SYNTHETIC LUBRICANT BASE STOCK
PROCESSES AND PRODUCTS
Margaret M. Wu(a) (b) and T. Rig Forbus(c)
(a) ExxonMobil Research & Engineering Co. Annandale, NJ 08801
(b) ExxonMobil Chemical Co. Synthetic Division, Edison , NJ 08818
(c) The Valvoline Co. of Ashland, Inc., Lexington, KY 40512
This chapter reviews the product and process for synthetic base stocks
produced from chemicals of well-defined chemical structures and in processes
tailored to optimize important properties and performance features. These
synthetic base stocks are critical components used in the formulation of many
synthetic lubricants. (In this chapter, we use “synthetic base stock“ to
represent the base fluid and “synthetic lubricant“ to represent formulated,
finished lubricant product.)
At the start of this chapter, we briefly discuss the background and the
driving force for using synthetic lubricants. The major part of the chapter
discusses the key synthetic base stocks - chemistry, synthesis processes,
properties, their applications in synthetic lubricant formulation and
advantages compared to petroleum-derived base stocks.
Many U.S. base oil manufacturers and formulators include some Group
includes varying degrees of chemical transformation. These base stocks are
usually produced by hydroprocessing or hydroisomerization, which is
typically part of a refining process1. Discussion of these hydroprocessed base
stocks can be found in the previous chapter. In this chapter, we limit
discussion to those synthetic base stocks produced from chemicals of well-
defined composition and structure.
, Suzzy C. Ho ,
II+ and Group III base stocks as synthetic, as their manufacturing process
106 Wu, Ho, and Forbus
1.1 Why Use Synthetic Lubricants?
Synthetic lubricants are used for two major reasons:
• When equipment demands specific performance features that can not be
met with conventional mineral oil-based lubricants. Examples are
extreme high or low operating temperature, stability under extreme
conditions and long service life.
• When synthetic lubricants can offer economic benefits for overall
operation, such as reduced energy consumption, reduced maintenance and
increased power output, etc.
Conventional lubricants are formulated based on mineral oils derived from
petroleum. Mineral oil contains many classes of chemical components,
including paraffins, naphthenes, aromatics, hetero-atom species, etc. Its
compositions are pre-determined by the crude source. Modern oil refining
processes remove and/or modify the molecular structures to improve the
lubricant properties, but are limited in their ability to substantially alter the
initial oil composition to fully optimize the hydrocarbon structures and
composition. Mineral oils of such complex compositions are good for
general-purpose lubrication, but are not optimized for any specific
performance feature. The major advantages for mineral oils are their low
cost, long history and user‘s familiarity. But this paradigm is now changing.
The trend with modern machines and equipment is to operate under
increasingly more severe conditions, to last longer, to require less
maintenance and to improve energy efficiency. In order to maximize machine
performance, there is a need for optimized and higher performance lubricants.
Synthetic lubricants are designed to maximize lubricant performance to match
the high demands of modern machines and equipment, and to offer tangible
performance and economic benefits.
1.2 What Is a Synthetic Base Stock?
Synthetic lubricants differ from conventional lubricants in the type of
components used in the formulation. The major component in a synthetic
lubricant is the synthetic base stock. Synthetic base stocks are produced from
carefully-chosen and well-defined chemical compounds and by specific
chemical reactions. The final base stocks are designed to have optimized
properties and significantly improved performance features meeting specific
equipment demands. The most commonly optimized properties are:
- Viscosity Index (VI). VI is a number used to gauge an oil‘s viscosity
change as a function of temperature. Higher VI indicates less viscosity
change as oil temperature changes - a more desirable property.
Conventional 5 cSt mineral oils generally have VIs in the range of 85 to
110. Most synthetic base stocks have VI greater than 120.
Synthetic Lubricant Base Stock Processes and Products 107
- Pour point and low temperature viscosities. Many synthetic base
stocks have low pour points, -30 to -70°C, and superior low-temperature
viscosities. Combination of low pour and superior low-temperature
viscosity ensures oil flow to critical engine parts during cold starting,
thus, offering better lubrication and protection. Conventional mineral oils
typically have pour points in the range of 0 to -20°C. Below these
temperatures, wax crystallization and oil gelation can occur, which
prevent the flow of lubricant to critical machine parts.
- Thermal/oxidative stability. When oil oxidation occurs during service,
oil viscosity and acid content increase dramatically, possibly corroding
metal parts, generating sludge and reducing efficiency. These changes can
also exacerbate wear by preventing adequate oil flow to critical parts.
Although oil oxidation can be controlled by adding antioxidants, in long
term service and after the depletion of antioxidant, the intrinsic oxidative
stability of a base stock is an important factor in preventing oil
degradation and ensuring proper lubrication. Many synthetic base stocks
are designed to have improved thermal oxidative stability, to respond well
to antioxidants and to resist aging processes better than mineral oil.
- Volatility. Synthetic base stocks can be made to minimize oil volatility.
For example, polyol esters have very low volatility because of their
narrow molecular weight distribution, high polarity and thermal stability.
Similarly, careful selection and processing of raw materials can influence
the finished properties of polyalphaolefins (PAO) base stocks.
- Other properties, including friction coefficient, traction coefficient,
biodegradability, resistance to radiation, etc. can be optimized for
synthetic base stocks as required for their intended applications.
1.3 A Brief Overview of Synthetic Lubricant History
Significant commercial development of synthetic lubricants started in the
early 1950‘s with the increased use of jet engine technology2. Jet engines
must be lubricated properly in extremely high and low temperature regimes
where mineral lubricants could not adequately function. Esters of various
chemical structures were synthesized and evaluated. Initially, dibasic esters
were used as base stock. Later, polyol esters with superior thermal/oxidative
stability, lubricity and volatility were developed to meet even more stringent
demands. These polyol esters are still in use today.
Another early application that demanded the use of synthetic lubricants
came in the mid-1960s during oil drilling in Alaska where conventional
mineral oil lubricants solidified and could not function in the severe Alaskan
cold weather3. Initially, a synthetic lubricant based on an alkylbenzene base
stock of excellent low temperature flow properties was used in the field. This
base stock was soon replaced by another base stock with better overall
properties, namely polyalphaolefins (PAO).
108 Wu, Ho, and Forbus
Research on PAO began at Socony-Mobil in early 1950s4. The early
researchers recognized the unique viscometric properties that could be
attained by the proper selection of starting olefins and reaction conditions in
the PAO synthesis. After many years of continuous improvements in
optimizing the compositions, processes and formulations, Mobil Corporation
introduced a synthetic automotive engine oil, Mobil SHC™ in Europe in
1973, followed by a fuel-saving SAE 5W-20 Mobil 1™ in the US. The
product was a commercial success and successive generations of Mobil 1™
continue to be the leading synthetic automotive crankcase lubricant today5.
