Note: Descriptions are shown in the official language in which they were submitted.
~78~7~
This invention relates to a process for the isomer-
ization of alkyl aromatic components. More particularly,
the present invention relates to an improved process
for C8 alkyl benzene isomeri~ation employing a crystalline
aluminosilicate-containing catalyst.
- The C8 alkyl benzenes, i.e., orthoxylene, metaxylene
paraxylene and eth~lbenzene, are each quite valuable
as substantially pure components. However, these materials
are often included in mixtures from which the individual
isomers may be recovered. In many instances, a single -
isomer is more valuable to a given producer than are
the other isomers in the mixture. Therefore, in order
to maximize ~he production of the desired isomer or isomers,
means for C8 alkyl benzene isomerization is often provided.
Many processes have been proposed for C8 alkyl
benzene isomerization. One of the more widely used processes
involves contacting a hydrocarbon feedstock, e.g., a
mixture of C8 alkyl benzenes, in at least one reaction
zone in the presence of added free molecular hydrogen
with a catalyst comprising at least one platinum group
metal component supported on an amorphous acidic material,
e.g., amorphous silica-alu~ina. Another such isomerization
process involves incorporating a crystalline aluminosilicate
component into the isomerization catalyst.
As the reaction zone contactlng progresses
- in each of these processes, carbonaceous material is
deposited on the catalyst, which material tends to deactivate
the catalyst. After a period of time, this deactivation
may become so severe as to cause the reaction zone to
be withdrawn from service and the catalyst contained
r
therein to be regenerated and/or reactivated. Extending
the on-stream period of time, i.e., cycle time, of the
catalyst would be advantageous since, for example, more
valuable C8 alkyl benzene product can be pro~uced.
Therefore, one object of the present invention
is to provide a catalytic C8 alkyl benzene isomerlzation
- process wherein the cycle time of the catalyst is extended.
Another object of the present invention is
to provide such a process wherein the deactivation o~
the catalyst with time is eliminated or reduced. -
A still further object of the present invention
is to provide such a process having improved catalytic isom-
erization activity and/or selectivity. Other objects and
advantages of the present invention will become apparent
hereinafter.
The present process for isomerizing at least
one C8 alkyl benzene includes (1) contacting a hydrocarbon
feedstock containing at least one C8 alkyl benzene isomer
in at least one reaction zone in the presence of added
free molecular hydro~en with solid particles, preferably
a fixed bed of solid particles, comprising at least
one crystalline aluminosilicate capable of promoting ~`
isomerization of C8 alkyl benzenes at C8 alkyl benzene
isomerization conditions to isomerize the isomer, to form
deactivating carbonaceous deposits on the solid particles
and, in many instances, to consume a minor portion of the
added hydrogen. A mixture containing at least two C8 alkyl
benzene isomers is recovered from the effluent of the reaction
zone. Often, the hydrocarbon feedstock comprises a major
amount, i.e. t at least about 50% by weight, of the C8 alkyl
benzenes, and preferably such feedstock comprises at least
about 80~ by weight of the C8 alkyl benzenes.
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The present improvement involves increasing the amount
of hydrogen added to the reaction zone as the contacting
progresses to maintain or, preferably, increase the hydrogen
-to hydrocarbon molar ratio entering the reaction zone and,
b~ so doing, providing ~or improved catalytic activity
of the solid particles. In other words, it has now been
discovered that the presently useful solid particles
respond to an increased hydrogen to hydrocarbon feedstock
molar ratio entering the reaction zone by exhibiting
an increased catalytic activity for promoting the isomerization
f CB alkyl benzenes. This increased catalytic activity
occasioned by increasing the hydrogen to hydrocarbon
molar ratio entering the reaction zone allows a longer
cycle time, and lower reaction temperatures for a given degree
of isomerization. These reduced reaction temperatures,
in turn, provide improved selectivity and reduced losses
f C8 alkyl benzenes to lighter components by cracking,
and the like. This is in complete contrast to the experience
with isomerization catalysts which contain substantially
20 no crystalline alum~nosilicate. Such catalysts often exhibit ~ -
reduced isomerization activity as the hydrogen to hydrocarbon
molar ratio is increased.
