[0001] Mineral oils containing paraffin wax have the characteristic of becoming less fluid
as the temperature of the oil decreases. This loss of fluidity is due to the crystallization
of the wax into plate-like crystals which eventually form a sponqy mass entrapping
the oil therein.
[0002] It has long been known that various additives act as wax crystal modifiers when blended
with waxy mineral oils. These compositions modify the size and shape of wax crystals
and reduce the adhesive forces between the crystals and between the wax and the oil
in such a manner as to permit the oil to remain fluid at a lower temperature.
[0003] Various pour point depressants have been described in the literature and several
of these are in commercial use. For example, U.S. Pat. No. 3,048,479 teaches the use
of copolymers of ethylene and C
3-C
S vinyl esters, e.q. vinyl acetate, as pour depressants for fuels, specifically heatinq
oils, diesel and jet fuels. Hydrocarbon polymeric pour depressants based on ethylene
and hiqher alpha-olefins, e.q. propylene, are also known. U.S. Patent 3,961,916 teaches
the use of a mixture of copolymers, one of which is a wax crystal nucleator and the
other a growth arrestor to control the size of the wax crystals.
[0004] United Kingdom Patent 1263152 suqqests that the size of the wax crystals may be controlled
by using a copolymer having a lower degree of side chain branchin
q.
[0005] It has also been proposed in for example United Kingdom Patent 1469016 that the copolymers
of di-n-alkyl fumarates and vinyl acetate which have previously been used as pour
depressants for lubricating oils may be used as co-additives with ethylene/vjnyl acetate
copolymers in the treatment of distillate fuels with high final boiling points to
improve their low temperature flow properties. According to United Kingdom Patent
1469016 these polymers may be C
6 to C
18 alkyl esters of unsaturated C
4 to C
8 dicarboxylic acids particularly lauryl fumarate and lauryl-hexadecyl fumarate. Typically
the materials used are esters with an average of about 12 carbon atoms (Polymer A).
It is notable that the additives are shown not to be effective in the "conventional"
fuels of lower Final Boiling Point (Fuels III and IV).
[0006] With the increasing diversity in distillate fuels, types of fuel have emerged which
cannot be treated by the existing additives or which require an uneconomically high
level of additive to achieve the necessary reduction in their pour point and control
of wax crystal size for low temperature filterability to allow them to be used commercially.
One particular group of fuels that present such problems are those which have a relatively
narrow, and/or low boilin
q ran
qe. Another type of fuel difficult to treat are those with hi
qh final boilinq points and yet another are the hiah wax content fuels typically found
in the far east. Fuels are frequently characterised by their Initial Boiling Point,
Final Boiling Point and the interim temperatures at which certain volume percentaoes
of the initial fuel have been distilled. Fuels whose 20% to 90% distillation point
differ within the range of from 70 to 100°C and/or whose 90% boiling temperature is
from 10 to 25
0C of the final boiling point and/or whose final boiling points are between 340 and
370°C are generally considered narrow boilin
q fuels and can be oarticularly difficult to treat sometimes being virtually unaffected
by additives or otherwise requiring very high levels of additive. Fuels having final
boiling points above 370°C are sometimes known as high final boiling fuels and are
also difficult to treat. All distillations referred to herein are according to ASTM
D86.
[0007] With the increase in the cost of crude oil, it has also become important for a refiner
to increase his production of distillate fuels and to optimise his operations using
what is known as sharp fractionation again resulting in distillate fuels that are
difficult to treat with conventional additives or that require a treat level that
is unacceptably high from the economic standpoint. Typical sharply fractionated fuels
also have a 90% to final boiling point range of 10 to 25
0C usually with a 20 to 90% boiling range of less than 100
oC, generally 50 to 100°C. Both types of fuel have final boiling points above 340°C
generally a final boiling point in the range 340
0C to 370°C especially 340°C to 365°C.
