Molecular sieve abstract
The selective isopropylation of a naphthyl compound to diisopropylnaphthalene
enhanced in the 26-diisopropylnaphthalene isomer is obtained in
the presence of an acidic crystalline molecular sieve catalyst having
twelve membered oxygen rings. The catalyst pore aperture dimension
ranges from 5.5 .ANG. to 7.0 .ANG.. The use of these shape selective
catalysts results in a diisopropylnaphthalene stream which is enhanced
in .beta. isomers and enhanced in the desired 26-diisopropylnaphthalene
isomer. A particularly preferred catalyst is synthetic Mordenite.
Specific catalyst modifications are also described to improve selectivity
to the desired 26-diisopropylnaphthalene isomer.
Molecular sieve claims
What is claimed is:
1. A process for obtaining diisopropylnaphthalene enriched in 26-diisopropylnaphthalene
which process comprises the steps of:
(a) providing a naphthyl compound selected from the group comprising
naphthalene, monoisopropylnaphthalene and mixtures thereof, to an
alkylation reactor;
(b) providing a catalyst comprising an acidic crystalline molecular
sieve having twelve membered oxygen rings and pore aperture widths
between 5.5 .ANG. and 7.0 .ANG.; and,
(c) reacting said naphthyl compound with propylene in said alkylation
reactor in the presence of said catalyst under conditions sufficient
to convert said naphthyl compound and propylene to diisopropylnaphthalene
to obtain a nonequilibrium distribution of alkylation reaction products
enriched in 26-diispropylnaphthalene.
2. The process of claim 1 wherein said diisopropylnaphthalene comprises
greater than 39 mole percent of 26-diisopropylnaphthalene.
3. The process of claim 1 wherein said diisopropylnaphthalene comprises
26-diisopropylnaphthalene and 27-diisopropylnaphthalene in a mole
ratio greater than 1.0.
4. The process of claim 1 wherein said diisopropylnaphthalene comprises
26-diisopropylnaphthalene and 27-diisopropylnaphthalene in a mole
ratio greater than 1.2.
5. The process of claim 1 further comprising recovering substantially
pure 26-diisopropylnaphthalene from said diisopropylnaphthalene.
6. The process of claim 1 wherein said catalyst is selected from
the group consisting of MeAPSO-46 Offretite, ZSM-12 and Synthetic
Mordenite.
7. The process of claim 6 wherein said acidic crystalline molecular
sieve is synthetic Mordenite.
8. The Process of claim 6 wherein said acidic crystalline molecular
sieve is ZSM-12.
9. The process of claim 6 wherein said acidic crystalline molecular
sieve is Offretite.
10. The process of claim 6 wherein said acidic crystalline molecular
sieve is MeAPSO-46.
11. The process of claim 6 wherein said catalyst is dealuminated
to obtain Si/Al between 5 and 100.
12. The process of claim 11 wherein said catalyst is calcined at
a temperature between 400.degree. C. and 1000.degree. C.
13. The process of claim 12 wherein acidic sites on the external
surface of said catalyst are deactivated.
14. The process of claim 6 wherein acidic sites on the external
surface of said catalyst are deactivated.
15. The process of claim 14 wherein said catalyst is dealuminated
to obtain Si/Al between 5 and 100.
16. The process of claim 14 wherein said catalyst is calcined at
a temperature between 400.degree. C. and 1000.degree. C.
17. The process of claim 14 wherein the acidic sites on the external
surface of said catalyst are deactivated by contacting the catalyst
with a deactivating reagent selected from the group consisting of
the halogen, hydridic and organic derivatives of Groups IIIA, IVA,
IVB, and VA.
18. The process of claim 14 wherein the acidic sites on the external
surface of said catalyst are deactivated by a process comprising
the steps of:
(a) filling the intracrystalline free pore volume of said catalyst
with a hydrocarbon to obtain an internally protected catalyst;
(b) treating said internally protected catalyst with an aqueous
acid or complexing agent which is insoluble in the hydrocarbon contained
within the intracrystalline pores; and,
(c) removing said hydrocarbon to recover said catalyst.
19. A process for obtaining diisopropylnaphthalene enriched in
26-diisopropylnaphthalene, which process comprises the steps of:
(a) providing a naphthyl compound selected from the group comprising
naphthalene, monoisopropylnaphthalene and mixtures thereof, and
propylene to an alkylation reactor;
(b) providing a catalyst to said alkylation reactor, said catalyst
prepared from an acidic crystalline molecular sieve having twelve
membered oxygen rings and pore aperture dimensions greater than
7.0 .ANG. by treatment of said crystalline molecular sieve to reduce
said pore aperture dimensions and wherein said catalyst provides
diisopropylnaphthalene enriched in 26-diisopropylnaphthalene according
to said process; and,
(c) reacting said naphthyl compound with propylene in said alkylation
reactor in the presence of said catalyst under conditions sufficient
to convert said naphthyl compound and propylene to diisopropylnaphthalene
to obtain a nonequilibrium distribution of alkylation reaction products
enriched in 26-diisopropylnaphthalene.
20. The process of claim 19 where said acidic crystalline molecular
sieve is selected from the group consisting of Zeolite L, Zeolite
Beta, faujasite, and SAPO-5.
21. The process of claim 19 wherein said diisopropylnaphthalene
comprises greater than 39 mole percent of 26-diisopropylnaphthalene.
22. The process of claim 19 wherein said diisopropylnaphthalene
comprises 26-diisopropylnaphthalene and 27-diisopropylnaphthalene
in a mole ratio greater than 1.0.
23. The process of claim 19 wherein said diisopropylnaphthalene
comprises 26-diisopropylnaphthalene and 27-diisopropylnaphthalene
in a mole ratio greater than 1.2.
