Molecular sieve abstract
A method for preparing one or more specific dimethyltetralins from
either 5-(o-, m-, or p-tolyl)-pent-1- or -2-ene or 5-phenyl-hex-1-
or -2-ene, and optionally for preparing one or more specific dimethylnaphthalenes
from the aforesaid dimethyltetralins is disclosed wherein the orthotolylpentene
or phenylhexane is cyclized to the dimethyltetralin using an ultra-stable
crystalline aluminosilicate molecular sieve Y-zeolite.
Molecular sieve claimsHaving described the invention, what is
claimed is:
1. A method for preparing one or more dimethyltetralins from 5-(o-
m-, or p-tolyl)-pent-1- or -2-ene or 5-phenyl-hex-1- or -2-ene as
the first feedstock, comprising: contacting the first feedstock
in liquid form with a solid cyclization catalyst comprising an ultra-stable
thermally stabilized or dealuminated crystalline aluminosilicate
molecular sieve Y-zeolite that has a silica-to-alumina molar ratio
of from about 3:1 to about 200:1 pore windows provided by twelve-membered
rings containing oxygen and a unit cell size of from 24.0 to about
24.7 Angstroms, and that contains from about 0.01 up to about 3.5
weight percent of sodium, calculated as elemental sodium, and based
on the weight of the zeolite and that is substantially free of adsorbed
water, and at an elevated temperature and at a pressure that is
sufficiently high to maintain the first feedstock substantially
in the liquid phase, to thereby cyclize the first feedstock to form
a first liquid product comprising one or more dimethyltetralins,
wherein water is at a concentration in the first feedstock of from
zero up to less than about 0.5 weight percent, based on the weight
of the feedstock, wherein (1) when the first feedstock comprises
5-(o-tolyl)-pent-1 or -2-ene, at least 80 weight percent of the
dimethyltetralin product formed is comprised by 15-, 16-, 25-
or 26-dimethyltetralin or a mixture thereof, (2) when the first
feedstock comprises 5-(m-tolyl)-pent-1 or -2-ene, at least 80 weight
percent of the dimethyltetralin product formed is comprised by 15-,
16-, 17-, 18-, 25-, 26-, 27- or 28-dimethyltetralin or a
mixture thereof, (3) when the first feedstock comprises 5-(p-tolyl)-pent-1
or -2-ene, at least 80 weight percent of the dimethyltetralin product
formed is comprised by 17-, 18-, 27- or 28-dimethyltetralin
or a mixture thereof, or (4) when the first feedstock comprises
5-phenyl-hex-1- or -2-ene, at least 80 weight percent of the dimethyltetralin
product formed is comprised of 13-, 14-, 23-, 57-, 58- or 67-dimethyltetralin
or a mixture thereof.
2. The method of claim 1 wherein the first feedstock comprises
5-(o-tolyl)-pent-1- or -2-ene and at least 80 weight percent of
the dimethyltetralin product formed comprises 15-, 16-, 25- or
26-dimethyltetralin or a mixture thereof.
3. The method of claim 1 wherein the first feedstock comprises
5-(m-tolyl)-pent-1- or -2-ene and at least 80 weight percent of
the dimethyltetralin product formed comprises 15-, 16-, 17-,
18-, 25-, 26-, 27-, or 28-dimethyltetralin or a mixture thereof.
4. The method of claim 1 wherein the first feedstock comprises
5-(p-tolyl)-pent-1- or -2-ene and at least 80 weight percent of
the dimethyltetralin product formed comprises 17-, 18-, 27- or
28-dimethyltetralin or a mixture thereof.
5. The method of claim 1 wherein the first feedstock comprises
5-phenyl-hex-1- or -2-ene and at least 80 weight percent of the
dimethyltetralin product formed comprises 13-, 14-, 23-, 57-,
58-, or 67-dimethyltetralin or a mixture thereof.
6. The method of claim 1 wherein the cyclization is performed at
a temperature in the range of from about 120.degree. C. to about
400.degree. C.
7. The method of claim 1 wherein the cyclization is performed on
a batch basis.
8. The method of claim 1 wherein the cyclization is performed on
a continuous basis with a space velocity of, or on a batch basis
with an effective space velocity of, from about 0.01 to about 100
parts of feedstock per part of the zeolite component of the cyclization
catalyst by weight per hour.
9. The method of claim 1 wherein said solid cyclization catalyst
comprises an acidic, ultrastable Y-zeolite having a unit cell size
in the range of about 24.2 to about 24.7 Angstroms, a silica-to-alumina
bulk molar ratio in the range of about 4:1 to about 10:1 and a
sodium content of about 0.05 to about 3.5 weight percent, calculated
as elemental sodium.
10. The method of claim 1 wherein said solid cyclization catalyst
comprises a relatively low acidity ultrastable Y-zeolite having
a unit cell size of no more than about 24.3 Angstroms, a silica-to-alumina
bulk molar ratio of at least about 12 and a sodium content of less
than about 0.4 weight percent, based on the weight of the zeolite
and calculated as elemental sodium.
11. A method for preparing one or more dimethyltetralins from 5-(o-,
m-, or p-tolyl)-pent-1- or -2-ene or 5-phenyl-hex-1- or -2-ene,
comprising:
(a) contacting a feedstock comprising 5-(o,m-, or p-tolyl)-pent-1-
or 2-ene or 5-phenyl-hex-1- or -2-ene in liquid form with a solid
cyclization catalyst comprising an acidic ultrastable, thermally
stabilized or dealuminated crystalline aluminosilicate molecular
sieve Y-zeolite that is substantially free of absorbed water, and
at an elevated temperature and at a pressure that is sufficiently
high to maintain the feedstock substantially in the liquid phase,
to thereby cyclize the first feedstock to form a liquid product
comprising one or more dimethyltetralins, wherein water is at a
concentration in the first feedstock of from zero up to less than
about 0.5 weight percent, based on the weight of the feedstock,
wherein (1) when the feedstock comprises 5-(o-tolyl)-pent-1- or
-2-ene, at least 80 weight percent of the dimethyltetralin product
formed is comprised of 15-, 16-, 25- or 26-dimethyltetralin
or a mixture thereof, (2) when the feedstock comprises 5-(m-tolyl)-pent-1-
or -2-ene, at least 80 weight percent of the dimethyltetralin product
formed is comprised of 15-, 16-, 17-, 18-, 25-, 26-, 27-
or 28-dimethyltetralin or a mixture thereof, (3) when the feedstock
comprises 5-(p-tolyl)-pent-1- or -2-ene, at least 80 weight percent
of the dimethyltetralin product formed is comprised of 17-, 18-,
27- or 28-dimethyltetralin or a mixture thereof, or (4) when the
feedstock comprises 5-phenyl-hex-1- or -2-ene, at least 80 weight
percent of the dimethyltetralin product formed is comprised of 13-,
14-, 23-, 57-, 58- or 67-dimethyltetralin or a mixture thereof;
(b) separating the resulting cyclization product mixture by distillation
at reduced pressure into a lighter, lower boiling fraction that
comprises the dimethyltetralin product and a heavier, higher boiling
fraction boiling above the boiling point of the dimethyltetralin
product, and withdrawing the resulting lighter fraction as distillation
overhead; and
(c) combining the resulting heavier fraction with a fresh supply
of the tolyl-pentene(s) or phenyl-hexene(s) employed in step (a),
cyclizing the resulting mixture under the cyclization conditions
employed in step (a), and separating the resulting cyclization product
mixture under the distillation conditions employed in step (b).
12. The method of claim 11 wherein in step (b), the heavier fraction
boils above about 240.degree. C. at 1 atmosphere.
