Oil additives and compositions

Details Oil additives and compositions Oil additives and compositions

1997-06-12

2001-06-19

Medley, Margaret (Department: 1714)

Fuel and related compositions

Liquid fuels

Containing organic -c

Reexamination Certificate

active

06248141

ABSTRACT:

This invention relates to oil compositions, primarily to fuel oil compositions, for example fuel oil compositions especially susceptible to wax formation at low temperatures, and to the use of additive compositions in such oil compositions to improve their low temperature properties.
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 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.
Effective wax crystal modification (as measured by CFPP (cold filter plug point) and other operability tests, as well as simulated and field performance) may be achieved by ethylene-vinyl acetate or propionate copolymer (EVAC or EVPC)-based flow improvers. CFPP, as used in this specification, is measured as described in “Journal of the Institute of Petroleum”, 52 (1966), 173.
In EP-A-45342 is described a cold flow additive, based on an EVAC modified by esterification with 2-ethylhexanoic, acrylic, and phthalic acids.
In “Wissenschaft und Technik” 42(6), 238 (1989), M. Ratsch & M. Gebauer describe cold flow additives including an EVAC esterified with, inter alia, n-hexanoic acid.
In U.S. Pat. No. 3,961,916, middle distillate flow improvers are described which comprise a wax growth arrestor and a nucleating agent, the former being preferably a lower molecular weight ethylene-vinyl ester copolymer with a higher ester content, the latter preferably a higher molecular weight copolymer with a lower ester content, the esters preferably, but not necessarily, both being vinyl acetate.
In DE-AS-2407158, middle distillate flow improvers are described, comprising a mixture of low molecular weight ethylene-vinyl ester and ethylene-acrylic acid ester copolymers, both containing at least 40 mole percent of the ester component.
It has, however, proved difficult to treat certain oils to reduce their CFPP. Particularly difficult are those with higher wax contents, i.e., in excess of 2.5% (measured at 10° C. below cloud point) and more especially above 2.9%, in particular, those with 3.0% wax or more. Especially difficult are those fuels obtained from high wax content crudes with a relatively low final boiling point, e.g., at most 370° C. and more especially at most 360° C.
The present invention is concerned to provide an oil, especially a fuel oil, additive effective to improve low temperature flow of a higher wax content oil, and is based on the observation that certain copolymers of ethylene with an unsaturated ester are effective cold flow improvers having advantages over previously proposed compositions for such oils.
In a first aspect, the present invention provides the use of an oil soluble ethylene copolymer having in addition to units derived from ethylene units of the formula
—CH
2
CROOCR
1
— or —CH
2
CRCOOR
1
—  I,
wherein R represents H or CH
3
and R
1
represents a hydrocarbyl group having at least 2 carbon atoms, to improve the low temperature properties of an oil having a wax content of at least 2.5% by weight, measured at 10° C. below cloud point by differential scanning calorimetry.
In a second aspect, the invention provides a composition comprising an oil having a wax content of at least 2.5%, measured at 10° C. below cloud point by differential scanning calorimetry, and a minor proportion of an ethylene copolymer having in addition to units derived from ethylene units of the formula I as defined above.
The invention is especially applicable to oils having, by weight, a wax content of at least 2.9%, and more especially to those having a wax content of at least 3.0%. More especially, the invention is useful in oils having a final boiling point of up to 370° C., particularly oils with a final boiling point up to 360° C.
Advantageously, the molar proportion of units I in the ethylene copolymer is up to 35%. In one embodiment of the invention, the molar proportion is more especially from 1 to 25%, preferably from 10 to 20%, and most preferably from 11 to 16%. In this embodiment, advantageously, the number average molecular weight of the copolymer, measured by gel permeation chromatography, is at most 14000, more advantageously in the range of 1400 to 7000, preferably from 2000 to 5500, and most preferably about 4000.
In a second embodiment, the polymer according to the invention may contain up to 10, preferably from 1 to 7.5, molar per cent of ester units and have a number average molecular weight of at most 20,000, preferably from 3,000 to 10,000.
Advantageously, the linearity of the polymer as expressed by the number of methyl groups per 100 methylene units, as measured by proton NMR, is from 1 to 15.
As used in this specification the term “hydrocarbyl” refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon character. Among these, there may be mentioned hydrocarbon groups, including aliphatic, (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl or cycloalkenyl), aromatic, aliphatic and alicyclic-substituted aromatic, and aromatic-substituted aliphatic and alicyclic groups. Aliphatic groups are advantageously saturated. These groups may contain non-hydrocarbon substituents provided their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl group is substituted, a single (mono) substituent is preferred. Examples of substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl. The groups may also or alternatively contain atoms other than carbon in a chain or ring otherwise composed of carbon atoms. Suitable hetero atoms include, for example, nitrogen, sulfur, and, preferably, oxygen. Advantageously, the hydrocarbyl group contains at most 30, preferably at most 15, more preferably at most 10 and most preferably at most 8, carbon atoms. Advantageously, the hydrocarbyl group contains at least 3 carbon atoms.
Advantageously R represents H. Advantageously R
1
represents an alkenyl or as indicated above, preferably, an alkyl group, which is advantageously linear. If the alkyl or alkenyl group is branched, for example, as in the 2-ethylhexyl group, the &agr;-carbon atom is advantageously part of a methylene group. Advantageously, the alkyl or alkenyl group contains up to 29 carbon atoms, preferably from 2 to 14 carbon atoms, and more preferably from 3 to 9, especially 3 to 7, carbon atoms. As examples of alkyl or alkenyl groups there may be mentioned propyl, n-butyl, iso-butyl, and isomers, preferably the linear isomers, of pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and icosyl, and their corresponding alkenyl, advantageously alk-omega-enyl, radicals. R
1
most preferably represents pentyl or heptyl

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