U.S. patent application number 11/042938 was filed with the patent office on 2005-06-16 for process and catalysts for c8 alkylaromatic isomerization.
Invention is credited to Maher, Gregory F., Nemeth, Laszlo T..
Application Number | 20050131261 11/042938 |
Document ID | / |
Family ID | 34314223 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050131261 |
Kind Code |
A1 |
Nemeth, Laszlo T. ; et
al. |
June 16, 2005 |
Process and catalysts for C8 alkylaromatic isomerization
Abstract
A liquid or partially liquid phase process for isomerizing a
non-equilibrium mixture of xylenes and ethylbenzene uses a zeolitic
catalyst system preferably based on zeolite beta and on
pentasil-type zeolite. The invention obtains an improved yield of
para-xylene from the mixture relative to prior art processes in a
more economical manner. A preferred beta zeolite is a
surface-modified zeolite beta resulting from acid washing of a
templated native zeolite at conditions insufficient to effect bulk
dealumination. A preferred pentasil zeolite is a MFI-type.
Inventors: |
Nemeth, Laszlo T.;
(Barrington, IL) ; Maher, Gregory F.; (Aurora,
IL) |
Correspondence
Address: |
JOHN G TOLOMEI, PATENT DEPARTMENT
UOP LLC
25 EAST ALGONQUIN ROAD
P O BOX 5017
DES PLAINES
IL
60017-5017
US
|
Family ID: |
34314223 |
Appl. No.: |
11/042938 |
Filed: |
January 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11042938 |
Jan 25, 2005 |
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10736312 |
Dec 15, 2003 |
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6872866 |
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Current U.S.
Class: |
585/481 ;
585/477 |
Current CPC
Class: |
Y02P 20/52 20151101;
C07C 2521/04 20130101; C07C 5/2708 20130101; C07C 5/2708 20130101;
C07C 2521/08 20130101; C07C 2529/70 20130101; C07C 15/08
20130101 |
Class at
Publication: |
585/481 ;
585/477 |
International
Class: |
C07C 005/22 |
Claims
What is claimed is:
1. A process for the isomerization of xylenes comprising contacting
an aromatics-containing hydrocarbon feed stream with a catalyst
system comprising a beta zeolite and a pentasil zeolite selected
from the group of zeolite types consisting of MFI, MEL, MTW, TON or
mixtures thereof, under isomerization conditions and recovering a
product stream comprising a greater amount of para-xylene than in
the feed stream, wherein the amount of para-xylene in the product
is at least 90 mol-% of the approach to an equilibrium amount of
para-xylene to total xylenes and wherein the conversion of
ethylbenzene over the catalyst system is at least 20 mol-%.
2. The process of claim 1 wherein the catalyst system is contacted
under at least partial liquid phase conditions.
3. The process of claim 2 wherein the at least partial phase liquid
conditions include the absence of added hydrogen.
4. The process of claim 1 wherein the isomerization conditions
comprise a space velocity from about 0.1 to about 20 hr.sup.-1, a
temperature from about 100.degree. to about 400.degree. C. and a
pressure from about 10 kPa to about 5 MPa absolute.
5. The process of claim 4 wherein the isomerization conditions
comprise a space velocity from about 0.5 to about 10 hr.sup.-1, a
temperature from about 150.degree. to about 300.degree. C. and a
pressure from about 100 kPa to about 3 MPa absolute.
6. The process of claim 1 wherein the catalyst system is
essentially free of a hydrogenation metal component.
7. The process of claim 6 wherein the catalyst system is
essentially free of hydrogenation metal component by containing
less than 0.1 mass-% amount of said metal.
8. The process of claim 1 wherein the catalyst system further
comprises a binder selected from the group consisting of alumina,
silica, and mixtures thereof.
9. The process of claim 8 wherein the binder is alumina.
10. The process of claim 1 wherein the pentasil zeolite is a
MFI-type zeolite.
11. The process of claim 1 wherein the beta zeolite is a surface
modified beta zeolite.
12. The process of claim 11 wherein the surface modified beta
zeolite results from acid washing of a templated native
zeolite.
13. A process for the isomerization of xylenes comprising
contacting a C.sub.8 aromatics containing hydrocarbon feed stream,
which comprises ethylbenzene, with a catalyst system comprising a
beta zeolite catalyst and a MFI-zeolite catalyst under at least
partially liquid phase at isomerization conditions, and recovering
a product stream comprising para-xylene, wherein the amount of
para-xylene in the product is at least 90 mol-% of the approach to
an equilibrium amount of para-xylene to total xylenes and wherein
the conversion of ethylbenzene over the catalyst system is at least
20 mol-%.
14. The process of claim 13 wherein the binder is selected from the
group consisting of alumina, silica, zeolites, and mixtures
thereof.
15. The process of claim 13 wherein the beta zeolite catalyst is
essentially free of a metal hydrogenation component.
16. The process of claim 13 wherein the isomerization conditions
comprise a space velocity from about 0.5 to about 10 hr.sup.-1, a
temperature from about 150.degree. to about 300.degree. C. and a
pressure from about 100 kPa to about 3 MPa absolute.
17. The process of claim 16 wherein the isomerization conditions
further comprise the absence of a substantial amount of
hydrogen.
18. The process of claim 17 wherein the substantial amount of
hydrogen is less than or equal to the hydrogen solubility in the
liquid phase.
