Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
" ~ 32~23
Improved Fuel Additives
Reference is made to related subject matter in Canadian
Applications Numbered 547,643 and 547,644.
Mineral oils containing paraffin wax such as the
distillate fuels used as diesel fuel and heating oil have
the characteristic of becoming less fluid as the
temperature of the oil decreases. This loss of fluidity
is due to the crystallisation of the wax into plate-like
crystals which eventually form a spongy mass entrapping
the oil therein, the temperature at which the wax
crystals begin to form being known as the Cloud Point,
the temperature at which the wax prevents the oil pouring
is known as the Pour Point.
It has long been known that various additives act as Pour
Point depressants when blended with waxy mineral oils.
These compositions modify the size and shape of wax
crystals and reduce the cohesive 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 so being pourable and able to pass through
coarse filters.
Various Pour Point depressants have been described in the
literature and several of these are in commercial use.
For example, US Patent No. 3,048,479 teaches the use of
copolymers of ethylene and Cl-Cs vinyl esters, e.g. vinyl
acetate, as Pour Point depressants for fuels,
specifically heating oils, diesel and jet fuels.
Hydrocarbon polymeric pour depressants based on ethylene
and higher alpha-olefins, e.g. propylene, are also
known. US Patent 3,252,771 relates to the use of
polymers of Cl6 to Clg alpha-olefins with aluminium
trichloride/alkyl halide catalysts as pour depressants in
distillate fuels of the ~broad boiling~, easy-to-treat
types available in the United States in the early 1960's.
.~ ~
-2 - 1 3~ ~6 23
1 In the late 1960's, early 1970's, greater emphasis was
placed upon improving the filterability of oils at
temperatures between the Cloud Point and the Pour Point
as determined by the more severe Cold Filter Plugging
Point ~CFPP) Test (IP 3~9/80) and many patents have sinc~
been issued relating to additives for improving fuel
performance in this test. US Patent 3,961,916 teaches
the use of a mixture of copolymers to control the size of
the wax crystals. United Ringdom Patent 1,263,152
suggests that the size of the wax crystals may be
controlled by using a copolymer having a lower degree of
side chain branching.
It has also been proposed in, for example, United Kingdor
Patent 1,469,016, that the copolymers of di-n-alkyl
fumarates and vinyl acetate previously used as pour
depressants for lubricating oils may be used as
co-additives with ethylene/vinyl acetate copolymers in
the treatment of distillate fuels with high final boiling
points to improve their low temperature flow properties.
It has also been proposed to use additives based on
olefin/maleic anhydride copolymers. For example, U.S.
Patent 2,542,542 uses copolymers of olefins such as
octadecene with maleic anhydride esterified with an
alcohol such as lauryl alcohol as pour depressants and
United Kingdom Patent 1,468,588 uses copolymers of
C22-C2g olefins with maleic anhydride esterified with
behenyl alcohol as co-additives for distillate ~uels.
Similarly, Japanese Patent Publication 5,654,037 uses
olefin/maleic anhydride copolymers which have been
reacted with amines as Pour Point depressants.
3 1329~3
1 Japanese Patent Publication 5,654,~38 uses the
derivatives of the olefin/maleic anhydride copolymers
together with conventional middle distillate flow
improvers such as ethylene vinyl acetate copolymers.
Japanese Patent Publication 5,540,640 discloses the use
of olefin~maleic anhydride copolymers (not esterified)
and states that the olefins used should contain more than
20 carbon atoms to obtain CFPP activity. United Kingdom
Patent 2,192,012 uses mixtures of certain esterified
olefin/maleic anhydride copolymers and low molecular
weight polythene, the esterified copolymers being
ineffective when used as sole additives.
The improvement in CFPP activity from incorporation of
the additives of these Patents is achieved by modifying
1~ the size and shape of the wax crystals forming to produce
mostly needle like crystals generally of particle size 10
microns or bigger typically 30 to 100 microns. In
operation of diesel engines at low temperatures, these
crystals do not pass through the vehicle paper fuel
filters but form a permeable cake on the filter allowing
the liquid fuel to pass, the wax crystals will
subsequently dissolve as the engine and the fuel heats
up, which can be by the bulk fuel being heated by
recycled fuel. A build up of wax can, however, block the
filters, leading to diesel vehicle starting problems and
problems at the start of driving in cold weather or
failure of heating systems.
With the aid of a computer, it is possible to calculate
accurately the geometry of the n-alkane wax crystal
- 30 lattice and the energetically preferred geometry of a
potential additive molecule in a simple and most
convenient way. The results become especially clear when
they are subsequently graphically represented with the
aid of a plotter or a graphics terminal. This method is
known as ~molecular modellingD.
132~23
--4
Computer programs us~f~l for this purpose are
commercially available and a particularly use~ul series
of programs is distributed by the firm Chemical Desigr~
Ltd., Oxford, England (Technical Director: E.K. Davies)
under the designation Chem-X~*
In the attached drawings:
Fig. 1 is a schematic diagram showing paraffin crystal growth;
Fig. 2 is a schematic diagram of the crystal structure of paraffin
before and after the addition of an additive;
Fig. 3 is a photograph of a wax crystal plate;
Fig. 4 shows an enlarged top view of the crystal lattice of a
paraffin platelet;
Fig. 5 shows the best case conformation of phthalic diamide;
Fig. 6 shows the distorted conformation of phthalic diamide
resulting from reminimisation;
Fig. 7 shows the best case conformation of maleic diamide;
Fig. 8 shows the distorted conformation of maleic diamide resulting
from reminimisation;
Fig. 9 shows the conformation of succinic acid;
Fig. 10 shows the conformation of succinic acid upon rotation
around a C-C single bond;
Fig. 11 is a molecular model of Additive l;
Fig. 12 is a graph showing pressure drops across a main filter;
Fig. 13 is a graph of the performance results of Example 8.
B~
~ ~ 4a
132~23
The growth of paraffin crystals takes place by
association of single paraffin molecules with their long
side to the edge of an existing paraffin platelet as is
schematically shown in Fig. 1. The association to the
top or bottom side of the platelet is energetically
unfavourable because in this case, only one end of the
paraffin chain molecule interacts with the existing
crystal. The association mainly occurs in the
crystallographic (001) plane (compare Fig. 2). The (001)
plane contains the greatest number of strongest
intermolecular bonds and thus demoinates the crystal fro
form large flat rhombohedral plates (Fig.3). The next
most stable face on the crystal is the (llx) (eg the
(110)). The intermolecular association is strongest
where the n-alkane molecules are closest, thus the ~110)
slice is stronger than the (100) slice.
The crystal grows by extending the (001) plane. Thus it
is important to note that the edges o~ this plane are the
rapidly advancing faces and these are the (llx) (eg the
(110)) and the (100) to a lesser extent. Consequently,
growth is mostly controlled by the advance of the (llx)
plane.
As the ~head to head~ bonds are relatively weak we
qenerally only consider one molecular (001) plane
therefore we can assume that the (110), (111) etc. planes
are equivalent for our purposes as the lattice springs
and relative orientations of adjacent molecules stocked
side-by-side are the same (Fig.4).
