Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21'~~~1~
WO 95/17361 ~ PCT/US94/14168
-1-
NAPHTHALENE ALRYLATION WITH PARTIAL RARE EARTH
$XCHANGED CATALYST
This invention relates to the production of alkylated
naphthalenes and substituted naphthalenes.
Alkylaromatic fluids have been proposed for use as
certain types of functional fluids where good thermal and
oxidative properties are required. For example, U.S.
Patent No. 4,714,794 (Yoshida) describes the monoalkylated
naphthalenes as having excellent thermal and oxidative
stability, low vapor pressure and flash point, good
fluidity and high heat transfer capacity and other
properties which render them suitable for use as thermal
medium oils. The use of a mixture of monoalkylated and
polyalkylated naphthalenes as a base for synthetic
functional fluids is described in U.S. Patent no. 4,604,491
(Dressler) and Pellegrini U.S. 4,211,665 and 4,238,343
describe the use of alkylaromatics as transformer oils.
The alkylated naphthalenes are usually produced by the
alkylation of naphthalene or a substituted naphthalene in
the presence of an acidic alkylation catalyst such as a
Friedel-Crafts catalyst, for example, an acidic clay as
described in Yoshida U.S. 4,714,794 or Dressler U.S.
4,604,491 or a Lewis acid such as aluminum trichloride as
described in Pellegrini U.S. 4,211,665 and 4,238,343. The
use of a catalyst described as a collapsed silica-alumina
zeolite as the catalyst for the alkylation of aromatics
such as naphthalene is disclosed in Boucher U.S. 4,570,027.
The use of various zeolites including intermediate pore
size zeolites such as ZSM-5 and large pore size zeolites
such as zeolite L and ZSM-4 for the alkylation of various
monocyclic aromatics such as benzene is disclosed in Young
U.S. 4,301,316.
In the formulation of functional fluids based on the
alkyl naphthalenes, it has been found that the preferred
alkyl naphthalenes are the mono-substituted naphthalene
since they provide the best combination of properties in
the finished product: because the mono-alkylated
CA 02174512 2005-02-18
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naphthalenes possess -fewer benzylic hydrogens than the
corresponding di-substituted or polysubstituted versions,
they have better oxidative stability and therefore form
better functional fluids and additives. In addition, the
mono-substituted naphthalenss have a kinematic viscosity in
the desirable range of about 5-8 mn2/s (at 100'C.) when
working with alkyl substituents of 14 to 18 carbon atoms
chain length. Although the mono-alkylated naphthalsnes may
be obtained in admixture with more highly alkylated
naphthalenes using conventional Friedel-Crafts catalysts
such as those mentioned above or by the use of seolites
such as USY, the selectivity to the desired mono-alkylated
naphthalenes is not as high as desired.
Several recent advances have been made in this area
which improve the yields of the desired mono-alkylated
naphthenes.
U.S. Patent 5,034,563, Ashjian et al. teaches use of a
zeolite containing a bulky cation. The use of, a.g., USY
with rations having a radius of at least 2.5
~ Angstroms,(.25 nm) increases selectivity for desired products.
Taught as suitable were aeolites containing hydrated
rations of metals of Group IA, divalent rations, especially
of Group IiA, and rations of the Rare Earths. The patent
had examples in which H, NH4, Na were added to USY zeolite
by a procedure imrolving forming a slurry of ssolite and
liquid, 1 hour of stirring, decantation, and a repeat of
the exchange procedure.
U.S. Patent 5,177,284, Le et al. discusses the
desirable properties of alkylated naphthalene fluids with
higher alpha:beta ratios, including improved thermal and
oxidative stability. Le et al found that several
parameters influenced the alpha: beta ratio of the alkylatsd
naphthalene products, including steaming the $eolite,
lowering the alkylation temperature; or use of acid-treated
clay. Steamed UsY catalyst gave excellent results in the
axamples. The patentees also mentioned use of zsolites
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with reduced activity due to base exchange, alkaline earth
ion exchange and use of boron-zeolite beta.
U.B. Patent 5,191,135 Dwysr et al. discloses the
effect of co-feeding water for this reaction when using a
large pore zeolite catalyst, such as $eolite Y. Adding
from 1 - 3 wt ~ water to the feed improved the alkylation
reaction, a result attributed to suppression of zeolite
acid site activity.
U.B. Patent 5,191,134, Le discloses a similar
io alkylation process using MCM-41.
