Molecular sieve abstract
The invention relates to a process for producing alkylated aromatic
hydrocarbons, preferably with an oxygen or sulfur containing alkylating
agent, in the presence of a multi-component molecular sieve catalyst
composition that includes a molecular sieve and an active metal
oxide. The invention is also directed to methods of making and formulating
the multi-component molecular sieve catalyst composition useful
in producing alkylated aromatics.
Molecular sieve claims
We claim:
1. A method for making a multi-component molecular sieve catalyst
composition, the method comprising the step of combining a) at least
one active metal oxide having a CO.sub.2/NH.sub.3 Chemisorption
Molar Ratio of at least 0.5 b) a molecular sieve synthesized from
the combination of at least two of the group consisting of a silicon
source, a phosphorous source, and an aluminum source, optionally
in the presence of a templating agent, and c) a binder or a matrix
material or both.
2. The method of claim 1 wherein the at least one active metal
oxide comprises a non-acidic metal oxide.
3. The method of claim 1 wherein the at least one active metal
oxide comprises at least one metal oxide selected from the group
consisting of Group 2 Group 3 Group 4 Lanthanide Series, and
Actinide Series metal oxides.
4. The method of claim 1 wherein the at least one active metal
oxide comprises at least one of an active yttrium metal oxide, an
active lanthanum metal oxide, or an active scandium metal oxide.
5. The method of claim 2 wherein the at least one active metal
oxide comprises a zirconium or hafnium oxide combined with a lanthanum
oxide.
6. The method of claim 1 wherein the at least one active metal
oxide comprises at least one combination of one or more metal oxide
a where said combination was prepared by co-precipitation of said
one or more metal oxide and said combination is itself active.
7. The method of claim 1 wherein the at least one active metal
oxide comprises at least one active metal oxide which has been calcined
prior to the step of combining.
8. The method of claim 2 wherein the multi-component molecular
sieve catalyst composition has a Half-life Enhancement index (HLEI)
greater than about 2.
9. The method of claim 1 wherein the multi-component molecular
sieve catalyst composition has an HLEI greater than about 10.
10. The method of claim 1 wherein the multi-component molecular
sieve catalyst composition has an HLEI greater than about 20.
11. The method of claim 1 wherein the molecular sieve comprises
crystals with a framework-type selected from the group consisting
of MFI, MTT, and MWW; and the binder, if any, and the matrix material,
if any, are different from each active metal oxide contained in
the multi-component molecular sieve catalyst composition.
12. The method of claim 1 wherein the weight ratio of all active
metal oxides contained in the multi-component molecular sieve catalyst
composition to the molecular sieve contained in the multi-component
molecular sieve catalyst composition, excluding any binders or matrix
material, is in the range of about 1:100 to about 2:1.
13. The method of claim 1 wherein the weight ratio of all active
metal oxides contained in the multi-component molecular sieve catalyst
composition to the molecular sieve contained in the multi-component
molecular sieve catalyst composition, excluding any binders or matrix
material, is in the range of about 1:50 to about 1:2.
14. The method of claim 1 wherein the molecular sieve, binder,
and matrix material are combined prior to combining the at least
one active metal oxide.
15. A method of making a multi-component molecular sieve catalyst
composition, the method comprising the steps of: (a) synthesizing
a molecular sieve by the method comprising the steps of: (i) forming
a first reaction mixture of at least two of the group consisting
of a silicon source, a phosphorous source, and an aluminum source;
and (ii) removing the molecular sieve from the first reaction mixture;
(b) forming an active metal oxide having a CO.sub.2/NH.sub.3 Chemisorption
Molar Ratio of at least 0.5 by the method comprising the steps of:
(i) forming a second reaction mixture of at least one metal oxide
precursor and a precipitating agent; (ii) removing the active metal
oxide having a CO.sub.2/NH.sub.3 Chemisorption Molar Ratio of at
least 0.5 from the second reaction mixture; and (c) combining the
molecular sieve and the active metal oxide.
16. The method of claim 15 wherein the active metal oxide has been
calcined prior to step (c).
17. The method of claim 15 wherein the molecular sieve and the
active metal oxide are combined with a binder or a matrix material
or both to form a multi-component molecular sieve catalyst composition.
18. The method of claim 15 wherein the molecular sieve is combined
with a matrix material or a binder or both to form a molecular sieve
catalyst composition which is then combined with the active metal
oxide.
19. The method of claim 15 wherein the molecular sieve catalyst
composition and the active metal oxide are further combined with
a matrix material or a binder or both.
20. The method of claim 15 wherein the weight ratio of the active
metal oxide to the molecular sieve, excluding any binders or matrix
material, is in the range of about 1:100 to about 2:1.
21. The method of claim 15 wherein the weight ratio of the active
metal oxide to the molecular sieve, excluding any binders or matrix
material, is in the range of about 1:50 to about 1:2.
22. A multi-component molecular sieve catalyst composition comprising:
(a) at least one active metal oxide selected in the group consisting
of Group 2 Group 3 Group 4 Lanthanide Series, and Actinide a
Series metal oxides, wherein said active metal oxide having a CO.sub.2/NH.sub.3
Chemisorption Molar Ratio of at least 0.5; (b) a binder or a matrix
material or both; and (c) a metallosilicate molecular sieve.
Molecular sieve description
FIELD OF THE INVENTION
The present invention relates to a conversion process utilizing
a multi-component molecular sieve catalyst composition to alkylate
aromatics. The invention is also directed to a method of making
the molecular sieve catalyst composition by physically mixing solids
or particulates comprising at least one active metal oxide with
one or more molecular sieve materials.
BACKGROUND OF THE INVENTION
A variety of processes for alkylating aromatics using conventional
aluminosilicate molecular sieve catalysts are commercially available.
Various aromatic compounds are either naturally present in or are
traditionally produced from petroleum feedstock by catalytic reforming
processes.
Aromatics alkylation is an important procedure for producing many
useful chemical products. For example, para-xylene, which can be
produced by alkylating toluene with methanol, constitutes an important
starting material for manufacturing synthetic polyester fibers,
films, and resins. These polyester materials have many practical,
well known uses, such as in fabrics, carpets, and apparel. Other
alkylated aromatics have similar roles.
Methanol, the preferred alcohol for para-xylene production from
a toluene feedstock, is typically synthesized from the catalytic
reaction of hydrogen, carbon monoxide and/or carbon dioxide in a
methanol reactor in the presence of a heterogeneous catalyst. For
example, in one synthesis process methanol is produced using a copper/zinc
oxide catalyst in a water-cooled tubular methanol reactor.
Molecular sieves are porous solids having pores of different sizes
including crystalline molecular sieves such as zeolites, as well
as carbons and oxides. The most commercially useful molecular sieves
for the petroleum and petrochemical industries are crystalline molecular
sieves. Crystalline molecular sieves in general have a one-, two-,
or three-dimensional crystalline pore structure having uniformly
sized pores of molecular scale within each dimension. These pores
selectively adsorb molecules that can enter the pores and exclude
those molecules that are too large.
Examples of some potentially useful molecular sieves for aromatics
alkylation include aluminosilicate molecular sieves as described
in co-pending U.S. patent application Ser. No. 09/866907 (ITQ-13)
and in U.S. Pat. No. 3702886 (ZSM-5), U.S. Pat. No. 4076842
(ZSM-23), U.S. Pat. No. 4397827 (ZSM-48), and U.S. Pat. No. 4954325
(MCM-22), all of which are herein fully incorporated by reference.
Aluminosilicate molecular sieves, also known as zeolites, contain
a three-dimensional microporous crystalline framework structure
of [SiO.sub.4] and [AlO.sub.4] corner sharing tetrahedral units.
Zeolites are generally synthesized by the hydrothermal crystallization
of a reaction mixture of silicon and aluminum sources. Other metallosilicate
molecular sieves with various metals (such as, for example, gallium,
iron, and/or boron) substituted for aluminum in some portion of
the crystalline framework are also known in the art.
Aluminum and phosphorus containing molecular sieve crystals (for
example, ALPO and SAPO) can be produced by the hydrothermal crystallization
of a reaction mixture of silicon, aluminum, and phosphorus sources
along with at least one templating agent as described, for example,
in U.S. Pat. No. 4440871 which is herein fully incorporated by
reference.
Molecular sieves are often formed into molecular sieve catalyst
compositions to improve their durability and to facilitate handling
in commercial conversion processes. These molecular sieve catalyst
compositions are formed by combining a molecular sieve with a matrix
material and/or a binder. Although the use of binders and matrix
materials are known for use with molecular sieves to form molecular
sieve catalyst compositions useful in alkylating aromatics, these
binders and matrix materials typically only serve to provide desired
physical characteristics to the catalyst composition and have little
to no effect on conversion and selectivity of the molecular sieve.
