Selective production of para-xylene

Process for the selective production of para-xylene by methylation of toluene in the presence of a catalyst comprising a crystalline aluminosilicate zeolite, said zeolite having a silica to alumina ratio of at least about 12 and a constraint index, as hereinafter defined, within the approximate range of 1 to 12, which catalyst has undergone prior modification by the addition thereto of phosphorus oxide and magnesium oxide, each in an amount of at least about 0.25 percent by weight.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for the selective production of 
para-xylene by catalytic production of para-xylene in the presence of a 
phosphorous and magnesium-containing crystalline aluminosilicate zeolite 
catalyst. 
2. Description of the Prior Art 
Alkylation of aromatic hydrocarbons utilizing crystalline aluminosilicate 
catalysts has heretofore been described. U.S. Pat. No. 2,904,607 to Mattox 
refers to alkylation of aromatic hydrocarbons with an olefin in the 
presence of a crystalline metallic aluminosilicate having uniform pore 
openings of about 6 to 15 Angstrom units. U.S. Pat. No. 3,251,897 to Wise 
describes alkylation of aromatic hydrocarbons in the presence of X- or 
Y-type crystalline aluminosilicate zeolites, specifically such type 
zeolites wherein the cation is rare earth and/or hydrogen. U.S. Pat. No. 
3,751,504 to Keown et al. and U.S. Pat. No. 3,751,506 to Burress describe 
vapor phase alkylation of aromatic hydrocarbons with olefins, e.g., 
benzene with ethylene, in the presence of a ZSM-5 type zeolite catalyst. 
The alkylation of toluene with methanol in the presence of a cation 
exchanged zeolite Y has been described by Yashima et al. in the Journal of 
Catalysis 16, 273-280 (1970). These workers reported selective production 
of para-xylene over the approximate temperature range of 200.degree. C., 
with the maximum yield of para-xylene in the mixture of xylenes, i.e., 
about 50 percent of the xylene product mixture, being observed at 
225.degree. C. Higher temperatures were reported to result in an increase 
in the yield of meta-xylene and a decrease in production of para- and 
ortho-xylenes. 
U.S. Pat. No. 3,965,208 describes the methylation of toluene, under 
conditions such that the formation of meta-xylene is suppressed and the 
formation of ortho- and para-xylene is enhanced carried out in the 
presence of a catalyst comprising a crystalline aluminosilicate zeolite of 
the ZSM-5 type which has been modified by the addition thereto of a small 
amount of a Group VA element. My previous patent, U.S. Pat. No. 4,011,276, 
describes the disproportionation of toluene by subjecting the same to 
disproportionation conditions in the presence of a catalyst comprising a 
crystalline aluminosilicate zeolite of the ZSM-5 type which has been 
modified by the addition thereto of a minor proportion of an oxide of 
phosphorus and a minor proportion of an oxide of magnesium to produce 
benzene and xylenes rich in the para isomer. 
While the above noted prior art is considered of interest in connection 
with the subject matter of the present invention, the methylation process 
described herein utilizing a catalyst of a crystalline aluminosilicate 
zeolite having a silica/alumina ratio of at least about 12, a constraint 
index within the approximate range of 1 to 12 and which has been modified 
by the addition thereto of a minor proportion of an oxide of phosphorus 
and a minor proportion of an oxide of magnesium to thereby achieve 
unexpectedly high selective production of para-xylene has not, insofar as 
is known, been heretofore described. 
Of the xylene isomers, e.g., ortho-, meta- and para-xylene, the latter is 
of particular value being useful in the manufacture of terephthalic acid 
which is an intermediate in the manufacture of synthetic fibers such as 
"Dacron". Mixtures of xylene isomers either alone or in further admixture 
with ethylbenzene, generally containing a concentration of about 24 weight 
percent para-xylene in the equilibrium mixture, have been previously 
separated by expensive superfraction and multistage refrigeration steps. 
Such process, as will be realized, has involved high operation costs and 
has a limited yield. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there has been discovered a 
process for selectively producing para-xylene in preference to meta-xylene 
or ortho-xylene by reaction of toluene with a methylating agent in the 
presence of a catalyst comprising a crystalline aluminosilicate zeolite, 
said zeolite having a silica to alumina ratio of at least about 12 and a 
constraint index of from 1 to 12, which catalyst has been modified by the 
addition thereto of a minor proportion of an oxide of phosphorus and a 
minor proportion of an oxide of magnesium. 