We did additional Work to see if we could further
improve this alkylation process. We wanted to increase the
efficiency of the reaction both in terms of conversion and
yields.
We found that a large pore $eolite, such as seolite Y,
gave unexpected results When incompletely exchanged with
rare earths. We achieved~very high comrersions of both
olefin and naphthalene, with essentially all of the product
being mono-alkylated, rather than di- or poly-alkylated.
ZO Accordingly, the present invention provides a process for
preparing long chain alkyl substituted naphthalenes which
comprises alkylating a naphthalene with an alkylating agent
possessing an alkylating aliphatic group having at least
six carbon atoms under alkylation reaction conditions in
the presence of an alkylation catalyst comprising a porous
crystalline seolfte containing exchangeable sites and Rare
Enrth rations associated with at least soma of the
exchangeable sites but lass than 50 ~ of the exchangeable
sites to form the alkylated naphthalene possessing at least
one alkyl. group derived from the alkylating~agent.
In a mare limited embodiment, the present invention
provides a process for preparing long chain alkyl
substituted naphthalenss which comprises reacting
naphthalene with an olefin containing at least 8 carbon
atoms as an alkylating agent under alkylation reaction
conditions and in the presence of an alkylation catalyst
WO 95/17361 t ~ PCT/LTS94/14168
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comprising an ultrastable Y zeolite with exchangeable sites
containing Rare Earths associated with from 7.5 to 30 ~ of
the exchangeable sites, to form an alkylated naphthalene
possessing at least one alkyl group derived from the
alkylating agent.
The starting materials for the production of the
alkylated naphthalenes are naphthalene and substituted
naphthalenes which may contain one or more short chain
alkyl groups containing up to eight carbon atoms, such as
methyl, ethyl or propyl. Suitable alkyl-substituted
naphthalenes include alpha-methylnaphthalene,
dimethylnaphthalene and ethylnaphthalene. Naphthalene
itself is preferred since the resulting mono-alkylated
products have better thermal and oxidative stability than
the more highly alkylated materials for the reasons set out
above.
The alkylating agents which are used to alkylate the
naphthalene include any aliphatic or aromatic organic
compound having one or more available alkylating aliphatic
~ groups capable of alkylating the naphthalene . The
alkylatable group itself should have at least 6 carbon
atoms, preferably at least 8, and still more preferably at
least 12 carbon atoms. For the production of functional
fluids and additives, the alkyl groups on the alkyl-
naphthalene preferably have from 12 to 30 carbon atoms,
with particular preference to 14 to 18 carbon atoms. A
preferred class of alkylating agents are the olefins with
the requisite number of carbon atoms, for example, the
hexenes, heptenes, octenes, nonenes, decenes, undecenes,
dodecenes. Mixtures of the olefins, e.g. mixtures of C12
C20 or c14-C18 olefins, are useful. Branched alkylating
agents, especially oligomerized olefins such as the
trimers, tetramers, pentamers, etc., of light olefins such
as ethylene, propylene, the butylenes, etc., are also
useful. Other useful alkylating agents which may be used,
although less easily, include alcohols (inclusive of
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monoalcohols, dialcohols, trialcohols, etc.) such as
hexanols, heptanols, octanols, nonanols, decanols,
undscanols and dodecanols: and alkyl halides such as hexyl
chlorides, octyl chlorides, dodecyl chlorides: and higher
homologs.
The alkylation reaction between.the naphthalene and
the alkylating agent is carried out in the presence of a
zeolite catalyst which contains a cation of certain
specified radius. The molecular size of the alkylation
products will require a relatively large pore size in the
zeolite in order for the products to leave the zeolite,
indicating the need for a relatively large pore size in the
zeolits, which will also tend to reduce diffusion
limitations with the long chain alkylating agents. The
large pore size zeolites are the most useful zeolits
catalysts for this purpose although the less highly
constrained intermediate pore size zsolites may also be
used, as discussed below. The large pore sine zeolites are
zeolites such as faujasite, the synthetic fau~asites~
(zeolites X and Y), zeolite L, ZSM-4, ZSM-18, ZSM-20,
mordenite and offretite which are generally useful for this
purpose and characterized by the presence of a 12-msmbersd
oxygen ring system in the molecular structure and by the
existence of pores with a minimum dimension of at least 7.4
(.74 nm), as described by ~'rilette st al. in J. Catalysis
~1,x18-222 (1981). see also Chen et al. ~ha~ie-Selective
Catalysj,s in Industrial Ap~lic one, (Chemical industries;
Vol. 36) Marcel Dekker Inc., New York 1989, IsHN 0-8247-
7856-1 and 8oelderich et al. an~rew. 1~~. Int. Ed. Bngl. 2~
226-246 (1988), especially pp.226-229. The large pore size
zeolites may also be characterized by a "Constraint Index"
of not more than 2, in most cases not more than 1. 8eolite
beta, a zeolite having a structure characterized by twelve-
membered pore openings, fs included in this class of
zeolites although under certain circumstances it has a
Constraint Index approaching the upper limit of 2 which is
WO 95/17361 ; PCT/US94/14168
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usually characteristic of this class of zeolites. The
method for determining Constraint Index is described in U.
