Note: Descriptions are shown in the official language in which they were submitted.
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HYDROFLUOROCARBON MISCIBLE SYNTHETIC ESTER LUBRICANT BASE
STOCK BLENDS
Background of the Invention
This invention relates to synthetic polyol ester lubricant base stocks, and
more
particularly to cross blends of high viscosity synthetic ester lubricant base
stocks with
conventional polyol ester base stocks suitable for use in compressor and
refrigeration
systems.
It is well known that chlorofluorocarbons previously utilized as propellants
in
aerosols and as refrigeration fluids are no longer used due to the adverse
impact on
the earth's ozone layer. Efforts to eliminate the use of chlorofluorocarbons
have led to
the development of alternative fluids that are highly or fully fluorinated
hydrocarbons.
Working refrigeration fluids generally include a minor amount of lubricant.
Typically, the refrigeration fluids include between about 5 to 15 or 20 parts
by weight
of lubricant with the balance being the fluorocarbon. In chlorofluorocarbon
systems,
lubricants were traditionally mineral oils which are fully miscible with the
chlorofluorocarbons. However, such lubricants are not miscible with the highly
or fully
fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane, commonly known as
HFC-134a, and other chlorine-free fluorocarbons including hydrofluorocarbon
(HFC)
having 1 to 3 carbon atoms and preferably 1 to 2 carbon atoms, for example,
difluoromethane (HFC-32), trifluoromethane (HFC-23), pentafluoroethane (HFC-
125),
1,1,2,2,-tetrafluoroethane (HFC-134), 1,1,1-trifluoroethane (HFC-143a), and
1,1-
difluoroethane (HFC-152a).
Although HFCs are not miscible with mineral oil, certain carboxylic esters of
polyhydroxy compounds, also known as polyol esters or POEs, are fully miscible
with
the highly or fully fluorinated fluids. The polyol ester lubricants are
prepared by the
condensation of certain polyols such as pentaerythritol, neopentyl glycol and
trimethylpropanol, and linear or branched nnonocarboxylic acids containing
between
about 4 to 10 carbon atoms. To improve miscibility, the carboxylic acid
mixture
typically includes 30-85 mole % 3, 5, 5 tri-methylhexanoic acid (iso-C-9).
However,
recent events have limited the availability of iso-C-9. This shortage of iso-C-
9 has
made it difficult and/or expensive to manufacture polyol esters using iso-C-9.
Accordingly, it is desirable to provide synthetic ester lubricant base stocks
miscible with HFCs having viscosities between about ISO 68 to 220 based on
cross
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blends of two or more base stocks. The blend is comprised of a high viscosity
synthetic base stock formed by condensation of neopentylpolyol and linear and
branched monocarboxylic acids, wherein little or no iso-C-9 is used in the
carboxylic
acid mix, and a conventional polyol ester base stock. The cross blend is
miscible
with HFCs notwithstanding the limited use of iso-C-9, and provides an
economical
base stock in times where supplies of iso-C-9 are limited.
Summary of the Invention
It is an object of the present invention to produce a wide range of polyol
ester
lubricants that are miscible with HFCs with minimum or no use of iso-C-9 in
the
carboxylic acid reaction mixture.
Another object of the present invention is to provide a lubricant base stock
for
air-conditioning and refrigeration systems.
Another object of the present invention is to provide an economical process of
making synthetic ester base stocks that have sufficient miscibility with HFC
refrigerants with limited use of iso-C-9 carboxylic acids.
Another object of the present invention is to provide a synthetic ester base
stock that has sufficient miscibility with HFC refrigerants with limited use
of iso-C-9
carboxylic acids that exhibits superior wear and increases compressor
efficiency.
In accordance with the invention, cross blends of synthetic ester lubricants
suitable for use with a wide range of HFC refrigeration fluids are provided.
Applicants
have discovered that cross blends of i) conventional polyol ester base stocks
of
varying viscosities; and ii) iso 120 to 140 high viscosity base stock, formed
with little
or no iso-C-9, provides a range of high and low viscosity polyol ester base
stocks that
are miscible with HFC refrigeration fluids and exhibit superior protection
against
wear.
Detailed Description of the Invention
In the following description, for purposes of explanation and not limitation,
specific details are set forth in order to provide a thorough understanding of
the
present invention. However, it will be apparent to one skilled in the art that
the
present invention may be practiced in other embodiments that depart from these
specific details. Detailed descriptions of well-known processes, acids, and
methods
for manufacturing the same are omitted so as not to obscure the description of
the
present invention.