Many of the toluene alkylation processes use catalytic materials
which are prone to rapid catalyst deactivation, usually due to coke
formation, under typical reaction conditions and, therefore, require
constant regeneration. This regeneration requirement usually necessitates
the use of higher cost technology such as fluid bed reactors wherein
the catalyst is continuously regenerated.
Although a variety of treatments have been disclosed for improving
conversion, improving product selectivity, and/or reducing coke
formation, there is still a significant problem with rapid catalyst
de-activation due to coke formation at the reaction conditions required
for alkylation of aromatics. It would therefore be desirable to
have an improved molecular sieve catalyst composition having longer
lifetimes and, preferably, also having better conversion rates,
product selectivity, and commercially desirable operability and
cost advantages.
SUMMARY OF THE INVENTION
This invention provides for a multi-component molecular sieve catalyst
composition, a method for making or formulating the multi-component
molecular sieve catalyst composition, and a process for using the
multi-component molecular sieve catalyst composition to produce
one or more alkylated aromatics.
In one embodiment the invention is directed to a method for making
the multi-component molecular sieve composition of the invention
by combining, contacting, mixing, or the like, a molecular sieve
and at least one active metal oxide, preferably a non-acidic metal
oxide. Preferably the molecular sieve is synthesized from the combination
of two or more of a silicon source, an aluminum source, and a phosphorous
source, optionally in the presence of a templating agent, and the
active metal oxide is an oxide of a Group 2 Group 3 Group 4 Lanthanide
Series, or Actinide Series metal. More preferred active metal oxides
are combinations of a Group 4 metal oxide with one or more selected
from Group 2 Group 3 Lanthanide Series, or Actinide Series metal
oxides. Even more preferred are i) zirconium and/or hafnium oxides
combined with a Group 3 metal oxide such as scandium, lanthanum,
or yttrium metal oxide or ii) yttrium oxide. More preferably, the
molecular sieve is an intermediate pore size aluminosilicate molecular
sieve and the metal oxide is a zirconium and/or hafnium metal oxide
co-precipitated with lanthanum oxide. Even more preferably, the
active metal oxide is a co-precipitated combination of zirconium
and lanthanum oxides, and the molecular sieve composition is a ZSM-5
catalyst modified as described U.S. Pat. No. 6423879 which is
herein fully incorporated by reference.
In another embodiment the invention relates to a method for making
a multi-component molecular sieve catalyst composition by combining,
contacting, mixing, or the like, a molecular sieve, a matrix material,
a binder, and at least one active metal oxide, wherein the active
metal oxide is different from both the binder and the matrix material.
Preferably, the active metal oxide is a non-acidic oxide of a Group
2 Group 3 Group 4 Lanthanide Series, or Actinide Series metal,
and the molecular sieve is synthesized from the combination of two
or more of a silicon source, an aluminum source, and a phosphorous
source, optionally in the presence of a templating agent. In a more
preferred embodiment, the molecular sieve and the binder and/or
matrix material are made into a formulated molecular sieve catalyst
composition that is then contacted, mixed, combined, spray dried,
or the like, with at least one active metal oxide, preferably an
active non-acidic Group 2 Group 3 Group 4 Lanthanide Series,
and/or Actinide Series metal oxide, and more preferably a Group
4 metal oxide such as hafnium or zirconium metal oxide combined
with a Group 2 Group 3 Lanthanide Series, or Actinide Series metal
oxide.
In one more embodiment, the multi-component molecular sieve catalyst
composition, formulated with a binder and/or matrix or otherwise,
of the invention, discussed above, has a Half-life Enhancement Index
(HLEI) significantly greater than catalyst compositions without
an active metal oxide, that have, by definition, a HLEI of 1. HLEI
is the ratio of the half-life of the multi-component molecular sieve
catalyst composition described herein to that of the molecular sieve
or molecular sieve catalyst composition in the absence of an active
metal oxide. Determination of HLEI is discussed later in this patent
specification.
In still another embodiment of the invention, a multi-component
molecular sieve catalyst composition is made by a method comprising
the steps of: (i) synthesizing a molecular sieve by the method comprising
the steps of: (a) forming a first reaction mixture of at least two
of the group consisting of a silicon source, a phosphorous source,
and an aluminum source, optionally containing one or more templating
agents, and (b) removing the molecular sieve from the first reaction
mixture; (ii) producing an active metal oxide by the method comprising
the steps of: (a) forming a second reaction mixture of at least
one active metal oxide precursor, (b) removing an active metal oxide
from the second reaction mixture, and (iii) combining the molecular
sieve and the active metal oxide. Preferably the active metal oxide
is calcined prior to combining the molecular sieve and the active
metal oxide.
In yet another embodiment, the invention is directed to a process
for alkylating aromatics in the presence of any of the above multi-component
molecular sieve catalyst compositions. In particular, the process
involves alkylating aromatics, preferably toluene, with an alkylating
agent, preferably an oxygen- or a sulfur containing alkylating agent,
more preferably an alkylating agent comprising an alcohol, and most
preferably an alkylating agent comprising methanol, in the presence
of one or more of the multi-component molecular sieve catalyst compositions
discussed above.
The invention is also directed to a composition of matter of any
one of the multi-component molecular sieve catalyst compositions
described above. The invention is further directed to a multi-component
molecular sieve catalyst composition comprising the use of at least
one active metal oxide in combination with a molecular sieve, optionally
including a matrix material and/or a binder, in which the active
metal oxides are different from the matrix material and/or the binder,
for use in alkylating aromatics using an oxygen- or sulfur-containing
alkylating agent.
DETAILED DESCRIPTION OF THE INVENTION
Introduction
This invention is directed toward a multi-component molecular sieve
catalyst composition, a method for making or formulating the multi-component
molecular sieve catalyst composition, and a process for alkylating
aromatics using the multi-component molecular sieve catalyst composition.
It has been found that combining a molecular sieve with an active
metal oxide results in a multi-component molecular sieve catalyst
composition capable of alkylating one or more aromatics preferably
in the presence of oxygenates, more particularly methanol, with
a longer half-life than the molecular sieve alone. The preferred
active metal oxides are those having a Group 2 (for example calcium
and magnesium), Group 3 (for example scandium, yttrium, and lanthanum),
Group 4 (for example zirconium and hafnium), Lanthanide Series (for
example cerium, praseodymium, and neodymium), and/or Actinide Series
(for example thorium and protactinium) metal from the Periodic Table
of Elements using the IUPAC format described in the CRC Handbook
of Chemistry and Physics, 79th Edition, CRC Press, Boca Raton, Fla.
(1998). Also, surprisingly, the multi-component molecular sieve
catalyst compositions have longer lifetimes, at least in part because
they are less susceptible to coke formation which is well known
to reduce catalyst activity. It has also been discovered that the
multi-component molecular sieve catalyst compositions are often
more selective to para-xylene when toluene is used as the feedstock.
In this regard, in particular in the conversion of toluene to at
least para-xylene, the production of less desirable ortho- and meta-xylene
is reduced.
Molecular Sieves
Molecular sieves have various chemical, physical, and framework
characteristics. Molecular sieves have been classified by the Structure
Commission of the International Zeolite Association according to
the rules of the IUPAC Commission on Zeolite Nomenclature. A framework-type
describes the topology and connectivity of the tetrahedrally coordinated
atoms constituting the framework and makes an abstraction of the
specific properties for those materials. Molecular sieves for which
a structure has been established are assigned a three letter code
and are described in the Atlas of Zeolite Framework Types, 5th edition,
Elsevier, London, England (2001), which is herein fully incorporated
by reference.
Non-limiting examples of these molecular sieves include intermediate
pore size molecular sieves having a pore size in at least one dimension
from about 5 .ANG. to about 7 .ANG., including, for example, AEL,
EUO, FER, HEU, MEI, MEL, MFI, MFS, MTT, MTW, MWW, and TON structure
type molecular sieves. Non-limiting examples of specific intermediate
pore size molecular sieves include ITQ-13 (not yet assigned a structure
type), MCM-22 ZSM-5 ZSM-11 ZSM-12 ZSM-22 ZSM-23 ZSM-34 ZSM-35
ZSM-38 ZSM-48 ZSM-50 and ZSM-57. Examples of large pore molecular
sieves include molecular sieves having a pore size of at least about
7 .ANG. such as AET, AFI, BEA, EMT, FAU, LTL, MAZ, MEI, MOR, OFF,
and VFI structure type molecular sieves. Non-limiting examples of
large pore molecular sieves include for example mazzite, offretite,
Zeolite L, VPI-5 Zeolite Y, Zeolite X, omega, Beta, ZSM-3 ZSM-4
ZSM-18 ZSM-20 and SAPO-37. Non-limiting examples of the preferred
molecular sieves, particularly for methylating a toluene containing
feedstock into xylenes, include AEL, BEA, FAU, FER, LTL, MFI, MOR,
MTT, MTW, MWW, and TON structure types. For a naphthalene feedstock,
preferred molecular sieve configurations would include, but not
be limited to, BEA, FAU, MOR, and MWW structure types. In one preferred
embodiment, the molecular sieve of the invention has an MFI topology
(such as ZSM-5) or an MTT topology (such as ZSM-23), or a combination
thereof, most preferably an MFI topology.
