Note: Descriptions are shown in the official language in which they were submitted.
WO 93/10066 2 1 2 3 ~ 2 6 PCl/US91/08783
~:
:
DEHYDROCYCLIZATION OF POLYALPHA-OLEFIN LUBRICANTS :~
'' '
This invention relates to novel compositions of
, polyalpha-olefin (PAO) oligomers containing aromatic
structures useful as lubricant basestock and lubricant
additives and to their means of preparation. More
particularly, the invention relates to novel lubricant
compositions having high viscosity index (VI) and
enhanced thermal stability prepared by dehydrocyclization
of polyalpha-olefin oligomers that exhibit high VI and
low pour point.
The synthesis of oligomeric hydrocarbon fluids, ~-
which have improved performance over those of mineral oil
based lubricants, has been the subject of important j;
research and development in the petroleum industry for
many years and has led to the relatively recent market
introduction of a number of superior polyalpha-olefin
synthetic lubricants, primarily based on the oligomeri-
zation of alpha-olefins or l-alkenes. The thrust of the
industrial research effort on synthetic lubricants has
been toward fluids exhibiting us~ful viscosities over a
wide range of temperature, i.e., improved viscosity
index, while also showing lubricity, thermal and
oxidative stability and pour point equal to or better
than mineral oil. These new synthetic lubricants lower
friction and hence increase mechanical efficiency over a
wider range of operating conditions than mineral oil
lubricants.
Notwithstanding their generally superior
properties, PAO lubricants are often formulated with
additives, or an additive package, to enhance those
properties for specific applications. The more commonly
used additives include oxidation inhibitors, rust
inhibitors, metal passivators, antiwear agents, extreme
pressure additives, pour point depressants, detergent-
dispersants, viscosity index (VI) improvers, foam
WO93/10066 PCT/US91/08783
2123~26
inhibitors and the like. This aspect of the lubricant
arts is specifically described in Kirk-Othmer
"Encyclopedia of Chemical Technology", 3rd edition, Vol.
14, pp. 477-526.
Lube additive packages are complex and costly
materials. Therefore, a significantly superior new
lubricant is one in which the properties conferred on
lube mixture by known additives are intrinsic to the
structure of the new lubricant molecule, obviating or at
least reducing the need for additives. Consequently,
improvements in lubricant technology pursued by artisans
in the field flow from both new additive development
addressed to deficiencies in lubricant oligomers and new
oligomer development for inherently better properties to
displace additives. Increasing the aromaticity of lube
mixtures is known to improve thermal stability and anti-
wear properties. However, in view of the paraffinic
nature of PAO lubricants aromatic additives to PAO are
often confronted with problems of solubility that limit
their usefulness or require the ~se of costly disper-
sants.
Alkylated aromatics are known in the prior art as
lubricant additives for their antiwear properties,
thermal and oxidative stability as disclosed in U.S.
Patent Nos. 4,211,665, 4,238,343, 4,604,491 and
4,714,7944. Antiwear properties of alkylnaphthalene
lubricating fluids are presented in Khimiya i
Tekhnologiya Topliv i Masel, No. 8, pp. 28~29, August,
1986.
Recently, novel lubricant compositions ~referred
to herein as HVI-PAO) comprising polyalpha-olefins and
methods for their preparation employing as catalyst
reduced chromium on a silica support have been disclosed :
in U.S. Patent Nos. 4,827,064 and 4,827,073. The process
comprises contacting C6-C20 l-alkene feedstock with
reduced valence state chromium oxide catalyst on porous :`
silîca support under oligomerizing conditions in an
W093/l~u~ 2 1 2 3 4 2 6 PCT/US91~08783
oligomerization zone whereby high viscosity, high VI
liquid hydrocarbon lubricant is produced having branch
ratios less than 0.19 and pour point below -15-C.
Lubricants produced by the process cover the full range
s of lubricant viscosities and exhibit a remarkably high VI
and low pour point even at high viscosity. The molecular
structure of HVI-PAO is novel and comprises the product
of an essentially regular head to tail polymerization of
alpha-olefin, thus providing an oligomer with large
pendant alkyl groups on the recurring polymeric unit.