*Trade Mark
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132~623
--5
1 Fig. 3 which is a Photograph of a wax crystal plate shows
that the macroscopic appearance of the platelets is
dominated by the (001) plane. It is these platelets
which can block filters in fuel lines for example in
vehicles.
According to the present invention, this problem is
overcome by inhibiting or at least strongly reducing the
crystal growth in the (001) plane and the (110) and (lll)
directions.
This can produce waxy fuels having wax crystals of
sufficiently small size at low temperatures to pass
through filters typically used in diesel engines and
heating oil systems and is achieved by the addition of
certain additives.
The present invention therefore provides the use as an
additive for wax containing distillate fuel of a compound
containing at least 2 substituent groups having a spacing
and configuration such that they may occupy the positions
of wax molecules in the ~001) plane intersecting with the
(110) and/or (lll) planes in crystals of the wax, the
substituent groups being alkyl, alkoxy alkyl or
polyalkoxy alkyl having at least 10 atoms in the main
chain.
The occupation of the planes of the crystal may be
explained by reference to Fig. 4 which shows an enlarged
top view the crystal lattice of of a paraffin platelet.
The direction of view corresponds with the long axis of
the paraffin chains. Or each paraffin molecule, only two
carbon atoms and four hydrogen atoms (the latter only
shown once) can be seen because the other atoms are below
the atoms shown since all carbon atoms of a molecule lie
in one molecular symmetry plane. It can be seen from
Fig. 4 that the distances between two molecules in the
(1~0) plane and the ~110) plane, respectively, are
virtually the same.
-6 - 1329623
1 These distances are designated ~b~ and ~d~ in Fig. 4 and
b = 4.9 ~ and d = 4.5 ~. The main difference between the
(100) and the (110) (or more rigorously the (llx) where x
is 0 or an integer) planes is the relative orientation of
adjacent paraffin molecules. Within the (100) plane, the
molecular symmetry planes of single molecules are
parallel to each other, i.e. the dihedral angle is 0.
In the crystallographic (110) plane, the dihedral angle
between the molecular symmetry planes of adjacent
molecules is about 82.
According to the invention the additives should occupy
the positions of paraffin molecules which are designated
by ~C~ and ~D~ in Fig. 4. This is only possible if the
distance between the substituents is about 4.5 to 5.0
in an energetically available conformation and the
dihedral angle between the local symmetry planes of the
two substituents is about 82, preferably from 75 to 50.
A molecule can be modelled by either reading its known
atomic co-ordinates into a computer or by building the
structure according to the rules of chemical physics with
the aid of the computer. Subsequently the structure can
be refined by for example:
(a) calculation of the fractional charges on every atom
from electronegativity differences (force field
method) or quantum mechanical techniques (e.g. CND0,
~.C.P.E. 141, Indiana University);
(b) optimising the structure using molecular mechanics
~compare ~Molecular Mechanics~, U. Burkert and N.L.
Allinger, ACS, 1982~;
132~23
1 ~c) minimising the overall energy by optimising the
conformation, i.e. by ~otation around rotating
bonds. Care needs to be taken here as the
environment on the wax crystal surface is different
from that in the gas phase or in solution and it i
possible that the additive molecule co-crystallises
with the paraffin in a conformation which is not the
energetically most favourable conformation in the
gas phase. Also allowance must be made for the fact
that the additive cannot assume a conformation which
is hindered by sterical or electronic factors.
Using the following criteria, it can be checked whether
an additive molecule fits into the (001) plane of the
paraffin crystal lattice in the desired positions C and D
since:
(l) The distance between the substituents in the molecule
must be approximately equal to the distance between
two adjacent paraffin molecules in the (001) plane
intersecting with the (llx) plane, i.e. about 4.5 ~.
The relative orientation of the substituents should
7 match the arrangement of the n-alkanes in the (llO)
direction, i.e. the dihedral angle between the local
symmetry planes of the su~stituents should be
approximately 82C. The distance and the angle can be
easily measured using the computer programs.
(2) when the additive molecule should fit into the wax
crystal lattice structure, and ~dock~ into two vacant
lattice sites.
Compounds previously suggested as additives are certain
derivatives of phthalic acid, maleic acid, succinic acid
and vinylindene olefins. None of the compounds cited meets
; criterium (l) described above. This is illustrated with
respect to the following selected examples.
-8 - 13~62~
1 (a) phthalic diamide in the best case assume the
conformation shown in Fig. S. in which the distance
between the substituents and the dihedral angle are
too small. The conformation is energetically
unfavourable because of stericai hindrance.
Reminimisation leads to the distorted conformation
shown in Fig. 6.
(b) The situation is similar for maleic diamide as can be
seen in Fig. 7. Because of steric hindrance
reminimisation leads to the distorted conformation of
Fig.8.
(c) Because of steric hindrance succinic acid cannot
assume a conformation which comes near to the special
arrangement according to the invention
(compare Fig. 9). By rotation around a C-C single
bond the succinic acid switches over to the
conformation shown in Fig. lO.
The improvement in CFPP activity from incorporation of
these previous additives of these Patents is achieved by
modifying the size and shape of the wax crystals forming to
produce mostly needle like crystals generally of particle
size lO000 nanometres or bigger typically 30000 to lO00~0
nanometres. In operation of diesel engines at low
temperatures, these crystals do not pass through the
vehicle paper fuel filters but f~rm a permeable cake on
the filter allowing the liquid fuel to pass, the wax
crystals will subsequently dissolve as the engine and the
fuel heats up, which can be by the bulk fuel being heated
by recycled fuel. A build up of wax can, however, block
the filters, leading to diesel vehicle starting problems
and problems at the start of driving in cold weather
similarly it can lead to failure sf fuel heating systems.
In this Application the following test methods are used.
-9- 13~9623
1 The Wax Appearance Temperature (WAT) of the fuel is
measured by differential scanning calorimetry (DSC). In
this test a small sample of fuel (25 microlitres) is
cooled at 2C/minute together with a reference sample of
similar thermal capacity but which will not precipitate
wax in the temperature range of interest (such as
kerosene). An exotherm is observed when crystallisation
commences in the sample. ~or example, the WAT of the
fuel may be measured by the extrapolation technique on
the Mettler TA 2000B*
The wax content of the fuel is derived from the DSC trace
by integrating the area enclosed by the base line and the
exotherm down to the specified temperature. The
calibration having been previously performed on a known
amount of crystallising wax.
The wax crystal average particle size is measured by
analysing a Scanning Electron Micrograph of a fuel sample
at a magnification of between 40D0 and 8000 times and
measuring the longest dimension of at least 40 out of 88
points on a predetermined grid. We find that providing
the average size is less than 4000 nanometres the wax
will begin to pass through the typical paper filters used
in diesel engines together with the fuel although we
prefer that the size be below 3000 nanometres, more
preferably below 2500 and most preferably below 2000
nanometres especially below 1000 nanometres where the
real benefits of passage of the crystals through the
paper fuel filters is achieved. The actual size
attainable depends upon the original nature of the fuel
and the nature and amount of additive used but we have
found that these sizes and smaller are attainable.
