Note: Descriptions are shown in the official language in which they were submitted.
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Ffeld ofthe Invention
The present invention relates generally to organic acid corrosion
inhibitors for antifreeze coolant formulations. More particularly, the present
s invention relates to C$ mono-carboxylic acids, or isomers and/or salts
thereof, and
neo-decanoic acids, or isomers and/or salts thereof, for use in antifreeze
coolant
concentrates and compositions as corrosion inhibitors to provide prolonged
corrosion protection to the metal surfaces in cooling and/or heating systems,
such
as those found in internal combustion engines.
i o Background of the Invention
Corrosion has long been a problem when certain metals or alloys are
used in applications in which they come into contact with an aqueous medium.
For
example, in heat-transfer systems, such as those found in internal combustion
engines, alcohol-based heat transfer fluids (i. e., antifreezes) can be very
corrosive to
i s the metal surfaces of the .heat-transfer systems. Compounding this problem
is that
the corrosion is accelerated under normal engine operating conditions (i.e.,
high
' temperatures and pressures). Aluminum surfaces, are particularly susceptible
to
corrosion. See, Darden et al., "Monobasic/Diacid Combination as Corrosion
Inhibitors in Antifreeze Formulations," Worldwide Trends in Engine Coolants.
20 .ooling,~,~tem Materials and Testing, SAE Int'1 SP-811, Paper #900804, pp.
135-
51 (1990) ("SAE SP-811").
CA 02238174 1999-02-17
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Corrosion inhibitors have been used to address these
problems. For example, triazoles, thiazoles, borates,
silicates, phosphates, benzoates, nitrates, nitrites and
molybdates have been used in antifreeze formulations. See,
e.g., United States patent No. 4,873,011; see also, SAE SP-811
at pp. 135-138, 145-146. However, such corrosion inhibitors
have several problems, including toxicity (e. g., borates,
nitrites, and molybdates), expense, and inadequate long-term
protection. See United States patent No. 4,946,616, col. 1,
lines 31-45; United States patent No. 4,588,513, col. 1, lines
55-64; SAE SP-811, pp. 137-138. Also, most of these
inhibitors are metal-specific and as such, require multi-
component formulations making them more difficult and more
expensive to prepare commercially. See Canadian Patent No.
1,142,744, pp. 2-3.
Organic acids, such as mono- and/or di-carboxylic
acids, have also been used as corrosion inhibitors. See,
e.g., United States patent Nos. 4,382,008 (combination of
C7-C13 di-carboxylic acid and conventional corrosion
inhibitors); 4,448,702 (di-carboxylic acids having 3 or more
carbons); 4,647,392 (combination of monobasic and dibasic
acids); and 4,946,616 (combination of C10 and C12 diacids).
However, such organic acid formulations also suffer
from a number of problems. For example, sebacic acid, which
is used in several commercial antifreezes (e. g., Texaco's
"Havoline"* Extended Life AntiFreeze/Coolant; General Motors'
* Trade-mark
61009-341(S)
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"Dex-Cool"* Anti-Freeze/Coolant; Canadian Tire's "Motomaster"*
Long Life and is currently used in the standard formulation
set forth by the British Military (see Specification TS 10177,
"Antifreeze, Inhibited Ethanediol, AL-39"), is more difficult
to use commercially since it is commercially available as a
solid, and as such requires heat to dissolve it in a heat
transfer fluid. Also, sebacic acid is generally more
expensive and difficult to obtain commercially since currently
there is only one domestic industrial supplier (Union Camp
to Corporation). See SAE SP-811, pp. 141-142. Also, sebacic
acid and higher di-carboxylic acids, tend to have poor
solubility in antifreeze formulations using hard water. See
United States patent No. 4,578,205, col. 1, lines 52-64.
* Trade-mark
61009-341(S)
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European patent publication No. 479,470 relates to corrosion
inhibitors having at least one acid of the formula:
R
3
$ R2-C-COOH
Ri
wherein the groups RI, R2 and R3 are the same or different Ci-Clo alkyls or
where
one of Rt, R2 and R3 is H, and the other two R groups are CI-Clo alkyls.