19. The process of claim 17 wherein the substantial amount of
hydrogen is less than 1 wt-%.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Division of copending application Ser.
No. 10/736,312 filed Dec. 15, 2003, the contents of which are
hereby incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to catalytic hydrocarbon
conversion, and more specifically to the use of a catalyst system
comprising pentasil zeolite such as MFI-type zeolite and beta
zeolite in aromatics isomerization, and even more specifically to a
process without hydrogen addition to convert a non-equilibrium feed
depleted in para-xylene into an equilibrium product that is
enriched in para-xylene.
BACKGROUND OF THE INVENTION
[0003] The xylenes, para-xylene, meta-xylene and ortho-xylene, are
important intermediates that find wide and varied application in
chemical syntheses. Para-xylene upon oxidation yields terephthalic
acid that is used in the manufacture of synthetic textile fibers
and resins. Meta-xylene is used in the manufacture of plasticizers,
azo dyes, wood preservers, etc. Ortho-xylene is feedstock for
phthalic anhydride production.
[0004] Xylene isomers from catalytic reforming or other sources
generally do not match demand proportions as chemical
intermediates. Further, xylene isomers are generally present with
ethylbenzene, which is difficult to separate or to convert.
Para-xylene in particular is a major chemical intermediate with
rapidly growing demand, but amounts to only 20 to 25% of a typical
C.sub.8 aromatics stream. Adjustment of isomer ratio to demand can
be effected by combining xylene-isomer recovery, such as adsorption
for para-xylene recovery, with isomerization to yield an additional
quantity of the desired isomer. Isomerization converts a
non-equilibrium mixture of the xylene isomers that is lean in the
desired xylene isomer to a mixture approaching equilibrium
concentrations.
[0005] Various catalysts and processes have been developed to
effect xylene isomerization. In selecting appropriate technology,
it is desirable to run the isomerization process as close to
equilibrium as practical in order to maximize the para-xylene
yield; however, associated with this is a greater cyclic C.sub.8
loss due to side reactions. The approach to equilibrium that is
used is an optimized compromise between high C.sub.8 cyclic loss at
high conversion (i.e., very close approach to equilibrium) and high
utility costs due to the large recycle rate of unconverted C.sub.8
aromatics. Catalysts thus are evaluated on the basis of a favorable
balance of activity, selectivity and stability.
[0006] Catalysts containing molecular sieves have become prominent
for xylene isomerization in the past quarter-century or so. U.S.
Pat. No. 3,856,872, for example, teaches xylene isomerization and
ethylbenzene conversion with a catalyst containing ZSM-5
(MFI-type), ZSM-12 (MTW-type (IUPAC Commission on Zeolitic
Nomenclature)), or ZSM-21 zeolite. U.S. Pat. No. 4,899,011
discloses isomerization of C.sub.8 aromatics using two zeolites
such as ZSM-5 with different crystal sizes, each of which is
associated with a strong hydrogenation metal. U.S. Pat. No.
4,939,110 discloses a catalyst for isomerization using two metals
and a pentasil zeolite, which includes ZSM-12 (MTW-type) zeolite.
U.S. Pat. No. 6,222,086 and U.S. Pat. No. 6,576,581 disclose a dual
catalyst system for aromatics isomerization using at least one
non-zeolitic molecular sieve and one zeolitic aluminosilicate. U.S.
Pat. No. 6,448,459 discloses a liquid phase isomerization stage and
a gas phase isomerization stage with EUO-type zeolite.
[0007] U.S. Pat. No. 4,962,258 discloses a process for liquid phase
xylene isomerization over gallium-containing, crystalline silicate
molecular sieves as an improvement over aluminosilicate zeolites
ZSM-5, ZSM-12 (MTW-type), and ZSM-21 as shown in U.S. Pat. No.
3,856,871. The '258 patent refers to borosilicate work, as
exemplified in U.S. Pat. No. 4,268,420, and to zeolites of the
large pore type such as faujasite or mordenite. U.S. Pat. No.
5,744,673 discloses an isomerization process using beta zeolite and
exemplifies the use of gas phase conditions with hydrogen.
[0008] U.S. Pat. No. 5,763,720 discloses a gas phase C.sub.9
aromatics transalkylation process with a treated MTW-type or
alternatively with a treated beta zeolite, both with a
hydrogenation metal component; U.S. Pat. No. 5,942,651 further
discloses a two zeolite system with the first zeolite from U.S.
Pat. No. 5,763,720 combined with a second zeolite with smaller
pores such as ZSM-5. A two zeolite catalyst system for
transalkylation was also disclosed in U.S. Pat. No. 5,789,641 with
a first catalyst of mordenite and a second catalyst of mazzite.
Other processes have referred to zeolite beta in the context of
ethylbenzene production. U.S. Pat. No. 4,891,458 discloses a
process for alkylation or transalkylation of an aromatic
hydrocarbon, such as benzene, with an olefin alkylating agent or
polyalkyl aromatic hydrocarbon transalkylating agent, under at
least partial liquid phase conditions over zeolite beta. U.S. Pat.
No. 5,030,786 discloses a dehydration process to reduce the water
level for a mono-alkyl-benzene production process based on zeolite
beta or zeolite Y. U.S. Pat. No. 5,750,814 teaches that the use of
beta in a process for ethylbenzene production, via alkylation,
which actually minimizes xylene production (see column 3, line 27).
