Note: Descriptions are shown in the official language in which they were submitted.
~63235
Middle Distillate Compositions with Im~oved Low
Temperature Flow Properties
1 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 spongy mass entrapping
the oil therein.
It has long been known that various composltions 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 wax and oil in such a manner as to permit
the oil to remain fluid at a lower temperature.
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 C3-C5 vinyl
esters, e.g. vinyl acetate, as pour 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. 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.
- 2 - ~2~ S
1 Similarly United Kingdom Patent 1263152 suggests that
the size of the wax crystals may be controlled by
using a copolymer having a lower degree of side chain
branching.
With the increasing diversity in distillate fuels,
types of fuel have emerged which cannot be treated by
the existing additives or which require an uneconomi-
cally high level of additive. One particular group of
fuels that present such problems are those which have
a relatively narrow boiling range. Fuels are frequently
characterised by their Initial ~oiling Point, Final
Boiling Point and the interim temperatures at which
certain volume percentages of the initial fuel have
distilled. Fuels whose 20% to 9Q% distillation
point differ within the range of from 65 to 100C
especially 70 to 100C (ASTM D86) and 90~ boiling
temperature is generally from 10 to 30C especially 10
to 25C of the final boiling point have been found
particularly difficult to treat sometimes being
virtually unaffected by additives or otherwise requiring
very high levels of additive. All distillations
referred to herein are according to ASTM D86
Furthermore with the increase in the cost of crude oil
it has also become important for a refiner to increase
25 his procuction ot distillate fuels and to optimise
_ 3 _ ~2~35
l his operations using what is known as sharp fraction-
ation again resulting in distillate fuels that
are difficult to treat with conventional additives or
that require a treat level than is unacceptably high
for the economic standpoint. Typical sharply ~raction-
ated fuels have a 90% to final boiling point of 10 to
20C usually with a 20 to 90~ boiling range of 90 to
110C. Both types of fuel have final boiling points
above 350C generally a final boiling point in the
range 350C to 375C especially 350C to 370C.
The copolymers of ethylene and vinyl acetate which
have found widespread use for improving the fiow of
the previously widely available distillate fuels
generally contained up to about 30 wt ~ vinyl acetate
where the additive was used to control the size of wax
crystals forming in the fuel or they contained around
36 wt % or more vinyl acetate where their prime
function was to lower the pour point of the distillate
fuel. We have not found either of these types of
additive to be effective in the treatment of the
narrow boiling and/or sharply fractionated fuels
described above.
We~have, however, found that copolymers of ethylene
and vinyl esters of carboxylic acids containing from 1
to 4 carbon atoms containing from 32 to 35 wt ~ of the
, ....
_ 4 _ ~2~3~35
l vinyl ester and having a number average molecular
weight of from 1000 to 6000 are particularly effective
in the treatment of these of fuels.
The present invention therefore provides the use as an
additive for improving the flow properties of a
distillate petroleum fuel oil whose 20~ and 90~
distillation points differ within the range of from 65
to 100C, and/or for improving the flow properties of
a distillate fuel whose 90% to final boiling point is
10 to 20C of an additive comprising a copolymer of
ethylene and a vinyl ester of a carboxylic acid
containing l to 4 carbon atoms containing 32 to 35 wt
% of the vinyl ester and having a number average
molecular weight of lO00 to 6000.
The present invention further provides a distillate
fuel whose 20% and 90% distillation point differ
by 65 to 100C and whose 90% boiling temperature is
from 10 to 30C of the final boiling point and/or
whose 90~ to final boiling point is 10 to 20~C and
containing from 50 to 500 ppm (parts per million) of a
copolymer of ethylene and a vinyl ester of a carboxylic
acid containing 1 to 4 carbon atoms containing 32 to
35 wt ~ of the vinyl ester and having a number average
molecular weight of 1000 to 6000.