13. The method of claim 11 wherein, when steps (a)-(c) are performed
on a batch basis, from about 0.01 to about 2 parts by weight of
the heavier fraction from step (b) are combined in step (c) per
part by weight of fresh supply of tolyl-pentene(s) or phenyl-hexene(s).
14. The method of claim 13 wherein, from about 0.05 to about 0.35
parts by weight of the heavier fraction from step (b) are combined
in step (c) per part by weight of the fresh supply of tolyl-pentene(s)
or phenyl-hexene(s).
15. The method of claim 11 wherein, when steps (a)-(c) are performed
continuously, from about 0.2 to about 20 parts by weight of the
heavier fraction from step (b) are combined in step (c) per part
by weight of the fresh supply of tolyl-pentene(s) or phenyl-hexene(s).
16. The method of claim 15 wherein from about 1 to about 5 parts
by weight of the heavier fraction from step (b) are combined in
step (c) per part by weight of the fresh supply of tolyl-pentene(s)
or phenyl-hexene(s).
17. The method of claim 11 wherein, when steps (a)-(c) are performed
on a batch basis, the sequence of steps (b) and (c) is repeated
from one to about 100 times.
18. The method of claim 11 wherein, when steps (a)-(c) are performed
continuously, a portion of the catalyst is periodically withdrawn
and replaced with fresh catalyst.
19. The method of claim 11 wherein the following additional steps
are performed:
(d) cracking the resulting separated heavier fraction from step
(c) in the presence of a solid cracking catalyst at a cracking temperature
in the range of from about 120.degree. C. to about 450.degree. C.,
which temperature is at least 10.degree. C. above the temperature
employed for the cyclization of step (c) and at a pressure that
is sufficiently high to maintain the heavier fraction being cracked
substantially in the liquid phase; and
(e) separating the resulting cracking product mixture by distillation
at reduced pressure into a lighter, lower boiling fraction that
comprises the dimethyltetralin product and a heavier, higher boiling
fraction that boils above the boiling point of the dimethyltetralin
product.
20. The method of claim 19 wherein the heavier fraction in step
(e) boils above about 240.degree. C. at one atmosphere.
21. The method of claim 19 wherein the cracking temperature in
step (d) is in the range of from about 180.degree. C. to about 330.degree.
C.
22. The method of claim 19 wherein the cracking temperature in
step (d) is at least 30.degree. C. above the cyclization temperature
in step (c).
23. The method of claim 19 wherein the cracking catalyst comprises
the catalyst employed for cyclization in steps (a) and (c).
24. The method of claim 19 wherein in step (e) the heavier fraction
boils above about 240.degree. C.
25. The method of claim 11 wherein said solid cyclization catalyst
comprises an acidic, ultrastable Y-zeolite having a unit cell size
in the range of about 24.2 to about 24.7 Angstroms, a silica-to-alumina
bulk molar ratio in the range of about 4:1 to about 10:1 and a
sodium content of about 0.05 to about 3.5 weight percent, calculated
as elemental sodium.
26. The method of claim 11 wherein said solid cyclization catalyst
comprises a relatively low acidity ultrastable Y-zeolite having
a unit cell size of no more than about 24.3 Angstroms, a silica-alumina
bulk molar ratio of at least about 12 and a sodium content of less
than about 0.4 weight percent, based on the weight of the zeolite
and calculated as elemental sodium.
27. A method for preparing one or more of dimethylnaphthalenes
comprising contacting the first liquid product from claim 1 as a
second feedstock in liquid form with a solid dehydrogenation catalyst
in a reaction vessel at an elevated temperature and at a pressure
that is sufficiently high to maintain the second feedstock substantially
in the liquid phase, to thereby effect conversion of the aforesaid
first liquid product in an equilibrium dehydrogenation reaction
to form hydrogen and a second liquid product comprising said one
or more dimethylnaphthalenes, and removing a substantial portion
of the hydrogen being formed in the dehydrogenation reaction from
the reaction vessel to thereby shift the aforesaid equilibrium toward
the formation of the aforesaid one or more dimethylnaphthalenes,
wherein (a) when 15-, 16-, 25-, or 26-dimethyltetralin or a
mixture thereof comprises at least 80 weight percent of the dimethyltetralin
product formed in (1) of claim 1 and present in the second feedstock,
at least 80 weight percent of the dimethylnaphthalene product in
the second liquid product is comprised of 15-, 16- or 26-dimethylnaphthalene
or a mixture thereof, or (b) when 15-, 16-, 17-, 18-, 25-,
26-, 27- or 28-dimethyltetralin or a mixture thereof comprises
at least 80 weight percent of the dimethyltetralin product formed
in (2) of claim 1 and present in the second feedstock, at least
80 weight percent of the dimethylnaphthalene product in the second
liquid product is comprised of 15-, 16-, 17-, 18-, 26- or 27-dimethylnaphthalene
or a mixture thereof or (c) when 17-, 18-, 27- or 28-dimethyltetralin
or a mixture thereof comprises at least 80 weight percent of the
dimethyltetralin product formed in (3) of claim 1 and present in
the second feedstock, at least 80 weight percent of the dimethylnaphthalene
product in the second liquid product is comprised of 17-, 18-,
or 27-dimethylnaphthalene or a mixture thereof or (d) when 13-,
14-, 23-, 57-, 58- or 67-dimethyltetralin or a mixture thereof
comprises at least 80 weight percent of the dimethyltetralin product
formed in (4) of claim 1 and present in the second feedstock, at
least 80 weight percent of the dimethylnaphthalene product in the
second liquid product is comprised of 13-, 14- or 23-dimethylnaphthalene
or a mixture thereof.
28. A method for isomerizing at least 20 weight percent of the
total of (1) the 15-, and 16-dimethylnaphthalenes in the second
liquid product in (a) of claim 27 to 26-dimethylnaphthalene, (2)
the 15-, 16-, 17-, and 18-dimethylnaphthalenes in the aforesaid
second liquid product in (b) of claim 27 to 27-dimethylnaphthalene
and 26-dimethylnaphthalene, (3) the 17- and 18-dimethylnaphthalene
in the aforesaid second liquid product in (c) of claim 27 to 27-dimethylnaphthalene,
or (4) the 13- and 14-dimethylnaphthalene in the aforesaid second
liquid product in (d) of claim 27 to 23-dimethylnaphthalene, comprising:
contacting the aforesaid second liquid product in liquid form with
a solid isomerization catalyst comprising either beta zeolite or
an acidic ultrastable crystalline Y-zeolite having a silica-to-alumina
molar ratio of from about 4:1 to about 10:1 having pore windows
provided by twelve-membered rings containing oxygen and a unit cell
size of from about 24.2 to about 24.7 angstroms, and at an elevated
temperature and at a pressure that is sufficiently high to maintain
the isomerization feedstock substantially in the liquid phase.
Molecular sieve description
FIELD OF THE INVENTION
This invention relates generally to a method for preparing a dimethyltetralin
and more particularly concerns a method for preparing primarily
a specific dimethyltetralin or a mixture of specific dimethyltetralins
from either 5-(o-, m-, or p-tolyl)-pent-1- or -2-ene or 5-phenyl-hex-1-
or -2-ene in the presence of a Y-type crystalline aluminosilicate
molecular sieve zeolite.
DESCRIPTION OF PRIOR ART
Naphthalene dicarboxylic acids are monomers that are known to be
useful for the preparation of a variety of polymers. For example,
poly(ethylene 26-naphthalate) prepared from 26-naphthalene dicarboxylic
acid and ethylene glycol has better heat resistance and mechanical
properties than polyethylene terephthalate and is useful in the
manufacture of films and fibers.
Dimethylnaphthalenes are desirable feedstocks for oxidation to
the corresponding naphthalene dicarboxylic acids. A known conventional
process for producing a naphthalene dicarboxylic acid comprises
the oxidation of a dimethylnaphthalene with oxygen in the liquid
phase in an acetic acid solvent at an elevated temperature and pressure
and in the presence of a catalyst comprising cobalt, manganese and
bromine components.