U.S. Pat. No. 5,811,612 discloses that diethylbenzene can be
transalkylated with benzene to produce ethylbenzene. U.S. Pat. No.
6,440,886 discloses a surface-modified zeolite beta by treating a
templated native zeolite with an acid prior to template-removal
calcination.
SUMMARY OF THE INVENTION
[0009] Most gas phase processes are capital intensive and require
installation of a fired heater, compressor, and gas-liquid
separation system. A liquid phase process reduces required
equipment to a reactor and heat exchanger thus saving considerable
capital. Also, most gas phase processes use hydrogen to promote
stability, which can be eliminated in a liquid phase process, thus
saving hydrogen consumption and reducing loss of aromatics rings
due to hydrogen saturation.
[0010] Accordingly, a principal object of the present invention is
to provide a liquid phase process for the isomerization of
alkylaromatic hydrocarbons. More specifically, the process of the
present invention is directed to catalytic isomerization of C.sub.8
aromatic hydrocarbons over a beta zeolite and a pentasil zeolite
such as MFI-type zeolite in order to obtain improved yields of
desired xylene isomers.
[0011] Another broad embodiment of the present invention is
directed toward a catalyst system for the isomerization of
alkylaromatics based upon contacting a C.sub.8-aromatics rich
hydrocarbon feed stream comprising less than the equilibrium amount
of para-xylene with a catalyst comprising beta zeolite and a
catalyst comprising a pentasil zeolite such as MFI-zeolite. The
contacting occurs under at least partial liquid phase conditions in
the absence of substantial hydrogen and allows a product stream to
be recovered which comprises a greater amount of para-xylene than
the feed stream. Preferably the amount of para-xylene in the
product stream is at or greater than the equilibrium amount.
[0012] These, as well as other objects and embodiments will become
evident from the following detailed description of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The feedstocks to the aromatics isomerization process of
this invention comprise isomerizable alkylaromatic hydrocarbons of
the general formula C.sub.6H.sub.(6-n)R.sub.n, where n is an
integer from 2 to 5 and R is CH.sub.3, C.sub.2H.sub.5,
C.sub.3H.sub.7, or C.sub.4H.sub.9, in any combination and including
all the isomers thereof. Suitable alkylaromatic hydrocarbons
include, for example but without so limiting the invention,
ortho-xylene, meta-xylene, para-xylene, ethylbenzene,
ethyltoluenes, tri-methylbenzenes, di ethylbenzenes,
tri-ethylbenzenes, methylpropylbenzenes, ethylpropylbenzenes,
di-isopropylbenzenes, and mixtures thereof.
[0014] A particularly preferred application of the catalyst system
of the present invention is the isomerization of a C.sub.8 aromatic
mixture containing ethylbenzene and xylenes. Generally the mixture
will have an ethylbenzene content of about 1 to about 50 mass-%, an
ortho-xylene content of 0 to about 35 mass-%, a meta-xylene content
of about 20 to about 95 mass-% and a para-xylene content of 0 to
about 30 mass-%. The aforementioned C.sub.8 aromatics are a
non-equilibrium mixture, i.e., at least one C.sub.8 aromatic isomer
is present in a concentration that differs substantially from the
equilibrium concentration at isomerization conditions. Usually the
non-equilibrium mixture is prepared by removal of para-, ortho-
and/or meta-xylene from a fresh C.sub.8 aromatic mixture obtained
from an aromatics-production process.
[0015] The alkylaromatic hydrocarbons may be utilized in the
present invention as found in appropriate fractions from various
refinery petroleum streams, e.g., as individual components or as
certain boiling-range fractions obtained by the selective
fractionation and distillation of catalytically cracked or reformed
hydrocarbons. Concentration of the isomerizable aromatic
hydrocarbons is optional; the process of the present invention
allows the isomerization of alkylaromatic-containing streams such
as catalytic reformate with or without subsequent aromatics
extraction to produce specified xylene isomers and particularly to
produce para-xylene. A C.sub.8 aromatics feed to the present
process may contain nonaromatic hydrocarbons, i.e., naphthenes and
paraffins, in an amount up to about 30 mass-%. Preferably, the
isomerizable hydrocarbons consist essentially of aromatics, to
ensure pure products from downstream recovery processes. Moreover,
a C.sub.8 aromatics feed that is rich in undesired ethylbenzene can
be supplied such that it can be converted to xylenes or other
non-C.sub.8 compounds in order to further concentrate desired
xylene species.
[0016] According to the process of the present invention, an
alkylaromatic hydrocarbon feed mixture, in the absence of a
substantial amount of hydrogen, is contacted with two or more
catalysts of the type hereinafter described in an
alkylaromatic-hydrocarbon isomerization zone. A substantial amount
of hydrogen refers to greater than dilute amounts, which may
already be present, by being dissolved in the liquid, and further
refers to the fact that no hydrogen is added. It is preferred that
the absence of a substantial amount of hydrogen be less than or
equal to the hydrogen solubility in the liquid phase, which will be
less than 1 wt-%. Contacting may be effected using the catalyst
system in a fixed-bed system, a moving-bed system, a fluidized-bed
system, a slurry system, and an ebullated-bed system or in a
batch-type operation. In view of the danger of attrition loss of
valuable catalysts and of the simpler operation, it is preferred to
use a fixed-bed system. In this system, the feed mixture is
preheated by suitable heating means to the desired reaction
temperature, such as by heat exchange with another stream if
necessary, and then passed into an isomerization zone containing a
fixed bed or beds of catalyst(s). The isomerization zone may be one
or more separate reactors with suitable means therebetween to
ensure that the desired isomerization temperature is maintained at
the entrance to each zone. The reactants may be contacted with the
catalyst bed in upward-, downward-, or radial-flow fashion, and the
reactants may be in the liquid phase or a mixed liquid-vapor
phase.
