, that difference was only 350 µm. Because no statistical data are available for the BOTD, one can make some assumptions if the BOTD is compared to the ASTM tests. One assumption is that, similar to both the SLBOCLE and HFRR, the repeatability of the BOTD may be such that the wear scars of 310-450 µm are essentially the same. Additionally, a wear scar of 660 µm is siginificantly different from that of 450 µm. However, because the lubricity of the soy-blended fuels are so much better than the neat low-lubricity fuel using the SLBOCLE and HFRR, the question arises as to whether that 350 µm difference is large enough to distinguish between fuels with questionable lubricity. Conclusions The use of a biodiesel fuel such as SoyGold in blends in the 10-20% concentration range have been shown to improve the lubricity of highly refined diesel fuel.
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Currently, all commercial diesel fuels rely on “additive packages” to meet the complex requirements of SAE and other specifications. Severely hydroprocessed diesel fuels will require additives so that they meet lubricity as well as other requirements, and the role of soy diesel in these packages may become important. When adequate fuel supplies are of concern, it is promising that a blend with soy diesel may help extend the fuel supply. Acknowledgment The authors express appreciation to the Naval Air Systems Command, Air 4.4.5, Fuels and Lubricants Division, Patuxent, MD, for supporting this work. Literature Cited (1) Federal Register (CFR Parts 80 and 86), Vol. 55, No. 162, pp 34120ff, 8/21/90. (2) Clean Air Act Amendments of 1990, House of Representatives Report No. 101-952, 10/26/90. (3) Environmental Protection Agency, 40 CFR Parts 80 and 86, Federal Register Document, May 13, 1999; Vol. 64, No. 92. Internet: http://wais.acess.gpo.gov. (4) Mushrush, G. W.; Beal, E. J.; Hughes, J. M.; Wynne, J. H.; Sakran, J. V.; Hardy, D. R. Biodiesel Fuels: Use of Soy Oil as a Blending Stock for Middle Distillate Petroleum Fuels. Ind. Eng. Chem. Res. 2000, 39 (10), 3945-3948. (5) Grabel, L. Lubricity Properties of High-Temperature Jet Fuels; U.S. Navy NAPC Report No. NAPTC-PE-112; Naval Air Propulsion Center: Aug 1977. (6) Nikanjam, M.; Henderson, P. T. Lubricity of Low Sulfur Diesel Fuels; SAE Technical Paper Series 932740; SAE: Warrendale, PA, 1993. (7) MIL Spec, Military Specifications, Turbine Fuel, Aviation, Grades JP-4, JP-5, and JP-5/JP-8 ST, MIL-DTL-5624T, 1998. (8) MIL Spec, Military Specifications, Turbine Fuels, Aviation,
Kerosene Types, NATO F-34 (JP-8), NATO F-35, and JP-8+100, MIL-DTL-83133E, 1999. (9) Lacey, P. I.; Westbrook, S. R. The Effect of Increased Refining on the Lubricity of Diesel Fuel. 5th International Conference on Stability and Handling of Liquid Fuels, Rotterdam, The Netherlands, Oct 3-7, 1994; Giles, N., Ed.; U.S. Department of Energy: Washington, DC, pp 743-760. (10) Anastopoulos, G.; Lois, E.; Serdari, A.; Zanikos, F.; Stournas, S.; Kallogeros, S. Lubrication Properties of Low-Sulfur Diesel Fuels in the Presence of Specific Types of Fatty Acid Derivatives. Energy Fuels 2001, 15, 106-112. (11) Graboski, M. S.; McCormick, R. L. Combustion of Fat and Vegetable Oil Derived Fuels in Diesel Engines. Prog. Energy Combust. Sci. 1998, 24, 125-164. (12) ASTM Standard Test Method for Determination of Total Sulfur in Light Hydrocarbons, Motor Fuels and Oils by Ultraviolet Fluorescence. Annual Book of ASTM Standards; ASTM: Philadelphia, 1999; Part 0.05.03, ASTM D5453-00. (13) ASTM Standard Test Method for Hydrocarbon Types in Liquid Petroleum Products by Fluorescent Indicator Adsorption. Annual Book of ASTM Standards; ASTM: Philadelphia, 1999; Part 0.05.01, ASTM D1319-98. (14) ASTM Standard Test Method for Evaluating Lubricity of Diesel Fuels by the Scuffing Load Ball-on-Cylinder Lubricity Evaluator (SLBOCLE). Annual Book of ASTM Standards; ASTM: Philadelphia, 2000; Part 0.05.04, ASTM D6078-99. (15) ASTM Standard Test Method for Evaluating Lubricity of Diesel Fuels by the High-Frequency Reciprocating Rig (HFRR). Annual Book of ASTM Standards; ASTM: Philadelphia, 2000; Part 0.05.04, ASTM D6079-99. (16) ASTM Standard Specification for Fuel Oils. Annual Book of ASTM Standards; ASTM: Philadelphia, 1997; Part 0.05.01, ASTM D975-96.
Received for review July 23, 2001 Revised manuscript received November 19, 2001 Accepted November 21, 2001 IE010624T