However,
i o this publication does not disclose any specific combination of mono-
carboxylic acids
nor does it teach or suggest which combinations would be useful. In fact, the
only
mufti-acid combinations disclosed include sebacic acid, which as previously
discussed has several disadvantages.
Corrosion inhibitors containing neo-decanoic acid (a mono-
i s carboxylic organic acid) have also been suggested. United States patent
No.
4,390,439 ("Schwartz et al.") relates to the use of neo-decanoic acid as a
corrosion
inhibitor in hydraulic fluids. However, Schwartz et al. does not teach or
suggest
other organic acids (except benzoic acid) used alone or in combination with
neo-
decanoic acid as a corrosion inhibitor.
2 o SAE SP-811 also describes neo-decanoic acid as a possible
corrosion inhibitor. However, SAE SP-811 relates to the use of combinations of
mono-carboxylic acids and di-carboxylic acids, including sebacic acid, as
corrosion
inhibitors. Also, although SAE SP-811 suggests that neo-decanoic acid is
ei~ective
as a corrosion inhibitor, SAE SP-811 teaches away from the use of neo-decanoic
2 s acid since it states that "[t]he use of neodecanoic acid is limited by
solubility
considerations ..." (p. 147). '
Thus, it would be desirable to provide an ei~ective corrosion
. inhibitor that is easy to prepare and uses readily available raw materials.
' S_umm,~r~ofthe Invention
s o It is an objective of this invention to provide improved organic acid
corrosion inhibitors comprising a Ca mono-carboxylic acid component, or
isomers
CA 02238174 1999-02-17
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and/or salts thereof, and a neo-decanoic acid, or isomers
and/or salts thereof. The addition of relatively small
amounts of neo-decanoic acid to a C8 mono-carboxylic acid
component results in surprisingly improved corrosion
inhibiting properties as compared to conventional corrosion
inhibitors, other organic acid corrosion inhibitors, and
corrosion inhibitors comprising only the C8 mono-carboxylic
acid component or neo-decanoic acid alone. The C8 mono-
carboxylic acid component is preferably 2-ethylhexanoic acid
or neo-octanoic acid, and more preferably 2-ethylhexanoic
acid.
Optionally, these corrosion inhibitors may also
comprise other organic acid corrosion inhibitors such as di-
carboxylic acids, and conventional corrosion inhibitors such
as triazoles, as well as other additives such as anti-foaming
agents, dyes, pH buffers, scale inhibitors, sequestration and
dispersion agents.
Another objective of this invention is to provide
antifreeze coolant formulations comprising these corrosion
inhibitors and methods of using the formulations for corrosion
protection of metal surfaces in heating and/or cooling
systems, primarily of internal combustion engines.
Brief Description of the Drawings
Figure lA shows an example of a Type I pitting
potent ial t ime-graph result ing from the formulat ion of
Example 4.
Figure 1B shows an example of a Type I+ pitting
61009-341(S)
CA 02238174 1999-02-17
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potential time-graph resulting from the formulation of
Example 3.
Figure 1C shows an example of a Type II pitting
potent ial t ime-graph result ing f rom the formulat ion of
Example 2.
Detailed Description of the Invention
In order that this invention may be more fully
understood, the following detailed description is set forth.
According to one aspect of the present invention
there is provided an antifreeze coolant concentrate comprising
a water-soluble liquid alcohol freezing point depressant and a
corrosion inhibitor composition for antifreeze formulations
comprising a mixture of C8 mono-carboxylic acids, or isomers
and/or salts thereof, and a neo-decanoic acid, or isomers
and/or salts thereof, wherein the corrosion inhibitor is
present in an amount such that the total mono-carboxylic acid
in the concentrate is from about 0.001% to about 5.0% (by
weight).
According to a further aspect of the present
invention there is provided an antifreeze coolant concentrate
comprising a water-soluble liquid alcohol freezing point
depressant and a corrosion inhibitor composition comprising a
C8 mono-carboxylic acid, or isomer and/or salt thereof, and a
neo-decanoic acid, or isomer and/or salt thereof, wherein the
corrosion inhibitor is present in an amount such that the
total mono-carboxylic acid in the concentrate is from about
0.001% to about 5.0% (by weight).