S. Patent No. 4,016,218, together with values for typical
zeolites and of the significance of the Index in U.S.
Patent No.4,861,932, to which reference is made for a
description of the test procedure and its interpretation.
Zeolites whose structure is that of a ten membered
oxygen ring, generally regarded as the intermediate pore
size zeolites may also be effective catalysts for this
alkylation reaction if their structure is not too highly
constrained. Thus, zeolites such as ZSM-12 (Constraint
Index 2) may be effective catalysts for this reaction. The
zeolite identified as MCM-22 is a useful catalyst for this
reaction. MCM-22 is described in U.S. Patent 4,954,325 to
which reference is made for a description of this zeolite.
Thus, zeolites having a Constraint Index up to 3 will
generally be found to be useful catalysts, although the
activity may be found to be dependent on the choice of
alkylating agent, especially its chain length, a factor
which imposes diffusion limitations upon the choice of
zeolite.
A highly useful zeolite for the production of the
mono-alkylated naphthalenes is zeolite Y in the ultrastable
form, usually referred to as USY. When this material
contains hydrated cations, it catalyses the alkylation in
good yields with excellent selectivity. Zeolite USY is a
material of commerce, available in large quantities as a
catalyst for the cracking of petroleum. It is produced by
the stabilization of zeolite Y by a procedure of repeated
ammonium exchange and controlled steaming. Processes for
the production of zeolite USY are described in U. S.
Patents Nos. 3,402,966 (McDaniel), 3,923,192 (Maher) and
3,449,070 (McDaniel); see also Wojciechowski, Catalytic
Cracking, Catalysts. Chemistry and Kinetics, (Chemical
Industries Vol. 25), Marcel Dekker, New York, 1986, ISBN
WO 95/17361 PCT/US94/14168
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0-8247°7503-8, to which reference is made for a description
of zeolite USY, its preparation and properties.
We prefer to use a small crystal Y zeolite, in the 0.2
to 0.4 ~cm range, although the 0.6 to 1.3 ~Cm material which
is more typical of Y zeolite crystals may also be used.
Rare Earth Exchange
The selected zeolite catalyst contains a critical
amount of one or more of the Rare Earths. Suitable are Y,
La and any of the Lanthanum Series of Rare Earths, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, HO, Er, Tm Yb, arid Lu.
Especially preferred are Ce, Y and La. In most
applications, mixtures of rare earths will be preferred, as
these are readily available commercially and much less
expensive than purified rare earth elements. The mixed
rare earths typically used to produce zeolite Y based
cracking catalysts serve well.
If the zeolite does not contain the desired amount of
rare earths they may be introduced by ion-exchange in the
conventional manner using a solution of the exchanging
cation.
The amount of rare earth exchange is critical.
Although essentially complete exchange, such as that
obtained in the two step exchange procedure of U.S. Patent
5,034,563, gives a catalyst that will work, complete
exchange does not give optimum results.
We discovered that it is important to have less than
50 % of the total number of exchangeable sites associated
with Rare Earths (RE). Preferably less than 35 % of the
exchangeable sites contain Rare Earths, and most preferably
less than 20 % exchange is preferred. Optimum results are
seen with 12.5 to 17.5 % Rare Earth exchange, ideally, with
15 % exchange. As used herein, the total ion exchange
capacity of the catalyst may be determined by the
temperature programmed ammonia desorption method described
WO 95/17361 , , a . PCT/LTS94J14168
~ ~.'~ ~51~
by G. T. Kerr and A. W. Chester in Thermochimica Acta,
113-124 (1971).