Since the early introduction of synthetic lubricants in automotive and
industrial applications, many products from numerous companies have
followed. The total synthetic lubricant market in 1998 amounted to about 200
million gallons/yr, approximately 2% of the total lubricant volume5.
However, it is estimated to grow at 5-10% per year, much higher than
conventional lubricant (less than 2% per year). Although the volume of
synthetic lubricants is relatively small compared to conventional lubricants,
the overall economic impact from synthetic lubricants is much larger than just
the volume number alone, since synthetic lubricants improve energy
efficiency, productivity, reliability and reduce waste, etc.
2. OVERVIEW OF SYNTHETIC BASE STOCKS
Of the total world wide synthetic base stock volume, over 80% are
represented by three classes of materials6
- PAO (45%)
- Esters, including dibasic ester and polyol esters (25%)
- Polyalkyleneglycol (PAG) (10%)
Other smaller volume synthetic base stocks include alkylaromatics, such as
alkylbenzenes and alkylnaphthalenes, polyisobutylenes, phosphate esters and
silicone fluids. Among these synthetic base stocks, with the exception of
phosphate esters and silicones, the starting materials are all derived from basic
petrochemicals - ethylene, propylene, butenes, higher olefins, benzene,
toluene, xylenes, and naphthalenes, as illustrated in Figure 1.
As expected, the major producers of PAO, esters, PIB and alkylaromatics
are integrated petroleum companies that supply conventional mineral oil base
stocks and petrochemicals as well as various synthetic base stocks. PAG,
phosphate esters and silicone fluids are manufactured by chemical companies
that produce these fluids on a much larger scale mainly for other applications.
Their use as lubricant base stocks is only a fraction of the total market. Table
1 summarizes the major synthetic base stock producers.
Synthetic Lubricant Base Stock Processes and Products 109
Figure 1. Most synthetic base stocks are derived from petrochemicals
Table 1. Summary of major synthetic base stocks and producers
Synthetic Base Stock Major Manufacturer Relative price*
PAO ExxonMobil Chemical Co.,
BP, Chevron Phillips Chemical Co., Fortum
Dibasic ester ExxonMobil Chemical Co., Henkel Corp., Hatco
Corp., Inolex Chemical Co.
Polyol ester ExxonMobil Chemical Co., Henkel Corp., Hatco
Corp., Inolex Chemical Co., Kao Corp.,
PAG Dow Chemical Co., BASF 4-10
Alkylaromatic ExxonMobil Chemical Co., Pilot Chemical Co.,
Inolex Chem. Co.
Mineral oil ExxonMobil, Motiva Enterprise, ChevronTexaco,
Valero, BP, Shell, etc.
* Estimated relative price vs. Group I mineral oil
3. SYNTHETIC BASE STOCK - CHEMISTRY,
PRODUCTION PROCESS, PROPERTIES AND USE
PAO with viscosities of 2 to 100 cSt at 100°C are currently produced and
marketed commercially7. The low viscosity PAO of 4 to 6 cSt account for
more than 80% of the total volume. The remaining are mainly medium to
high viscosity products of 10 to 100 cSt.
110 Wu, Ho, and Forbus
3.1.1 Chemistry for PAO Synthesis
1-Decene is the most commonly used starting olefin for PAO (Figure 2).
It is produced as one member of the many linear alpha-olefins (LAO) in an
ethylene growth process, which yields C4 to C20 and higher LAO according to
the Schulz-Flory distribution8. Typically, 1-decene constitutes about 10-25%
of the total LAO fraction, depending on the process technology.
To make PAO, the linear 1-decene is further polymerized using Friedel-
Crafts catalysts to give C20, C30, C40, C50, and higher olefin oligomers.
C6, C8, C10, C12, C14, C16, C18, C20, etc.
The degree of polymerization depends on the type of catalyst used and
. Generally, BF
type catalysts give a lower degree of
polymerization. By careful choice of co-catalyst types and reaction
conditions, the BF
process produces mostly C
oligomers that yield
low viscosity base stocks of 4-8 cSt. AlCl
-based catalysts are more suitable
for higher viscosity PAO synthesis because they produce oligomers with C
and higher olefin enchainment species. If a C
fraction is produced, it is
usually separated and recycled. Fractions containing C
and higher olefin
oligomers are then hydrogenated to yield fully saturated paraffinic PAO.
PAO is a class of molecularly engineered base stock with optimized
viscosity index, pour point, volatility, oxidative stability and other important
synthesized polyalphaolefin oligomers of C
compared their lubricant properties, as summarized in Table 2.
Figure 2. Reaction scheme for converting ethylene into PAO
lubricant base oil properties. Researchers at ExxonMobil have systematically
Synthetic Lubricant Base Stock Processes and Products 111
Table 2. Lubricant base stock property comparison: C30-C42 hydrocarbons made from different
Kinematic Viscosity, cSt, at
Number 100°C 40°C -40°C Viscosity
decamers C30 7.3 62.3 >99,000 70 --
pentamers C30 3.8 18.1 7,850 96 --
tetramers C32 4.1 20.0 4,750 106 --
trimers C30 3.7 15.6 2,070 122 <-55
trimers C33 4.4 20.2 3,350 131 <-55
trimers C36 5.1 24.3 13,300 144 -45
tetramers C40 5.7 29.0 7,475 141 <-55
pentamers C40 5.6 30.9 10,225 124 --
trimers C42 6.7 33.8 Solid 157 -20
These data show that the oligomers made from propylene, 1-hexene and 1-
octene have relatively low VI and very high viscosity at -40°C. Oligomers
from 1-tetradecene have high VI but also have undesirable high pour point
and are solid at -40°C. Oligomers from 1-decene have the best combination
of high VI, low pour point and -40°C viscosity.
Historically, the market dynamics of LAO supply and demand further
drove the trend toward the use of 1-decene as a raw material. Among all the
major LAO from the ethylene growth process (Figure 2), C6 and C8 LAO are
used as co-monomer in the linear low-density polyethylene production; C12-16
LAO are used in the manufacture of linear alkylbenzene detergent; C18 and
C20 LAO are used in additives. 1-Decene is not in high demand for other
chemical manufacturing and its use as raw material for synthetic base stocks
makes a perfect match. When 1-decene supply became tight, other LAO,
such as C8 and C12
starting olefins for PAO production. Since 2001, 1-decene supply has
increased significantly due to several LAO expansion projects and new
production coming on-line around the world11.
