Tribology Transactions, 50: 82-87, 2007
C Society of Tribologists and Lubrication Engineers
Copyright ISSN: 1040-2004 print / 1547-357X online
DOI: 10.1080/10402000601105581
Alkylated Naphthalenes as High-Performance Synthetic
Lubricating Fluids
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MICHEL J. HOURANI, ED T. HESSELL, RICHARD A. ABRAMSHE, and JAMES LIANG
King Industries, Inc.
Norwalk, Connecticut
Alkylated naphthalene is a unique class of synthetic fluids
with outstanding thermo-oxidative and hydrolytic stability, low
volatility, and good solubility characteristics. This paper discusses the flexibility of this technology to achieve a balance of
physical and chemical properties. In particular, fluid properties
including thermo-oxidative stability, viscosity, aniline point, and
volatility are related to chemical variations. Also, new elastohydrodynamic (EHD) film thickness and pressure-viscosity coefficient data show the good performance of this family of fluids
as compared to synthetic esters.
performance attributes. This paper discloses some of our recent
findings.
GENERAL STRUCTURE OF AN ALKYLATED
NAPHTHALENE
Alkylated naphthalenes have the general structure shown in
Fig. 1. The core naphthalene system consists of two fused sixmembered rings with an electron-rich, conjugated π system. It is
this extended aromatic system that imparts the unique thermooxidative stability to this class of compounds. However, the alkyl
groups attached to the naphthalene also can make an important
contribution to the characteristics of the compound. In particular,
the alkyl groups control most of the physical characteristics of
the compound, such as viscosity, pour point, and volatility. The
physical properties of the material will primarily depend on the
length of the alkyl group, as well as the number of alkyl groups on
the naphthalene ring.
KEY WORDS
Synthetic Lubricants; Alkylated Naphthalenes; Elastohydrodynamic Lubrication; Physical Properties; Lubricant Stability;
Oxidation; Radiation; Additive Solubility
INTRODUCTION
SYNTHESIS OF ALKYLATED NAPHTHALENES
The alkylation of aromatic compounds to make liquids suitable as lubricants has been practiced for many decades (Wu and
Ho (1)). In general, the connection of long-chain alkyl groups
to an extended aromatic framework provides a combination of
properties, such as good additive solubility and excellent thermooxidative stability relative to mineral base oils. The alkylation
of naphthalene has also been practiced for many years (Larsen,
et al., Koelbel, H. (2)) and there are many composition (3), process (4), and applications (5) patents covering this chemistry.
We have actively pursued the alkylation of naphthalene since
the early 1950’s, primarily as an intermediate for the preparation of alkylated naphthalene sulfonic acids. Several years ago
we became interested in extending our technology to custom design alkyl naphthalenes for a variety of specialty lubricant applications. It has been well known for some time that alkylated
naphthalenes offer advantages over other synthetic fluids useful as base oils, especially in the area of thermo-oxidative and
hydrolytic stability. Our current research is focused on various
alkylated naphthalene structures and their physical properties and
There is an extensive body of research on the alkylation of
naphthalene. This paper will present only a brief introduction to
selected aspects of the synthesis of alkylated naphthalenes.
Alkylated naphthalenes are most easily prepared by the
Friedel-Crafts alkylation of naphthalene with an alkylating agent
in the presence of an acid catalyst (Fig. 2). Although almost any
alkylating agent, such as an alcohol, an alkyl halide, or an olefin,
may be used, the most commonly used alkylating agent is an olefin.
Out of many possible alkylating olefins, the most commonly used
olefin for a lubricant base stock is an alpha-olefin in which the double bond resides at one terminus of the alkyl chain. Under normal
Friedel-Crafts conditions the reaction produces a complex mixture of alkylated naphthalenes having different numbers of alkyl
groups on the naphthalene ring.
The naphthalene alkylation reaction depends on many factors
such as the catalyst type, temperature, ratio of the alkylating agent
to naphthalene, and the manner in which the reactants are combined. Many different types of catalysts are suitable for the reaction including Lewis acids, strong protic acids, heterogeneous solid
catalysts such as zeolites, or acid-treated clays (Olah, et al. (6)).