Typically dimethylnaphthalenes are found in refinery or coal-derived
streams as mixtures of all of the ten possible dimethylnaphthalene
isomers. However, separation of these isomers is very difficult
and expensive. Consequently, methods for producing specific dimethylnaphthalenes
or mixtures of two or three specific dimethylnaphthalenes in high
purity and quality are highly desirable. One type of such method
is a multistep synthesis involving (1) the formation of an alkenylbenzene
by the reaction of o-, m- or p-xylene or ethylbenzene with butadiene,
(2) the cyclization of the resulting alkenylbenzene to form one
or more dimethyltetralins belonging to one or two of three groups
of three isomeric dimethyltetralins--that is, either group A containing
the 15-, 16-, 25- and 26-dimethyltetralins, group B containing
the 17-, 18-, 27- and 28-dimethyltetralins, or group C containing
the 13-, 14-, 23-, 57-, 58- and 67-dimethyltetralins--(3)
the dehydrogenation of the dimethyltetralin(s) to form the corresponding
dimethylnaphthalene(s), and (4) the isomerization of the resulting
dimethylnaphthalene(s) to the desired specific dimethylnaphthalene.
For example, Thompson. U.S. Pat. Nos. 3775496; 3775497; 3775498;
3775500 disclose processes for the cyclization of specific alkenylbenzenes
to one or more specific dimethyltetralins at 200.degree.-450.degree.
C. in the presence of any suitable solid acidic cyclization catalyst
such as acidic crystalline zeolites as well as silica-alumina, silica-magnesia
and silica-alumina-zirconia and phosphoric acid, followed by the
dehydrogenation of the resulting dimethyltetralin(s) in the vapor
state to the corresponding dimethylnaphthalene(s) in a hydrogen
atmosphere at 300.degree.-500.degree. C. and in the presence of
a solid dehydrogenation catalyst such as noble metals on carriers
and chromia-alumina, and thereafter isomerization of each of the
aforesaid dimethylnaphthalene(s) to the desired isomer within the
triad of dimethylnaphthalenes to which the isomer being isomerized
belongs, at 275.degree.-500.degree. C. in the presence of a solid
acidic isomerization catalyst of the same type as described in respect
of the cyclization disclosed therein. In the alternative, both the
cyclization and isomerization reactions can be performed in the
liquid phase, in which case the cyclization is performed at 200.degree.-275.degree.
C. with a solid phosphoric acid catalyst, at 70.degree. -140.degree.
C. with an acidic ion exchange resin, an acidic crystalline zeolite,
hydrofluoric or sulfuric acid as the catalyst or a siliceous cracking
catalyst.
More specifically, Thompson, U.S. Pat. No. 3775496 discloses
the cyclization of 5-(m-tolyl)-pent2-ene to 16- and 18-dimethyltetralins,
which are then dehydrogenated to 16- and 18-dimethylnaphthalenes,
which in turn are isomerized to 26- and 27-dimethylnaphthalenes,
respectively. Thompson, U.S. Pat. No. 3775497 discloses the cyclization
of 5-phenyl-hex-2-ene to 14-dimethyltetralin which is then dehydrogenated
to 14-dimethylnaphthalene, which is in turn isomerized to 23-dimethylnaphthalene.
Thompson, U.S. Pat. No. 3775498 discloses the cyclization of 5-(o-tolyl)-pent-2-ene
to 15-dimethyltetralin, which is then dehydrogenated to 15-dimethylnaphthalene,
which is in turn isomerized to 26-dimethylnaphthalene. Thompson,
U.S. Pat. No. 3775500 discloses the cyclization of 5-(p-tolyl)-pent-2-ene
to 17-dimethyltetralin, which is then dehydrogenated to 17-dimethylnaphthalene,
which in turn is isomerized to 27-dimethylnaphthalene.
Shimada et al., U.S. Pat. No. 3780119 disclose a method for the
isomerization of dimethylnaphthalene by the use at a temperature
above 260.degree. C. of a mordenite catalyst in which a metal form
of mordenite is in excess of 20 weight percent of the mordenite,
with the metal being selected from the group consisting of lithium,
sodium, potassium, magnesium, calcium, strontium, barium, zinc and
aluminum.
Suld et al., U.S. Pat. No. 3803253 disclose a method for the
hydroisomerization of a dimethylnaphthalene by the use of a combination
of a hydrogenation catalyst and a calcium-containing zeolite catalyst,
such as a calcium-exchanged synthetic faujasite, for example, a
Y-type molecular sieve.
Shima et al., U.S. Pat. No. 3806552 disclose a method for the
isomerization of dimethylnaphthalenes in the gas phase by the use
of a mixed catalyst consisting of (a) 65-95 weight percent of a
hydrogen form of mordenite in which above 80 weight percent of the
metal cations are replaced with hydrogen ions, and (b) 5-35 weight
percent of catalyst selected from the group consisting of bentonite
and fuller's earth.
Hedge, U.S. Pat. No. 3855328 discloses a method for the isomerization
of dimethylnaphthalenes by the use of a Type Y alumino silicate
zeolite at 120.degree.-300.degree. C. in the liquid phase. The catalysts
have aluminum-to-silicon atomic ratios of 0.1-1.0.
Ogasawara et al., U.S. Pat. No.3888938 disclose a method for
the isomerization of dimethylnaphthalenes in the liquid phase by
the use of a mixed catalyst consisting of (a) 70-95 weight percent
of a hydrogen form of mordenite in which above 80 weight percent
of the metal cations are replaced with hydrogen ions, and (b) 5-30
weight percent of a promoter selected from the group consisting
of bentonite and fuller's earth.
Hedge et al., U.S. Pat. No. 3928482 disclose the isomerization
of either dimethyldecalins, dimethyltetralins or dimethylnaphthalenes
in the presence of an alumino silicate zeolite containing polyvalent
metal cations in exchange positions, such as a rare earth-exchanged
Type Y zeolite.
Yokayama et al., U.S. Pat. No. 3957896 disclose the selective
isomerization of dimethylnaphthalenes in the presence of any kind
of natural or synthetic, solid acid catalyst, such as Y-type zeolite
as well as silica-alumina, silica-magnesia, silica-zirconia, silica-alumina-zirconia,
fuller's earth, natural or synthetic mordenite, X-type zeolite,
A-type zeolite and L-type zeolite. These catalysts may be substituted
partly or wholly by hydrogen or metal. Furthermore, these catalysts
can be unsupported or supported on carriers.
Onodera et al., U.S. Pat. No. 4524055 disclose a crystalline
aluminosilicate zeolite that is useful in the isomerization of dimethylnaphthalenes
and has a silica-to-alumina mole ratio of 10 to 100 specific x-ray
lattice distances, and a specific cyclohexane-to-n-hexane adsorption
ratio of at least 0.7.
Maki et al., U.S. Pat. No. 4556751 disclose the isomerization
of dimethylnaphthalenes in the presence of a crystalline aluminosilicate
having a pentasil structure and a silica-to-alumina molar structure
of 12 or higher. In addition, the aluminosilicate may contain some
other metals as non-exchangeable metals.
A problem in all such prior art methods is the presence of other
dimethylnaphthalene isomers and unconverted dimethyltetralin and
alkenylbenzene as impurities and by-products in the finally obtained,
desired specific dimethylnaphthalene isomer. The presence of such
impurities and by-products markedly reduces the utility and commercial
value of the desired dimethylnaphthalene isomer, especially as a
precursor for the formation of a naphthalene dicarboxylic acid for
use as a monomer in the manufacture of a polymer. In addition, catalysts
tend to deactivate relatively rapidly at the high temperatures employed
in vapor phase processes. Therefore, it is highly desirable to employ
liquid phase processes and to improve the completeness of each step
in the aforesaid multistep synthesis and the selectivity of each
step therein for the production of the desired product therefrom.
