Fuel and related compositions – Liquid fuels – Heterocyclic carbon compound containing a hetero ring having...
Reexamination Certificate
2002-01-17
2004-01-06
Toomer, Cephia D. (Department: 1714)
Fuel and related compositions
Liquid fuels
Heterocyclic carbon compound containing a hetero ring having...
C044S394000, C044S395000
Reexamination Certificate
active
06673131
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improved fuel additive compositions. The fuel additives of the invention provide improved low temperature flow and filterability to distillate fuels, such as diesel fuels, and are substantially non-discoloring and non-corrosive. Distillate fuels containing the fuel additive compositions are also provided.
2. Description of the Prior Art
Distillate fuels such as diesel fuels tend to exhibit reduced flow at low temperatures due in part to formation of waxy solids in the fuel. The reduced flow of the distillate fuel affects transport and use of the distillate fuels in refinery operations and internal combustion engine. This is a particular problem during the winter months and especially in northern regions where the distillates are frequently exposed to temperatures at which solid formation begins to occur in the fuel, generally known as the cloud point (ASTM D 2500) or wax appearance point (ASTM D 3117). The formation of waxy solids in the fuel will in time essentially prevent the ability of the fuel to flow, thus plugging transport lines such as refinery piping and engine fuel supply lines. Under low temperature conditions during consumption of the distillate fuel, as in a diesel engine, wax precipitation and gelation can cause the engine fuel filters to plug which can be simulated in the laboratory using tests such as the low-temperature flow test (LTFT). This test, ASTM Designation D 4539-98, estimates the filterability of diesel fuels in automotive equipment at low temperatures. For the test, fuel samples are cooled at a prescribed rate and at the desired temperature and each 1° C. interval thereafter, a specimen of the fuel is filtered through a 17 &mgr;m screen utilizing a vacuum system. The minimum LTFT pass temperature is the lowest temperature at which the prescribed volume of fuel (180 ml) can be filtered in 60 seconds or less. Alternatively, a single fuel specimen may be cooled in the above-described manner and tested at a specified temperature to determine whether it passes or fails at that temperature.
As used herein, distillate fuels encompass a range of fuel types, typically including but not limited to kerosene, intermediate or middle distillates, lower volatility distillate gas oils and higher viscosity distillates. Grades encompassed by the term include Grades No. 1-D, 2-D and 4-D for diesel fuels as defined in ASTM D975, incorporated herein by reference. The distillate fuels are useful in a range of applications, including use in automotive diesel engines and in non-automotive applications under both varying and relatively constant speed and load conditions.
Distillate fuels are comprised of a mixture of hydrocarbons including normal and branched-chain paraffins, olefins, aromatics and other polar and non-polar compounds, and cold flow behavior is a function of the relative proportion of these various hydrocarbon components. Normal paraffins typically have the lowest solubility and therefore tend to be the first solids to separate from the fuel as the temperature is decreased. At first, individual paraffin crystals will appear but as more crystals form they will ultimately create a gel-like network which inhibits flow. The compositional makeup of fuels can vary widely depending on the crude oil source and how deeply the refiner cuts into the crude oil. With mounting pressure on refiners to increase production of distillate fuels, they are increasingly producing fuels with amounts and types of hydrocarbon components which render the fuels unresponsive to additives heretofore capable of imparting acceptable cold flow properties to the fuels. These fuels are referred to within the industry as “hard-to-treat” fuels.
A number of compositional features can contribute to the unresponsiveness of hard-to-treat fuels to flow additives, including one or more of the following: a narrow molecular weight distribution of waxes; the virtual absence of high molecular weight waxes; inordinately large amounts of very high molecular weight waxes; a higher percentage (total) of wax; and a higher average carbon number for the normal paraffin component. While it is difficult to generate a single set of parameters which define hard-to-treat fuels, they are typically characterized by one or more of the following distillation parameters (as determined by test method ASTM D 86 incorporated herein by reference): the temperature differential between the 20% distilled and 90% distilled fractions; the temperature differential between the 90% distilled fraction and the final boiling point; and the final boiling point.
Useful cold flow improvers for distillate fuels, including hard-to-treat fuels, are disclosed in U.S. Pat. No. 6,203,583. The cold flow additives of the invention are a combination of an ethylene/vinyl acetate/isobutylene copolymer with one or more of a maleic anhydride/&agr;-olefin copolymer component, a polyimide component and an alkylphenol component. Similar compositions useful as wax anti-settling agents and cloud point depressants for distillate fuels are disclosed in U.S. Pat. Nos. 6,206,939 and 6,143,043, respectively.
While certain of the above-mentioned additives do improve cold flow properties of distillate fuels to some extent, there continues to be a need for additives which exhibit enhanced performance, particularly for hard-to-treat fuels. For example, there is an ongoing need for cold flow improver additives which do not interact with the distillate fuel or other additives commonly contained therein and, in turn, discolor the fuel or cause the formation of undesirable deposits upon storage. Cold flow improver additives which tend to discolor distillate fuels, either by interaction with other additives, e.g., stabilizers, or by other means, can interfere with or mask dyes which are added to differentiate fuels, such as dyes added to tax-exempt off-road fuel. Accordingly, it would be highly advantageous if cold flow improver fuel additive compositions were available which provided both improved cold flow performance and stability for distillate fuels. It would be even more useful if the fuel additives were substantially non-acidic to prevent corrosion of metal storage tanks and transfer lines.
SUMMARY OF THE INVENTION
The present invention relates to improved fuel additive compositions and to distillate fuels, including hard-to-treat distillate fuels, containing said additives. The additives of the invention impart improved low temperature flow and filterability to distillate fuels and also serve to stabilize the fuels against the development of undesirable color or deposits upon storage. The fuel additives are a combination of an olefin/vinyl carboxylate polymer with first and second polyimides of specific structure. More specifically, the additives comprise (a) an olefin/vinyl carboxylate polymer selected from the group consisting of ethylene/vinyl acetate copolymers; ethylene/vinyl acetate/isobutylene terpolymers and mixtures thereof; (b) a first polyimide corresponding to the general formula
where R
1
is an alkyl group with an average carbon number of 22 to 26 carbon atoms and n
1
is from about 1.5 to 8; and (c) a second polyimide corresponding to the general formula
where R
2
is an alkyl group with an average carbon number greater than 30 and n
2
is from about 1.5 to 8; said first polyimide and said second polyimide present at a weight ratio of 1:5 to 5:1 and the weight ratio of olefin/vinyl carboxylate polymer to the combined weight of said first and second polyimides ranging from 4:1 to 1:4.
Improved distillate fuel compositions containing 100 to 5000 ppm of the above-defined additives are also provided.
DETAILED DESCRIPTION
In accordance with the present invention, fuel additive compositions are provided which impart significantly improved cold flow properties, i.e., flowability and filterability, to distillate fuels and particularly hard-to-treat distillate fuels. Additionally, the fuel additive compositions of the invention do not adversely affect fuel stability.
The a
Baracka Gerald A.
Equistar Chemicals LP
Heidrich William A.
Toomer Cephia D.
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