61009-341(Sj
CA 02238174 1999-02-17
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According to another aspect of the present invention
there is provided an antifreeze coolant concentrate
comprising: a) from about 90~ to about 98$ (by weight) of a
liquid-alcohol freezing point depressant; b) from about 2.0$
to about 5.0~ (by weight) of a mixture of 2-ethylhexanoic
acid, or isomer and/or salt thereof, and neo-decanoic acid, or
isomer and/or salt thereof= c) from 0 to about 0.5~ (by
weight) of tolyltriazole; and d) an alkali metal hydroxide in
an amount sufficient to adjust the pH of the concentrate to
between about 6.9 and about 9.6.
According to a still further aspect of the present
invention there is provided a method for inhibiting corrosion
of the metal components in internal combustion engines
comprising the step of contacting the metals to be protected
with the antifreeze coolant composition as defined above.
The corrosion inhibitors of this invention comprise
a C8 mono-carboxylic acid component (i.e., a single C8 mono-
carboxylic acid or mixtures of C8 mono-carboxylic acids), or
isomers and/or salts thereof, and a neo-decanoic acid
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component, or isomers and/or salts thereof. Neo-decanoic acid is a neoacid
which
is a type of mono-carboxylic acid. The term "neoacid" refers to trialkylacetic
acids
having the following general structure:
Ri
R3 - c - cooH
I
Rz
wherein the groups Rt, R2 and R3 are alkyl groups. Neoacids such as neo-
octanoic
i o and neo-decanoic acids are readily available, for example, from Exxon
Chemical
Company.
The addition of a relatively small amount of neo-decanoic acid to a
Cg mono-carboxylic acid component results in surprisingly improved corrosion
inhibiting properties as compared to corrosion inhibitors having conventional
and/or
i s organic acid components, as well as corrosion inhibitors comprising only
the Cg
mono-carboxylic acid component or neo-decanoic acid alone.
Preferably, the corrosion inhibitors of this invention comprise either
2-ethylhexanoic acid ("2-EHA") or neo-octanoic acid, or isomers and/or salts
thereof, and neo-decanoic acid, or isomers and/or salts thereof. As with neo-
~ o decanoic acid, 2-EHA and neo-octanoic acid are less expensive than sebacic
acid
and more readily available (2-EHA may be obtained from, for example, ALLCHEM
Industries, Inc., ASHI.AND Chemical Co., BASF Corp., Brook-Chem Inc.,
EASTMAN Chemical Group and Union Carbide Corp.; neo-octanoic acid is
available from, for example, Exxon Chemical Company). Also, these mono-
2 s carboxylic acids are available as liquids rather than solids (as is
sebacic acid) and as
such, they are more easily used to prepare corrosion inhibitors on a
commercial
scale.
~ The acid components of the corrosion inhibitors of this invention
may alternatively be in the form of an alkali metal salt, ammonium salt or
amine salt.
s o Preferred salts are the alkali metal salts, and most preferred are sodium
or
potassium salts of the mono-carboxylic acids.
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The corrosion inhibitors of this invention may also
include one or more additional corrosion inhibitors, such as
triazoles, thiazoles, di-carboxylic acids, phosphates,
borates, silicates, benzoates, nitrates, nitrites, molybdates,
or alkali metal salts thereof. The preferred corrosion
inhibitors of this invention further comprise a triazole or
thiazole, more preferably, an aromatic triazole or thiazole
such as benzotriazole, mercaptobenzothiazole or tolyltriazole
("TTZ") and most preferably, TTZ.
Other additives may also be used depending on the
application. Suitable additives include anti-foaming agents
(e.g., "PM-5150" from Union Carbide Corp., "Pluronic L-61*"
from BASF Corp., and "Patco* 492" or "Patco 415" from American
Ingredients Company), dyes (e. g., "Alizarine Green*", "Uranine
Yellow*" or "Green AGS-liquid*" from Abbey Color Inc., "Orange
II*(Acid Orange 7)" or "Intracid Rhodamine* WT (Acid Red 388)"
from Crompton & Knowles Corp.), pH buffers, scale inhibitors,
and/or sequestration and dispersion agents (e.g., "bequest"*
from Monsanto Chemical Company, "Bayhibit"* from Miles Inc.,
"Nalco" or "NaIPREP"* from Nalco Chemical Company).