In this regard, it is known that in the presence of an acid catalyst,
the dimethylnaphthalene isomers are isomerizable within each triad
of dimethylnaphthalene isomers--that is, within the 15-, 16- and
26-dimethylnaphthalenes of triad A, within the 17-, 18-, and
27-dimethylnaphthalenes of triad B, and within the 13-, 14- and
23-dimethylnaphthalenes of triad C. It is also known that the interconversion
of a dimethylnaphthalene isomer within one of the aforesaid triads
to a dimethylnaphthalene isomer within another of the aforesaid
triads occurs to a relatively lesser extent. Consequently, it is
highly desired to improve the selectivity of the cyclization step
in the aforesaid multistep synthesis for the formation of dimethyltetralin
isomers that belong to the same triad to which also belongs the
specific desired dimethyltetralin isomer, which upon dehydrogenation
is converted to the desired specific corresponding dimethylnaphthalene
isomer. It is also highly desired to improve the selectivity and
completeness of the isomerization step in the aforesaid multistep
synthesis for the formation of the specific dimethylnaphthalene
isomer desired.
OBJECTS OF THE INVENTION
It is therefore a general object of the present invention to provide
an improved method for manufacturing with an improved yield and
selectivity a specific dimethyltetralin isomer or set of dimethyltetralin
isomers by the cyclization of an alkenylbenzene which meets the
aforementioned requirements for selectivity and completeness and
catalyst activity.
It is a related object of the present invention to provide an improved
method for manufacturing with an improved yield and selectivity
a specific dimethylnaphthalene isomer or set of dimethylnaphthalene
isomers by the cyclization of an alkenylbenzene to form a specific
dimethyltetralin isomer or set of dimethyltetralin isomers and then
dehydrogenating the dimethyltetralin(s).
It is another related object of the present invention to provide
an improved method for manufacturing with an improved yield and
selectivity a specific dimethylnaphthalene isomer or set of specific
dimethylnaphthalene isomers by the cyclization of an alkenylbenzene
to form a specific dimethyltetralin isomer or set of dimethyltetralin
isomers and then dehydrogenating the dimethyltetralin(s) and isomerizing
the resulting dimethylnaphthalene(s).
Other objects and advantages of the method of the present invention
will become apparent upon reading the following detailed description
and appended claims.
SUMMARY OF THE INVENTION
The objects are achieved by an improved method for preparing a
dimethyltetralin (DMT) from 5-(o-, m-, or p-tolyl)-pent-1- or -2-ene
or 5-phenyl-hex-1- or -2-ene as the first feedstock, comprising:
contacting the first feedstock in liquid form with a solid cyclization
catalyst comprising a Y-type, crystalline aluminosilicate molecular
sieve zeolite that is substantially free of adsorbed water, and
at an elevated temperature and at a pressure that is sufficiently
high to maintain the first feedstock substantially in the liquid
phase, to thereby cyclize the first feedstock to form a first liquid
product comprising a mixture of dimethyltetralins, wherein, if present,
the concentration of water in the first feedstock is less than about
0.5 weight percent, based on the weight of the feedstock, wherein
either (a) the first feedstock comprises 5-(o-tolyl)-pent-1- or
-2-ene and 15-, 16-, 25- or 26-dimethyltetralin or mixtures
thereof comprise at least 80 weight percent of the mixture of dimethyltetralins
formed, (b) the first feedstock comprises 5-(m-tolyl)-pent-1- or
-2-ene and 15-, 16-, 17-, 18-, 25-, 26-, 27-, or 28-dimethyltetralin,
or mixtures thereof comprise at least 80 weight percent of the mixture
of dimethyltetralins formed, (c) the first feedstock comprises 5-(p-tolyl)-pent-1-
or -2-ene and 17-, 18-, 27-, or 28-dimethyltetralin, or mixtures
thereof comprise at least 80 weight percent of the mixture of dimethyltetralins
formed, (d) the first feedstock comprises 5-phenyl-1- or -2-hexene
and 13-, 14 -, 23-, 57-, 58- or 67-dimethyltetralin or mixtures
thereof comprise at least 80 weight percent of the mixture of dimethyltetralins
formed.
This invention is also a method for preparing one or more dimethyltetralins
from 5-(o-, m-, or p-tolyl)-pent-1- or -2-ene or 5-phenyl-hex-1-
or -2-ene as the first feedstock, comprising: contacting the first
feedstock in liquid form with a solid cyclization catalyst comprising
an ultra-stable crystalline aluminosilicate molecular sieve Y-zeolite
that has a silica-to-alumina molar ratio of from about 3:1 to about
200:1 pore windows provided by twelve-membered rings containing
oxygen and a unit cell size of from about 24.0 to about 24.7 Angstroms,
and that contains from about 0.01 up to about 3.5 weight percent
of sodium, calculated as elemental sodium, and based on the weight
of the zeolite and that is substantially free of adsorbed water,
and at an elevated temperature and at a pressure that is sufficiently
high to maintain the first feedstock substantially in the liquid
phase, to thereby cyclize the first feedstock to form a first liquid
product comprising one or more dimethyltetralins, wherein water
is at a concentration in the first feedstock of from zero up to
less than about 0.5 weight percent, based on the weight of the feedstock,
wherein (1) when the first feedstock comprises 5-(o-tolyl)-pent-1-
or -2-ene, at least 80 weight percent of the dimethyltetralin product
formed is comprised by 15-, 16-, 25- or 26-dimethyltetralin
or a mixture thereof, (2) when the first feed stock comprises 5-(m-tolyl)-pent-1-
or -2-ene, at least 80 weight percent of the dimethyltetralin product
formed is comprised by 15-, 16-, 17-, 18-, 25-, 26-, 27-
or 28-dimethyltetralin or a mixture thereof, (3) when the first
feedstock comprises 5-(p-tolyl)-pent-1- or -2-ene, at least 80 weight
percent of the dimethyltetralin product formed is comprised by 17-,
18-, 27- or 28-dimethyltetralin or a mixture thereof, or (4)
when the first feedstock comprises 5-phenyl-hex-1- or -2-ene, at
least 80 weight percent of the dimethyltetralin product formed is
comprised of 13-, 14-, 23-, 57-, 58- or 67-dimethyltetralin
or a mixture thereof.
In another aspect, this invention is an improved method for preparing
one or more dimethyltetralins from 5-(o-, m-, or p-tolyl)-pent-1-
or -2-ene or 5-phenyl-hex-1- or -2-ene as the first feedstock, comprising:
(a) contacting the first feedstock in liquid form with a solid cyclization
catalyst comprising a crystalline aluminosilicate molecular sieve
Y-zeolite that is substantially free of absorbed water, and having
a silica-to-alumina bulk molar ratio in the range of about 3:1 to
about 200:1 pore windows provided by twelve-membered rings containing
oxygen, a unit cell size in the range of about 24.0 to about 24.7
Angstroms, and a sodium content of about 0.01 to about 3.5 weight
percent, calculated as elemental sodium and based on the weight
of the zeolite; at an elevated temperature and at a pressure that
is sufficiently high to maintain the feedstock substantially in
the liquid phase to thereby cyclize the first feedstock to form
a liquid product comprising one or more dimethyltetralins, wherein
water is at a concentration in the feedstock of from 0.0 up to less
than about 0.5 weight percent, based on the weight of the feedstock,
wherein (1) when the first feedstock comprises 5-(o-tolyl)-pent-1-
or -2-ene, at least 80 weight percent of the dimethyltetralin product
formed is comprised of 15-, 16-, 25- or 26-dimethyltetralin,
(2) when the first feedstock comprises 5-(m-tolyl)-pent-1- or -2-ene,
at least 80 weight percent of the dimethyltetralin product formed
is comprised of 15-, 16-, 17-, 18-, 25-, 26-, 27- or 28-dimethyltetralin
or a mixture thereof, (3) when the first feedstock comprises 5-(p-tolyl)-pent-1-
or -2-ene, at least 80 weight percent of the dimethyltetralin product
formed is comprised of 17-, 18-, 27- or 28-dimethyltetralin
or a mixture thereof, and (4) when first feedstock comprises 5-phenyl-1-
or -2-hexene, at least 80 weight percent of the dimethyltetralin
product formed is comprised of 13-, 14-, 23-, 57-, 58- or 67-dimethyltetralin
or a mixture thereof; (b) separating the resulting cyclization product
mixture by distillation at reduced pressure such that a lighter
fraction comprising the dimethyltetralin product is separated as
the overhead from a heaver fraction comprising materials boiling
above the dimethyltetralins; and (c) combining the resulting heavier
fraction with a fresh supply of the tolylpentene(s) or phenyl-hexene(s)
employed in step (a) and cyclizing the resulting mixture under the
cyclization conditions recited in step (a).
