Oil compositions

Details Oil compositions Oil compositions

2000-02-07

2003-04-29

Medley, Margaret (Department: 1714)

Fuel and related compositions

Liquid fuels

Containing organic -c

C044S388000, C044S400000, C044S447000

Reexamination Certificate

active

06554876

ABSTRACT:

This invention relates to oil compositions susceptible to the formation of wax at low temperatures, and to materials capable of improving the low temperature flow, and particularly filterability, characteristics of such oils. This invention especially relates to fuel oils especially those having narrow boiling ranges and having relatively high wax contents, and to additives for treatment thereof.
The problem of wax formation in oils is well known in the art.
In particular, lubricating and 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 oil will still flow is known as the pour point.
As the temperature of fuel oils fall and approach 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 fuel 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, crystallises as platelets; certain additives, usually referred to as cold flow improves, inhibit this, causing the wax to adopt an acicular habit, the resulting needles being more likely to pass through a filter than platelets.
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. Such additives may be referred to as wax anti-settling additives. European Patent Application No. 0 061 895 generically describes flow improver additives for distillate fuels which are polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof containing at least two C
10
to C
30
linear saturated alkyl groups and a polyoxyalkylene glycol of molecular weight 100 to 5,000, the alkyl group in said polyoxyalkylene glycol containing from 1 to 4 carbon atoms. Example 18 discloses a discrete ester of the formula:
formed by the reaction of an ethoxylated C
18
linear alcohol and one mole of behenic acid. Its combination with other additives is not disclosed. Examples of polyethylene glycol dibehenate (i.e. diester) compounds are used in combination with other cold flow additives.
There exists in the art a continual need for more effective low temperature flow and filterability improvers and in particular for additives showing enhanced wax crystal modification over prior-art materials.
It has now surprisingly been found that certain esters or ethers of certain ethoxylated alcohols show surprisingly improved performance over the specific compounds disclosed in EP-A-0 061 895, when used in combination with other cold flow improvers as additives for improving the low temperature flow and filterability properties of oil systems.
In a first aspect therefore, the invention provides an additive composition comprising components (a) and (b), wherein (a) is selected from the group consisting of:
(a
1
) one or more esters obtainable by the reaction of (i) an aliphatic monocarboxylic acid having 10 to 40 carbon atoms, and (ii) an alkoxylated aliphatic monohydric alcohol wherein the alcohol has greater than 10 carbon atoms prior to alkoxylation and wherein the degree of alkoxylation is 5 to 30 moles of alkylene oxide per mole of alcohol, or
(a
2
) one or more ethers obtainable by the reaction of reactant (ii) above with (iii) an aliphatic hydrocarbon compound bearing an electrophilic group, or
(a
3
) a mixture of a
1
and a
2
;
and wherein component (b) is a cold flow improver additive different from component (a).
In a second aspect, the invention provides an oil composition comprising an oil and a minor proportion of the additive composition of the first aspect of the invention.
In a third aspect, the invention provides the use of the additive composition of the first aspect of the invention to improve the low temperature properties of an oil.
The additives of the first aspect of the invention have been found to be surprisingly effective wax crystal modifying additives, in particular for fuel oils. Without being bound to any particular theory, it is thought that the degree of alkoxylation and nature of the aliphatic substituents in the ester and/or ether, in combination with the other cold flow improver, provide the excellent improvements obtained with these materials.
THE FIRST ASPECT OF THE INVENTION (ADDITIVE)
Component a
1
The ester may be formed from a single acid reactant (i) and single alcohol reactant (ii), or from mixtures of acids (i) or alcohols (ii) or both. In the latter cases, a mixture of ester products will be formed which may be used without separation if desired, or separated to give discrete products before use.
The acid reactant (i) preferably has 18 to 30 carbon atoms, more preferably 18 to 22 carbon atoms such as 20 or 22 carbon atoms. The acid is preferably a saturated aliphatic acid, more preferably an alkanoic acid. Alkanoic acids of 18 to 30 carbon atoms are particularly useful. n-Alkanoic acids are preferred. Such acids include behenic acid and arachidic acid, with behenic acid being preferred. Where mixtures of acids are used, it is preferred that the average number of carbon atoms in the acid mixture lies in the above-specified ranges and preferably the individual acids within the mixture will not differ by more than 8 (and more preferably 4) carbon numbers.
The alcohol reactant (ii) is preferably derived from an aliphatic monohydric alcohol having no more than 40 and preferably no more than 28 carbon atoms, and more preferably in the range of from 18 to 26 (or better no more than 24) carbon atoms, prior to alkoxylation. The range of 20 to 22 is particularly advantageous for obtaining good wax crystal modification. The aliphatic alcohol is preferably a saturated aliphatic alcohol, especially alkanol (i.e. an alkyl alcohol). Alkanols having 20 to 28 carbon atoms, and particularly 20 to 26, such as 20 to 22 carbon atoms are preferred. n-Alkanols are most preferred, particularly those having 20 to 24 carbon atoms, and preferably 20 to 22 carbon atoms.
The degree of alkoxylation of the aliphatic monohydric alcohol is preferably 10 to 25 moles of alkylene oxide per mole of alcohol, more preferably 15 to 25 moles. The alkoxylation is preferably ethoxylation, although propoxylation or butoxylation can also be used successfully. Mixed alkoxylation, for example a mixture of ethylene and propylene oxide units, may also be used.
Where the alcohol reactant (ii) is a mixture of alcohols, this mixture may comprise a single aliphatic alcohol alkoxylated to varying degrees, or a mixture of aliphatic alcohols alkoxylated to either the same or varying degrees. Where a mixture of aliphatic alcohols is used, the average carbon number prior to alkoxylation should be above 18 and preferably within the preferred ranges recited above. Preferably, the individual alcohols in the mixture should not differ by more than

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