*Trade ~ark
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,i, .~ ,''
-lo- ~32~623
1 Using the additives according to this invention allows
such small wax crystals in the fuel to be obtained which
results in significant benefit in diesel engine
operability. This may be demonstrated by pumping
stirred fuel through a diesel filter paper as used in a
V.W. Golf*or Cummins*diesel engine at from 8 to 15
ml/second and 1.0 to 2.4 litres per minute per square
metre of filter surface area at a temperature at least
5C below the wax appearance temperature with at least
0.5 wt~ of the fuel being present in the form of solid
wax. Both fuel and wax are considered to successfully
pass through the filter if one or more of the following
criteria a.e satisfied.
(i) When 18 to ~0 litres of fuel have passed through the
filter the pressure drop across the filter does not
exceed 50 kiloPascals (kPa), preferably 25 kPa, more
preferably lO kPa, most preferably 5 kPa.
(ii~ At least 60%, preferably at least 80%, more
preferably at least 90 wt.~ of the wax present in
the original fuel, as determined by the DSC test
previously described is found to be present in the
fuel leaving the filter.
(iii) Whilst pumping 18-20 litres of fuel through the
filter, the flow rate always remains at above 60% of
the initial flow rate and preferably above 80%.
The portion of crystals passing through the vehicle
filter and the operability benefit arising from small
crystals are highly dependant on crystal length although
crystal shape is also significant. we find that
cube-like crystals tend to pass through filters slightly
more easily than do flat crystals and, when they do not
pass, offer less resistance to fuel flow. Nonetheless
the preferred crystal form is a flat form, which in
*Trade Mark
D
ll 1329S23
1 principle allows more wax to be laid down as the
temperature falls and more wax precipitates before the
critical crystal length is reached than would a crystal
of the same length in cube-like form.
The fuels obtained by the techniques of the present
invention have outstanding benefits compared to previous
distillate fuels improved in their cold flow properties
by the addition of conventional additives. Por example
the fuels are operable at temperatures nearer the Pour
Point and not restricted by the inability to pass the
CFPP test since they either pass the CFPP test at
significantly lower temperatures or obviate the need to
pass that test. The fuels also have improved cold start
performance at low temperatures not relying on
recirculation of warm fuel to remove undesirable wax
deposits. Furthermore the wax crystals tend to remain in
suspension rather than settle and form waxy layers in
storage tanks as occurs with fuels treated with
conventional additives.
Distillate fuels within the general class of those
boiling from 120C to 500C vary significantly in their
boiling characteristics, n-alkane distributions and wax
contents. Fuels from Northern Europe generally having
lower final boiling points and cloud points than those in
Southern Europe. The wax contents are generally greater
than 1.5% (at 10C below the WAT). Similarly fuels fro~
other countries round the world vary in the same way with
their respective climates but the wax content also
depends on the source of the crude oil. A fuel derived
from a Middle Eastern crude is likely to have a lower wax
content than one derived from one of the waxy crudes such
as those from China and Australia.
-12- 1329623
1 The extent to which the very small crystals can be
obtained depends upon the nature of the fuel itself, and
in some fuels it may not be possible to produce extremely
small crystals. If this situation arises the fuel
characteristics may be modified to enable such small
crystals to be obtained by for example adjustment of
refinery conditions and blending to enable the use of
suitable additives.
Since the wax precipitating from distillate fuels is
mostly all normal alkanes which crystallize in an
orthorhombic unit cell via a rotator or hexagonal form as
is reported in the literature by for example, A. ~uller
in Proc. Roy. Soc. A. 114, 542, (1927), ibid. 120, 437,
(1928 ibid.), 127, 417, (1930), ibid. 138, 514, ~1932),
A. E. Smith in J. Chem. Phys., 21, 2229, (1953) and P. W.
Teare in Acta. Cryst., 12, 294, (1959). As mentioned, the
two factors that are important in matching of the
additive molecule to the wax crystal structure; firstly,
the separation between the n-alkane chains in selected
crystal planes where the important distances to match are
those in the (110) and (111) etc. planes or directions
and to a lesser extent in the (100) plane.
The chains of the additive must occupy the lattice sites
(more than one) in positions on the axes at right angles
~5 to the axis of the n-alkane chains in the crystal. ~hese
separations are in the order of 4.5 to 5.5 ~ and the
closer the chains on the additives are to these distances
the more effective the additive. Secondly, although
p~ssibly less important, the relative orientations of the
3~ additive molecule chains preferably match those of the
n-alkanes in the crystal. The n-alkyl chains on the
additive must be able to match closely the
inter-molecular spacings of the n-alkanes in the wax
crystal along the (100) and/or (110) and (111) planes
-13- 13 ~ ~ ~23
1 where the intersect with the (001) plane and be able to
attain conformations which allow the chains to orient
themselves to similar angles to those of the n-alkanes in
the above-mentioned crystal planes. It is found that
these spacin~s and orientations of the chains on the
additive molecule can best be achieved by placing them on
adjacent carbon atoms in a cyclic or ethylenically
unsaturated compound provided they are in a cis
orientation.
The matching is preferably also achieved along the length
of the n-alkane chains of the wax and the total chain
length of the additive is preferably of the same order of
magnitude as the average chain length in the wax. The
wax precipitation from the fuel or oil is generally a
range of n-alkanes and hence the reference to the average
dimensions.
The additives therefore generally contain alkyl
preferably n-alkyl chains or chain segments which can
co-crystallize with the wax. We have found that there
should be two or more such chains per molecule and that
these should be located on the same side of the additive
molecule. It is desirable that the additive molecule has
two distinct ~sides~. One ~side- will contain the
co-crystallizable alkyl chains and the other ~sidea will
contain the least number of hydrocarbon groups possible
to block or prevent further crystallization after the
additive molecule has co-crystallized into the n-alkane
lattice sites on the wax crystals. It is also desirable
that this blockingn group is located half way or
approximately half way down the co-crystallizable n-alkyl
chains on the additive.
132~62~
-14-
1 The additives we prefer to use are of the formula
A ~ ",,X R1
B'''' ~ Y - R2
in which -y-R2 is So3(-)(+JNR3R2, -So3(-)(+)HNR3R2),
-So3(-)(+)H2NR3R2, -S03(-)(~)H3NR2,
-So2NR3R2 or -S03R2;
-X-Rl is -y-R2 or -CoNR3Rl,
- 10 -C2 ( - ) ( + ) NR3Rl, --C2 ( - ) ( + ) HNR3Rl,
-C2 ( - ) ( + ) H2NR3Rl, -C2 ( - ) ( + ) H3NRl,
-R4 -COORl, -NR3CoRl,
R40Rl, _R40CoRl ,_R4Rl,
-N(CoR3)Rl or Z(-)(+)NR3Rl;
-z(~) is S03(-) or -C02(-);
Rl and R2 are alkyl, alkoxy alkyl or polyalkoxy alkyl
containing at least 10 carbon atoms in the main chain;
R3 is hydrocarbyl and each R3 may be the same or
different and R4 is nothing or is Cl to Cs alkylene and in
A ~
C
B -
13.~9623
_14a-
the carbon-carbon (C-C) bond is either a) ethylenically
unsaturated when A and B may be alkyl, alkenyl or
substituted hydrocarbyl groups containing 1 to 22 carbon
atoms or b) part of a cyclic structure which may be
aromatic, polynuclear aromatic or cyclo-aliphatic.
