Note: Descriptions are shown in the official language in which they were submitted.
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-1-
AVIATION PHOSPHATE ESTER FUNCTIONAL
FLUIDS WITH ENHANCED ACID SCAVENGING PROPERTIES
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001] The present invention relates to aviation phosphate ester functional
fluids resistant to acid build-up.
RELATED ART
[0002] Phosphate ester based functional fluids are well known in the
lubrication art and have been utilized for years as electronic coolants, power
transmission and hydraulic fluids and refrigeration equipment fluids to
mention a
few. Hydraulic fluids which are to be used in aircraft applications must meet
certain performance criteria among which are thermal stability, fire
resistance,
low susceptibility to viscosity changes over a wide range of temperatures,
hydrolytic stability and good lubricity.
[0003] In current available commercial hydraulic fluids, phosphate esters are
the most commonly used base stocks of which tributyl phosphate, isopropylated
triphenyl phosphates, n-butyl diphenyl phosphate, and di-n-butyl phenyl
phosphate are widely used components. Phosphate ester based functional fluids
useful as aircraft hydraulic fluids have been described in U.S. Patents
5,464,551,
3,723,320 and 3,679,587.
[0004] The commercial aircraft system designers have opted to use phosphate
esters because of the superior fire resistance properties of phosphate esters.
However, the reduced fire risk is accompanied by a debit in various
performance
parameters such as lesser stability when compared to the hydrocarbon based
fluids or silicate ester fluids also in use.
[0005] Phosphate esters tend to absorb atmospheric moisture readily and
build up high concentrations of water (0.3 to 1% water, sometimes more). Like
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-2-
all esters, these fluids have the potential to hydrolyze (react with water to
form
alcohols and acids). The presence of high concentrations of water typically
results in extent of hydrolysis setting the life of the fluid (point at which
the fluid
has to be replaced). The OEMs Acid Number specification limit for in-service
fluids has been set at 1.5 mg KOH/g.
[0006] Particular mixtures of phosphate esters have been identified as being
useful as the base fluid for phosphate ester based functional fluids,
especially
those used in aircraft. Thus references can be made to Slcydrol LD-4 which
reportedly contains 30-35 wt% di-butyl phenyl phosphate, 50 to 60 wt% tri-
butyl
phosphate, 5 to 10 wt% viscosity index improver, 0.13 to 1 wt% diphenyldithio-
ethane copper corrosion inhibitor, 0.005 to 1 wt% perfluoroallcylsulfonic acid
salt anti-erosion agent, 4 to 8 wt% acid scavenger and about 1 wt% 2,6 di
tertiary butyl p-cresol as an antioxidant.
[0007] As aircraft hydraulic systems have advanced and operating conditions
have become more severe, special phosphate ester base stocks have been
described. USP 5,464,551 describes a base stock comprising between about 10
to 100 wt% of a trialkyl phosphate, between about 0 and 70 wt% dialkyl aryl
phosphate and from about 0 to 25 wt% alkyl diaryl phosphate, the sum of the
proportionate amount of each component equally 100%. Specifically, it is
stated
that the alkyl substitutent of the trialkyl phosphate contains between 3 and 8
carbons, preferably between 4 and 8 carbons, more preferably between 4 and 5
carbons and are bonded to the phosphate moiety via a primary carbon. Prefer-
ably the alkyl substitutents of the tri alkyl phosphate, the di alkyl aryl
phosphate
and the alkyl di aryl phosphate are isoalkyl groups, substantially iso C4 and
iso
C5 allcyl groups.
[0008] Another advance in base fluid is described in WO 96/17517, published
June 13, 1996, which teaches a phosphate ester base stock comprising 60 to
95 wt% of a tri alkyl phosphate and about 5 to 40 wt% of a second component
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-3-
selected from the group consisting of triaryl phosphate, a mixture of triaryl
phosphate and linear polyoxy allcylene material, and a linear polyoxyl
alkylene
material, which base stock is free of di alkyl aryl phosphate and alkyl di
aryl
phosphate. In such base fluid the allcyl groups are, aliphatic and alicyclic
group
wherein the aliphates group are straight or branched chain, and contain
independently, 1 to 12 carbon atoms and di aryl groups are, independently,
phenyl or alkyl substituted phenyl having from 7 to 20 carbon atoms.
