Fuel and related compositions – Liquid fuels – Containing organic -c
Patent
1997-07-01
2000-11-07
Medley, Margaret
Fuel and related compositions
Liquid fuels
Containing organic -c
44395, C10L 118
Patent
active
061430447
DESCRIPTION:
BRIEF SUMMARY
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 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 flow 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.
In "Wissenschaft und Technik" 42(6), 238 (1989), M. Ratsch & M. Gebauer describe cold flow additives including an EVAC which has been hydrolysed and reesterified with, inter alia, propionic, n-pentanoic and n-hexanoic acids. A preference is expressed for esterifying acids to be straight-chain; a branched chain 3-methyl butanoic acid esterified copolymer gave significantly inferior results to those obtained using n-pentanoic acid esterified material.
In JP-A-58129096, cold flow additives comprising ethylene-vinyl carboxylic acid esters are described, the esterifying acid having a total carbon atom number of from 4 to 8, the additives being especially useful in a narrow boiling middle distillate fuel oil. The degree of branching of the main chain as measured by proton NMR is said to be at at least 6 alkyl branches per 100 methylene groups.
In WO 94/00536, cold flow additives comprising a terpolymer of ethylene and two different unsaturated esters are disclosed. Terpolymers are also described in EP-A-493769, the starting monomers being ethylene, vinyl acetate, and vinyl neo-nonanoate or -decanoate, and in the references cited in the search report on that application.
In British Specification No. 913715, ethylene-vinyl ester copolymers are proposed as pour point depressants for middle distillate fuels; as esterifying acids there are mentioned saturated aliphatic carboxylic acids containing from 4 to 10, 12, and 18 carbon atoms in their alkyl groups, the examples including n-octanoic acid.
British Specification No. 1,314,855 discloses terpolymers prepared from ethylene, vinyl acetate, and a vinyl ester of a long-chain carboxylic acid. Suitable long chain acids include C.sub.8 -C.sub.30 saturated carboxylic acids, for example lauric, myristic, palmitic and stearic acids. The terpolymers are described as useful viscosity index modifiers in lubricating oil compositions.
British Specification No. 1,244,512 discloses terpolymers of ethylene, a vinyl ester of a C.sub.2 to C.sub.4 mono-carboxylic acid and a copolymerisable unsaturated ester having C.sub.10 to C.sub.22 alkyl groups. The latt
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patent: 3447915 (1969-06-01), Otto
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Bock Jan
Brod Ramah Jessica
Davies Brian William
Ibrahim Tuncel
Exxon Chemical Patents Inc
Medley Margaret
Toomer Cephia D.
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