The ring atoms in such cyclic compound are preferably
carbon atoms, but could, however, include a ring N, S or
o atom to give a heterocyclic compound.
~3~623
-15-
1 Examples of aromatic based compound from which the
additives may be prepared are
~ ~ 0
O O
In which the aromatic group may be substituted.
Alternatively they may be obtained from polycyclic
compounds, that is those having two or more ring
structures which can take various forms. They can be (a)
condensed benzene structures, tb) condensed ring
structures where none or not all rings are benzeneJ (c)
rings joined end-on~, (d) heterocyclic compounds (e)
; 15 non-aromatic or partially saturated ring systems or (f)
three-dimensional structures.
Condensed benzene structures from which the compounds may
be derived include for example naphthalene, anthracene,
phenathrene and pyrene.
The condensed ring structures where none or not all rings
are benzene include for example Azulene, Indene,
Hydroindene, Fluorene, Diphenylene. Compounds where
rings are joined end-on include for example diphenyl.
Suitable heterocyclic compounds from which they may be
derived include for example Quinoline, Pyrindine,
Indole, 2:3 dihydroindole, benzofuran, coumarin,
isocoumarin, benzothiophen, carbazole and
thiodiphenylamine. Suitable non-aromatic or partially
saturated ring systems include decalin
(decahydronaphthalene), ~-Pinene, cadinene, bornylene.
Suitable 3-dimensional compounds include for example
norbornene, bicycloheptane (norbornane~, bicyclo octane
and bicyclo octene.
-16- 1329623
l The two substituents X and Y must be attached to
adjoining ring atoms in the ring when there is only one
ring or to adjoining ring atoms in one of the rings where
the compound is polycyclic. In the latter case this
means that if one were to use naphthalene these
substituents could not be attached to the 1,8- or 4,5-
positions, but would have to be attached to the 1,2-,
2,3-, 3,4-, 5,6-, 6,7- or 7,8- positions.
These compounds are reacted to give the esters, amines,
amides, half-esters/half amides, half ethers or salts
used as the additives. Preferred additives are the salts
of a secondary amine which has a hydrogen- and
carbon-containing group or groups containing at least lO
preferably at least 12 carbon atoms. Such amines or
salts may be prepared by reacting the acid or anhydride
previously described with an amine or by reacting a
secondary amine derivative with carboxylic acids or
anhydrides. Removal of water and heating are generally
necessary to prepare the amides from the acids.
Alternatively the carboxylic acid may be reacted with an
alcohol containing at least lO carbon atoms or a mixture
of an alcohol and an amine.
The hydrogen- and carbon-containing groups in the
substituents are preferably hydrocarbyl groups, although
halogenated hydrocarbyl groups could be used, preferably
only containing a small proportion of halogen atoms (e.g.
chlorine atoms), for example less than 20 weight per
cent. The hydrocarbyl groups are preferably aliphatic,
e.g. alkylene. They are preferably straight chain.
Unsaturated hydrocarbyl groups, e.g. alkenyl, could be
used but they are not preferred.
-17- 1329623
1 The alkyl groups preferably have at least 10 carbon
atoms, preferably 10 to 22 carbon atoms, for example 14
to 20 carbon atoms and are preferably straight chain or
branched at the 1 or 2 positions. If branching exists in
over 20% of the alkyl chains then the branches must be
methyl. The other hydrogen- and carbon-containing groups
can be shorter e.g. less than 6 carbon atoms or may if
desired have at least 10 carbon atoms. Suitable alkyl
groups include methyl, ethyl, propyl, hexyl, decyl,
dodecyl, tetradecyl, eicosyl and docosyl (behenyl).
Suitable alkylene groups include hexylene, oct~lene,
dodecylene and hexadecylene but these are not preferred.
In the preferred embodiment where the intermediate is
reacted with the secondary amine, one of the substituents
will preferably be an amide and the other will be an
amine or dialkylammonium salt of the secondary amine.
The especially preferred additives are the amides and
amine salts of secondary amines.
In order to obtain the fuels of this invention these
additives will generally be used in combination with
other additives and Examples of the other additives
include those termed as ~comb~ polymers which have the
general formula:
~ E ~ ~ L }
m n
-18- 132~623
1 where D = R, C0.0R, OCO.R, R'C0.0R or OR
E = H or CH3 or D or R'
G = H, or D
m = 1.0 (homopolymer) to 0.4 (mole ratio)
J = H, R', Aryl or Heterocyclic group, R'CO.OR
K = H, C0.OR', OCO.R', OR', CO2H
L = H, R', CO.OR', OCO.R', Aryl, CO2H
n = O.O to 0.6 (mole ratio)
R ~ C10
R'~ Cl
Another monomer may be terpolymerized if necessary.
Where these other additives are copolymers of alpha
olefins and maleic anhydride they may conveniently be
prepared by polymerising the monomers solventless o} in a
solution of a hydrocarbon solvent such as heptane,
benzene, cyclohexane, or white oil, at a temperature
generally in the range of from 20C to 150C and usually
promoted with a peroxide or azo type catalyst, such as
benzoyl peroxide or azo-di-isobutyro-nitrile, under a
blanket of an inert gas such as nitrogen or carbon
dioxide, in order to exclude oxygen. It is preferred but
not essential that equimolar amounts of the olefin and
maleic anhydride be used although molar proportions in
the range of 2 to 1 and 1 to 2 are suitable. Examples of
olefins that may be copolymerised with maleic anhydride
are l-decene, l-dodecene, l-tetradecene, l-hexadecene,
l-octodecene.
The copolymer of the olefin and maleic anhydride may be
esterified by any suitble technique and although
preferred it is not essential that the maleic anhydride
be at least 50% esterified. Exampl~s of alcohols which
may be used include n-decan-l-ol, n-dodecan-l-ol,
-lg- 1329623
1 n-tetradecan-l-ol, n-hexadecan-l-ol, n-octadecan-l-ol.
The alcohols may also include up to one methyl branch per
chain, for example, l-methyl, pentadecan-l-ol, 2-methyl,
tridecan-l-ol. The alcohol may be a mixture of normal
and single methyl branched alcohols. Each alcohol may ~e
used to esterify copolymers of maleic anhydride with any
of the olefins. It is preferred to use pure alcohols
rather than the commercially available alcohol mixtures
but if mixtures are used then Rl refers to the average
number of carbon atoms in the alkyl group, i~ alcohols
that contain a branch at the 1 or 2 positions are used
refers to the straight chain backbone segment of the
alcohol. When mixtures are used, it is important that no
more than 15~ of the Rl groups have the value rl~2.
The choice of the alcohol will, of course, depend upon
the choice of the olefin copolymerised with maleic
anhydride so that ~ + Rl is within the range 18 to 38.
The preferred value of R + Rl may depend upon the boiling
characteristics of the fuel in which the additive is to
be used
These comb polymers may also be fumarate polymers and
copolymers such as those described in our European Patent
Applications 0153176, 0153177, 85301047 and 85301048.
Other suitable comb polymers are the polymers and
copolymers of alpha olefins and the esterified copolymers
of styrene and maleic anhydride.