[0008] In addition there is at times a need to lower what is known as the cloud point of
distillate fuels; the cloud point beinq the temperature at which the wax begins to
crystallise out from the fuel as it cools. This need is applicable to both the difficult
to treat fuels described above and the entire range of distillate fuels which typically
boil in the range 120
oC to 500o
C.
[0009] The copolymers of ethylene and vinyl acetate which have found widespread use for
improving the flow of the previously widely available distillate fuels have not been
found to be effective in the treatment of the narrow boiling and/or sharply fractionated
fuel described above. Furthermore use of mixtures as illustrated in United Kingdom
Patent 1469016 have not been found effective.
[0010] In our European Patent Applications 85301047.8, 85301048.7, 85301675.6 and 85301676.4,
we claim that copolymers containing very specific alkyl groups, such as specific n-alkyl
fumarate/vinyl acetate copolymers, are effective in both lowering the pour point of
the difficult to treat fuels described above and controllina the size of the wax crystals
to allow filterability including those of the lower final boiling point in which the
additives of United Kingdom Patent 1469016 were ineffective. We claim in these Applications
that these copolymers are effective in lowering the cloud point of many fuels over
the entire range of distillate fuels.
[0011] We have now found that although if one uses relatively highly branched fumarate ester
they are not effective additives the presence of a methyl branch on the alkyl chain
in the 1 or 2 position in the alkyl group does not detract from their performance
as an additive and can have economic and performance benefits.
[0012] The present invention therefore provides the use for improving the flow properties
of a distillate petroleum fuel oil boiling in the range 120°C to 500°C of an additive
comprising a polymer or copolymer containing at least 25 wt.% of an alkyl ester of
the general formula
wherein R
1 and R
2 are hydroqen or a C
1 alkyl group, e.q., methyl, R
4 is COOR
3, hydrogen or a C
1 to C
4 alkyl group preferably COOR
3 and R
3 has an average number of carbon atoms from 12 to 20 and contains a methyl branch
at the 1 and/or 2 position and the ester polymer or copolymer contains no more than
10 wt.% of ester monomer containinq alkyl qroups containing more than 20 carbon atoms
and preferably no more than 20 wt.% of ester monomer in which the alkyl group contains
fewer than 12 carbon atoms.
[0013] The composition of R
3 may vary within the polymer structure and some of the R
3 groups may be n-alkyl but no more than 10 wt.% should contain more branches than
the methyl groups at the 1 and/or 2 position. The additives are preferably used in
an amount from 0.0001 to 0.5 wt.%, based on the weiqht of the distillation petroleum
fuel oil, and the present invention also includes such treated distillate fuel.
[0014] The copolymer may be of a di-n alkyl ester of a dicarboxylic and may also contain
from 25 to 70 wt.% of a vinyl ester, an alkyl acrylate, methacrylate or alpha olefin.
[0015] The polymers used in the present invention preferably have a number average molecular
weight in the range of 1000 to 100,000, preferably 1,000 to 30,000 as measured, for
example, by Vapor Pressure Osmometry. The esters used to make the copolymers may be
prepared by esterifying the particular mono- or di-carboxylic acid with the appropriate
alcohol or mixture of alcohols. Examples of other unsaturated esters, are the alkyl
acrylates and methacrylates.
[0016] The dicarboxylic acid mono and di-ester monomers may be copolymerized with various
amounts, e.q. 5 to 70 mole %, of other unsaturated esters or olefins. Such other esters
include short chain alkyl esters having the formula:
where R' is hydrogen or a C
1 to C
4 alkyl group, R"1 is -COOR"" or -OOCR"" where R" is a C
1 to C
5 alkyl group branched or unbranched, and R"' is R" or hydrogen. Examples of these
short chain esters are methacrylates, acrylates, fumarates and maleates, the vinyl
esters such as vinyl acetate and vinyl propionate being preferred. More specific examples
include methyl methacrylate, isopropenyl acetate and butyl and isobutyl acrylate.
[0017] Our preferred copolymers contain from 40 to 60 mole % of a dialkyl fumarate and 60
to 40 mole % of vinyl acetate.