Dehydrocyclization is a well known reaction in the
organic chemical arts for the conversion of linear and
branched alkanes to aromatic compounds, as described in
Royals "Advanced Organic Chemistry", Prentice-Hall, Inc.,
pp. 145-147. The reaction is carried out typically by
catalysis with dehydrogenation catalysts and proceeds
through ring closure and dehydrogenation to provide an
aromatic structure. The dehydrocyclization reaction can
be characterized as a type of aromatization reaction and
the terms are used interchangeably herein.
It has been found that aromatic structures can be
introduced into the molecular structure of polyalpha-
olefin lubricant oligomers by subjecting the polyalpha-
olefin to a dehydrocyclization reaction which converts a
portion of the pendant or branching alkyl groups in the
recurring polymeric unit of PAO to aromatic structures.
When the starting material for dehydrocyclization is
HVI-PAO, it has been determined that carrying out the `
dehydrocyclization reaction produces a lubricant oligomer
with increased aromaticity without significantly
degrading the viscometric properties of the HVI-PAO,
particularly the high VI of the starting material. As a
result, PAO and HVI-PAO are produced containing aromatic
structures that lend increased thermal stability, wear
resistance and solubilizing characteristics to the liquid
lubricant oligomers so modified. The improved
solubilizing characteristics are particularly important
WO93/10066 PCT/US91/08783
2 ~3 ~26 4
for improving the solubility of aromatic additives in the
modified lubricant oligomer.
The polyalpha-olefins produced by the dehydro-
cyclization process comprise novel compositions of matter
containing up to five weight percent of aromatic
structure attached as pendant groups to the backbone of
the polyalpha-olefin structure.
For the more preferred HVI-PA0 oligomers, the
compositions have the recurring polymeric structure:
~-CH2-CH-~n~CH2 CIH ~m
(CH2)X R
CH3
where x is 5 to ll, n is less than 500 and the
ratio of n to m is between 200 and 20; wherein R contains
x+l carbon atoms comprising aryl, aralkyl or alkylaryl.
More particularly, the instant invention discloses
a process for the dehydrocyclization of C6-C20 polyalpha-
olefin which comprises contacting the polyalpha-olefin
with dehydrocyclization catalyst in a dehydrocyclization
reaction zone under dehydrocylclization conditions
whereby modified polyalpha-olefin is produced containing
aromatic structures.
The process is more specifically directed to the
dehydrocyclization of HVI-PA0 wherein the
polyalpha-olefin comprises the product of the
oligomerization of alpha-olefins containing 6 to 20
carbon atoms, or mixtures of such olefins. The
oligomerization comprises contacting the olefins under
oligomerization conditions, at reaction temperature of
900 to 250C with a chromium catalyst on a porous
support, which catalyst has been treated by oxidation at
a temperature of 200 to 900C in the presence of an ~;
oxidizing gas and then by treatment with a reducing agent
at a temperature and for a time sufficient to reduce the
catalyst to a lower valence state. The oligomerization
produces an oligomeric liquid lubricant composition
comprising C30-Cl300 hydrocarbons having a branch ratio
W093/10066 212 3 4 2 ~ PCT/US91/08783
of less than O.l9, weight average molecular weight
between 420 and 45,000, number average molecular weight
between 420 and 18,000, molecular weight distribution,
i.e. (weight average molecular weight)/(number average
molecular weight), between l and 5 and pour point below
-l5C.
In the drawings, Figure l is a plot showing the
relationship of hydrogen flow rate to aromaticity in the
product of the present invention.
Figure 2 is a plot showing the relationship of
hydrogen flow rate to bromine number in the product of
the instant invention.
The polyalpha-olefin oligomers used as starting
material in the dehydrocyclization step of the process of
the instant invention are conventional commercially
available PA0 or HVI-PA0 prepared as subsequently
described. The conventional PA0 is typically prepared by
Lewis acid or Ziegler catalyst initiated oligomerization
of linear l-alkenes and can be obtained from commercial
sources. The more commonly available commercial PA0 is
prepared by oligomeri~ation of l-decene with aluminum
chloride catalyst. The oligomer contains a preponderance
of C short chain alkyl branches of less than 8 carbon
atoms.