Compared to a conventional thermodynamic equilibrium xylene mixture in 
which the para:meta:ortho ratio is approximately 1:2:1, the process 
described herein affords a xylene product in which the para-xylene content 
may exceed 90 percent. The improved yields of para-xylene reduces the cost 
of separation of para-xylene from its isomer which is the most expensive 
step in the current method employed for producing para-xylene. 
The present process comprises methylation of toluene in the presence of a 
catalyst comprising a particular crystalline aluminosilicate zeolite 
modified by the addition thereto of phosphorus oxide and magnesium oxide, 
each in an amount of at least about 0.25 percent by weight. 
The crystalline aluminosilicate zeolite employed is a member of a novel 
class of zeolites exhibiting some unusual properties. These zeolites 
induce profound transformation of aliphatic hydrocarbons to aromatic 
hydrocarbons in commercially desirable yields and are generally highly 
effective in conversion reactions involving aromatic hydrocarbons. 
Although they have unusually low alumina contents, i.e., high silica to 
alumina ratios, they are very active even when the silica to alumina ratio 
exceeds 30. The activity is surprising since catalytic activity is 
generally attributed to framework aluminum atoms and cations associated 
with these aluminum atoms. These zeolites retain their crystallinity for 
long periods in spite of the presence of steam at high temperature which 
induces irreversible collapse of the framework of other zeolites, e.g., of 
the X and A type. 
An important characteristic of the crystal structure of this class of 
zeolites is that it provides constrained access to, and egress from the 
intracrystalline free space by virtue of having a pore dimension greater 
than about 5 Angstroms and pore windows of about a size such as would be 
provided by 10-membered rings of oxygen atoms. It is to be understood, of 
course, that these rings are those formed by the regular disposition of 
the tetrahedra making up the anionic framework of the crystalline 
aluminosilicate, the oxygen atoms themselves being bonded to the silicon 
or aluminum atoms at the centers of the tetrahedra. Briefly, the preferred 
type zeolites useful in this invention possess, in combination: a silica 
to alumina mole ratio of at least about 12; and a structure providing 
constrained access to the crystalline free space. 
The silica to alumina ratio referred to may be determined by conventional 
analysis. This ratio is meant to represent, as closely as possible, the 
ratio in the rigid anionic framework of the zeolite crystal and to exclude 
aluminum in the binder or in cationic or other form within the channels. 
Although zeolites with a silica to alumina ratio of at least 12 are 
useful, it is preferred to use zeolites having higher ratios of at least 
about 30. Such zeolites, after activation, acquire an intracrystalline 
sorption capacity for normal hexane which is greater than that for water, 
i.e., they exhibit "hydrophobic" properties. It is believed that this 
hydrophobic character is advantageous in the present invention. 
The type zeolites useful in this invention freely sorb normal hexane and 
have a pore dimension greater than about 5 Angstoms. In addition, the 
structure must provide constrained access to larger molecules. It is 
sometimes possible to judge from a known crystal structure whether such 
constrained access exists. For example, if the only pore windows in a 
crystal are formed by 8-membered rings of oxygen atoms, then access by 
molecules of larger cross-section than normal hexane is excluded and the 
zeolite is not of the desired type. Windows of 10-membered rings are 
preferred, although, in some instances, excessive puckering or pore 
blockage may render these zeolites ineffective. Twelve-membered rings do 
not generally appear to offer sufficient constraint to produce the 
advantageous conversions although puckered structures exist such as TMA 
offretite which is a known effective zeolite. Also, structures can be 
conceived, due to pore blockage or other cause, that may be operative. 
Rather than attempt to judge from crystal structure whether or not a 
zeolite possesses the necessary constrained access, a simple determination 
of the "constaint index" may be made by passing continuously a mixture of 
an equal weight of normal hexane and 3-methylpentane over a small sample, 
approximately 1 gram or less, of catalyst at atmospheric pressure 
according to the following procedure. A sample of the zeolite, in the form 
of pellets or extrudate, is crushed to a particle size about that of 
coarse sand and mounted in a glass tube. Prior to testing, the zeolite is 
treated with a stream of air at 1000.degree. F. for at least 15 minutes. 
The zeolite is then flushed with helium and the temperature adjusted 
between 550.degree. F. and 950.degree. F. to give an overall conversion 
between 10% and 60%. The mixture of hydrocarbons is passed at 1 liquid 
hourly space velocity (i.e., 1 volume of liquid hydrocarbon per volume of 
zeolite per hour) over the zeolite with a helium dilution to give a helium 
to total hydrocarbon mole ratio of 4:1. After 20 minutes on stream, a 
sample of the effluent is taken and analyzed, most conveniently by gas 
chromatography, to determine the fraction remaining unchanged for each of 
the two hydrocarbons. 