[0009] Phosphate ester functional fluids are formulated with an acid
scavenger to prevent acid build-up. U.S. Patents 3,723,320, 3,941,708 and
5,464,551 disclose epoxide acid scavengers for use in phosphate ester based
functional fluids and teach that the preferred epoxides are 3,4-
epoxycycloalkyl
carboxylates.
[0010] The use of alkyl epoxides including the 3,4-epoxycycloalkyl
carboxylate acid scavengers currently used in commercial phosphate ester based
functional fluid compositions result in fluids which are susceptible to the
forma-
tion of carboxylic acids (weak acids) during use in an aircraft. During
service in
an aircraft, the acid nuinber of the phosphate ester based functional fluid
can
reach 1.6 mg KOH/g despite the presence of the epoxide acid scavenger in the
fluid. The acidity is explained by the hydrolysis of the carboxylate group of
the
epoxide acid scavenger that lead to a wealc carboxylic acid and an alcohol.
This
reaction is illustrated below:
0 0
11 C-OR C-OH
+ H20 + ROH
0 0
where R is an alkyl group containing from 2 to 12 carbon atoms.
[0011] Carbodiimides are well known acid scavengers. Dr. Achim
Fessenbecker, Rhein Chemie Rheinau GmbH (NLGI, vol. 61, 3, p. 10, 1996)
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-4-
disclosed that the Total Acid Number (TAN) of isopropylphenyl phosphate
containing a carbodiilnide was reduced in a coke bottle test as compared with
the
pure base fluid and thus carbodiimide was deemed capable of neutralizing
strong
acids as phosphoric acids.
[0012] USP 6,235,687 relates to lubricating oils exhibiting anti-rust
properties that are obtained by adding to the lubricating oil an acidic anti-
rust
additive and an acid scavenger such as carbodiiinide, in a specific sequence.
[0013] USP 5,614,483 relates to lubricant base materials containing ester
groups that may be stabilized by adding a small quantity of carbodiiinides and
the service life lubricants manufactured therefrom may be decisively extended.
[0014] USP 6,143,702 discloses lubricating oils of enhanced oxidation
stability that are obtained by adding to the lubricating oil a mixture
comprising
n-phenyl-l-naphthyl amine and an acid scavenger such as carbodiimide.
DESCRIPTION OF THE INVENTION
[0015] The present invention is directed to a phosphate ester based functional
fluid comprising a major amount of a organic phosphate ester base oil and a
minor additive amount of a combination of alkyl epoxy and carbodiimide acid
scavengers.
[0016] The functional fluids of the present invention include a major amount
of an organic phosphate ester base stock.
[0017] Phosphate ester base fluids are generally of the formula:
0
1
RO-P- OR
I
OR
wherein each R is the saine or different and selected from alkyl or alkoxy
allcyl
group having 2 to 20 carbon atoms, aryl groups (e.g., phenyl) and substituted
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-5-
aryl groups containing up to 20 carbon atoms where the substituents are alkyl,
phenyl, allcyl phenyl or phenyl alkyl and wherein the alkyl group contain form
1
to 10 carbons.
[0018] Typical organo phosphate ester base stocks include esters selected
from triallcyl phosphates, triaryl phosphates, diallcyl aryl phosphates, alkyl
diaryl
phosphates, and alkylated triaryl phosphates that contain from 3 to 8,
preferably
from 3 to 6, more preferably 3 to 5 carbon atoms in the alkyl groups and
mixtures thereof. Examples of the foregoing esters include tri-n-butyl
phosphate, tri-isobutyl phosphate, tri-sec-butyl phosphate, di-isobutyl pentyl
phosphate, tri-2-ethyl hexyl phosphate, n-butyl di-isobutyl phosphate, di-
isobutyl
n-butyl phosphate, n-butyl diphenyl phosphate, isobutyl diphenyl phosphate, di-
isobutyl phenyl phosphate, tri-n-pentyl phosphate, tri-isopentyl phosphate,
triphenyl phosphate, isopropylated triphenyl phosphates and butylated
triphenyl
phosphates. Preferably, the trialkyl phosphate esters are those of tri-n-butyl
phosphate, tri-isobutyl phosphate and mixtures thereof.
[0019] The alkyl substituted phenyl groups of the triaryl phosphates include
phenyl groups having from 1 to 3 alkyl substituents wherein the alkyl groups
are
straight a branched chain groups of form 1 to 14 carbon atoms and further, ,
wherein each allcyl substituted phenyl group has a maximum of up to 20
carbons.