Preferred molecular sieves include intermediate and large pore
configurations, preferably having an average pore diameter in the
range of about 3.5 .ANG. to about 15 .ANG., more preferably in the
range from about 5 .ANG. to about 7 .ANG..
Aluminosilicate molecular sieves have been described in detail
in numerous publications, including, for example, co-pending U.S.
patent application Ser. No. 09/866907 (ITQ-13) and U.S. Pat. No.
3702886 (ZSM-5), U.S. Pat. No. 4076842 (ZSM-23), U.S. Pat. Nos.
4397827 and 4358397 (ZSM-48), and U.S. Pat. No. 4954325 (MCM-22).
Silicon, aluminum, and phosphorous based molecular sieves and metal
containing silicon, aluminum, and phosphorous based molecular sieves
are also known in the art. Other molecular sieves include those
described in R. Szostak, Handbook of Molecular Sieves, Van Nostrand
Reinhold, New York, N.Y. (1992), which is herein fully incorporated
by reference.
The synthesis of molecular sieves is described in many of the references
known to those skilled in the art. Generally, molecular sieves are
synthesized by the hydrothermal crystallization of one or more of
a source of aluminum, a source of phosphorous, a source of silicon,
a templating agent, and a metal containing compound. Typically,
a combination of sources of silicon, aluminum, and/or phosphorous,
optionally with one or more templating agents and/or one or more
metal containing compounds are placed in a sealed pressure vessel,
optionally lined with an inert plastic such as polytetrafluoroethylene,
and heated under a crystallization pressure and temperature until
a crystalline material is formed, which is then recovered by filtration,
centrifugation, and/or decanting.
Aluminosilicate molecular sieves can be crystallized over a wide
range of silicon (Si) to aluminum (Al) ratios. This Si/Al.sub.2
ratio is one factor that dictates the level of acidity or acid activity
a particular molecular sieve will exhibit. Normally, the higher
the Si/Al.sub.2 ratio, the less acidic an aluminosilicate molecular
sieve will be and usually less prone to coking. The crystal size
and the dimensions of the channel system are also important variables
affecting coke formation. A high Si/Al.sub.2 ratio is generally
preferred for alkylation processes using aluminosilicates. In one
embodiment, the molecular sieve, as synthesized, is an aluminosilicate
molecular sieve having a Si/Al.sub.2 ratio greater than 12 preferably
between 40 and 1000 and most preferably between 100 and 500 all
as measured prior to any treatment of the molecular sieve to reduce
its diffusivity. Different constraints and preferences will apply
to molecular sieves containing phosphorous; for example in SAPOs,
lower silica content correlates to lower acidity.
Method for Making Molecular Sieve Catalyst Compositions
The crystals of molecular sieve can be formed into a wide variety
of forms. Generally speaking, the particles can be in the form of
a powder, a granule, or a molded product, such as an extrudate having
particle size sufficient to pass through a 2 mesh (Tyler) screen
and be retained on a 400 mesh (Tyler) screen. In cases where the
catalyst is molded, such as by extrusion, the crystals can be extruded
before drying or partially dried and then extruded or the crystals
can be calcined to remove organic template and then extruded. All
of these forms will be referred to herein as "crystals."
In the case of many catalysts, it is desirable that crystalline
molecular sieves be incorporated with binder material resistant
to the temperature and other conditions employed in organic conversion
processes. Such binder materials include synthetic or naturally
occurring substances as well as inorganic materials such as clay,
silica, and/or metal oxides. The latter may be either naturally
occurring or in the form of gelatinous precipitates or gels including
mixtures of silica and metal oxides. Naturally occurring clays which
can be composited with the zeolite include those of the montmorillonite
and kaolin families, which families include the sub-bentonites and
the kaolins commonly known as Dixie, McNamee-Georgia and Florida
clays or others in which the main mineral constituent is halloysite,
kaolinite, dickite, nacrite, or anauxite. Such clays can be used
in the raw state as originally mined or initially subjected to calcination,
acid treatment, or chemical modification. In one embodiment, the
binder is different from the active metal oxide.
In addition to the foregoing materials, the molecular sieves may
be composited with a porous matrix material, such as alumina, silica-alumina,
silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,
and silica-titania, as well as ternary compositions, such as silica-alumina-thoria,
silica-alumina-zirconia, silica-alumina-magnesia, and silica-magnesia-zirconia.
The molecular sieve may also be composited with materials such as
the zeolitic materials which are disclosed in U.S. Pat. No. 5993642
which is herein fully incorporated by reference. In one embodiment,
the matrix material is different from the active metal oxide.
The relative proportions between the molecular sieve component
and the binder and/or matrix material will vary widely with the
molecular sieve content ranging from about 1 to about 99 percent
by weight, more preferably in the range of about 10 to about 70
percent by weight of molecular sieve component, and still more preferably
from about 20 to about 50 percent.
In one embodiment, the binder, the molecular sieve, and the matrix
material are combined in the presence of a liquid to form a molecular
sieve catalyst composition. The combination is then subjected to
calcination.
Upon combining the molecular sieve and the matrix material, optionally
with a binder, in a liquid to form a slurry, mixing, preferably
rigorous mixing is needed to produce a substantially homogeneous
mixture containing the molecular sieve composition. Non-limiting
examples of suitable liquids include one or a combination of water,
alcohol, ketones, aldehydes, and/or esters. The most preferred liquid
is water.
The molecular sieve composition, the matrix material, and the optional
binder are in the same or different liquid and are combined in any
order, together, simultaneously, sequentially, or a combination
thereof. In a preferred embodiment, the same liquid, preferably
water, is used. The molecular sieve composition, matrix material,
and optional binder are combined in a liquid as solids, substantially
dry or in a dried form, or as slurries, together or separately.
If solids are added together as dry or substantially dried solids,
it is preferable to add a limited and/or controlled amount of liquid.
In one embodiment, the uniform slurry of the molecular sieve, binder,
and matrix materials is fed to a forming unit that produces the
formed molecular sieve catalyst composition. The forming unit may
be a spray dryer maintained at a temperature sufficient to remove
most of the liquid from the slurry and from the resulting molecular
sieve catalyst composition. The resulting catalyst composition when
formed in this way takes the form of microspheres. In an alternative
embodiment, the molecular sieve catalyst composition may be formed
into tablets, pellets, granules, beads or the like through a process
such as auger extrusion. To facilitate such an extrusion process,
extrusion aids such as polymers, for example poly vinyl acetate
(PVA), or cellulose derivatives may be added to the formulation
during mixing.
Once the molecular sieve catalyst composition is formed in a substantially
dry or dried state, to further harden and/or activate the formed
molecular sieve catalyst composition, a heat treatment such as calcination,
at an elevated temperature is usually performed. A conventional
calcination environment is air that typically includes a small amount
of water vapor. Typical calcination temperatures are in the range
from about 400.degree. C. to about 1000.degree. C., preferably
from about 500.degree. C. to about 800.degree. C., and most preferably
from about 550.degree. C. to about 700.degree. C., preferably in
a calcination environment such as air, nitrogen, helium, flue gas
(combustion product lean in oxygen), or any combination thereof.
In a preferred embodiment, the molecular sieve catalyst or molecular
sieve catalyst composition is heated in air from room temperature
to about 540.degree. C., at a heating rate of about 5.degree. C./min
and then the temperature is maintained at about 540.degree. C. for
about 4 hours to about 6 hours.
The molecular sieves and molecular sieve catalyst compositions
prepared by the process of the present invention may be further
ion exchanged before or after calcination either to replace at least
in part the original alkali metal present in the zeolite with a
different cation, e.g. a metal such as nickel, copper, zinc, palladium,
platinum, calcium, or rare earth metal, or to provide a more acidic
form of the molecular sieve by exchange of alkali metal with intermediate
ammonium, followed by calcination of the ammonium form to provide
the acidic hydrogen form. The acidic form of the molecular sieve
may be readily prepared by ion exchange using a suitable acidic
reagent such as ammonium nitrate. The molecular sieve may then be
calcined at a temperature of about 400.degree. C. to about 550.degree.