_ 5 ~63235
1 The copolymer of the ethylene and vinyl ester of the
carboxylic acid may be a mixture of two copolymers
such as those generally described in United States
Patent 3,961,916 which may or may not contain the same
vinyl ester. In particular we find that an additive
combination containing at least 10 parts by weight of
the growth arrestor for each part by weight of the wax
crystal nucleator is suitable for treating this type
of fuel. The mixture being particularly useful
since it allows added flexibility.
A preferred embôdiment of the present invention
therefore provides the use as an additive for improving
the flow properties of a distillate petroleum fuel oil
whose 20% to 90~ distillation points dlffer within the
range of from 65 to 100C, and/or of a distillate fuel
whose 90% boiling temperature is from 10 to 30C
preferably 10 to 20C of the final boiling point an
additive comprising from 10 to 15 parts by weight of a
synthetic polymeric material having the property of a
wax growth arrestor in said fuel for each part of a
synthetic polymeric material having the properties of
a wax growth stimulator, said wax growth arrestor and
- 6 - ~Z6323S
1 growth stimulator being copolymers of ethylene and
vinyl esters of carboxylic acids containing from 1 to
4 carbon atoms the average ester content of said
copolymers being in the range 32 to 35 wt.% and the
number average molecular weight thereof being in the
range 1000 to 6000.
In a further embodiment the present invention provides
a distillate fuel whose 20% to 90% boiling fraction
differ in their boiling point by from 65 to 100C
and/or a distillate fuel whose 90% to final boiling
point is 10 to 20C containing from 50 to 500 ppm
parts per million of an additive mixture of 10 to 15
parts by weight of a synthetic polymeric material
having the property of a wax growth arrestor in said
fuel for each part of a synthetic polymeric material
having the properties of a wax growth stimulator said
growth arrestor and growth stimulator being copolymers
of ethylene and vinyl esters of carboxylic acids
containing from 1 to 4 carbon atoms, the average ester
content of said copolymers belng in the range 32 to 35
wt.% and the number average molecular weight thereof
being in the range 1000 ~o 6000.
.
. ~ .
_ 7 ~ 3~35
1 The fuels whose 20~ to 90~ distillation points differ
within the range 65 to 100C their 90% boiling temperature
generally is from lO to 30C of the final boiling
points generally have a final boiling point above 350C
usually between 350C and 375C more usually between
350C and 370C. The fuels whose 90% to final boiling
point is 10 to 20C usually have a 20 to 90% distillation
ranye of from 90 to 110C and also generally have
final boiling points above 350C usually between 350C
and 375C more usually between 350C and 370C.
Where the additive is a mixture the wax growth
stimulator or nucleator is a synthetic polymeric
material which is soluble in the distillate at temper-
atures substantially above the saturation temperature
but on cooling o the distillate progressively separates
out in the form of small particles as the temperature
of the distillate approaches the saturation point,
e.g. is cooled from a point slightly above (e.g. 10C
above; preferably about 5C above) said saturation
temperature. The term "saturation temperature" is
defined as the lowest temperature at which solute,
e.g. wax, cannot be crystallized out of the solution
even if known crystallization inducement methods are
used. Whilst not known certainly it is believed that
as cooling continues, additional nucleator particles
separate out in a more or less continuous manner.
These additional particles act as nucleators for
- 8 - 12~3~35
1 continued wax crystallization, which in effect, would
prevent substantial supercooling of the distillate.
The advantages of having fresh nucleator particles
formed continuously is that the supersaturation of the
distillate with n-paraffins is kept at the lowest
possible level thus facilitating a molecule of growth
arrestor to build itself into the growth center of
growing crystals and by so doing to stop the further
growth.
The inhibitory effect of a growth arrester is
believed to result from the presence of bulky groups
in its molecule. Additional nucleator should separate
out to replace the deactivated growth centers. The
wax growth arrester is more soluble in said distillate
than said nucleator and it acts as a growth arrester
as the wax crystal forms.
The nucleator should not be insoluble in the distillate
at elevated temperatures nor should it start to
separate out at a temperature substantially above that
at which wax crystalli~ation can occur. If nucleators
separate out at a temperature substantially above the
temperature at which crystalli~ation can occur, then
they tend to settle at the bottom of the vessel
holding the distillate, instead of remaining dispersed
within the distillate. This factor is especially
important when the distillate is subjected to repeated
:
1263235
g
1 warming and cooling as during the warm and cool parts
of a dav since it does not result in adequate redisper-
sion of the nucleant particles in the distillate.