Examples of triaryl phosphate esters include, by way of example tri(isopropyl
phenyl) phosphate, tri (tert-butylated phenyl) phosphate, tri cresyl
phosphate,
and the like and mixtures thereof.
[0020] Combinations of tri alkyl phospjiates and tri aryl phosphates include a
mixture of tributyl phosphate and tri (isopropylphenyl) phosphate at about a
6:1
to 7:1 ratio, and a mixture of tri butyl phosphate and tri (butylated phenyl)
phosphate at about a 6:1 to 7:1 ratio.
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-6-
[0021] The organo phosphate ester base stock useful in the present invention,
therefore comprises about 10 to 100 wt% of a triallcyl phosphate, about 0 to
75
wt% of a diallcyl aryl phosphate, about 0 to 30 wt% of an allcyl diaryl
phosphate
and about 0 to 15 wt% of a triaryl phosphate. Preferably the alkyl groups of
the
esters contain 3 to 5 carbons, more preferably 3 to 4 carbons.
[0022] The phosphate ester based fluid typically comprises a fire resistant
phosphate ester base oil and a viscosity index improver, an acid scavenger and
an erosion inhibitor. The fluid may also contain one or more rust inhibitors,
one
or more antioxidants, one or more metal corrosion inhibitor.
[0023] It has been discovered that the epoxide acid scavengers currently used
in such functional fluids are not effective in neutralizing the carboxylic
acids
produced in the in-service fluid. It also has been discovered that the
carbodiimides are very effective in neutralizing the carboxylic acids but not
effective in neutralizing strong acids (alkyl phosphoric acids) produced by
the
hydrolysis of the phosphate ester based functional fluids. The combination of
an
epoxide and carbodiimide acid scavengers, however, provide a combination to
reduce the acidity produced by the alkylated phosphoric acids and carboxylic
acids in the phosphate ester based functional fluids during use in
environments
containing water, e.g., in aircraft hydraulic systems.
[0024] The functional fluids of the present invention contain an anti-erosion
additive to inhibit flow-induced electrochemical corrosion.
[0025] Suitable erosion inhibitors are disclosed, for example, in U.S. Patents
5,464,551 and 3,679,587, the entire disclosures of which are incorporated
herein
by reference in their entirety. Preferred erosion inhibitors include the
alkali
metal salts, and preferably the potassium salt, of a perfluoroalkyl or
perfluoro-
cycloalkyl sulfonate as disclosed in USP 3,679,587. Such perfluoroalkyl and
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-7-
perfluorocycloallcyl sulfonates preferably encompass allcyl groups of from 1
to
carbon atoms and cycloalkyl groups of from 3 to 10 carbon atoms.
[0026] Suitable anti-erosion additives are alkali metal salts of
perfluorooctyl
sulfonic acids such as FC-98 or FC-95, from, for example, 3M, Minneapolis,
Minnesota.
[0027] The erosion inhibitor is employed in an alnount effective to inhibit
erosion in the power transmission mechanisms of an aircraft and, preferably,
is
einployed in an amount of from about 0.01 to about 0.5 wt%, based on the total
weight of the hydraulic fluid composition and more preferably from about 0.02
to about 0.1 wt%. Mixtures of such anti-erosion agents can be used.
[0028] In addition to containing the major amount of a phosphate ester base
stock and the small amount of the erosion inhibitor, the functional fluids of
the
present invention also include from about 4 wt% to about 20 wt% of auxiliary
additives as previously indicated selected from the group consisting of anti-
oxidants, acid scavengers, viscosity index (VI) improvers, rust inhibitors,
defoamers and metal corrosion inhibitors.
[0029] The hydraulic fluid compositions of this invention can further
optionally comprise an antioxidant or mixture of antioxidants in an amount
effective to inhibit oxidation of the hydraulic fluid or any of its
components.
[0030] Useful antioxidants include triallcylphenols, polyphenols, phenyl alpha
naphthyl amines (PANA) and di(allcylphenyl) amines.