The "constraint index" is calculated as follows: 
##EQU1## 
The constraint index approximates the ratio of the cracking rate constants 
for the two hydrocarbons. Zeolites suitable for the present invention are 
those having a constraint index in the approximate range of 1 to 12. 
Constraint Index (CI) values for some typical zeolites are: 
______________________________________ 
CAS C.I. 
______________________________________ 
ZSM-5 8.3 
ZSM-11 8.7 
ZSM-12 2 
ZSM-38 2 
ZSM-35 4.5 
TMA Offretite 3.7 
Beta 0.6 
ZSM-4 0.5 
H-Zeolon 0.4 
REY 0.4 
Amorphous Silica-Alumina 0.6 
Erionite 38 
______________________________________ 
It is to be realized that the above constraint index values typically 
characterize the specified zeolites but that such are the cumulative 
result of several variables used in determination and calculation thereof. 
Thus, for a given zeolite depending on the temperature employed within the 
aforenoted range of 550.degree. F. to 950.degree. F., with accompanying 
conversion between 10% and 60%, the constraint index may vary within the 
indicated approximate range of 1 to 12. Likewise, other variables such as 
the crystal size of the zeolite, the presence of possible occluded 
contaminants and binders intimately combined with the zeolite may affect 
the constraint index. It will accordingly be understood by those skilled 
in the art that the constraint index, as utilized herein, while affording 
a highly useful means for characterizing the zeolites of interest is 
approximate, taking into consideration the manner of its determination, 
with probability, in some instances, of compounding variable extremes. 
However, in all instances, at a temperature within the above-specified 
range of 550.degree. F. to 950.degree. F., the constraint index will have 
a value for any given zeolite of interest herein with the approximate 
range of 1 to 12. 
The class of zeolites defined herein is exemplified by ZSM-5, ZSM-11, 
ZSM-12, ZSM-35 and ZSM-38 and other similar materials. U.S. Pat. No. 
3,702,886 describing and claiming ZSM-5 is incorporated herein by 
reference. 
ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, the 
entire contents of which are incorporated herein by reference. 
ZSM-12 is more particularly described in U.S. Pat. No. 3,832,449, the 
entire contents of which is incorporated herein by reference. 
ZSM-35 is more particularly described in U.S. Pat. No. 4,016,245, the 
entire contents of which is incorporated herein by reference. 
ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859, the 
entire contents of which is incorporated herein by reference. 
The specific zeolites described, when prepared in the presence of organic 
cations, are catalytically inactive, possibly because the intracrystalline 
free space is occupied by organic cations from the forming solution. They 
may be activated by heating in an inert atmosphere at 1000.degree. F. for 
one hour, for example, followed by base exchange with ammonium salts 
followed by calcination at 1000.degree. F. in air. The presence of organic 
cations in the forming solution may not be absolutely essential to the 
formation of this type zeolite; however, the presence of these cations 
does appear to favor the formation of this special type of zeolite. More 
generally, it is desirable to activate this type catalyst by base exchange 
with ammonium salts followed by calcination in air at about 1000.degree. 
F. for from about 15 minutes to about 24 hours. 
Natural zeolites may sometimes be converted to this type zeolite catalyst 
by various activation procedures and other treatments such as base 
exchange, steaming, alumina extraction and calcination, in combinations. 
Natural minerals which may be so treated include ferrierite, brewsterite, 
stilbite, dachiardite, epistilbite, heulandite, and clinoptilolite. The 
preferred crystalline aluminosilicates are ZSM-5, ZSM-11, ZSM-12, ZSM-38 
and ZSM-35 with ZSM-5 particularly preferred. 
In a preferred aspect of this invention, the zeolites hereof are selected 
as those having a crystal framework density, in the dry hydrogen form, of 
not substantially below about 1.6 grams per cubic centimeter. It has been 
found that zeolites which satisfy all three of these criteria are most 
desired because they tend to maximize the production of gasoline boiling 
range hydrocarbon products. Therefore, the preferred zeolites of this 
invention are those having a constraint index as defined above of about 1 
to about 12, a silica to alumina ratio of at least about 12 and a dried 
crystal density of not less than about 1.6 grams per cubic centimeter. The 
dry density for known structures may be calculated from the number of 
silicon plus aluminum atoms per 1000 cubic Angstroms, as given, e.g., on 
Page 19 of the article on Zeolite Structure by W. M. Meier. This paper, 
the entire contents of which are incorporated herein by reference, is 
included in "Proceedings of the Conference on Molecular Sieves, London, 
April 1967," published by the Society of Chemical Industry, London, 1968. 
