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
range from 5.5 .ANG. to 7.0 .ANG.. The user of these shape selective
catalysts results in a diisopropylnephthalene stream which is enhanced
in .beta. isomers and enhanced in the desired 26-diisopropylnaphthalene
isomer. A particularly preferred catalyst is synthetic Mordenite
having a specific Si/Al ratio and NMR characteristics. Specific
catalyst modifications are also described to improve selectivity
to the desired 26-diisopropylnaphthalene isomer.
Molecular sieve claims
We claim:
1. A process for producing a diisopropylnaphthalene stream enriched
in 26-diisopropylnaphthalene comprising the steps of:
(a) contacting a naphthyl compound selected from naphthalene, monoisopropylnaphthalene,
and mixtures thereof with propylene in the presence of an acidic
crystalline molecular sieve catalyst having twelve membered oxygen
rings and pore aperture widths between 5.5.ANG.and 7.0.ANG.which
catalyst is dealuminated to obtain a Si/Al ratio between 5-100 and
the .sup.27 Al--MAS--NMR ratio is less than 5.0 under conditions
sufficient to convert the naphthyl compound and propylene to diisopropylnaphthalene;
and
(b) recovering the diisopropylnaphthalene.
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
ration greater than 1.0.
4. The process of claim 1 further comprising recovering substantially
pure 26-diisopropylnaphthalene from said diisopropylnaphthalene.
5. The process of claim 1 wherein said catalyst is selected from
the group consisting of MeAPSO-46 Offretite, ZSM-46 and synthetic
Mordenite.
6. The process of claim 5 wherein said acidic crystalline molecular
sieve is synthetic Mordenite.
7. The process of claim 5 wherein said acidic crystalline molecular
sieve is ZSM-12.
8. The process of claim 5 wherein said acidic crystalline molecular
sieve is Offretite.
9. The process of claim 5 wherein said acidic crystalline molecular
sieve is MeAPSO-46.
10. The process of claim 6 wherein the synthetic Mordenite was
hydrogen-form Mordenite prior to dealumination.
11. The process of claim 1 wherein said catalyst is calcined at
a temperature between 400.degree. C. and 1000.degree. C.
12. The process of claim 11 wherein acidic sites on the external
surface of said catalyst are deactivated.
13. The process of claim 5 wherein acidic sites on the external
surface of said catalyst are deactivated.
14. The process of claim 13 wherein said catalyst is calcined at
a temperature between 400.degree. C. and 1000.degree. C.
15. The process of claim 13 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, hydrotic and organic derivatives of Groups IIIA, IVA,
IVB, and VA.
16. The process of claim 13 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,
17. A process for producing a diisopropylnaphthalene stream enriched
in 26-diisopropylnaphthalene comprising the steps of:
(a) contacting a naphthyl compound selected from naphthalene, monoisopropylnaphthalene,
mixtures thereof with propylene in the presence of an acidic crystalline
molecular sieve catalyst having twelve membered oxygen rings and
pore aperture dimensions which have been reduced to less than about
7.0.ANG.by treatment which catalyst is dealuminated to obtain a
Si/Al ratio between 3--100 and the .sup.27 Al--MAS--NMR ratio is
less than 5.0 under conditions sufficient to convert the naphthyl
compound and propylene to a diisopropylnaphthalene stream; and
(b) recovering the diisopropylnaphthalene.
18. The process of claim 17 wherein said acidic crystalline molecular
sieve is selected from the group consisting of Zeolite L, Zeolite
Beta, faujasite, and SAPO-5.
19. The process of claim 17 wherein said diisopropylnaphthalene
comprises greater than 39 mole percent of 26-diisopropylnaphthalene.
20. The process of claim 17 wherein said diisopropylnaphthalene
comprises 26-diisopropylnaphthalene and 27-diisopropylnaphthalene
in a mole ratio greater than 1.0.
21. The process of claim 17 wherein said diisopropylnaphthalene
comprises a 26-diisopropylnaphthalene and 27-diisopropylnaphthalene
in a mole ratio greater than 1.2.
22. The process of claim 17 further comprising recovering substantially
pure 26-diisopropylnaphthalene from said diisopropylnaphthalene.
23. The process of claim 17 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, hydrotic and
organic derivatives of Groups IIIA, IVA, IVB, and VA.
24. The process of claim 18 wherein said catalyst is calcined at
a temperature between 400.degree. C. and 1000.degree. C.
25. The process of claim 24 wherein acidic sites on the external
surface of said catalyst are deactivated.
26. The process of claim 18 wherein acidic sites on the external
surface of said catalyst are deactivated.
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 26 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, hidrotic and organic derivatives of Groups IIIa, IVA,
IVB, and VA.
29. The process of claim 26 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.
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-hydroxy-benzoic
acid, 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.
##STR1##
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 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-diisopropylnaphthalene. 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.
In any manufacture of diisopropylnaphthalene, it is clear that
some monoisopropyl- and triisopropyl-products 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 propyl 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.. Particularly, preferred shape selective
materials are those having specific NMR characteristic which are
believed to represent materials having very little non-framework
aluminum in the interstices of the materials. 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 suitable catalyst is one
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. An especially desirable material is a
synthetic Mordenite which has been dealuminated to a Si/Al ratio
between about 5 and 100 (or between 5 and 50) and which display
certain characteristic NMR spectra. Also preferred are those materials
which have been surface-deactivated in the manner specified below.
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-, triand higher polyalkylnaphthalenes.
FIGS. 2-6 are plots of the log of naphthalene conversion versus
time for a number of different catalysts where naphthalene conversion
is expressed as the natural logarithm of the naphthalene molar concentration
remaining divided by the initial naphthalene molar concentration.
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 Stanley Whittingham (Academic Press,
1982).
ZSM-12 belongs structurally to the Mordenite 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 Zeolites,"
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.
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 (26hedron) 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. 165-167 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.-monoalkylate 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
stearic bulk of the substituent for monoalkylates of naphthalene.
See Table 2. This is predicted to hold true for dialkylates as well. |