Presented at the STLE/ASME International Joint Tribology
Conference in San Antonio, Texas
October 23-25, 2006
Manuscript approved August 29, 2006
Review led by Lois Gschwender
CHARACTERIZATION OF ALKYLATED NAPHTHALENES
As previously mentioned, the alkylation of naphthalene with
an olefin results in a complex mixture of molecules of various
82
Alkylated Naphthalenes
TABLE 1—PHYSICAL
NAPHTHALENES
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Fig. 1—General structure of an alkylated naphthalene.
molecular weights and alkyl chain isomers. A gas chromatograph
(GC) of one such composition is shown in Fig. 3. Each group
of peaks in the chromatograph is a mixture of alkyl chain isomers of roughly equivalent molecular weight and boiling point,
the molecular weight being determined by the number of alkyl
chains attached to the naphthalene ring. They are identified as
monoalkylnaphthalene (MAN), dialkylnaphthalene (DAN), and
polyalkylnaphthalene (PAN). The relative amount of each component can be adjusted through selective distillation and/or blending to provide a lubricant with the required physical properties
for a specific application. For example, the DANs have very low
volatility for high-temperature applications and the PANs have
extremely low volatility for higher temperature and vacuum applications.
PHYSICAL PROPERTIES OF ALKYLATED
NAPHTHALENES
The physical properties of alkylated naphthalenes depend primarily on two major factors:
r
r
the length of the alkyl groups
the number of alkyl groups attached to the naphthalene (degree of alkylation)
Alkylated naphthalenes suitable for lubricant applications
were prepared for this study and their physical properties are
shown in Table 1.
Pour Point
The pour points of the alkylated naphthalenes increase with
increasing substitution on the naphthalene ring. Pour point is critical for low-temperature applications. Even if the viscosity index
(VI) of a fluid is excellent, it is not usable at low temperatures if
its pour point is high.
Fig. 2—Friedel-Crafts alkylation of naphthalene.
83
PROPERTIES
Kinematic viscosity @ 40◦ C (cSt)
Kinematic viscosity @ 100◦ C (cSt)
Viscosity index
Pour point (◦ C)
Aniline point (◦ C)
Flash point (◦ C)
OF
SELECTED
ALKYLATED
DAN
PAN #1
PAN #2
114
13.5
110
−39
94
260
177
18.7
118
−26
103
285
193
19.8
118
−21
107
320
Aniline Point and Additive Solubility
Aniline point is an indirect measure of the polarity of a substance and its ability to solubilize polar materials. The aniline point
is defined as the temperature where an equal volume mixture of
aniline and the test fluid exists as a single phase. A low aniline
point is indicative of a fluid with higher polarity and good solubilizing characteristics. Data in Table 1 show that aniline points
of PAN fluids are higher than DAN fluid, indicative of decreasing
polarity with a higher degree of alkylation.
Volatility by TGA Analysis
There are several ways to measure volatility of these base
synthetic fluids. Noack volatility, the commonly reported number, measures the % weight loss of a fluid at 250◦ C, 20 mm vacuum under air purge for 60 min. Another approach is by thermal
gravitational analysis (TGA). In this study, we used two TGA
methods, one under ambient atmospheric pressure following the
ASTM D 3850 protocol (20◦ C/min scan rate), and another is under 0.1 Torr vacuum (10◦ C/min scan rate), which was developed
by Wright-Patterson Air Force Base. As expected, the results in
Table 2 show that the higher the degree of alkylation, the lower
the volatility. The PAN #2 showed extreme low volatility under
high vacuum, lending itself to vacuum applications.
CHEMICAL PROPERTIES
Thermal Stability
The pure thermal stability of an organic compound in the absence of oxygen primarily depends on the strength and polarity of
the chemical bonds in the molecule. Alkylated naphthalenes are
aromatic hydrocarbons containing only covalent C C and C H
bonds, which have very high bond dissociation energies (C H
bond ∼100 kcal/mol; C C bonds ∼ 85 kcal/mol). However, in the
M. J. HOURANI ET AL.
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84
Fig. 3—Gas chromatograph of an alkylated naphthalene mixture.
presence of metal catalysts, such as iron or copper, the thermal
stability of synthetic hydrocarbons may be lessened.