When the crystal structure is unknown, the crystal framework density may 
be determined by classical pyknometer techniques. For example, it may be 
determined by immersing the dry hydrogen form of the zeolite in an organic 
solvent which is not sorbed by the crystal. It is possible that the 
unusual sustained activity and stability of this class of zeolites is 
associated with its high crystal anionic framework density of not less 
than about 1.6 grams per cubic centimeter. This high density, of course, 
must be associated with a relatively small amount of free space within the 
crystal, which might be expected to result in more stable structures. This 
free space, however, is important as the locus of catalytic activity. 
Crystal framework densities of some typical zeolites are: 
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Void Framework 
Zeolite Volume Density 
______________________________________ 
Ferrierite 0.28 cc/cc 1.76 g/cc 
Mordenite .28 1.7 
ZSM-5, -11 .29 1.79 
Dachiardite .32 1.72 
L .32 1.61 
Clinoptilolite .34 1.71 
Laumontite .34 1.77 
ZSM-4 (Omega) .38 1.65 
Heulandite .39 1.69 
P .41 1.57 
Offretite .40 1.55 
Levynite .40 1.54 
Erionite .35 1.51 
Gmelinite .44 1.46 
Chabazite .47 1.45 
A .5 1.3 
Y .48 1.27 
______________________________________ 
When synthesized in the alkali metal form, the zeolite is conveniently 
converted to the hydrogen form, generally by intermediate formation of the 
ammonium form as a result of ammonium ion exchange and calcination of the 
ammonium form to yield the hydrogen form. In addition to the hydrogen 
form, other forms of the zeolite wherein the original alkali metal has 
been reduced to less than about 1.5 percent by weight may be used. Thus, 
the original alkali metal of the zeolite may be replaced by ion exchange 
with other suitable ions of Groups IB to VIII of the Periodic Table, 
including, by way of example, nickel, copper, zinc, palladium, calcium or 
rare earth metals. 
Generally, however, the zeolite either directly or via initial ammonium 
exchange followed by calcination, is preferably hydrogen exchanged such 
that a predominate proportion of its exchangeable cations are hydrogen 
ions. In general, it is contemplated that more than 50 percent and 
preferably more than 75 percent of the cationic sites of the crystalline 
aluminosilicate zeolite will be occupied by hydrogen ions. 
The above crystalline aluminosilicate zeolites employed are contacted with 
a phosphorus compound. Representative phosphorus-containing compounds 
include derivatives of groups represented by PX.sub.3, RPX.sub.2, R.sub.2 
PX, R.sub.3 P, X.sub.3 PO, (XO).sub.3 PO, (XO).sub.3 P, R.sub.3 P=O, 
R.sub.3 P=S, RPO.sub.2, RPS.sub.2, RP(O)(OX).sub.2, RP(S)(SX).sub.2, 
R.sub.2 P(O)OX, R.sub.2 P(S)SX, RP(OX).sub.2, RP(SX).sub.2, ROP(OX).sub.2, 
RSP(SX).sub.2, (RS).sub.2 PSP(SR).sub.2, and (RO).sub.2 POP(OR).sub.2, 
where R is an alkyl or aryl, such as a phenyl radical and X is hydrogen, 
R, or halide. These compounds include primary, RPH.sub.2, secondary, 
R.sub.2 PH and tertiary, R.sub.3 P, phosphines such as butyl phosphine; 
the tertiary phosphine oxides R.sub.3 PO, such as tributylphosphine oxide, 
the tertiary phosphine sulfides, R.sub.3 PS, the primary, RP(O)(OX).sub.2, 
and secondary, R.sub.2 P(O)OX, phosphonic acids such as benzene phosphonic 
acid; the corresponding sulfur derivatives such as RP(S)(SX).sub.2 and 
R.sub.2 P(S)SX, the esters of the phosphonic acids such as diethyl 
phosphonate, (RO).sub.2 P(O)H, dialkyl alkyl phosphonates, (RO).sub.2 
P(O)R, and alkyl dialkylphosphinates, (RO)P(0)R.sub.2 ; phosphinous acids, 
R.sub.2 POX, such as diethylphosphinous acid, primary, (RO)P(OX).sub.2, 
secondary, (RO).sub.2 POX, and tertiary, (RO).sub.3 P, phosphites; and 
esters thereof such as the monopropyl ester, alkyl dialkylphosphinites, 
(RO)PR.sub.2, and dialkyl alkylphosphonite, (RO).sub.2 PR esters. 