It is contemplated that the corrosion inhibitors of
this invention may be used in numerous applications where
metal surfaces (e. g., aluminum, copper, iron, steel, brass,
solder or other alloys) are in contact with an aqueous medium.
For example, they may be used in conjunction with hydraulic
fluids, aqueous cutting oils, paints, soluble oils, metal
* Trade-mark
61009-341(S)
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cutting fluids, aircraft deicers, and greases.
The corrosion inhibitors of this invention are
particularly well-suited for use in antifreeze coolant
formulations, such as antifreeze coolant concentrates and
compositions, for internal combustion engines.
In antifreeze coolant concentrates, a minor amount
of the corrosion inhibitor is added to a major amount of a
water-soluble liquid alcohol freezing point depressant. The
corrosion inhibitor may be added in an amount from about
0.001 to about 5.0~ (total mono-carboxylic acid by weight in
the concentratey, and preferably, from about 2.0~ to about
5.0$. The corrosion inhibitor comprises a C8 mono-carboxylic
acid component, or isomers and/or salts thereof, and a
relatively small amount of neo-decanoic acid, or isomers
and/or salts thereof. The amount of
61009-341(S)
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WO 97120901 PCT/IIS96/I8657 -
neo-decanoic acid used is that which is sufficient to result in a corrosion
inhibitor
exhibiting a synergistic effect as compared to the corrosion inhibiting
effectiveness
of the individual acid components. Preferably, the corrosion inhibitor
comprises the
Cs mono-carboxylic acid component and neo-decanoic acid in the ratio from
about
J
s 100:1 to about 1:1, and more preferably, about 3:1. In one preferred
embodiment,
the corrosion inhibitor comprises an amount sufficient of the C8 mono-
carboxylic
acid component such that in the antifreeze coolant concentrate, this component
is
present from about 2.4% to about 3.3% (by weight), and more preferably about
3.1%. The neo-decanoic acid is present in an amount sufficient such that its
i o concentration in the antifreeze coolant concentrate is from about 0.8% to
about
I .1 % (by weight), and more preferably about 1.0%.
The antifreeze coolant concentrate may also include one or more
additional corrosion inhibitors, such as triazoles, thiazoles, di-carboxylic
acids,
phosphates, borates, silicates, benzoates, nitrates, nitrites, moiybdates or
alkali
s s metal salts thereof. Such additional corrosion inhibitors may be added at
concentrations of up to about 5.5% (by weight). Preferably, the antifreeze
coolant
concentrate comprises up to about 0.8% (by weight} of a triazole or thiazole,
and
more preferably, up to about 0.5%.
The major portion of the antifreeze coolant concentrate (i.e., 75%-
2 0 99.999% {by weight), preferably 90%-99.999% {by weight)) comprises a
liquid
alcohol freezing point depressant. Suitable liquid alcohol freezing point
depressants
include any alcohol or heat transfer medium capable of use as a heat transfer
fluid
and preferably is at least one alcohol, selected from the group consisting of
methanol, ethanol, propanol, ethylene glycol, diethylene glycol, triethylene
glycol,
2 s propylene glycol, dipropylene glycol, butylene glycol, glycerol, the
monethylether of
glycerol, the dimethylether of glycerol, aikoxy alkanols (such as
methoxyethanol)
and mixtures thereof. The preferred alcohol is selected from the group
consisting
of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol
and
mixtures thereof.
3o The antifreeze coolant concentrate may also comprise a sufficient
amount of an alkali metal hydroxide to adjust the pH to between about 6.0 to
about
CA 02238174 1998-OS-21
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_g_
I0.0, preferably to about 6.9 to about 9.6. Formulations having a pH less than
about 6.0 or more than about 10.0 tend to be corrosive to metal surfaces.