The thermal stability of the alkylated naphthalenes was evaluated using the Federal Test Method 3411. In this test, the compounds were heated at 274◦ C for 96 h in a sealed glass tube with a
steel coupon in the absence of moisture and oxygen. The changes
in viscosity, acid number, and discoloration and corrosion of the
steel coupon were all indicative of fluid decomposition. The results
in Table 3 show that alkylated naphthalenes do not undergo any
significant decomposition. Also, Cincinnati Milicron tests were
conducted at stressed conditions of 150◦ C and 200◦ C instead of the
standard 135◦ C protocol. The results showed insignificant sludge
formation and viscosity increase changes at 150◦ C for all the alkylated naphthalenes (Table 4a); however, the polyalkylated naphthalenes PAN #1 and PAN #2 showed improved performance over
DAN at 200◦ C (Table 4b), indicating that the polyalkylation not
only reduces the volatility but also enhances the thermal performance of these products.
TABLE 2—VOLATILITY
NAPHTHALENES
BY
TGA
ANALYSIS OF
Onset temperature at atmospheric
pressure
T1/2 temperature at atmospheric
pressure
Onset temperature under 0.1 Torr
vacuum
T1/2 temperature under 0.1 Torr
vacuum
SELECTED ALKYLATED
DAN
PAN #1
PAN #2
256◦ C
297◦ C
311◦ C
344◦ C
360◦ C
367◦ C
260◦ C
285◦ C
292◦ C
286◦ C
316◦ C
321◦ C
Thermo-Oxidative Stability
The thermo-oxidative stability of the alkylated naphthalenes
was evaluated using the ASTM D 2272 rotory pressure vessel oxidation test (RPVOT) and pressure differential scanning calorimetry (PDSC).
Rotating Pressure Vessel Oxidation Test (RPVOT)
The RPVOT test utilizes an oxygen-pressure vessel to evaluate
the oxidation stability of fluids at 150◦ C in the presence of water
and a copper catalyst coil. The test fluid, water, and the copper
coil, contained in a covered glass container, are placed in a vessel
equipped with a pressure gauge. The vessel is charged with oxygen
to a pressure of 621 kPa (90 psi), placed in a constant temperature
oil bath at 150◦ C, and rotated axially at 100 rpm at an angle of 30◦
TABLE 3—THERMAL
NAPHTHALENES
% Change in kinematic
viscosity @ 40◦ C
Initial acid number (mg
KOH/g)
Change in acid number
Change in metal weight
(mg/cm2 )
Appearance of metal
Sediment
Original oil appearance
Final oil appearance
Test cell appearance
STABILITY
OF
SELECTED
ALKYLATED
DAN
PAN #1
PAN #2
+0.6%
+0.7%
+0.1%
0
0
0.02
0
+0.017
0
+0.034
−0.02
+0.033
Dull brown
None
Light yellow
Light yellow
Clean
Dull brown
None
Light yellow
Light yellow
Clean
Dull brown
None
Yellow
Yellow
Clean
FTM 3411 test @274◦ C for 96 h in sealed glass tube with a steel coupon.
Alkylated Naphthalenes
TABLE 4A—CINCINNATI MILICRON∗ THERMAL STABILITY
LECTED ALKYLATED NAPHTHALENES
% Viscosity change
Acid number change (mg KOH/g)
Total sludge (mg/100 ml)
Whatman precipitate (mg/100 ml)
Millipore precipitate (mg/100 ml)
CM color class—Copper
CM color class—Steel
∗ Test
OF
SE-
DAN
PAN #1
PAN #2
3.8
0.03
0.45
0.15
0.40
2
1.5
2.1
0.03
0.65
0.25
0.40
3
1
4.0
0.02
0.5
0.1
0.4
2.5
1
run at 150◦ C.
85
TABLE 5—ROTARY PRESSURE VESSEL OXIDATION TEST (RPVOT)
ALKYLATED NAPHTHALENES
PAO∗
Induction time (minutes)
– neat fluid
Induction time (minutes)
with 0.2% DTBP
Induction time (minutes)
with 0.2% ZnDTP
Induction time (minutes)
with 0.2% DPA
DAN
PAN #1
OF
PAN #2
19.4
87.0
89.0
101.2
44.2
179.8
204.0
241.6
220.4
231.6
157.2
138.2
34.2
409.8
532.2
521.2
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∗ PAO
from the horizontal. The time period required for the pressure to
drop to 175 kPa (25.4 psi) is taken as the measure of the oxidation
stability of the test sample. The longer the induction time, the
better is the oxidative stability of the material.