Examples of other additives which may be used together
with the cyclic compound are the polyoxyalkylene esters,
ethers, ester/ethers and mixtures thereof, particularly
those containing at least one, preferably at least two
Clo to C30 linear saturated alkyl groups and a
polyoxyalkylene glycol group of molecular weight 100 to
5,000 preferably 200 to 5,000, the alkyl group in said
-20- 13~6~3
1 polyoxyalkylene glycol containing from 1 to 4 carbon
atoms. These materials form the subject of European
Patent 0,061,895 B. Other such additives are described
in United States Patent 4 491 455.
The preferred esters, ethers or ester/ethers useful in
the present invention may be structurally depicted by the
~ormula:
R-0tA)-0-R~
where R and R~ are the same or different and may be
i) n-alkyl
,' O
ii) n-alkyl - C
iii) n-alkyl - 0 - ~ - (CH2)n -
O
iv) n-alkyl - 0 - C (CH2)n ~ ~ ~
the alkyl group being linear and saturated and containing
10 to 30 carbon atoms, and A represents the
polyoxyalkylene segment of the glycol in which the
alkylene group has 1 to 4 carbon atoms, such as
polyoxymethylene, polyoxyethylene or polyoxytrimethylene
moiety which is substantially linear; some degree of
branching with lower alkyl side chains (such as in
polyoxypropylene glycol) may be tolerated but it is
preferred the glycol should be substantially linear, A
may also contain nitrogen.
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
.
-21- ~329623
1 and it is preferred to use a Clg-C24 fatty acid,
especially behenic acids. The esters may also be
prepared by esterifying polyethoxylated fatty acids or
polyethoxylated alcohols.
Polyoxyalkylene diesters, diethers, ether/esters and
mixtures thereof are suitable as additives with diester
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 or polyethylene
glycol, polypropylene glycol or
polyethylene/polypropylene glycol mixtures are preferred.
The additives used may also contain ethylene unsaturated
ester copolymer flow improvers. The unsaturated monomers
which may be copolymerised with ethylene include
unsaturated mono and diesters of the
general formula:
R6 H
C = C~
R5 ~ ~ R7
wherein R6 is hydrogen or methyl, Rs is a -OOCRB group
wherein R8 is hydrogen or a Cl to C2g, more usually Cl to
C17, and preferably a Cl to cg, straight or branched
chain alkyl group; or Rs is a -COORg group wherein R8 is
~ -22- 1329623
1 as previously described but is not hydrogen and R7 is
hydrogen or -COORg as previously defined. The monomer,
when R6 and R7 are hydrogen and R5 is -OOCRg, includes
vinyl alcohol esters of Cl to C2~, more usually Cl to
Clg, monocarboxylic acid, and preferably C2 to C2g, more
usually Cl to Clg, monocarboxylic acid, and preferably C2
to Cs monocarboxylic acid. Examples of vinyl esters
which may be copolymerised with ethylene include vinyl
acetate, vinyl propionate and vinyl butyrate or
1~ isobutyrate, vinyl acetate being preferred. When these
are used, we prefer that the copolymers contain from 5 to
40 wt.% of the vinyl ester, more preferably from 10 to 35
wt.% vinyl ester. They may also be mixtures of two
copolymers such as those described in US Patent
3,961,916. It is preferred that these copolymers have a
number average molecular weight as measured by vapour
phase osmometry of 1,000 to 10,000, preferably 1,000 to
5,000.
The additives used may also contain other polar
compounds, either ionic or non-ionic, which have the
capability in fuels of acting as wax crystal growth
inhibitors. Polar nitrogen containing compounds have
been found to be especially effective when used in
- combination with the glycol esters, ethers or
ester/ethers. These polar compounds are generally amine
salts and/or amides formed by reaction of at least one
molar proportion of hydrocarbyl substituted amines with a
molar proportion of hydrocarbyl acid having 1 to 4
carboxylic acid groups or their anhydrides; ester/amides
-23- 132~623
1 may also be used containing 30 to 300, preferably 50 to
150 total carbon atoms. These nitrogen compounds are
described in US Patent 4,211,534. Suitable amines are
usually long chain C12-C40 primary, secondary, tertiary
or quaternary amines or mixtures thereof but shorter
chain amines may be used provided the resulting nitrogen
compound is oil soluble and therefore normally containins
about 30 to 300 total carbon atoms. The nitrogen
compound preferably contains at least one straight chain
C8 to C24 alkyl segment.
Suitable amines include primary, secondary, tertiary or
quaternary, but preferably are secondary. Tertiary and
~uaternary amines can only form amine salts. Examples of
amines include tetradecyl amine, cocoamine, hydrogenated
tallow amine and the like. Examples of secondary amines
include dioctacedyl amine, methyl-behenyl amine and the
like. Amine mixtures are also suitable and many amines
derived from natural materials are mixtures. The
preferred amine is a secondary hydrogenated tallow amine
of the formula HNRlR2 where in Rl and R2 are alkyl groups
derived from hydrogenated tallow fat composed of
approximately 4% C14, 31% C16~ 59% C18-
Examples of suitable carboxylic acids land their
anhydrides) for preparing these nitrogen compounds
include cyclohexane, 1,2 dicarboxylic acid, cyclohexene,
1,2 dicarboxylic acid, cyclopentane 1,2 dicarboxylic
acid, naphthalene dicarboxylic acid and the like.
Generally, these acids will have about 5-13 carbon atoms
in the cyclic msiety. Preferred acids useful in the
132~23
-24-
1 present invention are benzene dicarboxylic acids such as
phthalic acid, isophthalic acid, and terephthalic acid.
Phthalic acid or its anhydride is particularly
preferred. The particularly preferred compound is the
amide-amine salt formed by reacting l molar portion of
phthalic anhydride with 2 molar portions of
di-hydrogenated tallow amine. Another preferred compound
is the diamide formed by dehydrating this amine-amine
salt.
~ydrocarbon polymers may also be used as part of the
additive combination to produce the fuels of the
invention. These may be represented with the following
general formula:
rT H~ ~U H~
lT T ~ C - C
where T = H or R'
U z H, T or Aryl
v = l.0 to 0.0 (mole ratio)
w = 0.0 to l.0 (mole ratio)
Rl is alkyl.
These polymers may be made directly from ethyenically
unsaturated monomers or indirectly by for example
hydrogenating ~he polymer made from other monomers such
as isoprene and butadiene.
-25- 132~623
1 A particularly preferred hydrocarbon polymer is a
copolymer of ethylene and propylene having an ethylene
content is preferably between 50 and 60% ~w/w).
The amount of additive required to produce the distillate
fuel oil of this invention will vary according to the
fuel but is generally 0.001 t~ 0.5 wt.%, for example 0.01
to 0.1 wt.% (active matter) based on the weight of fuel.
The additive may conveniently be dissolved in a suitable
solvent to form a concentrate of from 20 to 90, e.g. 30
to 80 wt.% in the solvent. Suitable solvents include
kerosene, aromatic naphthas, mineral lubricating oils etc.
The present invention is illustrated by the following
examples in which the size of the wax crystals in the
fuel was measured by placing samples of fuel in 2 oz.
bottles in cold boxes held about 8C above fuel cloud
point for l hour while fuel temperature stabilises. The
box is then cooled at 1C an hour down to the test
temperature, which is then held.
