Note: Descriptions are shown in the official language in which they were submitted.
~ W093/25628 2 1 ~ 7 2 5 7 PCT/US93/04885
POLYOL E8TER ~EAVY D~TY COMPRES~OR L~BRIC~N$~
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of copend-
ing International Application No. PCT/US92/04438 designat-
ing the United States and filed June 3, 1992, the entire
5 disclosure of which, except to the extent contrary to any
explicit statement herein, is hereby incorporated herein
by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
10 This invention relates to lubricant base stocks,
which can also serve as complete lubricants in some cases;
compounded lubricants, which include at least one additive
for such purposes as improving high pressure resistance
and/or wear resistance, corrosion inhibition, and the like
15 along with the lubricant base stocks which contribute the
primary lubricity to the compounded lubricants; refriger-
ant working fluids including lubricants according to the
in~ention along with primary heat transfer fluids; and
methods for using these materials. The lubricants and
20 lu~ricant base stocks are generally suitable for use with
most or all halocarbon refrigerants and are particularly
suitable for use with substantially chlorine-free, fluoro-
group-containing organic refrigerating heat transfer flu-
ids such as pentafluoroethane, 1,1-difluoroethane, 1,1,1-
25 trifluroethane, and tetrafluoroethanes, most particularly1,1,1,2-tetrafluoroethane. The lubricants and base
stoc~s, in combination with these heat transfer fluids,
are particularly suitable for lubricating compressors that
require ISO grades from about 320 to about 1000 because of
30 their heavy duty cycles.
Statement of Related Art
. . Chlorine-free heat transfer fluids are desirable for
use in refrigerant systems, because their escape into the
W093/25628 ~ 2 1 3 7 2 PCT/US93/0 ~S
atmosphere causes less damage to the environment than the
currently most commonly used chlorofluorocarbon heat trans-
fer fluids such as trichloro~luoromethane and dichlorodi-
fluoromethane. The widespread commercial use of chlorine-
s free refrigerant heat transfer fluids has been hindered,
however, by the lack of commercially adequate lubricants.
This is particularly true for one of the most desirable
working fluids, 1,1,1,2-tetrafluoroethane, commonly known
in the art as "Refrigerant 134a" or simply "R134a". Other
fluoro-substituted ethanes are also desirable working flu-
ids.
Esters of hindered polyols, which are defined for
this purpose as organic molecules containing at least five
carbon atoms, at least 2 -OH groups, and no hydrogen atoms
directly bonded to any carbon atom that is directly bonded
to a carbon atom bearing an -OH group, have already been
recognized in the art as high quality lubricant basestocks
for almost any type of refrigeration machinery employing a
fluorocarbon refrigerant, particularly one free from
chlorine. The following patents and published patent ap-
plications teach many general classes and specific exam-
ples of polyol esters useful as refrigerant lubricants
with chlorine-free fluoro group cont~;n;ng heat transfer
fluids: US 4,851,144; UK 2 216 541; US 5,021,179; US 5,
zs 096,606; WO 90/12849 (Lubrizol); EP O 406 479 (Kyodo Oil);
EP O 430 6S7 (Asahi Denka KK); EP O 435 2S3 (Nippon Oil);
EP O 445 610 and 0 445 611 (Hoechst AG); EP 0449 406; EP O
458 584 (Unichema Chemie BV); and EP O 485 979 (Hitachi).
PESCRIPTION OF THE INV~N~ION
Except in the claims and the operating examples, or
where otherwise expressly indicated, all numerical quant-
ities in this description indicating amounts of material
or conditions of reaction and/or use are to be understood
as modified by the term "about" in defining the broadest
scope of the invention. Practice of the invention within
the boundaries corresponding to the exact quantities stat-
ed is usually preferable, however.