The chemical composition of PAO is very simple. Using 4 cSt PAO as an
example, it is made of ~ 85% C30 and ~15% C40 hydrocarbons. It has a
narrow molecular weight distribution compared to typical 4 cSt mineral oils.
The gas chromatograms in Figure 3 show that 4 cSt PAO has few low
, have been successfully incorporated with 1-decene as the
112 Wu, Ho, and Forbus
molecular weight components of less than C30 that can degrade oil volatility,
flash and fire point. Figure 3 also shows that the C30 fraction of PAO is not a
single compound but a mixture of many isomers. This is because the PAO
from BF3 process contains many isomers, each with different types of
branching12. This irregular branching may be beneficial to some of PAO‘s low
temperature properties, e.g. pour point.
Figure 3. Gas chromatograph comparison of a 4 cSt PAO with a 4 cSt Group III base stock
3.1.2 Manufacturing Process for PAO
Commercial production of PAO using a BF3 catalyst generally involves a
multi-stage, continuous stirred tank reactor (CSTR) process9. In early
production technology, the catalyst was destroyed with diluted aqueous alkali
after polymerization. More recent patents disclosed improved processes using
BF3 catalyst recycle to reduce catalyst usage, minimize process waste and
improve process economics13.
3.1.3 Product Properties
The physical properties of some commercial PAO are summarized in
Synthetic Lubricant Base Stock Processes and Products 113
Table 3. General product properties of commercial PAO from ExxonMobil Chemical Company
Fluid type SHF-
1.7 4.1 5.8 8.0 10.0 39 100
5 19 31 48 66 396 1,240
262 2,900 7,800 19,000 39,000 -- --
Viscosity Index -- 126 138 139 137 147 170
Pour Point,°C -66 -66 -57 -48 -48 -36 -30
Flash Point., °C 157 220 246 260 266 281 283
0.798 0.820 0.827 0.833 0.835 0.850 0.853
3.1.4 Comparison of PAO with Petroleum-based Mineral Base Stocks
PAO have different chemical compositions compared to mineral oil base
stocks. The American Petroleum Institute (API) categorizes lubricant base
stocks into five categories, designated Group I to V. The definition of each
base stock group is summarized in Table 4.
Table 4. Definition of API category I to V lubricant base stock
Group I (Conventional, solvent refined)* <90 >0.03 80-120
Group II (Hydroprocessed)* >/= 90 </=
Group III (Severely hydroprocessed or isomerized
>/= 90 </=
Group IV Polyalphaolefins
Group V All other base stocks not included in
Group I, II, III or IV (e.g. esters, PAG,
-- -- --
* - comments in parentheses are not included in the original API definition
PAO is classified by itself as a Group IV base stock. In addition to the
differences listed in Table 3, PAO also contains no cyclic paraffins,
naphthenes or aromatics, whereas Group I, II and III base stocks contain
different amounts of aromatics ranging from <1% to >40%14. With the
increasing presence of aromatics and/or naphthenes, oxidative stability and
low temperature properties of these fluids are typically degraded. Also, as
shown earlier in Figure 3, PAO have discrete carbon numbers with relatively
long linear hydrocarbon branches, whereas mineral base stocks contain a
continuum of carbon number. As a result, PAO usually have lower volatility.
Table 5 compares the basic properties of low and high viscosity PAO
versus Group I to Group III mineral oil base stocks.
114 Wu, Ho, and Forbus
Table 5. Typical property comparison of PAO with Group I to III mineral oil
Low Viscosity High Viscosity
Grp I Grp II Grp III PAO Bright
Kinematic Viscosity @100°C, cSt 3.8 5.4 4.1 4.1 30.5 100
Kinematic Viscosity @40°C, cSt 18 30 19 19 470 1,240
Viscosity Index 92 115 127 126 94 170
Pour Point, °C -18 -18 -15 -66 -18 -30
Cold Crack Simulator @ -20°C, cP -- -- 750 620 -- --
Noack Volatility, wt% 32 15 14 12 -- --
Aniline point, °C 100 110 118 119 97 >170
• PAO have superior viscometrics properties compared to mineral oil base
Data in Table 5 show that PAO has higher VI and lower pour point than
Group I and II base stocks. Compared to Group III base stocks, PAO has
comparable VI, but much lower pour point and improved low-temperature
viscosity as measured by Cold Cranking Simulator (CCS) viscosity at -20°C.
In an actual engine oil formulation, this lower CCS viscosity observed with
PAO results in a wider SAE cross-grade (5W-40) than with Group III base
stock (10W-40)15. The lower low-temperature viscosity translates into better
fuel economy during the engine warm up period.
Data in Table 5 show that PAO has lower volatility than Group I to III
base stocks. This lower volatility is the result of the unique chemical
compositions of PAO - 100% relatively linear paraffin, little low molecular
weight hydrocarbons of less than C30 (Figure 3). Low volatility is
advantageous for decreased oil consumption and reduced emissions.
• PAO show intrinsic oxidative stability and excellent response to
antioxidant additive treatment.
It has been demonstrated that the un-formulated PAO base stock treated
with 0.5 wt% antioxidant resists oxidation for more than 2500 minutes in a
standard rotary bomb oxidation test (RBOT, D2272 method). In comparison,
similarly treated Group II and III base stock started to oxidize much earlier, at
less than 800 or 1700 minutes, respectively16.
This oxidative stability translates into performance advantages in actual
engine oil tests (Figure 4).15
Figure 4 shows that a fully formulated engine oil with PAO has much
lower viscosity increase than with Group III or with Group I/II base stocks in
standard length, 64-hour ASTM Sequence IIIE engine test. In an extended-
length, 256-hour test, the viscosity increase for PAO-based lubricant is still
much less than the maximum increase allowable for this test. In contrast,
Group III or Group I/II based engine lubricants become too viscous to
measure. Performance advantages in fuel efficiency and oil consumption are
PAO has lower volatility.
Synthetic Lubricant Base Stock Processes and Products 115
Figure 4. Comparison of viscosity increase in ASTM Sequence IIIE engine test for fully
formulated lubricants based on PAO vs. Group III or I/II base stocks17
PAO are available from 2 to 100 cSt at 100°C. The high viscosity PAO
maintain excellent VI and low pour point (Table 3 and 5), in a manner that is
superior to the highest viscosity mineral oil base stock - bright stock. High
viscosity PAO are important when blending with low viscosity fluid to
formulate high viscosity grade industrial oils. When used to blend with low
viscosity mineral oil, the high viscosity PAO also significantly improves the
oxidative stability of the blended base stocks compared to using mineral
• PAOs have high aniline point, indicating low polarity.
