Low lead aviation gasoline blend

Details Low lead aviation gasoline blend Low lead aviation gasoline blend

1999-12-09

2002-09-17

Toomer, Cephia D. (Department: 1714)

Fuel and related compositions

Liquid fuels

Lead-containing organic compound

C044S447000, C044S448000, C585S014000

Reexamination Certificate

active

06451075

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reduced or low lead aviation gasoline blend which satisfies the requirements of ASTM D 910 or deviates therefrom only in the inclusion of an oxygenate. In particular the invention relates to such an aviation gasoline blend which comprises at least about 50% by volume 2,2,4-trimethylpentane and contains less than the maximum of 0.53 mL/L of lead specified by ASTM D 910.
2. The Prior Art Background
Tetraethyl lead (TEL) was used for years to increase octane in both automotive and aviation gasoline fuels. On Jan. 1, 1996 TEL was banned from use in automotive gasoline fuels by the EPA Clean Air Act. The General Aviation industry is concerned that these criteria will be extrapolated to aviation gasoline fuels so as to increase the cost and affect the reliability and/or consistency thereof. This concern is exacerbated because aviation gasoline fuel generally must have a higher octane than automotive fuel. Moreover, consumers in the general aviation industry require a gasoline fuel product which has a consistent and reliable octane rating so as to provide an appropriate consistent performance level.
Generally speaking, aviation gasoline fuels today must meet the requirements of ASTM D 910 (1996). Presently relevant criteria of ASTM D 910 are set forth below in TABLE 1.
TABLE 1
D 5191
Vapor pressure
38.0-49.0 kPa
D 3338
Heat of combustion, net
43.5 MJ/kg min
D 5059
Lead content
0.53 mL/L max
D 2700
Motor octane number (MON)
99.5 min
(BRE/30.2in/300F)
D 909
ASTM Supercharge rating
130.0 min
(1.31 mL TEL/gal)
Performance number
D 86
Distillation, ° C., % evaporated
10%
 75 max
40%
 75 min
50%
105 max
90%
135 max
Final boiling point
170 max
Sum of 10% + 50%
evaporated
135 min
Recovery
97% min
Residue
1.5% max
Loss
1.5% max
ASTM D 910 also excludes oxygenates. To meet the criteria of ASTM D 910, most aviation gasoline fuels today comprise a blend containing about 70 volume % alkylate, about 10 volume % isopentane and about 20 volume % toluene. Approximately 2 gm of TEL is added to each gallon of the blend to appropriately increase the MON to the specified level. This is the maximum amount of lead allowed by the ASTM D 910 specification. The very stringent specifications set by ASTM D 910 (1996) for aviation gasoline fuels, particularly the supercharge octane rating, the MON, the vapor pressure and the distillation criteria greatly reduce the options available to blend a satisfactory aviation gasoline fuel without using a lead additive to increase the octane level. In fact most prior art aviation gasoline fuel blends have necessarily included the maximum amount of lead permitted.
The ASTM D 910 (1996) specification sets only a maximum level for lead. Accordingly, aviation gasoline with no lead would be suitable assuming all other criteria are met. At this point in time the EPA is adamant about reducing or eliminating lead in aviation gasoline and it is believed that the main reason that the EPA has not yet moved on this point is that there currently is no solution to the problem of achieving high enough octane in aviation gasoline fuels without using lead. Were the EPA to move now, it might lead to the destruction of the entire general aviation industry.
So a major unsolved problem in the general aviation industry today is how to provide an aviation gasoline fuel which meets all of the criteria of the ASTM D 910 (1996) specification without using lead as an additive. Stated another way, the problem is how to reduce or eliminate the need for lead in aviation gasoline fuels.
SUMMARY OF THE INVENTION