~ W093/25628 i' 2 1 3 7 2 5 7 PCT/US93/04885
More specifically, ester mixtures according to this
invention should have a viscosity of not more than 1300,
more preferably not more than llO0, still more preferably
not more than 990, centistokes at 40 C. Independently,
5 ester mixtures according to this invention should have a
viscosity of at least 300, or with increasing preference
in the order given, at least 450, 600, or 810, centistokes
at 40 C.
It has now been found that selected polyol esters pro-
vide high quality lubrication for this kind of service.
Specifically effective are esters or mixtures of esters
made by reacting (i) a mixture of alcohol molecules se-
lected from the group consisting of 2,2-dimethylol-1-buta-
nol (also known as "trimethylolpropane" and often abbrevi-
1'5 ated hereinafter as "TMP"); di-trimethylolpropane (often
abbreviated hereinafter as "DTMP"), a molecule with four
hydroxyl groups and one ether linkage, formally derived
from two molecules of TMP by removing one hydroxyl group
from one of the TMP molecules and one hydrogen atom from a
20 hydroxyl group of the other TMP molecule to form water and
join the two remainders of the original TMP molecules with
an ether bond; 2,2-dimethylol-1,3-propanediol (also known
as "pentaerythritol" and often abbreviated hereinafter as
"PE"~; and di-pentaerythritol (often abbreviated herein-
25 after as "DPE"), a molecule with six hydroxyl groups andone ether bond, formally derived from two PE molecules by
the same elimination of the elements of water as described
above for DTMP, tri-pentaerythritol (often abbreviated
hereinafter as "TPE"), a molecule with eight hydroxyl
30 groups and two ether bonds, formally derived from three PE
molecules by an analogous elimination of the elements of
two molecules of water as described above (for elimination
of a single water molecule) for DTMP and DPE; and tri-tri-
methylolpropane (hereinafter often abbreviated as "TTMP"),
35 a molecule with five hydroxyl groups and two ether bonds,
formally derived from three TMP molecules by the same
. elimination of the elements of two molecules of water as
W093/25628 2~1 3:7 2~ ~ PCT~US93/0 ~ 5
described above for TPE, with (ii) a mixture of acid mol-
ecules selected from the group consisting of all the
straight and branched chain monobasic and dibasic carbox-
ylic acids with from four to twelve carbon atoms each,
s with the alcohol moieties and acyl groups in the mixture
of esters selected subject to the constraints that (a) a
total of at least 15 %, or, with increasing preference in
the order gi~en, at least 27, 36, 45, 51, 56, or 62 %, of
the acyl groups in the mixture are 2-methylbutanoyl or 3-
methylbutanoyl groups, which are jointly abbreviated here-
inafter as "acyl groups from tor of] i-C5 acid"; (b) the
ratio of the % of acyl groups in the mixture that contain
8 or more carbon atoms and are unbranched to the % of acyl
groups in the mixture that are both branched and contain
not more than six, preferably not more than five, carbon
atoms is not greater than 1.56, more preferably not great-
er than 1.21, or still more preferably not greater than
1.00; (c) the % of acyl groups in the ester mixture that
contain at least nine carbon atoms, whether branched or
zo not, is not greater than 81, or increasingly more prefer-
ably, not greater than 67 or 49; and (d) not more than 2,
more preferably not more than 1, or still more preferably
not more than 0.4, % of the acyl groups in the ester mix-
ture are from acid molecules with more than two carboxyl
groups each; and (e) at least 13.8, or with increasing
preference in the order given, at least 15.3, 16.2, 17.0,
17.6, 18.2, or 18.9 %, of the acyl groups in the ester mix-
ture are dibasic; and a total of at least 82, or with in-
creasing preference in the order given, at least 85, 89,
93, 96, or 99 % of the monobasic acyl groups in the acid
mixture have either five or six, or more preferably exact-
ly five, carbon atoms each. In all these percentages,
acyl qroups are counted as a single group, irrespective of
the number of valences they have. For example, each mole-
cule of adipic acid yields a single, dibasic, acyl group
when completely esterified.