The results of tests run on the alkylated naphthalenes are
reported in Table 5. The alkylated naphthalenes show excellent
thermo-oxidative stability under the conditions of the test as compared to an equal viscosity PAO. They also show improved oxidation resistance response with DTBP (di-tertbutylphenol) and
especially alkylated DPA anti-oxidants vs. the PAO, but reduced
response with ZnDTP in PAN. This could be the result of the
electron-rich naphthalene portion of the molecules which may
scavenge radicals and disrupt the oxidation process making them
more oxidative stable with and without anti-oxidants. The reduced
response with ZnDTP in PAN was unexpected and somewhat surprising but it could be related to the additive response of ZnDTP
to the various fluids where an optimum dose level is necessary for
each fluid. This merits further future investigation.
Pressure Differential Scanning Calorimetry (PDSC)
PDSC is an analytical technique that offers additional insight
into the fundamental thermo-oxidative stability of materials. This
is a calorimetric test that measures the induction time to an onset
of exotherm or endotherm under specific conditions of temperature and atmosphere. The exotherm or endotherm is associated
with decomposition of the fluid. For this study, two protocols were
used. One is a TA Instruments Model 910 PDSC interfaced to a Series 2000 Thermal Analyst computer. Samples were weighed into
open aluminum pans and heated at a rate of 40◦ C/min to 160◦ C and
then held isothermally until an exotherm was observed. All tests
were run under an atmosphere of 1036 kPa (150 psi) high-purity
TABLE 4B—CINCINNATI MILICRON∗ THERMAL STABILITY OF SELECTED
ALKYLATED NAPHTHALENES
% Viscosity change
Acid number change (mg KOH/g)
Total sludge (mg/100 ml)
Whatman precipitate (mg/100 ml)
Millipore precipitate (mg/100 ml)
CM color class—Copper
CM color class—Steel
∗ Test
run at 200◦ C.
DAN
PAN #1
PAN #2
25.3
0.09
1.40
0.20
1.40
5
8
11.8
0.07
0.60
0.10
0.40
2
5
13.6
0.09
1.40
1.00
0.40
2.5
4.5
of viscosity 114 (cSt) @40◦ C (blend of 65% PAO 40/35%
PAO 4).
air to accelerate the rate of decomposition. Results from this protocol are shown in Table 6. Another protocol was ASTM D 3895,
which requires a 5-mg sample in an aluminum pan and heated at
a rate of 50◦ C/min to an isothermal temperature of 190◦ C under
an atmosphere of 3452 kPa (500 psi) high-purity oxygen. Results
from this protocol are also shown in Table 6. In all cases, the neat
alkylated naphthalenes exhibited excellent oxidation stability vs.
other base oils.
EHD FILM THICKNESS AND PRESSURE VISCOSITY
COEFFICIENT
The elastohydrodynamic behavior of a lubricating fluid is a
good theoretical measure of the film-forming potential of the fluid
to protect the metal surface at different speeds and temperatures.
A WAM machine shown in Fig. 4 was used for these EHD tests,
varying the entraining or rolling velocity from 0 to 10 m/s and
the temperature from 25◦ C to 100◦ C. Under these conditions, the
fluid film thickness was measured between 10 and 2000 nm and
the pressure-viscosity coefficient of each fluid was calculated.
The WAM machine, developed by Wedeven Associates in Edgmont, PA (www.wedeven.com), utilizes an optical interferometer
to create interference fringes that correspond to the fluid film
thickness between a specially coated Pyrex disc and a smooth
2-cm-diameter steel ball. The test machine reservoir is filled with
the test fluid and the disc is lowered by a computer-controlled actuator such that a 44.4-N load between the steel ball and the glass disc
is achieved. Three load cells provide feedback to the actuator such
that the contact load is held constant. A peristaltic pump directs
TABLE 6—PDSC OXIDATION STABILITY
THALENES (INDUCTION TIME IN MIN)
DAN
PAN #1
PAN #2
114 (cSt) PAO
7 (cSt) Group III
80% (7cSt) Group III/20% DAN
80% 7 (cSt) Group III/20%
various esters
OF
ALKYLATED NAPH-
Protocol #1
ASTM D3895
160◦ C/150 psi
190◦ C/500psi
14
6
14
<1
<1
<1
21
<1
86
M. J. HOURANI ET AL.
TABLE 8—EHD FILM THICKNESS AND PRESSURE-VISCOSITY COEFFICIENT
POLYOL ESTERS (PE) VS. MAN
OF
4 cSt (PE)
nm
EHD film thickness at 2 170
m/s and 45◦ C
EHD film thickness at 2 40
m/s and 100◦ C
×10−9 (Pa)−1
8.5
Pressure-viscosity
coefficient at 2 m/s
and 45◦ C
Pressure-viscosity
3.9
coefficient at 2 m/s
and 100◦ C
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Fig. 4—WAM set up for EHD film thickness measurement.