Table 5 shows that low viscosity PAO has a higher aniline point than
Group I mineral oils, 119°C vs. 100°C (Table 5). A more pronounced
difference is observed for high viscosity fluids (>170°C vs. 97°C). The
higher aniline points of PAO mean that they are much less polar than Group I
oils. Generally, lubricant additives and oil oxidation by-products are highly
polar chemical species. As aniline point has relevance to solvency, additives
and oil oxidation by-products are not very soluble in PAO alone. As a result,
a polar co-base stock, such as ester or alkylaromatic, is usually added to the
formulation to improve the solvency of PAO in a finished lubricant. These
co-base stocks can also assist other performance features, such as seal
compatibility and improved lubricity.
• PAO possess other important properties, depending on application:
- Compatibility or miscibility with mineral oil at all concentration levels
without phase separation or detrimental effects when cross-
- Hydrolytic stability
PAO are available in wide viscosity range.
116 Wu, Ho, and Forbus
- 10% higher thermal conductivity and heat capacity than comparable
mineral oil, allowing equipment to run at lower temperature and
improve wear performance18
- Lower traction coefficients than conventional fluids, resulting in better
energy efficiency for many industrial oil applications6
- PAO are non-greasy and non-comedogenic
In summary, PAO have superior VI, pour point, low-temperature viscosity,
volatility, and oxidative stability and are available in a wide viscosity range
compared to conventional Group I, II or III mineral oils.
3.1.5 Recent Developments – SpectraSyn Ultra as Next Generation
Following the success with PAO, ExxonMobil Chemical Co. recently
introduced a new generation of PAO, trade-named SpectraSyn UltraTM.
SpectraSyn UltraTM is produced from the same raw material as PAO, 1-
decene, using proprietary catalyst technology19, 20. Table 6 summarizes the
properties of commercial SpectraSyn UltraTM products.
Compared to traditional PAOs, SpectraSyn UltraTM PAO have even
higher VI, lower pour point and are available in higher viscosity ranges. This
unique class of fluid can be used in automotive engine oil and industrial oil
formulations to provide advantages in terms of shear stability, viscometrics
properties, thickening power and increased lubricant film thickness.
Table 6. Product properties of next generation PAO - SpectraSyn UltraTM
Kinematic Viscosity @100°C, cSt 150 300 1,000
Kinematic Viscosity @40°C, cSt 1,500 3,100 10,000
Viscosity Index 218 241 307
Pour Point,°C -33 -27 -18
Flash Point., °C >265 >265 >265
Specific Gravity @15.6°C/15.6°C 0.850 0.852 0.855
PAO is the workhorse base stock for most synthetic lubricants. Low
viscosity PAO are used in synthetic automotive crankcase and gear lubricants,
industrial oils and greases. High viscosity PAO have found great utility in
industrial oils and greases.
Synthetic automotive engine oils command the largest volume among
synthetic lubricant products. Taking advantage of the many superior
properties of PAO base stocks, performance advantages of synthetic engine
oils based on PAO over mineral oil-based engine oils are well-documented in
scientific and trade literature21. They include:
Synthetic Lubricant Base Stock Processes and Products 117
- Improved engine wear protection
- Extended oil drain interval
- Excellent cold starting performance
- Improved fuel economy
- Reduced oil consumption
- Excellent low-temperature fluidity and pumpability
- High temperature oxidation resistance
Many of these performance advantages are directly attributable to the
intrinsically superior properties of PAO, such as high VI, low pour point, low
low-temperature viscosity, high oxidative stability, low volatility, etc.
The advantage of using synthetic engine oil is further supported by the fact
that many automakers use synthetic lubricant as the “factory fill“ lubricant for
their high performance cars. For example, in 2003, Mobil 1™ is used as
factory-fill lubricant for the Corvette, all Porsches, Mercedes-Benz AMG
models, Dodge Viper, Ford Mustang Cobra R and Cadillac XLR22.
PAO blended with mineral oil are also used in many partial synthetic
lubricant formulations. In this case, PAO is used as a blending stock to
improve the volatility, high or low-temperature viscosity, oxidative stability,
etc. of the mineral oil blend.
Synthetic industrial oils and greases, formulated with PAO, have many
specific performance and economic advantages over conventional
lubricants6,21a. For example, in industrial gear/circulation oils, PAO-based
lubricants offer the following documented advantages:
− Energy savings, longer fatigue life and lowered temperatures of
operation due to lower traction coefficients
− Wider operating temperature range due to higher VI and better
− Reduced equipment down-time, reduced maintenance requirements
and longer oil life due to the excellent stability of PAO base stock
Because PAO is available in high viscosity grades (up to 100 cSt at
100°C), high ISO grade synthetic industrial oils with improved performance
features are more easily formulated. This option is not available for mineral
In compressor oil applications, PAO-based lubricants have advantages due
to their better chemical inertness and resistance to chemical attack. Synthetic
compressor oils are used in corrosive chemical environments, for example, in
sulfuric acid or nitric acid plants. PAO-based lubricants are also used in
refrigeration compressor applications due to their excellent low temperature
fluidity, lubricity and generally wider operating temperature range.
Other synthetic industrial oil applications with PAO-based lubricants,
greases based upon PAO are used in industrial equipment, aviation and
include gas turbine, wind turbine and food-grade gear lubricants. Synthetic
automotive applications that take advantage of the wide operating
118 Wu, Ho, and Forbus
temperature range, high degree of stability and other desirable properties and
features offered by PAO base stocks.
Recently, PAO is finding its way into personal care products such as
shampoos, conditioners and skin lotions because it provides emolliency in
addition to good skin feel and is non-greasy and non-comedogenic. It is also
used in off-shore drilling fluids because of its good lubricity. New
applications for PAO are continuously emerging.
3.2 Dibasic, Phthalate and Polyol Esters - Preparation,
Properties and Applications
Lard and vegetable oil, both ester-type compounds derived from natural
sources, have been used as lubricants throughout human history. After World
War II, thousands of synthetic esters were prepared and evaluated as lubricant
base stocks for jet engine lubricants.2
3.2.1 General Chemistry and Process
Esters are made by reacting carboxylic acids with alcohols. The
elimination of water is shown by the following equation:
The reaction proceeds by heating the mixture to 150°C or higher with or
without a catalyst9. Catalysts such as p-toluenesulfonic acid or titanium(IV)
isopropoxide, are typically used to facilitate reaction rates. The reaction is
driven to completion by continuous removal of water from the reaction
medium. Sometimes, one component is used in a slight excess to ensure
complete conversion. The final product is purified over an adsorbent to
remove trace water and acids, both of which are detrimental to base stock
quality. Commercially, esters are generally produced by batch processes.