HVI-PA0 oligomers used as starting material in the
present invention are prepared by the oligomerization of
C6-C20 alpha-olefins in contact with reduced valence
state chromium oxide catalyst on porous support. It has
been found that the process described herein to produce
the HVI-PA0 oligomers can be controlled to yield
oligomers having weight average molecular weight between
420 and 60,000 and number average molecular weight
between 420 and 24,000. Measured in carbon numbers,
molecular weights range from C24 to C5000, with
3s number-averaged molecular weight of C30 to C2l00 and a
preferred range of C30 to Cl400. Molecular weight
WO93/lO0~ 2 1 2 3 4 2 6 PCT/US9l/08783
distributions, defined as the ratio of weight averaged
molecular to number averaged molecular weight, range from
1.00 to 5, with a preferred range of 1.01 to 3.
l-hexene HVI-PAO oligomers of the present inven-
tion have been shown to have a very uniform linear C4branch and contain regular head-to-tail connections
indicative of the following structure as confirmed by
NMR:
(-CH-CH-)n
(CH2)3
CH3
The oligomerization of l-decene by reduced valence
state, supported chromium also yields a HVI-PAO with a
structure analogous to that of 1-hexene oligomer. The
lubricant products after distillation to remove light
fractions and hydrogenation have characteristic C-13 NMR
spectra confirming regular head-to-tail oligomerization
of the alpha-olefin to produce a structure with mainly
large alkyl group branches.
In general, the HVI-PAO oligomers have the
following regular head-to-tail structure where n can be 3
to 17:
- ( CH2 -C~ ) x
(CH2)n
CH3
with some head-to-head connections. `~
Olefins suitable for use as starting material in
the preparation of HVI-PA0 include those olefins
containing from 2 to 20 carbon atoms such as ethylene,
propylene, l-butene, l-pentene, l-hexene, l-octene,
l-decene, l-dodecene and l-tetradecene and branched chain
isomers such as 4-methyl-1-pentene. Also suitable for
use are olefin-containing refinery feedstocks or
effluents. However, the olefins used are preferably
alpha-olefinic as for example l-heptene to l-hexadecene
and more preferably l-octene to l-tetradecene, or
mixtures of such olefins.
WOg3/l~K~ 212 3 ~ 2 G PCT/US91/08783
HVI-PAO oligomers of alpha-olefins have a low
branch ratio of less than O.l9 and superior lubricating
properties compared to the alpha-olefin oligomers with a
high branch ratio, as produced in all known commercial
methods. HVI-PA0 alpha-olefin oligomers are prepared by
oligomerization reactions in which a major proportion of
the double bonds of the alpha-olefins are not iæomerized.
These reactions include alpha-olefin oligomerization by
supported metal oxide catalysts, such as Cr compounds on
silica or other supported IUPAC Periodic Table Group VIB
compounds. The catalyst most preferred is a lower
valence Group VIB metal oxide on an inert support.
Preferred supports include silica, alumina, titania,
silica alumina, magnesia and the like. -~
The branch ratios used to characterize HVI-PAO are
defined as the ratios of CH3 groups to CH2 groups in the
lube oil calculated from the weight fractions of methyl
groups obtained by infrared methods, as published in
AnalYtical Chemistrv, Vol. 25, No. lO, p. 1466 (1953). ~-
Branch ratio = wt fraction of methyl aroup
l-(wt fraction of methyl group)
The supported metal oxide catalysts are preferably
prepared by impregnating metal salts in water or organic
solvents onto the support. Any suitable organic solvent
known to the art may be used, for example, ethanol,
methanol, or acetic acid. The solid catalyst precursor
2s is then dried and calcined at 200 to ~OO^C by air or
other oxygen-containing gas. Thereafter the catalyst is
reduced by any of several various and well known reducing
agents such as, for example, C0, H2, NH3, H2S, CS2,
CH3SCH3, CH3SSCH3, metal alkyl containing compounds such
as R3Al, R3B, R2Mg, RLi, R2Zn, where R is alkyl, alkoxy,
aryl and the like. Preferred are C0 or H2 or metal alkyl
containing compounds.