BRIEF DESCRIPTION OF THE DRAWING
For a more complete understanding of this invention, reference
should now be made to the embodiments illustrated in greater detail
by the results presented in the accompanying drawing and described
below by way of examples of the invention. In the drawing, FIG.
1 is a series of plots of the yields of 15-dimethyltetralin from
the cyclization of 5-o-tolyl-2-pentene in Examples 19-23 involving
5 different cyclization catalysts.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable feedstocks for use in the cyclization of the method of
the present invention are 5-(o-, m-, or p-tolyl)-pent-1- or -2-ene
or 5-phenyl-hex-1- or -2-ene. In the method of the present invention,
the cyclization step is followed preferably by a dehydrogenation
step and more preferably by first a dehydrogenation step and second
an isomerization step.
When 5-(o-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization
step of the present invention, 15-, 16-, 25-, or 26-dimethyltetralin
or a mixture thereof comprises at least 80 preferably at least
85 weight percent of the dimethyltetralins produced therefrom, which
resulting dimethyltetralins are in turn the feedstock and are converted
in the dehydrogenation step of the present invention to the corresponding
15-, 16- and 26-dimethylnaphthalenes (DMNs), which are then the
feedstock in the isomerization step of the present invention and
are converted therein to 26-dimethylnaphthalene.
When 5-(m-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization
step, 15- 16- 17-, 18- 25- 26-, 27- or 28-dimethyltetralin
or a mixture thereof comprises at least 80 preferably at least
85 weight percent of the dimethyltetralins produced therefrom, which
dimethyltetralins are in turn the feedstock and are converted in
the dehydrogenation step to the corresponding 15-, 16-, 17-,
18- 26- and 27-dimethylnaphthalenes, which are then the feedstock
in the isomerization step and are converted to 26- and 27-dimethylnaphthalenes.
When 5-(p-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization
step, 17-, 18-, 27- or 28-dimethyltetralin or a mixture thereof
comprises at least 80 preferably at least 85 weight percent of
the dimethyltetralins produced therefrom, which dimethyltetralins
are in turn the feedstock and are converted in the dehydrogenation
step to the corresponding 17-, 18- and 27-dimethylnaphthalenes
which are then the feedstock and are converted in the isomerization
step to 27-dimethylnaphthalene.
When 5-phenyl-1- or -2-hexene is the feedstock to the cyclization
step, 13-, 14-, 23-, 57 58-, or 67-dimethyltetralin or a
mixture thereof comprises at least 80 preferably at least 85 weight
percent of the dimethyltetralins produced therefrom, which dimethyltetralins
are in turn the feedstock and are converted in the dehydrogenation
step to the corresponding, 13-, 14- and 23-dimethylnaphthalenes,
which are then the feedstock in the isomerization step and are convened
to 23-dimethylnaphthalene.
In the method of the present invention, each of the aforesaid cyclization,
dehydrogenation and isomerization reactions is performed in the
liquid phase at an elevated temperature and at a sufficiently high
pressure to ensure that the feedstock for the particular step is
maintained in the liquid phase. By elevated temperature it is meant
a temperature sufficiently high so that a significant portion of
the feedstock for the respective reaction is converted to the desired
product using preselected catalyst levels and reaction times for
batch processes, or preselected space velocities for continuous
processes. Preferably, the cyclization reaction is performed at
a temperature in the range of about 120.degree. C., more preferably
about 150.degree. C., to about 400.degree. C., more preferably to
about 350.degree. C. Most preferably the cyclization reaction is
performed at a temperature in the range of about 150.degree. C.
to about 300.degree. C. The cyclization reaction is preferably performed
at a pressure in the range of about 0.05 more preferably about
0.1 to about 20.0 more preferably to about 5.0 atmospheres absolute.
The dehydrogenation reaction is preferably performed at a temperature
in the range of about 200.degree. C., more preferably about 220.degree.
C., to about 500.degree. C., more preferably to about 450.degree.
C. Most preferably, the dehydrogenation reaction is performed at
a temperature in the range of about 220.degree. C. to about 420.degree.
C. Preferably, the dehydrogenation reaction is performed at a pressure
in the range of about 0.1 more preferably about 1.0 to about 30.0
more preferably to about 20.0 atmospheres absolute. The isomerization
reaction is preferably performed at a temperature in the range of
about 200.degree. C., more preferably about 240.degree. C., to about
420.degree. C., more preferably to about 380.degree. C. Most preferably
the isomerization reaction is performed at a temperature in the
range of about 240.degree. C. to about 350.degree. C. The isomerization
reaction is preferably performed at a pressure in the range of about
0.1 more preferably about 0.5 to about 20.0 more preferably 5.0
atmospheres absolute.
Each of the cyclization, dehydrogenation and isomerization reactions
can be performed with or without a solvent for the respective feedstock.
Preferably a solvent is not employed in the aforesaid steps. If
employed, a solvent in any of the aforesaid steps must be inert
under the conditions employed and suitably comprise a paraffin such
as a tetradecane, or an aromatic hydrocarbon such as anthracene,
or mixtures thereof, which preferably boils above about 270.degree.
C. In the cyclization step, if water is present, its concentration
is less than 0.5 weight percent, preferably less than 0.1 weight
percent, based on the weight of the alkenylbenzene feedstock. More
preferably, water is not present in the cyclization reaction medium.
Each of the cyclization, dehydrogenation and isomerization steps
of the method of the present invention can be performed either batchwise
or continuously. The reaction apparatus to be used in each aforesaid
step can be of any known type such as a fixed bed, moving bed, fluidized
bed, liquid phase suspended bed or a solid-liquid mixture in a stirred
tank. Generally, however, the use of a fixed bed is commercially
preferred for continuous operation. When conducting the dehydrogenation
reaction of this invention in a continuous manner, it is advantageous
to use two or more fixed bed reactors in series. Hydrogen formed
during the dehydrogenation reaction is preferably removed from the
product mixture between such fixed bed reactors arranged in series.
The improved conversion of the feedstock and selectivity for the
production of the desired product or set of products for each of
the cyclization, dehydrogenation and isomerization steps of the
method of this invention are the result of the temperature and pressure
conditions employed and the high activity and selectivity of the
catalysts employed in each aforesaid step, which in turn permits
the use of less severs conditions such that greater selectivity
and reduced catalyst deactivation can be achieved.