The choice of acid and alcohol determines the ester molecular weights,
viscometrics and low temperature properties, volatility, lubricity, as well as
the thermal, oxidative and hydrolytic stabilities23. The structure-property
relationships of ester base stocks are well documented in the literature.
Compared to PAO and mineral oil, ester fluids have a higher degree of
polarity, contributing to the following unique properties:
− Superior additive solvency and sludge dispersancy
− Excellent lubricity
− Excellent biodegradability
− Good thermal stability
Acid Alcohol Este
Synthetic Lubricant Base Stock Processes and Products 119
Three classes of esters are most often used as synthetic base stocks -
dibasic ester, polyol ester and aromatic ester. Some basic properties of these
esters are summarized in the Table 7.
Table 7. Basic properties of ester base stocks
Viscosity, cSt Wt% Wt%
100°C 40°C VI Pour
Adipate Iso-C13H27 5.4 27 139 -51 4.8 92
Sebacate Iso-C13H27 6.7 36.7 141 -52 3.7 80
n-C8/C10 PE(c) 5.9 30 145 -4 0.9 100
n-C5/C7/iso-C9 PE 5.9 33.7 110 -46 2.2 69
n-C8/C10 TMP(c) 4.5 20.4 137 -43 2.9 96
Iso-C9 TMP 7.2 51.7 98 -32 6.7 7
n-C9 NPG(c) 2.6 8.6 145 -55 31.2 97
Di- and mono-acids NPG 7.7 40.9 160 -42 -- 98
Phthalate Iso-C13H27 8.2 80.5 56 -43 2.6 46
Phthalate Iso-C9 5.3 38.5 50 -44 11.7 53
Trimellitate Iso-C13H27 20.4 305 76 -9 1.6 9
Trimellitate C7/C9 7.3 48.8 108 -45 0.9 69
(a) Noack Volatility : 250°C, 20 mm-H2O, and one hour with air purge
(b) by CEC-L-33-A-96 test, % degradable in 21 days
(c) PE: pentaerythritol, TMP: trimethylolpropane, NPG: neopentylglycol
3.2.2 Dibasic Esters
Dibasic esters are made from carboxylic diacids and alcohols. Adipic acid
(hexanedioic acid) is the most commonly used diacid (Figure 5). Because it is
linear, adipic acid is usually combined with branched alcohols, such as 2-
ethylhexanol or isotridecanols (C13H27OH) to give esters with balanced VI
and low temperature properties (Figure 5). Dibasic ester is most often used as
a co-base stock with PAO to improve solvency and seal swell properties of
the final lubricants.
- 2 H2O
Figure 5. Synthesis of adipate ester
120 Wu, Ho, and Forbus
3.2.3 Polyol Esters
The most common polyols used to produce synthetic polyol ester base
stocks are pentaerythritol (PE), trimethylolpropane (TMP) and
neopentylglycol (NPG), (Figure 6). By carefully choosing the degree of
branching and size of the acid functions, polyol esters with excellent
viscometric properties - high VI and very low pour points – can be produced
Figure 6. Synthesis of polyol esters
In addition to excellent viscometric properties, polyol esters have the best
thermal resistance to cracking. This is because polyols lack β-hydrogen(s)
adjacent to the carbonyl oxygen and thus can not undergo the same facile β-H
transfer reaction as the dibasic esters (Figure 7). This cracking by β-H
transfer leads to two neutral molecules and is a relatively low energy process.
Polyol esters can only be cracked by C-O or C-C bond cleavage, leaving two
free radicals - a very high-energy process requiring extremely high
temperature. Therefore, polyol esters are thermally stable up to 250°.
Figure 7. Cracking reaction mechanism for esters - β−Η effect
+3 RCOOH + 2 RCOOH
PE ester TMP este
+ 4 RCOOH
Synthetic Lubricant Base Stock Processes and Products 121
Among the three polyol ester types, the thermal stability ranking is:
PE esters > TMP esters > NPG esters.
3.2.4 Aromatic Esters
Phthalic anhydride or trimellitic anhydride are converted into esters by
reactions with alcohols as shown in Figure 8. Phthalic anhydride is produced
cheaply and in large volume from oxidation of ortho-xylene. The largest use
of phthalate esters is in the plasticizer market. Only a small fraction of its
production is consumed by the synthetic lubricants market. Phthalate esters
generally have superior hydrolytic stability than adipic esters because the
ortho di-ester groups are electronically less available and sterically more
hindered24. However, they have lower VIs, 50-70, because of their high
polarity and the presence of branched alcohol chains. They are used in
special industrial oil applications where VI is not a critical parameter.
Trimellitate esters are specialty products and relatively expensive. They are
of high viscosity and usually are more resistant to oxidation than adipic esters.
Figure 8. Synthesis of phthalate and trimellitate esters
3.2.5 General Properties and Applications of Ester Fluids
Solvency and dispersancy - Ester fluids are quite polar due to their high
oxygen contents. They have high solubility for many commonly used
additives. They also have high solubility for the polar acids and sludges
generated by oxidation processes during service. This property makes ester
based lubricant “clean“ compared to hydrocarbon-based lubricants.
Typically, low viscosity ester fluids are soluble with non-polar PAO base
stocks. These properties make them excellent for use as co-base stocks with
PAO in many synthetic automotive and industrial lubricants. Generally, 5 to
25% esters are used with PAO in finished lubricant formulations.
- 3 H2O
- 2 H2O
122 Wu, Ho, and Forbus
Hydrolytic stability24 - Hydrolysis of esters to give acids and alcohols is a
facile reaction and can proceed at elevated temperatures in the presence of
water. Hydrolysis of ester generates acid that can be very corrosive to metal
components and can catalyze the base stock decomposition process.
Therefore, hydrolytic stability of esters is an important issue. Much work has
been carried out to improve the hydrolytic stability by varying the
composition of acids and alcohols. Generally, esters made from aromatic
acids or from more sterically hindered acids, such as 2-alkyl substituted acids
or neo-acids, have improved hydrolytic stabilities. Proper branching of the
acids protect the carbonyl ester function from the detrimental attack of water.
The presence of impurity, such as trace acid or metal, can catalyze the
decomposition and hydrolysis of ester. Compared to PAO or alkylaromatic
base stocks, ester hydrolysis is always an issue of concern in many lubrication
Volatility - Ester fluids generally have lower volatility compared to PAO
and mineral oil of comparable viscosities. A General volatility ranking for
base stocks are as follows:
PE ester > TMP ester > dibasic ester > PAO >> Group I or II mineral oil.