For a typical catalyst, comprising 20 - 50 wt % USY
zeolite in a conventional binder or matrix as discussed
below, the optimum RE content will be 1 wt %, equivalent to
a rare earth content corresponding to less than 15 % of the
total number of exchangeable sites. RE contents may range
from 0.025 to 2.5 wt %, preferably 0.05 to 2 wt %, and most
preferably, 0.2 to 1.5 wt %.
Expressed in terms of the role the Rare Earths play in
our catalyst, we believe the RE content is in the sodalite
cages, not in the supercage of the zeolite. The '563
patent was directed to bulky cations in the supercage.
When our low RE catalyst is calcined, the RE is believed to
go into the sodalite cage. Commercially, such partial
exchange is easy to do, a solution with the desired amount
of RE may be simply sprayed onto a moving bed or layer of
suitable zeolite, either neat zeolite or composited with a
matrix. .
Binders may be incorporated to improve crush strength
and other physical properties. Suitable materials include
naturally occurring clays, e.g., bentonite and kaolin as
well as the oxides referred to above, silica, alumina, and
mixtures thereof.
The relative proportions of zeolite, present in finely
divided crystalline form oxide matrix may vary widely, with
the crystalline zeolite content ranging from 1 to 90
percent by weight and more usually, particularly When the
composite is prepared in the form of beads, in the range of
2 to 80 weight percent of the composite.
The stability of the alkylation catalyst of the
invention may be increased by steaming. U.S. Patent Nos.
4,663,492; 4,594,146; 4,522,929; and 4,429,176, describe
conditions for the steam stabilization of zeolite catalysts
which can be utilized to steam-stabilize the catalyst. The
steam stabilization conditions include contacting the
~WO 95/17361 PCT/LTS94/14168
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catalyst with, e.g., 5-100 steam at a temperature of at
least 300°C (e. g., 300-650°C) for at least one hour (e. g.,
1-200 hours) at a pressure of 100 - 2,500 kPa, e.g.
steaming with 75-100 steam at 315°-500°C and atmospheric
pressure for 2-25 hours. The steam stabilization treatment
may, as described in the above-mentioned patents, take
place under conditions sufficient to initially increase the
Alpha Value of the catalyst, and produce a steamed catalyst
having a peak Alpha Value. If desired, steaming can be
continued to subsequently reduce the Alpha Value from the
peak Alpha Value to an Alpha Value which is substantially
the same as the Alpha Value of the unsteamed catalyst.
The catalyst performance may be further improved by
partial ammonium exchange, e.g., ammonium exchanged and
then calcined at 400°C (752°F) to remove only some of the
ammonia.
Alkylation Process Conditions
Conventional alkylation conditions and equipment can
be used. These will be briefly reviewed for completeness,
but these conditions, per se, form no part of the claimed
invention.
The alkylation process of this invention is conducted
such that the organic reactants, i.e., the alkylatable
aromatic compound and the alkylating agent, are brought
into contact with the zeolite catalyst in a suitable
reaction zone such as, for example, in a flow reactor
containing a fixed bed of the catalyst composition, under
effective alkylation conditions. Such conditions typically
include a temperature of from 100°C to 400°C, a pressure of
from 20.3 to 25325 kPa (0.2 to 250 atmospheres), a feed
weight hourly space velocity (WHSV) of from about 0.1 hr 1
to 10 hr 1 and an alkylatable aromatic compound to
alkylating agent mole ratio of from 0.1:1 to 50:1,
preferably from 4:1 to 1:4 e.g. from 2:1 to 1:2. The WHSV
is based upon the weight of the catalyst composition
WO 95/17361 PCT/US94/14168
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employed, i.e., the total weight of active catalyst (and
binder if present).
Preferred reaction conditions include a temperature
within the approximate range of from 100°C to 350°C, a
pressure of from 101 to 2533 kPa (1 to 25 atmospheres), a
WHSV of from 0.5 hr 1 to 5 hr 1 and an alkylatable aromatic
compound to alkylating agent mole ratio of from 0.5:1 to
5:1. When using naphthalene as the aromatic compound, the
pressure should preferably be maintained at a value of at
least 350 kPa gauge (50 psig) in order to prevent the
naphthalene from subliming into the overhead of the
alkylation reactor; the required pressure may be maintained
by inert gas pressurization, preferably with nitrogen. The
reactants can be in either the vapor phase or the liquid
phase and can be neat, i.e., free from intentional
admixture or dilution with other material, or they can be
brought into contact with the zeolite catalyst composition
with the aid of carrier gases or diluents such as, for
example, hydrogen or nitrogen. The alkylation can be
carried out as a batch-type reaction typically employing a
closed, pressurized, st~.rred reactor with an inert gas
blanketing system or in a semi-continuous or continuous
operation utilizing a fixed or moving bed catalyst system.