Other
additives, as described above, may also be used depending on the application.
The antifreeze formulations most commonly used are antifreeze
s coolant compositions. In these formulations, an antifreeze concentrate is
usually
diluted with water such that between 10% to about 90% (by weight) water is
present in the composition, and preferably from about 25% to about 75% (by
weight) water, with the balance being the antifreeze coolant concentrate.
It will be appreciated by one of skill in the art that the amount of
1 o corrosion inhibitor (and its composition) used in a specific antifreeze
coolant
formulation may vary when minor adjustments are made to the other components
of
the formulations.
The present invention also provides methods for inhibiting corrosion
of the metal components in internal combustion engines. Such methods comprise
i s the step of contacting the metals to be protected with the inventive
corrosion
inhibitors described above.
In order that this invention may be better understood, the following
examples are set forth.
2 o Twenty-six different antifreeze coolant concentrates were prepared
(Examples 1-26). The components of these formulations are described in Tables
1-
4 below. Each formulation contained ethylene glycol as the water-soluble
liquid
alcohol freezing point depressant, sodium hydroxide ("NaOH") to adjust the pH
to
about 9.0, sodium tolyltriazole ("NaTTZ"), and deionized water, in the
specified
2 s amounts.
Examples 1-4, as shown in Table 1 below, correspond to known
antifreeze coolant concentrates and serve as control formulations. These
Examples
include a formulation comprising conventional corrosion inhibitors (Example I
), a
formulation comprising an organic acid (mono-carboxylic acid based) corrosion
3 o inhibitor (Example 2, contains primarily only organic acid corrosion
inhibitors and a
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WO 97/20901 PCTlUS96/18657
-9-
small amount of NaTTZ), and formulations comprising conventional corrosion
inhibitors as well as organic acid components (di-carboxylic acid based)
(Examples
3 and 4).
Table 1
Control Formulations
Ezample No.
Component (wt%) 1 2 3 4
Ethylene Glycol 93.76 94.3 95.7 95.6
NaTTZ, 50% sol. 0.22 0.5 0.2 0.4
1 o NaN03, 40% sol. 0.26 0 0.5 0.5
Na,Mo04, 35% sol. 0.51 0 0.2 0
Borax, 20% sol. in Ethylene Glycol2.1 0 0 0
Phosphoric Acid, 75% sol. 0.18 0 0 0
Na-Mercaptobenzothiazole 0.55 0 0 0
Na-Silicate, Grade 40 sol. 0.33 0 0 0
NaOH, 50% sol. 0.68 1.7 1.3 1.4
Deionized Water 1.34* 0.1 0.1 0.1
2-Ethvlhexanoic Acid 0 3.2 0 0
Sebacic Acid (solid) 0 0.2 0 2.0
2 o Dodecanedioic Acid 0 0 2.0 0
Neo-Heptanoic Acid 0 0 0 0
Neo-Octanoic Acid 0 0 0 0
Neo-Decan is A id 0 0 0 0
Galvanostatic Pitting Potential:-270 1000 470 150
2 s Ep,mV (I) {II) (I+) (I)
{TYPe)
ASTM D-4340 ~ 0.3 ~ 0.8 ~ 0.8 ~
{corrosion rate, mg/cm2/week) 0.7
* Also includes antifoam, dye, and silicone
CA 02238174 1998-OS-21
WO 97/20901 PCT/US96/I8657
_10_
Examples 5-8 as shown in Table 2 below, are mono-carboxylic acid
antifreeze concentrates each having only a single acid component: 2-EHA
(Example 5), neo-heptanoic acid (Example 6), neo-octanoic acid (Example 7) and
neo-decanoic acid (Example 8).
s Table 2
Formulations of One of 2-EHA, Neo-Heptanoic Acid
Neo-Octanoic Acid or Neo-DPCariOIC Acid
Ezample
No.