(Of course, for all the types of esters described
~ W093/25628 ` 2~1 3 7 2 ~ 7 PCT/US93/04885
herein as part of the invention, it is possible to obtain
the same esters or mixture of esters by reacting acid de-
rivatives such as acid anhydrides, acyl chlorides, and
esters of the acids with lower molecular weight alcohols
than those desired in the ester products according to this
invention, instead of reacting the acids themselves. The
acids are generally preferred for economy and are normally
specified herein, but it is to be understood that the es-
ters defined herein by reaction with acids can be equally
well obtained by reaction of alcohols with the correspond-
ing acid derivatives, or even by other reactions. The
only critical feature is the mixture of acyl groups and
alcohol moieties in the final mixture of esters formed.)
Preferably, with increasing preference in the order
given, a total of at least 60, 75, 85, 90, 95, or 98 ~ of
the hydroxyl groups in the mixture of alcohols that could
be reacted to make the mixture of esters according to this
invention are PE, DPE, and/or TPE molecules, and independ-
ently, with increasing preference in the order given, at
least 60, 75, 85, 90, 95, or 98 % of the hydroxyl groups
in the mixture of alcohols that could be reacted to make
esters according to this invention are PE molecules. In-
dependently, in the mixtures of acids that could be react-
ed with alcohols to make the esters according to this in-
Z5 vention, with increasing preference in the order given, at
least 60, 75, 85, 90, 95, or 98 % of the monobasic acid
molecules in the acid mixture consist of molecules having
no more than ten carbon atoms each and, with increasing
preference in the order given, at least 60, 75, 85, 90,
95, or 98 % of the dibasic acid molecules in the acid mix-
ture consist of molecules having no more than ten carbon
atoms each, or more preferably from five to seven carbon
atoms each. Most preferably, with increasing preference
in the order given, a total of at least 60, 75, 85, 90,
95, or 98 % of the monobasic acid molecules in the acid
mixture consist of molecules having either five or nine
carbon atoms each.
W093/25628 ~ '` PCT/US93/0
~ ~3~t2~ ~5
These preferences for the acyl groups and alcohol moi-
eties in esters according to this invention are based on
empirically determined generali2ations. In order to
achieve the desired range of viscosity, it is advantageous
to have a substantial fraction of dibasic acids and of al-
cohols with at least four hydroxyl grou~s. Among the com-
mercially available hindered alcohols that satisfy this
criterion, PE is less expensive than DTMP and is free from
the ether linkage in DTMP, which increases the hygroscop-
icity of the esters formed and thereby may promote unde-
sirable corrosion of the metal surfaces lubricated.
When the number of carbon atoms per molecule is nine
or more, not even branching is sufficient to produce ade-
quate solubility ~y itself, so that an upper limit on the
fraction of such acids is independently required. In gen-
eral, a minimum amount of the particularly advantageous i-
Cs acid is specified to aid in solubilizing the parts of
the esters in the mixture that contain dibasic acids or
those with eight or more carbon atoms.
For both performance and economic reasons, it has
been found that ~ive carbon monobasic acids and six carbon
dibasic acids are the most preferred constituents.
It is to be understood that only the desired alcohols
and acids are explicitly specified, but some amount of the
sort of impurities normally present in commercial or in-
dustrial grade products can be tolerated in most cases.
For example, "commercial pentaerythritol" normally con-
tains only a~out 85 - 90 mole % of pure pentaerythritol,
along with 10 - 15 mole % of di-pentaerythritol, and com-
mercial pentaerythritol is satisfactory for use in making
lubricant esters according to this invention in many cas-
es. In general, however, it is preferred, with increasing
preference in the order given, that not more than 25, 21,
17, 12, 8, 5, 3, 2, 1, 0.5, or 0.2 ~ of either the hydrox-
yl groups in the alcohol mixtures specified herein or of
the carboxyl groups in the acid mixtures specified herein
should be part of any molecules other than those exp}icit-
~ W093/25628 2 1 3 7 2 5 7 PCT/US93/04885
ly specified for each type of lubricant base stock. Per-
centages of specific chemical molecules or moieties speci-
fied herein, such as the percentages of carboxyl and hy-
droxyl groups stated in the preceding sentence, are to be
5 understood as number percentages, which will be mathemat-
ically identical to percentages by chemical equivalents,
with Avogadro's number of each specified chemical moiety
regarded as a single chemical equivalent.