Lubricity - Polar ester fluids show mild boundary film protection at lower
temperature. At lower temperature, esters interact with the metal surface via
polar interaction, forming a chemisorbed surface film, which can provide
better lubrication than the less polar mineral oil or non-polar PAO. When
esters decompose, they produce acids and alcohols. Higher molecular weight
degree of wear protection and friction reduction. However, none of these
interactions are strong enough to persist when surface or oil temperature rises
much above 100°C. At higher temperature, significant wear protection can
only be achieved by the use of anti-wear or extreme-pressure (EP) additives.
A drawback for the ester high polarity is that esters can compete with metal
surface for polar additives, resulting in less efficient usage of anti-wear and
EP additives. Therefore, in formulations using esters, it is important to
choose the proper additives and concentration levels to obtain the full benefit
of the lubricity from both the additives and esters.
Biodegradability - By carefully choosing the molecular compositions,
esters of excellent biodegradability can be produced. Generally, esters from
more linear acids and alcohols have better biodegradability.
Applications25 - Esters, both dibasic and polyol esters, are used as co-base
stocks with PAO or other hydrocarbon base stocks in synthetic automotive
engine lubricants and industrial lubricants. Polyol esters are used in aircraft
turbine oils due to their excellent thermal and oxidative stabilities, good
lubricity, high VI and excellent low temperature properties (<-40°C)21a.
Esters are also used in synthetic compressor oils for ozone-friendly
refrigeration units. Because of their high biodegradability and low toxicity,
esters are often the base oils of choice for many environmentally-aware
acids can bind with the metal surfaces to form a film that can offer some
Synthetic Lubricant Base Stock Processes and Products 123
lubricants or single-pass lubrication applications where ecological impact is
Although ester chemistry has been studied extensively, new esters with
unique performance improvements have continuously been reported in the
literature26. For example, esters with high stability were made from highly
branched acids and polyols. Polyol esters formulated with ashless additives
can be used as high performance biodegradable hydraulic fluids.
3.3 Polyalkylene Glycols (PAG)
PAG is an important class of industrial chemicals. Its major use is in
polyurethane applications. Outside of polyurethane applications, only 20%
of the PAG is used in lubricant applications. Compared to PAO or esters,
PAG have very high oxygen content and hydroxyl end group(s). These
unique chemical features give them high water solubility and excellent
lubricity. PAG was first developed as water-based, fire-resistant hydraulic
oils during World War II for military use. Other applications have been
developed subsequently to take advantage of their unique properties.
3.3.1 Chemistry and Process
PAG are synthesized by oligomerization of alkylene oxides over a base
catalyst with an initiator R‘OH (Figure 9)27. When the initiator is water
(R‘=H), the final PAG has two hydroxyl end groups. When the initiator is an
alcohol (R=alkyl group), one of the end groups is an alkoxy group (RO-). The
most commonly used alcohol is n-butanol, although large alcohols have also
been used for special applications. Phenol, thiols or thiophenol are also used
Figure 9. Reaction scheme for PAG synthesis
Ethylene oxide (EO), propylene oxide (PO), butylene oxides (BO) or
combinations of these epoxides are used as starting materials for PAG
syntheses. Longer chain alkylene oxides are sometimes added to improve
their compatibility with hydrocarbons. PAG with a wide range of viscosities,
124 Wu, Ho, and Forbus
VIs, pour points, water solubilities and oil-compatibilities are produced by
choosing the proper initiators, monomers, reaction conditions and post
treatments. The reaction is highly exothermic (22.6 kcal/mole) and heat
removal is important to avoid side-reactions or broadening of the product
molecular weight distribution.
3.3.2 Product Properties
Table 8 summarizes the typical lubricant properties of selected PAG
produced from EO, PO and BO with several different initiators.28
Table 8. Lube properties of PAG fluids from EO, PO and BO with different initiator
E300 EO OH/OH 300 5.9 36 118 -10 1.125 i s
E600 EO OH/OH 600 11.0 72 154 22 1.126 I s
P425 PO OH/OH 425 4.6 33 26 -45 1.007 -- --
P1200 PO OH/OH 1200 13.5 91 161 -40 1.007 -- i
PB200 PO Bu/OH 910 8.3 44 180 -48 0.9831 -- i
EP530 EO/PO OH/OH 2000 25 168 192 -32 1.017 -- --
EPB100 EO/PO Bu/OH -- 4.8 101 174 -57 1.0127 -- s
EPB260 EO/PO Bu/OH -- 11.0 56.1 210 -37 1.0359 -- s
B100-500 BO OH/OH 500 5.1 44.3 3 -30 0.975 s s
B100-2000 BO OH/OH 2000 24.7 234.7 142 -26 0.970 s i
BO Bu/OH 1500 15.8 117.1 153 -30 0.961 s i
EO-based fluids are typically waxy and have poor low temperature
properties. They have high water miscibility and are typically used to
formulate water-based lubricants, especially fire-resistant hydraulic oil. PO-
based fluids are excellent lubricant base stocks with high VI and low pour
point. They have lower solubility in water than EO-based fluids but are not
EO/PO-based fluids have a better combination of VI and low pour points
than PO-based products. They are used as base stocks in industrial
BO-based PAG have improved oil solubility and are not water-soluble.
PAG generally have excellent lubricity and low friction coefficients
compared to mineral oil as shown in Table 9. These properties result from the
facile surface chemisorption of the oxygenate functions or through hydrogen
bonding of the terminal OH groups with the metal surface.
Other unique properties for PAG include:
− superior solvency - they dissolve additives, decomposition products
− non-varnishing and low ash - they leave little or no residue or carbon
black upon decomposition
Synthetic Lubricant Base Stock Processes and Products 125
Table 9. Lubricating properties of selected PAG fluids28
EO/PO 500 4.6 19 161 -46 0.53 120-140 0.15 water
EO/PO 1300 15 76 218 -42 0.44 180-200 0.11 water
PO 700 6 27 179 -44 0.53 160-180 0.19 oil (d)
PO 1300 14 73 193 -35 0.57 120-140 0.12 none
(a) by DIN 51350 method
(b) determined by oscillation of a steel ball on a steel disc at 30°C under a load of 200 N
(c) determined by mixing equal proportions of water and PAG or oil and PAG.
(d) partially soluble in oi
The major use of PAG is in the industrial oil area29:
− Fire resistant hydraulic fluids. Water-soluble PAG are fire resistant, low
toxicity and have excellent lubricity and anti-wear properties.
− Textile oils. PAG are non-varnishing, non-staining and can be washed
away with water.