The hydrogen to hydrocarbon feedstock (i.e., the
C8 alkyl benzene portion thereof) molar ratio entering the
reaction zone containing a non-crystalline alumino silicate
isomerization catalyst is often in the range of about 3:1
to about 8:1. Howeve`r, because of the present surprising
discovery, the hydrogen to hydrocarbon feedstock mola~ ratio
entering a reaction zone having at least one of the presently ;
useful alumino silicate-containing catalysts is preferably
in the range of about 3:1 to about 30:1, more preferably
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about 9:1 to about 20:1. In many instances with the aluminosilicate-containing catalysts, the hydrogen to hydrocarbon
feedstock molar ratio is maintained in the range of about
3:1 to about 8:1 at or near the beginning of the catalyst-
cycle, i.e., when hydrocarbon feedstock is first contacted
with the catalyst. As this contacting progresses, e.g.,
after at least about 100 to 1000 hours of such hydrocarbon
feed-catalyst contacting, the hydrogen to hydrocarbon feedstock
molar ratio is increased, preferably in the range of about
9:1 to about 20:1, to obtain the maximum benefits of the
present invention.
The catalytic materials used in this invention
comprise crystalline aluminosilicates, of either natural
or synthetic origin, having an ordered internal structure.
These materials are possessed of high surface area per gram
and are microporous. The ordered structure gives rise to
a definite pore size, related to the structural nature of
the ordered internal structure. Several forms are commercially
available. For example, a 5A material indlcates a material
of A structure and a pore size of about 5 A diameter. A
13X material is one of X faujasite structure and 10-13 A
pore diameter, and so on. There are also known materials
of Y faujasite structure, and others. Many of these materials
may be converted to the H or acid form, wherein a hydrogen
occupies the cation site. For example, such a conversion
may be had with many such materials by ion-exchange with
an ammonium ion. followed by heating to drive off NH3, or
by controlled acid leaching. In general, the H form is
more stable in materials having higher Si/Al ratios, such
as about 2.5/1 and above.
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One material having substantial ~ alkyl
benzene isomerization catalytic activity is H mordenite.
~lordenite is a material occurring naturally as the hydrated
sodium salt corresponding to: ~`
Na8(AlO2)9(Si2)40 24H~O `-`
This mordenite material may be leached with dilute
hydrochloric acid to arrive at an H or acid form. Preferably,
the mordenite material useful in the present invention contains
more than about 50 percent in the acid form.
Another type oE high activity isomerization catalyst
may be prepared by using conventional 13X molecular sieve,
e.g., such as is described in U.S. Patent 2,882,244. This
material may be base exchanged with a solution of rare-earth -
chlorides (containing 4 percent of REC13.6H2O) at about
180-200F. to remove sodium ions from the aluminosilicate
complex and replace at least some of them with the chemical
equivalent of rare-earth ions. After washing free of soluble
material and drying, there is produced an REX alumino-silicate
containing about 1.0-1.5 percent (wt.) of sodium and about
20 to 30 percent (wt.) of rare-earth ions calculated as
23
Materials incorporating both metal base exchange ~ `
and an ammonia base exchange may be obtained by treating '~
simultaneously or serially with metal salts and ammonia,
followed by heating, to get metal-hydrogen forms of the
crystalline aluminosilicate.
Similar preparations having isomerization catalytic
activity may include a variety`of crystalline aluminosilicates,
such as Y faujasites, gmelinite, chabazite, and the like.
For a fuller discussion of the nature of aluminosilicates
and their method of preparation attention is also directed
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- ~ " ' ` ' ' . ' ' ' ' ` ` '
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7i~
to U.S. Patent 3,033,778 to Frilette, and U.S. Paten~ 3,013,989
to Freeman.
According to the inven~ion, the aluminosilicate-
containing catalysts may be varied within wide limits as
to aluminosilicate emplo~ed, cation character and concentration,
and added components incorporated by precipitation, ion
exchange, adsorption and the like. Particularly important
variables are silica to alumina ratio, pore diameter and
spatial arrangement of cations. The cations may ~e protons
(acid) derived by base exchange with solutions of acids
or ammonium salts, the ammonium ion ~ecomposing on heating
to leave a proton. Polyvalent metals may be supplied as
cations, as such or as spacing or stabilizing agents in
acid aluminosilicates for stabilization. In addition to
the rare-earth metals mentioned above, other suitable
cations for exchange in the aluminosilicates include, for
example, magnesium, calcium, manganese, cobalt, zinc, silver
and nickel.
