Process for isomerization of alkylaromatics

An improved process for the isomerization of non-equilibrium C.sub.8 aromatics is presented which utilizes a catalytic composition prepared by a novel method of incorporating magnesium into a crystalline aluminosilicate. The catalyst comprises an alumina matrix, a magnesium-containing zeolite, and a Group VIII metal component. It has also been found that the method of magnesium addition can dramatically affect the selectivity to para-xylene, as measured by the loss of C.sub.8 aromatics due to undesirable side-reactions. The method of the instant invention involves addition of the magnesium to a hydrogel comprising pseudoboehmite and zeolite.

FIELD OF THE INVENTION 
This invention relates to an improved process for the isomerization of 
xylenes and conversion of ethylbenzene. More specifically, the invention 
utilizes a catalyst composition consisting essentially of alumina, a Group 
VIII metal component, and a magnesium form zeolite. 
BACKGROUND OF THE INVENTION 
The xylenes, namely ortho-xylene, meta-xylene and para-xylene, are 
important chemicals and find wide and varied application in industry. 
Ortho-xylene is a reactant for the production of phthalic anhydride. 
Meta-xylene is used in the manufacture of plasticizers, azo dyes, wood 
preservers, etc. Para-xylene upon oxidation yields terephthalic acid which 
is used in the manufacture of synthetic textile fibers. 
As a result of the important applications to which the individual xylene 
isomers are subjected, it is often very important to be able to produce 
high concentrations of a particular xylene. This can be accomplished by 
converting a non-equilibrium mixture of the xylene isomers, which mixture 
is low in the desired xylene isomer, to a mixture which approaches 
equilibrium concentrations. Various catalysts and processes have been 
devised to accomplish the isomerization process. For example, it is well 
known in the art that catalysts such as aluminum chloride, boron fluoride, 
liquid hydrofluoric acid, and mixtures of hydrofluoric acid and boron 
fluoride can be used to isomerize xylene mixtures. 
Industrially, isomerization of xylenes and conversion of ethylbenzene is 
performed to produce para-xylene. A typical processing scheme for this 
objective comprises: (a) isomerizing a C.sub.8 alkylaromatic mixture to 
near equilibrium in an isomerization reaction zone; (b) separating out 
para-xylene using, for example, molecular sieve technology, to obtain a 
para-xylene rich stream and a stream rich in other xylenes; and, (c) 
recycling the stream rich in other xylenes to the isomerization reaction 
zone. 
The present invention is particularly concerned with the isomerization 
reaction step which may be used in an overall process directed to 
para-xylene production. An important parameter to consider in this 
isomerization reaction step is the degree of approach to xylene 
equilibrium achieved. The approach to equilibrium that is used is an 
optimized compromise between high C.sub.8 aromatic ring loss at high 
conversion (i.e. very close approach to equilibrium) and high utility 
costs due to the large recycle rate of unconverted ethylbenzene, 
orthoxylene, and meta-xylene. Also contributing to the recycle stream are 
C.sub.8 naphthenes which result from the hydrogenation of ethylbenzene. 
It is desirable to run the isomerization process as close to equilibrium as 
possible in order to maximize the para-xylene yield, however, associated 
with this is a greater cyclic C.sub.8 loss due to sidereactions. Cyclic 
C.sub.8 hydrocarbons include xylenes, ethylbenzene, and C.sub.8 
naphthenes. The correlation of cyclic C.sub.8 loss versus the distance 
from xylene equilibrium is a measure of catalyst selectivity. Thus there 
is a strong incentive to develop a catalyst formulation which minimizes 
cyclic C.sub.8 loss while maximizing para-xylene yield. 
Numerous catalysts have been proposed for use in xylene isomerization 
processes such as mentioned above. More recently, a number of patents have 
disclosed the use of crystalline aluminosilicate zeolite-containing 
catalysts for isomerization and conversion of C.sub.8 alkylaromatics. 
Crystalline aluminosilicates generally referred to as zeolites, may be 
represented by the empirical formula: 
EQU M.sub.2/n O.Al.sub.2 O.sub.3.xSiO.sub.2.yH.sub.2 O 
in which n is the valence of M which is generally an element of Group I or 
II, in particular, sodium, potassium, magnesium, calcium, strontium, or 
barium, and x is generally equal to or greater than 2. Zeolites have 
skeletal structures which are made up of three-dimensional networks of 
SiO.sub.4 and AlO.sub.4 tetrahedra, corner-linked to each other by shared 
oxygen atoms. Zeolites with high SiO.sub.4 /Al.sub.2 O.sub.3 ratio have 
received much attention as components for isomerization catalysts. 