The above descriptions for each of the acid and al-
cohol mixtures reacted to produce lubricànt esters accord-
ing to this invention refers only to the mixture of acids
or alcohols that actually reacts to form esters and does
not necessarily imply that the mixtures of acids or alco-
hols contacted with each other for the purpose of reaction
15 will have the same composition as the mixture that actu-
ally reacts. In fact, it has been found that reaction be-
tween the alcohol(s) and the acid(s) used proceeds more
effectively if the quantity of acid charged to the reac-
tion mixture initially is enough to provide an excess of
20 10 - 2S % of equivalents of acid over the equivalents of
alcohol reacted with the acid. (An equivalent of acid is
defined for the purposes of this specification as the
- amount containing one gram equivalent weight of carboxyl
groups, while an equivalent of alcohol is the amount con-
Z5 taining one gram equivalent weight of hydroxyl groups.)
The composition of the mixture of acids that actually re-
acted can be determined by analysis of the product ester
mixture for its acyl group content.
In making most or all of the esters and mixtures of
30 esters preferred accordinq to this invention, the acid(s)
reacted will be lower boiling than the alcohol(s) reacted
and the product ester(s). When this condition obtains, it
is preferred to remove the bulk of any excess acid remain-
ing at the end of the esterification reaction by distilla-
35 tion, most preferably at a low pressure such as 1 - 5
torr.
After such vacuum distillation, the product is often
W093~25628 X ~ 3 7 2 ~ 7 PCT/US93/0 ~5
ready for use as a lubricant or lubricant base stock ac-
cording to this invention. If further refinement of the
product is desired, the content of free acid in the prod-
uct after the first vacuum distillation may be further
5 reduced by treatment with epoxy esters as taught in U. S.
Patent 3,485,754 or by neutralization with any suitable
alkaline material such as lime, alkali metal hydroxide, or
alkali metal carbonates. If treatment with epoxy esters
is used, excess epoxy ester may be removed by a second
10 distillation under very low pressure, while the products
of reaction between the epoxy ester and residual acid may
be left behind in the product without harm. If neutrali-
zation with alkali is used as the refinement method, sub-
sequent washing with water, to remove any unreacted excess
~s alkali and the small amount of soap formed from the excess
fatty acid neutralized by the alkali, is strongly pre-
ferred before using the product as a lubricant and/or base
stoc~ according to this invention.
Under some conditions of use, the ester(s) as de-
20 scribed herein will function satisfactorily as completelubricants. It is generally preferable, however, for a
complete lubricant to contain other materials generally
denoted in the art as additives, such as oxidation resist-
ance and thermal stability improvers, corrosion inhibi-
Z5 tors, metal deactivators, lubricity additives, viscosityindex improvers, pour and/or floc point depressants, de-
tergents, dispersants, antifoaming agents, anti-wear
agents, and extreme pressure resistant additives. Many
additives are multifunctional. For example, certain ad-
30 ditives may impart both anti-wear and extreme pressure
resistance properties, or function both as a metal de-
activator and a corrosion inhibitor. Cumulatively, all
additives prefera~ly do not exceed 8 % by weight, or more
preferably do not exceed 5 % by weight, of the total com-
35 pounded lubricant formulation.
An effective amount of the foregoing additive typesis generally in the range from 0.01 to 5 % for the anti-
~ W093/25628 ~ 2 1 3 ~ 2 5 7 PCT/US93/04885
oxidant component, 0.01 to 5 % for the corrosion inhibitorcomponent, from 0.001 to 0.5 % for the metal deactivator
component, from 0.5 to 5 % for the lubricity additives,
from 0.01 to 2 % for each of the viscosity index improvers
s and pour and/or floc point depressants, from 0.1 to 5 %
for each of the detergents and dispersants, from 0.001 to
0.1 % for anti-foam agents, and from 0.1 - 2 ~ for each of
the anti-wear and extreme pressure resistance components.