The preferred crystalline aluminosilicates are
the hydrogen and/or polyvalent metal forms of synthetically
prepared faujasite and mordenite, particularly, mordenite
having an effective diameter of about 6 angstrom units (A)
and a mole ratio of silica to alumina of about 6 to about
15, and more particularly, the hydrogen form of mordenite.
A particularly preferred crystalline aluminosiiicate is
acid-extracted mordenite having an SiO2/A12O3 ratio
above about 10. One method of forming this material involves
subjecting the ordinary form of mordenite having a SiO2/A12O3
of about 9 to 10 to the action of a strong acid such as
hydrochloric acid, sulfuric acid, hydrofluoric acid and
the like, at conditions effecting the removal or extraction
of at least a portion of the aluminum from the mordenite.
Typically, this procedure can be used to obtain mordenite
having a SiO2/A12O3 ratio of about 11 or more.
One preferred class of crystalline aluminosilicates
useful in the present invention are those materials in which
hydrogen, polyvalent metals and mixtures thereof occupy
at least about 50~j and more preferably, at least about
90%, of the cation positions o~ the aluminosilicate structure.
One particularly preferred isomerization catalyst
comprises a carrier material, preferably containing alumina,
and at least one crystalline aluminosilicate, as defined
above. Such catalyst preferably also includes at least
one platinum group metal component. In addition, in some
cases, the composite may contain a rhenium component.
It is preferred that the carrier material, e.g., alumina,
utilized in this catalyst be a porous, adsorptive, high-
surface area material having a surface area of about 2S
to about 500 or more square meters per gram. Suitable
alumina materials are the aluminas known as gamma-, eta-
and theta-alumina. In addition, in some embodiments, the
carrier material may contain minor proportions of other
well known refractory inorganic oxides such as silica,
silica-alumina, zirconia, magnesia, etc. The carrier material
often comprises about 25~ to about 99%, preferably about
40% to about 9S~, by weight of the presently useful catalysts.
Regarding the method of incorporating the crystalline
aluminosilicate into the carrier material, the crystalline ;~-
aluminosilicate may be combined directly with an aluminum
hydroxyl chloride sol prior to its formation in the alumina
carrier material. An advantage of this method is the relative
ease with which the crystalline aluminosilicate can be uniformly
distributed in the resultlng carrier material.
One preferred method for preparing the carrier
material involves the following steps: forming an aluminum
.:
.. . . .
37~
hydroxyl chloride sol by digesting aluminum in HCl to result
in a sol having a weight ratio of aluminum to chloride of
about 1.0 to about 1.4; evenly distributing the crystalline
aluminosilicate throughout the sol; gelling the resultant
mixture to produce a hydroyel or particles of a hydrogel;
then finishing the hydrogel into the carrier material by
standard aging, washing, drying and calcination steps.
See U.S. Patent No. 2,620,314 for details as to one preferred
method of forming the resultant mixture into spherical particles.
The amount of crystalline al-uminosilicate in the
fully compounded catalyst is preferably about 1% to about
75% by weight and, more particularly about 5% to about
60% by weight. By the expression "finely divided" it
is meant that the crystalline aluminosilicate is used in
a particle size having an average diameter of about 1 to
about 100 microns, with best results obtained with particles
of average diameter of less than about 40 microns;
Preferably, the presently useful isomerization
catalyst contains at least one metallic component. It is
intended to include as platinum group metals, platinum,
palladium, ruthenium, iridium, rhodium and osmium. The
platinum group metailic component, such as platinum or
palladium, may exist within the final catalytic composite
as a compound such as an oxide, sulfide, halide, etc., or
as an elemental metal. Generally, the amount of the platinum
group metallic component present in the final catalyst is
small compared to the quantities of the other components
combined therewith. In fact, the platinum group metallic
component generally comprises about 0.02% to about 1.0% by
weight of the final catalytic composite, calculated on an
elemental basis. Excellent results are obtained when the
catalyst contains about 0.2 percent to about 0.9 percent
by weight of the platinum group metal.
