Fuel and related compositions – Liquid fuels – Heterocyclic carbon compound containing a hetero ring having...
Reexamination Certificate
1999-05-13
2001-03-20
Medley, Margaret (Department: 1714)
Fuel and related compositions
Liquid fuels
Heterocyclic carbon compound containing a hetero ring having...
C044S351000, C044S394000, C044S395000
Reexamination Certificate
active
06203583
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fuel additives which are useful as cold flow improvers and fuel compositions incorporating these additives.
BACKGROUND OF THE INVENTION
Distillate fuels such as diesel fuels tend to exhibit reduced flow at reduced temperatures due in part to formation of solids in the fuel. The reduced flow of the distillate fuel affects the transport and use of the distillate fuels not only in the refinery but also in an internal combustion engine. If the distillate fuel is cooled to below a temperature 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), solids forming in the fuel in time will essentially prevent the flow of the fuel, plugging piping in the refinery, during transport of the fuel, and in inlet lines supplying an engine. Under low temperature conditions during consumption of the distillate fuel, as in a diesel engine, wax precipitation and gelation can cause the engine fuel filter to plug which can be simulated in the laboratory with tests such as cold filter plugging point. In addition to contributing to filter plugging, gelation of the fuel may also cause flow problems which can be evaluated by a pour point test method, published as ASTM D 97. A test container of fuel is cooled in a bath and the container is periodically removed to determine if the fuel flows. The test is completed when the fuel fails to move when the container is held horizontally for 5 seconds. Fuel movement at this point is prevented by the formation of an interlocking wax structure; as little as 2% wax out of solution can prevent flow of the remaining 98% liquid fuel.
As used herein, distillate fuels encompass a range of fuel types, typically including but not limited to kerosene, intermediate 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 D 975. 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.
The cold flow behavior of a distillate fuel such as diesel fuel is a function of its composition. The fuel is comprised of a mixture of hydrocarbons including normal paraffins, branched paraffins, olefins, aromatics and other non-polar and polar compounds. As the diesel fuel temperature decreases at the refinery, during transport, storage, or in a vehicle, one or more components of the fuel will tend to separate, or precipitate, as a wax.
The components of the diesel fuel having the lowest solubility tend to be the first to separate as solids from the fuel with decreasing temperature. Straight chain hydrocarbons, such as normal paraffins, typically have the lowest solubility in the diesel fuel. Generally, the paraffin crystals which separate from the diesel fuel appear as individual crystals. As more crystals form in the fuel, they ultimately create a network in the form of a gel to eventually prevent the flow of the fuel.
It is known to incorporate additives into diesel fuel to enhance the flow properties of the fuel at low temperatures. These additives are generally viewed as operating under either or both of two primary mechanisms. In the first, the additive molecules have a configuration which allows them to interact with the n-paraffin molecules at the growing ends of the paraffin crystals. The interacting additive molecules by steric effects act as a cap to prevent additional paraffin molecules from adding to the crystal, thereby limiting the dimensions of the existing crystal. The ability of the additive to limit the dimensions of the growing paraffin crystal is evaluated by low temperature optical microscopy or by the pour point depression (PPD) test, ASTM D 97, discussed generally above.
In the second mechanism, the flow modifying additive may improve the flow properties of diesel fuel at low temperatures by functioning as a nucleator to promote the growth of smaller size crystals. This modified crystal shape permits improved flow by altering the n-paraffin crystallization behavior, which is normally evaluated by tests such as the Cold Filter Plugging Point (CFPP) Test, IP 309.
Additional, secondary, mechanisms involving the modification of wax properties in the fuel by incorporation of additives include, but are not limited to, dispersal of the wax in the fuel and solubilization of the wax in the fuel.
The range of available diesel fuels includes Grade No. 2-D, defined in ASTM D 975 as a general purpose, middle distillate fuel for automotive diesel engines, which is also suitable for use in non-automotive applications, especially in conditions of frequently varying speed and load. Certain of these Grade No. 2-D (No. 2) fuels may be classified as being hard to treat when using one or more additives to improve flow. A hard-to-treat diesel fuel is either unresponsive to a flow improving additive, or requires increased levels of one or more additives relative to a normal fuel to effect flow improvement.
Fuels in general, and diesel fuels in particular, are mixtures of hydrocarbons of different chemical types (i.e., paraffins, aromatics, olefins, etc.) wherein each type may be present in a range of molecular weights and carbon lengths. Resistance to flow is a function of one or more properties of the fuel, the properties being attributed to the composition of the fuel. For example, in the case of a hard-to-treat fuel the compositional properties which render a fuel hard to treat relative to normal fuels include a narrower wax distribution; the virtual absence of very high molecular weight waxes, or inordinately large amounts of very high molecular weight waxes; a higher total percentage of wax; and a higher average normal paraffin carbon number range. It is difficult to generate a single set of quantitative parameters which define a hard-to-treat fuel. Nevertheless, some of the measured parameters which tend to identify a hard-to-treat middle distillate fuel include a temperature range of less than 100° C. between the 20% distilled and 90% distilled temperatures (as determined by test method ASTM D 86), a temperature range less than 25° C. between the 90% distilled temperature and the final boiling point (see ASTM D 86), and a final boiling point above or below the temperature range 360° to 380° C.
Hard-to-treat fuels are particularly susceptible to cold flow impairment due to the composition of the fuel. In a hard-to-treat fuel a large quantity of wax tends to settle at a faster rate. As a result, attachments form irregularly on the face of the crystal and increase the difficulty for a flow improver to arrest growth.
There continues to be a demand for additives which improve the flow properties of distillate fuels. Further, there remains a need for additive compositions which are capable of improving the flow properties of hard-to-treat fuels.
SUMMARY OF THE INVENTION
It has been found that ethylene vinyl acetate isobutylene terpolymer combined with either certain imide or maleic anhydride olefin copolymer additives with at least a minimum concentration by weight of substituents on the additives having a specified range of carbon chain lengths, alone or in combination with alkyl phenols having a specified range of carbon chain lengths, and optionally an ethylene vinyl acetate copolymer, will significantly improve the cold flow properties of certain distillate fuels such as No. 2 diesel fuel beyond what is expected from the terpolymer alone or from other ethylene vinyl acetate-based cold flow improvers. It has been found in addition that ethylene vinyl acetate isobutylene terpolymer combined with certain alkyl phenol additives and optionally an ethylene vinyl acetate copolymer will also significantly improve the cold flow properties of certain distillate fuels such as No. 2 diesel fuel.
Copending application Ser. No. 09/311,465 filed on the same date herewith is directed to cert
Equistar Chemicals LP
Guo Shao
Medley Margaret
LandOfFree
Cold flow improvers for distillate fuel compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cold flow improvers for distillate fuel compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cold flow improvers for distillate fuel compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2541077