Fuel and related compositions – Liquid fuels – Containing organic -c
Reexamination Certificate
1998-12-02
2001-02-13
Howard, Jacqueline V. (Department: 1764)
Fuel and related compositions
Liquid fuels
Containing organic -c
C585S009000
Reexamination Certificate
active
06187065
ABSTRACT:
This invention relates to additives for improving the low temperature properties, particularly flow and/or filterability properties, of oils and to oil compositions exhibiting such improved properties.
Many oils, particularly those derived from petroleum sources or from animal or vegetable oils and fats, are susceptible to the formation of wax at low temperatures. This problem is well known in the art.
In particular, fuel oils, whether derived from petroleum or from animal or vegetable sources, contain components that at low temperature tend to precipitate as large crystals or spherulites 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 oil will still flow is known as the pour point.
As the temperature of fuel oils fall and approach 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 fuel problems are well recognised 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. The wax from a diesel fuel, which is primarily an n-alkane wax, crystallises as platelets; certain additives, usually referred to as cold flow improves, inhibit this, causing the wax to adopt an acicular habit, the resulting needles being more likely to pass through a filter than platelets.
A further problem encountered at temperatures low enough for wax to form in a fuel is the settlement of the wax to the lower region of any storage vessel. This has two effects; one in the vessel itself where the settled layer of wax may block an outlet at the lower end, and the second in subsequent use of the fuel. The composition of the wax-rich portion of fuel will differ from that of the remainder, and will have poorer low temperature properties than that of the homogeneous fuel from which it is derived.
There are various additives available which change the nature of the wax formed, so that it remains suspended in the fuel, achieving a dispersion of waxy material throughout the depth of the fuel in the vessel, with a greater or lesser degree of uniformity depending on the effectiveness of the additive on the fuel. Such additives may be referred to as wax anti-settling additives.
Petroleum waxes, i.e. waxes derived from petroleum sources, comprise complex mixtures of hydrocarbons, including normal and branched alkanes and cycloalkanes. A wide variety of petroleum waxes have been produced commercially and such waxes differ in the relative proportions of different hydrocarbon components, a result of differences both in petroleum source materials and in the separation and processing techniques employed to obtain a particular wax. Waxes may, for example, be obtained by dewaxing of wax-containing petroleum distillate fractions, involving physical separation and subsequent fractionation of the separated waxy material into individual waxes suitable for particular applications and having particular properties.
The art describes certain waxes as suitable additives for improving the low temperature properties of fuel oils. EP-A-0 239 320 describes the addition to distillate fuels of n-alkanes in an amount sufficient to raise the amount of C
24
and above n-alkanes in the resulting composition to above 0.35 wt %, whereby the response of such fuels to conventional low temperature flow improvers is improved. U.S. Pat. No. 4,210,424 describes additive compositions comprising normal paraffinic wax of average molecular weight in the range of 300 to 650. Examples of suitable normal paraffinic waxes include slack wax and slop wax. Such waxes may consist of C
20
to C
45
n-alkanes.
GB 1,465,175 and GB 1,468,791 describe the use of microcrystalline waxes having melting points in the range of 145° F. to 190° F. (approximately 63° C. to 88° C.) and number average molecular weights in the range of 490 to 800. Exemplified is a wax of melting point 167° F. (75° C.) and number average molecular weight of 634, containing 22.6% n-paraffins. Such waxes are described as useful for improving the low temperature flowability of petroleum middle distillate fuels in combination with a hydrocarbyl succinamic acid or amine or ammonium salt thereof (GB 1,465,175) or a halogenated homo- or copolymer of ethylene (GB 1,468,791).
GB 1,465,176 describes the use of an essentially saturated, amorphous, normally solid petroleum hydrocarbon fraction having a melting point in the range of 80° F. to 140° F. (approximately 27° C. to 60° C.) and having number average molecular weights in the range of 475 to 600. Exemplified is an amorphous fraction having a melting point of 115° F. (approximately 46° C.), aromatic content of 7.4% and total alkane content of 91.6%, and obtained as a by-product from the dewaxing of a heavy paraffinic crude oil. Such amorphous materials are also described as effective low temperature additives in combination either with halogenated homo- or copolymers of ethylene or with succinamic acids or amine or ammonium salts thereof.
We have now discovered that a certain type of petroleum wax shows excellent performance as a low temperature flow improver additive for oils, and especially fuel oils, as well as being easily handled at normal operating temperatures. Such a wax gives excellent results in combination with a variety of low temperature flow improver additives and improves the effects thereof in a variety of oils.
In a first aspect, this invention provides an additive composition comprising one or more petroleum waxes, characterised in that at least one wax has a melting point in the range of 42° C. to 59° C. and a refractive index in the range of 1.445 to 1.458, measured at 70° C.
In a second aspect, the invention provides an additive concentrate composition comprising the additive composition of the first aspect in admixture with a compatible solvent thereof.
In a third aspect, this invention provides a fuel oil composition comprising fuel oil and a minor proportion either of the composition of the first or second aspect or of at least one petroleum wax having a melting point in the range of 42° C. to 59° C. and a refractive index in the range of 1.445 to 1.458, measured at 70° C.
Other aspects of the invention include the use of the additive of the first aspect or wax defined under the first aspect, or of the concentrate of the second aspect, in a fuel oil to improve the low temperature flow properties thereof; a method for improving same properties of a fuel oil, comprising the addition thereto of the additive, wax or concentrate; an oil refinery or depot containing the additive, wax, concentrate or fuel oil composition; and a fuel oil combustion or transportation system containing the fuel oil composition.
The additive composition (first aspect of the invention).
The additive comprises one or more petroleum waxes having the above-defined melting point and refractive index characteristics.
Waxes have conventionally been defined by reference to their gross physical characteristics, in view of the large and varied number of hydrocarbon components which they contain, and the difficulties in separating such closely-homologous hydrocarbon molecules. “Industrial waxes” by H. Bennett and published in 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. According to this invention, a certain sub-class of waxes—namely those having certain defined ranges of melting point and refractive index are particularly effective for improving the low temperature flow properties of oils, and especially fuel oils such as middle distillate fuel oils. Whilst not
Exxon Chemical Patents Inc
Howard Jacqueline V.
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