C. to remove ammonia and create the hydrogen form. Particularly
preferred cations will depend on the use of the zeolite and include
hydrogen, rare earth metals, and metals of Groups 2 3 4 8 9
10 11 12 13 and 14 of the Periodic Table of the Elements.
In another preferred embodiment, the molecular sieve catalyst or
molecular sieve catalyst composition is first selectivated with
a selectivating agent prior to use in the alkylation process. The
term "selectivating agent" is used herein to indicate
substances that will increase the shape-selectivity (e.g., paraselectivity)
of the molecular sieve catalyst. Some non-limiting examples of selectivation
include treating the molecular sieve with phosphorus and/or boron
oxide, coke, or various silicon-containing compounds.
Selectivation may also be accomplished by exposing the catalyst
in a reactor bed to a thermally decomposable organic compound, e.g.,
toluene, at a temperature in excess of the decomposition temperature
of said compound, e.g., from about 480.degree. C. to about 650.degree.
C., more preferably 540.degree. C. to 650.degree. C.; at a weight
hourly space velocity (WHSV) in the range of from about 0.1 to 20
kg of feed per kg of catalyst per hour; at a pressure in the range
of from about 1 to 100 atmospheres; and in the presence of 0 to
about 2 moles of hydrogen per mole of organic compound, more preferably
from about 0.1 to about 2 moles of hydrogen per mole of organic
compound; and optionally in the presence of 0 to 10 moles of nitrogen
or another inert gas per mole of organic compound. This process
is conducted for a period of time until the desired quantity of
coke has deposited on the catalyst surface.
Furthermore, selectivation may be accomplished using organosilicon
compounds as selectivating agents. The organosilicon compounds used
in one embodiment comprise polysiloxane, including silicone and
siloxanes, and a silane including disilanes and alkoxysilanes. Organosilicon
compounds include siloxanes as represented by the general formula:
##STR00001## wherein R.sub.1 is hydrogen or a halogen, hydroxyl,
alkyl, halogenated alkyl, aryl aralkyl, halogenated aralkyl, alkaryl,
or halogenated alkaryl group. The hydrocarbon substituents generally
contain from 1 to about 10 carbon atoms, preferably methyl, ethyl,
or phenyl groups. R.sub.2 is selected from the same group as R.sub.1
and n is an integer of at least 2 and generally in the range of
3 to about 1000. The molecular weight of the organosilicon compound
employed is generally about 80 to about 20000 and preferably about
150 to about 10000. Examples of organosilicon compounds include,
but are not limited to, dimethyl silicone, diethyl silicone, phenylmethyl
silicone, methylhydrogen silicone, ethylhydrogen silicone, phenylhydrogen
silicone, methylethyl silicone, phenylethyl silicone, diphenyl silicone,
methyltrifluoropropyl silicone, ethyltrifluoropropyl silicone, polydimethyl
silicone, tetrachlorophenylmcthyl silicone, tetrachlorophenylethyl
silicone, tetrachlorophenylphenyl silicone, methylvinyl silicone,
and ethylvinyl silicone. The silicone compound need not be linear
but may be cyclic as for example hexamethyl cyclotrisiloxane, octamethyl
cyclotetrasiloxane, hexaphenyl cyclotrisiloxane, and octaphenyl
cyclotetrasiloxane. Mixtures of these compounds are also useful
as are silicones with other functional groups.
Other organosilicon compounds, including silanes and alkoxy silanes,
such as tetramethoxy silane, can also be utilized as selectivating
agents. These useful silicon-containing selectivating agents include
silanes characterized by the general formula:
##STR00002## wherein R, R.sub.1 R.sub.2 and R.sub.3 are independently
selected from the group consisting of hydrogen, hydroxyl, halogen,
alkyl, halogenated alkyl, alkoxy, aryl, and halogenated alkaryl
groups. Mixtures of these compounds are also useful.
Preferred silicon-containing selectivating agents include dimethylphenylmethyl
polysiloxane (e.g., Dow-550) and phenylmethyl polysiloxane (e.g.,
Dow-710), both available from Dow Chemical Co. in Midland, Mich.
Examples of suitable carriers for the selectivating agents, preferably
silicon compounds, include linear, branched, and cyclic alkanes
having five or more carbons. In the methods of the present invention
it is preferred that the carrier be a linear, branched, or cyclic
alkane having a boiling point greater than about 70.degree. C. and
most preferably containing 6 or more carbons. Optionally, mixtures
of low volatility organic compounds, such as hydrocracker recycle
oil, can be employed as carriers. The most preferred low volatility
hydrocarbon carriers of selectivating agents are decane and dodecane.
The catalyst can be selectivated by single or multiple treatments
with a liquid organosilicon compound in a liquid carrier followed
by calcination of the treated material in an oxygen containing atmosphere.
The catalyst can also be selectivated with both silica and coke.
Other techniques such as steaming and impregnation with various
compounds have also been found to alter the properties (e.g. activity,
selectivity, and/or stability) of the molecular sieve structure.
Active Metal Oxides
Active metal oxides of the invention are those metal oxides, different
from typical binders and/or matrix materials, that, when used in
combination with a molecular sieve, provide benefits in catalytic
conversion processes. Preferred metal oxides are those metal oxides
having a Group 2 Group 3 Group 4 Lanthanide Series, and/or Actinide
Series metal from the Periodic Table of Elements using the IUPAC
format described in the CRC Handbook of Chemistry and Physics, 79th
Edition, CRC Press, Boca Raton, Fla. (1998). More preferred active
metal oxides are Group 3 (preferably yttrium or lanthanum) oxides
alone or Group 4 metal oxides such as zirconium and/or hafnium oxide
in combination with a Group 2 and/or Group 3 metal oxide. In one
embodiment, the most preferred active metal oxide is an active yttrium
oxide. In another embodiment, the preferred active metal oxide is
a zirconium and/or hafnium metal oxide mixed with lanthanum oxide.
In yet another embodiment, the preferred active metal oxide is non-acidic
or basic. Active metal oxides of this invention include other oxides
such as MgO and hydrotalcite-derived mixed magnesium-aluminum non-acidic
oxides.
While there are many different benefits in catalytic conversion
processes, one of the most desirable is an extension of the catalyst
composition life. Quantification of the extension in the molecular
sieve catalyst composition life can be determined using the Half-life
Enhancement Index (HLEI) as defined by the following equation:
.times..times..times..times..times..times..times..times..times..times..tim-
es..times..times..times..times..times..times..times..times..times..times..-
times..times. ##EQU00001## where the half-life of the catalyst is
the processing time until the conversion of feedstock by the catalyst
falls below 50% of the initial conversion rate for that feedstock.
Similarly the half-life of the catalyst in combination with active
metal oxide, the multi-component molecular sieve catalyst composition,
is the processing time under the same test conditions and using
the same weight of molecular sieve until the conversion of feedstock
falls below 50% of the initial conversion rate for that feedstock.
HLEI is measured at conditions closely approximating the reaction
conditions under which either the molecular sieve catalyst composition
or the multi-component molecular sieve catalyst composition would
commercially be used, provided that reaction conditions for both
tests will be held constant, the weight hourly space velocity (WHSV)
will be held constant based on the quantity of molecular sieve present
in each test, and that quantity of molecular sieve will also be
held constant. Initial conversion percentage will be the conversion
percentage measured at some point within the first four hours of
reaction runtime, preferably within the first hour, and measured
at the same time on-stream for each of the molecular sieve catalyst
composition and the multi-component molecular sieve catalyst composition
being compared. All reaction conditions including WHSV with respect
to the molecular sieve, not the multi-component molecular sieve
catalyst composition, must be held constant for the individual half-life
determinations to get a meaningful HLEI comparison between the molecular
sieve or molecular sieve composition and the multi-component molecular
sieve composition.
A metal oxide that is not active will have little or no effect
on the lifetime of the catalyst composition, or will shorten the
lifetime of the catalyst composition, and will therefore have an
HLEI less than or approximately equal to 1. Active metal oxides
of the invention are those metal oxides, different from typical
binders and/or matrix materials, that, when used in combination
with a molecular sieve, provide a multi-component molecular sieve
catalyst composition that has an HLEI greater than 1. By definition,
a molecular sieve catalyst composition that has not been combined
with an active metal oxide will have an HLEI equal to 1.0.
In one embodiment, the active metal oxide, when combined with a
molecular sieve, enhances the HLEI of the molecular sieve in an
alkylation of toluene to produce xylenes, particularly para-xylene.
In another embodiment, the multi-component molecular sieve catalyst
composition of the invention, containing one or more active metal
oxides has an HLEI greater than 1. In a preferred embodiment, the
HLEI of the multi-component molecular sieve catalyst composition
containing one or more active metal oxides is preferably greater
than about 2 more preferably greater than about 10 even more preferably
greater than about 20 and most preferably greater than about 100.