Representative of zeolites having such high proportion of SiO.sub.4 
include mordenite and the ZSM variety. In addition to the zeolite 
component, certain metal promoters and inorganic oxide matrices have been 
included in isomerization catalyst formulations. Examples of inorganic 
oxides include silica, alumina, and mixtures thereof. Metal promoters such 
as Group VIII or Group III metals of the Periodic Table, have been used to 
provide a dehydrogenation functionality. The acidic function can be 
supplied by the inorganic oxide matrix, the zeolite, or both. 
When employing catalysts containing zeolites for the isomerization of 
alkylaromatics, characteristics such as acid site strength, zeolite pore 
diameter, and zeolite surface area become important parameters to consider 
during formulation development. Variation of these characteristics in a 
way that reduces side-reactions, such as, transalkylation, is required in 
order to achieve acceptable levels of cyclic C.sub.8 loss. 
It has been found that, if a catalyst is formulated with the components, 
and in the manner set forth hereinafter, an improved process for the 
conversion of a non-equilibrium mixture of xylenes containing ethylbenzene 
is obtained. 
OBJECTS AND EMBODIMENTS 
A principal object of the present invention is to provide an improved 
hydrocarbon conversion process and a novel catalyst composition for same. 
More specifically, the instant invention is aimed at an improved process 
for the isomerization of alkylaromatic hydrocarbons with minimal loss of 
C.sub.8 aromatic hydrocarbons. Accordingly, a broad embodiment of the 
invention is directed toward a process for the isomerization of a 
non-equilibrium feed mixture of xylenes containing ethylbenzene comprising 
contacting the feed mixture in the presence of hydrogen at isomerization 
process conditions with a catalyst consisting essentially of an alumina 
matrix, at least one Group VIII metal component, and 1 to 50 wt. % of a 
magnesium-containing zeolite, wherein the zeolite is either mordenite or a 
pentasil. 
Another embodiment is directed toward a process for the isomerization of a 
feed stream comprising a non-equilibrium mixture of xylenes containing 
ethylbenzene, which comprises contacting the feed in the presence of 
hydrogen at a temperature of from about 300.RTM. to 500.degree. C., a 
pressure of from about 5 to about 15 atmospheres, a liquid hourly space 
velocity of from about 0.5 to about 10 hr.sup.-1 with a catalyst 
consisting essentially of 75 to 95 wt. % gamma-alumina, 0.1 to 5 wt. % 
platinum, and 5 to 25 wt. % magnesium-containing mordenite wherein said 
catalyst is prepared by: (a) contacting a hydrogel comprising 
pseudo-boehmite and mordenite with an aqueous magnesium solution at a 
temperature of from 25.degree. to 100.degree. C. for 1 to 24 hours; (b) 
drying and calcining the resultant hydrogel of step (a) to convert the 
pseudo-boehmite alumina to essentially gamma-alumina; and, (c) 
impregnating the calcined hydrogel of step (b) with platinum. 
INFORMATION DISCLOSURE 
The prior art recognizes numerous isomerization processes employing a 
variety of catalyst formulations. However, it is believed that none of the 
prior art processes recognizes the use of the catalyst formulation and 
method of making same which forms an integral part of the instant 
invention. 
U.S. Pat. No. 3,792,100 (Sonoda et al) teaches a process for isomerizing 
xylenes using a catalyst composition comprising mordenite, which has 
supported thereon at least one metal selected from the group consisting of 
copper, silver, and chromium. This reference specifically teaches the 
removal of alkali or alkaline earth metal ions from the mordenite to allow 
for the addition of the above-named metals. No reference is made to the 
utility of either magnesium or a Group VIII metal. 
In another reference, U.S. Pat. No. 3,912,659 (Brandenburg et al), a 
catalyst composite useful for conversion of alkylaromatic hydrocarbons, is 
disclosed. Specifically, the catalyst is used in a disproportionation 
process, such as, conversion of toluene into benzene and mixed xylenes. 
The catalyst comprises a hydrogen form mordenite, an eta or gamma alumina 
binder, and a sulfided Group VIII metal impregnated on said mordenite. 
Patentee fails to disclose the utility of a magnesium-containing 
mordenite. 
U.S. Pat. No. 4,159,282 (Olson et al) teaches a process for isomerization 
of C.sub.8 alkylaromatics using a catalyst preferably containing a 
pentasil zeolite. Reference is made to the possible modification of the 
zeolite by incorporating therewith an amount of a difficultly reducible 
oxide, such as, magnesium. However, this reference is silent to the unique 
combination of a Group VIII metal, magnesium, zeolite, and gamma-alumina 
as disclosed herein. 
A reference similar to the '282 patent is U.S. Pat. No. 4,482,773 (Chu et 
al) which discloses an isomerization process wherein C.sub.8 aromatics are 
processed over a catalyst comprising HZSM-5, platinum and a Group II-A 
metal. Magnesium is the preferred Group II-A metal. However, the patent 
does not teach the use of either mordenite or an alumina matrix. 