The present invention provides a genuine solution to the problems discussed above. Thus, the invention provides a reduced lead aviation gasoline blend which satisfies the requirements of ASTM D 910. In particular, the invention provides an aviation gasoline fuel that comprises at least about 50.0 volume % 2,2,4-trimethylpentane (sometimes referred to simply as “isooctane”), whereby the lead content of the fuel may be reduced to less than 0.53 mL/L. Thus, the fuel of the invention may comprise at least about 50.0 volume % 2,2,4-trimethylpentane, meets the requirements of ASTM D 910, and contains less than 0.53 mL/L lead.
More particularly, the invention provides a gasoline blend which is suitable for use in an internal combustion airplane engine and which contains no more than 0.26 mL/L of lead and which may comprise from about 55.0 to about 65.0 volume % of 2,2,4-trimethylpentane. Preferably the gasoline blend of the invention may comprise from about 58.0 to about 62.0 volume % of the 2,2,4-trimethylpentane. More preferably the gasoline blend of the invention may comprise about 60.0 volume % of the 2,2,4-trimethylpentane. Ideally, the gasoline blend of the invention may comprise no more than about 85.0 volume % of the 2,2,4-trimethylpentane.
Through the use of the invention, the lead content of the gasoline blend may be reduced from the maximum allowed by ASTM D 910 to an amount which ranges from about 0.11 to about 0.15 mL/L. Preferably, and in accordance with one aspect of the invention, the lead content may range from about 0.12 to about 0.14 mL/L. Ideally, in accordance with this aspect of the invention, the lead content of the fuel may be about 0.13 mL/L. In fact, the lead content of the aviation fuel may be reduced to an amount which is no more than about 0.13 mL/L.
Through the use of another aspect of the invention, wherein the gasoline blend includes an oxygenate, the lead content of the gasoline blend may be reduced from the maximum allowed by ASTM D 910 to an amount which ranges from about 0.03 to about 0.07 mL/L. Preferably, in accordance with this aspect of the invention, the lead content may range from about 0.04 to about 0.06 mL/L. Ideally, in accordance with this aspect of the invention, the lead content of the fuel may be about 0.05 mL/L. In fact, the lead content of the aviation fuel may be reduced to an amount which is no more than about 0.05 mL/L.
A predominant feature of the invention is the use of a major amount of 2,2,4-trimethylpentane in the gasoline blend. As mentioned above, the content of this ingredient in the overall gasoline blend may be as low as 50.0% and as high as 85.0% by volume. Preferably, the blend may contain about 60.0 volume % of the 2,2,4-trimethylpentane. In accordance with another aspect of the invention the gasoline blend may contain about 67.0 volume % of said 2,2,4-trimethylpentane.
The aviation gasoline blend of the invention may also include a C
7
-C
11
aromatic hydrocarbon, a C
5
-C
6
aliphatic hydrocarbon and a C
4
aliphatic hydrocarbon. Preferably the blend may contain a sufficient amount of a C
7
-C
11
aromatic hydrocarbon to provide an appropriate supercharge rating. Furthermore, the blend may include a sufficient amount of a C
5
-C
6
aliphatic hydrocarbon to provide D-86 distillation control. Additionally, the blend may include a sufficient amount of a C
4
aliphatic hydrocarbon to provide D-86 distillation and RVP control.
In one highly preferred embodiment of the invention, the aviation gasoline blend may comprise from about 56.0 to about 64.0 volume % 2,2,4-trimethylpentane, from about 13.0 to about 17.0 volume % xylene, from about 12.0 to about 16.0 volume % methyl t-butyl ether, from about 6.5 to about 9.5 volume % isopentane, from about 2.0 to about 4.0 volume % isobutane and no more than about 0.1 mL/L tetraethyl lead. More preferably, the aviation gasoline blend of the invention may comprise from about 58.0 to about 62.0 volume % 2,2,4-trimethylpentane, from about 14.0 to about 16.0 volume % xylene, from about 13.0 to about 15.0 volume % methyl t-butyl ether, from about 7.0 to about 9.0 volume % isopentane, from about 2.5 to about 3.5 volume % isobutane and no more than about 0.07 mL/L tetraethyl lead. Ideally the blend may include about 60.0 volume % 2,2,4-trimethylpentane, about 15.0 volume % xylene, about 14.0 volume % methyl t-butyl ether, about 8.0 volume % isopentane, about 3.0 volume % isobutane and no more than about 0

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