Corresponding sulfur derivatives may also be employed including (RS).sub.2 
P(S)H, (RS).sub.2 P(S)R, (RS)P(S)R.sub.2, R.sub.2 PSX, (RS)P(SX).sub.2, 
(RS).sub.2 PSX, (RS).sub.3 P, (RS)PR.sub.2 and (RS).sub.2 PR. Examples of 
phosphite esters include trimethylphosphite, triethylphosphite, 
diisopropylphosphite, butylphosphite; and pyrophosphites such as 
tetraethylpyrosphosphite. The alkyl groups in the mentioned compounds 
contain one to four carbon atoms. 
Other suitable phosphorus-containing compounds include the phosphorus 
halides such as phosphorus trichloride, bromide, and iodide, alkyl 
phosphorodichloridites, (RO)PCl.sub.2, dialkyl phosphorochloridites, 
(RO).sub.2 PX, dialkylphosphionochloridites, R.sub.2 PCl, alkyl 
alkylphosphonochloridates, (RO)(R)P(O)Cl, dialkyl phosphinochloridates, 
R.sub.2 P(O)Cl and RP(O)Cl.sub.2. Applicable corresponding sulfur 
derivatives include (RS)PCl.sub.2, (RS).sub.2 PX, (RS)(R)P(S)Cl and 
R.sub.2 P(S)Cl. 
Preferred phosphorus-containing compounds include diammonium hydrogen 
phosphate, ammonium dihydrogen phosphate, diphenyl phosphine chloride, 
trimethylphosphite and phosphorus trichloride, phosphoric acid, phenyl 
phosphine oxychloride, trimethylphosphate, diphenyl phosphinous acid, 
diphenyl phosphinic acid, diethylchloro thiophosphate, methyl acid 
phosphate and other alcohol-P.sub.2 O.sub.5 reaction products. 
Reaction of the zeolite with the phosphorus compound is effected by 
contacting the zeolite with such compound. Where the treating phosphorus 
compound is a liquid, such compound can be in solution in a solvent at the 
time contact with the zeolite is effected. Any solvent relatively inert 
with respect to the treating compound and the zeolite may be employed. 
Suitable solvents include water and aliphatic, aromatic or alcoholic 
liquids. Where the phosphorus-containing compound is, for example, 
trimethylphosphite or liquid phosphorus trichloride, a hydrocarbon solvent 
such as n-octane may be employed. The phosphorus-containing compound may 
be used without a solvent, i.e., may be used as a neat liquid. Where the 
phosphorus-containing compound is in the gaseous phase, such as where 
gaseous phosphorus trichloride is employed, the treating compound can be 
used by itself or can be used in admixture with a gaseous diluent 
relatively inert to the phosphorus-containing compound and the zeolite 
such as air or nitrogen or with an organic solvent, such as octane or 
toluene. 
Prior to reacting the zeolite with the phosphorus-containing compound, the 
zeolite may be dried. Drying can be effected in the presence of air. 
Elevated temperatures may be employed. However, the temperature should not 
be such that the crystal structure of the zeolite is destroyed. 
Heating of the phosphorus-containing catalyst subsequent to preparation and 
prior to use is also preferred The heating can be carried out in the 
presence of oxygen, for example, air. Heating can be at a temperature of 
about 150.degree. C. However, higher temperatures, i.e., up to about 
500.degree. C. are preferred. Heating is generally carried out for 1-5 
hours but may be extended to 24 hours or longer. While heating 
temperatures above about 500.degree. C. can be employed, they are not 
necessary. At temperatures of about 1000.degree. C., the crystal structure 
of the zeolite tends to deteriorate. After heating in air at elevated 
temperatures, phosphorus is present in oxide form. 
The amount of phosphorus oxide incorporated with the zeolite should be at 
least about 0.25 percent by weight. However, it is preferred that the 
amount of phosphorus oxide in the zeolite be at least about 2 percent by 
weight, particularly when the same is combined with a binder, e.g. 35 
weight percent of alumina. The amount of phosphorus oxide can be as high 
as about 25 percent by weight or more depending on the amount and type of 
binder present. Preferably, the amount of phosphorus oxide added to the 
zeolite is between about 0.7 and about 15 percent by weight. 
