Mineral oils: processes and products – Products and compositions – Fuels
Reexamination Certificate
2000-05-02
2003-12-16
McAvoy, Ellen M. (Department: 1764)
Mineral oils: processes and products
Products and compositions
Fuels
C044S300000, C585S014000
Reexamination Certificate
active
06663767
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to blends of Fischer-Tropsch derived fuels and conventional petroleum fuels. More particularly, this invention relates to a blended fuel, useful in a diesel engine which is low in sulfur and demonstrates better than predicted emissions characteristics.
BACKGROUND
A concern for future diesel fuels is the ability to produce higher quality and cleaner burning diesel fuels without extensive and expensive reprocessing. Typical factors detrimental to fuel quality are high sulfur, high density, high end boiling and T95 points, (the temperature at which most all the material has boiled off, leaving only 5% remaining in the distillation pot) high aromatic and polyaromatic contents. These factors have been shown to have a detrimental effect on emissions. For example, see the Coordinating Research Council (CRC) study on heavy duty diesels in the United States reported in SAE papers 932735, 950250 and 950251, and the European Programme on Emissions, Fuels and Engine Technologies (EPEFE) study on light and heavy duty diesels reported in SAE papers 961069, 961074 and 961075.
In contrast, emissions measurements on Fischer-Tropsch diesel fuels, which have virtually nil sulfur, aromatic and polyaromatic contents demonstrate favorable emissions characteristics. A report by the Southwest Research Institute (SwRI) entitled “The Standing of Fischer-Tropsch Diesel in an Assay of Fuel Performance and Emissions” by Jimell Erwin and Thomas W. Ryan, III, NREL (National Renewable Energy Laboratory) Subcontract YZ-2-113215, Oct. 1993, details the advantage of Fischer-Tropsch fuels for lowering emissions when used neat, that is, use of pure Fischer-Tropsch diesel fuels.
Presently, there remains a need to develop an economic, low sulfur distillate fuel blend useful as a diesel fuel which has lowered emissions after combustion and allows a greater portion of the distillate to be used as a high value premium product. In particular, sulfur levels, emissions of solid particulate matter (PM), and nitrogen oxides (NOx) are important due to current and proposed environmental regulations. While it has been disclosed that Fischer-Tropsch fuels can be blended with conventional fuels, see for example U.S. Pat. No. 5,689,031 herein incorporated by reference, the ability to further improve such blends with respect to emissions provides a distinct economic advantage.
The citations of the several SAE papers referenced herein are:
P. J. Zemroch, P. Schimmering, G. Sado, C. T. Gray and Hans-Martin Burghardt, “
European Programme on Emissions, Fuels and Engine Technologies
-
Statistical Design and Analysis Techniques
”, SAE paper 961069.
M. Signer, P. Heinze, R. Mercogliano and J. J. Stein, “
European Programme on Emissions, Fuels and Engine Technologies
-
Heavy Duty Diesel Study
”, SAE paper 961074.
D. J. Rickeard, R. Bonetto and M. Signer, “, “
European Programme on Emissions, Fuels and Engine Technologies
-
Comparison of Light and Heavy Duty Diesels
”, SAE paper 961075.
K. B. Spreen, T. L. Ullman and R. L. Mason, “
Effects of Cetane Number, Aromatics and Oxygenates on Emissions from a
1994
Heavy
-
Duty Diesel Engine with Exhaust Catalyst
”, SAE paper 950250.
K. B. Spreen, T. L. Ullman and R. L. Mason, “
Effects of Cetane Number on Emissions from a Prototype
1998
heavy Duty Diesel Engine
”, SAE paper 950251.
Thomas Ryan III and Jimell Erwin, “
Diesel Fuel Composition Effect on Ignition and Emissions
”, SAE paper 932735.
M. Hublin, P. G. Gadd, D. E. Hall, K. P. Schindler, “
European Programme on Emissions, Fuels and Engine Technologies
-
Light Duty Diesel Study
”, SAE paper 961073.