[0018] The preferred ester polymers are qenerally prepared by polymerisinq the ester monomers
in a solution of a hydrocarbon solvent such as heptane, benzene, cyclohexane, or white
oil, at a temperature generally in the range of from 20
*C to 150°C and usually promoted with a peroxide or azo type catalyst, such as benzoyl
peroxide or azodiisobutyronitrile, under a blanket of an inert gas such as nitrogen
or carbon dioxide, in order to exclude oxygen.
[0019] The additives of the present invention are particularly effective when used in combination
with other additives known for improving the cold flow properties of distillate fuels
qenerally, although they may be used on their own to impart a combination of improvements
to the cold flow behaviour of the fuel.
[0020] The additives of the present invention are particularly effective when used with
the polyoxyalkylene esters, ethers, ester/esters and mixtures thereof, particularly
those containinq at least one preferably at least two C
10 to C
30 linear saturated alkyl groups and a polyoxyalkylene qlycol group of molecular weight
100 to 5,000 preferably 200 to 5,000, the alkyl gorup in said polyoxyalkylene alycol
containinq from 1 to 4 carbon atoms. These materials form the subject of European
Patent Publication 0061895 A2.
[0021] The preferred esters, ethers or ester/ethers useful in the present invention may
be structurally depicted by the formula:
where R and R
1 are the same or different and are preferably
the alkyl group being linear and saturated and containing 10 to 30 carbon atoms, and
A represents the polyokyalkylene segment of the alycol in which the alkylene group
has 1 to 4 carbon atoms, such as a polyoxymethylene, polyoxyethylene or polvoxytrimethylene
moiety which is substantially linear; some degree of branchin
q with lower alkyl side chains (such as in polyoxypropylene alycol) may be tolerated
it is preferred that the glycol should be substantially linear.
[0022] Suitable glycols generally are the substantially linear polyethylene glycols (PEG)
and polypropylene glycols (PPG) having a molecular weight of about 100 to 5,000 preferably
about 200 to 2,000. Esters are preferred and fatty acids containing from 10-30 carbon
atoms are useful for reacting with the glycols to form the ester additives and it
is preferred to use a C
18-C
24 fatty acid, especially behenic acids, the esters may also be prepared by esterifying
polyethoxylated fatty acids or polyethoxylated alcohols.
[0023] Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereof are suitable
as additives with diesters preferred for use in narrow boiling distillates whilst
minor amounts of monoethers and monoesters may also be present and are often formed
in the manufacturing process it is important for additive performance that a major
amount of the dialkyl compound is present. In particular stearic or behenic diesters
of polyethylene glycol, polvpropylene
qlycol or polyethylene/polypropylene glycol mixtures are preferred.
[0024] The additives of this invention may also be used with the ethylene unsaturated ester
copolymer flow improvers. The unsaturated monomers which may be copolymerized with
ethylene, include unsaturated mono and diesters of the general formula:
wherein R
6 is hydrogen or methyl a R
5 is a -OOCR
8 croup wherein R
8 is hydrogen or a C
1 to C
28, more usually C
1 to C
17, and preferably a C
1 to C
8, straight or branched chain alkyl group; or R
5 is a -COOOR
8 qroup wherein R
8 is as previously described but is not hydrogen and R
7 is hydrogen or -COORg as previously defined. The monomer, when R
5 and R
7 are hydrogen and R
5 is -OOCR
8, includes vinyl alcohol esters of C
1 to C
29, more usually C
1 to C
18, monocarboxylic acid. Examples of vinyl esters which may be copolymerised with ethylene
include vinyl acetate, vinyl propionate and vinyl butyrate and isobutyrate, vinyl
acetate being preferred. We prefer that the copolymers contain from 20 to 40 wt.%
of the vinyl ester more preferably from 25 to 35 wt.% vinyl ester. They may also be
mixtures of two copolymers such as those described in United States Patent 3961916.