The amount of phosphorus oxide incorporated with the zeolite by reaction 
with elemental phosphorus or phosphorus-containing compound will depend 
upon several factors. One of these is the reaction time, i.e., the time 
that the zeolite and the phosphorus-containing source are maintained in 
contact with each other. With greater reaction times, all other factors 
being equal, a greater amount of phosphorus is incorporated with the 
zeolite. Other factors upon which the amount of phosphorus incorporated 
with the zeolite is dependent include reaction temperatures, concentration 
of the treating compound in the reaction mixture, the degree to which the 
zeolite has been dried prior to reaction with the phosphorus-containing 
compound, the conditions of drying of the zeolite after reaction of the 
zeolite with the treating compound, and the amount and type of binder 
incorporated with the zeolite. 
The zeolite containing phosphorus oxide is then further combined with 
magnesium oxide by contact with a suitable compound of magnesium. 
Representative magnesium-containing compounds include magnesium acetate, 
magnesium nitrate, magnesium benzoate, magnesium proprionate, magnesium 
2-ethylhexoate, magnesium carbonate, magnesium formate, magnesium oxylate, 
magnesium amide, magnesium bromide, magnesium hydride, magnesium lactate, 
magnesium laurate, magnesium oleate, magnesium palmitate, magnesium 
silicylate, magnesium stearate and magnesium sulfide. 
Reaction of the zeolite with the treating magnesium compound is effected by 
contacting the zeolite with such compound. Where the treating compound is 
a liquid, such compound can be in solution in a solvent at the time 
contact with the zeolite is effected. Any solvent relatively inert with 
respect to the treating magnesium compound and the zeolite may be 
employed. Suitable solvents include water and aliphatic, aromatic or 
alcoholic liquid. The treating compound may also be used without a 
solvent, i.e. may be used as a neat liquid. Where the treating compound is 
in the gaseous phase, it can be used by itself or can be used in admixture 
with a gaseous diluent relatively inert to the treating compound and the 
zeolite such as helium or nitrogen or with an organic solvent, such as 
octane or toluene. 
Heating of the magnesium compound impregnated catalyst subsequent to 
preparation and prior to use is preferred. The heating can be carried out 
in the presence of oxygen, for example, air. Heating can be at a 
temperature of about 150.degree. C. However, higher temperatures, i.e. up 
to about 500.degree. C. are preferred. Heating is generally carried out 
for 1-5 hours but may be extended to 24 hours or longer. While heating 
temperatures above about 500.degree. C. may be employed, they are 
generally not necessary. At temperatures of about 1000.degree. C., the 
crystal structure of the zeolite tends to deteriorate. After heating in 
air at elevated temperatures, the oxide form of magnesium is present. 
The amount of magnesium oxide incorporated in the calcined phosphorus 
oxide-containing zeolite should be at least about 0.25 percent by weight. 
However, it is preferred that the amount of magnesium oxide in the zeolite 
be at least about 1 percent by weight, particularly, when the same is 
combined with a binder, e.g. 35 weight percent of alumina. The amount of 
magnesium oxide can be as high as about 25 percent by weight or more 
depending on the amount and type of binder present. Preferably, the amount 
of magnesium oxide added to the zeolite is between about 1 and about 15 
percent by weight. 
The amount of magnesium oxide incorporated with the zeolite by reaction 
with the treating solution and subsequent calcination in air will depend 
on several factors. One of these is the reaction time, i.e. the time that 
the zeolite and the magnesium-containing source are maintained in contact 
with each other. With greater reaction times, all other factors being 
equal, a greater amount of magnesium oxide is incorporated with the 
zeolite. Other factors upon which the amount of magnesium oxide 
incorporated with the zeolite is dependent include reaction temperature, 
concentration of the treating compound in the reaction mixture, the degree 
to which the zeolite has been dried prior to reaction with the treating 
compound, the conditions of drying of the zeolite after reaction of the 
zeolite with the magnesium compound and the amount and type of binder 
incorporated with the zeolite. 
After contact of the phosphorus oxide-containing zeolite with the magnesium 
reagent, the resulting composite is dried and heated in a manner similar 
to that used in preparing the phosphorus oxide-containing zeolite. 
In practicing the desired methylation process, it may be desirable to 
incorporate the modified zeolite in another material resistant to the 
temperatures and other conditions employed in the methylation process. 