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The platinum group metallic component may bein~orporated in the catalytic composite in any suitable
manner such as coprecipitation or cogellation with the
carrier material, ion-exchange with the carrier material,
e.g., alumina hydrogel, or impregnation either before, during
or after incorporation of the alumino silicate component
into the carrier material and either after or before calcination
of the carrier materia], etc. The preferred method of
incorporating this component involves the utilization of
water soluble compounds of the platinum group metals with ~
which the carrier material is combined by an impregnation
technique. Thus~ the platinum group metal may be added
to the carrier material by co-mingling the latter with an
aqueous solution of chloroplatinic acid. Other water-soluble
compounds of platinum may be employed as impregnation solutions
and include ammonium chloro-platinate, platinum chloride,
dinitro diamino platinum, etc. In one preferred embodiment,
the platinum group metal is incorporated, e.g., by impregnation,
into the carrier material prior to the alumino silicate
being added. In this embodiment, the crystalline alumino
silicate component of the final catalyst is preferably sub-
stantially free of platinum group metal. In another preferred ;
embodiment, the carrier material is impregnated after it
has been calcined in order to minimize the risk of washing
away the valuable platinum metal compounds. However,
in some cases, it may be advantageous to impregnate the
support when it is in a gelled state. Following the impregnation,
the resulting impregnated support is dried. Additional
components, e.g., crystalline alumino silicates, if any,
can be incorporated into the impregnated carrier materialusing conventional techniques. The presently useful catalysts
may be macroformed into particles using conventional techni-
_ g _ :,
.. ..
ques such as extrusion, tabletting, spheroidizing and thelike. These catalysts are also subjected to high temperature
calcination, preferably at temperatures of about 600~F.
to about 1500F. for a period of time in the range of about
0.5 hours to about 20 hours or more.
In one embodiment, the presently useful catalysts
- include a rhenium component. This component may be present
as an elemental metal, as a chemical compound, such as the
oxide, sulfide, halide, or in a physical or chemical association
with the carrier material and/or the other components of
the catalyst. Generally, the rhenium component is utilized
in an amount sufficient to result in a final catalytic composite
containing about 0.02 to about 1.0 wt. percent rhenium,
calculated as an elemental metal. The rhenium component
may be incorporated in the catalytic composite in any suitable
manner and at any stage in the preparation of the catalyst.
One preferred procedure for incorporating the rhenium component ;
involves the impregnation of the carrier material either
before, during, or after the other components referred to
above are added. The impregnation solution can, in some
cases, be an aqueous solution of a sultable rhenium salt
such as ammonium perrhenate, sodium perrhenate, potassium `~
perrhenate and the like salts. In addition, aqueous solutions
of rhenium halides such as the chlorides may be used if
desired; however, the preferred impregnation solution is
an aqueous solution of perrhenic acid. In general, the -
rhenium component can be impregnated either prior to, simultane-
ously with, or after the platinum group metallic component
is added to the carrier material. However, best results
are achieved when the rhenium component is impregnated ;
simultaneously with the platinum group metallic component.
Feed to the process of the invention can be a
substantially pure C
8 alkyl benzene isomer, a mixture of
' ' -1 0-
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C8 alkyl benzene isomers, or hydrocarbon fractions rich
in C8 alkyl benzene isomers. For example, a source of
C8 Alkyl benzene isomers is the C8 aromatic fraction recovered
from catalytic reformates or coal tars. The C8 alkyl benzene
fraction remaining after separating and recovering all or
a part of a given isomer from such a source is a suitable
feed for the process of the invention Thus, paraxylene,
which is of growing importance, can be recovered from a
C8 catalytic reformate fraction by low temperature crystallization.
The mother liquor produced from such low temperature crystalli-
zation is deficient in paraxylene with respect to the thermo-
dynamic equilibrium concentration of C8 alkyl benzene isomers
and is an excellent ~eed to the present process.
The process of the invention is preferably carried
out at a temperature in the range of about 400 to about
900F. and more preferably about 550 to 800F. In general,
higher C8 alkyl benzene conversions are obtained as temperature
is increased~ although isomerization selectivity is reduced.
The isomerization reaction can be conducted over
a wide range of space velocities, such as a space velocity
in the range of about 0.5 to about 25, but is preferably at
a space velocity in the range of about 1 to about 10. In
general, conversion decreases with an increase in space
velocity, although selectivity is generally incrPased.