In another preferred embodiment, the half-life of the multi-component
molecular sieve composition under typical reactor conditions is
preferably greater than 1 day, more preferably greater than 10 days,
and most preferably greater than 2 months.
In one embodiment, the active metal oxide of the invention may
not consist solely or substantially of oxides of silicon, aluminum,
phosphorus, or combinations thereof.
In yet another embodiment, the active metal oxides of the invention
are non-acidic or basic metal oxides as determined by the molar
ratio of chemisorption of CO.sub.2 and NH.sub.3 over these metal
oxide materials. CO.sub.2 a mild acid, is used to titrate the basic
sites present on the metal oxide being tested. Likewise, NH.sub.3
a strong base, is titrated to indicate the acidic sites on the material.
Many factors determine the actual amount of chemisorption such as
surface area of the material (often significantly affected by the
metal oxide preparation method), the temperature at which the chemisorption
is tested, and the pressure at which the chemisorption is tested.
For the purposes of this invention, a "non-acidic" oxide
is defined as an oxide having a molar ratio of chemisorption of
CO.sub.2 per gram of metal oxide to the chemisorption of NH.sub.3
per gram of metal oxide greater than about 0.5 when tested as described
below.
Testing to determine the molar ratio of chemisorption of CO.sub.2
per gram of metal oxide to the chemisorption of NH.sub.3 per gram
of metal oxide was conducted using a Mettler TGA/SDTA 851 thermogravimetric
analysis system at ambient pressure. The metal oxide sample was
calcined in flowing air to about 700.degree. C. (except as noted
in Table 1) for about three hours, at least until a constant sample
weight was obtained. The temperature of the sample was then reduced
in flowing air (helium could also be used) to the desired temperature
of chemisorption. Next, the sample was allowed to equilibrate at
the desired temperature in flowing helium and weighed. Chemisorption
of carbon dioxide was measured at 100.degree. C., and chemisorption
of ammonia was measured at 250.degree. C. After being weighed, the
sample was subjected to a number of pulses (about 12 seconds/pulse)
of a gaseous mixture containing helium and either carbon dioxide
or ammonia until a constant weight was obtained. The gas mixtures
contained about 10 weight percent carbon dioxide or ammonia with
the remainder being helium. After each pulse of the gas mixture
being tested, the metal oxide sample was flushed with flowing helium
for about 3 minutes. About 20 separate pulses of the gas mixture
was used in each test. The increase in weight of the sample in terms
of mg/g metal oxide based on the metal oxide sample weight after
calcination was used to determine the moles of CO.sub.2 or NH.sub.3
adsorbed per gram of metal oxide.
Molar ratios of chemisorption of CO.sub.2 per gram of metal oxide
to the chemisorption of NH.sub.3 per gram of metal oxide for some
examples of metal oxide materials tested are shown in Table 1. Preferred
molar ratios of CO.sub.2/NH.sub.3 chemisorption, tested as described
above, are greater than about 0.5 more preferred ratios are greater
than about 0.75 and the most preferred ratios are greater than
about 1.0.
TABLE-US-00001 TABLE 1 Calcination CO.sub.2/NH.sub.3 Chemisorption
Material Tested Temperature, .degree. C. Molar Ratio TiO.sub.2 700
0.33 2% CeO.sub.x/ZrO.sub.2 700 0.33 5% CeO.sub.x/ZrO.sub.2 700
0.41 La.sub.2O.sub.3 700 0.86 La.sub.2O.sub.3 600 1.21 10% Y.sub.xO.sub.y/ZrO.sub.2
700 1.88 ZrO.sub.2 700 1.95 ZrO.sub.2 500 2.00 5% Y.sub.xO.sub.y/ZrO.sub.2
700 3.13 5% CaO.sub.x/ZrO.sub.2 700 3.77 5% La.sub.xO.sub.y/ZrO.sub.2
700 4.86 MgO 700 11.47 CeO.sub.2 700 12.27 Y.sub.2O.sub.3 700 14.95
The active metal oxides are prepared using a variety of methods.
It is preferable that the active metal oxide is made from an active
metal oxide precursor, such as a metal salt. Other suitable sources
of active metal oxides include compounds that form these metal oxides
during calcination, such as oxychlorides and nitrates. A further
suitable source of metal oxides includes salts containing the cation
of the desired metal, such as halides, nitrates, and acetates. Alkoxides
are also sources of metal oxides, for example zirconium n-propoxide.
In one embodiment, the active metal oxide is hydrothermally treated
under conditions that include a temperature of at least 80.degree.
C., preferably at least 100.degree. C. The hydrothermal treatment
typically takes place in a sealed vessel at greater than atmospheric
pressure, however, a preferred mode of treatment involves the use
of an open vessel under reflux conditions. Agitation of the active
metal oxide in the liquid medium, for example, by the action of
refluxing liquid and/or stirring, promotes the effective interaction
of the oxide with the liquid medium. The duration of the contact
of the oxide with the liquid medium is preferably at least 1 hour,
preferably at least 8 hours. The liquid medium for this treatment
preferably has a pH of about 7 or greater, preferably 9 or greater.
Non-limiting examples of suitable liquid media include water, hydroxide
solutions (including hydroxides of NH.sub.4.sup.+, Na.sup.+, K.sup.+,
Mg.sup.2+, and Ca.sup.2+), carbonate and bicarbonate solutions (including
carbonates and bicarbonates of NH.sub.4.sup.+, Na.sup.+, K.sup.+,
Mg.sup.2+, and Ca.sup.2+), pyridine and its derivatives, and alkyl/hydroxylamines.
In yet another embodiment, the active metal oxide is prepared by
first preparing a liquid solution comprising a source of an active
metal oxide, such as a salt of the metal. Suitable sources include,
but are not limited to, salts or mixtures of salts containing a
Group 2 Group 3 Group 4 Lanthanide Series, or Actinide Series
metal, such as nitrates, sulfates, and halides. This solution containing
a source of an active metal oxide is then subjected to conditions
sufficient to cause precipitation of the solid oxide material, such
as by the addition of a precipitating reagent to the solution, preferably
a base such as sodium hydroxide or ammonium hydroxide. Water is
a preferred solvent for these solutions. The temperature at which
the liquid medium is maintained during the precipitation is preferably
less than about 200.degree. C., more preferably in the range of
from about 0.degree. C. to about 200.degree. C. This liquid medium
is preferably maintained at an ambient temperature, for example
room temperature, or the liquid is cooled or heated. A preferred
range of temperatures for precipitation is from about 20.degree.
C. to about 100.degree. C. The resulting gel is preferably then
hydrothermally treated at temperatures of at least 80.degree. C.,
preferably at least 100.degree. C. The hydrothermal treatment typically
takes place in a sealed vessel at greater than atmospheric pressure
or at ambient pressures. The gel, in one embodiment, is hydrothermally
treated for up to 10 days, preferably up to 5 days, most preferably
up to 3 days. The resulting material is then recovered, for example
by filtration or centrifugation, washed, and dried. The resulting
particulate material is preferably then calcined, preferably in
an oxidizing atmosphere, at a temperature of at least 400.degree.
C., preferably at least 500.degree. C., more preferably from about
600.degree. C. to about 900.degree. C., and most preferably from
about 650.degree. C. to about 800.degree. C. The calcination time
is preferably up to 48 hours, more preferably for about 0.5 hours
to about 24 hours, and most preferably for about 1 hour to about
10 hours. In a most preferred embodiment, calcination is carried
out at about 700.degree. C. for about 1 hour to about 3 hours.
Although preferred methods of preparing metal oxides are described
above, other methods for preparing the active metal oxides are known
in the art and may be used within the scope of this invention.
In an embodiment, it is preferred to utilize two or more active
metal oxides, preferably one Group 4 metal oxide and one or more
selected from Group 2 Group 3 Lanthanide Series, and Actinide
Series metal oxides. When two or more metal oxides are used, they
may either be co-precipitated or precipitated separately and combined
with each other at any later stage of processing including as calcined
solid particles. When two or more metal oxides are used, the metal
oxides may be combined with each other before or after any one or
more metal oxides have been combined with the molecular sieve, including
any combination which also includes a binder and/or matrix material.
Any method of combining the active metal oxides with each other,
such as impregnation, regardless of whether or not other materials
are also combined with the metal oxides before, after, or at the
time of combining the metal oxides, is within the scope of this
invention.
In another embodiment, the metal oxides are combined in slurry
or hydrated state or in a substantially dry or dried state, preferably
the metal oxides are combined in a hydrated state. In a preferred
embodiment, the mixture of metal oxides can be considered as having
atomic level mixing of the two or more metals within the oxide,
in which such atomic level mixing is achieved during synthesis of
the mixed metal oxide. Such a mixed metal oxide will be considered
to be an active metal oxide if the mixed metal oxide, when used
in combination with a molecular sieve, provides an HLEI greater
than 1.0 in catalytic conversion processes, regardless of whether
or not all of the metal oxides incorporated into the mixed metal
oxide are individually active.