Such matrix 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 modified 
zeolite include those of 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 constitutent is halloysite, kaolinite, dickite, nacrite or 
anauxite. Such clays can be used in the raw state as orignally mined or 
initially subjected to calcination, acid treatment or chemical 
modification. 
In addition to the foregoing materials, the modified zeolites employed 
herein may be composited with a porous matrix material, such as alumina, 
silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, 
silica-berylia, silica-titania as well as ternary compositions, such as 
silica-alumina-thoria, silica-alumina-zirconia, silica-alumina magnesia 
and silica-magnesia-zirconia. The matrix may be in the form of a cogel. 
The relative proportions of finely divided modified zeolite an inorganic 
oxide gel matrix may vary widely with the zeolite content ranging from 
between about 1 to 99 percent by weight and more usually in the range of 
about 5 to about 80 percent by weight of the composite. 
Methylation of toluene in the presence of the above described catalyst is 
effected by contact of the toluene with a methylating agent, preferably 
methanol, at a temperature between about 250.degree. C. and about 
750.degree. C. and preferably between about 500.degree. C. and about 
700.degree. C. At the higher temperatures, the zeolites of high 
silica/alumina ratio are preferred. For example, ZSM-5 of 300 SiO.sub.2 
/Al.sub.2 O.sub.3 ratio and upwards is very stable at high temperatures. 
The reaction generally takes place at atmospheric pressure, but the 
pressure may be within the approximate range of 1 atmosphere to 1000 psig. 
The molar ratio of methylating agent to toluene is generally between about 
0.05 and about 5. When methanol is employed as the methylating agent a 
suitable molar ratio of methanol to toluene has been found to be 
approximately 0.1-2 moles of methanol per mole of toluene. With the use of 
other methylating agents, such as methylchloride, methylbromide, 
dimethylether, methyl carbonate, light olefins or dimethylsulfide, the 
molar ratio of methylating agent to toluene may vary within the aforenoted 
range. Reaction is suitably accomplished utilizing a weight hourly space 
velocity of between about 1 and about 2000 and preferably between about 5 
and about 1500. The reaction product consisting predominantly of 
para-xylene or a mixture of para- and ortho-xylene together with 
comparatively smaller amounts of meta-xylene may be separated by any 
suitable means, such as by passing the same through a water condenser and 
subsequently passing the organic phase through a column in which 
chromatographic separation of the xylene isomers is accomplished. 
The process of this invention may be carried out as a batch-type, 
semi-continuous or continuous operation utilizing a fixed or moving bed 
catalyst system. A preferred embodiment entails use of a fluidized 
catalyst zone wherein the reactants, i.e., toluene and methylating agent, 
are passed concurrently or countercurrently through a moving fluidized bed 
of the catalyst. The fluidized catalyst after use is conducted in an 
oxygen-containing atmosphere, e.g., air, at an elevated temperature, after 
which the regenerated catalyst is recycled to the conversion zone for 
further contact with the toluene and methylating agent reactants.

The following examples will serve to illustrate the process of the 
invention without limiting the same. 
EXAMPLE 1 
A catalyst containing 65 weight percent acid ZSM-5 and 35 weight percent 
alumina was prepared as follows: 
A sodium silicate solution was prepared by mixing 8440 lb. of sodium 
silicate (Q Brand--28.9 weight percent SiO.sub.2, 8.9 weight percent 
Na.sub.2 O and 62.2 weight percent H.sub.2 O) and 586 gallons of water. 
Afer addition of 24 lb. of a dispersant of a sodium salt of polymerized 
substituted benzenoid alkyl sulfonic acid combined with an inert inorganic 
suspending agent (Daxad 27), the solution was cooled to approximately 
55.degree. F. An acid alum solution was prepared by dissolving 305 lb. 
aluminum sulfate (17.2 Al.sub.2 O.sub.3), 733 lb. sulfuric acid (93%) and 
377 lb. sodium chloride in 602 gallons of water. The solutions were gelled 
in a mixing nozzle and discharged into a stirred autoclave. During this 
mixing operation, 1200 lb. of sodium chloride was added to the gel and 
thoroughly mixed in the vessel. The resulting gel was thoroughly agitated 
and heated to 200.degree. F. in the closed vessel. After reducing 
agitation, an organic solution prepared by mixing 568 lb. 
tri-n-propylamine, 488 lb. n-propyl bromide and 940 lb. methyl ethyl 
ketone was added to the gel. This mixture was reacted for 14 hours at a 
temperature of 200.degree.-210.degree. F. At the end of this period, 
agitation was increased and these conditions maintained until the 
crystallinity of the product reached at least 65% ZSM-5 as determined by 
X-ray diffraction. Temperature was then increased to 320.degree. F. until 
crystallization was complete. The residual organics were flashed from the 
autoclave and the product slurry was cooled. 