The catalyst employed in the cyclization method of this invention
comprises an ultrastable--that is, a thermally stabilized or dealuminated--crystalline
aluminosilicate Y-zeolite having a silica-to-alumina bulk molar
ratio in the range of from about 3:1 preferably from about 12:1
to about 200:1 preferably to about 100:1. having pore windows provided
by twelve-membered rings containing oxygen and a unit cell size
in the range of from about 24.0 preferably from about 24.1 to
about 24.7 preferably to about 24.6 Angstroms, having a sodium
content of from about 0.01 to about 3.5 weight percent, calculated
as elemental sodium and based on the weight of the zeolite.
The term "relatively low acidity" as used herein in reference
to a zeolite useful for the practice of this invention has reference
to the relatively few Bronsted acid sites in the crystalline zeolite
framework that provide sufficient acidity to catalyze the desired
cyclization but without the production of undesirably large amounts
of by-products. Substances that owe their acidity to the presence
of protons are termed Bronsted acids. In the case of crystalline
aluminosilicates or zeolites, a Bronsted acid site occurs in the
crystalline zeolite framework where an aluminum atom surrounded
by four oxygen atoms is present. Inasmuch as some of such Bronsted
acid sites are neutralized by alkali metal present in the crystalline
framework, the Bronsted acidity of a particular zeolite can be delineated
by specifying the bulk molar ratios of silica-to-alumina and sodium
oxide-to-alumina as set forth herein. In terms of the number of
framework Bronsted acid sites per unit cell of the crystalline zeolite
catalyst, for the purposes of the present method the catalyst has
an average of no more than 10 framework Bronsted acid sites, preferably
no more than about 4 such sites, per unit cell.
The term "ultrastable" as used herein in reference to
a zeolite has reference to a zeolite which has been thermally stabilized
or dealuminated to produce a synthetic zeolite having much improved
resistance to degradation under acid and hydrothermal conditions.
The term "zeolite Y" as used herein in reference to the
contemplated crystalline aluminosilicate molecular sieve has reference
to a zeolite which has the characteristic framework structure of
the faujasite mineral class. The term "bulk molar ratio"
as used herein denotes the molar ratio of the designated moieties
regardless of whether present in the crystalline framework of the
molecular sieve or not.
One preferred catalyst employed in the cyclization and/or cracking
step of the method of this invention comprises an acidic ultrastable--that
is, a thermally stabilized or dealuminated--Y-type crystalline aluminosilicate
zeolite having a silica-to-alumina molar ratio of from about 4:1
preferably from about 5:1 to about 10:1 preferably to about 6:1
and having pore windows provided by twelve-membered rings containing
oxygen, and a unit cell size of from about 24.2 preferably from
about 24.3 to about 24.7 preferably to about 24.6 Angstroms. A
suitable such zeolite is marketed by Union Carbide under the name
LZ-Y72 or LZ-Y20.
The aforesaid acidic zeolite employed in the catalyst for the cyclization
step of the method of this invention is in the hydrogen form and
contains from about 0.05 up to about 3.5 weight percent of sodium,
calculated as elemental sodium and based on the weight of the zeolite.
If the cyclization step is performed batchwise, the cyclization
catalyst preferably contains from about 1 to about 3.5 weight percent
of sodium, calculated as elemental sodium and based on the weight
of the zeolite. If the cyclization step is performed continuously,
the cyclization catalyst preferably contains from about 0.05 to
about 0.5 weight percent, calculated as elemental sodium and based
on the weight of the zeolite. Preferably, the cyclization catalyst
contains from about 0.01 preferably from about 0.05 to about 3
preferably to about 1.5 weight percent of a component comprising
a first metal selected from the group consisting of platinum, palladium,
iridium and rhodium, calculated as the elemental metal and based
on the weight of the catalyst. Most preferably this metal component
comprises platinum.
More preferably, especially when the cyclization is performed continuously,
this cyclization catalyst also contains from about 0.01 preferably
from about 1 to about 5 preferably to about 3 weight percent of
a component comprising a second metal selected from the group consisting
of copper, tin, gold, lead and silver, calculated as the elemental
metal and based on the weight of the catalyst. More preferably this
second metal component comprises copper, tin or gold.
A most preferred type of catalyst for use as the cyclization catalyst
and/or the cracking catalyst in the method of this invention is
another ultrastable zeolite Y in the hydrogen form and having a
relatively low acidity that has relatively lower alumina and sodium
oxide contents. The catalyst framework alumina concentration for
such zeolite is indicated in part by the unit cell size which, as
measured by x-ray diffraction, is no more than 24.3 Angstroms. The
silica-to-alumina bulk molar ratio is at least about 12:1 at least
about 20:1 and most preferably at least about 30:1. The sodium oxide-to-alumina
bulk molar ratio is in the range of from about 0.001:1 preferably
from about 0.01:1 to about 1:1 preferably to about 0.05:1. The
sodium content of this zeolite is less than about 0.4 preferably
less than about 0.23 weight percent, based on the weight of the
zeolite and calculated as elemental sodium. Commercially available
examples of this type of preferred zeolite are Conteka CBV 760 obtained
from Conteka Company, Leiden, the Netherlands, and Valfor CP 301-
26 obtained from PQ Corporation, Valley Forge, Pa. Conteka CBV 760
has a sodium oxide-to-alumina bulk molar ratio of about 0.05:1
a silica-to-alumina bulk molar ratio of about 50:1 and a sodium
content of about 0.08 weight percent based on the weight of the
zeolite and calculated as elemental sodium, has a unit cell size
of 24.2 Angstroms and a specific surface area of 720 square meters
per gram, and is in powder form. Valfor CP 301-26 has a sodium-oxide-to-alumina
bulk molar ratio of about 0.02:1 a silica-to-alumina bulk molar
ratio of about 80:1 a sodium content of about 0.02 weight percent
based on the weight of the zeolite and calculated as elemental sodium,
a unit cell size of 24.25 Angstroms, and a specific surface area
of about 775 square meters per gram, and is also in powder form.
When using this relatively low acidity, lower alumina and lower
sodium oxide zeolite Y catalyst it is preferable that the alkenylbenzene
feedstream contain no more than about 0.1 weight percent water.
The zeolites are preferably substantially free of adsorbed water.
If present on the zeolite, the adsorbed water can be removed from
the zeolite by heating it in a dry atmosphere at about 250.degree.
C. for 0.5-1 hour. In the alternative, and less preferably, the
presence of absorbed water at a concentration of up to 15 weight
percent of the catalyst can be tolerated if a reaction temperature
in the aforesaid range of at least 180.degree. C. is employed.
The aforesaid zeolites can be employed either unsupported or supported
on a porous refractory, inorganic oxide that is inert under the
conditions employed, such as silica, alumina, silica-alumina, magnesia,
bentonite or other such clays. If a support is employed, preferably
the support comprises silica, alumina, or silica-alumina. When a
support is employed, the zeolite comprises from about 10 preferably
from about 20 to about 90 preferably to about 80 weight percent
based on the weight of the catalyst.
If the cyclization is performed on a batch basis, the catalyst
is employed at a level in the range of from about 0.1 preferably
from about 1.0 to about 5 preferably to about 3 weight percent
of the zeolite component of the catalyst, based on the weight of
the alkenylbenzene feedstock, and the reaction time is from about
0.5 preferably from about 2 to about 10 preferably to about 6
hours. If the cyclization is performed on a continuous basis, the
space velocity is in the range of from about 0.1 preferably from
about 1 to about 100 preferably to about 50 parts of alkenylbenzene
feedstock per part of zeolite component of the catalyst by weight
per hour.
The zeolite catalyst used in the method of the present invention
can be either in a powdered form or in a granular form. A powdered
catalyst is conveniently mechanically dispersed by mixing action
in the liquid phase reactant employed. When in a granular form,
the granule size can vary widely, such as from about 0.03-inch to
about 1 inch in average maximum diameter, the exact size in any
given instance being influenced by the choice of particular fixed-bed
reactor wherein the granular form is to be employed and through
which the liquid phase reactant is circulated. As used herein, the
term "granular form" is generic to porous structures having
the various possible physical shapes, and made by the various possible
physical shapes, and made by the various possible preparation methods,
including compacting, extruding, and the like, and such term is
inclusive of both supported and unsupported zeolite catalyst forms.