U.S. Pat. No. 4,100,262 (Pelrine) discloses a method of preparation of 
zeolite ZSM-5 wherein in one embodiment, the patentee teaches that the 
original cations of the as synthesized ZSM-5 can be replaced with 
hydrogen, rare earth metals, aluminum, metals of Groups IIA, IIIB, IVB, 
VIB, VIII, IB, IIB, IIIA, and IVA. Similarly, U.S. Pat. No. 4,218,573 
(Tabak et al) discloses a process for isomerizing xylenes wherein the 
zeolite ZSM-5 used in the catalyst composition may be base exchanged with 
cations, such as, magnesium. Neither of the two patents recognized the 
utility of mordenite nor do the references disclose the novel method of 
preparation of the instant invention. 
In summary, it appears that the prior art only generally recognizes that 
zeolites have utility for isomerization of C.sub.8 alkylaromatics and that 
no single reference teaches nor suggests the invention claimed herein.

DETAILED DESCRIPTION OF THE INVENTION 
As mentioned above, this invention is concerned with the catalytic 
isomerization and conversion of a non-equilibrium mixture of C.sub.8 
aromatic hydrocarbons utilizing a catalyst consisting essentially of 
alumina, at least one Group VIII metal component, and 1 to 50 wt. % of a 
magnesium zeolite, wherein the zeolite is either mordenite or a pentasil. 
The improved process of the instant invention allows for a closer approach 
to xylene equilibrium resulting in a greater yield of para-xylene without 
the high loss of C.sub.8 aromatics common to prior art processes. 
The process of this invention is applicable to the isomerization of 
isomerizable alkylaromatic hydrocarbons of the general formula: 
EQU C.sub.6 H.sub.(6-n) R.sub.n 
where n is an integer from 2 to 5 and R is CH.sub.3, C.sub.2 H.sub.5, 
C.sub.3 H.sub.7, or C.sub.4 H.sub.9, in any combination and including all 
the isomers thereof. Suitable alkylaromatic hydrocarbons include, for 
example, ortho-xylene, metaxylene, para-xylene, ethylbenzene, 
ethyltoluenes, the trimethylbenzenes, the diethylbenzenes, the 
triethylbenzenes, methylpropylbenzenes, ethylpropylbenzenes, the 
diisopropylbenzenes, the triisopropylbenzenes, etc., and mixtures thereof. 
It is contemplated that any aromatic C.sub.8 mixture containing 
ethylbenzene and xylene may be used as feed to the process of this 
invention. Generally, such mixture will have an ethylbenzene content in 
the approximate range of 5 to 50 wt. %, an ortho-xylene content in the 
approximate range of 0 to 35 wt. %, a meta-xylene content in the 
approximate range of 20 to 95 wt. % and a para-xylene content in the 
approximate range of 0 to 15 wt. %. It is preferred that the aforemention 
C.sub.8 aromatics comprise a non-equilibrium mixture. The feed to the 
instant process, in addition to C.sub.8 aromatics, may contain nonaromatic 
hydrocarbons, i.e. naphthenes and paraffins in an amount up to 30 wt. %. 
The alkylaromatic hydrocarbons for isomerization may be utilized as found 
in selective fractions from various refinery petroleum streams, e.g., as 
individual components or as certain boiling range fractions obtained by 
the selective fractionation and distillation of catalytically cracked gas 
oil. The process of this invention may be utilized for conversion of 
isomerizable aromatic hydrocarbons when they are present in minor 
quantities in various streams. The isomerizable aromatic hydrocarbons 
which may be used in the process of this invention need not be 
concentrated. The process of this invention allows the isomerization of 
alkylaromatic containing streams such as reformate to produce specified 
xylene isomers, particularly para-xylene, thus upgrading the reformate 
from its gasoline value to a high petrochemical value. 
According to the process of the present invention, an alkylaromatic 
hydrocarbon charge stock, preferably in admixture with hydrogen, is 
contacted with a catalyst of the type hereinafter described in an 
alkylaromatic hydrocarbon isomerization zone. Contacting may be effected 
using the catalyst in a fixed bed system, a moving bed system, a fluidized 
bed system, or in a batch-type operation. In view of the danger of 
attrition loss of the valuable catalyst and of operational advantages, it 
is preferred to use a fixed bed system. In this system, a hydrogen-rich 
gas and the charge stock are preheated by suitable heating means to the 
desired reaction temperature and then passed into an isomerization zone 
containing a fixed bed of catalyst. The conversion zone may be one or more 
separate reactors with suitable means therebetween to ensure that the 
desired isomerization temperature is maintained at the entrance to each 
zone. It is to be noted that the reactants may be contacted with the 
catalyst bed in either upward, downward, or radial flow fashion, and that 
the reactants may be in the liquid phase, a mixed liquid-vapor phase, or a 
vapor phase when contacted with the catalyst. 