− Compressor and refrigeration oils. Low solubility of many industrial
gases, such as natural gas and ethylene, makes PAG suitable for gas
compressor applications. PAG are compatible with new refrigerants
− Metal working fluids. PAG are non-varnishing, have excellent lubricity
and anti-wear properties.
− Circulation/bearing/gear oil. Low friction coefficients and traction
properties of PAG lead to lower operating temperature and energy
consumption. They have good anti-wear properties and are non-
3.4 Other Synthetic Base Stocks
Polyisobutylene (PIB) fluids are produced by the oligomerization of
isobutylene in a mixed C4 stream over a BF3 or AlCl3 catalyst. PIB are
additives to increase lubricant viscosity. Table 10 summarizes the typical
properties of selected PIB fluids30. The VI and pour points of PIB are
comparable to those of conventional mineral oil. PIB usually have a lower
flash point and decompose easily into monomer at 200°C and higher. The
advantages of PIB are their high compatibility with most synthetic or mineral
base stocks and their relatively low cost compared to other synthetic base
(HFC-143a) and have excellent anti-wear properties.
seldom used by themselves. They are typically used as blend stocks or as
126 Wu, Ho, and Forbus
Table 10. Typical physical properties of PIB available from BP Chemical Co.
H-25 H-50 H-100 H-300 H-1500
Kinematic Viscosity @100°C, cSt 50 100 200 605 3000
Viscosity Index 87 98 121 173 250
Pour Point, °C -23 -13 -7 3 18
Bromine Number (?) 27 20 16.5 12 8
Flash Point, °C (a) 171 193 232 274 307
Molecular Weight (b) 635 800 910 1300 2200
(a) by Cleveland open cup ASTM D92 method.
(b) by gel permeation chromatography.
Alkylbenzenes and alkylnaphthalenes are produced by the alkylation of
benzene or naphthalene with olefins using Friedel-Crafts alkylation
catalysts31. Their typical properties are summarized in Table 11. One unique
feature of these alkylaromatic fluids is their very low pour points.
Alkylbenzenes are often mentioned in the patent literature as components for
CFC or HCFC refrigeration compressor oil. Alkylnaphthalenes are used in
synthetic automotive engine oil, rotary compressor oils, and other industrial
Table 11. Properties of alkylbenzene and alkylnaphthalenes base stocks
Fluid type Di-alkylbenzenes Di-alkylbenzenes Alkylnaphthalenes
Commercial source V-9050 from Vista
Zero 150 from
Synesstic™ 5 from
Kinematic Viscosity @100°C, cSt 4.3 4.4 4.7
Kinematic Viscosity @40°C, cSt 22.0 33.5 28.6
VI 100 25 74
Pour Point, °C -60 -40 -39
Flash Point, °C 215 170 222
Aniline Point, °C 78 -- 33
Phosphate esters are produced from phosphorus oxychloride with various
alcohols or phenols, or combinations of these hydroxyl compounds32. These
fluids generally have good thermal and oxidative stabilities and fire-
resistancy. However, because of their high polarity, poor VI-pour point
balance, facile hydrolysis33 and inferior elastomer and paint compatibility,
their use in general lubrication is limited. The major use for phosphate esters
is in fire-resistant hydraulic oils.
Synthetic lubricants have significantly raised the performance level of
automotive and industrial lubricants with the help of high-quality PAO base
stocks and tailored high-performance additive technologies. Equipment
builders, industrial users and general consumers have taken advantages of the
enhanced performance benefits afforded by synthetic lubricants - reduced
Synthetic Lubricant Base Stock Processes and Products 127
maintenance and waste, lower emissions and pollution, higher reliability and
efficiency, etc. As a result, in the last ten years, synthetic lubricants have
enjoyed yearly growth rates of 5-10%, a range considerably higher than for
conventional lubricants34. This growth rate has occurred despite the higher
initial costs of synthetic products. The higher initial costs have been
economically offset by the extended life and performance benefits afforded by
This trend is expected to continue in the finished lubricants market. In the
short-term, the growth for some PAO-based synthetic lubricants may slow
temporarily due to new competition from hydroprocessed base stocks 35.
However, high-performance synthetic base stocks and finished lubricants
should continue to prove their enhanced and well-documented values as
further demands on lubricant performance grow. The knowledgeable user,
who treats the lubricant as an active machine component and understands the
enhanced performance and associated economic benefits, will continue to
demand greater efficiency, reduced maintenance, lower emissions and longer
service life, etc, offered by high-quality synthetic lubricants. These factors
should increase market value and continue market growth for advanced
synthetic lubricants. To meet this demand, the leaders of the lubricant industry
will need to respond by developing and marketing next-generation, high
performance base stocks and products. ExxonMobil‘s SpectraSyn UltraTM
and Mobil 1TM with SuperSynTM-Antiwear technology are current examples of
1. J. Synth. Lubr., 2002, 18-4, Publisher‘s Note.
2. G. J. Bishop, Aviation Turbine Lubricant Development, J. Synth. Lubr., 1987, 4-1, 25.
3. Harlacher, E. A.; Krenowics, R.A.; Putnick, C.R. Alkylenzene Based Lubricants. Prep.
52D26P, 86th AICHE national meeting, Houston, April 1-5 1979.
4. (a) Garwood, W. E., Synthetic Lubricant, US Patent 2,937,129, 1960.
(b) Hamilton, L. A. and Seger, F. M. Polymerized Olefins Synthetic Lubricants, US
Patent 3,149,178, 1964.
5. (a) Lubricants World, “On Track for Growth , June 1999, 19.
(b) After-Market Business Vol. 100, n3, p. 32, March 2000 “It‘s Brand vs. Commodity in
Choosing Motor Oil
(c) Business Wire (23 July 2002), p. 328 “Mobil 1 Chosen as Factory-Fill Motor Oil for
The authors thank Hal Murray for his assistance in literature search and
Andrew Jackson, Mike Thompson, Charles Foster and Joan Kaminski for
their valuable comments about this chapter.
128 Wu, Ho, and Forbus
7. www.exxonmobilsynthetics.com or ExxonMobil Chemical Synthetics, P. O. Box 3272,
Houston, TX 77253-3272 (281-570-6000)
8. Lappin, G. R. Alpha-Olefins Application Handbook, Lappin, G. R.; Sauer, J. D. (Eds.),
Marcel Dekker: New York, 1989; 35.