WO93/10066 PCT/US91/08783
e
2123~126 8
Alternatively, the Group VIB metal may be applied
to the substrate in reduced form, such as CrII compounds.
The res~ltant catalyst is very active for oligomerizing
olefins at a temperature range from below room
temperature to 500 C at a pressure of 10 to 34,580 kPa
(0.1 atmosphere to 5000 psi). Preferably the oligomer-
ization is carried out at a temperature between 90 and
250-C. Contact time of both the olefin and the catalyst
can vary from one second to 24 hours. Very low catalyst
concentrations based on feed, from 10 wt % to 0.01 wt %,
are used to produce oligomers. The catalyst can be used
in a batch type reactor or in a fixed bedl continuous
flow reactor.
The following examples are presented to illustrate
the preparation of the HVI-PAO catalyst and oligomeriza-
tion process.
Example 1
Catalvst Preparation and Activation Procedure
1.9 grams of chromium (II) acetate
(Cr2(OCOCH3)42H2O) (5.58 mmole) (COD ercially obtained)
is dissolved in 50 ml of hot acetic acid. Then 50 grams
of a silica gel of 8-12 mesh size, a surface area of 300
m2/g, and a pore volume of 1 ml/g, also is added. Most
of the solution is absorbed by the silica gel. The final
mixture is mixed for half an hour on a rotavap at room
temperature and dried in an open-dish at room tempera-
ture. First, the dry solid (20 g) is purged with N2 at
250C in a tube furnace. The furnace temperature is then
raised to 400C for 2 hours. The temperature is then set
at 600C with dry air purging for 16 hours. At this time
the catalyst is cooled under N2 to a temperature of
300C. Then a stream of pure CO (99.99~ from Matheson)
is introduced for one hour. Finally, the catalyst is
cooled to room temperature under N2 and ready for use.
WO93/10066 PCTJUS91/08783
~123~2~
g
Example 2
A commercial chrome/silica catalyst which contains
1% Cr on a large-pore volume synthetic silica gel is
used. The catalyst is first calcined with air at 800C
for 16 hours and reduced with C0 at 300C for 1.5 hours.
Then 3.5 g of the catalyst is packed into a tubular
reactor and heated to 100C under the N2 atmosphere.
Purified l-decene is pumped through the reactor at 1830
to 2310 kPa (250 to 320 psi). The product is collected
periodically and stripped of light products having
boiling points below 343 C (650-F). High quality HVI-PA0
lubes with high VI are obtained as presented in the
following table.
Reaction WHSV Lube Product Properties
Temp.-C q/a/hrV at 40 C V at lOO C VI
120 2.51555.4cs 157.6cs 217
135 0.6 389.4 53.0 202
150 1.2 266.8 36.2 185
166 0.6 67.7 12.3 181
197 0.5 21.6 5.1 172
In the process of the instant invention the
HVI-PA0 oligomer is converted to oligomer containing
aromaticity in the structure of the oligomer molecule by
treating the HVI-PAo with dehydrocyclization. In the
process a portion of the pendant alkyl groups of the
oligomer are ring-closed and dehydrogenated to form
aromatic ring structures. Depending upon the
dehydrocycli~ation conditions employed it has been
discovered that up to 5 wt % aromatic structures can be
incorporated into the HVI-PAo molecular structure.
WO 93/10066 PCl/US91/08783
2123~26
Preferably, the dehydrocyclization reaction is performed
on HVI-PAO oligomers produced from C8-C14 alpha-olefins,
with l-decene a most preferred alpha-olefin material to
produce poly-l-decene oligomer.
C-13 NMR analysis of the products of the dehydro-
cyclization process of the present invention confirm that
the products comprise liquid lubricant hydrocarbon having
the recurring polymeric structure
~-CH2-CH-~n~~CH2~cH~]m
where x is 5 to311, n is less than 500 and the -
ra~io of n to m is between 200 and 20; wherein R contains
x+l carbon atoms comprising aryl, aralky} or alkylaryl.