A pre-prepared filter carrier~ consisting of a lO mm
diameter sintered ring, surrounded with a l mm wide
annular metal ring, supporting a 200 nanometres rated
silver membrane filter which is held in position by two
vertical pins, is then placed on a vacuum unit. A vacuum
of at least 80 kPa is applied, and the cooled fuel
dripped onto the membrane from a clean dropping pipette
until a small domed puddle just covers the membrane. The
fuel is dropped slowly to sustain the puddle for a few
minutes, after about 10-20 drops of fuel have been
applied the puddle is allowed to draindown leaving a very
thin dull matt layer of fuel wet wax cake on the
membrane. A thick layer of wax will not wash acceptably,
132~623
-26-
1 and a very thin one may be washed away. The optimal
layer thickness is a function of crystal shape, with
~leafy~ crystals needing thinner layers than ~nodular~
crystals. It is important that the final cake have a
matt appearance. A ~shiny~ cake indicates excessive
residual fuel and crystal ~smearing- and should be
discarded.
The cake is then washed with a few drops of methyl ethyl
ketone which are allowed to completely drain away. The
process is repeated a number of times. When washing is
complete the methyl ethyl ketone will disappear very
quickly, leaving a ~brilliant matt white~ surface which
will turn grey on application of another drop of methyl
ethyl ketone.
The washed sample is then placed in a cold desiccator,
and kept until ready for coating in the SEM. It may be
necessary to keep the sample refrigerated to preserve the
wax, in which case it should be stored in a cold box
prior to transfer ~in a suitable sample transfer
container) to the SEM to avoid ice cryctal formation on
the sample surface.
During coating, the sample must be kept as cold as
possible to minimise damage to the crystals. Electrical
contact with the stage is best provided for by a
retaining screw pressing the annular ring against the
side of a well in the stage designed to permit the sample
surface to lie on the instrument focal plane.
Electrically conductive paint can also be used.
~329623
-27-
1 Once coated, the micrographs are obtained in a
conventional way on the Scanning Electron Microscope.
The photomicrographs are analysed to determine the
average crystal size by fastening a transparent sheet
S with 88 points marked (as dots) at the intersections of a
regular, evenly spaced grid 8 rows and ll columns in
size, to a suitable micrograph. The magnification should
be such that only a few of the largest crystal are
touched by more than one dot and 4000 to 8000 times have
proved suitable. At each grid point, if the dot touches
a crystal dimension whose shape can be clearly defined,
the crystal may be measured. A measure of ~scatter~,
in the form of the Gaussian standard deviation of crystal
length with Bessel correction applied is also taken.
The wax content before and after the filter is measured
using a Differential Scanning Calorimeter DSC (such as
the du Pont 9900*series) capable of generating a plot
with an area of about 100 cm2/1% of fuel in the form of
wax with an instrument noise-induced output variation
with a standard deviation less than 2% of the mean output
signal.
The DSC is callibrated by using an additive to produce
large crystals certain to be removed by the filter,
running this calibration fuel at test temperature in the
rig and measuring the WAT of the thus dewaxed fuel on the
DSC. The samples of tank fuel and post-filter fuel to be
tested are then analysed on the DSC, and for each fuel
the area above base line down to the calibration fuel WAT
determined.
*Trade ~ark
.-
~` -28- 1329623
1 The ratio of DSC area for post filter sample X 100
DSC area for tank sample
is the % wax left after the filter.
The cloud point of distillate fuels was determined by th~
standard Cloud Point Test (IP-219 or ASTM-D 2500) other
measures of the onset of crystallisation are the Wax
Appearance Point (WAP) Test (ASTM D.3117-72) and the Wax
Appearance Temperature (WAT) are measured by different
scanning calorimetry using a Mettler TA 2~00B
differential scanning calorimeter.
The ability of the fuel to pass through a diesel vehicle
main filter was determined in an apparatus consisting of
a typical diesel vehicle main filter mounted in a
standard housing in a fuel line; the Bosch Type as used
in a 1980 VW 5O1f diesel passanger car, and a Cummins
FF105 as used in the Cummins NTC engine series are
appropriate. A reservoir and feed system capable of
supplying half a normal fuel tank of fuel linked to a
fuel injection pump as used in the VW Golf is used to
draw fuel through the filter from the tank at constant
flowrate, as in the vehicle. Instruments are provided to
measure pressure drop across the filter, the flow rate
from the injection pump and the unit temeratures.
Receptables are provided to receive the pumped fuel, both
~injected~ fuel and the surplus fuel.
In the test the tank is filled with 19 kilogrammes of
fuel and leak tested. When satisfactory, the temperature
is stabilised at an air temperature 8C above fuel cloud
point. The unit is then cooled at 3C/hour to the
desired test temperature, and held for at least 3 hours
-29- 1 32 9 ~2 3
1 for fuel temperature to stabilise. The tank is
vigorously shaken to fully disperse the wax present a
sample is taken from the tank and l litre of fuel removed
through a sample point on the discharge line immediately
after the tank and returned to the tank. The pump is
then started, with pump rpm set to equate to pump rpm at
a llO kph road speed. In the case of the VW Golf this is
l900 rpm, corresponding to an engine speed of 380G rpm.
Pressure drop across the filter and flow rate of fuel
from the injection pump are monitored until fuel is
exhausted, typically 30 to 35 minutes.
Providing fuel feed to the injectors can be held at 2
ml/sec (surplus fuel will be about 6.5 - 7 ml/sec? the
result is a ~PASS~. A drop in feed fuel flow to the
injectors signifies a ~BORDERLINE~ result; zero flow a
FAIL~.
Typically, a ~PASS~ result may be associated with an
increasing pressure drop across the filter, which may
rise as high as 60 kPA. Generally considerable
proportions of wax must pass the filter for such a result
to be achieved. A ~GOOD PASS~ is characterised by a run
where the pressure drop across the filter does not rise
above lO kPa, and is the first indication that most of
the wax has passed through the filter, and excellent
result has a pressure drop below 5kPa.
Additionally, fuel samples are taken from ~surplus~ fuel
and ~injector feed~ fuel, ideally every four minutes
throughout the test. These samples, together with the
pre-test tank samples, are compared by DSC to establish
the proportion of feed wax that has passed through the
filter. Samples of the pre-test fuel are also taken and
SEM samples prepared from them after the test to compare
wax crystal size and type with actual per~ormance.
1329623
-30-
1 The additives used were
Additive l
The N,N-dialkyl ammonium salt of 2-daialkylamido benzene
sulphonate where the alkyl groups are nC16-1g H33-37
prepared by reacting 1 mole of ortho-sulphobenzoic acid
cyclic anhydride with 2 moles of di-(hydrogenated) tallow
amine in a xylene solvent at 50% (w/w) concentration.
The reaction mixture was stirred at between 100C and the
refluxing temperature. The solvent and chemicals should
be kept as dry as possible so as not to enable hydrolysis
of the anhydride.
The product was analysed by 500 MHz Nulcear Magnetic
Resonance Spectroscopy which confirmed the structure to be
C-N(CH2-(CH2)14/16CH3)2
[~
So3(-)NH(+J( (CH2(-CH2)14/16CH3)2
The molecular model of this compound is given in Figure
11 .