In an embodiment where two or more metal oxides are combined, they
may be combined in any proportion. Mole percent of any one metal
oxide as compared to the total moles of metal oxides used in preparing
the active metal oxide may range from about 0% to about 100%, preferably
from about 1% to about 99%, more preferably from about 3% to about
97%, and most preferably from about 5% to about 95%.
In an embodiment, where the active metal oxide contains one or
more Group 4 metal oxides and a second metal oxide consisting of
any combination of one or more metal oxides selected from Group
2 Group 3 Lanthanide Series, and Actinide Series metal oxides,
the mole ratio of the Group 4 metal oxides to the second metal oxide,
taken as a group, is in the range of from 1000:1 to 1:1000 based
on the total moles of the Group 4 and second metal oxides, preferably
the mole ratio is in the range of from about 500:1 to about 1:2
more preferably from about 100:1 to about 1:1 and most preferably
from about 50:1 to about 2:1.
In yet another embodiment, the active metal oxide, preferably containing
a Group 4 metal oxide and a second metal oxide consisting of any
combination of one or more metal oxides selected from Group 2 Group
3 Lanthanide Series, or Actinide Series metal oxides, has 1 percent
to 25 percent by weight of the second metal oxide combination based
on the total weight of the active metal oxide, more preferably from
about 1 percent to about 20 percent, and most preferably from about
1 percent to about 15 percent.
Some preferred combinations of metal oxides include a zirconium
and/or hafnium metal oxide from Group 4 with either a Group 2 calcium
oxide or a Group 3 lanthanum and/or yttrium oxide.
In a preferred embodiment the metal oxides are calcined either
before or after being combined.
Multi-Component Molecular Sieve Composition
The multi-component molecular sieve composition of the invention
includes any one of the molecular sieves and/or molecular sieve
compositions previously described mixed with any one or more of
the active metal oxides described above. In one embodiment, more
than one type of molecular sieve is used in the multi-component
molecular sieve catalyst composition. Preferably, the molecular
sieves are those resulting from the synthesis mixture of phosphorous-,
aluminum-, and/or silicon-containing components, preferably while
stirring and/or agitating and/or seeding with a crystalline material,
optionally with an alkali metal, in a solvent such as water, and
optionally with one or more templating agents, to form a synthesis
mixture that is then heated under crystallization conditions of
pressure and temperature as are known in the art. More preferably,
the molecular sieve is an intermediate pore size metallosilicate
molecular sieve, and most preferably an intermediate pore size aluminosilicate
molecular sieve. Even more preferably, the active metal oxide is
a co-precipitated combination of zirconium and lanthanum oxides,
and the molecular sieve composition is a ZSM-5 catalyst modified
as described U.S. Pat. No. 6423879 hereafter referred to as "steamed
ZSM-5."
In one embodiment, the crystals of molecular sieve are first formed
and are then combined with the active metal oxide, preferably in
a substantially dry, dried, or calcined state, most preferably the
crystals of molecular sieve and solid particles of active metal
oxide are physically mixed in their calcined state to form the multi-component
molecular sieve catalyst composition of the invention. In another
embodiment, one or more active metal oxides or their precursors
are added to the synthesis mixture for making a molecular sieve
as described above and co-precipitated with the molecular sieve.
Alternatively the crystals of molecular sieve and active metal oxides
are mixed before drying.
Without being bound by any particular theory, it is believed that
intimate mixing of the molecular sieve, either as crystals or as
a molecular sieve catalyst composition, and one or more active metal
oxides improve conversion processes using the multi-component molecular
sieve catalyst composition of the invention. Intimate mixing may
be achieved by any method known in the art, such as mixing with
a mixer muller, drum mixer, ribbon/paddle blender, kneader, or the
like.
In one embodiment, the multi-component molecular sieve catalyst
composition has a weight ratio of the active metal oxide to the
molecular sieve in the range of from about 1:1000 to about 8:1
preferably in the range from about 1:100 to about 2:1 and more
preferably from about 1:50 to about 1:1.
In one embodiment, where the molecular sieve synthesized above
is formulated into a molecular sieve catalyst composition, the active
metal oxide is then combined with the formulated molecular sieve
catalyst composition. It is also an embodiment of the invention
that a first formulated molecular sieve catalyst composition is
combined with an active metal oxide, and the resulting multi-component
molecular sieve catalyst composition is then itself mixed with a
binder and/or matrix material which could then be formed into desired
shape and sized particles by well-known techniques such as spray
drying, pelletizing, extrusion, and the like.
Without being bound by any particular theory, the addition of active
metal oxides appears to have the effect of intercepting coke precursors,
thereby interrupting the coke formation process. This effect is
expected to allow the use of catalysts that may not have previously
been commercially viable for use in aromatics alkylation.
The beneficial effect of active metal oxides in extending the lifetime
of various catalyst compositions is expected to extend to all microporous
materials including, but not limited to, metal-containing microporous
materials, as well as to non-microporous materials such as silica-alumina
and amorphous acid catalysts.
Process For Using the Multi-Component Molecular Sieve Catalyst
Compositions
The molecular sieve compositions and catalyst compositions described
above are useful in a variety of processes including: cracking,
of for example a naphtha feed to one or more light olefins or higher
molecular weight (MW) hydrocarbons to lower MW hydrocarbons; hydrocracking,
of for example heavy petroleum and/or cyclic feedstock; isomerization,
of for example aromatics such as xylene; polymerization, of for
example one or more olefins to produce a polymer product; reforming;
hydrogenation; dehydrogenation; dewaxing, of for example hydrocarbons
to remove straight chain paraffins; absorption, of for example alkyl
aromatic compounds for separating out isomers thereof; alkylation,
of for example aromatic hydrocarbons such as benzene and alkyl benzene,
optionally with propylene to produce cumene or with long chain olefins;
transalkylation, of for example a combination of aromatic and polyalkylaromatic
hydrocarbons; dealkylation; hydrodecylization; disproportionation,
of for example toluene to make benzene and para-xylene; oligomerization,
of for example straight and branched chain olefins; and dehydrocyclization.
The preferred process of the invention is a process directed to
the alkylation of a feedstock comprising one or more aromatic hydrocarbons
to one or more alkyl aromatics in the presence of an alkylating
agent. The most preferred process of the invention is a process
directed to the alkylation of a feedstock comprising toluene to
one or more xylene isomers, preferably predominantly para-xylene.
The term "aromatic" in reference to the alkylatable compounds
which are useful herein is to be understood in accordance with its
art-recognized scope which includes alkyl substituted and unsubstituted
mono- and polynuclear compounds. Compounds of an aromatic character
which possess a hetero atom are also useful provided they do not
act as catalyst poisons under the reaction conditions selected.
Substituted aromatic compounds which can be alkylated herein must
possess at least one hydrogen atom directly bonded to the aromatic
nucleus. The aromatic rings can be substituted with one or more
alkyl, aryl, alkaryl, alkoxy, aryloxy, cycloalkyl, halide, nitro,
sulfono, and/or other groups which do not interfere with the alkylation
reaction.
Suitable aromatic hydrocarbons include, but are not limited to,
benzene, toluene, xylene, naphthalene, anthracene, naphthacene,
perylene, coronene, and phenanthrene.
Generally the alkyl groups which can be present as substituents
on the aromatic compound contain from one to about 22 carbon atoms,
preferably from one to about eight carbon atoms, and most preferably
from one to about four carbon atoms.
Suitable alkyl substituted aromatic compounds include toluene,
xylene, isopropylbenzene, normal propylbenzene, alpha-methylnaphthalene,
ethylbenzene, cumene, mesitylene, durene, p-cyxene, butylbenzene,
pseudocumene, o-diethylbenzene, m-diethylbenzene, p-diethylbenzene,
isoamylbenzene, isohexylbenzene, pentaethylbenzene, pentamethylbenzene;
1234-tetraethylbenzene; 1235-tetramethylbenzene; 124-triethylbenzene;
123-trimethylbenzene, m-butyltoluene; p-butyltoluene; 35-diethyltoluene;
oethyltoluene; p-ethyltoluene; m-propyltoluene; 4-ethyl-m-xylene;
dimethylnaphthalenes; ethylnaphthalene; 23-dimethylanthracene;
9-ethylanthracene; 2-methylanthracene; o-methylanthracene; 910-dimethylphenanthrene;
and 3-methyl-phenanthrene. Higher molecular weight alkylaromatic
hydrocarbons can also be used as starting materials and include
aromatic bydrocarbons such as are produced by the alkylation of
aromatic hydrocarbons with olefin oligomers. Such products are frequently
referred to in the art as alkylate and include hexylbenzene, nonylbenzene,
dodecylbenzene, pentadecyclbenzene, hexyltoluene, nonyltoluene,
dodecyltoluene, pentadecytoluene, to name a few. Very often alkylate
is obtained as a high boiling fraction in which the alkyl group
attached to the aromatic nucleus varies in size from about C.sub.6
to about C.sub.12.