The synthetic polymeric materials used as wax growth
stimulators and wax growth arresters may contain the
same or different vinyl esters.
For the purpose of this invention, wax crystal growth
stimu~ators, wax nucleators and nucleants for wax are
all considered equivalent terms and are used inter-
changeably.
Wax growth arresters (hereinafter sometimes referredto as wax arresters), generally include in their
molecular structure wax-like polymethylene segments
which are capable of building themselves into the
lattice of the wax crystals at the point of lattice
dislocation, and also contain bulky groups which
prevent incorporation of further molecules of n-paraffins
at the point of lattice dislocation and by so doing
stop further growth of crystal.
A good synthetic polymeric wax nucleator, can be
chosen by visually comparing a transparent container
~containing a 0.1 to 3.0 wt.% solution of the potential
nucleator in a distillate to an identical container
~with the same distillate having no additive, as the
temperature of the two materials is lowered. The onset
1263~3S
-- 1 o --
1 of the wax crystallization from the distillate
containing a polymeric material which has nucleator
characteristics will occur at a higher temperature
than that at which the crystallization will start in
the absence of said nucleator. ~imilarly, a wax
arrester usually is characterized by the ability to
delay onset of crystalli2ation.
The synthetic polymers used as nucleating agents and
as wax growth arresters are copolymers of ethylene
and vinyl ester and may contain the same or different
ester monomer.
With the preferred additive that is a mixture of
polymers as described above the vinyl ester content
and molecular weight are the average over the mixture.
The additive may however also be single polymer by
which is meant material produced in a single polymer-
isation. In this instance the materials may be
obtained by the well known high pressure or solution
polymerisation techniques that have previously been
suggested ~or the production of ethylene vinyl ester,
especially vinyl acetate copolymers for fuel additives.
Typical vinyl esters for both mixtures and single
polymers include vinyl acetater vinyl propionate, and
vinyl butyrate.
" ~;263235
l The rlow improvers when incorporated into the distillate
fuels preferably are effective in:
l. maintaining these fuels fluid at the operating
temperatures,
2. arresting the growth of separating wax crystals
when the oils are submitted to slow cooling,
i.e. 0.2F to 2F./hr, which are typical of the
rates encountered when "oil in bulk" is exposed
to atmospheric cooling.
0 3. arresting the growth of separating wax crystals
when the oils are submitted to fast cooling,
i.e. 10F. to 100F./hr/. which are typical of
the rates encountered when relatively warm oil
enters transfer lines and is there suddenly
exposed to low temperatures.
All three above-quoted criteria are desired in order
to assure that a fuel is pumpable and filterable under
the conditions of its distribution and it use.
As mentioned where mixtures of polymers are used the
molecular weight is the average of the two polymers and
in general, the preferred number average molecular
weight (VPO) for the nucleator will be within the
range of 500-6000, more preferably 1200-6000. Specifically,
~ for example, a relatively low molecular weight ethylene-
vinyl ester copolymer with a relatively high vinylester content has been found to act as a wax growth
- 12 ~ ~2~32~5
l arrester. On the other handl a relatively high
molecular weight copolymer of ethylene with a vinyl
ester which copolymer has a relatively low content
of vinyl ester acts ais a nucleating agent. Even more
specifically, blends containing ethylene/vinyl acetate
copolymers of number average molecular weights from
1200-6000 (VPO) with vinyl acetate contents of about
32-50 wt.% (e.g. about 11 to 25 mole % ester) as the
wax arresters and ethylene/vinyl acetate copolymers of
about S00-10,000 (VPO) number average molecular weight
with qinyl acetate comonomer proportions by weight of
1-30 wt.% (e.g. about 0.3 to 12 mole % ester) as the
wax growth stimulators have been found to be highly
effective. Where the nucleant is an ethylene/vinyl
acetate copolymer its number average molecular weight
is preferably at least 500, preferably 1000, higher
and/or the ester content at least 5% lower than
the corresponding property of the wax growth
arrester.