[0017] Isomerization catalysts comprising single or multiple
combinations of zeolites beta and pentasil type (such as MTW) may
be contained in separate reactors, arranged sequentially in the
same reactor, mixed physically, or composited as a single catalyst.
The use of the term catalyst system is understood to encompass all
of these conceptual options. By employing a single reactor,
however, savings are realized in piping, instrumentation and other
appurtenances. Physical mixing of the catalysts would facilitate
synergistic reactions of the catalysts, but separation and recovery
of catalyst components would be more difficult. The system of
catalysts optionally may be repeated in one or more additional
stages, i.e., reactants from the contacting of the feed are
processed in another sequence of multiple catalysts.
[0018] In an alternative embodiment of the invention, therefore,
the reactor contains a physical mixture of individual catalysts
containing the beta zeolite and the MTW-type zeolite. In this
embodiment, particles are mechanically mixed to provide the
catalyst system of the invention. The particles can be thoroughly
mixed using known techniques such as mulling to intimately blend
the physical mixture. Although the first and second particles may
be of similar size and shape, the particles preferably are of
different size and/or density for ease of separation for purposes
of regeneration or rejuvenation following their use in hydrocarbon
processing.
[0019] As yet another alternative embodiment of the present
invention, a physical mixture of beta zeolite and MTW-type zeolite
is contained within the same catalyst particle. In this embodiment,
the sieves may be ground or milled together or separately to form
particles of suitable size, preferably less than 100 microns, and
the particles are supported in a suitable matrix. Optimally, the
matrix is selected from an inorganic oxide hereinafter described.
As a variant of this embodiment, the zeolites are as a
multi-compositional, multi-phase composite having contiguous
phases, especially wherein one phase comprises a deposition
substrate upon which another phase is deposited as an outer
layer.
[0020] The alkylaromatic feed mixture, preferably a non-equilibrium
mixture of C.sub.8 aromatics, is contacted with the isomerization
catalysts at suitable alkylaromatic-isomerization conditions. Such
conditions comprise a temperature ranging from about 100.degree. to
about 400.degree. C. or more, and preferably in the range from
about 150.degree. to 300.degree. C. The pressure generally is from
about 10 kPa to about 5 MPa absolute, preferably from about 100 kPa
to about 3 MPa absolute. A sufficient volume of catalyst comprising
the catalyst system is contained in the isomerization zone to
provide a liquid hourly space velocity with respect to the
hydrocarbon feed mixture of from about 0.1 to 20 hr.sup.-1, and
preferably 0.5 to 10 hr.sup.-1. If the two or more catalysts are
contained in separate beds, different operating conditions within
the above constraints may be used within each of the beds in order
to achieve optimum overall results.
[0021] The particular scheme employed to recover an isomerized
product from the effluent of the reactors of the isomerization zone
is not deemed to be critical to the instant invention, and any
effective recovery scheme known in the art may be used. Typically,
the liquid product is fractionated to remove light and/or heavy
byproducts to obtain the isomerized product. Heavy byproducts
include A.sub.10 compounds such as dimethylethylbenzene. In some
instances, certain product species such as ortho-xylene or
dimethylethylbenzene may be recovered from the isomerized product
by selective fractionation. The product from isomerization of
C.sub.8 aromatics usually is processed to selectively recover the
para-xylene isomer, optionally by crystallization. Selective
adsorption is preferred using crystalline aluminosilicates
according to U.S. Pat. No. 3,201,491. Improvements and alternatives
within the preferred adsorption recovery process are described in
U.S. Pat. No. 3,626,020, U.S. Pat. No. 3,696,107, U.S. Pat. No.
4,039,599, U.S. Pat. No. 4,184,943, U.S. Pat. No 4,381,419 and U.S.
Pat. No. 4,402,832, incorporated herein by reference.
[0022] As noted hereinabove, the present invention is drawn to a
catalyst system and its use in isomerization of C.sub.8 aromatics
comprising a beta zeolite first catalyst and a MTW-type zeolite
second catalyst, optionally having various contents of
platinum-group metal components. The mass ratio of first catalyst
to second catalyst depends primarily on the feedstock composition
and desired product distribution, with a first:second catalyst mass
ratio of from about 1:50 to about 50:1 being preferred and from
about 1:20 to 20:1 being especially preferred. The catalyst system
of the invention may include other catalysts, either molecular
sieve-based or amorphous. Such other catalysts include but are not
limited to zeolite mordenite, zeolite Y, ZSM-5, PSH-3, MCM-22,
MCM-36, MCM-49, and MCM-56. Zeolite Y is described in U.S. Pat. No.
3,130,007.
[0023] An essential component of the first catalyst of the present
invention therefore is at least one zeolite beta molecular sieve.
