Fuel and related compositions – Liquid fuels – Containing organic -c
Reexamination Certificate
1998-08-04
2001-05-29
McAvoy, Ellen M. (Department: 1764)
Fuel and related compositions
Liquid fuels
Containing organic -c
C508S475000
Reexamination Certificate
active
06238447
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, to copolymers for use with such fuel oil compositions, and to methods for their manufacture.
Fuel oils, whether derived from petroleum or from vegetable sources, contain components, e.g., alkanes, 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 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 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 alkane wax, crystallizes as platelets; certain additives inhibit this and cause the wax 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 cold filter plugging point (CFPP) and other operability tests, as well as simulated and field performance) may be achieved by ethylene-vinyl acetate (EVAC) or propionate copolymer-based flow improvers.
British Specification No. 1,086,036, EP-A-527,322 and EP-A-518,406 describe terpolymers suitable as latices for coatings, these terpolymers being formed by copolymerizing ethylene with a vinyl ester of a tertiary or quaternary aliphatic carboxylic acid and a further ester monomer which may be vinyl acetate.
British Specification No. 1,314,855 describes terpolymers of ethylene, vinyl acetate and a vinyl ester of a long-chain carboxylic acid which may be a saturated carboxylic acid having 8 to 30 carbon atoms. The only branched-chain carboxylic acid specifically disclosed is isostearic acid (C
18
). These terpolymers are described as useful in lubricating oils as viscosity index improvers.
British Specification No. 1,244,512 describes terpolymers of ethylene, a vinyl ester of a C
2
to C
4
monocarboxylic acid and an unsaturated ester having a C
10
to C
22
alkyl group, and preferably of the formula.
Wherein X is hydrogen or a methyl group, and Y is a OOCR or —COOR wherein R is preferably a C
10
to C
16
straight chain or branched chain alkyl group. All the specifically disclosed esters wherein Y is OOCR have straight chain alkyl groups.
WO 96/07718 discloses oil soluble ethylene terpolymers containing ethylene units and different vinyl ester units, and their use as additives for improving the low temperature flow properties of fuel oil compositions. Polymer examples 1 to 4 inclusive on page 19 (Table 1) are ethylene-vinyl acetate-vinyl 2-ethyl hexanoate terpolymers having various proportions of the two unsaturated esters, as well as differing number average molecular weights and branching characteristics.
The polymers of WO 96/07718 are effective low temperature flow improvers and have the advantage of being manufactured from commercially available vinyl ester monomers. However, there is a continual need in the art to produce more effective polymers giving improved performance. Surprisingly, it has now been found that certain detailed characteristics of the polymer structure may be controlled to provide more effective additives. In particular, Applicant has found that optimal performance can be defined by reference to Mn, the degree of branching and the proportions of monomer units of the formula (I) and II present in the polymer.
In a first aspect therefore, this invention provides an additive composition comprising an oil soluble ethylene polymer comprising, in addition to units derived from ethylene, units of the formula:
and units of the formula:
wherein each R
1
and R
2
group independently represents hydrogen or methyl; each R
3
group independently represents an alkyl group having between 1 and 4 carbon atoms; each R
4
group independently represents a branched chain alkyl group having up to 15 carbon atoms and different from R
3
;
characterised in that the value P for the polymer lies within the range of 25 to 60, P being defined as:
P
=
number
average
molecular
weight
(
Degree
of
branching
)
(
mole
%
of
units
(
I
)
)
(
mole
%
of
units
(
II
)
)
wherein the degree of branching of the polymer is the number of methyl groups per 100 methylene units, as measured by proton NMR and corrected for the number of methyl and methylene groups in R
3
and R
4
groups.
In a second aspect, this invention provides an additive concentrate composition comprising the additive of the first aspect and a mutually-compatible solvent thereof.
In a third aspect, this invention provides an oil composition comprising an oil and a minor amount of the composition of the first or second aspect.
In a fourth aspect, this invention provides the polymer defined under the first aspect.
In a fifth aspect, this invention provides the use of the polymer of the fourth aspect, or of the composition of the first or second aspects, to improve the low temperature flow properties of an oil.
In the sixth aspect, this invention provides a method for improving the low temperature properties of an oil, comprising admixture of the oil with the composition of the first or second aspects, or the polymer of the fourth aspect.
The polymers defined under this invention prove highly effective in comparison to analogous polymers not having a P value satisfying the range recited above.
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Infineum USA L.P.
McAvoy Ellen M.
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