Fuel and related compositions – Liquid fuels – Containing organic -c
Patent
1997-10-23
1999-05-25
Howard, Jacqueline V.
Fuel and related compositions
Liquid fuels
Containing organic -c
44395, C10L 118
Patent
active
059066636
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, and to additive compositions for such fuel oil compositions.
Fuel oils, whether derived from petroleum or from 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 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, causing the wax to adopt an acicular habit, the resulting needles being more likely to pas 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.
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.
Although the way in which CFPP depressants and wax anti-settling additives function is not completely understood, there is evidence that their effectiveness depends to a significant extent on matching of the alkanes in the fuel to alkyl or alkylene chains in the additive, the growth of the alkane wax crystals being affected, for example, by the co-crystallization of an alkyl chain of similar length in an additive.
EP-A-493,769 describes the use of certain terpolymers as additives for petroleum distillates, in particular their use in improving the flowability of middle distillates as measured by the Cold Filter Plugging Point (CFPP) test. The terpolymers are made by polymerising ethylene, vinyl acetate, and vinyl neo-nonanoate or decanoate.
A problem in using said terpolymers is that, although their CFPP performance is satisfactory immediately after they are used to treat a distillate fuel, the CFPP performance of a so-treated fuel deteriorates with time. Such deterioration over time is referred to herein as `CFPP regression`.
The present invention provides a way of meeting the problem of CFPP regression encountered with such terpolymers, by use of a specific co-additive. Through use of such a co-additive, excellent CFPP performance is also achieved.
Thus, a first aspect of the invention is an oil-soluble additive comprising components (A) and (B) wherein ethylene, units of the formula: ##STR1## and units of the formula ##STR2## wherein R.sup.1 and R.sup.2, which may be the same or different, each represents H or methyl; and a number average molecular weight i
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Brown Gerald Ivan
Goberdhan Dhanesh Gordon
Exxon Chemical Patents Inc.
Howard Jacqueline V.
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