[0025] It is preferred that these copolymers have a number average molecular weiqht as measured
by vapor phase osmometry og 1000 to 6000, preferably 1000 to 3000.
[0026] The additives of the present invention may also be used in distillate fuels in combination
with polar compounds, either ionic or nonionic, which have the capability in fuels
of actina as wax crystal growth inhibitors. Polar nitroqen containing compounds have
been found to be especially effective when used in combination with the qlycol esters,
ethers or ester/ethers and such three component mixtures are within the scope of the
present invention. These polar compounds are preferably amine salts and/or amides
formed by rection of at least one molar proportion of hydrocarbyl substituted amines
with a molar proportion of hydrocarbyl acid having 1-4 carboxylic acid groups or their
anhydrides; ester/amides may also be used generally they contain a total of 30 to
300 carbon atoms preferably 50 to 150 carbon atoms. These nitrogen compounds are described
in U.S. Patent 4,211,534. Suitable amines are usually long chain C
12-C
40 primary, secondary, tertiary or quarternary amines or mixtures thereof but shorter
chain amines may be used provided the resulting nitrogen compound is oil soluble and
therefore normally containing about 30 to 300 total carbon atoms. The nitrogen compound
preferably contains at least one straight chain C
8-C
40 preferably C
14-C
24 alkyl se
qment.
[0027] Suitable amines include primary, secondary, tertiary or quaternary, but preferably
are secondary. Tertiary and quarternary amines can only form amine salts. Examples
of amines include tetradecyl amine, cocoamine, hydrogenated tallow amine and the like.
Examples of secondary amines include dioctadecyl amine, methyl-behebyl amine and the
like. Amine mixtures are also suitable and many amines derived from natural materials
are mixtures. The preferred amin is a secondary hydro
qenated tallow amine of the formula HNR
IR
2 wherein R
1 and R
2 are alkyl groups derived from hydrogenated tallow fat composed of approximately 4%
C
14, 31% C
16, 59% C
18.
[0028] Examples of suitable carboxylic acids for preparing these nitroqen compounds (and
their anhydrides) include cyclo-hexane dicarboxylic acid, cyclohexene dicarboxylic
acid, cyclopentane dicarboxylic acid, dialpha-naphthyl acetic acid, naphthalene dicarboxylic
acid and the like. Generally these acids will have about 5-13 carbon atoms in the
cyclic moiety. Preferred acids useful in the present invention are benzene dicarboxylic
acids such as phthalic acid, ortho-phthalic acid, and tera-phthalic acid. Ortho-phthalic
acid or its anhydride is particularly preferred. The particularly preferred amine
compound is the amide-amine salt formed by reactinq 1 molar portion of phthalic anhydride
with 2 molar portions of di-hydrogenated tallow amine. Another preferred compound
is the diamide formed by dehydrating this amide-amine salt.
[0029] The relative proportions of additives used in the mixtures are from 0.5 to 20 parts
by weight of the polymer of the invention containing the n-alkyl groups containing
an average of 12 to 18 carbon atoms to 1 part of the other additive or additives,
more preferably from 1.5 to 9 parts by weight of the polymer of the invention.
[0030] The additive systems of the present invention may be used in any type of distillate
petroleium oil boiling in the ranqe 120°C to 500
0C. The preferred average number of carbon atoms in the groups of R
3 will depend upon the type of fuel being treated. For example, we find polymers and
copolymers in which the backbone (ie straight segments) of R
3 contains from 12 to 14 carbon atoms (ie R
3 itself contains 13 to 15 carbon atoms) to be particularly effective in the so called
narrow boiling distillates whereas those in which the backbone of R
3 contains an average of from 13 to 16 carbon atoms (ie R
3 itself contains 14 to 17 carbon atoms) are more effective in treating the high final
boiling point fuels. The optimum value for R
3 may also depend upon whether the polymer is used as the sole additive or in admixture
with other additives. We further find that although R
3 should be in the range of 12 to 18 carbon atoms for distillate fuels as a whole we
prefer that the compound chosen to treat a particular fuel contain a high proportion
of alkyl groups having the average number of carbon atoms. For example, where a polymer
with a C
12 to C
14 backbone is to be used we prefer that it contains no more than 10 wt.% of monomer
in which the backbone of R
3 contains more than 14 carbon atoms. Similarly when a polymer in which R
3 has a C
14 to C
16 backbone is to be used we prefer that no more than 10 wt.% of the ester monomer used
contains R
3 groups with a backbone with fewer than 14 carbon atoms.