SUMMARY OF THE INVENTION
According to an embodiment of this invention is provided a blended fuel, useful as a diesel fuel, wherein the fuel blend contains an undercut conventional diesel fuel, blended with a Fischer-Tropsch derived diesel fuel, such that the blend demonstrates better than expected emissions and a reduced sulfur content. In particular, the blend is an asymmetric diesel fuel blend comprising a Fischer-Tropsch derived hydrocarbon distillate having a T95 of at least 600° F. (316° C.), preferably at least 650° F. (343° C.), more preferably at least 700-750° F. (371° C.-399° C.), blended with a petroleum derived hydrocarbon distillate having an initial boiling point and a T95 no greater than 640° F. (378° C.), preferably a T95 no greater than 600° F. (316° C.) wherein the blend has a sulfur content of less than 500 wppm. The resultant diesel fuel blend is characterized by an initial boiling point ranging from at least 280° F.+ (138° C.+), preferably at least 300° F.+ (149° C.+), more preferably 320° F.+ (160° C.+) and a T95 up to about 700° F. (371° C.), preferably up to about 680° F. (360° C.), even more preferably up to about 660° F. (349° C.), still more preferably up to about 640° F. (378° C.) and contains:
Sulfur <500 wppm, preferably <150 wppm, more preferably <50 wppm, even more preferably <30 wppm,
Polyaromatics <11 wt %, preferably <wt 5%, more preferably <1 wt %,
Cetane number >50, preferably >55, more preferably >60,
Density from about 0.79 to about 0.85 wherein the Fischer-Tropsch distillate comprises 5-90 vol. % of the blended diesel fuel, preferably 20-80 vol. %, more preferably 30-80 vol. %.
A typical diesel fuel boils in the range of about 320-700° F. However, sulfur levels generally increase with boiling point, i.e., heavier diesel derived from crude oil has a higher sulfur content than lighter diesel. See Jimell Erwin, Thomas W. Ryan, III, “
The Standing of Fischer
-
Tropsch Diesel in an Assay of Fuel Performance and Emissions
”, NREL (National Renewable Energy Laboratory) Subcontract YZ-2-113215, October 1993. The blend of the invention provides a fuel having reduced sulfur levels and emissions levels lower than those predicted by standard correlations, e.g., European Program on Emissions Fuels and Engine Technologies, SAE Paper 961073, by eliminating the heavy end of the conventional diesel fuel and replacing the heavy end with a low sulfur Fischer-Tropsch derived diesel fuel boiling above the range of a normal diesel fuel. In addition to reducing sulfur levels, the diesel fuel blend of this invention outperforms predicted emissions levels, especially in emissions of nitrous oxides.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is flow-scheme diagram of fixed bed reactors connected in series and contained within an isothermal sand bath for production of a blend stock for use in one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The Fischer-Tropsch process is well known to those skilled in the art, see for example, U.S. Pat. Nos. 5,348,982 and 5,545,674 herein incorporated by reference. Typically the Fischer-Tropsch process involves the reaction of a synthesis gas feed comprising hydrogen and carbon monoxide fed into a hydrocarbon synthesis reactor in the presence of a Fischer-Tropsch catalyst, generally a supported or unsupported Group VIII, non-noble metal e.g., Fe, Ni, Ru, Co and with or without a promoter e.g., ruthenium, rhenium and zirconium. These processes include fixed bed, fluid bed and slurry hydrocarbon synthesis. A preferred Fischer-Tropsch process is one that utilizes a non-shifting catalyst, such as cobalt or ruthenium or mixtures thereof, preferably cobalt, and preferably a promoted cobalt, the promoter being zirconium or rhenium, preferably rhenium. Such catalysts are well known and a preferred catalyst is described in U.S. Pat. No. 4,568,663 as well as European Patent 0 266 898. The synthesis gas feed used in the process comprises a mixture of H
2
and CO wherein H
2
:CO are present in a ratio of at least about 1.7, preferably at least about 1.75, more preferably 1.75 to 2.5.
Regardless of the catalyst or conditions employed however, the high proportion of normal paraffins in the product produced by the Fischer-Tropsch process must be converted from waxy hydrocarbon feeds into more useable products, such as transportation fuels. Thus, conversion is accomplished prim
Bateman John Richard
Berlowitz Paul Joseph
Johnson Jack Wayne
Ryan Daniel Francis
Wittenbrink Robert Jay
ExxonMobil Research and Engineering Company
Martin Mark D.
McAvoy Ellen M.
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