The process of this invention for isomerizing an isomerizable alkylaromatic 
hydrocarbon is preferably effected by contacting the alkylaromatic, in a 
reaction zone containing an isomerization catalyst as hereinafter 
described, with a fixed catalyst bed by passing the hydrocarbon in a 
down-flow or radial flow fashion through the bed, while maintaining the 
zone at proper alkylaromatic isomerization conditions such as a 
temperature in the range from about 0.degree.-600.degree. C. or more, and 
a pressure of atmospheric to about 100 atmospheres or more. Preferably, 
the operating temperature ranges from about 300.degree.-500.degree. C. and 
the pressure ranges from 0.5-55 atmospheres. The hydrocarbon is passed, 
preferably, in admixture with hydrogen at a hydrogen to hydrocarbon mole 
ratio of about 0.5:1 to about 25:1 or more, and at a liquid hourly 
hydrocarbon space velocity of about 0.1 to about 20 hr.sup.-1 or more, 
most preferably at 0.5 to 10 hr.sup.-1. Other inert diluents such as 
nitrogen, argon, etc., may be present. 
In accordance with the present invention, the catalytic composite comprises 
an alumina matrix. This matrix is a porous refractory inorganic oxide 
material having the basic chemical formula of Al.sub.2 O.sub.3. Suitable 
alumina materials are the crystalline aluminas known as gamma-, eta-, and 
theta-alumina, with gamma- or eta-alumina giving best results. In 
addition, in some embodiments, the alumina carrier material may contain 
minor proportions of other well known refractory inorganic oxides such as 
silica, zirconia, magnesia, etc.; however, the preferred support is 
substantially pure gamma- or eta-alumina. Preferred carrier materials have 
an apparent bulk density of about 0.3 to about 0.8 g/cc and surface area 
characteristics such that the average pore diameter is about 20 to 300 
angstroms, the pore volume is about 0.1 to about 1 cc/g and the surface 
area is about 100 to about 500 m.sup.2 /g. In general, best results are 
typically obtained with a gamma-alumina carrier material which is used in 
the form of spherical particles having: a relatively small diameter (i.e. 
typically about 1/16-inch), an apparent bulk density of about 0.3 to about 
0.8 g/cc, a pore volume of about 0.7 ml/g, and a surface area of about 150 
to about 250 m.sup.2 /g. 
The preferred alumina carrier material may be prepared in any suitable 
manner and may be synthetically prepared or naturally occurring. Whatever 
type of alumina is employed, it may be activated prior to use by one or 
more treatments including drying, calcination, steaming, etc., and it may 
be in a form known as activited alumina, activated alumina of commerce, 
porous alumina, alumina gel, etc. For example, the alumina carrier may be 
prepared by adding a suitable alkaline reagent, such as ammonium 
hydroxide, to a salt of aluminum such as aluminum chloride, aluminum 
nitrate, etc., in an amount to form an aluminum hydroxide gel which upon 
drYing and calcining is converted to alumina. The alumina carrier may be 
formed in any desired shape such as spheres, pills, cakes, extrudates, 
powders, granules, tablets, etc., and utilized in any desired size. For 
the purpose of the present invention, a particularly preferred form of 
alumina is the sphere, and alumina spheres may be continuously 
manufactured by the well-known oil drop method which comprises: forming an 
alumina hydrosol by any of the techniques taught in the art and preferably 
by reacting aluminum metal with hydrochloric acid, combining the resultant 
hydrosol with a suitable gelling agent and dropping the resultant mixture 
into an oil bath maintained at elevated temperatures. The droplets of the 
mixture remain in the oil bath until they set and form hydrogel spheres. 
The spheres are then continuously withdrawn from the oil bath and 
typically subjected to specific aging treatments in oil and an ammoniacal 
solution to further improve their physical characteristics. The resulting 
aged and gelled particles are then washed and dried at a relatively low 
temperature of about 50.degree.-200.degree. C. and subjected to a 
calcination procedure at a temperature of about 450.degree.-700.degree. C. 
for a period of about 1 to about 20 hours. This treatment effects 
conversion of the alumina hydrogel to the corresponding crystalline 
gamma-alumina. See the teachings of U.S. Pat. No. 2,620,314 for additional 
details. 
An especially preferred method of preparing the alumina matrix involves the 
inclusion of a zeolite into the alumina hydrosol prior to dropping the 
hydrosol into an oil bath. This technique yields a hydrogel comprising 
pseudo-boehmite alumina and zeolite. The amount of zeolite added to the 
hydrosol can range from 1 to 50 wt. % zeolite based on the weight of the 
finished catalyst composite. Prior to drying and calcining the resultant 
hydrogen containing pseudo-boehmite alumina and zeolite, the hydrogel may 
be subjected to any number of steps to incorporate elements selected from 
the Group I-A to Group VIII metals. Calcination of the hydrogel transforms 
the pseudo-boehmite alumina into the more stable and commercially usable 
gamma-alumina. 