The presence of some water in the feed may improve
selectivity, e.g., operation with water addition to the
feed or hydration of the catalyst. In a fluid bed reactor
operating with 0.75 wt % water in the reaction mixture is
preferred.
The products comprising alkylated aromatics are
characterized by exceptional oxidative and thermal
stability. They may be separated from the reaction mixture
by stripping off unreacted alkylating agent and naphthalene
compound in the conventional manner. It has also been
found that the stability of the alkylated product may be .
improved by filtration over activated charcoal and by
alkali treatment to remove impurities, especially acidic
CA 02174512 2005-02-18
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by-products formed by oxidation during the course of the
reaction. The alkali treatment is preferably carried out
by filtration over a solid alkali material, preferably
calcium carbonate (lime). In a typical product work-up, it
has been found, for example, that the RBOT (Rotating Bomb
Oxidation Test) stability can be increased from a value of
184 minutes for an unstrapped product (C14-aikyl-
naphthalene) to 29o minutes if the unreacted materials are
removed by stripping and to 35o minutes if the stripped
product is filtered over lime (CaC03).
~i~l~...~
A commercially available catalyst containing 40 wt.%
USY (knit Cell Size = 24.45 A (244.5 nm)) in a clay and
silica sol matrix was amaaonium exchanged at room
temperature by slurrying the catalyst with 5 vol/vol of 1 N
NH,NO, for one hour. The catalyst was washed with water and
then reexchanged and washed using the same procedure. This
catalyst was then calcined for 5 hours in flowing air at a
series of temperatures ranging from 350'C to 538'C to
2o produce catalysts containing varying amounts of amononia.
The relative amounts of cation exchange sites in the
ammonium and protonic form are shown below:
Catalyst Calcination . NH,' Canc. H' Conc.
ID Temperature, 'C (meq/g) (meq/g)
A None 1.09 -0
8 350 0.85 0.24
C 375 0.64 0.45
D 400 0.59 0.50
8 425 0.54 0.55
F 450 0.34 0.75
G 538 -O- 1.09
The total ion exchange capacity of the catalyst as
determined by temperature programmed ammonia desorption
(Chester and Kerr method) is i.09 meq/g.
WO 95/17361 PCT/US94/14168
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EXAMPLE 2
In a series of six experiments, five parts of each of
the catalysts of Example 1 were combined with ninety-five
parts of naphthalene and 1-hexadecene in a 1:1.2 molar
ratio in a stirred vessel. The contents of the vessel were
then heated to 200°C and held at this temperature for four
hours. The contents of the vessel were analyzed using gas
chromatography to determine the amounts of unreacted
naphthalene, olefin, monoalkylate and dialkylate. The
results are summarized below:
Catalyst Naphthalene Hexadecene Monoalkylate Dialkylate
ID (wt.%) (wt.%) (wt.%) (wt.%)
A 32.3 67.7 0 0
B 20.3 42.6 37.0 0
C 15.5 35.7 48.3 0.5
D 6.3 19.2 72.9 1.6
E 13.5 30.1 55.4 1.0
F 12.2 29.6 56.6 1.6
G 12.9 27.7 59.1 0.3
EXAMPLE 3
A commercially available USY with the properties shown
below was combined with kaolin clay and a colloidal silica
(Nalco) and spray dried at a temperature of 177°C (350°F)
to produce a fluid catalyst containing 40 wt.% USY.
UC Lattice Parameter, A 24.29
Surface Area, m2/g 650
Sodium, ppm 445
Si02, wt. % 85. 8
A1203 , wt . % 10 . 8
Si02/A1203 (molar) 13.8
Ash at 1000°C gg.7
Real Density, g/ml 2.384
Sorption Capacities"
n-CB (p = 40 torr) 21.1
Cy-C6 (p = 40 torr) 19.8
H20 (p = 12 torr) 10.6
Surface area measured at P/Po = 0.03
WO 95/17361 PCT/US94/14168
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" Sorption Capacities are shown as wt ratios x 100
(= wt of sorbate x 100/wt of sorbate free zeolite)
This catalyst was ion exchanged with ammonium nitrate
using the procedure of Example 1 then calcined at 400°C in
flowing air for five hours to produce Catalyst H. Another
catalyst, Catalyst I, was prepared from the same base
ammonium exchanged material by calcining at 538°C in
flowing air for five hours.