Additive 2
A copolymer of ethylene and vinyl acetate content 17 wt.
molecular weight 35Q0 and a degree of side chain
branching of B methyls per 100 methylene groups as
measured by 500 MHz NMR.
1~2~623
-31-
1 Additive 3
A styrene-dialkyl maleate copolymer made by esterifying a
1:1 molar sytrene-maleic anhydride copolymer with 2 moles
of a 1:1 molar mixture of C12H2sO8 and C14H2gOH per mole
of anhydride groups were used in the esterification
tslight excess, 5% alcohol used) step using p-toluene
sulphonic acid as the catalyst (1/10 mole) in xylene
solvent which gave a molecular weight (Mn) of 50,000 and
contained 34 (w/w) untreated alcohol.
Additive 4
The dialkyl-ammonium salts of 2-N,N dialkylamido benzoate
formed by mixing one molar proportion of phthalic
anhydride with two molar proportions of di-hydrogenated
tallow amine at 60C.
1~ The results were as follows.
ExamPle 1
Fuel Characteristics
Cloud point -14C
Wax Appearance TemperatUre -18.6C
Initial Boiling Point 178C
20% 23~C
~0~ 318C
Final Boiling Point 355C
Wax content at -25C 1.1 wt.~
250 p.p.m. sf each of Additives 1, 2 and 3 were
incorporated in the fuel and the test temperature was
-25C. The wax crystal size was found to be 1200
nanometres long and above gO wt.% of the wax passed
through the Cummins FF105 filter.
-32- 1329~23
1 During the test, passage of wax was further evidenced by
observing the pressure drop over the filter, which only
increased by 2.2 kPa.
Example 2
Example 1 was repeated and the wax crystal size was found
to be 1300 nanometres and the maximum final pressure drop
across the filter was 3.4 kPa.
ExamPle 3
Fuel characteristics
Cloud point 0C
Wax Appearance Temperature -2.5C
Initial Boiling Point 182C
20% 220~
90% 354C
Final Boiling Point 385C
Wax content at test temperature 1.6 wt~.
250 p.p.m. of each of Additives 1, 2 and 3 were used and
the wax crystal size was found to be 1500 nanometres and
about 75 wt% of the wax passed through the Bosch
145434106 filter at the test temperature of -8.5C. The
maximum pressure drop across the filter was 6.5 k~a.
Example 4
Example 3 was repeated and found to give wax crystal size
2000 nanometres long of which about 50 wt.% passed
through filter giving a maximum pressure drop of 35.3 kPa.
~33- ~32~23
1 Example 5
The fuel used in Example 3 was treated with 400 ppm of
Additive 1 and 100 ppm of a mixture of Additive 2 and
tested as in Example 3 at -8C at which temperature the
wax content 1.4 wt.%. The wax crystal size was found to
be 2500 nanometres and 50 wt.% of the wax passed through
the filter with a maximum final pressure drop of 67.1 kPa.
When using this fuel in the test rig, pressure drop rose
rather quickly and the test failed. We believe this is
because as shown in the photograph the crystals are flat
and flat crystals that fail to pass the filter tend to
cover the filter with a thin, impermeable layer. ~Cube
like~ (or nodularn) crystals on the other hand wnen not
passing through the filters, collect in a comparatively
loose cake~, through which fuel can still pass until the
mass becomes so great that the filter fills and the total
thickness of wax cake~ is so great that the pressure
drop again is excessive.
Example 6 (Comparative)
The fuel used in Example 3 was treated with 500 ppm of a
mixture of 4 parts of Additive 4 and l part of Additive 2
and tested at -8C, the wax crystal size was found to be
6300 nanometres and 13 wt.% of the wax passed through the
filter.
This example is among the very best examples of the prior
art, where excellent results are achieved without crystal
passage.
1329623
-34-
1 A scanning electron micrograph of the wax crystals
forming in the fuel of Examples 1 to 6 are Figures 1 to 6
hereof.
Examples 1-4, therefore show that if crystals can pass
through the filter reliably and the excellent cold
temperature performance can be extended to much higher
fuel wax contents than heretofore practicable and also at
temperatures further below fuel Wax Appearance Point than
heretobefore practicable. This is without regard to fuel
system considerations such as the ability of recycle fuel
from the engine to warm the feed fuel being drawn from
the fuel tank, the ratio of feed fuel flow to recycle
fuel, the ratio of main filter surface area to feed fuel
flow and the size and position of prefilters and screens.
These examples how that for the filters tested crystal
lengths below about 1800 nanometres result in
dramatically better fuel performance.
Example 7
In this Example Additive 1 was added to a distillate fuel
having the following characteristics:
IBP 180C
20% 223C
90% 336C
FBP 365C
Wax Appearance Temperature 5.5C
Cloud Point -3.5C
For comparison purposes the following additives were also
added to the distillate fuel:
-35_ 132~623
1 Additive A: A mixture of ethylene/vinyl acetate
copolymers, one of which was Additive 2 (1 part by
weight) and the other one (3 parts by weight) with a
vinyl acetate content of 36 wt.%, molecular weight ~Mn)
of 2000 a degree of side chain branching of between 2 and
3 methyls per 100 methylene groups as measured by 500 MHz
NMR.
Additive B: A mixture of Additives 4 and 2 the mole
ratio being 4:1.
Additive C: The dibehenate of a polyethylene glycol
mixture having an average molecular weight of 600.
Additive D: An ethylene/propylene copolymer, the
ethylene content being 56 wt.~, and the number average
molecular weight being approximately 60,000.
The additives were added in the quantities shown in the
following table and tests carried out according to the
PCT, details of which are as follows:
PROGRAMMED COOLING TEST (PCT)
This is a slow cooling test designed to correlate with
the pumping of a stored heating oil. The cold flow
properties of the fuel containing the additives are
determined by the PCT as follows. 300 ml of fuel are
cooled linearly at 1C/hour to the test temperature and
the temperature then held constant. After 2 hours at the
test temperature, approximately 20 ml of the surface
layer is removed by suction to prevent the test being
influenced by the abnormally large wax crystals which
tend to form on the oil/air interface during cooling.
-36- 1329623
1 Wax which has settled in the bottle i~ dispersed by
gentle stirring, then a CFPPT(13 filter assembly is
inserted. The tap is opened to apply a vacuum of 500 mm
of mercury, and closed when 200 ml of fuel have passed
through the filter into the graduated receiver: A PASS
is recorded if the 200 ml are collected with ten seconds
trhough a given mesh size of a FAIL if the flow rate is
too slow indicating that the filter has become blocked.
The mesh number passed at the test temperature is
recorded.
(1) CFPPT - Cold Filter Plugging Point Test (CFPPT)
described in detail in ~Journal of the Institute of
Petroleum~, Vol. 52, No. 510, June 1966, pp. 173-185.
Example 8
The fuel used in this Example had the following
characteristics:
(ASTM-D86)
IBP 190C
20% 246C
gO% 346C
FBP 374C
Wax Appearance Temperature -1.5C
Cloud Point +2.0C
It was treated with 1000 parts per million of active
ingredient of the following additives:
-37-
1329623
1 (E) A mixture of Additive 2 (l part by weight) and
Additive 4 (9 parts by weight).