9. (a) Sacks, M. A private report of Process Economic Program, SRI International, Report
no. 125, Synthetic Lubricant Base Stocks, May 1979
(b) Bolan, R. E. A private report of Process Economic Program, SRI International, Report
no. 125A, Synthetic Lubricant Base Stocks, Sept. 1989
10. Brennan, J. A. Wide-Temperature Range Synthetic Hydrocarbons Fluids, Ind. Eng. Chem.
Prod. Res. Dev., 1980, 19, 2-6
11. (a) “Strong Demand for Synthetic Lubricants Lead to Increased Investment in LAO
Production“, Ind. Lubr. Tribology, 2002, 54(1), 32. (b)
http://www.the-innovation-group.com/ChemProfiles/Alpha Olefins (Linear).htm
12. Shubkin R.L.; Baylerian, M. S.; Maler, A. R. Olefin Oligomer Synthetic Lubricants :
Structure and Mechanism of Formation, Ind. Eng. Chem. Prod. Res. Dev., 1980, 19, 15-19
13. Hope, K. D.; Ho, T. C.; Archer, D. L.; Bak, R. J.; Collins, J. B.; Burns, D. W. Process for
Recovering Boron Trifluoride From a Catalyst Complex, US Patent 6,410,812, 2002.
14. Cerny, J.; Pospisil, M.; Sebor, G. Composition and Oxidative Stability of Hydrocracked
Base Oils and Comparison with a PAO, J. Synth. Lubr., 2001, 18-3, 199.
15. ExxonMobil Chemical Co. Sales Brochure. ExxonMobil Chemical Synthetics, P. O. Box
3272, Houston, TX 77253-3272 (281-570-6000)
16. Lubes-n-Greases, March 2002, p. 39, PAO Problem Solver by Chevron Phillips Chemical
17. Mattei, L.; Pacor, P.; Piccone, A. Oils With Low Environmental Impact for Modern
Combustion Engines, J. Synth. Lubr., 1995, 12-3, 171.
18. (a) Synthetic Lubricants and High Performance Functional Fluids, 2nd ed., Rudnick, L.
R.; Shubkin, R. L. (Eds.), Marcel Dekker: New York, 1999; 21.
(b) Lubes-n-Greases, January 2003, p. 39, PAO Problem Solver by Chevron Phillips
19. (a) Wu, M. M. High Viscosity-Index Synthetic Lubricant Compositions, US Patent
(b) Wu, M. M. High Viscosity-Index Synthetic Lubricant Process, US Patent 4,827,073,
20. (c) ExxonMobil SuperSynTM - A New Generation of Synthetic Fluid, Society of
Tribologists and Lubrication Engineers Annual Meeting, Las Vegas, Nevada, May 26,
21. (a) Law, D. A.; Lohuis, J. R.; Breau, J. Y.; Harlow, A. J.; Rochette, M. Development and
Performance Advantages of Industrial, Automotive and Aviation Synthetic Lubricants, J.
Synth. Lubr., 1984, 1-1, 6-33.
(b) Bergstra, R. J.; Baillargeon, D. J.; Deckman, D. E.; Goes, J. A. Advanced Low
Viscosity Synthetic Passenger Vehicle Engine Oils, J. Synth. Lubr., 1999, 16-1, 51.
(c) Bleimschein, G.; Fotheringhan, J.; Plomer A. On the Road to New Diesel Regs -
Synthetic Lubes Push on With Fuel to Burn, Lubes-n-Greases, November 2002, p. 22
22. www.mobil1.com What auto experts say.
23. (a) Szydywar, J. Ester Base Stocks, J. Synth. Lubr., 1984, 1-2, 153.
(b) Debuan, F.; Hanssle, P. Aliphatic Dicarboxylic Acid Esters for Synthetic Lubricants,
J. Synth. Lubr., 1985, 1-4, 254.
(c) Zeman, A.; Koch, K.; Bartle, P., Thermal Oxidative Aging of Neopentylpolyol Ester
Oils: Evaluation of Thermal-Oxidative Stability by Quantitative Determination of
Volatile Aging Products, J. Synth. Lubr., 1985, 2-1, 2-21.
6. Murphy, W. R.; Blain, D. A.; Galiano-Roth, A. S.; Galvin P. A. Synthetic Basics -
Benefits of Synthetic Lubricants in Industrial Applications, J. Synth. Lubr., 2002, 18-4,
Synthetic Lubricant Base Stock Processes and Products 129
24. Boyde, S. Hydrolytic Stability of Synthetic Ester Lubricants, J. Synth. Lubr., 2000, 16-4,
25. Carnes, K, Ester? Ester Who? Lubricants World, October 2002, p. 10
26. (a) Schlosberg, R. H.; Chu, J. W.; Knudsen, G. A.; Suciu, E. N.; Aldrich, H. S. High
Stability Esters for Synthetic Lubricant Applications, Lubr. Eng., 2001, 21.
(b) Duncan, C.; Reyes-Gavilan J.; Costantini, D.; Oshode, S. Ashless Additives and New
Polyol Ester Base Oils Formulated for Use in Biodegradable Hydraulic Fluid
Applications, Lubr. Eng., September 2002, p. 18
27. Kussi, S. Chemical, Physical and Technological Properties of Polyethers as Synthetic
Lubricants, J. Synth. Lubr., 1985, 2-1, 63.
28. The Dow Chemical Co., Midland, Michigan 48674, Dow Polyglycol product brochure.
29. Matlock, P. L.; Brown, W. L.; Clinton, N. A. Polyalkylene Glycols, Chapter 6, In
Synthetic Lubricants and High Performance Functional Fluids, 2nd Ed. Rudnick, L. R.;
Shubkin, R. L. (Eds.), Marcel Dekker: New York, 1999; p. 159.
31. Wu, M. M. Alkylated Aromatics, Chapter 7, In Synthetic Lubricants and High
Performance Functional Fluids, 2nd Ed. Rudnick, L. R.; Shubkin, R. L. (Eds.), Marcel
Dekker: New York, 1999; p. 195.
32. Marino, M. P.; Placek, D. G., Phosphate Esters, Chapter 4, Synthetic Lubricants and High
Performance Functional Fluids, 2nd Ed. Rudnick, L. R.; Shubkin, R. L. (Eds.), Marcel
Dekker: New York, 1999; p. 103
33. Okazaki, M. E.; Abernathy, S. M. Hydrolysis of Phosphate-Based Aviation Hydraulic
Fluids, , J. Synth. Lubr., 1993, 10-2, 107.
34. Petroleum Technology Quartery, Vol. 4, #4, Winter/2000, p. 22
35. Slower growth forecast for PAO lubes, Lube Report, Industry News from Lubes-n-
Greases, Vol. 2 Issue 16, April 17, 2002.
(d) Denis, J. The Relationships between Structure and Rheological Properties of
Hydrocarbons and Oxygenated Compounds Used as Base Stocks, J. Synth. Lubr., 1984, 1-