Zeolite beta is described in U.S. Pat. No. 3,308,069 and U.S. Re
28,341. Suitable zeolite betas include, but are not limited to,
pristine zeolite beta in which the H+ ion has at least partially
replaced the contained metal cation, as disclosed in EP 432,814 B1;
and zeolite beta into which certain quantities of alkaline,
alkaline-earth, or metallic cations have been introduced by ion
exchange, as disclosed in U.S. Pat. No. 5,672,799. Various
modifications of zeolite beta are also suitable for use in this
invention. Suitable modified zeolite betas include, but are not
limited to, zeolite beta which has been modified by steam treatment
and ammonium ion treatment, as disclosed in U.S. Pat. No.
5,522,984; and zeolite beta in which the H+ ion has at least
partially replaced the contained metal cation, with the zeolite
beta being modified by isodiorphous substitution of aluminum by
boron, gallium, or iron, as disclosed in EP 432,814 B1. Suitable
zeolites for use in this invention also include zeolites that are
synthesized by modified preparation methods, such as, but not
limited to, a preparation method comprising forming a reaction
mixture comprising water, a source of silicon dioxide, a source of
fluoride ions, a source of tetraethylammonium cations, and,
optionally, a source of an oxide of a trivalent element, as
disclosed in WO 9733830.
[0024] A highly preferred zeolite beta for use in the present
invention is disclosed in U.S. Pat. No. 5,723,710, the teachings of
which are incorporated herein by reference. This preferred zeolite
is a surface-modified zeolite beta which results from acid washing
of a templated native zeolite beta. That is, the formation of the
surface-modified zeolite beta starts with a templated beta where
the template is, for example, a tetraalkylammonium salt, such as
tetraethylammonium salt. The templated zeolite beta is acid washed
in order to protect the internal sites of the zeolite and to
prevent dealumination. The templated zeolite beta is treated with a
strong acid at a pH between about 0 up to about 2, although a pH
under 1 is preferred. Acids which may be used include nitric acid,
sulfuric acid, phosphoric acid, and so forth. For example, a weak,
0.01 molar nitric acid may be used in conjunction with ammonium
nitrate to perform the acid wash, although substantially higher
concentrations, up to about 20 wt-% nitric acid, are preferred.
Nitric acid is a preferred acid since it is a non-complexing acid
and therefore does not encourage dealumination. Treatment of the
templated zeolite beta with strong acid may be effected over the
temperature range between about 20.degree. C. (68.degree. F.) up to
about 125.degree. C. (257.degree. F.). It is important that acid
washing be done under conditions not so severe as to effect
dealumination.
[0025] The time over which acid washing is conducted in preparing
the preferred zeolite is quite temperature dependent. The formation
of the surface-modified zeolite beta should avoid significant bulk
dealumination of the zeolite. Thus, as a general statement it can
be said that acid washing should be done for a time insufficient to
effect dealumination. For example, using 0.01 molar nitric acid and
about 40% ammonium nitrate at 70.degree. C. (158.degree. F.),
contact times of 2 to 3 hours are found adequate to modify the
environment of surface aluminum without causing significant bulk
dealumination. Using about 15% nitric acid with ammonium nitrate to
treat about 25 wt-% slurry at 85.degree. C. (185.degree. F.), a
90-minute treatment is effective. The dependent variables in acid
washing include acid concentration, slurry concentration, time and
temperature, and suitable conditions at which surface-modified
zeolite beta can be prepared without significant bulk dealumination
are readily determined by the skilled artisan.
[0026] Next the template is removed by calcination at temperatures
in the range of 550.degree. to 700.degree. C. (1022.degree. to
1292.degree. F.). Calcination conditions are well known in the art
and need not be elaborated upon here. Therefore, in the more usual
case after the templated zeolite beta is acid washed it is mixed
with a conventional binder, extruded, and the extrudate is
ultimately calcined. But the critical portion of the preparation of
the preferred zeolite is the acid wash of the templated beta
according to the foregoing description.
[0027] The preferred zeolitic aluminosilicates of the second
catalyst are selected from those which have a silica-to-alumina
(Si:Al.sub.2) ratio greater than about 10, preferably greater than
20 and less than about 45, and a pore diameter of about 5 to 8
angstroms (.ANG.). Specific examples of suitable zeolites using
IWPAC Commission on Zeolite Nomenclature are the MFI, MEL, EUO,
FER, MFS, MTT, MTW, TON, MOR and FAU types of zeolites. Pentasil
zeolites MFI, MEL, MTW and TON are preferred, and MTW-type
zeolites, often designated ZSM-12, are especially preferred.
[0028] The preparation of the preferred MTW-type zeolites by
crystallizing a mixture comprising an alumina source, a silica
source and templating agent using methods well known in the art.
U.S. Pat. No. 3,832,449, which is herein incorporated by reference,
more particularly describes an MTW-type zeolite using
tetraalkylammonium cations. U.S. Pat. No. 4,452,769 and U.S. Pat.
No. 4,537,758, which are incorporated herein by reference, use a
methyltriethylammonium cation to prepare a highly siliceous
MTW-type zeolite.