In one embodiment of this invention, under conditions at which
the cyclization reaction is substantially complete, the resulting
cyclization product mixture can be separated by distillation at
reduced pressure into a relatively lighter (or lower boiling) fraction
that contains the dimethyltetralin product and a relatively heavier
(or higher boiling) fraction that boils above the boiling point(s)
of the dimethyltetralin product. The reduced pressure is preferably
in the range of from about 0.03 up to less than about 1.0 atmosphere.
The heavier fraction boils preferably above 240.degree. C. and more
preferably above 250.degree. C. at atmospheric pressure.
The heavier fraction of the aforesaid cyclization product mixture,
which is the distillation bottom, remains in the cyclization reactor
or is recycled to it, and is next combined with a fresh supply of
the tolyl-pentene(s) or phenyl-hexene(s) employed as the feedstock
in the aforesaid cyclization step, and the resulting mixture is
subjected to the aforesaid cyclization conditions. Under conditions
at which the cyclization reaction is substantially complete, the
resulting cyclization product mixture is separated by distillation
at reduced pressure into a relatively lighter (or lower boiling)
fraction that contains the dimethyltetralin product and a relatively
heavier (or higher boiling) fraction that boils above the boiling
points of the dimethyltetralin product. The reduced pressure is
preferably in the range of from about 0.03 up to about 1.0 atmosphere.
The heavier fraction boils preferably above 240.degree. C. and more
preferably above 250.degree. C. at atmospheric pressure. In a preferred
embodiment of the method of this invention, either immediately after
the cyclization or at least ultimately, the lighter fraction, which
is the distillate, is dehydrogenated such that the dimethyltetralin(s)
therein are convened to the corresponding dimethylnaphthalenes.
Again, the heavier fraction of the cyclization product mixture,
which generally is the distillation bottoms, remains in the cyclization
reactor or is recycled to it, and is combined with a fresh supply
of the tolyl-pentene(s) or phenyl-hexene(s) employed as the feedstock
in the aforesaid cyclization step, and the resulting mixture is
subjected to the aforesaid cyclization conditions. In a batch operation,
the heavier fraction and fresh supply of tolyl-pentene(s) or phenyl-hexene(s)
are combined at a ratio of from about 0.01 part, preferably from
about 0.05 part, to about 2 preferably to about 0.35 parts, by
weight of the heavier fraction per part of the aforesaid fresh supply.
In a continuous operation, the heavier fraction and the fresh supply
of tolyl-pentene(s) or phenyl-hexane(s) are combined at a ratio
of from about 0.2 part, preferably from about 1 part to about 20
parts, preferably to about 5 parts by weight of the heavier fraction
per part of fresh supply.
This sequence of cyclization of a mixture of fresh tolyl-pentene(s)
or phenyl-hexene(s) and the distillation bottoms of the reduced
pressure distillation of the products from the previous cyclization
run, followed by reduced pressure distillation of the resulting
cyclization products and combination of the resulting distillation
bottoms with fresh tolyl-pentene(s) or phenyl-hexene(s) can be repeated
until the activity of the cyclization catalyst declines to such
an extent that the reaction times become excessive. Typically, in
a batch operation this sequence of cyclization, separation and recycle
of the distillation bottoms to the cyclization step is repeated
up to 100 times, preferably from 5 to 30 times for a given charge
of catalyst. Typically, in a continuous operation, relatively small
amounts of the catalyst would be removed from the reactor and replaced
in the reactor with fresh catalyst in order to maintain the desired
catalyst activity.
At the end of a continuous cyclization run or at the end of a series
of batch cyclization runs, the distillation bottoms from the last
reduced pressure distillation can be subjected to cracking at a
temperature in the range of from about 120.degree. C., preferably
from about 180.degree. C., to about 450.degree. C., preferably to
about 330.degree. C., which temperature is higher than the temperature
at which the cyclization was performed by at least 10.degree. C.,
preferably by at least 30.degree. C. The cracking operation is performed
at a pressure that is sufficiently high so that the materials being
cracked are substantially in the liquid phase, and generally the
pressure is from about 0.03 preferably from about 0.1 to about
10 preferably to about 2.0 atmospheres absolute. The cracking
operation can be performed using as the cracking catalyst the same
catalyst that had been employed as the cyclization catalyst. In
the alternative, suitable cracking catalysts include any catalyst
that is conventionally employed for acid-catalyzed reactions, such
as silica-alumina, acidic molecular sieves, mineral acids or acidic
ion exchange resins.
The resulting cracked products include dimethyltetralins which
are then separated by distillation at a reduced pressure in the
range of from about 0.03 to less than about 1.0 atmosphere into
a lighter (or lower boiling) fraction which contains the dimethyltetralin
product and a relatively heavier (or higher boiling) fraction that
boils above the boiling point(s) of the dimethyltetralin product.
In a preferred embodiment of the method of this invention either
immediately after the cracking treatment or at least ultimately,
the lighter fraction which is the distillate is dehydrogenated to
convert the dimethyltetralins therein to dimethylnaphthalenes. Thus,
cracking the distillate bottoms from the last cyclization enhances
the degree of the conversion of the tolyl-pentene(s) or phenyl-hexene(s)
to dimethyltetralins, and, after the combination of cyclization,
distillation and dehydrogenation steps, of dimethylnaphthalenes.
Similarly, the heavy cracked products which remain as the distillate
bottoms after the combination of cyclization and distillation steps
represent only a minor fraction of the total amount of comparably
heavy materials that would have been produced in an equal number
of cyclization and without subjecting the heavy cyclization products
to further treatment in accordance with this method of this invention.
Thus, this embodiment produces greater relative amounts of useful
dimethylnaphthalenes and produces a cyclization product mixture
distillate as feedstock for subsequent dehydrogenation, which distillate
contains substantially smaller amounts of relatively heavier cyclization
products which have an adverse effect on the subsequent dehydrogenation
and isomerization steps.
The catalyst employed in the dehydrogenation step of the method
of this invention is any solid dehydrogenation catalyst that is
capable of effecting the dehydrogenation and exhibiting a reasonable
lifetime under the conditions employed, including catalysts such
as noble metals on carriers such as reforming catalysts. Aluminas,
silicas, alumina-silicas, and activated carbons are examples of
suitable carriers or supports. The noble metals include, for example,
platinum, palladium, ruthenium and rhenium. The noble metal component
can also comprise mixtures of two or more noble metals. Preferably,
palladium on an active carbon or alumina support containing from
about 0.5 more preferably from about 1.0 to about 15 more preferably
to about 10 weight percent of palladium, calculated as elemental
palladium and based on the weight of the catalyst, is employed as
the dehydrogenation catalyst.
Other preferred dehydrogenation catalysts include platinum on activated
carbon or alumina supports, rhenium on activated carbon or alumina
supports and mixtures of platinum and rhenium on activated carbon
or alumina supports, wherein the platinum and rhenium are each present
from about 0.01 preferably 0.05 to about 10.0 preferably 5.0
weight percent calculated as the element and based on the weight
of the catalyst. A more preferred dehydrogenation catalyst comprises
a mixture of platinum and rhenium on gamma alumina where the platinum
and rhenium are each present in the range of about 0.1 to about
1.0 weight percent calculated as the element, and based on the weight
of the catalyst. A support material such as an alumina or other
non-combustible support material has an advantage over a carbon
support material in that the non-combustible support can be exposed
to air or other source of oxygen-containing gas at an elevated temperature
to regenerate a deactivated catalyst. Consequently, such a catalyst
can be cycled wherein between each cycle of use as a dehydrogenation
catalyst the catalyst is regenerated with an oxygen-containing gas
at an elevated temperature. Preferably the level of oxygen in the
oxygen-containing gas is about 1 wt % to about 25 wt %, the regeneration
temperature is in the range of about 400.degree. C. to about 600.degree.