All these percentages are by weight and are based on the
total lubricant composition. It is to be understood that
more or less than the stated amounts of additives may be
more suitable to particular circumstances, and that a
single molecular type or a mixture of types may be used
for each type of additive component. Also, the examples
15 listed below are intended to be merely illustrative and
not limiting, except as described in the appended claims.
Examples of suitable oxidation resistance and thermal
stability improvers are diphenyl-, dinaphthyl-, and phenyl-
naphthyl-amines, in which the phenyl and naphthyl groups
zo can be substituted, e.g., N,N'-diphenyl phenylenediamine,
p-octyldiphenylamine, p,p-dioctyldiphenylamine, N-phenyl-
1-naphthyl amine, N-phenyl-2-naphthyl amine, N-(p-dodecyl)-
phenyl-2-naphthyl amine, di-1-naphthylamine, and di-2-
naphthylamine; phenothazines such as N-alkylphenothia-
25 zines; imino(bisbenzyl); and hindered phenols such as 6-
(t-butyl) phenol, 2,6-di-(t-butyl) phenol, 4-methyl-2,6-
di-(t-butyl) phenol, 4,4'-methylenebis(-2,6-di-{t-butyl}
phenol), and the like.
Examples of suitable cuprous metal deactivators are
30 imidazole, benzamidazole, 2-mercaptobenzthiazole, 2,5-di-
mercaptothiadiazole, salicylidine-propylenediamine, pyr-
azole, benzotriazole, tolutriazole, 2-methylbenzamidazole,
3,5-dimethyl pyrazole, and methylene bis-benzotriazole.
Benzotriazole derivatives are preferred. Other examples
35 of more general metal deactivators and/or corrosion inhib-
itors include organic acids and their esters, metal salts,
and anhydride~, e.g., N-oleyl-sarcosine, sorbitan monoole-
~ 2 1 3 72 5 7 PCT/US93/0 ~S
ate, lead naphthenate, dodecenyl-succinic acid and its par-
tial esters and amides, and 4-nonylphenoxy acetic acid;
primary, secondary, and tertiary aliphatic and cycloali-
phatic amines and amine salts of organic and inorganic ac-
ids, e.g., oil-soluble alkylammonium carboxylates; hetero-
cyclic nitrogen containing compounds, e.g., thiadiazoles,
substituted imidazolines, and oxazolines; quinolines, qui-
nones, and anthraquinones; propyl gallate; barium dinonyl
naphthalene sulfonate; ester and amide derivatives of al-
kenyl succinic anhydrides or acids, dithiocarbamates, di-
thiophosphates; amine salts of alkyl acid phosphates and
their derivatives.
Examples of suitable lubricity additives include long
chain derivatives of fatty acids and natural oils, such as
esters, amines, amides, imidazolines, and borates.
Examples of suita~le viscosity index improvers in-
clude polymethacrylates, copolymers of vinyl pyrrolidone
and methacrylates, polybutenes, and styrene-acrylate co-
polymers.
Examples of suitable pour point and/or floc point de-
pressants include polymethacrylates such as methacrylate-
ethylene-vinyl acetate terpolymers; alkylated naphthalene
derivatives; and products of Friedel-Crafts catalyzed con-
densation of urea with naphthalene or phenols.
Examples of suitable detergents and/or dispersants in-
clude polybutenylsuccinic acid amides; polybutenyl phos-
phonic acid derivatives; long chain alkyl substituted aro-
matic sulfonic acids and their salts; and metal salts of
alkyl sulfides, of alkyl phenols, and of condensation prod-
ucts of alkyl phenols and aldehydes.