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Cross Blend Materials
The synthetic ester base stock blend of the present invention comprises a
cross blend of a) certain high viscosity synthetic ester base stocks and b)
conventional synthetic ester base stocks.
High Viscosity PoIyol Ester
The high viscosity polyol ester base stock is formed by condensation of
neopentylpolyol and a mix of linear and branched monocarboxylic acids in an
excess
of hydroxyl groups, wherein little or no iso-C-9 is used in the carboxylic
acid mix. The
method of making such a high viscosity synthetic ester base stock is disclosed
in
to U.S. Patent No. 6,774,093.
In one embodiment, the high viscosity base stock is a blend of esters which
form the reaction product of a two step process. In the initial step a
neopentyl polyol
having from 8 to 10 carbon atoms is reacted with an acid or acid mixture of
linear C4
¨ C10 acids and/or branched C5 ¨ C10 acids in the presence of an excess of
hydroxyl
16 groups to carboxyl groups in the presence of an acid catalyst to form a
partial
polyneopentylpolyol ester mixture. The excess of hydroxyl groups is necessary
to
promote the polymerization of the partial esters and the molar ratio of acid
or acid
mixture to the polyol can be varied depending on the desired rate of reaction,
degree
of condensation and the ultimate desired viscosity of the base stock. When the
20 anticipated water of reaction has been removed from the reaction vessel to
yield a
product of desired viscosity, the resulting partial polyneopentylpolyol ester
is then
reacted with an excess of an acid or acid mixture that can vary or be the same
acid
mixture used in the initial step to yield the high viscosity ester product.
More particularly, the high viscosity polyol ester used in the cross blend of
the
25 present invention has a viscosity of iso 120 to 140 and is made in
accordance with
the method described above and in the '093 patent using a blend of
pentaerythritol
and dipentaerythritol reacted with a blend of carboxylic acids selected from
one or
more of C5, iso-05, C7, hexanoic, iso-C9 and Cg monocarboxylic acids.
In one embodiment the iso 120 to 140 high viscosity polyol ester is made
30 using a 60/40 blend of pentaerythritol and dipentaerythritol reacted with
carboxylic
acids selected from one or more of nC5, iso-05, nC7, hexanoic and C9 in the
presence of an excess of hydroxyl groups to carboxyl groups. The reaction
continues until it yields a product of the desired viscosity. A high density
polyol ester
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having a viscosity between iso 120 and iso 140 provides sufficient miscibility
with
refrigerant R134a from -38 C to 80 C even without the use of iso-Cg as one of
the
carboxylic acids.
Conventional Polyol Ester
Conventional polyol ester base stocks, as used herein, is intended to mean
synthetic ester base stocks prepared by standard condensation reaction of
neopentylpolyol and a selection of linear and branched monocarboxylic acids.
The conventional ester base stocks of the present invention are polyol ester
based lubricants made by a conventional condensation reaction of polyols and
carboxylic acids. The conventional polyol ester base stocks have a viscosity
range
from iso 20 to iso 350 and are available from a number of sources including
Castrol
Industrial North America Inc. Warrenville, IL under the IcematicTm brand,
Cognis
(under the Evergreen TM brand name), Uniqema Corporation RL series, CPI's
SolestTM brand of POEs, Mobil [AL ArcticTM, JEC,and Nippon Oil.
Lubricating Oil Composition
A variety of additives may be added to the cross-blends to make the fully-
blended refrigeration lubricant. These additives include: anti-oxidants, anti-
wear
additives and metal deactifiers.
Anti-oxidants
A fully-blended refrigeration lubricant may contain from about 0.01% to 1% by
weight, alternatively from about 0.05% to 0.5% by weight, alternatively from
about
0.10 c1/0 to about 0.20% by weight, of one or more antioxidants.
Anti-oxidants reduce the tendency of lubricating oils to deteriorate in
service.
This deterioration can be evidenced by increased oil viscosity and by the
products of
oxidation such as acids, sludge and varnish-like deposits on the metal
surfaces. In
one embodiment 0.10wt% BHT is used.
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Anti-wear agent
A fully blended refrigeration lubricant may also contain from about 0.0075% to
3% by weight, alternatively from about 0.01% to about 2% by weight,
alternatively
from about 0.06% to about 1 % by weight, of one or more anti-wear agents.
Anti-wear agents, as their name implies, reduce wear of metal parts. Anti-
wear agents commonly used in refrigeration lubricants include VanlubeTM 672
which
is available from RT Vanderbilt and tricresyl phosphate (TCP) antiwear
additives.
