Fuel and related compositions – Liquid fuels – Containing organic -c
Reexamination Certificate
1998-12-02
2002-10-01
McAvoy, Ellen M. (Department: 1764)
Fuel and related compositions
Liquid fuels
Containing organic -c
C044S393000, C044S394000, C044S459000, C508S450000, C508S451000, C508S496000, C508S497000, C508S475000
Reexamination Certificate
active
06458175
ABSTRACT:
This invention relates to oil compositions, primarily to fuel oil compositions, and more especially to fuel oil compositions susceptible to wax formation at low temperatures, and to additive compositions for such fuel oil compositions.
Heating oils and other distillate petroleum fuels, for example, diesel fuels, contain alkanes that at low temperature tend to precipitate as large crystals of wax in such a way as to form a gel structure which causes the fuel to lose its ability to flow. The lowest temperature at which the fuel will still flow is known as the pour point.
As the temperature of the fuel falls and approaches the pour point, difficulties arise in transporting the fuel through lines and pumps. Further, the wax crystals tend to plug fuel lines, screens, and filters at temperatures above the pour point. These problems are well recognized in the art, and various additives have been proposed, many of which are in commercial use, for depressing the pour point of fuel oils. Similarly, other additives have been proposed and are in commercial use for reducing the size and changing the shape of the wax crystals that do form. Smaller size crystals are desirable since they are less likely to clog a filter; certain additives inhibit the wax from crystallizing as platelets and cause it to adopt an acicular habit, the resulting needles being more likely to pass through a filter than are platelets. The additives may also have the effect of retaining in suspension in the fuel the crystals that have formed, the resulting reduced settling also assisting in prevention of blockages.
Effective wax crystal modification (as measured by CFPP and other operability tests, as well as simulated and field performance) may be achieved by ethylene-vinyl acetate or propionate copolymer (EVAC or EVPC)-based flow improvers.
In U.S. Pat. No. 3,961,916, middle distillate flow improvers are described which comprise a wax growth arrestor and a nucleating agent, the former being preferably a lower molecular weight ethylene-vinyl ester copolymer with a higher ester content, the latter preferably a higher molecular weight copolymer with a lower ester content, the esters preferably, but not necessarily, both being vinyl acetate.
In WO 94/00515, middle distillate flow improvers are disclosed which contain a mixture of two different ethylene-vinyl ester copolymers, or a single ethylene copolymer with two different vinyl esters, as nucleator optionally in admixture with an ethylene-vinyl ester copolymer arrestor, and a comb polymer, and other cold flow additives.
Similarly WO 94/00536 describes flow improvers containing a mixture of two different ethylene-vinyl ester copolymers, or a single ethylene copolymer with two different vinyl esters, as arrestor in admixture with an ethylene-vinyl ester copolymer nucleator and other cold flow additives.
Although ethylene unsaturated copolymers are very effective flow improvers in many middle distillate fuels, they are of limited utility in fuels of high wax content, i.e., with a wax content of at least about 3%, and more especially at least 3.5%, by weight or more at 10° C. below cloud point. Such a fuel is particularly difficult to treat if, in addition to a high waxy content, it is also characterized by a relatively low final boiling point, e.g., at most 370° C. and sometimes at most 360° C., or a narrow boiling range, e.g., one for which when distilled under ASTM D-86 conditions the 90%-20% temperature difference is in the range of from 700 to 100° C., for example at most 85° C. Earlier fuels of this type primarily originated from high waxy crude oils found in the Far East and Australia, but more recently, as a result of the requirement to reduce the sulphur and polynuclear hydrocarbon contents of fuels used in Europe and elsewhere, changes to refinery practices have taken place which have resulted in such fuels being produced worldwide.
In EP-A-239320 it is disclosed that the low temperature properties of a narrow-boiling, high wax content, fuel, having a narrow n-alkane distribution, may be improved by adding to the fuel an n-alkane mixture to effect a substantial increase in its content of C
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and higher n-alkanes.
The alkanes are added in the form of a wax, or a gas oil, and enhance the response of the fuel to ethylene-vinyl acetate copolymer cold flow improvers. The addition of several (e.g., 5 to 7) per cent by weight of a high boiling fraction to a fuel comprising heavy and medium gas oils and kerosene to improve its response is a common refinery practice.
The present invention is concerned to provide an oil, especially a fuel oil, additive effective to improve the low temperature flow properties of an oil, especially one having a wax content of at least 3.0% at 10° C. below cloud point (wax appearance temperature) and/or a 90%-20% (as measured by ASTM D-86) boiling range of at most 100° C. The invention is based on the observation that a composition comprising a saturated hydrocarbon mixture having a substantial content of C
15
molecules and higher, a nucleator other than an ethylene-vinyl acetate copolymer, and a wax growth arrestor is an effective cold flow improver even at a low treat rate, for example, below 1 % by weight of active ingredients based on the weight of the fuel.
In a first aspect, the present invention provides an additive composition comprising
(a) a mixture of saturated hydrocarbons, at least some of which have a number of carbon atoms within the range of from 15 to 60,
(b) a nucleating agent, other than an ethylenevinyl acetate copolymer and other than a mixture as defined in (a), and
(c) a wax growth arrestor, the weight ratio of (a):(b) being at least 0.85:1.
Advantageously the (a):(b) weight ratio is at least 0.9:1 and is preferably at least 1:1.
The composition may contain two or more nucleating agents (b); advantageously it contains two or more arrestors (c) and preferably, it contains two or more of both components (b) and (c). The composition may also contain two or more mixtures of hydrocarbons (a), which is advantageous if the mixtures differ in their carbon number contents. It is to be understood that the composition may contain an ethylene-vinyl acetate copolymer nucleating agent, in addition to the required component (b).
In a second aspect, the invention provides an additive composition comprising:
(a) at least two different mixtures of saturated hydrocarbons, in each of which mixtures there are at least some hydrocarbons having a number of carbon atoms within the range of 15 to 60,
(b) optionally, a nucleating agent, other than a mixture as defined in (a), and
(c) a wax growth arrestor.
The composition of the second aspect may contain two or more nucleating agents (b), and advantageously contains two or more arrestors (c).
When (b) is present, the (a):(b) weight ratio is advantageously at least 0.85:1, preferably at least 0.9:1 and more preferably at least 1:1.
Advantageously, component (a) the saturated hydrocarbon mixture comprises or the different mixtures comprise normal (linear) alkanes. Advantageously, the mixture has or mixtures have a boiling range from about 230 to 510° C. Advantageously, the mixture(s) contain(s) a spread of at least 16 carbon atoms from the lowest to the highest carbon number. Preferably, the mixture contains a substantial proportion of C
24
to C
32
, more preferably a substantial proportion of C
24
to C
28
, hydrocarbons, by weight. Advantageously, the number average molecular weight is in the range of 350 to 450. Advantageously, the mixture is a wax.
Waxes have conventionally been defined by reference to their physical characteristics, in view of the large and varied number of hydrocarbon components which they contain, and the difficulties in separating such closely related, and often homologous, hydrocarbon molecules. “Industrial Waxes”, H. Bennett, 1975, describes the different types of petroleum wax and indicates that the characteristics of melting point and refractive index have proved useful in classifying the variety of waxes available from different sources. Waxes are also typically
Lehmann Edwin William
Tack Robert Dryden
Exxon Chemical Patents Inc.
McAvoy Ellen M.
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