The ammonia content and water content of these
catalysts were analyzed by TPAD and by determination of
loss on ignition at 700°C. The results are summarized
below:
Catalyst Calcination NHs+ Conc. H+ Conc. H20 Conc.
ID Temperature, °C (meq/g) (meq/g) (wt.%)
H 400 0.04 0.06 2.0
I 538 -0- 0.10 0.1
E~A~iPLE 4
Five parts of each of the catalysts of Example 3 were
combined with ninety-five parts of naphthalene and 1-
hexadecene in a 1:1.2 molar ratio in a stirred vessel. The
contents of the vessel were then heated to 200°C and held
at this temperature for four hours. The contents of the
vessel were analyzed using gas chromatography to determine
the amounts of unreacted naphthalene, olefin, monoalkylate
and dialkylate.
The results are summarized below:
Catalyst Naphthalene Hexadecene Monoalkylate Dialkylate
ID (wt.%) (wt.%) (wt.%) (wt.%)
H 3.1 8.3 79.7 8.9
I 4.9 5.9 63.0 26.2
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EZ111IpLE 5
Five parts of Catalyst J, a commercially available
rare earth containing USY (REUSY) catalyst having the
properties shown below were combined with ninety-five parts
of naphthalene and 1-hexadecene in a 1:1.2 molar ratio in a
stirred vessel.
~pertfes i,~ the Catalyst Used in This Exayle
RB,sO, content, wt. % 1. 0
Unit Cell Lattice Parameter, A (nm) 24.57 (245.7)
Ammonia Content, meq/g 0.5s
Ash, wt.% (at 700'C) 89.5
The contents of the vessel were then heated to 200'C
and held at this temperature for four hours. The contents
of the vessel were analyzed using gas chromatography to
15; determine the amounts of unreacted naphthalene, olefin,
monoaikylate and dialkylate. The results are summarised
below:
Catalyst Naphthalene Hexadecene Monoslkylate Dialkylate
ID (wt.%) (wt.%) (wt.%) (wt.%)
J 2.5 13.6 82.1 1.8
Five parts of Catalyst K, a commercially available
rare earth containing USY (Ri~USY) catalyst having the
properties shown below were combined with ninety-five parts
of naphthalene and 1-hexadecene in a 1:1.2 molar ratio in a
stirred vessel.
Properties of the Catalyst Used in This Example
RE=O~ content, wt. % 3. 0
Unit Cell Lattice Parameter, nm(A) 245.7(24.57)
Ammonia Content, meq/g 0.50
Ash, wt.% (at 700'C) 80
W0 95/17361 PCT/US94/14168
-'r-.
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The contents of the vessel were then heated to 200°C
and held at this temperature for four hours. The contents
of the vessel were analyzed using gas chromatography to
determine the amounts of unreacted naphthalene, olefin,
monoalkylate and dialkylate. The results are summarized
below:
Catalyst Naphthalene Hexadecene Monoalkylate Dialkylate
ID (wt.%) (wt.%) (wt.%)
K 24.3 50.2 25.0 0.5
Comparison of the results of Examples 5 and 6 show
that the rare earth content of the catalysts can affect
yields and that the lower rare earth concentration (i.e., 1
wt.%) is preferred. The rare earth content of the
preferred catalyst (Example 5) would correspond to less
than 15% of the total number of exchangeable sites. This
demonstrates the importance of partial Rare Earth exchange.
While we do not know exactly why our catalyst works so
much better than the prior art catalyst with more RE, we
believe the difference may be due to the fate of RE. We
believe that the RE in our new catalyst, e.g., the USY with
1 wt ~ RE, is in the sodalite cages, not in the supercage.
The '563 patent was directed to bulky cations in the
supercage. When our low RE catalyst is calcined, the RE
goes into the sodalite cage. Preferably most of the rare
earths are in the supercage, and ideally essentially all of
the rare earths are in the supercage.
Commercially partial exchange is easy to achieve, a
solution with the desired amount of RE may be simply
sprayed on the zeolite or the catalyst in the desired
amount.
Results may be further improved by ammonium exchange
followed by calcination to convert no more than about half
of the ammonium form to the protonic form. It is also
beneficial to have some water present, but the amount of
WO 95/17361 . PCT/US94/14168
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water found in most commercial grade naphthalene supplies
(typically 0.75 wt %) is enough.