All molecular weights specified herein are "number
average molecular weights", which are molecular
~weights as measured by Vapor Phase Osmometry (VPO),
e.g. using Mechrolab Vapor Phase Osmometer 301A. The
vinyl acetate cantents are determined by saponifica~ion.
:
_ 13 _ ~ ~ ~3~35
1 Thus, relative to the growth arrester, the nucleator
can comprise an ethylene-vinyl acetate copolymer of a
higher molecular weight if the vinyl acetate content
of both polymeric materials is about equal. Where
two synthetic polymers are used they may be made
separately or they can be made consecutively in one
batch by varying the reaction conditions. Thus, the
reaction conditions can be selected so that the
initial polymerization reaction produces a polymer
having primarily nucleator characteristics and the
reaction conditions can be changed to produce a
polymer having primarily wax growth arresting properties
or vice versa. In this manner, a mixture of polymers
can be produced having both types of functions.
In the specific embodiment of the invention which
employs two different copolymers of ethylene and
vinyl acetate the relationships between the concentration
of vinyl acetate in the copolymer and molecular weight
of the copolymers are important since they are
factors which determines the role of the particular
~copolymer in the fuel. That is, they determine, given
the other polymer properties are similar whether or
not the copolymer as a whole will be performing within
the composition as a wax arrester or as a wax nucleating
agent.~ Thus, very generally as a rule of thumb, the
nucleating agents~should have relatively long poly-
.
- 14 - ~ ~63~35
1 methylene segments, and so as these synthetic
polymers approach low molecular weight ranges, the
proportion of vinyl acetate should also decrease. On
the other hand, as the molecular weight increases, the
proportion of vinyl acetate should also increase.
Thus, the specific wax nucleating agents will comprise
a copoly~er of ethylene and a relatively low proportion
of vinyl acetate with a relatively high molecular
weight.
The wax arrester on the other hand will, in general,
be a relatively low molecular weight copolymer of a
relatively high vinyl acetate content since the
function of wax arresting depends more on the presence
of bulky groups, such as ester groups, attached to the
backbone of the molecule of the copolymer.
Although the separate copolymers may be blended
directly in the fuel, it will normally be found
desirable to prepare a concentrate. This may be
effected by first associating each with a separate
solvent, but most preferably by dissolving each in a
common solvent. Thus, both the preferred relatively
lower molecular weight high vinyl acetate (second)
copolymer and the preferred first , the relatively
high molecular weight low vinyl acetate copolymer, may
be dissolved ln a kerosene or heavy aromatic naphtha.
Preferred~concentrates will contain 5-60%, preferably
~:
_ 15 _ ~ ~63235
1 10-50% total copolymer with the balance being a
hydrocarbon oil solvent.
The arrester copolymers may be prepared by known
procedures employing free-radical initiators, preferably
organic peroxide compounds. Suitable procedures are
high temperature and high pressure processes or the
solution processes U.S~ specifications, such as U.S.
Pat. Nos. 3~048,479 or 3,093,623 and United Kingdom
Patent Specification 1263152.
In one aspect the fuels to which the present invention
relates are diffïcult to treat with conventional
additives because of the relatively narrow boiling
range of the 20% to 90~ degree fraction of the fuel,
the 90% fraction boiling from 65 to 100~C above that
of the 20~ fraction and/or because of the relatively
small gap between the 90~ boiling point and the final
boiling point of less than 25~C and even, in some
instances less than 20C.
Desirably, there is present a total of 0.001% to 0.5%
20 by weight of additive, based on the weight of fuel;
preferably 0.005 to 0.1%, most preferably 0.01 to
0.04%, all percents being weight percents. Where a
mixture is used the pol~meric materials are used in
- 16 ~ ~2~35
l ratios of 10 to 15 parts by weight of growth arrester,
per part of the nucleator.