The zeolite component of the present invention may be selected from either 
mordenite or a pentasil. Mordenite is a crystalline aluminosilicate of the 
zeolite type which is well known to the art as an adsorption agent and as 
a catalytic agent in hydrocarbon conversion reactions. Mordenite, as 
typically manufactured or found in nature, is highly siliceous and is 
characterized by a silica (SiO.sub.2) to alumina (Al.sub.2 O.sub.3) mole 
ratio of about 10. Two synthetic types of mordenite are available; 
"large-port" and "small-port" mordenites. Studies of the adsorption 
behavior of mordenite and the first synthetic types indicated that the 
pore structure was considerably smaller than the structure indicated. 
These types are referred to as small-port mordenite; they exhibit an 
adsorption diameter of about 4 angstroms. By varying synthesis conditions, 
a large-port mordenite has been synthesized which possesses the adsorption 
properties expected for the structure. After activation (dehydration), 
large-port mordenite adsorbs large molecules such as benzene and 
cyclohexane which are completely excluded by the small-port variety. The 
large-port mordenite is preferred in the instant invention. The mordenite 
crystalline structure comprises four-and five-membered rings of SiO.sub.4 
and AlO.sub.4 tetrahedra so arranged that the resulting crystal lattice 
comprises pores and channels running parallel along the crystal axis to 
give a tubular configuration. This structure is unique among some zeolite 
crystalline aluminosilicates in that the channels do not intersect and 
access to the cages or activities can be only one direction. For this 
reason, the mordenite structure is frequently referred to as 
two-dimensional in contrast to the other known crystalline 
aluminosilicates such as faujasite in which the cavities can be entered 
from three directions. 
As stated, mordenite, as commercially available, has an SiO.sub.2 /Al.sub.2 
O.sub.3 mole ratio of about 10 and is usually characterized as being in 
the sodium form. Before the sodium form of mordenite can be utilized as an 
effective catalyst for hydrocarbon conversion reactions, it must be first 
converted to the hydrogen form and/or ion exchanged to replace the alkali 
metal ion (typically sodium) with a desired metal cation. Mordenite, since 
it has a high initial SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio and is more 
acid resistant than faujasite, may be converted to the hydrogen form by 
replacing the sodium ion with a hydrogen ion by treatment with an aqueous 
solution of a mineral acid. Alternatively, the hydrogen ion can be 
incorporated by ion exchange with ammonium hydroxide and then calcining 
the ammonium form mordenite. Hydrogen ion exchanged mordenites are often 
termed H-mordenite and are illustrated in U.S. Pat. No. 3,281,482. The 
catalytic activity of mordenites may also be increased by extracting a 
portion of the alumina from the mordenite crystal structure, as well as 
simultaneously ion exchanging hydrogen ions, by treatment with mineral 
acids under relatively severe temperatures and contact time. What is 
produced are aluminum-deficient mordenites maintaining the same gross 
crystal structure in terms of gross interatomic distances as the original 
mordenite, as measured by X-ray diffraction patterns. Mordenites that have 
been so acid extracted typically have an SiO.sub.2 /Al.sub.2 O.sub.3 ratio 
in excess of 25:1 which may extend to 100:1 or more. These acid extracted 
mordenites are exemplified by U.S. Pat. No. 3,480,539. Acid extracted 
mordenites which are particularly effective and active catalysts have 
SiO.sub.2 /Al.sub.2 O.sub.3 ratios in excess of 50:1. However, we have 
found that the use of dealuminated mordenites causes increased loss of 
C.sub.8 cyclics. Although the mechanism is not proven, we speculate that 
the increased cyclics loss is due to an increase in zeolite pore diameter 
upon dealumination. This increased pore size reduces steric constraints on 
the transition state for transalkylation, leading to increased C.sub.8 
cyclics loss by transalkylation. 
It is preferred that sodium cation removal be accomplished by ammonium ion 
exchange. The NH.sub.4 -mordenite that results is converted to hydrogen 
form mordenite during calcination. In the preferred embodiment, this 
ammonium ion exchange is already achieved to some extent by the treatment 
of the hydrogel spheres with ammoniacal solutions during aging, and 
completed during the subsequent washing with 0.5 wt. % NH.sub.3 /H.sub.2 O 
solution at 95.degree. C. 
Alternatively, the zeolite component of the present invention may be a 
pentasil crystalline aluminosilicate zeolite. "Pentasil" is a term used to 
describe a class of shape selective zeolites. This novel class of zeolites 
is well known to the art and is typically characterized by a 
silica-to-alumina mole ratio of at least about 12. Suitable descriptions 
of the pentasils may be found in U.S. Pat. Nos. 4,159,282, 4,163,018, and 
4,278,565, all of which are incorporated herein by reference. Of the 
pentasil zeolites, the preferred ones are ZSM-5, ZSM-8, ZSM-11, ZSM-23, 
and ZSM-35, with ZSM-5 being particularly preferred. 