Reformate containing substantial quantities of benzene, toluene,
xylene and/or other alkylatable aromatic compounds also constitutes
a useful feed for the alkylation process of this invention.
The multi-component molecular sieve catalyst compositions described
above are particularly useful in alkylation processes using oxygen
and/or sulfur-containing alkylating agents. Suitable alkylating
agents include, but are not limited to, alcohols (such as methanol,
ethanol, and isopropanol), alcohol precursors (such as syngas, preferably
in combination with an alcohol synthesis catalyst), ethers (such
as dimethyl ether), esters, and carbonates (such as dimethyl carbonate).
Typically, an alkylating agent stream might contain one or more
aliphatic-containing compounds that include alcohols, amines, carbonyl
compounds (for example aldehydes, ketones, and carboxylic acids),
ethers, halides, mercaptans, sulfides, and the like, and mixtures
thereof. The aliphatic moiety of the aliphatic-containing compounds
typically contains from 1 to about 50 carbon atoms, preferably from
1 to 20 carbon atoms, more preferably from 1 to 10 carbon atoms,
and most preferably from 1 to 4 carbon atoms. Non-limiting examples
of aliphatic-containing compounds include alcohols such as methanol
and ethanol; alkyl-mercaptans such as methyl mercaptan and ethyl
mercaptan; alkyl-sulfides such as methyl sulfide; alkyl-amines such
as methyl amine; alkylethers such as dimethyl ether, diethyl ether
and methylethyl ether; alkyl-halides such as methyl chloride and
ethyl chloride; alkyl ketones such as dimethyl ketone; formaldehydes;
and various acids such as acetic acid.
In a preferred embodiment of the process of the invention, the
alkylating agent contains one or more oxygenates, more specifically
one or more organic compounds containing at least one oxygen atom.
In the most preferred embodiment of the process of invention, the
oxygenate in the alkylating agent is one or more alcohols, preferably
aliphatic alcohols where the aliphatic moiety of the alcohols has
from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms,
and most preferably from 1 to 4 carbon atoms. The alcohols useful
as alkylating agents in the process of the invention include lower
straight and branched chain aliphatic alcohols and their unsaturated
counterparts.
Non-limiting examples of oxygenates include methanol, ethanol,
n-propanol, isopropanol, methyl ethyl ether, dimethyl ether, diethyl
ether, diisopropyl ether, formaldehyde, dimethyl carbonate, dimethyl
ketone, acetic acid, and mixtures thereof. In a preferred embodiment,
the alkylating agent is selected from one or more of methanol, ethanol,
dimethyl ether, diethyl ether, or a combination thereof; more preferably
methanol and/or dimethyl ether; and most preferably methanol.
Non-limiting examples of alkylated aromatic hydrocarbons include
toluene, xylenes, ethylbenzene, propylbenzenes, butylbenzenes, ethyltoluenes,
diethylbenzenes, methylnapthlalenes, and dimethylnaphthalenes.
In one preferred embodiment, the molecular sieve is an aluminosilicate;
the active metal oxide is an active Group 4 metal oxide that has
been modified by a Group 2 Group 3 Lanthanide Series, and/or Actinide
Series metal oxide; and the alkylating agent is methanol. In a more
preferred embodiment, the molecular sieve is steamed ZSM-5 and the
active metal oxide is yttrium oxide or a co-precipitated combination
of lanthanum oxide with zirconium and/or hafnium oxide.
The feedstock, in one embodiment, contains one or more diluents,
typically used to reduce the concentration of the feedstock, which
are generally non-reactive to the feedstock or multi-component molecular
sieve catalyst composition. Non-limiting examples of diluents include
helium, argon, hydrogen, nitrogen, carbon monoxide, carbon dioxide,
water, essentially non-reactive paraffins (especially alkanes such
as methane, ethane, and propane), essentially non-reactive aromatic
compounds, and mixtures thereof. The diluent is used either in a
liquid or a vapor form, or a combination thereof and may be either
added directly to a feedstock entering into a reactor or added directly
into a reactor, either at the front end or in staged additions down
the length of the bed. The preferred diluents are hydrogen and water,
with hydrogen and water together being more preferred, and a homogenous
gas phase mixture of water and hydrogen being most preferred. Hydrogen
gas used as a diluent also acts as an anti-coking agent. Surprisingly,
the addition of water as a diluent in the reactor further enhances
the HLEI benefits seen with the use of multi-component molecular
sieve catalyst compositions. Preferably, hydrogen and/or added water
are present in a molar ratio between about 1:100 and about 10:1
with respect to total moles of the aromatic compound(s) and the
alkylating agent(s) combined (hereafter together referred to as
"reactants") and more preferably, hydrogen and water combined
are present in a molar ratio between about 1:1 and about 5:1 with
respect to the total moles of the reactants.
An alternative embodiment would include hydrogen and carbon monoxide
in the feedstock mixture and at least one component in the catalyst
that is capable of forming an alkylating agent, such as methanol,
from hydrogen and carbon monoxide. For the purposes of this invention,
the term "alkylating agent" will be understood to include
alkylating agents formed in such parallel reactions whether or not
the alkylating agent itself is part of the feed to the reactor,
and any hydrogen added for the purpose of forming the alkylating
agent would not be counted in the preferred molar ratios of hydrogen
to reactants as described above.
The process for alkylating aromatics, especially using an alkylating
agent comprising one or more oxygenates, in the presence of a multi-component
molecular sieve catalyst composition of the invention, is carried
out in a reactor system operating at conversion conditions and containing
at least one reactor, where the reactor is a fixed bed reactor or
a fluidized bed reactor (including a turbulent bed reactor), preferably
a fixed bed reactor. In a preferred embodiment, a feedstock containing
the alkylatable aromatic and an oxygen- or sulfur-containing alkylation
agent are introduced to a reactor system containing a multi-component
molecular sieve catalyst composition and one or more alkylated aromatics
are recovered from the effluent exiting the reactor system.
This invention is applicable to a broad range of aromatic alkylation
processes, preferably those in which methanol reacts with an aromatic
compound, or mixture of aromatics, to add methyl groups. The conversion
of benzene to toluene, xylenes, and/or C.sub.9+ aromatics and the
conversion of toluene to xylenes and/or C.sub.9+ aromatics are examples
of aromatic methylation. In one embodiment, the aromatic compound
is a relatively pure compound, and in another embodiment, the aromatic
compound is contained in a mixture of aromatics and non-aromatics,
such as reformate. In the fuels area, methylation of reformats or
other C.sub.6 C.sub.7 streams could lower benzene content as well
as increase fuel yields and octane values. For fuels, high selectivity
to the para-isomer is not crucial, but para-selectivity is desirable
for chemicals applications.
It will be recognized by those skilled in the art that the longer
half-life of the multi-component molecular sieve catalyst composition
would generally either allow its use in existing reactors, perhaps
operating under modified reaction conditions, or allow the use of
less complex reactor designs for new equipment. Reactor design is
beyond the scope of this invention, but it will be recognized by
those skilled in the art that this multi-component molecular sieve
catalyst composition will allow a greater range of choices in the
design and/or retrofit of reactors to be used for aromatics alkylation
processes, and this invention is not limited to any particular reactor
configuration. For example, it is contemplated that plug flow, fixed
bed, or fluidized bed processes are used in combination, particularly
in different reaction zones within a single or multiple reactor
system.
The reaction temperature employed in the alkylation process, specifically
within the reactor system, is generally in the range of from about
200.degree. C. to about 1000.degree. C., preferably from about 250.degree.
C. to about 700.degree. C., more preferably from about 300.degree.
C. to about 700.degree. C., yet more preferably from about 350.degree.
C. to about 650.degree. C., yet even more preferably from about
400.degree. C. to about 600.degree. C., and most preferably from
about 500.degree. C. to about 580.degree. C.
The reaction pressure employed in the alkylation process, specifically
within the reactor system, varies over a wide range including autogenous
pressure. The conversion pressure is based on the partial pressure
of the feedstock exclusive of any diluent therein. Typically the
conversion pressure employed in the process is in the range of from
about 30 kPa to about 7 MPa, preferably from about 100 kPa to about
3.5 MPa, and most preferably from about 150 kPa to about 900 kPa.
When the multi-component molecular sieve catalyst composition does
become coked, it can be regenerated using any regeneration technique
suitable for the materials included in the multi-component molecular
sieve catalyst as will be known to those skilled in the art.