a continuous jet of test fluid to the inlet region between the ball
and the disc. A small fixed thermocouple within the flooded inlet
region is used to define the test temperature. This thermocouple
provides feedback to a temperature controller, which regulates
the heaters within the reservoir such that a constant inlet fluid
temperature is achieved. When the test temperature is reached
within 1◦ C, the operator increases the disc speed and the freewheeling ball increases to the same speed at the same rate as does
the disc. As soon as the speed is increased, an EHD fluid film is
produced between the ball and the disc. At this point, an image
of the EHD lubricated contact is grabbed and saved. Subsequent
increases in disc speed are made and the corresponding images
are grabbed until the targeted speed is reached. This procedure
creates a series of images of an EHD lubricated contact at various rolling velocities and with constant temperature. An optical
software called AChILES (Automatic Chromatic Interferogram
Laboratory Evaluation System) continuously maps and converts
all of the colors observed within the dynamic EHD contact into
film thickness. Pressure-viscosity coefficients are then calculated
using Hamrock-Dowson film thickness theory (Hamrock and
Dowson (7)).
Using this method, the alkylated naphthalenes DAN and PAN
#1 were tested. Their EHD film thicknesses and corresponding
TABLE 7—EHD FILM THICKNESS AND PRESSURE-VISCOSITY COEFFICIENT
ALKYLATED NAPHTHALENES (AN)
OF
EHD film thickness at 2 m/sec and
25◦ C
EHD film thickness at 2 m/sec and
45◦ C
EHD film thickness at 2 m/sec and
100◦ C
Pressure-viscosity coefficient at 2 m/s
and 25◦ C
Pressure-viscosity coefficient at 2 m/s
and 45◦ C
Pressure-viscosity coefficient at 2 m/s
and 100◦ C
4 cSt (MAN) 6.5 cSt (PE)
DAN
PAN #1
nm
1800
nm
2000
800
1000
200
225
×10−9 (Pa)−1
21.0
×10−9 (Pa)−1
12.5
16.0
12.1
12.9
10.8
nm
225
nm
310
52
80
×10−9 (Pa)−1 ×10−9 (Pa)−1
15.6
8.8
7.5
6.6
pressure-viscosity coefficients are shown in Table 7. The film thickness is proportional to viscosity to an exponential power of ∼0.71
and therefore one would expect a higher film thickness with higher
viscosity, but generally both samples show high film thickness.
Also, in order to compare the performance of alkylated naphthalenes vs. other synthetic fluids such as polyol esters at equal
viscosity, a sample of MAN was made with a 4cSt viscosity at
100◦ C (40◦ C aniline point, −48◦ C pour point, 200◦ C flash point,
VI = 22) and compared to standard 4cSt and 6.5cSt polyol esters
used in turbine engine oils by the US military. Table 8 shows that
the pressure-viscosity coefficients were higher for the alkylated
naphthalene than both polyol esters. Again, since the film thickness is proportional to viscosity, the 6.5cSt polyol ester showed
the highest film thickness; however, at equal viscosity of 4cSt, the
alkylated naphthalene outperformed the polyol ester.
RADIATION STABILITY
Very recently, a study conducted at the University of Nicolaus
Copernicus in Poland focused on the radiation stability of alkylated naphthalenes vs. standard and fully formulated base oils.
They evaluated the radiation chemical yield of hydrogen. Atomic
hydrogen plays an important role in damage mechanisms, called
hydrogen embrittlement, affecting rolling bearings. For example, a
rise in just over 1 ppm of hydrogen distributed throughout a bearing ball during a high-pressure test was found to cause significant
bearing damage. A quantitative gas chromatography technique
was developed to analyze low concentrations of molecular hydrogen in the head space above irradiated oils. Their results, shown in
Table 9, suggest that the alkylated naphthalene has a significantly
higher radiation stability than other base oils, neat or fully formulated. The G-value is the radiation chemical yield and it represents
TABLE 9—RADIATION STABILITY
100 EV RADIATION ENERGY
OF
ALKYLATED NAPHTHALENE
AT
G-value (H2 )
8 (cSt) Paraffinic oil—neat
11 (cSt) Fully formulated vacuum pump oil (based
on mineral oil)
DAN—neat
3.2
1.7
0.5
Alkylated Naphthalenes
the number of hydrogen molecules formed as a result of expenditure of radiation energy of 100 eV. The G-value is therefore a
measure of the sensitivity of the base oil against radiation.