It is also within the scope of the present invention that the particular 
pentasil selected may be a gallosilicate. Gallosilicates have essentially 
the same structure as the ZSM-type zeolites described hereinabove, except 
that all or part of the aluminum atoms in the aluminosilicate crystal 
framework are replaced by gallium atoms. This substitution of the aluminum 
by gallium is usually performed prior to or during synthesis of the 
zeolite. The gallium content for this particular type of pentasil, 
expressed as mole ratios of SiO.sub.2 to Ga.sub.2 O.sub.3, range from 20:1 
to 400:1 or more. 
Regardless of the type of zeolite used, it is desired that the zeolite be 
predominantly in the sodium form prior to its commingling with the alumina 
matrix. In a preferred embodiment, the zeolite is commercially obtained in 
the sodium form and used directly with the alumina hydrosol. The hydrosol 
is then dispersed into an oil bath as described above to form a hydrogel. 
Upon forming the hydrogel containing the pseudo-boehmite alumina and 
zeolite, the addition of magnesium to zeolite is performed. Although not 
exactly understood, superior results are obtained, as exemplified in the 
examples to follow, when the magnesium is introduced to the zeolite at the 
hydrogel stage as opposed to either the addition after the hydrogel has 
been dried and calcined or to the zeolite prior to addition to the alumina 
hydrosol. It is believed that the zeolite in the hydrogel is more readily 
susceptible to ion exchange with magnesium. It is also believed that 
having pseudo-boehmite present, as opposed to gamma-alumina, during 
contacting with the magnesium solution greatly reduces the possibility 
that the magnesium will ion exchange with the alumina matrix. Thus, a more 
efficient use of magnesium is obtained by following the method of the 
instant invention. The amount of magnesium-containing zeolite may range 
from 1 to 50 wt. % baseo on the weight of the finished catalyst composite. 
Preferably, the amount of magnesium-containing zeolite ranges from 5 to 25 
wt. % of the finished catalyst. 
Any suitable magnesium compound may be used to introduce the magnesium 
cation into the zeolite. Representative magnesium compounds include 
magnesium nitrate, magnesium benzoate, magnesium propionate, magnesium 
2-ethylhexoate, magnesium carbonate, magnesium formate, magnesium oxalate, 
magnesium amide, magnesium bromide, magnesium chloride, magnesium acetate, 
magnesium lactate, magnesium laurate, magnesium oleate, magnesium 
palmitate, magnesium silicylate, magnesium stearate, and magnesium 
sulfide. It is preferred that the magnesium compound be in solution in 
order to facilitate the contact with the hydrogel. Any solvent relatively 
inert to the hydrogel and the magnesium compound may be employed. Suitable 
solvents include water and aliphatic, aromatic, or alcoholic liquid. 
Contacting the magnesium-containing solution with the hydrogel is carried 
out at a temperature from 0.degree. to 150.degree. C. The preferred 
temperature range is from about 25.degree. to 100.degree. C. The time of 
contact can vary from about 1 to 24 hours. The physical means for 
contacting the magnesium-containing solution with hydrogel can be 
accomplished by a plurality of methods, with no one method having a 
particular advantage. Such contacting methods may include, for example, a 
stationary bed of hydrogel particles in an agitated solution, a stationary 
bed of hydrogel particles in a continuously flowing solution, a stationary 
bed of hydrogel particles in a static solution or any other means which 
efficiently contacts the magnesium-containing solution with the hydrogel 
comprising the pseudo-boehmite and zeolite. 
The amount of magnesium incorporated into the zeolite should be such that 
greater than 50% of the available ion exchange sites are occupied. The 
amount of magnesium may range from 0.1 wt. % of the finished catalyst to 
as high as 10 wt. %. By "finished catalyst", it is meant the final 
catalyst formulation suitable for contact with the hydrocarbon feed. 
Preferably, the amount of magnesium present in the finished catalyst 
composition is between 0.5 and 5 wt. %. 
It is contemplated that other metals may be directly substituted in place 
of magnesium to provide the desired feature of the invention, namely, 
allowing for a close approach to xylene equilibrium while minimizing the 
loss of C.sub.8 aromatics. Such alternative metals include calcium, 
lanthanum, and copper or mixtures of these metals. 