[0031] Representative antioxidants include, by way of example, phenolic
antioxidants, such as 2,6-di-tert-buty-p-cresol, tetralcis[methylene(3,5-di-
tert-
butyl-4-hydroxyhydrocinnamate)]-methane (Irganox 1010 from Ciba Geigy),
bis (3,5 di-tert-butyl-4 hydroxyphenyl) methane (Ethanox 702 from Ethyl
corporation), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert butyl-4-hydroxyphenyl)
benzene (Ethanox 330 from Ethyl Corporation) and the like; amine antioxidants
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-8-
including, by way of example, diarylamines, such as di(noctylphenyl) amine
(Vanlube 81), phenyl-a-naphthylamine, (noctylphenyl) naphthylamine
(Irganox L06), alkylphenyl-a-naphthylamine, or the reaction product of
N-phenylbenzylamine with 2,4,4-trimethylpentene (Irganox L-57 from Ciba
Geigy), diphenylamine, ditoylamine, phenyl tolyamine, 4,4'-diaminodiphenyl-
amine, di-p-methoxydiphenylamine, or 4-cyclohexylaminodiphenylamine. Still
other suitable antioxidants include aminophenols such as N-butylaminophenol,
N-methyl-N-amylaminophenol and N-isooctyl-p-aminophenol as well as
mixtures of any such antioxidants.
[0032] A preferred mixture of antioxidants comprises 2,6-di-tert-butyl-p-
cresol and di(octylphenyl)amine (e.g., a 1:1 mixture). Another preferred
mixture
of antioxidants is 2,6-di-tert-butyl-p-cresol, di(octylphenyl)amine and 6-
methyl-
2,4-bis (octylthio)-methyl] -phenol (e.g., 1:2:4 mixture). Still another
preferred
mixture of antioxidants is 2,6-di-tert-butyl-p-cresol, di(octylphenyl)amine
and
tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane (e.g., a
1:2:3 mixture).
[0033] The antioxidant or mixture of antioxidants is einployed in an amount
effective to inhibit oxidation of the hydraulic fluid. The antioxidant or
mixture
of antioxidants is employed in an amount ranging from about 0 to about 3 wt%,
more preferably from about 0.5 to 2.5 wt% and still more preferably at from
about 1 to 2 wt% based on the total weight of the hydraulic fluid composition.
[0034] Viscosity Index Improver (VI) additives useful in hydraulic fluid
compositions of this invention include polyacrylate esters and poly (alkyl
methacrylate) esters of the type described in U.S. Patents 5,817,606 and
3,718,596, the disclosures of which are incorporated herein by reference in
their
entirety.
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-9-
[0035] Typically, the viscosity index improver is of high molecular weight,
having a number average molecular weight between about 50,000 and about
100,000 and a weight average molecular weight between about 200,000 and
350,000. Viscosity index improvers are commercially available from Rohm and
Haas Company and referred to as poly (alkyl methacrylate) PA-7570, PA 6703,
PA 6744 and PA 6961-PMN. The hydraulic fluid compositions of this invention
can contain from about 3 wt% to about 10 wt% of the viscosity index improver
(or an active ingredient basis), preferably about 4 to about 6 wt% (on an
active
ingredient basis) based on the total weight of the functional fluid
composition.
The VI iinprover can be mixed with a portion of the phosphate ester base
stock,
typically as a 1:1 mixture and then added to the balance of the functional
fluid.
[0036] Rust inhibitors suitable in this invention include metal corrosion
inhibitors such as benzotriole derivatives and dihydroimidazole derivatives
such
as Amine-O commercially available from Ciba-Geigy and Vanlube RI-G
commercially available from Vanderbilt. Other suitable rust inhibitors include
those described in U.S. Patents 5,035,084, 4,206,067 and 5,464,551 the entire
disclosures of which are incorporated herein by reference in their entirely.
Additional non-limiting examples include calcium dinonylnaphthalene sulfonate,
a Group I or Group II metal overbased and/or sulfurized phenate, sulfonate or
carboxylate, a compound of the formula:
R4N[CH2CH(R5)OH]2
wherein R4 is selected from the group consisting of alkyl of from 1 to 40
carbon
atoms, -COOR6 and -CH2CH2N[CH2CH(R5)OH]2 where R6 is allcyl of from 1
to 40 carbon atoms, and each R5 is independently selected from the group con-
sisting of hydrogen and methyl, including N,N,N',N'-tetrakis(2-hydroxypropyl)
ethylene diamine and N,N-bis(2-hydroxyethyl) tallowamine (e.g., N tallow
amine alkyl-2,2'-iminobisethanol, sold under the trade name Ethomeen T/12),
and diphenyl dithioethane (sold under the tradename FH-132).
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-10-
[0037] The Group I and Group II metal overbased and/or sulfurized phenates,
preferably are either sulfurized Group I or Group II metal phenates (without
CO2
added) having a Total Base Number (TBN) of from greater than 0 to about 200
or a Group I or Group II metal overbased sulfurized phenate having a TBN of
from 75 to 400 prepared by the addition of carbon dioxide during the
preparation
of the phenate. More preferably, the metal phenate is a potassium or calcium
phenate. The phenate advantageously modifies the pH to provide enhanced
hydrolytic stability.