Component (wt%) 5 6 7 8
i Ethylene Glycol 94.7 94.7 94.6 94.7
o
NaTTZ, 50% sol. 0.5 0.5 0.5 0.5
NaN03, 40% sol. 0 0 0 0
Na2Mo04, 35% sol. 0 0 0 0
NaOH, 50% sol. 1.5 1.5 1.6 1.5
15 Deionized Water 0.1 0.1 0.1 0.1
2-Ethylhexanoic Acid 3.2 0 0 0
Sebacic Acid (solid) 0 0 0 0
Dodecanedioic Acid 0 0 0 0
Neo-Heptanoic Acid 0 3.2 0 0
2 Neo-Octanoic Acid 0 0 3.2 0
o
Neo-Decanoic Acid 0 0 0 3.2
Galvanostatic Pitting Potential: 1640 1445 2030 -112
Ep,mV (II) (II) (II) (I)
(Type )
ASTM D-4340 0.8 0.6 0.6 0.7
2s (corrosion rate, mg/cmz/week)
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Examples 9-14, as shown in Table 3 below, contain corrosion
inhibitors comprising mixtures of 2-EHA and neo-decanoic acid (Examples 9-11 )
' and neo-octanoic and neo-decanoic acids (Examples 12-14).
CA 02238174 1998-OS-21
WO 97/20901 PCT/US96118657
- .12 -
1
,. .-.
O~ O O O - O O O O O O N ~ ~ O
t~ O
M et"v~ ~n ~ ~O ~O M ..~, ~n
.-1Q~ O O O --'O O O O O .-...;.~ ~ p
O
N ~t '~ O O '~ '-'O O O O ~t o0 N .~ o0
~ O~ O - O N O N ~ O
c
E
as
1 W ...1et ~ ~. "" pp C' ~ + N
~ Ov O O O - O O O O O O N .-.
..~.r
00 V'1
O ~' ~ et "" ~p ~O '~ ..~,
~ Q\ O O O --~O -~ O O O O
x
M
>,..
U
v
E" C~ Wit'N O O ~1.~ ~' O O O O 00 ~ r.~. W
C ~ O ~- O N O N i O
4..
x
a>
w
0 3
N
c 3 a: a'
H
w
'- a ~,
cz, ~ '~ ~.
o ~ a
V o 0
-0 a. '
o _ ,", o v~ 'v .'d:o N
O ~ cOn Q .~ 0
v, O w: . U_ d' U U y o
0o \ U vr U d a ~ v
U M ~n ect . .O U U O
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f~ N ~ ~ ~ 1 1 I ' C
w z C~ O U W ~ O G7 U U C~
z z z A N ~ a z z z c~ CIA
Q
0
CA 02238174 1998-OS-21
WO 97/20901 PCTlUS96118657
-13-
The remaining antifreeze coolant concentrates, Examples 15-26, as
shown in Table 4 below, contain comparative corrosion inhibitors. These
formulations either contain mixtures of 2-EHA and neo-octanoic acid (Examples
15-17), or mixtures of neo-heptanoic acid with 2-EHA (Examples 18-20), neo-
n octanoic acid (Examples 21-23) or neo-decanoic acid (Examples 24-26).
CA 02238174 1998-OS-21
WO 97/2090f PC'i'/US96/I8657
_ 14 _
m ' w ~c r. ao ~
~ O O O G O O C O _+~
N O
O tn tD tD
~ O O O H C O O O O .-
v
N ~ C O t0 r O O 'vt ~ cD
O N
O O O v O
O In f0 r ? fD - CO
N
O O O O O O O CVO ~ C
b 47 tD f0(O ~ t0
O O O O O .-.
O O ~ O
b O
tf1 fD r b ~ - in
N ~ C O O O O O O C O
N
~ N In r OD tr CD
N ~ O O C O O N O
W
C O O
b ~ t(7 In .-t0 (O ~ N
O O O O O -
tn
G
O O
N
~y
In tO r er CD nb" O
O V C = G
O O O ( O O O CO
i
4.