For the particular case of the dehydrocyclization of
poly-l-decene produced by the HVI-PA0 process C-13 NMR
analysis supports the conclusion of the aforestated ;-
structure where x is equal to 7. The poly-l-decene
dehydrocyclization product has a viscosity of at least
2cS at lOO-C and a viscosity index of at least 130.
The catalysts used to affect the
dehydrocyclization reaction of poly-alpha-olefin
oligomers in the present invention includes those
typically and conventionally employed to affect
dehydrocyclization of alkanes, well known to those
skilled in the organic chemical arts. These include
Group VIII metals of the CAS version of the Periodic
Table of the Elements, in particular platinum and
palladium. Such catalysts are included on a solid
support structure which may be taken from materials such
as alumina, silica, clays, charcoal and zeolites. In the
present invention zeolites and, more particularly, large
pore zeolites have been found useful. Such zeolites
include Beta, ZSM-12, Y, which possess a Constraint Index
no greater than 2 with alpha values ranging between 1
and 100.
A convenient measure of the extent to which a
zeolite provides controlled access to molecules of
WO93/10066 2 1 2 3 ~ 2 ~ PCT~US91/08783
11
varying sizes to its internal structure is the
aforementioned Constraint Index of the zeolite. The
method by which Constraint Index is determined is
described fully in U.S. Patent No. 4,016,218, to which
reference is made for details of the method.
The zeolite(s) selected for use herein will -~
generally possess an alpha value of at least 1, `
preferably at least 10 and more preferably at least 50.
"Alpha value", or "alpha number", is a measure of zeolite
acidic functionality and is more fully described together
with details of its measurement in U.S. Patent No. ~
4,~16,218, J. CatalYsis, 6, pp. 278-287 (1966) and J. ;-
Catalysis, 61, pp. 390-396 (1980). Zeolites of low
acidity (alpha values of less than 200) can be achieved -`
by a variety of techniques including (a) synthesizing a
zeolitè with a high silica/alumina ration, (b) steaming,
(c) steaming followed by dealuminization and (d)
substituting framework aluminum with other species. For
example, in the case of steaming, the zeolite(s) can be
exposed to steam at elevated temperatures ranging from
260 to 650-C (500- to 1200-F) and preferably
from 399- to S38-C (750 to lOOO-F). This treatment can
be accomplished in an atmosphere of 100% steam or an
atmosphere consisting of steam and a gas which is
substantially inert to the zeolite. A similar treatment
can be accomplished at lower temperatures employing
elevated pressure, e.g., at from 177 to 371C (350 to
700F) with from 1,010 to 20,200 kPa (10 to 200
atmospheres). Specific details of several steaming
procedures may be gained from the disclosures of U.S.
Patent Nos. 4,325,994; 4,374,296: and 4,418,235.
It has been discovered that a particularly useful
catalyst for the process comprises zeolite Beta bound
with approximately 35 wt % alumina and containing 0.6%
platinum. This catalyst was steamed to yield an
effective catalyst for dehydrocyclization having an alpha
value of 50.
WO 93/10066 PCI/US91/08783
2123426
12
The process of the present invention can be run
under aromatization conditions which include hydrogen
feed or flow to the reactor. Hydrogen can be co-fed at a
rate between 0 and 900 v/v (0 and 5000 SCF/BBL).
However, as illustrated in Figure l, the hydrogen flow
rate effects the degree of aromatization achieved. The
highest aromatic content is to be found when hydrogen
flow rate is zero as shown in Figure 1. Hydrogen flow
rate also affects the degree of residual unsaturation
remaining in the product following dehydrocyclization.
The starting material HVI-PA0 typically contains at least `;~
one olefinic group per oligomer molecule. The degree to
which this unsaturation is eliminated in the final
product is influenced by hydrogen flow rate as shown in ~-
Figure 2. At high hydrogen flow rates bromine numbers
less than l are achieved whereas at no hydrogen flow the
bromine number for the poly-l-decene HVI-PA0
- aromatization product is greater than 6.