Metal Deactifier
A fully blended refrigeration lubricant may also contain from about 0.001% to
0.1% by weight, alternatively from about 0.0075% to about 0.05% by weight, of
one
or more metal deactifier such as tolutriazole (available from Ciba Specialty
Chemicals
under the trade name lrgametTM TTZ) and sebacic acid corrosion inhibitors. In
one
embodiment 0.01% by weight of tolutriazole (TTZ) is used.
Other additives
Other additives include acid blockers such as Texaco's Cadura TM E-10.
Blending Conditions
The cross blends of the present invention are made by blending high viscosity
polyol ester having a viscosity in the range of iso 120 to iso 140 with
conventional
polyol esters of viscosity grade iso 20 to iso 350 to achieve the desired
final viscosity.
The high viscosity and conventional polyol esters along with a selection of
additives,
if any, are blended in a steam-jacketed stainless kettle at a temperature
range of
120 C to 180 C for around 24 hours.
The desired viscosity grade of the cross blends is achieved by blending in
accordance with the following cross blend chart.
Cross Blends
iso 32 iso 68 iso 120 iso 220
cross-blend cross-blend cross-blend cross-blend
High viscosity
POE 15 wt /0 iso 120 73 wt /0 iso 120
100 wt% iso 120 60 wt% iso 120
Conventional
POE 85 wt% iso 20 27 wt% iso 20
40 wt% iso 350
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EXAMPLES
The Examples are for illustration only and not intended to limit the scope of
the
invention.
Example I ¨ High Density Polyol Esters Miscible with 134a
The following example illustrates that only certain high viscosity polyol
esters
made in accordance with the '093 patent are miscible with R 134a.
COMPOSITION
Made using '093
process
polyol, MOL% 100% 100% 100% 100% 100% 100%
Acids MOL%
nC5 100% 50% 56% 5% 66%
nC6
nC7 20%
nC9
nC8
3 METHYL
VALERIC 10% 10%
iso-05 34% 34%
Hexanoic 10%
2-EH 70% 95%
iso-C9 50%
Other Additives
BHT % 0.10% 0.10% 0.10% 0.10% 0.10% 0.10%
Physical/Chemical
Properties
Reacted Viscosity 220 220 232 139 196 120-139
40C 220 220 232 139 , 196
120
R134a Miscibility at
Room temp C Not Not Not -38 Not -39
The data demonstrates that only high viscosity polyol esters having a
viscosity in the
range of iso 120 to iso 140 are miscible with R 134a. Thus, the cross blends
should
be made with high viscosity polyol esters in this range.
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Example II ¨ Cross Blends
Cross Blend % iso C-9 Blend %
anti-wear BHT%
Sample No. additive
TTZ%
1 0 27% SW20 0.03% 0.10%
73% VG120
2 0 27% SW20 0.00% 0.10%
73% VG120
3 0 27% SW20 0.015% 0.10%
73% VG120
4 0 27% SW20 0.0075% 0.10%
73% VG120
0 100% VG120 0.00% 0.10%
0.01%
6 45 40% SW 350 0.00% 0.10%
60% VG120
VG120= high viscosity grade of iso 120 available from Hatco Corporation
SW20= iso 20 POE available from Castro! Industrial North America
5 SW68= iso 68 POE available from Castro! IndustrialNorth America
SW220= iso 220 POE available from Castro! Industrial North America
SW350= iso 350 POE available from Castro! Industrial North America
Example III ¨ Wear Data
The wear properties of the cross blends were tested in accordance with ASTM
D2670 Falex Pin and Vee Block Test. The Falex Pin & Vee Block Test evaluates
the
extreme pressure properties or wear characteristics of a lubricant. The
machine
rotates a test pin against two stationery Vee Blocks at 290 rpm. Load is
applied to
the Vee blocks through a ratchet mechanism and the test specimen is immersed
in
the cross blend lubricant while R-134a refrigerant is bubbled up through the
lubricant.
A 250 lb load was applied for the first 5 minute break-in period and a 400 lb
load was
applied for the 30 minute duration of the test. Wear is measured and reported
as the
number of teeth the ratchet mechanism advances in order to maintain constant
load
during the prescribed test time. The results for the cross blends are in Table
III.
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Table Ill Falex Pin and Vee Block Wear Data average of three runs
Wear Data measured in Mass in grams Lost
Cross Blends Tooth Count Pin Vee
Block 1 Vee Block 2
Sample No.
1 7 0.0016 -0.0007 0.0002
2
3 152 0.0142 0.00052
0.00022
4 13.751 0.01321 0.00071
0.00021
6
Conventional POEs
lcematic SW 68 - 23.5 0.01961 0.00071
0.000851
fnl Average of 4 runs
fn2 Average of 3 runs
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