24. The process of claim 19 further comprising recovering substantially
pure 26-diisopropylnaphthalene from said diisopropylnaphthalene.
25. The process of claim 19 wherein said treatment comprises deactivating
acidic sites on the internal surface of said catalyst with a reagent
selected from the group consisting of the halogen, hydridic and
organic derivatives of Groups IIIA, IVA, IVB, and VA.
26. The process of claim 20 wherein said catalyst is modified to
obtain Si/Al between 3 and 100.
27. The process of claim 26 wherein said catalyst is calcined at
a temperature between 400.degree. C. and 1000.degree. C.
28. The process of claim 27 wherein acidic sites on the external
surface of said catalyst are deactivated.
29. The process of claim 20 wherein acidic sites on the external
surface of said catalyst are deactivated.
30. The process of claim 29 wherein said catalyst is modified to
obtain Si/Al between 3 and 100.
31. The process of claim 29 wherein said catalyst is calcined at
a temperature between 400.degree. C. and 1000.degree. C.
32. The process of claim 29 wherein the acidic sites on the external
surface of said catalyst are deactivated by contacting said catalyst
with a deactivating reagent selected from the group consisting of
the halogen, hydridic and organic derivatives of Groups IIIA, IVA,
IVB, and VA.
33. The process of claim 29 wherein the acidic sites on the external
surface of said catalyst are deactivated by a process comprising
the steps of:
(a) filling the intracrystalline free pore volume of said catalyst
with a hydrocarbon to obtain an internally protected catalyst;
(b) treating said internally protected catalyst with an aqueous
acid or complexing agent which is insoluble in the hydrocarbon contained
within the intracrystalline pores; and,
(c) removing said hydrocarbon to recover said catalyst.
34. A process of alkylating naphthalene to obtain a mixture of
substituted aromatic compounds enriched in 26-diisopropylnaphthalene,
comprising the steps of contacting naphthalene with propylene in
the presence of a catalyst under conditions sufficient to convert
said naphthalene and propylene to diisopropylnaphthalene, wherein
said catalyst comprises synthetic mordenite.
35. The process of claim 34 wherein said catalyst is dealuminated
to obtain a Si/Al ratio between 5 and 100.
Molecular sieve description
TECHNICAL FIELD
This invention relates generally to isopropylation of naphthyl
compounds to obtain diisopropylnaphthalenes, and more specifically
this invention relates to the use of shape selective catalysts whose
pores are configured to selectively obtain the desired 26-diisopropylnaphthalene
isomer while minimizing the production of undesirable diisopropylnaphthalene
isomers, triisopropylnaphthalenes and tetraisopropylnaphthalenes.
BACKGROUND OF THE INVENTION
A new class of thermoplastic polymers, known as thermotropic liquid
crystal polymers ("LCP"), has recently been introduced
to the marketplace. These polymers combine the advantageous feature
of moldability with multidirectional mechanical strength superior
to other thermoplastics formerly available. Generally, these new
LCP materials are polyesters made up of planar, linear disubstituted
aromatics. Examples of some LCPs currently in use are p-hydroxybenzoic
acid, 5 p-hydroquinone, 44'-dihydroxybiphenyl and 2-hydroxy, 6-napthenoic
acid.
Other LCPs would appear commercially attractive if either 26-dihydroxynaphthalene
or 26-dicarboxynaphthalene were readily available. Unfortunately,
these materials are not commercially produced because cheap, readily
available feed stocks do not exist. A viable feed stock, which is
convertible into either the dihydroxy or dicarboxy monomers, based
upon known technology, is 26-diisopropylnaphthalene.
Before proceeding with any description of the isopropylation reaction
system, it is important to first review the nomenclature and numbering
scheme for the various substituted naphthalene isomers. Equation
1 shows the positional reference numbers. Non-hydrogen bearing carbons
are unnumbered because no substitution takes place in these positions.
EQUATION 1
There are two possible isomers which are formed in the monoisopropylation
of naphthalene. Substitution occurs only in the 1 and 2 positions
and is respectively denoted .alpha. and .beta.. Any monoisopropyl
substitution which takes place in positions 3 through 8 is identical
to the .alpha. and .beta. positions due to their interrelationship
in symmetry.
Multiple naphthalene isopropylation is usually denoted by the position
number. Some literature references follow the numbering convention
just described, while other references discuss the isomers in terms
of the .alpha. and .beta. terminology. Thus, the 26 isomer is the
double .beta. isomer.
Table 1 describes the statistical distribution of the various diisopropylates
using these designations, and assuming that no ortho diisopropylation
occurs, e.g., 12-, 23- and 18-diisopopropylnaphthalene. In Table
1 it is shown that there are seven disubstituted isomers, of which
two of them, (26- and 27-) are the double .beta. product.
TABLE 1 ______________________________________ NORMALIZED TYPE
ISOMER EOUIVALENTS FREQUENCY ______________________________________
.alpha.,.beta. 16 16 = 47 = 25 = 38 2 17 17 = 46 = 35 =
28 2 13 13 = 24 = 57 = 68 2 .alpha.,.alpha. 14 14 = 58
1 15 15 = 48 1 .beta.,.beta. 26 26 = 37 1 27 27 = 36 1
______________________________________
In any manufacture of diisopropylnaphthalene, it is clear that
some monoisopropyl- and triisopropylproducts and a mix of diisopropyl
isomers will also be obtained. In any crude diisopropylnaphthalene
product which is not particularly enriched in one diisopropylnaphthalene
isomer, isomer separation by thermal distillation is very inefficient
and difficult because the boiling points of 26-diisopropylnaphthalene
and 27-diisopropylnaphthalene are very close. Similarly, diisopropylnaphthalene
isomer separation by fractional crystallization using melting points
is inefficient and suffers from yield problems because of the loss
of the desired product in the mother liquor, and because of large
recycle streams.