CONCLUSIONS
The physical and chemical properties of three alkylated naphthalenes have been compared. All of the alkylated naphthalenes
exhibit outstanding thermo-oxidative stability. In addition, the
polyalkylated naphthalenes have low volatility, even under vacuum, and exhibited excellent thermal stability. These synthetic
fluids also have good film thickness and pressure-viscosity coefficients for surface protection.
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ACKNOWLEDGEMENTS
The authors thank Ed Snyder and Lois Gschwender of the
Wright-Patterson Air Force Base for the vacuum TGA tests.
REFERENCES
(1) Wu, M. M. and Ho. S. (2006), Alkylated Aromatics. In: Synthetics, Mineral
Oils, and Bio-Based Lubricants. L. R. Rudnik, ed., Taylor & Francis, Boco
Raton, FL, Ch. 7, pp. 139–155.
(2) Larsen, R. G., Thorpe, R. E., Armfield, F. A., (1942), Ind. Eng. Chem. 34,
pp 183–193. Koelbel, H. (1948), Synthesis of Lubricants via the Alkylation
of Naphthalene. Erdoel Kohle 1, pp 308–318.
87
(3) Ho, S. C. and Wu, M. M. (1993), US 5,254,274: Alkylaromatic Lubricant Fluids. Dressler, H., Meilus, A. A. (1986), US 4,604,491: Synthetic Lubricants.
Yoshida, T., Watanabe, H. (1987), US 4,714,794: Synthetic Oils. Bridwell, B.
W., Johnson, C. E. (1976), US 3,959,399 Mono-Alkylation of Naphthalene.
(4) Ashjian, H., Le, Q. N., Marler, D. O., Shim, J. and Wong, S. S. (1991), US,
5,034,563: Naphthalene Alkylation Process. Angevine, P. J., Degnan, T. F.,
Marler, T. O. (1991), US 5,001,295: Process for Preparing Dialkylnaphthalene. Motoyuki, M., Yamamoto, K., McWilliams, J. P., Bundens, R. G.
(1998), US 5,844,064: Process for Preparing Dialkylnaphthalene. Ardito,
S.C., Ashjian, H., Degnan, T. F., Helton, T. E. (1995), US 5,457,254: Naphthalene Alkylation Process Using Mixed H/NH3 Form Catalyst. Solofo,
J., Moreau, P., Geneste, P., Finiels, A. (1993), US 5,210,350: Method for
Preparing an Alkylated Aromatic Product with an Alkylation Zeolite and
a Dealkylation Zeolite. Fraenkel, D., Levy, M., Cherniavsky, M. (1986),
US 4,593,137: Para-selective and Beta-Selective Crystallized Glass Zeolite
Alkylation Catalyst. Aufdembrink, B. A., Kresge, C. T., Le, Q. N., Shim,
J. Wong, S. S. (1990), US 4,912,277: Process for the Preparing Long Chain
Alkyl Aromatic Compounds.
(5) Le, Q. N. and Shim, J. (1997), US 5,602,08: Lubricant Composition of Polyalpha-Olefins and Alkylated Aromatic Fluids. Pelligrini, Jr.; J. P. (1980), US
4,238,343: High Fire Point Alkylated Aromatic Fluid. Nipe, R. N. (1999),
WO 00/08119: High Performance Lubricating Oils. Krinker, R. (1997), WO
98/02510: A Lubricant Comprising an Alkylated Naphthalene and an Ester. Tolfa, J. C., Lilje, K. C. (2000), US 6,127,324: Lubricating Composition
Containing a Blend of a Polyalkyllene Glycol and an Alkyl Aromatic and
Process of Lubrication.
(6) Olah, G. A. (1963), Friedel-Crafts and Related Reactions. vol 1-2. Interscience. Olah, G. A., Krishnamurti, R., Surya, G. K. (1991), Friedel-Crafts
Alkylations. In: Comprehensive Organic Synthesis. Vol 3.
(7) Hamrock, B. J. and Dowson, D. (1981), Ball Bearing Lubrication: Elastohydrodynamics of Elliptical Contacts, John Wiley & Sons, Inc.