EXAMPLES
In order to provide a better understanding of the present invention
including representative advantages thereof, the following examples
are offered. Example 1 will describe the synthesis of the mixed
metal oxide for the multi-component catalysts. Example 2 (Comparative)
will demonstrate the performance of a ZSM-23 molecular sieve catalyst
composition and Example 3 will demonstrate the performance of the
multi-component molecular sieve catalyst composition containing
the ZSM-23 molecular sieve catalyst composition. Examples 4 and
5 6 and 7 and 9 and 10 respectively, will similarly provide comparisons
between molecular sieve catalyst compositions without an active
metal oxide and multi-component molecular sieve catalyst compositions
using the same type of molecular sieve catalyst composition physically
mixed by stirring with particles of an active metal oxide mixture.
Example 1
Preparation of Active Metal Oxide
Fifty grams of ZrOCl.sub.2.8H.sub.2O were dissolved with stirring
in 300 ml of distilled water. Another solution containing 4.2 grams
of La(NO.sub.3).sub.3.6H.sub.2O and 300 ml of distilled water was
prepared. These two solutions were combined with stirring. The pH
of the final mixture was adjusted to approximately 9 by the addition
of concentrated ammonium hydroxide (28.9 grams). This slurry was
then put in polypropylene bottles and placed in a steam box (100.degree.
C.) for 72 hours. The product formed was recovered by filtration,
washed with excess water, and dried overnight at 85.degree. C. A
portion of this product was calcined to 700.degree. C. in flowing
air for 3 hours to produce a mixed metal oxide (La.sub.xO.sub.y/ZrO.sub.2)
containing a nominal 5 weight percent lanthanum based on the final
weight of the mixed metal oxide.
For Examples 2 through 10 catalyst performance data were obtained
using a downflow fixed-bed reactor with the following operating
conditions, unless otherwise noted: Temperature=500.degree. C. Pressure=100
kPa H.sub.2 to reactants molar ratio=0.8 Pure methanol and toluene
feeds at 1:3 molar ratio WHSV=3.9 h.sup.-1 based on molecular sieve
catalyst composition Catalyst load=2.0 g of molecular sieve catalyst
composition for all tests For the 1:3 molar feed mixture, the maximum
toluene conversion expected from reaction with methanol would be
about 33%. Methanol utilization is reported as (moles of methanol
converted)/(moles of xylene formed--moles of benzene formed). Benzene
is subtracted to account for any xylene formed by the disproportionation
of toluene to xylene plus benzene.
For the multi-component molecular sieve catalyst compositions,
a physical mixture of 2.0 g of the molecular sieve catalyst composition
and 0.4 g of the mixed metal oxide was used. The toluene and methanol
weight hourly space velocities were kept constant relative to the
amount of molecular sieve catalyst composition in the bed.
Example 2 Comparative
The reaction described above was run using a molecular sieve catalyst
composition containing 65 weight percent ZSM-23 molecular sieve
(further described in U.S. Pat. No. 4076842) with a Si/Al.sub.2
ratio about 100 which had been bound with an alumina-rich binder
constituting 35 weight percent of the composition. The catalyst
load was 2.0 g. The resulting toluene conversion, para-xylene selectivity,
and methanol utilization at 2 20 40 60 and 80 hours are shown
in Table 2.
Example 3
This example used the same reaction conditions as Example 2 but
0.4 g of the La.sub.xO.sub.y/ZrO.sub.2 product from Example 1 was
added to 2.0 g of the ZSM-23 molecular sieve catalyst composition
(as described in Example 2) as a physical mixture of particles to
form a multi-component molecular sieve catalyst composition. The
catalytic performance of the multi-component molecular sieve catalyst
composition (ZSM-23 with La.sub.xO.sub.y/ZrO.sub.2) at 2 20 40
and 170 hours is also shown in Table 2.
The data show that addition of La.sub.xO.sub.y/ZrO.sub.2 to the
aluminosilicate catalyst bed improved the catalyst activity, selectivity
to para-xylene (which increased steadily with time to about 68%
at the end of the test), and the catalyst life. The multi-component
molecular sieve catalyst composition containing La.sub.xO.sub.y/ZrO.sub.2
maintained approximately constant toluene conversion activity for
170 hrs, while the molecular sieve catalyst composition activity
in Example 2 dropped to approximately half the initial toluene conversion
after 27 hours and approximately zero at 80 hours. The HLEI in this
test was greater than 6.3 and has not been extrapolated to the
time at which toluene conversion by the multi-component molecular
sieve composition would have dropped to half of its initial value.
Example 4 Comparative
An alumina-bound ZSM-5 catalyst composition that had been treated
with silicone three times, with calcination after each silicone
treatment, and steamed for 24 hours at 1000.degree. F. was tested
at the same conditions as Example 2 to provide a comparison case
for this molecular sieve catalyst composition.
Example 5
Two grams of the same catalyst composition as described in Example
4 was mixed with 0.4 grams of the La.sub.xO.sub.y/ZrO.sub.2 of Example
1 and tested at the same conditions as Example 3. The results for
Examples 4 and 5 at 2 20 60 and 106 hours are shown in Table
2. The toluene conversion for the molecular sieve catalyst composition
in Example 4 (silicone-treated ZSM-5) dropped to approximately half
of the initial conversion rate after about 63 hours, while the toluene
conversion for the multi-component molecular sieve catalyst composition
stayed roughly constant at about 15% for over 106 hours, indicating
that the HLEI in this comparison is greater than 1.7. Methanol utilization
and para-xylene selectivity were also higher for the multi-component
molecular sieve catalyst composition.
Example 6 Comparative
A molecular sieve catalyst composition with 25 weight percent ZSM-5
molecular sieve crystals having a Si/Al.sub.2 ratio of 450 was spray
dried with 5 weight percent phosphorus and clay and then steamed
at 1090.degree. C. to produce steamed ZSM-5. This molecular sieve
catalyst composition was run in a fixed bed downflow reactor at
a temperature of 585.degree. C., a pressure of 280 kPa, an H.sub.2
to reactants molar ratio of 2:1 with pure methanol and toluene
feeds at a 1:2 molar ratio, an H.sub.2O to reactants molar ratio
of 2:1 and a WHSV of 8 h.sup.-1. The catalyst load was 2.0 g. Catalyst
performance data for 2 10 20 and 30 hours are shown in Table
2.
Example 7
The same temperature, pressure, and flow rates were maintained
as in Example 6 but 0.4 g of the La.sub.xO.sub.y/ZrO.sub.2 material
of Example 1 was added to 2.0 g of the comparison molecular sieve
catalyst composition described in Example 6 as a physical mixture
of particles. The catalytic performance of the molecular sieve catalyst
composition comparative sample and of the multi-component molecular
sieve catalyst composition are shown in Table 2.
The data show that addition of La.sub.xO.sub.y/ZrO.sub.2 to the
aluminosilicate catalyst bed improved toluene conversion, methanol
utilization, and catalyst life. The multi component molecular sieve
catalyst composition containing La.sub.xO.sub.y/ZrO.sub.2 maintained
approximately constant toluene conversion for 170 hours, at which
point the H.sub.2O co-feed was discontinued in an effort to cause
the catalyst to require regeneration. Even so, the toluene conversion
had not yet dropped to 50% of the initial conversion rate at 300
hours. In contrast, the performance of the molecular sieve catalyst
composition alone (Example 6) dropped to very low toluene conversion
over a period of 30 hours, reaching 50% of the initial toluene conversion
at approximately 7.5 hours. Again, not extrapolating the half-life
of the multi-component molecular sieve catalyst composition beyond
the time tested, the HLEI is greater than 22.7. It should be noted
that although the initial data points for these two examples were
reported for different times, the HLEI would by inspection still
have been 20 or more had those data points been taken at the same
run time.
Example 8
The multi-component molecular sieve catalyst composition used in
Example 7 was run for 380 hours, with the water pump shut down at
170 hours to speed de-activation, then regenerated in-situ at 530.degree.
C. with air flow of 100 cc/min for 10 hours. The regenerated multi-component
molecular sieve catalyst composition's performance at the same reaction
conditions as were used in Examples 6 and 7 shows that this multi-component
molecular sieve catalyst composition is regenerable After 280 hours
on-stream the toluene conversion was 20%, methanol utilization was
50%, and para-xylene selectivity was 91%.
Example 9 (Comparative)
An alumina-bound ZSM-48 catalyst which had been treated with silicone
three times, with calcination after each silicone treatment, and
steamed for 24 hrs at 1000.degree. F., was run at the same conditions
as Example 2 to provide a comparison case for this catalyst composition.
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