[0038] Each of these components are either commercially available or can be
prepared by art recognized methods. For example, Group II metal overbased
sulfurized phenates are commercially available from Chevron Chemical
Company, San Ramon, California under the trade name OLOA including,
OLOA 219 , OLOA 216Q and the like and are described by Campbell, USP
5,318,710, and by MacKinnon, USP 4,206,067. Likewise, N,N,N',N'-tetrakis
(2-hydroxy-propyl) ethylenediamine is disclosed by MacKinnon, USP
4,324,674. The disclosures of each of these patents are incorporated herein by
reference in their entirety.
[0039] Group I or II metal dinonylnaphthalene sulfonates, such as calcium
dinonylnaphthalene sulfonate (Na-Sul 729 commercially available from King
industries) may also be used as a rust inhibitor in the hydraulic fluid
composition
in an amount ranging from 0.2 to 1.0 wt% of the hydraulic fluid coinposition.
[0040] The rust inhibitor or mixture of rust inhibitors is employed in an
amount effective to inhibit the formation of rust. The rust inhibitor is
employed
in an amount ranging from about 0 to about 1 wt%, preferably 0.001 to about
1 wt%, more preferably about 0.005 to about 0.5 wt%, and still more preferably
at about 0.01 to 0.1 wt% based on the total weight of the hydraulic fluid
composition. In a preferred embodiment, the rust inhibitor comprises a mixture
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-11-
of N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine and a Group II metal
overbased phenate (e.g., a 5:1 mixture). In another preferred embodiment, the
rust inhibitor comprises a mixture of N,N-bis(2-hydroxyethyl)tallowamine
(Ethomeen T/12) and a Group II metal overbased phenate (e.g., a 5:1 mixture).
[0041] The functional fluid compositions of this invention further comprise
an acid control additive, acid receptor, or acid scavenger (all three terms
used as
synonyms in the patent and public literature) in an amount sufficient to
neutralize acids formed in such functional fluids, especially functional
fluids
utilized as aircraft hydraulic fluids, such as phosphoric acid and its partial
esters.
Suitable acid control additives are described, for example, in U.S. Patents
5,464,551, 3,723,320 and 4,206,067, the disclosures of which are incorporated
herein in their entirety.
[0042] Preferred acid control additives have the formula:
0
R IC
OR
OC R'
R'
where R is selected from the group consisting of an allcyl group of from 1 to
10
carbon atoms, substituted alkyl of from 1 to 10 carbon atoms and containing
from 1 to 4 ether oxygen atoms therein and cycloalkyl of from 3 to 10 carbon
atoms, each R' is independently selected from the group consisting of
hydrogen,
alkyl of from 1 to 10 carbon atoms and -C(O)OR" where R" is alkyl of from 1 to
carbon atoms optionally containing from 1 to 4 ether oxygen atoms, therein
or cycloalkyl of from 3 to 10 carbon atoms.
[0043] Preferred acid scavengers of the above formula are the monoepoxide
2-ethylhexyl 7-oxabicyclo[4.1.0]heptane-3-carboxylic acid, which is disclosed
in
USP 3,723,320, or mono epoxide 2-(ethoxy ethoxy) ethyl 7-oxabicyclo [4.1.0]
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-12-
heptane-3-carboxylate or mixtures thereof, and monoepoxide 7-oxa-bicyclo
[4.1.0]-heptane-3,4-dicarboxylic acid, dialkyl esters (e.g., the di-isobutyl
ester).
Dialkyl esters of this monoepoxide are also disclosed in USP 3,723,320. The
trialkyl and tetraallcyl esters are prepared via conventional Diels-Alder
reaction
procedures via a suitable unsaturated trialkyl or tetraalkyl ester and a
suitable
1,3-diene. The Diels-Alder reaction provides for 4 + 2 cyclo addition to
provide
for a cyclohexene derivative having the suitable trialkyl or tetraalkyl
esters. The
unsaturation in the cyclohexane is utilized to provide for epoxide formation
via
conventional methods.
[0044] Suitable unsaturated trialkyl and tetraallcyl esters are known in the
art.
For example, tetraethyl ethylene tetracarboxylate is available from Fluka
(Ronkonoma, NY). The alkyl groups of this tetraethyl ester can readily be
exchanged via conventional techniques to provide for other esters as defined
above.