The product was washed by decantation using a flocculant of polyammonium 
bisulfate. The washed product containing less than 1% sodium was filtered 
and dried. The weight of dried zeolite was approximately 2300 lb. 
The dried product was mixed with alpha alumina monohydrate and water (65% 
zeolite, 35% alumina binder on ignited basis) then extruded to form of 
1/16 inch pellet with particle density &lt;0.98 gram/cc and crush strength of 
&gt;20 lb./linear inch. 
After drying, the extruded pellets were calcined in nitrogen (700-1000 
SCFM) for 3 hours at 1000.degree. F., cooled and ambient air was passed 
through the bed for 5 hours. The pellets were then ammonium exchanged for 
one hour at ambient temperature (240 lb. ammonium nitrate dissolved in 
approximately 800 gallons of deionized water). The exchange was repeated 
and the pellets washed and dried. Sodium level in the exchanged pellets 
was less than 0.05 weight percent. 
The dried pellets were calcined in a nitrogen-air mixture (10-12.5% 
air-90-87.5% nitrogen) for 6 hours at 1000.degree. F. and cooled in 
nitrogen alone. 
EXAMPLE 2 
To a solution of 7 grams of 85% H.sub.3 PO.sub.4 in 10 ml. of water was 
added 10 grams of HZSM-5 extrudate prepared as in Example 1. The extrudate 
was permitted to remain in such solution at room temperature overnight. 
After filtration and drying at 120.degree. C. for 3 hours, it was calcined 
at 500.degree. C. for 3 hours to give 11.5 grams of phosphorus-modified 
ZSM-5. 
Ten grams of the above phosphorus-modified ZSM-5 was then added to a 
solution of 25 grams of magnesium acetate tetrahydrate in 20 ml. of water 
which was permitted to stand at room temperature overnight. After 
filtration and drying at 120.degree. C., it was calcined at 500.degree. C. 
for 3 hours to give 10.9 grams of magnesium-phosphorus-modified ZSM-5. 
Analysis showed the modifier concentration to be 7.4 weight percent 
phosphorus and 4.2 weight percent magnesium. 
EXAMPLE 3 
A mixture of toluene and methanol wherein the molar ratio of toluene to 
methanol was 4 was passed over the catalyst of Example 2 at a weight 
hourly space velocity of 10.5 (based on total catalyst) at 450.degree. C. 
Conversion of toluene was 8.5 percent and the concentration of para-xylene 
in total xylenes was 98.5 percent. 
EXAMPLES 4-7 
A toluene-methanol mixture having a molar ratio of toluene to methanol of 4 
was passed over the catalyst of Example 2 at a weight hourly space 
velocity of 3.4 under varying temperature conditions set forth below with 
the resulting toluene conversion and para-xylene production. 
______________________________________ 
Para-Xylene 
Temp. % Toluene Concentration In 
Example .degree.C. 
Conversion Total Xylenes 
______________________________________ 
4 450 11.2 97.4 
5 500 14.8 97.2 
6 550 19.6 96.5 
7 600 23.5 93.4 
______________________________________ 
EXAMPLES 8-11 
A phosphorus-magnesium-modified ZSM-5 catalyst prepared in a manner similar 
to that of Example 2 but containing 2.9 weight percent phosphorus and 4.9 
weight percent magnesium was employed for alkylation of toluene with 
methanol. 
A feed mixture wherein the molar ratio of toluene to methanol was 4 was 
passed over the above catalyst at a weight hourly space velocity of 10 
under varying temperature conditions set forth below with the resulting 
toluene conversion and para-xylene production. 
______________________________________ 
Para-Xylene 
Temp. % Toluene Concentration In 
Example .degree.C. 
Conversion Total Xylenes 
______________________________________ 
8 400 9.4 98.3 
9 450 11.0 97.1 
10 500 14.4 96.0 
11 550 18.8 94.1 
______________________________________ 
It will be seen from the foregoing examples that in every instance 
utilizing the phosphorus-magnesium-modified ZSM-5 catalyst, methylation of 
toluene afforded a very marked increased in selectivity for para-xylene 
production over the concentration of this component, i.e., about 24 weight 
percent, in the normal equilibrium mixture of xylene isomers.