The present invention provides a process for reacting a naphthyl
compound selected from the group comprising naphthalene, monoisopropylnaphthalene
and mixtures thereof, with a propy containing moiety, preferably
propylene, to obtain diisopropylnaphthalene enriched in 26-diisopropylnaphthalene,
above its expected equilibrium proportion. The shape selective catalyst
for this process comprises an acidic crystalline molecular sieve
having twelve-membered oxygen rings and pore apertures with dimensions
between 5.5 .ANG. and 7.0 .ANG.. Preferably, the 26-diisopropylnaphthalene
isomer comprises greater than 39 mole percent of the total diisopropylnaphthalenes
obtained. It is also preferred that the ratio of 26-diisopropylnaphthalene
to 27-diisopropylnaphthalene in the reaction product is greater
than 1.0 preferably greater than 1.2.
Therefore, it is an object of this invention to provide an efficient
and selective process for the isopropylation of naphthyl compounds
to obtain a higher yield of 26 diisopropylnaphthalene in relation
to 27-diisopropylnaphthalene, while simultaneously minimizing the
formation of unwanted byproducts.
It is a further object of this invention to provide shape selective
catalysts whose pore size and configuration are designed to maximize
the yield of the desired 26-diisopropylnaphthalene isomer relative
to the sum of the other diisopropylnaphthalenes, while minimizing
formation of higher substituted species.
It is still a further object of this invention to provide a process
to selectively obtain enhanced levels of 26-diisopropylnaphthalene
using a naphthyl product feed stream comprising naphthalene, monoisopropylnaphthalene,
and mixtures thereof.
These and further objects of the invention will become apparent
to those of ordinary skill in the art with reference to the following
description.
SUMMARY OF THE INVENTION
A process for obtaining diisopropylnaphthalene enriched in 26-diisopropylnaphthalene
is described which comprises the steps of providing a naphthyl compound
selected from the group comprising naphthalene, monoisopropylnaphthalene
and mixtures thereof, and a propyl containing moiety, preferably
propylene, to an alkylation reactor. A catalyst comprising an acidic
crystalline molecular sieve having twelve membered oxygen rings
and pore aperture dimensions between 5.5 .ANG. and 7.0 .ANG.. The
naphthyl compound is reacted with a propyl containing moiety such
as propylchloride, propylalcohol, or preferably propylene, in the
presence of the provided catalyst under conditions sufficient to
convert said naphthyl compound and propyl containing moiety to diisopropylnaphthalene.
In a preferred embodiment, 26-diisopropylnaphthalene comprises
at least 39 mole percent of the diisopropylnaphthalenes obtained
according to the process. In another preferred embodiment, the ratio
of 26-diisopropylnaphthalene to 27-diisopropylnaphthalene which
is obtained according to the process is greater than 1.0 preferably
greater than 1.2. Crystalline molecular sieve catalysts are selected
from the group comprising MeAPSO-46 Offretite, ZSM-12 and synthetic
Mordenite. Preferred catalysts are synthetic Mordenite and ZSM-12
with pore aperture dimensions of 6.5 .ANG., 7.0 .ANG. and 5.5 .ANG.,
5.7 .ANG. and 6.2 .ANG., respectively. These preferred catalysts
can be used in the isopropylation reaction without any pretreatment
to modify the pore aperture dimensions. Synthetic Mordenite is particularly
preferred. Other useful catalysts may be obtained by treatment of
an acidic crystalline molecular sieve having pore aperture dimensions
greater than 7.0 .ANG. selected from the group consisting of Zeolite
L, Zeolite Beta, faujasite and SAPO-5 to reduce the dimensions
of the pore aperture.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a stepwise description of the isopropylation of naphthalene
to the mono-, di-, tri-and higher polyalkylnaphthalenes.
DETAILED DESCRIPTION OF THE INVENTION
Before proceeding with a detailed description of the present invention,
it is first necessary to define a series of terms which relate to
the physical characteristics and configuration of the acidic crystalline
molecular sieve catalysts used in the present invention. Much of
this terminology arises out of the literature concerning those crystalline
aluminosilicate polymers known as zeolites. These acidic crystalline
molecular sieve structures are obtained by the building of a three
dimensional network of AlO.sub.4 and SiO.sub.4 tetrahedra linked
by the sharing of oxygen atoms. The framework thus obtained contains
pores, channels and cages or interconnected voids. As trivalent
aluminum ions replace tetravalent silicon ions at lattice positions,
the network bears a net negative charge, which must be compensated
for by counterions (cations). These cations are mobile and may occupy
various exchange sites depending on their radius, charge or degree
of hydration, for example. They can also be replaced, to various
degrees, by exchange with other cations. Because of the need to
maintain electrical neutrality, there is a direct 1:1 relationship
between the aluminum content of the framework and the number of
positive charges provided by the exchange cations. When the exchange
cations are protons, the molecular sieve is acidic. The acidity
of the sieve is therefore determined by the amount of proton exchanged
for other cations with respect to the amount of aluminum.
Crystalline molecular sieve structures are often defined in terms
of the number of their tetrahedral units (T atoms). For example,
in sodalite the silica and alumina tetrahedra are linked together
to form a cubooctahedron, an octahedron truncated perpendicularly
to all C.sub.4 - axes. The sodalite unit is built from four and
six membered oxygen rings. The mordenite framework is built from
chains of tetrahedra cross linked by oxygen bridges. Each Al or
Si tetrahedron is, in addition, part of a five-membered oxygen ring.
The chains are then interconnected to obtain the mordenite structure.