The catalyst of the instant invention also contains at least one Group VIII 
metal component. Preferably, this Group VIII metal is selected from the 
platinum group metals. Of the platinum group metals, which include 
palladium, rhodium, ruthenium, osmium and iridium, the use of platinum is 
preferred. The platinum group component may exist within the final 
catalyst composite as a compound such as an oxide, sulfide, halide, 
oxysulfide, etc., or as an elemental metal or in combination with one or 
more other ingredients of the catalyst. It is believed that the best 
results are obtained when substantially all the platinum group component 
exists in the elemental state. The platinum group component generally 
comprises from about 0.01 to about 2 wt. % of the final catalytic 
composite, calculated on an elemental basis. It is preferred that the 
platinum content of the catalyst be between about 0.1 and 1 wt. %. The 
preferred platinum group component is platinum, with palladium being the 
next preferred metal. The platinum group component may be incorporated 
into the catalyst composite in any suitable manner such as by 
coprecipitation or cogelation with the preferred carrier material, or by 
ion-exchange or impregnation of the carrier material. The preferred method 
of preparing the catalyst normally involves the utilization of a 
water-soluble, decomposable compound of a platinum group metal to 
impregnate the calcined hydrogel material. For example, the platinum group 
component may be added to the calcined hydrogel by commingling the 
calcined hydrogel with an aqueous solution of chloroplatinic or 
chloropalladic acid. An acid such as hydrogen chloride is generally added 
to the impregnation solution to aid in the distribution of the platinum 
group component through the calcined hydrogel particles. 
After addition of the Group VIII metal component, the calcined hydrogel 
comprising gamma-alumina, magnesium-containing zeolite, and platinum is 
dried at a temperature ranging from about 100.degree. to about 320.degree. 
C. for a period of at least 2 to about 24 hours or more, and finally 
calcined or oxidized at a temperature ranging from about 450.degree. to 
about 650.degree. C. in air or oxygen atmosphere for a period of about 0.5 
to about 10 hours in order to convert all of the metallic components to 
the corresponding oxide form. The resultant oxidative composite is 
preferably subjected to a substantially water-free reduction step prior to 
its use in the isomerization of hydrocarbons. This step is designed to 
selectively reduce the platinum group component to the elemental metallic 
state, while maintaining the magnesium component in a positive oxidation 
state, and to ensure a uniform and finely divided dispersion of the 
metallic components throughout the catalyst. Preferably, a substantially 
pure and dry hydrogen stream (i.e. less than 20 vol. ppm H.sub.2 O) is 
used as the reducing agent in this step. The reducing agent is contacted 
with the oxidized catalyst at conditions including a reduction temperature 
ranging from about 200.degree. to about 650.degree. C. and a period of 
time of about 0.5 to 10 hours effective to reduce substantially all of the 
platinum group component to the elemental metallic state. 
The resulting reduced catalytic composite may, in some cases, be 
beneficially subjected to a presulfiding operation designed to incorporate 
in the catalytic composite from about 0.05 to about 0.5 wt. % sulfur 
calculated on an elemental basis. Preferably, this presulfiding treatment 
takes place in the presence of hydrogen and a suitable sulfurcontaining 
compound such as hydrogen sulfide, lower molecular weight mercaptans, 
organic sulfides, etc. Typically, this procedure comprises treating the 
reduced catalyst with a sulfiding gas such as a mixture of hydrogen and 
hydrogen sulfide having about 10 moles of hydrogen per mole of hydrogen 
sulfide at conditions sufficient to effect the desired incorporation of 
sulfur, generally including a temperature ranging from about 10.degree. up 
to about 593.degree. C. or more. It is generally a good practice to 
perform this presulfiding step operation under substantially water-free 
conditions. 
The following example is presented for purpose of illustration only and is 
not intended to limit the scope of the present invention. 
EXAMPLE 
This example presents the results from four different processes. Each 
process was evaluated using a pilot plant flow reactor processing a 
non-equilibrium C.sub.8 aromatic feed comprising 52.2 wt. % metaxylene, 
18.7 wt. % ortho-xylene, 0.1 wt. % para-xylene, 21.3 wt. % ethylbenzene, 
and 0.1 wt. % toluene, with the balance being nonaromatic hydrocarbons. 
This feed was contacted with 100 cc of catalyst at a liquid hourly space 
velocity of 2, and a hydrogen to hydrocarbon mole ratio of 4. Reactor 
pressure and temperature were adjusted to cover a range of conversion 
values in order to develop the relationship between C.sub.8 ring loss and 
approach to xylene equilibrium (as determined by product para-xylene to 
total xylene weight ratio). At the same time, at each temperature, the 
pressure was chosen to maintain a constant mole ratio of C.sub.8 
naphthenes to C.sub.8 aromatics of approximately 0.06. 
Initial catalyst preparation for each of the processes described 
hereinbelow proceeded as follows. A first solution was prepared by adding 
a zeolite to enough alumina hydrosol, prepared by digesting metallic 
aluminum in hydrochloric acid, to yield a zeolite content in the finished 
catalyst equal to about 10 wt. %. As described hereinbelow, the zeolite 
was either a mordenite or a pentasil. To this first solution is added a 
second solution of hexamethylenetetramine (HMT). These two solutions were 
mixed to form a homogeneous admixture which was then dispersed as droplets 
into an oil bath at a temperature of about 95.degree. C. The droplets 
remained in the oil bath until they set and formed hydrogel spheres. The 
spheres were removed from the oil bath and washed with an aqueous solution 
containing about 0.5 wt. % ammonia. At this point in the preparation the 
hydrogel spheres which are commonly referred to as "wet hopper spheres" 
(WHS), were either directly dried and calcined or contacted with a 
magnesium-containing solution. 