(F) The commercial ethylene vinyl acetate copolymer
additive marketed by Exxon Chemicals as ECA 5920*
(G) A mixture of:
l part Additive l
l part Additive 3
l part Additive D
l part of Additive K
(H) The commercial ethylene vinyl acetate copolymer
additive marketed by Amoco as 2042E*
(I) The commercial ethylene vinyl propionate copolymer
additive marketed by BASF as Reroflux 5486*.
(J) No additive.
(K) The reaction product of 4 moles of di-
hydrogenated-tallow amine and 1 mole of pyromellitic
anhydride. The reaction is performed solventless at
150C, stirring under nitrogen for 6 hours.
The following performance characteristics of these fuels
were then measured.
(i) The ability of the fuel to pass through the
diesel fuel main filter at -9C, and the
percentage of wax passing through the filter with
the following results:
*Trade Mark
--.~
,~
-38- 132~S23
1 Additive Time to ~ of Wax
Failure Passing
E ll minutes 18-30
F 16 minutes 30%
G No Failure 90-100%
H 15 minutes 25~
I 12 minutes 25%
J 9 minutes 10%
(ii) The pressure drop across the main filter against
time and the results are shown graphically in
Figure 12.
(iii) The wax settling in the fuels was measured by
cooling lO0 mls of fuel in a graduated measuring
cylinder. The cylinder is cooled at 1C/hour
from a temperature preferably 10C above the
fuel's Cloud Point but not less than 5C above
the fuel's Cloud Point to the test temperature,
which is then held for a prescribed time. The
test temperature and soak time depend upon the
application, i.e. diesel fuel and heating oil.
It is preferred that the test temperature be at
least 5C below the Cloud Point and the minimum
cold soak time at the test temperature be at
2S least 4 hours. Preferably the test temperature
should be 10C or more below the fuel's Cloud
Point and the soak period should be 24 hours or
more.
After the end of the soak period the measuring
cylinder is examined and the extent of wax
crystal settling is visually measured as the
height of any wax layer above the bottom of the
cylinder tO mls~ and expressed in terms of a
percentage of the total volume (lO0 mls). Clear
fuel may be seen ~bove the settled wax crystals
and this form of measure~ent is often sufficient
to form a judgement on the wax settling.
1329623
-39-
1 Sometimes the fuel is cloudy above a settled wax
crystal layer or the wax crystals can be seen to
be visibly denser as they appr~ach the bottom of
the cylinder. In this case a more quantitative
method of analysis is used. Here the top ~% (5
mls) of fuel is sucked off carefully and ~tored,
the next 45~ is sucked off and discarded, the
next 5% is suckeâ off and stored, the next 35% is
sucked off and discarded and finally the bottom
10% is collected after warming to dissolve the
wax crystals. These stored samples will
henceforth be referred to as Top, Middle and
Bottom samples respectively. It is important
that the vacuum applied to remove the samples be
fairly low, i.e. 200 mm water pressure, and that
the top of the pipette is placed just on the
surface of the fuel to avoid currents in the
liquid which could disturb the concentration of
wax at different layers within the cylinder. The
samples are then warmed to 60C for 15 minutes
and examined for wax content by Differential
Scanning Calorimetry (DSC) as previously
described.
In this instance a Mettler TA 2000B DSC machine
was used. A 25 ~1 sample is placed in the sample
cell and regular kerosine in the reference cell
then they are cooled at 22C/minute from 6~C to
at least 10C but preferably 20C above the Wax
Appearance Temperature (WAT) then it is cooled at
2C/minute to approximately 20C below the WAT.
A reference must be run of the unsettled,
uncooled treated fuel. The extent of wax
settling then correlates with the ~AT (or ~WAT =
~3~9~23
-40-
1 WAT settled sample - WAT original). Negative
values indicate dewaxing of the fuel and positive
values indicate wax enrichment through settling.
The wax content may also be used as a measure of
settling from these samples. This is illustrated
by % WAX or ~ % WAX ( %Wax = % Wax settled
sample - % wax original) and, once again negative
values indicate dewaxing of the fuel and positive
values indicate wax enrichment through settlinq.
In this example the fuel was cooled at 1C/hr
from +10C down to -9C and cold soaked for 48
hours prior to testing. The results were as
follows:
Additive Visual Wax WAT C Data Settled Samples
SettlingToP 5% Middle 5% Bottom 10%
E Cloudy -10.80 -4.00 -3.15
throughout
Denser at bottom
P 50% clear-13.35 -0.80 -0.40
above
G 100% -7.85 -7.40 -7.50
35% clear-13.05 -8.50 +0.50
- above
I 65% clear
above
J 100% Semi-gel-6.20 -6.25 -6.40
(The results are also shown graphically in Figure 13).
-41- 1329623
1 WAT original ~
(Unsettled ~uel~ Top 5% Middle 5~ Bottom 10%
E -6.00 -4.80 +2.00 +2.85
F -5.15 -8.20 +4.35 +4.75
~ -7.75 -0.10 +0.35 +0.25
H -5.00 -8.05 -3.50 +4.50
J -6.20 0.00 -0.05 -0.20
(Note that significant depression of the WAT can be
achieved by the most effective additive tG))
% WAT (Settled SamPles)
Top 5% Middle 5~ Bottom 10
E -0.7 +0.8 +0.9
~ -0.8 +2.1 +2.2
G ~0.0 +0.3 +0.1
H -1.3 -0.2 +1.1
J -0.1 +0.0 ~0.1
These results show that as the crystal size is reduced by
the presence of additives, the wax crystals settle
relatively quickly. For example, untreated fuels when
cooled below their cloud points tend to show little wax
crystal settling because the plate-like crystals
int~rlock and cannot tumble freely in the liquid and a
gel-like structure is set up but when a flow improver is
added the crystals may be modified so their habit becomes
less plate-like and tends to form needles of sizes in the
range of tens of micrometers which can move freely in the
liquid and settle relatively rapidly. This wax crystal
settling can cause problems in storage tanks and vehicle
systems. Concentrated wax layers may be unexpectedly
drawn off, especially when the fuel level is low or the
tank disturbed ~e.g. when a vehicle corners), and filter
blockage may occur.
1329623
-42-
l If the wax crystal size can be reduced still further to
below 10 nanometres then the crystals settle relatively
slowly and wax Anti Settling can result giving the
benefits in fuel performance compared to the case of a
fuel with settled wax crystals. If the wax crystal size
can be reduced to below approximately 4 nanometres then
the tendency of the crystals to settle is almost
eliminated within the time of fuel storage. If the
crystal sizes are reduced to the preferred size of below
2 nanometres claim then the wax crystals remain suspended
in the fuel for the many weeks required in some storage
systems and the problems of settling are substantially
eliminated.
(iv) The CFPP performance which was as follows:
l5Additive CFPP TemPerature(C) CFPP Depression
E -14 11
F -20 17
G -20 17
H -20 17
I -19 16
J -3
(v) The average crystal size which was found to be:
Additive Size
(Nanometers)
E 4400
F 10400
G 2600
H 10800
I 8400
J Thin plates in
excess of 50,000