C~
f0 b
I y f1 t0 r b Q - CO
O O O C O O O O (V O
tD _ O
to'0'~ fD <O 10 N CO
-
r C~ O O O O O O O ~ O
fD _ O
b V' ~ t0 V' (D ~ cD
=
e~O O O O O fV O O O O r C
Y
E
d
E
'c
c :
a
a 53~ ~ '
a d
L
Z Z ~ ~ V ~ ~ ~ Z G
Z c Q
W7 O N
r~ .wl
CA 02238174 1998-OS-21
WO 97/20901 PCT/US96/I8657 -
-15-
Each of the formulations tested was prepared in a mixing vessel at
room temperature (approximately 20°C) and at a pressure of 91-I 11 KPa.
In each
case, ethylene glycol was added first. to the mixing vessel and while being
agitated,
the remaining components were added in the following order: acid components,
s NaOH, NaTTZ, water, and other corrosion inhibitors, if any. All of the
components were obtained commercially as follows: ethylene glycol from Union
Carbide; NaTTZ, 50% solution, from PMC Specialties Group; NaN03, 40%
solution, from Chilean Nitrate Sales Corp; NaZMo04, 35% solution, from North
Metal & Chemical Company; NaOH, 50% solution, from Occidental Petroleum;
Zo 2-EHA from ASHLAND Chemical Co.; Sebacic acid from Union Camp
Corporation; dodecanedioic acid from DuPont; and the neo-acids were from Exxon
Chemical Company.
After preparation, each of the formulations of the examples was
subjected to the Ford Motor Company Laboratory Test Method BL 5-I, "A Rapid
is Method to Predict the Effectiveness of Inhibited Coolants in Aluminum Heat
Exchangers" (Galvanostatic Pitting Potential Test) and ASTM D-4340 "Standard
Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under
Heat-Rejecting Conditions" (Aluminum Hot Surface Test). These tests, described
below, are well known analyses used to evaluate the effectiveness of corrosion
2 o inhibitors in engine coolants.
C'Talvanostatic Pitting Potential
The Galvanostatic Pitting Potential Test is a standard
electrochemical technique used to evaluate the effectiveness of corrosion
inhibitors
in the prevention of pitting corrosion. This test is used to predict the
effectiveness
2 s of engine coolants in preventing pitting and crevice formation on aluminum
heat
exchanger alloys. The test measures the pitting potential (Ep) of aluminum
alloys in
an engine coolant. See Ford Motor Company, BL 5-i, supra. The test procedure
is well known. See, Wiggle et al., "The Effectiveness of Engine Coolant
Inhibitors
for Aluminum," S',onrosion 80, National Association of Corrosion Engineering
so Conference, Paper #69 and Wiggle et al., "A Rapid Method to Predict the
Effectiveness of Inhibited Engine Coolants in Aluminum Heat Exchangers," SAE
CA 02238174 1999-02-17
- 16 -
Paper #800800, Society of Automotive Engineers, Passenger Car
Meeting, June 1980, Dearborn, Michigan.
This test provides a measure of how well the
corrosion inhibitor prevents the breakdown of the protective
oxide film and subsequent pit formation on the sample metal,
and provides a measure of how well the inhibitor repassivates
the surface once initial pit formation has begun. In general,
the results from this test can be categorized in one of three
t ype s .
In the first (Type I) (as depicted in Figure lA),
upon polarization of the metal surface, the potential
increases rapidly to some maximum level within the first few
seconds. The passive film then ruptures followed by a rapid
decrease in the potential. The pitting potential levels off
once an equilibrium is reached between the potential, pit
growth and pit repassivation. Figure lA depicts the results
of this test on the formulation of Example 4.
In the second (Types I+) (depicted in Figure 1B),
the passive film rupture occurs almost immediately upon
polarization. The potential initially decreases, but then
begins to rise with time. This rise is indicative of the
formation of a current inhibiting film on the metal surface.
Figure 1B depicts the results of this test on the formulation
of Example 3.
In the third type (Type II) (depicted in Figure 1C),
the potential does not decrease after rupture. Instead, the
potential increases rapidly to a noble potential which
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remained constant or increased slightly throughout the test.
Figure 1C depicts the results of this test on the formulation
of Example 2.