- It has been determined that the process of this
invention can be conducted at temperatures between 50-
and 700-C, press~res between 940 and 7000 kPa (20 and
1000 psig) and liquid hourly space velocity (L~SV)
between 0.1 and 10. Preferably, the dehydrocyclization
conditions comprise a temperature between 100- and 300~C,
a pressure between 2170 and 4240 kPa (300 and 600 psig),
and LHSV between 0.4 and l.
The following Examples illustrate the dehydro-
cyclization process of the present invention and the
properties of the products produced therefrom. The
Examples are presented strictly for illustration purposes
and are not intended to limit the scope of the invention.
The feedstock used in Examples 3-6 is HVI-PA0
liquid lubricant and prepared in a fixed bed reactor
according to the procedures previously described. The
3S oligomerization conditions and properties of the l-decene
WO93/10~6 212 3 '~ 2 ~3 PCT/US91/08783
13
HVI-PA0 oligomer starting material produced in a fixed
bed reactor are as follows: reaction temperature 165~C,
pressure 380 kPa (40 psig), WHSV 2.5, lube yield 63.6~,
viscosity at 40-C 130.4 cS, viscosity at lOO-C 19.7 cS,
viscosity index 173.1.
In Examples 3-6 the dehydrocyclization process
carried out on the feedstock was conducted in a fixed bed
reactor containing an aromatization catalyst comprising ;~
zeolite Beta containing 35 wt % alumina and 0.6 wt ~ ;~
platinum. The catalyst is steamed to an alpha value of
50. All of the experiments are conducted at 0.5 LHSV and
a unit pressure of 2860 kPa (400 psig). The hydrogen
flow rate to the reactor is varied between 0 and 900 v/v
(0 and 5000 SCF/B8L). Specific experimental conditions
and properties of the product produced are described in
Table 1.
TABLE 1
Example Feed3 4 5 6
Reactor Temp. 124(256) 129(264)129(264) 146(295)
C(-F)
LHSV ~.48 0.51 0.50 O.S0
Pressure, kPa 2860(~00) 2860(400) 2860(400) 2860(400)
(psig)
H2 Flow,ml/min 21 0 80 75
Yieldj wt % 83.3 92.5 40.0 46.7
Bromine No. 10.5 3.9 6.6 0.5 1.0
Color Clear Brown BrownYellow Yellow
KV, 40 C 30.4 186.1 191.4 151.1 277.2
KV, 100C 19.7 26.1 25.8 22.9 34.2
Visc. Index 173.1 175.2 168.7 181.1 169.5
Wt % Aromatic 0.0 2.2 3.2 1.3 0.5
From the above data it is evident that a
significant degree of aromaticity can be incorporated in
HVI-PAO by the described process. As shown in Table 1,
and as previously noted, aromatic structure formation
varies as a function of hydrogen flow rate with the
highest aromatic content achieved under conditions of no
hydrogen flow. Remarkably, the viscosity indices of the
aromatized HVI-PA0 remains high with little or no
decrease compared to the viscosity index of the starting
material. Also, under conditions of high hydrogen flow
WO93/10~6 PCT/US91/08783
2123~26 14
rate to the dehydrocyclization zone or reactor there is
an appreciable reduction in bromine number signifying
concurrent hydrotreatment as well as aromatization of the
HVI-PA0 oligomer. Accordingly, those products with
lowered bromine numbers can avoid subsequent ~;
hydrotreatment typically employed to stabilize the
lubricant product.
These Examples serve to illustrate that between
0.4 and 5 wt % of aromatic structure, based on total
product weight, can be incorporated into HVI-PA0 to
provide new compositions as determined by C-13 NMR.
T~ese are new liquid lubricant compositions comprise
C24-C5000 hydrocarbons, said composition having a branch
ratio of less than O.l9, weight average molecular weight
between 420 and 60,000, number average molecular weight
between 420 and 24,000, molecular weight distribution
between l and 5, pour point below -15-C and containing
between 0.4 and 4 wt ~ of aromatic structure.
Although the present invention has been described
with preferred embodiments, it is to be understood that
modifications and variations may be resorted to, without
departing from the spirit and scope of this invention, as '
those skilled in the art will readily understand. Such
modifications and variations are considered to be within
the purview and scope of the appended claims.