[0029] The beta zeolite and the MTW-type zeolite each preferably
are respectively composited with a binder for convenient formation
of catalyst particles, either onto the same particle or separate
particles. The proportion of beta zeolite in the first catalyst is
about 5 to 90 mass-% , preferably about 10 to 80 mass-%, the
remainder other than metal and other components discussed herein
being the binder component. The relative proportion of MTW-type
zeolite in the second catalyst may range from about 1 to about 99
mass-%, with about 50 to about 90 mass-% being preferred for liquid
phase isomerization.
[0030] As mentioned previously, a binder will be used for both the
first and second catalysts, and thus each catalyst will contain a
zeolite that will typically be used in combination with a
refractory inorganic oxide binder. The binder should be a porous,
adsorptive support having a surface area of about 25 to about 500
m.sup.2/g. It is intended to include within the scope of the
present invention binder materials which have traditionally been
utilized in hydrocarbon conversion catalysts such as: (1)
refractory inorganic oxides such as alumina, titania, zirconia,
chromia, zinc oxide, magnesia, thoria, boria, silica-alumina,
silica-magnesia, chromia-alumina, alumina-boria, silica-zirconia,
phosphorus-alumina, etc.; (2) ceramics, porcelain, bauxite; (3)
silica or silica gel, silicon carbide, clays and silicates
including those synthetically prepared and naturally occurring,
which may or may not be acid treated, for example, attapulgite
clay, diatomaceous earth, fuller's earth, kaolin, kieselguhr, etc.;
(4) crystalline zeolitic aluminosilicates, either naturally
occurring or synthetically prepared such as FAU, MEL, MFI, MOR
types, in hydrogen form or in a form which has been exchanged with
metal cations, (5) spinels such as MgAl.sub.2O.sub.4,
FeAl.sub.2O.sub.4, ZnAl.sub.2O.sub.4, CaAl.sub.2O.sub.4, and other
like compounds having the formula MO Al.sub.2O.sub.3 where M is a
metal having a valence of 2; and (6) combinations of materials from
one or more of these groups.
[0031] A preferred refractory inorganic oxide for use in the
present invention is alumina. Suitable alumina materials are the
crystalline aluminas known as the gamma-, eta-, and theta-alumina,
with gamma- or eta-alumina giving the best results.
[0032] A form for the catalyst composite is an extrudate. The
well-known extrusion method initially involves mixing of the
molecular sieve with optionally the binder and a suitable peptizing
agent to form a homogeneous dough or thick paste having the correct
moisture content to allow for the formation of extrudates with
acceptable integrity to withstand direct calcination. Extrudability
is determined from an analysis of the moisture content of the
dough, with moisture content in the range of from about 30 to about
50 wt-% being preferred. The dough is then extruded through a die
pierced with multiple holes and the spaghetti-shaped extrudate is
cut to form particles in accordance with techniques well known in
the art. A multitude of different extrudate shapes is possible,
including, but not limited to, cylinders, cloverleaf, dumbbell and
symmetrical and asymmetrical polylobates. It is also within the
scope of this invention that the extrudates may be further shaped
to any desired form, such as spheres, by marumerization or any
other means known in the art.
[0033] An alternative form of the composite is a sphere
continuously manufactured by the well-known oil drop method.
Preparation of alumina-bound spheres generally involves dropping a
mixture of molecular sieve, alumina sol, and gelling agent into an
oil bath maintained at elevated temperatures. Alternatively,
gelation of a silica hydrosol may be effected using the oil-drop
method. One method of gelling this mixture involves combining a
gelling agent with the mixture and then dispersing the resultant
combined mixture into an oil bath or tower which has been heated to
elevated temperatures such that gelation occurs with the formation
of spheroidal particles. The gelling agents that may be used in
this process are hexamethylene tetraamine, urea or mixtures
thereof. The gelling agents release ammonia at the elevated
temperatures which sets or converts the hydrosol spheres into
hydrogel spheres. The spheres are then continuously withdrawn from
the oil bath and typically subjected to specific aging treatments
in oil and an ammoniacal solution to further improve their physical
characteristics.
[0034] Preferably the resulting composites are then washed and
dried at a relatively low temperature of about 50.degree. to
200.degree. C. and subjected to a calcination procedure at a
temperature of about 450.degree. to 700.degree. C. for a period of
about 1 to about 20 hours.
[0035] The catalysts optimally are subjected to steaming to tailor
their acid activity. The steaming may be effected at any stage of
the zeolite treatment, but usually is carried out on the composite
of zeolite binder prior to incorporation of an optional
platinum-group metal. Steaming conditions comprise a water
concentration of about 5 to 100 vol-%, pressure of from about 100
kPa to 2 MPa, and temperature of between about 600.degree. and
1200.degree. C.; the steaming temperature preferably between about
650.degree. and 1000.degree. C., more preferably at least about
750.degree. C. and optionally may be about 775.degree. C. or
higher. In some cases, temperatures of about 800.degree. to
850.degree. C. or more may be employed. The steaming should be
carried out for a period of at least one hour, and periods of 6 to
48 hours are preferred. Alternatively or in addition to the
steaming, the composite may be washed with one or more of a
solution of ammonium nitrate, a mineral acid, and/or water. The
washing may be effected at any stage of the preparation, and two or
more stages of washing may be employed. Composites may also be
treated with silica or carbon materials by means well known in the
art.