[0031] The additive systems of the present invention may conveniently be supplied as concentrates
for incorporation into the bulk distillate fuel. These concentrates may also contain
other additives as required. These concentrates preferably contain from 3 to 75 wt.%,
more preferably 3 to 60 wt.%, most preferably 10 to 50 wt.% of the additives preferably
in solution in oil. Such concentrates are also within the scope of the present invention.
[0032] The present invention is illustrated by the following examples in which the effectiveness
of the additives of the present invention as filterability improvers were compared
with other similar additives in the response of the oil to the additives Cold Filter
Plugging Point Test (CFPP) which is carried out by the procedure described in detail
in "Journal of the Institute of Petroleum", Volume 52, Number 510, June 1966, pp.
173-185. This test is designed to correlate with the cold flow of a middle distillate
in automotive diesels.
[0033] In brief, a 40 ml sample of the oil to be tested is cooled in a bath which is maintained
at about -34°C to give non-linear cooling at about 1
oC/min. Periodically (at each one degree Centigrade drop in temperature starting from
at least 2
0C above the cloud point) the cooled oil is tested for its ability to flow through
a fine screen in a prescribed time period using a test device which is a pipette to
whose lower end is attached an inverted funnel which is positioned below the surface
of the oil to be tested. Stretched across the mouth of the funnel is a 350 mesh screen
having an area defined by a 12 millimetre diameter. The periodic tests are each initiated
by applying a vacuum to the upper end of the pipette whereby oil is drawn through
the screen up into the pipette to a mark indicating 20 ml of oil. After each successful
passage the oil is returned immediately to the CFPP tube. The test is repeated with
each one degree drop in temperature until the oil fails to fill the pipette within
60 seconds. This temperature is reported as the CFPP temperature. The difference between
the CFPP of an additive free fuel and of the same fuel containing additive is reported
as the CFPP depression by the additive. A more effective flow improver gives a greater
CFPP depression at the same concentration of additive.
[0034] The fuel used in these examples was:
The Additives used were as follows:
[0035] Additive 1: A copolymer of a di C16 alkyl fumarate obtained by reaction of 2-hexadecanol
with fumaric acid and vinyl acetate prepared by solution copolymerisation of a 1 to
1 mole ratio mixture at 80°C usinq azo diisobutyronitrile as catalyst in cyclohexane.
[0036] Additive 2: A similar copolymer obtained from the commercially available alcohol
Dobanol 45 containinq primary n C
14 and C
15 alcohols but with a small amount of the 2 methyl analogue and for comparison similar
alkyl fumarate obtained from C
14 alcohol, a mixture of
n C14 and n C
16 alcohols and n C
16 alcohol.
[0037] The additives were tested in admixture at a 4:1 ratio with an Additive n which was
an oil solution containing 63 wt.% of a combination of polymers comprising 3 parts
by weight of an ethylene/vinyl acetate copolymer of number avera
qe molecular weiqht 2500 and vinyl acetate content of 36 wt.% and 1 part by weight
of a copolymer of ethylene and vinyl acetate of number average molecular weight 3500
and a vinyl acetate content of about 17 wt.%.
[0038] The results obtained are as follows:
[0039] The drop in CFPP temperature when using the mixture of ethylene vinyl acetate copolymers
above was:
[0040] In order to further illustrate the invention various blends of an iso C
10 fumarate/vinyl acetate copolymer and a normal C
14 fumarate/vinyl acetate copolymer were prepared and evaluated in the fuel previously
used in the CFPP test with the followinq results.