Space velocity, as the term is used herein, refers to WHSV
and is expressed as weight of feedl per hour, per unit
weight of catalyst. Total reaction pressure is preferably
in the range of about 100 to abollt 1500 pounds per square
inch ~uge (p.s.i.g.) and more preferably about 500 to
1000 p.s.i.g.
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The following examples illustrate more clearly
process methods of the present invention. However, these
illustrations are not to be interpreted as speci~ic limita-
tions on this invention.
EXAMPLES
A series of C8 alkyl benzene isomerization experiments
- was run to illustrate certain of the advantages of the
present invention. The feedstock employed in each of these
experiments had substantially the following composition:
Feedstock Wt. %
Benzene 0.06
Toluene 1.32
Ethylbenzene 20.00
Paraxylene 9.40
Metaxylene 55.53
Orthoxylene 13.29
Cg + Alkyl Benzenes0.05
The catalyst was disposed in a fixed bed reaction zone. The
following reaction conditions were employed:
Pressure 175 psig.
WHSV 4
Temperature 850F.
H2/H'C Mole Ratio as inbicated
A first catalyst, hereinafter designated as Catalyst ;
A, comprised 25~ by weight of a calcium exchanged hydrogen
form of zeolite Y and 75% by weight of an alumina derived
from hydrous alumina predominating in alumina trihydrates.
_. . .
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8~
The ~lumina component of Catalyst A also included about ~--
0.6% by weight (based on the alumina) of platinum, calculated
as elemental metal. The catalyst was in the form of substan-
tially cylindrical extrudates having a diameter of about
1/16 incbes and a length of about 1/4 inches.
Two experiments, as described above, were performed
using this catalyst. The H2/H'C mole ratio employed in
each of these experiments and the relative catalytic activity
for C8 alkyl benzene isomerization after 100 hours on stream
0 at each set of conditions were as follows:
CATALYST A
Test Number 1 2
H2/H'C Mole Ratio 4:1 10:1
Relative Catalytic Activity .59 1.9
for C8 Alkyl Benzene
Isomerization after 100
hours on Stream
-A second catalyst, hereinafter designated as Catalyst
B, comprised 45% by weight of hydrogen mordenite, 45% by
weight of an alumina derived from hydrous alumina predominating
in a~umina trihydrates and 10~ by weight of amorphous silica-
alumina. The alumina component of Catalyst B also included
about 0.8~ by weight (based on the alumina) of platinum,
calculated as elemental metal. This Catalyst B was in the
form of substantially~cylindrical extrudates having a diameter
of about 1/16 inches and a length of about 1/4 inches.
Two experiments, as described above, were performed
using this catalyst. The H2J~'C mole ratio employed in
- each of these experiments and the relative catalytic activitiçs
~0 for C8 alkyl benzene isomerization after 100 hour~ and 300
hours on stream at each set of conditions were as follows:
. , " , ' '' ~ ' ',
7~ 7~7
CATALYST B
Test Number ` 3 4
H2/~'C Mole Ratio 4:1 10:1
Relative Catalytic Activity
for C Alkyl Benzene Isomer-
ization after:
100 Hours on Stream 1.4 4.9
300 Hours on Stream 1.2 4.4
A third catalyst, hereinafter designated Catalyst
C comprising amorphous silica-alumina (with about 27% by
weight of silica based upon the total silica alumina-content),
about 0.35% by weight platinum (calculated as elemental
metal), and containing essentially no crystalline alumino
silicate or ~eolite was tested under the same conditions
as Test Nu~bers 1 and 3. Based upon correlations known
to provide accurate process variable relationships,
this work was projected to a H2/HIC mole ratio of 10:1. Such
projection indicated that the relative catalytic activity
for C8 alkyl benzene isomerization of Catalyst C actually was
reduced at a H2/H'C mole ratio of 10:1 relative to such
,activity at a H2/H'C mole ratio of 4:1.
The above data illustrate one important and surprising
characteristic of C8 alkyl benzene isomerization employing
zeolite-containing catalysts. Such processing gives increased
C8 alkyl benzene isomerization relative catalytic activity
with increasing H2/H'C mole,ratio. This result is in direct
contrast with processing involving a conventional, non-
zeolite-containing catalyst.
While this invention has been described with respect
to various specific examples and em.bodiments, it is to be
understood that the invention is not limited thereto and
that it can be variously practiced within the scope of the
following claims.
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