Fuel and related compositions – Liquid fuels – Containing organic -c
Reexamination Certificate
1998-12-02
2001-07-03
Medley, Margaret (Department: 1714)
Fuel and related compositions
Liquid fuels
Containing organic -c
C044S394000, C044S395000, C044S397000, C044S400000, C044S403000
Reexamination Certificate
active
06254650
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 additives for use in such fuel oil compositions, and to the use of the additives to improve the cold flow properties of fuels.
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 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. 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 flow improvers, for example, by ethylene-vinyl acetate (EVAC) or propionate copolymers.
The present invention provides an additive composition, suitable to improve cold flow characteristics of an oil, comprising
(i) an oil-soluble hydrogenated block diene polymer, comprising at least one crystallizable block, obtainable by end-to-end polymerization of a linear diene, and at least one non-crystallizable block, the non-crystallizable block being obtainable by 1,2-configuration polymerization of a linear diene, by polymerization of a branched diene, or by a mixture of such polymerizations,
(ii) a mixture of saturated hydrocarbons, at least some of which have a number of carbon atoms within the range of from 15 to 60, and
(iii) a wax growth arrestor.
The invention also provides the use of a composition comprising components (i) and (ii) as a nucleating agent to improve the cold flow properties of an oil.
In British Specification No. 1490563, there is disclosed the use of a hydrogenated homopolymer of butadiene or a copolymer of butadiene with a C
5
to C
8
diene as a cold flow improver for fuels. The copolymer is produced by polymerizing, e.g., a butadiene-isopropene mixture. GB-A-2087425 describes the use of a reaction product of a cyclic anhydride with an N-alkyl polyamine combined with, inter alia, a hydrogenated butadiene-isoprene copolymer.
WO 92/16567, the entire disclosure of which is incorporated herein by reference, describes hydrogenated block copolymers of butadiene and, inter alia, isoprene, and oleaginous compositions containing them. Their use is predominantly as viscosity index improvers in lubricating oils, but there are also references to use in fuels.
WO 92/16568, the entire disclosure of which is incorporated herein by reference, describes hydrogenated block polymers containing 1,4-butadiene and 1,2-butadiene addition products. Their uses are said to be similar to those of the polymers of WO 92/16567.
Advantageously, the hydrogenated block copolymer used in the present invention comprises at least one substantially linear crystallizable segment or block and at least one segment or block that is essentially not crystallizable. Without wishing to be bound by any theory, it is believed that when butadiene is homopolymerized with a sufficient proportion of 1,4 (or end-to-end) enchainments to provide a substantially linear polymeric structure then on hydrogenation it resembles polyethylene and crystallizes rather readily; when a branched diene is polymerised on its own or with butadiene a branched structure will result (e.g., a hydrogenated polyisoprene structure will resemble an ethylene-propylene copolymer) that will not readily form crystalline domains but will confer fuel oil solubility on the block copolymer.
Advantageously, the block copolymer before hydrogenation comprises units derived from butadiene only or from butadiene and at least one comonomer of the formula
CH
2
═CR
1
—CR
2
═CH
2
wherein R
1
represents a C
1
to C
8
alkyl group and R
2
represents hydrogen or a C
1
to C
8
alkyl group. Advantageously the total number of carbon atoms in the comonomer is 5 to 8, and the comonomer is advantageously isoprene. Advantageously, the copolymer contains at least 10% by weight of units derived from butadiene.
After hydrogenation, the copolymer advantageously contains at least 10%, preferably at least 20%, and most preferably from 25 to 60%, by weight of at least one crystalline or crystallizable segment composed primarily of methylene units; to this end the crystallizable segment before hydrogenation advantageously has an average 1,4 or end-to-end enchainment of at least 70 preferably at least 85, mole per cent. The hydrogenated block copolymer comprises at least one low crystallinity (or difficultly crystallizable) segment composed of methylene and substituted methylene units, derived from one or more alkyl-substituted monomers described above, e.g., isoprene and 2,3-dimethylbutadiene.
Alternatively, the low crystallinity segment may be derived from butadiene by 1,2 enchainment, in which the segment has before hydrogenation an average 1,4 enchainment of butadiene of at most 30, preferably at most 10, percent. As a result, the polymer comprises 1,4-polybutadiene as one block and 1,2-polybutadiene as another. Such polymers are obtainable by, e.g., adding a catalyst modifier, as described in the above-identified WO92/16568.
A further advantageous block copolymer is a hydrogenated tapered block or segmented copolymer, advantageously of butadiene and at least one other conjugated diene, preferably isoprene. Such a block copolymer may be obtained by anionically copolymerizing in hydrocarbon solution in, for example, a batch reactor, a mixture containing butadiene monomer and at least one other conjugated diene monomer to form a precursor copolymer having at least 75 weight percent 1,4-configuration of the butadiene and at least one other conjugated diene and then hydrogenating said precursor copolymer.
During the initial formation of the unhydrogenated precursor copolymer of butadiene and at least one other conjugated diene, butadiene will be preferentially polymerized. The concentration of monomers in solution changes during the course of the reaction in favour of the other conjugated diene as the butadiene is depleted. The result is a precursor copolymer in which the copolymer chain is higher in butadiene concentration in the chain segments grown near the beginning of the reaction and higher in the other conjugated diene concentration in the chain segments formed near the end of the reaction. These copolymer chains are accordingly described as tapered in composition. Upon hydrogenation the butadiene rich portion of the polymer becomes rich in methylene units. Therefore, in each of these hydrogenated generally linear copolymer molecules two longitudinal segments are present, gradually merging into each other without sharp boundaries. One of the outer segments consists nearly completely of methylene units derived from the hydrogenation of the butadiene in the 1,4-configuration and contains only small amounts of substituted methylene units derived from the hydro
Exxon Chemical Patents Inc
Medley Margaret
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