Mordenite is defined as having twelve-membered oxygen rings. The
mordenite pore structure consists of elliptical and noninterconnected
channels parallel to the c axis of the orthorhombic structure with
pore aperture dimensions of 6.5 .ANG. and 7.0 .ANG.. A more complete
characterization of the zeolites can be found in E.G. Derouane,
"Diffusion and Shape-Selective Catalysis in Zeolites,"
Intercalation Chemistry, Ed. by M. Stanley Whittingham (Academic
Press, 1982).
ZSM-12 belongs structurally to the Modenite group of zeolites.
The pore structure of ZSM-12 consists of linear, non-interpenetrating
channels which are formed by twelve-membered rings and possess pore
aperture dimensions of 5.5 .ANG., 5.7 .ANG. and 6.2 .ANG.. See Jacobs,
P.A. et al., "Synthesis of High Silica Aluminosilicate Zeoliters,"
Studies in Surface Science and Catalysis #33 Elsevier, 1987 page
301. See also. Meier, W.M., "Atlas of Zeolite Structure Types"
2nd ed., Structure Commission of the International Zeolite Association,
1987). Offretite is a 12-oxygen ring zeolite with a pore aperture
dimension of 6.7 .ANG. and 6.8 .ANG. in which the structure also
contains a 14-hedron cage.
The basic building block for one series of catalysts useful in
the present invention is AlPO.sub.4. There are three recognized
generic substitutions: metals (Me), elements (El) isomorphically
substituted for either aluminum or phosphorous (respectively) in
the framework, and SiO.sub.4 groups (SAPO) incorporated into the
structure of the molecular sieve. Example of Me substitution for
aluminum are Mg, Fe, Mn, Co and Zn. Example of El substitutions
for phosphorous are As, B, Be, Ga, Ge, Li and Ti.
In the present invention, silica containing structures of the 46
type provide the correct type and strength of acid sites to allow
for selective alkylation of naphthalene.
MeAPSO-46 is also a 12-oxygen ring zeolite with a pore aperture
dimension of 6.2 .ANG. and 6.4 .ANG..
According to the present invention, acidic crystalline molecular
sieve catalysts containing twelve membered oxygen rings are useful
in the isopropylation reaction of naphthyl compounds.
Pore structure (dimensions and network) varies greatly among zeolites.
Without modifications of the zeolite structure, the lowest pore
aperture dimension is about 2.6 .ANG. and the highest is 7.4 .ANG..
Pores may lead to linear, parallel, or interconnected channels or
may give access to larger intracrystalline cavities, sometimes referred
to as cages. For all zeolites, the pore opening is determined by
the free aperture of the oxygen ring that limits the pore aperture.
The free diameter values given in the channel description and on
the ring drawings (not shown here) are based upon the atomic coordinates
of the type species in the hydrated state and an oxygen radius of
1.35 .ANG., as determined from x-ray crystallographic data. Both
minimum and maximum values are given for noncircular apertures.
In some instances, the corresponding interatomic distance vectors
are only approximately coplanar; in other cases the plane of the
ring is not normal to the direction of the channel. Close inspection
of the framework and ring drawings should provide qualitative evidence
of these factors. Some ring openings are defined by a very complex
arrangement of oxygen atoms. We have included references to publications
which contain extensive drawings and characterization data. The
relevant portions of those references are incorporated herein. It
should be noted that crystallographic free diameters may depend
upon the hydration state of the zeolite particularly for the more
flexible frameworks. It should also be borne in mind that effective
free diameters can be temperature dependent. Maximum values for
the four-, six-, eight-, ten-, and twelve-membered oxygen rings
have been calculated to be 2.6 .ANG., 3.6 .ANG., 4.2 .ANG., 6.3
.ANG. and 7.4 .ANG., respectively.
As used throughout the instant specification, the term "pore
aperture" is intended to refer to both the pore mouth at the
external surface of the crystalline structure, and to the intracrystalline
channel, exclusive of cages. When a crystalline molecular sieve
is hereinafter characterized by a "pore aperture dimension,"
we intend to adopt the geometric dimensional analysis defined as
"crystallographic free diameter of channels" in Meier,
W. M., Olson, D. H., Atlas of Zeolite Structure Types, (Butterworth's,
1987 2d Rev. Ed.) The term "dimension" is preferred over
"diameter") because the latter term implies a circular
opening, which is not always accurate in crystalline molecular sieves.
Shape selective reactions occur when the zeolite framework and
its pore structure allow substrate molecules of a given size and
shape to reach active sites located in the intracrystalline free
space, and allow product molecules of a given size and shape to
diffuse out of the intracrystalline free space. It is therefore
important to characterize accurately the pore structure that is
encountered in the various crystalline molecular sieve frameworks.
The nature of interconnecting channels in acidic crystalline molecular
sieve catalysts is important in determining their physical and chemical
properties. Three types of channel systems have been defined: a
one dimensional system, such as found in analcime, does not permit
intersection of the channels; two dimensional systems can be found
in certain zeolites; and, three dimensional systems have intersecting
channels. There are two types of three dimensional channels; in
one, the channels are equidimensional, i.e., the pore aperture dimension
of all the channels is equal, regardless of the direction. The second
type consists of three-dimensional, intersecting channels, but the
channels are not equidimensional; the pore aperture dimension depends
upon the crystallographic direction. See Donald W. Breck, "Zeolite
Molecular Sieves: Structure, Chemistry, and Use," at pp. 59-60
(John Wiley & Sons, 1974).
Crystalline molecular sieves with three-dimensional channels can
also contain larger intracrystalline cavities known as cages. These
cavities may accommodate substrate molecules and, in principal,
play a role in shape selective reactions. For example, sodalite
has sodalite cages, as does faujasite. Faujasite is a 12-oxygen
ring zeolite with a pore aperture dimension of 7.4 .ANG. and also
has supercages (26-hedron) with a cage dimension of 11.8 .ANG..
