Mineral oils: processes and products – Products and compositions – Fuels
Reexamination Certificate
2000-07-25
2004-06-29
Medley, Margaret B. (Department: 1714)
Mineral oils: processes and products
Products and compositions
Fuels
C585S001000, C585S014000
Reexamination Certificate
active
06755961
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to stable, inhibited middle distillates and their preparation. More particularly, this invention relates to stable, inhibited middle distillates, useful as fuels e.g., kerosene, diesel or as fuel blending components, in which a Fischer-Tropsch derived distillate is blended with a virgin distillate.
BACKGROUND OF THE INVENTION
Distillate fuels derived from Fischer-Tropsch processes are often hydrotreated to eliminate unsaturated materials, e.g., olefins, and most, if not all, oxygenates. The hydrotreating step is often combined with mild hydroisomerization resulting in the formation of iso-paraffins, often necessary for meeting pour point specifications for distillate fuels, particularly fuels heavier than gasoline, e.g., diesel and jet fuels.
Fischer-Tropsch distillates, by their nature, have essentially nil sulfur and nitrogen, these elements having been removed upstream of the Fischer-Tropsch reaction because they are poisons, even in rather small amounts, for known Fischer-Tropsch catalysts. As a consequence, Fischer-Tropsch derived distillate fuels are inherently stable, the compounds that may lead to instability, e.g., by oxidation, having been removed either upstream of the reaction or downstream in subsequent hydrotreating steps. While stable, these distillates have no inherent inhibitors for maintaining oxidative stability. Thus, upon the onset of oxidation, as in the formation of peroxides, a measure of oxidative stability, the distillate has no inherent mechanism for inhibiting oxidation. These materials may be viewed as having a relatively long induction period for oxidation, but upon initiation of oxidation, the material efficiently propagates oxidation.
Virgin distillates as may be obtained from conventional petroleum sources are usually a constituent of distillate fuels, and contain sulfur in varying concentrations. The addition, usually small amounts, of virgin distillate to Fischer-Tropsch distillates provides a facile method for stabilizing Fischer-Tropsch derived fuels against oxidation.
SUMMARY OF THE INVENTION
In accordance with this invention, a blended middle distillate, useful as a fuel or a fuel blending component, and having both stability and resistance to oxidation comprises: a Fischer-Tropsch (F-T) derived distillate and a virgin distillate fraction, and wherein the sulfur content of the blend is ≧1 ppm by wt.
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Berlowitz Paul J
Cook Bruce R.
Wittenbrink Robert J.
Marin Mark D.
Medley Margaret B.
Simon Jay
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