Most commercial antifreeze formulations have a
pitting potential ranging from -200 to +200 mV. Generally,
the higher (more positive) the Ep value is at a fixed current
density, the more effect ive the ant ifreeze formulat ion is in
preventing pitting corrosion. See Ford Motor Company, HL 5-1,
supra; Wiggle et al., Paper #69, supra, and SAE Paper #800800,
su ra; and SAE SP-811, supra, at p. 138, right col., line 44.
The results of the Galvanostatic Pitting Potential
Corrosion Test for the formulations of Examples 1-26 are set
forth in Tables 1-4, above. For each of the formulations, the
pitting potential was determined using a current density of
100uA/cm2.
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As shown in Tables 1-4 above, corrosion inhibitors comprising a C,
' mono-carboxylic acid and neo-decanoic acid (Examples 9-14, Table 3) exhibit
Ep
values that are either above or within the acceptable range of -200 to x-200
mV
Indeed, corrosion inhibitors comprising a C, mono-carboxylic acid and a
relatively
s small amount of neo-decanaic acid (Examples 9 and 12, Table 3 ) exhibited
the
highest Ep values of all the formulations tested including those of the
control group
(Examples 1-4, Table 1}.
Also, the corrosion inhibitors comprising a C, mono-carboxylic acid
and a relatively small amount of neo-decanoic acid (Examples 9 and 12, Table 3
)
:.o exhibited surprisingly higher Ep values than those expected from the Ep
values
exhibited by formulations containing only a single mono-carboxylic acid
component.
For example, a small amount of neo-decanoic acid added to 2-EHA (Example 9,
Table 3 ) resulted in a formulation with a synergistic Ep of 2340 mV as
compared to
the Ep values of the formulations that contained only 2-EHA ( 1640 mV, Example
.s 5, Table 2) or neo-decanoic acid {-t 12 mV, Example 8, Table 2). Similarly,
a
small amount of neo-decanoic acid added to neo-octanoic acid (Example 12,
Table
3 ) resulted in a formulation with a synergistic Ep of 2620 mV as compared to
the
Ep values of the formulations that contained only neo-octanoic acid (2030 mV,
Example 7, Table 2) or neo-decanoic acid (-I I2 mV, Example 8, Table 2).
z ~ The higher synergistic Ep values were not observed when using
corrosion inhibitors comprising two C, mono-carboxylic acids without neo-
decanoic acid (Examples IS-17, Table 4), or using corrosion inhibitors
comprising
neo-heptanoic acid and a C, mono-carboxylic acid (Examples 18-Z3, Table 4).
Similarly, adding a small amount of neo-decanoic acid to neo-heptanoic acid
z s (Examples 24-26, Table 4) did not result in a synergistic affect when
compared to
,. the formulations that contained only neo-heptanoic acid (Example 6, Table
2) or
neo-decanoic acid (Example 8, Table 2).
J
~ST'~I D-4340 4luminum Hat Surface Test
The Aluminum Hot Surface Test is another standard technique used
3 o to evaluate the effectiveness of corrosion inhibitors. This test measures
the
corrosion rate of a metal sample resulting from the corrosive properties of
RECTiFfED SHEET (RULE 91)
(SAIEP
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antifreeze formulations. According to ASTM D-3306, the maximum allowed
corrosion rate resulting from a tested sample is 1.0 mg/cm'/week. The results
for
this test are also set forth in Tables 1-4 above. As shown in the Tables
above, the
antifreeze concentrates comprising a C, mono-carboxylic acid and a small
amount
s
s of neo-decanoic acid (Examples 9 and 12, Table 3) resulted in a corrosion
rate of
0.8 and 0.4 mg/cm2/week, respectively, less than the ASTM D-3306 standard of
1.0
mg/cmz/week. This illustrates that the corrosion inhibitors of this invention
not
only protect aluminum from pitting corrosion, but also from cavitation erosion
that
occurs in aluminum cylinder heads.
:. o One skilled in the art will appreciate that the present invention can be
practiced by other than the above-described embodiments, which are presented
herein far the purpose of illustration and not of limitation, and that the
present
invention is limited only by the claims that follow.
RECTIFIED SHEET (RULE 91)
ISA/EP