Wide Type A Zeolite has cages having free dimension of 11.4 .ANG..
See E.G. Derouane, "Diffusion and Shape-Selective Catalysis
in Zeolites," Intercalation Chemistry, at pp. 112-114 Ed.
by M. Stanley Whittingham (Academic Press, 1982). See also Thaddeus
E. Whyte et al., "Catalytic Materials: Relationship between
Structure and Reactivity," at pp. 65-167 ACS Symposium Series
248 (American Chemical Society, 1984).
Having defined some of the terms used to describe the crystalline
molecular sieve catalyst component, it is time to turn to the organic
substrate for the alkylation reaction system of the instant invention.
The substrate is a naphthyl compound selected from the group comprising
naphthalene, monoisopropylnaphthalene and mixtures thereof. The
isopropylation of naphthalene is known to occur in stepwise manner
beginning with monoalkylates, dialkylates, trialkylates, etc. The
exact scheme of this progression is set forth more completely in
FIG. 1 which also reveals the interconnectivity of the various alkylated
species. Of particular interest to the present invention are the
different routes and intermediates to the 26-diisopropylnaphthalene
isomer. This isomer can be formed directly by the .beta. isopropylation
of the .beta.-mono-alkylate or by isomerization of .alpha.,.alpha.
and .alpha.,.beta. dialkylates.
The equilibrium data for the monoisopropylation of naphthalene
is important since the 26 isomer is the .beta., .beta. product
and because the .beta. isomer is the preferred thermodynamic species
for the monoalkylate. It has been shown by Olah (U.S. Pat. No. 4288646)
that the concentration of the .beta. product increases with the
steric bulk of the substituent for monoalkylates of naphthalene.
See Table 2. This is predicted to hold true for dialkylates as well.
TABLE 2 ______________________________________ Equilibrium Composition
of Mono-Alkylnaphthalene Alkyl .alpha., % .beta., % ______________________________________
Methyl 24.5 75.5 Ethyl 9.5 90.5 Isopropyl 1.5 98.5 tert-Butyl 0
100 ______________________________________
In the prior art, a considerable number of catalysts have been
shown to be effective for the monoisopropylation of naphthalene.
(See Table 3.) An equilibrium distribution of products for the monoalkylation
has been obtained over zeolite catalysts. (Kemme, U.S. Pat. No.
4026959.) It is shown that the concentration of the .beta. isomer
is a function of the nature of the alkylation catalyst and the reaction
operating conditions. It has also been shown that the isomerization
of .alpha. to .beta. was dependent upon temperature, catalyst charge,
time and substrate water content.
TABLE 3 ______________________________________ Monoisopropylation
of Naphthalene with Propylene over Various Catalysts Product Reaction
.alpha. + .beta. Composition % Catalyst Solvent Temp .degree.C.
Yield .alpha. .beta. ______________________________________ Nafion-H
-- 220 37 10 90 HF heptane 78 91.2 3 97 H.sub.3 PO.sub.4 / -- 200
36 73 27 Kieselguhr H.sub.2 SO.sub.4 -- 10 90 54 36 AlCl.sub.3 --
100 -- 4 96 RE-Y -- 218 93 -- -- BF.sub.3.Et.sub.2 O .about.10 69
70 30 ______________________________________
Few literature references, however, describe catalysts or conditions
for the direct preparation of 26 diisopropylnaphthalene. Teijin
describes the preparation of the di-.beta. product using an AlCl.sub.3
catalyst by direct alkylation (Japanese Patent No. J75011379-B)
or via transalkylation (Japanese Patent No. J75010586-B.) Haseltine
(U.S. Pat. No. 4064068) teaches the equilibrium product composition
for about 2:1 propylene/ naphthalene reaction at 120.degree. C.
over excess AlCl.sub.3. See Table 4.
TABLE 4 ______________________________________ Weight and Mole
% Products for Diisopropylated Naphthalene Alkylate: Naphtha- Yield
lene Mono Di Tri Other Total ______________________________________
Yield, 7 26 53 12 2 88 Weight % Yield 11 30 49 10 1 -- Mole % Yield,
Mole % -- 33 54 11 1 -- Isopropy- lated Product Composition ______________________________________
For the production of 26-diisopropylnaphthalene, there are two
important measures of the distribution of diisopropylated species
obtained. One is the % of 26-diisopropylated naphthalene among
all diisopropylated naphthalenes. The other is the ratio of the
26- and 27- isomers. The values of these measures in an equilibrium
distribution of diisopropylated naphthalene species have been determined
using silica-alumina, which is a non-shape selective catalyst (see
Example 1). A distribution at equilibrium contains 39% 26-diisopropylnaphthalene
among all diisopropylnaphthalenes and a 26-/27- isomer ratio of
1.0.
With non-shape selective catalysts, it is believed that the highest
% of 26-diisopropylnaphthalene among all diisopropylnaphthalenes
is at equilibrium, 39%. Therefore, in order to achieve selectivities
of the desired 26-diisopropylnaphthalene higher than the equilibrium
yield, it was recognized that it is first necessary to increase
the yield of the .beta. monoisopropylnaphthalene isomer generally,
and then to kinetically increase the production of the 26 isomer
relative to the 27 isomer.
According to the present invention, the use of a shape selective
acidic crystalline molecular sieve catalyst provides a kinetic distribution
of diisopropylnaphthalenes substantially different from the equilibrium
distribution. Kinetically, the 26 isomer is more rapidly obtained
from the .beta. monoiisopropylnaphthalene precursor than the 27
isomer. Since the .beta. isomer is the precursor for the desired
26 isomer, an increase in the amount of .beta. isomer substrate
will ultimately improve both the yield and selectivity to the desired
26 isomer.