Examples of suitable anti-foam agents include sili-
cone polymers and some acrylates.
Examples of suitable anti-wear and extreme pressure
resistance agents include sulfurized fatty acids and fatty
acid esters, such as sulfurized octyl tallate; sulfurized
terpenes; sulfurized olefins; organopolysulfides; organo
phosphorus derivatives including amine phosphates ! alkyl
~ W093/25628 ~ 2 1 3 ~ 2 S 7 PCT/US93/0~85
acid phosphates, dialkyl phosphates, aminedithiophos-
phates, trialkyl and triaryl phosphorothionates, trialkyl
and triaryl phosphines, and dialkylphosphites, e.g., amine
salts of phosphoric acid monohexyl ester, amine salts of
dinonylnaphthalene sulfonate, triphenyl phosphate, tri-
naphthyl phosphate, diphenyl cresyl and dicresyl phenyl
phosphates, naphthyl diphenyl phosphate, triphenylphos-
phorothionate; dithiocarbamates, such as an antimony di-
alkyl dithiocarbamate; chlorinated and/or fluorinated hy-
o drocarbons, and xanthates.
Under some conditions of operation, it is believed
that the presence in lubricants of the types of polyether
polyols that have been prominent constituents of most pri-
or art lubricant base stocks taught as useful with fluoro-
carbon refrigerant working fluids are less than optimally
stable and/or inadequately compatible with some of the
most useful lubricant additives. Thus, in one embodiment
of this invention, it is preferred that the lubricant base
stocks and lubricants be substantially free of such poly-
ether polyols. By "substantially free", it is meant that
the compositions contain no more than about 10 % by
weight, preferably no more than about 2.6 % by weight, and
more preferably no more than about 1.2 % by weight of the
materials noted.
One major embodiment of the present invention is a
refrigerant working fluid comprising both a suitable heat
transfer fluid such as a fluorocarbon and a lubricant ac-
cording to this invention. Preferably, the refrigerant
working fluid and the lubricant should have chemical char-
acteristics and be present in such a proportion to each
other that the working fluid remains homogeneous, i.e.,
free from visually detectable phase separations or turbid-
ity, over the entire range of working temperatures to
which the working fluid is exposed during operation of a
refrigeration system in which the working fluid is used.
This working range may vary from -600 C to as much as
+175 C. It is often adequate if the working fluid re-
W093J25628 ~ ~3~ æ~ PC~/US93/0
mains single phase up to +300 C, although it is increas-
ingly more preferable if the single phase behavior is
maintained up to 40, 56, 71, 88, or 100 C. Similarly,
it is often adequate if the wor~ing fluid compositions
5 remains a single phase when chilled to oo C, although it
is increasingly more preferable if the single phase behav-
ior persists to -10, -20, -30, -40, or -55 C. Single
phase mixtures with chlorine free hydrofluorocarbon re-
frigerant working fluids are usually obtained with the
suitable and preferred types of esters described above.
Inasmuch as it is often difficult to predict exactly
how much lubricant will be mixed with the heat transfer
fluid to form a working fluid, it is most preferable if
the lubricant composition forms a single phase in all
15 proportions with the heat transfer fluid over the temper-
ature ranges noted above. This however, is a very strin-
gent re~uirement, and it is often sufficient if there is
single phase behavior over the entire temperature range
for a working fluid mixture containing up to 1 % by weight
20 of lubricant according to this invention. Single phase
~ehavior over a temperature range for mixtures containing
up to 2, 4, 10, and 15 % ~y weight of lubricant is suc-
cessively more preferable.
In some cases, single phase behavior is not required.