[0036] Catalysts of the invention may optionally comprise a
hydrogenation metal, especially a platinum-group metal, including
one or more of platinum, palladium, rhodium, ruthenium, osmium, and
iridium. But preferably, the catalysts of the invention may be
essentially free of any metal hydrogenation components, which are
considered unnecessary for liquid phase operation. By essentially
free of such metal is meant that the catalyst system contains less
than 0.1 mass-% amount of such metal. However, if present then the
optional hydrogenation metal is a platinum-group metal, and
preferably is platinum. The platinum-group metal generally
comprises from about 0.1 to about 2 mass-% of the final catalyst
calculated on an elemental basis. The platinum-group metal
component may exist within the final catalyst composite as a
compound such as an oxide, sulfide, halide, oxysulfide, etc., or as
an elemental metal or in combination with one or more other
ingredients of the catalyst composite. It is believed that the best
results are obtained when substantially all the platinum-group
metal component exists in a reduced state.
[0037] The optional platinum-group metal component may be
incorporated into the catalyst composite in any suitable manner.
One method of preparing the catalyst involves the utilization of a
water-soluble, decomposable compound of a platinum-group metal to
impregnate the calcined sieve/binder composite. Alternatively, a
platinum-group metal compound may be added at the time of
compositing the sieve component and binder. Complexes of platinum
group metals which may be employed in impregnating solutions,
co-extruded with the sieve and binder, or added by other known
methods include chloroplatinic acid, chloropalladic acid, ammonium
chloroplatinate, bromoplatinic acid, platinum trichloride, platinum
tetrachloride hydrate, platinum dichlorocarbonyl dichloride,
tetramine platinic chloride, dinitrodiaminoplatinum, sodium
tetranitroplatinate (II), palladium chloride, palladium nitrate,
palladium sulfate, diaminepalladium (II) hydroxide,
tetraminepalladium (II) chloride, and the like. It is within the
scope of the present invention that the catalyst composites may
contain other metal components. Such metal modifiers may include
rhenium, tin, germanium, lead, cobalt, nickel, indium, gallium,
zinc, uranium, dysprosium, thallium, and mixtures thereof.
Catalytically effective amounts of such metal modifiers may be
incorporated into the catalysts by any means known in the art to
effect a homogeneous or stratified distribution.
[0038] The catalysts of the present invention may contain a halogen
component, comprising fluorine, chlorine, bromine or iodine or
mixtures thereof, with chlorine being preferred. Preferably,
however, the catalyst contains no added halogen other than that
associated with other catalyst components.
[0039] The catalyst composites are dried at a temperature of from
about 100.degree. to about 320.degree. C. for a period of from
about 2 to about 24 or more hours and, usually, calcined at a
temperature of from about 400.degree. to about 650.degree. C. in an
air atmosphere for a period of from about 0.1 to about 10 hours
until the metallic compounds present are converted substantially to
the oxide form. If desired, the optional halogen component may be
adjusted by including a halogen or halogen-containing compound in
the air atmosphere.
[0040] The resultant calcined composites optimally are subjected to
a substantially water-free reduction step to ensure a uniform and
finely divided dispersion of the optional metallic components. The
reduction optionally may be effected in the process equipment of
the present invention. Substantially pure and dry hydrogen (i.e.,
less than 20 vol. ppm H.sub.2O) preferably is used as the reducing
agent in this step. The reducing agent contacts the catalyst at
conditions, including a temperature of from about 200.degree. to
about 650.degree. C. and for a period of from about 0.5 to about 10
hours, effective to reduce substantially all of the Group VIII
metal component to the metallic state. In some cases the resulting
reduced catalyst composite may also be beneficially subjected to
presulfiding by a method known in the art to incorporate in the
catalyst composite from about 0.05 to about 1.0 mass-% sulfur
calculated on an elemental basis.
EXAMPLES
[0041] The following examples are presented only to illustrate
certain specific embodiments of the invention, and should not be
construed to limit the scope of the invention as set forth in the
claims. There are many possible other variations, as those of
ordinary skill in the art will recognize, within the spirit of the
invention.
Example I
[0042] Samples of the three catalysts comprising zeolites were
prepared for comparative pilot-plant testing.
[0043] Catalyst A contained zeolite mordenite bound by alumina
prepared in accordance with the teachings of U.S. Pat. No.
4,861,935. As received, mordenite powder was mixed with alumina
powder to an approximate weight ratio of 9: 1, peptized, extruded,
and acid washed by means known in the art.
[0044] Catalyst B contained aluminum-phosphate-bound MFI type
zeolite prepared in accordance with U.S. Pat. No. 6,143,941. A
first solution was prepared by adding phosphoric acid to an aqueous
solution of hexamethylenetetraamine (HMT) in an amount to yield a
phosphorus content of the finished catalyst equal to about 11
mass-%. A second solution was prepared by adding an
ammonia-exchanged MFI-type zeolite having an Si/Al.sub.2 ratio of
about 39 to enough alumina sol, prepared by digesting metallic
aluminum in hydrochloric acid, to yield a zeolite content in the
finished catalyst equal to about 67 mass-%. These two solutions
were commingled to achieve a homogeneous admixture of HMT,
phosphorus, alumina sol, and zeolite. This admixture was dispersed
as droplets into an oil bath maintained at about 93.degree. C. The
droplets remained in the oil bath until they set and formed
hydrogel spheres having a diameter of about 1.6 mm. The spheres
were removed from the oil bath, water washed, air dried, and
calcined at a temperature of about 550.degree. C. Then the calcined
spheres were subjected to steaming at a temperature of about
660.degree. C. in an atmosphere of 40% steam in air. The steamed
spheres were then metal-impregnated using a solution of tetraamine
platinum chloride. Upon completion of the impregnation, the
catalyst was dried, oxidized, and reduced to yield a catalyst
containing about 0.04 mass-% platinum.