EXAMPLE 1
To determine the percent 26-isomer among all diisopropylnaphthalenes
and the 26-/27-isomer ratio in an equilibrium product distribution,
naphthalene was alkylated using a non-shape selective catalyst under
equilibrium conditions such that thermodynamic equilibration of
products was obtained.
90.0 grams naphthalene was alkylated using 10.0 grams SiO.sub.2
-Al.sub.2 O.sub.3 (Grace) under conditions where the naphthalene/catalyst
weight ratio was 9 and the propylene was fed from a heated reservoir
at a constant rate of 25 cc/min using a mass flow controller. The
temperature of the reaction was 275.degree. C.
TABLE 5 ______________________________________ Equilibrium Product
Distribution for Naphthalene Alkylation Using SiO.sub.2 -Al.sub.2
O.sub.3 Naphth. mol % mol % mol % 26/27 % 26 Conv. Mono Di Poly
Ratio In Di ______________________________________ 23.4 91.9 8.1
0.0 1.00 36.8 94.2 31.1 51.5 17.4 1.03 38.5 ______________________________________
The mole percents mono, di, and polyisopropylnaphthalenes obtained
at 94.2% conversion agree excellently with the data of Haseltine,
see Table 4. This demonstrates that the 26/27-isomer ratio and
the percent 26-isomer among all diisopropylnaphthalenes at this
conversion show the same equilibrium distribution (% 26 and 26/27-ratio)
among the diisopropylnaphthalenes at lower naphthalene conversion.
The present invention utilizes an acidic crystalline molecular
sieve catalyst which has twelve-membered oxygen rings and a pore
aperture dimension between 5.5 .ANG. and 7.0 .ANG.. According to
the present invention, a naphthyl compound selected from the group
comprising naphthalene, monoisopropylnaphthalene and mixtures thereof,
is fed to an alkylation reactor. The naphthyl compound is reacted
with a propyl containing moiety, preferably propylene, in the presence
of the acidic crystalline molecular sieve catalyst having twelve-membered
oxygen rings and a pore aperture width between 5.5 .ANG. and 7.0
.ANG., preferably between 6.5 .ANG. and 7.0 .ANG.. The alkylation
reaction is conducted at a propylene/naphthyl compound feed ratio
between 0.1 and 10 preferably between 1.0 and 2.0 and elevated
temperatures and pressures, generally between 100.degree. C. and
400.degree. C., preferably between 250.degree. C. and 350.degree.
C., and between 1 and 100 atmospheres, preferably 1 to 10 atmospheres.
These process conditions lead to a diisopropylnaphthalene product
which typically contains greater than 39 mole percent diisopropylnaphthalene
and a ratio of 26-diisopropylnaphthalene to 27-diisopropylnaphthalene
greater than 1.0. Under optimum catalyst selection and reaction
conditions, a ratio of 26-diisopropylnaphthalene to 27-diisopropylnaphthalene
greater than 1.2 can be achieved. In a particularly preferred embodiment,
the acidic crystalline molecular sieve catalyst is synthetic Mordenite.
Substantially pure 26-diisopropylnaphthalene can be recovered
from the diisopropylnaphthalene products in a multi-stage separation
scheme. In one embodiment, the diisopropylnaphthalene product is
first fractionally distilled to obtain a low boiling fraction which
contains unreacted naphthalene and monoisopropylnaphthalene, a middle
fraction containing the diisopropylnaphthalenes, and a high boiling
fraction containing triisopropylnaphthalene and tetraisopropylnaphthalenes.
26-diisopropylnaphthalene is obtained from the middle fraction
by cooling the liquid to a temperature between 0.degree. C. and
-20.degree. C. to fractionally crystallize the 26-isomer from the
other diisopropylnaphthalenes. The mother liquor from the crystallization
can be subjected to a second crystallization step, or it can then
be combined with the low boiling and high boiling fractions, and
subjected to transalkylation before recycle to the alkylation reactor,
along with fresh naphthalene.
In another embodiment, the recycle stream from the separations
section (fractional distillation and crystallization) is combined
with a fresh naphthalene feed stream in an equilibration reactor.
This recycle mixture containing naphthalene, monoisopropylnaphthalenes,
diisopropylnaphthalenes, and higher alkylates is brought to thermodynamic
equilibrium over a solid acid catalyst. The equilibrium mixture
contains .beta. monoisopropylnaphthalene as the predominant product.
The equilibrated feed, enriched in .beta. monoisopropylnaphthalene,
is then passed to the alkylation reactor where it is combined with
propylene at a mole ratio of about one to one.
The use of the term naphthyl compound throughout this specification
contemplates both of the above described process schemes, as well
as fresh naphthalene feed by itself.
While synthetic Mordenite has been described with reference to
a particularly preferred embodiment of the present invention, there
are other catalysts which can be used in the alkylation reaction
to achieve an alkylation product enriched in both total diisopropylnaphthalenes
and in the desired 26-diisopropylnaphthalene. When Mordenite is
used, only external surface acid site deactivation is required.
(See below). ZSM-12 can also be used without modification analagous
to Mordenite. Offretite and MeAPSO-46 also fall into the first class
of catalysts whose pore aperture dimensions are between 5.5 .ANG.
and 7.0 .ANG., prior to any modification to the pores.