[0045] The use of such di-, tri- and tetraalkyl esters of this monoepoxide
provide for enhanced seal compatibility for the formulation of this invention
as
well as with conventional formulations employing conventional trihydrocarbyl
phosphate basestocks with the ethylene propylene seals used in aircraft
hydraulic
systems.
[0046] The swelling of ethylene propylene seals in an aircraft hydraulic
system due to contact of said seals with an aircraft hydraulic fluid
coinposition
containing 7-oxabicyclo-[4.1.0]heptane-3-carboxylic acid, 2-ethylhexyl ester
as
the acid scavenger is further reduced by:
(a) replacing at least a portion of the monoepoxide 2-ethylhexyl 7-oxabicyclo-
[4. 1.0] heptane-3-carboxylic acid, acid scavenger with an acid scavenger of
the formula:
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-13-
O
R IC
OR
0( R'
R'
where R is selected from the group consisting of an alkyl group of from 1 to
10
carbon atoms optionally containing from 1 to 4 ether oxygen atoms therein, and
cycloalkyl of from 3 to 10 carbon atoms, each R' is independently selected
from
the group consisting of hydrogen, alkyl of from 1 to 10 carbons atoms and
-C(O)OR where R is as defined above, with the proviso that at least one of R'
is
-C(O)OR.
[0047] Preferably, at least 20%, and more preferably from about 20% to
about 100% of the 7-oxabicyclo-[4.1.0]heptane-3-carboxylic acid, 2-ethyhexyl
ester acid scavenger is replaced by the di ester acid scavenger.
[0048] The acid control additive whether as mono- di-, tri- or tetra-ester is
employed in an amount effective to scavenge the acid generated, typically as
partial esters of phosphoric acid, during use of the functional fluid,
especially
during use as an aircraft hydraulic fluid. Preferably, the acid control
additive is
employed in an amount ranging from about 4 to about 10 wt%, based on the total
weight of the hydraulic fluid coinposition, and more preferably from 5 to 8
wt%
and still more preferably from 6 to 8 wt%, based on the total weight of the
fluid.
[0049] Carbodiimides suitable in this invention might be mono carbodiimides
or poly carbodiimides. Useful carbodiimides are illustrated by the following
structural formula
Ri-(N=C=N)õ-Rz
wherein Rl and R2 are the same or different and are hydrogen, hydrocarbyl
groups, preferably hydrocarbyl group containing 1 to 20 carbons, more prefer-
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-14-
ably 1 to 18 carbons, or nitrogen and/or oxygen containing hydrocarbyl groups
and n is 1 to 5, preferably 1 or 2. Thus R' and R 2 can be CI-CIZ aliphatic
groups,
C6-C1$ aromatic groups or aromatic-aliphatic groups. Thus R' and R2 may be,
for example, hydrogen, alkyl groups such as methyl, ethyl, propyl, isopropyl,
butyl, isobutyl, pentyl, 2-methylbutyl, hexyl, heptyl, octyl, 2-ethylhexyl,
nonyl,
decyl, undecyl, dodecyl and the like, alkenyl groups such as propenyl,
butenyl,
isobutenyl, pentenyl, 2-ethylhexenyl, octenyl and the like, cycloalkyl groups
such as cyclopentyl, cyclohexyl, methyl-cyclopentyl, ethylcyclopentyl and the
like, aryl groups such as alkyl substituted phenyl groups for example toluyl,
isopropylphenyl, diisopropylphenyl and the like, aralkyl groups such as
benzyl,
phenetyl and the like. Carbodiilnides wherein n is 1 are monocarbodiimides
exemplified by the following:
di-isopropyl carbodiimide, di-n-butyl carbodiimide, methyl-tert-butyl
carbodiimide, diphenyl carbodiimide, di-p-tolyl carbodiiinide, 2,2'-diethyl-
diphenyl carbodiimide, 2,2'-diethoxy-diphenyl carbodiimide, 2,2',6,6'-
tetraethyldiphenyl carbodiimide and the like. The preferred carbodiimide is
the 2,2',6,6'-tetraisopropyldiphenyl carbodiimide such as Additin RC8500
commercially available from Rheine Chemie.