25 The term "miscible" is used in the refrigeration lubrica-
tion art and hereinafter, except when part of the phrase
"miscible in all proportions", when two phases are formed
but are readily capable of being mixed into a uniform dis-
persion that r~m~jn~ stable as long as it is at least mod-
30 erately agitated mechani~ally. Some refrigeration (andother) compressors are designed to operate satisfactorily
with such miscible mixtures of refrigerant working fluid
and lubricant. In contrast, mixtures that lead to coagu-
lation or significant thicken; ng and form two or more
35 phases are unacceptable commercially and are designated
herein as "immiscible". Any such mixture described below
is a comparative example and not an embodiment of the
12
~ W093/25628 ` 21~7~5~ PCT/US93/04885
present invention.
Another major embodiment of the invention is the use
of a lubricant according to the invention, either as total
lubricant or lubricant base stock, in a process of operat-
s ing refrigerating machinery in such a manner that the lub-
ricant is in contact with the refrigerant working fluid.
The practice of the invention may be further under-
stood and appreciated by consideration of the following
examples and comparative examples.
General Ester SYnthesis Procedure
The alcohol(s) and acid(s) to be reacted, together
with a suitable catalyst such as dibutyltin diacetate, tin
oxalate, phosphoric acid, and/or tetrabutyl titanate, were
charged into a round bottomed flask equipped with a stir-
rer, thermometer, nitrogen sparging means, condenser, and
a recycle trap. Acid(s) were charged in about a 15 % mol-
ar excess over the alcohol(sj. The amount of catalyst was
from 0.02 to 0.1 % by weight of the weight of the total
acid~s) and alcohol(s) reacted.
The reaction mixture was heated to a temperature be-
tween about 220 and 230 C, and water from the resulting
reaction was collected in the trap while refluxing acids
were returned to the reaction mixture. Partial vacuum was
maintained above the reaction mixture as necessary to
achieve a reflux rate of between 8 and 12 % of the orig-
inal reaction mixture volume per hour.
The reaction mixture was sampled occasionally for de-
termination of hydroxyl number, and after the hydroxyl num-
ber had fallen below 5.0 mg of KOH per gram of mixture,
the majority of the excess acid was removed by distilla-
tion after applying the highest vacuum obtainable with the
apparatus used, corresponding to a residual pressure of
about 0.05 torr, while maintaining the reaction temper-
ature. The reaction mixture was then cooled, and any re-
sidual acidity was removed, if desired, by treatment with
lime, sodium hydroxide, or epoxy esters. The resulting
lubricant or lubricant base stock was dried and filtered
WO 93/2~628
2 ~.3 7 2 ~ PCr/US93/0~5
before phase compatibility testing.
General Procedure for Phase Com~atibilitY Testin~
One milliliter ("ml"~ of the lubricant to be tested
is placed into a thermal shock resistant, volumetrically
graduated glass test tube 17 millimeters ("mm") in diam-
eter and 145 mm long. The test tube is then stoppered and
placed into a cooling bath regulated to -29 + 0.2 C. Af-
ter the tube and contents have equilibrated in the cooling
bath for 5 minutes ("min"), sufficient refrigerant working
fluid is added to give a total volume of 10 ml.
At least 15 min after the working fluid has been add-
ed, during which time the tube and contents have been
e~uilibrating in the cooling bath and the contents may
have ~een agitated if desired, the tube contents are visu-
ally ~m j ~ed for evidence of phase separation. If there
is any such phase separation, the tube is shaken to deter-
mine whether the combination can ~e rated as miscible or
is totally unacceptable.
If there is no evidence of phase separation at -29
C, the temperature of the cooling bath is usually lowered
at a rate of 0.3 per min until phase separation is ob-
served. The temperature of first observation of phase
separation, if within the ran~e of the cooling e~uipment
used, is then noted as the insolubility onset temperature.
Com~osition of Specific Example
A suitable ester mixture as described above was pre-
pared by reacting a mixture of alcohol molecules in which
99.9 % were P~ molecules, with most of the remainder being
DPE molecules, with a mixture of acid molecules that in-
cluded 80 % of 3-methyl~utanoic acid and 19 % of adipic
acid, with the remainder predominantly other five car~on
monobasic acids. This ester mixture had a viscosity at
40 C of about 900 centistokes.
14