However, other catalysts may also be considered which have aperture
dimensions in excess of 7.0 .ANG.. These other catalysts are obtained
by a combination of modifications of commercially available, acidic
crystalline molecular sieve products. Zeolite L, Zeolite Beta, faujasite
and SAPO-5 are twelve membered oxygen rings whose pore aperture
dimensions typically exceed 7.0 .ANG.. SAPO is an acronym for silicoaluminophosphate
molecular sieves, first reported in 1984. U.S. Pat. No. 4440871
to B. M. Lok et al. MeAPO is an acronym for metal aluminophosphate
molecular sieves reported in U.S. Pat. No. 4567029 to S. T. Wilson
et al. The numbers following the acronym are arbitrary and bear
no relationship to structural numbers used previously in the literature,
e.g. ZSM-5. For a more complete characterizations of each of the
catalyst members discussed above, please see Flanigen, E. M. et
al., Stud.Surf.Sci.Cat., 28 pp. 103-112. See also E. G. Derouane,
"Diffusion and Shape-Selective Catalysis in Zeolites,"
Intercalation Chemistry, at pp. 112-114 Ed. by M. Stanley Whittingham
(Academic Press, 1982). See also, S. Ernst, Zeolites, Vol. 7 p.
458 (1987) for a good discussion of ZSM-12.
The preferred Si/Al ratio in Zeolite L is 3.0. The structure of
Zeolite L consists of columns of symmetrical .epsilon.-D6R-.epsilon.
units crosslinked to others by single oxygen bridges; planar 12-membered
rings produce wide channels parallel to the c-axis. The pore aperture
of zeolite L determined by x-ray crystallography was found to be
7.1 .ANG.. A more detailed description of the structure of zeolite
L can be found in D. W. Breck, John Wiley & Sons, page 113
1974.
SAPO-5 is structurally analogous to AlPO.sub.4 -5. AlPO.sub.4 -5
is a 12-ring sieve with a pore aperture of 7.3 .ANG.. A more detailed
description of the structure can be found in J. M. Bennett et al.,
Intrazeolite Chemistry, ACS Symposium Series 218 American Chemical
Society, page 79 109 1983.
Before discussing any modifications to molecular sieves whose pore
aperture dimensions exceed 7.0 .ANG., it is first necessary to discuss
the concept of shape selective catalysts generally, and the basis
for choosing among the below-described modification procedures.
The use of shape selective catalysts to enhance the conversion
of substrate to the desired isomer involves the use of a catalyst
whose intracrystalline structure permits diffusion of the substrate
and the desired isomer under reaction conditions. According to the
present invention, certain catalyst modifications have been found
to provide a shape selective catalyst particularly beneficial to
the conversion of naphthalene and monoisopropylnaphthalene to the
desired 26-diisopropylnaphthalene product. Among these modifications
are dealumination, calcination, and external and internal surface
acid site modifications.
The preferred catalysts, Mordenite and ZSM-12 as well as Offretite
and faujasite, can be optimized to yield greater selectivities to
the desired 26-diisopropylnaphthalene without substantially altering
its pore aperture dimensions. One such modification to the preferred
catalysts is to dealuminate. Dealumination of acidic crystalline
molecular sieve materials can be achieved by exposing the solid
catalyst to mineral acids such as HCl. The desired degree of dealumination
will dictate the strength of acid used and the time during which
the crystalline structure is exposed to the acid. It is also common
to use a steam treatment, in combination with the acid leach, to
dealuminate zeolite materials. For additional methods of preparing
aluminum-deficient zeolites, see J. Scherzer, "The Preparation
and Characterization of Aluminum-Deficient Zeolites, "Thaddeus
E. Whyte et al., "Catalytic Materials: Relationship between
Structure and Reactivity," at pp. 156-160 ACS Symposium Series
248 (American Chemical Society, 1984). Dealumination according
to the instant invention is intended to achieve Si/Al ratio between
5 and 100 preferably between 5 and 50. Dealumination can also be
applied to the second class of molecular sieve materials whose pore
aperture dimensions exceed 7.0 .ANG..
A dealuminated crystalline molecular sieve can be calcined at temperatures
between 400.degree. C. and 1000.degree. C., preferably between 400.degree.
C. and 600.degree. C. Calcination serves to dehydrate or "heal"
Si-OH bonds or "nests" after dealumination. Healing these
nests provides for a more uniform pore structure within the crystalline
material, leading to structural stability and ultimately resulting
in improved selectivity.
The calcination conditions of a catalyst can critically effect
the catalytic activity. The selection of calcination gas, for example
oxygen or nitrogen, can effect catalyst species differently. In
general, calcination temperatures for crystalline molecular sieve
catalysts can vary from 300.degree. C. to 1000.degree. C. For a
Zeolite like Hydrogen Mordenite, the optimal temperature range was
found experimentally to lie between 400.degree. C. and 600.degree.
C., but preferentially at 500.degree. C. (Mathur, Kuldeep, Narain,
Ph.D. Thesis, University of Pittsburgh, 1977). In the case of H-Mordenite,
removal of extra and intra crystalline water can be accomplished
effectively in presence of an atmosphere of oxygen or nitrogen.
This, however, would not be true in the case of organic residues
present on the catalyst, as in a surface treated catalyst. In this
case, the calcination temperature and the calcination gas are both
important. In the presence of organic residues, preferably, a nitrogen
atmosphere is first used so that a minimal amount of water is obtained
when bringing the catalyst to calcination temperature. After a sufficient
time to carbonize the organic residue, the atmosphere is changed
to oxygen at a temperature sufficient to combust the carbonized
residue to CO.sub.2 while minimizing water formation.
Another catalyst treatment (without regard to the pore aperture
dimension of the starting material, thereby inclusive of both the
classes of catalysts discussed herein), according to the present
invention, involves catalyst external surface acid site removal
or blockage. The reason for external surface acid removal or blockage
is that inactivating the external surface of Zeolite catalyst will
increase its shape-selective character as otherwise, the external
surface acts as a non-shape selective catalyst. An additional reason
for external surface acid site blockage or removal relates to coking
on the catalyst surface. While benzene produces only a small amount
of coke on the catalyst surface because of the high stability of
the aromatic ring, unsaturated intermediates, such as cyclohexane,
cyclohexene and cyclohexadiene are able to condense on the acidic
function of the catalyst surface producing a substantial amount
of coke. See, Studies in Surface Science and Catalysis, 34 p. 143.