The present invention is illustrated by the following
- Examples in which an additive of the present invention
(additive A) was an oil solution containinq
63 wt.% of a combination of polymers comprising 13
parts by weight of a wax crystal growth arrestor
comprising an ethylene vinyl acetate copolymer of
number average molecular weight 2500 and vinyl acetate
content of 36 wt.% and 1 part by weight of wax crystal
simulator of number average molecular weight 3500 and
a vinyl acetate content of about 13 wt.% Additive B
was an oil solution containing 45 wt.% of an additive
combination of 3 parts by weight of the abovementioned
wax crystal growth arrestor and 1 part of the wax
crystal simulator according to United States Patent
3961916. Additive C is 50 wt.% solution in oil of an
ethylene acetate copolymer of number average molecular
weight 2000 and vinyl acetate content 30 wt.%.
-- l7
12f~235
1 The fuels used in the Examples were as follows:
Initial 20% 90~ Final
B.P. B~P. B.P. B.P.
C C C C
Fuel 1 200 248 334 360
Fuel 2 228 280 351 374
~uel 3 220 266 346 367
Fuel 4 224 268 341 359
Fuel 5 221 259 331 361
Fuel 6 244 264 336 360
10 Fuel 7 163 240 344 362
Fuel 8 160 234 344 358
Fuel 9 200 257 336 362
Fuel 10 213 264 338 360
In the Examples the Wax Crystal Size at Fast Cooling
Rates is measured by the Cold Filter Plugging Point
test (CFPP). This test is carried out by the procedure
described in "Journal of the Institute of Petroleum",
Volume 52, No. 510, June 1966, pp. 173-185. In brief,
the~CFPP test is carried out with a 45 ml sample of
,,
the oil to be tested. The oil placed in the ASTM
~cloud point jar is cooled in a bath maintained at
about --30F. Every two degrees drop in temperature,
starting from 4F. above the cloud point, the oil
:
is forced at a suction of 8 inches of water through a
filter element provided with a 350 mesh screen into a
~ plpette to a marX indicating a volume of 20 ml., at
: ~ ;
18 -
~63235
1 which time the oil is allowed to return by gravity
flow to the cooling chamber. The test is repeated with
each 2C drop in oil temperature until the oil fails
to fill the pipette in a period of 60 seconds to
the aforesaid mark. The results of the test are
reported as the Cold Filter Plugging Point which is
the highest temperature at which the oil fails to fill
the pipette.
The amounts of Additive A, Additive B and Additive C
required to achieve a 6C, 8C and 10C reduction in
the temperature at which these fuels would pass the
CFPP test were determined to be as follows:
Fuel 6C 8C 10C
Additive Additive Additive ~eduction Reductlon
A B C A B C A B C
1 410 760 700 5601050 not 7001360 not
possible possible
2 130 400 440 l90 540 620 250 650 n
3 420 700 - 500 850 - 520 820
4 7~0~ not 800 not 900 not
Fssible Fssible Fssible
780 ~ " 840 " not n
possible
6 250 - 1000 330 - 1000 410 - 1000
7 570 - 900 620 ~ 950 710 - 1100
8 S00 - 900 600 - 1000 700 - 1100
9 260 - not 370 - not 450 - not
possible Fossible possible
530 -- 570 -- 600 ~ n
~63~5
, g
1 In a further series of experiments the amount of
additive required to give a reduction of 6, 8 and 10C
in the CFPP value of various fuels was tested and
compared with the amounts required for additives
outside of the present invention.
The fuels used were: ~
Fuel No. IBP 20% 90~ F8P
11 107 244 351 381
12 113 242 355 375
13 200 248 334 360
14 220 263 350 373
220 266 346 367
16 221 259 331 361
17 222 260 32~ 354
18 228 280 351 374
and the additives used were A, 8 and C as used in the
previous example together with Additives D to H as
follows:
Wt. %
Vinyl Molecular
Additives - Acetate Weight
~ D 34.8 ~~ 2650
~ E 27.1 3170
- F 28.9 2590
G 28.2 2940
H 29.9 2300
; The results are given in the following table.
2~cii3235
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