[0050] Carbodiimides wherein n is greater than 1 are polycarbodiimides
exemplified by the following:
tetramethylene-w,co'-bis-(tert-butyl carbodiimide), hexamethylene-(O,O)'-bis-
(tert-butyl carbodiimide), tetramethylene-co,w'-bis-(phenyl carbodiimide) and
those compounds which may be obtained by heating aromatic polyiso-
cyanates such as 1,3-di-isopropyl-phenylene-2,4-isocyanate, 1-inethyl-3,5-
diethyl-phenylene-2,4-diisocyanate and 3,5,3',5'-tetra-isopropyl-diphenyl-
methane-4,4-di-isocyanate in the presence of tertiary amines, basically
reacting metal compounds, carboxylic acid metal salts or non-basic
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-15-
organometal compounds at a temperature of at least 120 C, according to the
process disclosed in German Patent 1,156,401.
[0051] Typical amounts of carbodiimide additive that can be used in the
functional fluid compositions of this invention are from about 0.05 to about
5.0 wt%, based on total weight of fluid, preferably from 0.5 to 3 wt% based on
total weight of fluid.
[0052] The invention is further described by reference of the following
coinparative examples and non-limiting examples.
[0053] In the Examples, the epoxide employed was 2-ethylhexyl-7-
oxabicyclo [4.1.0] heptane-3-carboxylic acid. Acid number was determined by
ASTM D-974.
EXAMPLE 1
[0054] In this Example, 10 gm of a used phosphate ester based hydraulic fluid
(Fluid 1) that contained 1.73% of residual epoxide acid scavenger was stirred
at
40 C for 72 hours with 0.1 gm (0.276 mmole) carbodiimide RC 8500 (Fluid 2),
and with 0.1 gm (0.387 mmole) epoxide acid scavenger (Fluid 3). The Fluid 1
had an initial acid number of 1.2 mg KOH/g attributable to the presence of
carboxylic acids. Fluid 2 of this invention containing the carbodiiinide gave
a
63.7% acid number reduction whereas Fluid 3 with additional epoxide acid
scavenger gave 27.1 % acid nuinber reduction, showing that the mere addition
of
more epoxide is not sufficient to control the acidity attributable to weak
carboxylic acids in the fluids.
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-16-
TABLE 1
Com op nent Fluid 1 Fluid 2 Fluid 3
Base oil
Tributyl phosphate, wt% 78.7086 77.7086 78.7086
Triaryl phosphates, wt% 11.80 11.80 11.80
Additives
VI Improver
Erosion Inhibitor
Rust Inhibitors wt% 7.7614 7.7614 7.7614
Antioxidants
Defoamer
Purple Dye
Epoxide Acid Scavenger, wt% 1.73 1.73 2.73
Carbodiimide, wt% (RC 8500) 0 1.0 0
Properties
Acid Number, mg KOH/g 1.2 0.436 0.875
Reduction % - 63.7 27.1
EXAMPLE 2
[0055] This Example demonstrates that the carbodiimide RC 8500 is very
effective in reducing the acid number of a petroleum fraction HAGO (Fluid 4)
containing naphthenic acids (carboxylic acids) whereas the epoxide acid
scavenger is not. Two 100 ml samples of Fluid 4 were heated at 80 C for 6
hours with 1 gm of each of the acid scavengers (Fluids 5 and 6) and the Acid
Number determined. The epoxide acid scavenger did not provide any acidity
reduction attributable to the weak carboxylic acids whereas the carbodiimide
gave 83.5% reduction of the acidity attributable to weak carboxylic acids.
TABLE 2
Fluid 4 Fluid 5 Fluid 6
HAGO Base oil - 6 hrs @ 80 C 6 hrs @ 80 C
Additive
Carbodiimide, wt% - 1.1 0
Epoxide Acid Scavenger, wt% - 0 1.1
Properties
Acid Number 1.21 0.20 1.21
Reduction, % 0 83.5 0
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-17-
EXAMPLE 3
[0056] This Example illustrates that the presence of up to 8.0 wt%
carbodiimide (RC 8500) in the phosphate ester based functional fluid (Fluid 7)
did not degrade the viscometric properties. Moreover, no additive drop out was
observed after one week storage at -65 F. The combination of as little as 1
wt%
of the carbodiimide with epoxide acid scavengers (Fluid 9) also did not
degraded
key fluid the properties yet reduced the TAN to a level below that achieved
using either the epoxide or the carbodiimide (at a higher concentration)
alone.
