Fuel and related compositions – Liquid fuels – Solid hydrocarbon polymer containing
Patent
1992-08-28
1996-06-11
Mulcahy, Peter D.
Fuel and related compositions
Liquid fuels
Solid hydrocarbon polymer containing
524239, C08L 116
Patent
active
055251285
DESCRIPTION:
BRIEF SUMMARY
This invention relates to fuel compositions, and more especially to fuel compositions susceptible to wax formation at low temperatures.
Heating oils and other distillate petroleum fuels, for example, diesel fuels, contain alkanes that at low temperature tend to precipitate as large crystals 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 naturally desirable since they are less likely to clog a filter; certain additives inhibit the wax from crystallizing as platelets and cause it 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.
The present invention is concerned to provide a fuel additive effective both to improve low temperature flow of the fuel and also to inhibit wax settling.
In one aspect, the present invention is directed to the use, as a wax crystal modifier in a fuel oil, of a copolymer derived from ethylene and at least one alpha-olefin of the formula CH.sub.2 .dbd.CHR.sup.1 wherein R.sup.1 represents an alkyl group having from 1 to 18 carbon atoms, at least 30% of the chains of which polymer have terminal ethenylidene unsaturation, the polymer having a number average molecular weight in the range of from 300 to 15000 and an ethylene content in the range of from 40 to 90 mole per cent, the polymer being obtainable by polymerization in the presence of a metallocene catalyst.
The invention also provides a fuel oil composition comprising the above-specified ethylene/alpha-olefin copolymer, advantageously one containing from 0.005% to 0.1%, preferably from 0.01 to 0.06%, by weight of the copolymer, based on the weight of the fuel oil. The fuel oil is more especially a middle distillate fuel oil and may be, for example, a straight run distillate or a fraction cracked either thermally or catalytically, or a mixture of any two or more such fuels.
The invention further provides a fuel oil additive concentrate comprising 2 to 90%, advantageously 5 to 50%, by weight of the specified copolymer in admixture with fuel oil or a solvent miscible with fuel oil.
The polymers employed in this invention are polymers of ethylene and at least one alpha-olefin having the formula H.sub.2 C.dbd.CHR.sup.1 wherein R.sup.1 is as defined above and wherein the polymer contains a high degree of terminal ethenylidene unsaturation. Preferably R.sup.1 in the above formula is alkyl of from 1 to 8 carbon atoms, and more preferably is alkyl of 1 carbon atom. Therefore, useful comonomers with ethylene in this invention include, in addition to propylene, butene-1, hexene-1, octene-1, 4-methylpentene-1, decene-1, dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecene-1 and mixtures thereof (e.g., mixtures of propylene and 1-butene, and the like).
The molar ethylene content of the polymers employed in this invention is advantageously from 50% to 80%, and preferably from 60% to 80%, although the peak of activity, as measured by the cold filter plugging point (CFPP) test varies somewhat depending on the molecular weight of the polymer and on the fuel under consideration. The CFPP test is that described in BS 2869, and the "Jour
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McAleer Andrew M.
Yearwood Gerald P.
Exxon Chemical Patents Inc.
Mehon John J.
Mulcahy Peter D.
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