[0045] Catalyst C contained zeolite beta prepared in accordance
with U.S. Pat. No. 5,723,710. Commercial zeolite beta chemically
comprising SiO.sub.2 92.2 wt-% and Al.sub.2O.sub.3 7.0 wt-%, with a
LOI of 24.3 wt-%, and a surface area by N.sub.2 BET of 672
m.sup.2/g, was obtained. To a solution of 1428 grams ammonium
nitrate in 3224 grams distilled water was added 932 grams of 70
wt-% nitric acid and the mixture was heated to 85.degree. C. The
zeolite beta (1416 grams dry weight) was added and this mixture was
stirred at 85.degree. C. for 90 minutes. The slurry was filtered
and washed using 10 liters of distilled water and then dried at
100.degree. C. for 16 hours. Then the zeolite was calcined in air
at 650.degree. C. for 3 hours.
[0046] Catalyst D contained MTW-type zeolite prepared in accordance
with U.S. Pat. No. 4,452,769. To a solution of 0.4 grams sodium
hydroxide in 9 grams distilled water was added 0.078 g aluminum
hydroxide hydrate and stirred until dissolved. A second solution of
1.96 grams of methyltriethylammonium halide (MTEA-Cl, note here the
chloride form was used instead of the bromide form) in 9 grams
distilled water was prepared and stirred until dissolved. Then,
both solutions were stirred together until homogenized. Next, 3
grams of precipitated silica was added, stirred for 1 hour at room
temperature and sealed in a Teflon-lined autoclave for 8 days at
150.degree. C. Zeolite type MTW was recovered after cooling,
filtering, and washing with distilled water. After drying a product
of 5 Na.sub.2O:1.25Al.sub.2O.sub.3:50SiO.sub.2:1000H.sub.2O:10(-
MTEA-Cl) with a N.sub.2 BET 454 m.sup.2/g, was obtained. To form
catalyst D, the dry MTW-zeolite powder was calcined and then
compressed to form pellets.
Example II
[0047] The catalysts were evaluated for liquid phase isomerization
of C.sub.8 aromatics using a pilot-plant flow reactor processing a
non-equilibrium C.sub.8 aromatic feed having the following
composition in wt-%:
1 Ethylbenzene 7.17 Para-xylene 0.03 Meta-xylene 70.46 Ortho-xylene
22.28 C.sub.9.sup.+ Aromatics 0.05 C.sub.9.sup.+ Non-aromatics
0.01
[0048] This feed was contacted with catalyst at a liquid hourly
space velocity of about 1.5 hr.sup.-1. Pressure was at 1200 kPa
sufficient to maintain liquid phase. Reactor temperature was
adjusted to effect a favorable conversion level. Catalyst C
appeared as the most stable catalyst during this testing. Results
were as follows:
2 Catalyst A B C Temperature, .degree. C. 247 245 246 EB
conversion, mol- % 19.7 2.1 50.1 C.sub.10 Aromatics 1.31 0.15 3.44
p-xylene/xylenes, mol- % 23.7 22.1 22.7
[0049] Catalyst C was particularly effective in converting
undesired ethylbenzene isomers while still achieving a good
proportion of para-xylene isomers in total xylene isomers.
Example III
[0050] A second series of catalytic tests was performed for liquid
phase isomerization of C.sub.8 aromatics using a pilot-plant flow
reactor processing a non-equilibrium C.sub.8 aromatic feed having
the following composition in wt-%:
3 Ethylbenzene 10.8 Meta-xylene 63.6 Ortho-xylene 25.4
C.sub.9.sup.+ 0.2
[0051] This feed was contacted with catalyst under constant
temperatures with an adjusted weight hourly space velocity (WHSV).
Pressure was about 1380 kPa. Results were as follows:
4 Catalyst C D (C & D) Temperature .degree. C. 245 245 240 EB
conversion, mol- % 35.1 2.2 37 p-xylene/xylenes, mol- % 20.1 22.3
22.5 % approach to pX/X equilibrium 82.6 91.7 92.5 WHSV, hr.sup.-1
1.3 0.5 0.4
[0052] The catalyst system of the present invention combined C and
D in a ratio with 50 volume-% of catalyst C to 50 volume-% of
catalyst D. The combination catalyst system was loaded in separate
sequential reactors, and was particularly effective in converting
undesired ethylbenzene isomers while still achieving a superior
approach to equilibrium para-xylene as part of total xylenes. Very
nearly the same ethylbenzene conversion can be accomplished with
the catalyst system combination as can be accomplished with
catalyst C alone. Very nearly the same approach to para-xylene
equilibrium can be accomplished with the catalyst system
combination as with catalyst D alone. Note that the "% approach to
pX/X equilibrium" is defined as percentage of the product mixture
relative to a calculated equilibrium amount of para-xylene under
conditions of room temperature and a pressure of 200 kPa, with a
number greater than 90% being considered at least near the
equilibrium amount.
* * * * *