TABLE 3
Component Fluid 7 Fluid 8 Fluid 9
Base Oil
Tributyl phosphate 72.18 74.48 74.18
Triaryl phosphates, wt% 12.10 12.10 12.10
Additives
VI Improver
Antioxidants
Rust Inhibitors % 7.72 7.72 7.72
~
Erosion Inhibitor 1
Defoamer
E oxide, wt% 0 5.70 5.0
Carbodiimide (RC-8500), wt% 8.0 0 1.0
Properties Target Limits
Specific Gravity, 25 C/25 C 0.9964 0.9973 0.9971 0.970 - 1.020
Viscosity -65 F, cSt 1752 1273 1324 2000 max
Viscosity -65 F, cSt(1) 1706 1261 1305 2000 max
Viscosity 100 F, cSt, 11.17 10.19 10.40 9.0-12.5
Acid Number, mg KOH/g 0.05 0.04 0.03 0.10 max
(1) After 1 week at -65 F. All three samples were Clear & Bright.
EXAMPLE 4
[0057] This Example demonstrates that whereas in Example 2 it is shown that
carbodiimides are good acid scavengers for weak carboxylic acids, the
carbodiimides such as RC 8500 are poor acid scavengers for the allcyl
phosphoric acids produced from the hydrolysis of the phosphate esters. About
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-18-
15 mL of the fluid was placed in sealed glass ampoules with a piece of copper
and steel wires to catalyze the hydrolysis. The fluid was spiked with water to
make total water content of 0.5 wt%. The ampoules were placed in an oven at
150 C. The Acid Number was determined as a function of time. The test is
completed when the Acid Number of the fluid has reached 1.5 mg KOH/g (fluid
life). The results showed that Fluid 7 containing 8.0 wt% carbodiimide reached
a 3.08 mg KOH/g after only 48 hours whereas Fluid 8 containing only the
epoxide acid scavenger went to 244 hours before reaching an Acid Number of
1.59 mg KOH/g. The combination of 1 wt% carbodiiinide and 5.0 wt% epoxide
(Fluid 9) performed well and reached an Acid Number of 1.88 mg KOH/g after
222 hours. It is important to note that Fluid 9 contained 0.7 wt% less epoxide
than Fluid 8.
TABLE 4
Fluid 7 Fluid 8 Fluid 9
Time, Acid Time, Acid Time, Acid
hours Number hours Number hours Number
0 0.05 0 0.04 0 0.03
48 3.08 48 0.02 48 0.01
96 0.02 96 0.03
144 0.04 144 0.04
192 0.06 192 0.06
222 0.24 222 1.88
240 0.40 240 4.83
244 1.59
Example 5
[0058] A fresh portion of a phosphate ester hydraulic fluid which did not
contain any acid scavengers was spiked with cekanoic acid to produce a test
fluid 10, the acid number of which was measured as 1.5.
[0059] This test fluid 10 was then treated with epoxide alone, carbodiimide
along and with a mixture of epoxide and carbodiimide. The fluids (Fluid 11,
Fluid 12, Fluid 13 and Fluid 14) are presented in Table 5 and the data after
72
CA 02615891 2008-01-18
WO 2007/011783 PCT/US2006/027497
-19-
hours show that the mixture of the carbodiimide and epoxide (Fluid 14) reduces
the acid number to a greater extent then just the epoxide alone at 5.70 g
epoxide
dose (Fluid 11) or carbodiimide alone at 1.0 g carbodiimide dose (Fluid 12).
TABLE 5
Fluid 10
Component
Fresh phosphate 467.50 gm
Ester hydraulic fluid 1.50 gm
Cekanoic acid 2.50 gm
water
Acid # (ASTM D-974) 1.5 mgKOH/g
Fluid 11
Component Acidity Reduction
Fluid 10 94.30 wt%
Epoxide 5.70 wt%
Acid # after 72 lirs (ASTM D-974) 1.169 mgKOH/g 22.1%
Fluid 13
Component Acidity Reduction
Fluid 10 92.00 wt%
RC 8500 8.00 wt%
Acid # after 72 hrs (ASTM D-974) 0.190 mgKOH/g 87.3%
Fluid 14
Component Acidity Reduction
Fluid 10 94.00 wt%
RC 8500 1.00 wt%
Epoxide 5.00 wt%
Acid # after 72 hrs (ASTM D-974) 0.903 mgKOH/g 40.0%
Fluid 12
Component Acidity Reduction
Fluid 10 99.00 wt%
RC 8500 1.00 wt%
Acid # after 72 hrs (ASTM D-974) 1.18 mgKOH/g 22.1%