The first process, designated as Run A, which is in accordance with the 
invention, utilized a catalyst wherein the zeolite contained in the 
hydrogel was hydrogen/ammonium form mordenite. A stationary bed of WHS, 
comprising the mordenite and pseudo-boehmite alumina, was contacted with 
an aqueous solution of 1.5 molal magnesium acetate by continuously 
circulating the solution at a rate of about 8 ml/minute. The temperature 
of the magnesium acetate solution was maintained at about 94.degree. C. 
for a period of about 20 hours. A deionized water wash using about 10 bed 
volumes was performed at the conclusion of the magnesium addition step. 
The WHS were then air dried at 11.degree. C. for about 12 hours and then 
calcined in air at a temperature of about 650.degree. C. 
The calcined WHS were then impregnated with a solution of chloroplatinic 
acid, containing 2 wt. % hydrochloric acid (based on calcined WHS), to 
yield a final platinum content of 0.28 wt. %. The impregnated spheres were 
oxidized and chloride adjusted at 525.degree. C., reduced in an 
environment of H.sub.2 at 565.degree. C., and sulfided with H.sub.2 S. The 
amount of magnesium-containing zeolite was about 9.8 wt. %, the magnesium 
content was 1.02 wt. %, and the sulfur content was 0.12 wt. %. The 
isomerization performance results from Run A are presented in FIG. 1. 
Run B was also performed in accordance with the instant invention. The 
process of Run B was essentially identical to that of Run A except the 
zeolite added to the alumina hydrosol comprised a hydrogen form ZSM-5 
zeolite having a silica to alumina mole ratio of 42. The platinum and 
magnesium contents of this catalyst were 0.32 wt. % and 0.95 wt. %, 
respectively. The sulfur content was targeted to be 0.11 wt. %. The 
isomerization performance results for Run B are also presented in FIG. 1. 
To demonstrate the superior performance of the process of the instant 
invention, two control processes were run. The first process, designated 
Run C and not in accordance with the instant invention, utilized a 
catalyst formulation that was prepared identically to the catalysts in 
Runs A and B, however, in Run C, there was no addition of magnesium to the 
zeolite. The zeolite used in Run C was the same sodium form mordenite used 
in Run A. The finished catalyst was analyzed for both platinum and 
magnesium. The platinum content was 0.32 wt. %, the magnesium content was 
less than 0.05 wt. %, and the sulfur content was 0.08 wt. %. Test results 
comparing the isomerization performance of Run C with Runs A and B are 
presented in FIG. 1. 
The second control process, designated as Run D, also not in accordance 
with the invention, was performed to demonstrate the importance of the 
means by which magnesium is added to the zeolite. The catalyst used in Run 
D was prepared in an identical manner as the catalyst of Run A except the 
magnesium acetate was impregnated onto the catalyst at 25.degree. C. after 
the WHS had been dried and calcined but prior to platinum addition. Thus 
the magnesium-containing solution was contacted with calcined spheres 
comprising gamma-alumina and mordenite. The platinum and magnesium levels 
were 0.30 wt. % and 0.57 wt. %, respectively. The sulfur content was 0.09 
wt. %. In order to accurately access the performance of this second 
control process, in particular, in order to conduct a comparison at the 
same Mg levels, it was necessary to prepare another catalyst in accordance 
with the instant invention following the procedure used for the catalyst 
of Run A. In preparing this catalyst, a temperature of 25.degree. C. was 
maintained during the contact of the WHS with the magnesium acetate 
solution. The platinum content was 0.3 wt. %, the magnesium content was 
0.56 wt. %, and the sulfur content was 0.02 wt. %. This catalyst was 
tested as Run E. A comparison of results for Run D, not of the invention, 
and Run E, in accordance with the invention, is graphically depicted in 
FIG. 2. 
Both FIGS. 1 and 2 graphically illustrate the same performance parameters. 
The x-axis is the concentration of para-xylene in the product, expressed 
as mole % relative to the total xylenes in the product. The y-axis 
represents the amount of C.sub.8 cyclic hydrocarbons lost due to side 
reactions. This parameter is defined as the sum of C.sub.8 aromatics and 
naphthenes in the feed minus the amount of C.sub.8 aromatics and 
naphthenes in the product divided by the C.sub.8 aromatic and naphthenes 
in the feed. 
The isomerization performance results presented in both FIGS. 1 and 2 
clearly indicate the advantage of the process of the instant invention. 
More specifically, if the results of the process of the instant invention 
is compared to those of the control runs, while operating at conditions to 
produce a product containing 22 mole percent para-xylene, about 25% less 
C.sub.8 aromatic hydrocarbons are lost due to side reactions.