Coke will also be formed at the catalyst pore mouth over time. This
buildup will cause the pores to become less accessible to substrate
molecules, and eventually close the pores, rendering these channels
inactive.
When using catalysts obtained by the treatment of crystalline molecular
sieve, whose pore aperture dimensions are initially above 7.0 .ANG.,
internal acid site modification is used to reduce the pore aperture
dimension to an extent which shows an enhanced 26-diisopropylnaphthalene
concentration above its equilibrium value. Unfortunately, we have
not presently obtained physical characterization data for the pore
aperture dimensions of the modified species. Instead, catalysts
with reduced pore aperture dimensions are best described with reference
to their performance in the isopropylation reaction under consideration.
Those crystalline molecular sieves which have been adequately modified
by internal acid site treatment will perform in the selective isopropylation
of naphthalene to provide a diisopropylnaphthalene which contains
at least 39 mole percent of 26-diisopropylnaphthalene, and a 26-/27-diisopropylnaphthalene
mole ratio greater than 1.0.
Generally speaking, crystalline molecular sieves may be treated
to modify internal acid sites by contact with a deactivating reagent
selected from the group consisting of the halogen, hydridic and
organic derivatives of Groups IIIA, IVA, IVB and VA. Preferred embodiments
of the internal acid site deactivating reagents include B.sub.2
H.sub.6 SiH.sub.4 and PH.sub.3. For a more complete discussion
of the internal acid site modification techniques, see A. Thijs
et al., J. Chem. Soc. Faraday Trans., 79 2821 (1983). See also,
J. Philippaerts et al., "The Implantation of Boron-Nitrogen
Compounds in Mordenite LP and Their Influence on the Adsorption
Properties," Stud. Surf. Sci. Catal., 28 1986 pp. 305-310.
The relevant portions of both references being hereby incorporated
into this specification.
In addition to the use of the above described deactivating reagents,
which tend to be non-specific, there is an intermediate level of
crystalline molecular sieve modification which can be used to perform
"pore mouth engineering." These reagents provide an intermediate
level since they are not specific for external acid site, but are
not entirely non-specific, leading to substantial internal acid
site modification. In selecting an intermediate deactivating reagent,
the characteristics and pore aperture dimensions of the starting
crystalline molecular sieve must be matched against the molecular
dimensions of the deactivating reagent.
It has been shown that chemical vapor deposition of Si(OCH.sub.3).sub.4
on H-mordenite can be successfully used to control the intracrystalline
pore aperture without substantially affecting the catalyst's internal
surface acidic properties. Si(OCH.sub.3).sub.4 can be deposited
irreversibly on zeolite, without entering the intracrystalline pores.
See Niwa, M. et al., J. Chem.Soc., Faraday Trans., 1 1984 80
3135-3145; Niwa, M. et al., "Modification of H-Mordenite by
Vapour-phase Deposition Method," J. Chem.Soc.Commun.. 1982
pp. 819-20.
Similarly, chemical vapor deposition of deactivating metal chlorides
such as SiCl.sub.4 GeCl.sub.4 TiCl.sub.4 and SnCl.sub.4 can be
effective to modify pore mouth structures without inactivating internal
surface acid sites. These metal molecules, with a range of molecular
dimensions, can be selected to be larger than the catalyst pore
aperture, thereby preventing substantial diffusion into the internal
pore. See Hidalgo, C. V. et al., Zeolites, 1984 4. April, p. 175-180.
It is also recognized that the deactivating agents can be contacted
with the molecular sieve in either solution or vapor phase.
As noted above, it is desirable in any case to deactivate external
surface acid sites, without regard to the pore aperture dimensions
of the starting crystalline molecular sieve, to prevent non-shape
selective reactions on the external surface. External surface acid
site deactivation can be obtained by either acid site blockage or
acid removal. One major limitation of both techniques, however,
is that the deactivating agent should be selected to preclude internal
surface diffusion. This limitation is easily met by the use of deactivation
agents in either liquid or gas phase, whose molecules are too large
to fit within even the largest pores of known zeolites. One such
molecule is triphenylchlorosilane. See Martens, J. A. et al., Zeolites,
1984 4 April, p. 98-100.
In another embodiment of external surface acid site modifications,
it is sometimes necessary to fill the intracrystalline pores with
a hydrocarbon to- obtain an internally protected catalyst. Thereafter,
either an aqueous acid or complexing agent, which is insoluble in
the hydrocarbon contained within the intracrystalline pore, is contacted
with the protected catalyst. Once the external surface has been
deactivated, then the hydrocarbon is removed from said intracrystalline
pores. In EP No. 86543 a non-polar organic substance is added to
the zeolite to fill its pores Subsequently, a deactivating agent
solution (in polar solvent) is introduced to the catalyst. Alkali
metal salt solutions, acting as ion exchange atoms to remove the
acidic proton associated with aluminum, are described as suitable
deactivating agents. See also U.S. Pat. No. 4415544 which teaches
the use of paraffin wax to seal off the pores prior to surface treatment
with hydrogen fluoride, which remove the aluminum.
Having described a broad range of catalyst modifications, it is
necessary to indicate that a combination of some or all of these
techniques can be considered in providing an optimized isopropylation
catalyst. In the claims appended hereto, we have attempted to indicate
a preferred chronological order of treatment steps based upon the
starting material, but is not our intent to be limited to a particular
order or combination of modifications.
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