C. and the time of exposure to the oxygen-containing gas at these
temperatures is that sufficient to regenerate the catalyst.
In the liquid phase dehydrogenation reactions of this invention,
when conducted in either a batch or continuous manner, and particularly
when using the preferred dehydrogenation catalysts, the addition
of hydrogen to the reaction mixture is not necessary to maintain
catalyst activity during extended catalyst use, i.e., the liquid
phase dehydrogenation reaction in the method of this invention wherein
a dimethyltetralin is dehydrogenated to a dimethylnaphthalene proceeds
in the absence of hydrogen added to the reaction mixture. Without
intending to be bound by a theory of operation, it appears that
during the liquid phase dehydrogenation method of this invention
wherein dimethyltetralins are dehydrogenated to dimethylnaphthalenes
using a dehydrogenation catalyst, and particularly the preferred
noble metal dehydrogenation catalysts disclosed herein, the hydrogen
generated during the dehydrogenation reaction effectively maintains
catalyst activity.
In the dehydrogenation method of this invention it is however advantageous
to remove at least some hydrogen during the liquid phase dehydrogenation
reaction. This is accomplished in a batch procedure by venting the
hydrogen from the vessel used to conduct the batch reaction. If
operating in a continuous mode, a plurality of series arranged fixed
bed reactors can be utilized with the hydrogen vented from the process
stream between fixed bed reactors.
If the dehydrogenation is performed on a batch basis, the catalyst
is employed at a level in the range of from about 0.005 preferably
from about 0.01 to about 1.0 preferably to about 0.2 weight percent
of the noble metal component, calculated as the elemental noble
metal and based on the weight of the dimethyltetralin feedstock,
and the reaction time is from about 1 preferably from about 2
to about 50 preferably to about 40 hours. If the dehydrogenation
is performed on a continuous basis, the space velocity is in the
range of from about 0.1 preferably from about 10 to about 5000
preferably to about 2000 parts of the dimethyltetralin feedstock
per part of the noble metal component (calculated as the elemental
noble metal) of the catalyst by weight per hour.
The catalyst employed in the isomerization step of the method of
this invention comprises either beta zeolite or an acidic ultrastable--that
is, a thermally stabilized or dealuminated--Y-type crystalline aluminosilicate
zeolite having a silica-to-alumina molar ratio of from about 4:1
preferably from about 5:1 to about 10:1 preferably to about 6:1
and having pore windows provided by twelve-membered rings containing
oxygen, and a unit cell size of from about 24.2 preferably from
about 24.3 to about 24.7 preferably to about 24.6 Angstroms. A
suitable such zeolite is marketed by Union Carbide under the name
LZ-Y72 or LZ-Y20. Water is not detrimental to catalytic activity
or selectivity in the isomerization process.
The isomerization catalyst preferably comprises beta zeolite. The
composition, structure and preparation of beta zeolite are described
in Wadlinger et al., U.S. Pat. No. 3308069 which in its entirety
is specifically incorporated herein by reference. The structure
of beta zeolite is also reported in J. Haggin, "Structure of
Zeolite Beta Determined," in Chemical & Engineering News,
p. 23 (Jun. 20 1988). Beta zeolite is also commercially available
from PQ Corporation.
The aforesaid ultrastable Y-type zeolite which can be employed
in the catalyst for the isomerization step of the method of this
invention is in the hydrogen form and contains from about 0.01
preferably from about 1 up to about 5 preferably up to about 3
weight percent of sodium, calculated as elemental sodium and based
on the weight of the zeolite.
Preferably the isomerization catalyst comprises a hydrogenation
component comprising a Group VIII metal, which more preferably is
palladium, platinum or nickel.
The aforesaid zeolite of the isomerization catalyst can be employed
either unsupported or supported on a porous refractory, inorganic
oxide that is inert under the conditions employed, such as silica,
alumina, silica-alumina, magnesia, bentonite or other such clays.
If a support is employed, preferably the support comprises silica,
alumina or silica-alumina. When a support is employed, the zeolite
comprises from about 10 preferably from about 20 to about 90
preferably to about 80 weight percent based on the weight of the
catalyst.
If the isomerization is performed on a batch basis, the catalyst
is employed at a level in the range of from about 0.1 preferably
from about 1.0 to about 5 preferably to about 3 weight percent
of the zeolite component of the catalyst, based on the weight of
the dimethylnaphthalene feedstock, and the reaction time is from
about 0.5 preferably from about 2 to about 10 preferably to about
6 hours. If the isomerization is performed on a continuous basis,
the space velocity is in the range of from about 0.1 preferably
from about 0.5 to about 20 preferably to about 10 parts of dimethylnaphthalene
feedstock per part of zeolite component of the catalyst by weight
per hour.
For each of the cyclization, dehydrogenation, and isomerization
reactions described hereinabove, it is preferable to conduct each
reaction at the lowest possible reaction temperature that provides
for the conversion of a significant portion of the reaction feedstock
to the respective product. At elevated reaction temperatures, coke,
tars and other reaction sideproducts tend to form more rapidly and
deposit on and deactivate the catalysts disclosed herein. However,
regardless of the reaction temperature used, as the catalyst ages
catalytic activity typically decreases. This decrease in catalyst
activity, which results in reduced feedstock conversion at preselected
reaction conditions such as reaction pressure, catalyst level, space
velocity and reaction temperature, can be offset somewhat by increasing
the reaction temperature. Consequently, a preferred procedure for
maximizing the useful life of the cyclization, dehydrogenation and
isomerization catalysts of this invention is to begin using the
catalysts at as low a reaction temperature that provides for the
conversion of a significant portion of the respective feedstock
and then increase the temperature of the reaction as the catalyst
ages so as to maintain desirable feedstock conversion levels. For
example, when using a batch process, the temperature of the reaction
can be raised with each successive batch. When using a continuous
process, the reaction temperature of the catalyst bed or continuous
stirred tank reactor can be raised as the catalyst ages. When using
an aged, i.e., partially deactivated, cyclization catalyst in the
method of this invention, a reaction temperature greater than 250.degree.
C. is suitable for maintaining the conversion of a significant portion
and preferably at least about 50 wt % and more preferably at least
about 70 wt % of the cyclization reaction feedstock to the desired
product or products. Preferably this temperature is in the range
of from about 255.degree. C. to about 400.degree. C. and more preferably
in the range of from about 260.degree. C. to about 320.degree. C.
Cyclization catalysts of this invention may also be reactivated
by raising the reaction temperature for a period of time, then returning
to the original reaction temperature. When employing an aged dehydrogenation
catalyst in the method of this invention, a reaction temperature
greater than 300.degree. C. is suitable for maintaining the conversion
of a significant portion and preferably at least about 50 wt % and
more preferably at least about 70 wt % of the dehydrogenation reaction
feedstock to the desired product or products. Preferably this temperature
is in the range of from about 305.degree. C. to about 500.degree.
C., and more preferably in the range of from about 310.degree. C.
to about 450.degree. C. When using an aged isomerization catalyst
in the method of this invention, a reaction temperature greater
than 300.degree. C. is suitable for maintaining the conversion of
a significant portion and preferably at least about 20 wt % of the
isomerization reaction feedstock to the desired product or products.
Preferably this temperature is in the range of from about 305.degree.
C. to about 420.degree. C., more preferably in the range of from
about 310.degree. C. to about 380.degree. C. |