Shape selective hydrocarbon conversion over pre-selectivated, activated catalyst

A process for a shape selective hydrocarbon conversion such as toluene disproportionation involves contacting a reaction stream under conversion conditions with a catalytic molecular sieve which has been pre-selectivated and concurrently activated by contact with a substantially aqueous solution of an organosilicon compound. The invention also includes a method for concurrently preselectivating and activating a catalyst and the shape selectivated, activated catalyst which results from this method.

CROSS-REFERENCE TO RELATED APPLICATION 
This application is related to copending U.S. patent applications Ser. Nos. 
850,104 and 850,105 both filed Mar. 12, 1992 which are herein incorporated 
by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to a process for shape selective 
hydrocarbon conversions such as the regioselective production of 
para-substituted compounds, e.g. para-xylene. The invention is also 
directed to a modified catalyst and method of modifying the catalyst. A 
catalytic molecular sieve is modified by treatment with an aqueous 
solution of a water soluble organosilicon compound. The catalytic activity 
and selectivity of the molecular sieve are both increased by the 
modification treatment. 
2. Description of the Prior Art 
The term shape-selective catalysis describes unexpected catalytic 
selectivities in zeolites. The principles behind shape selective catalysis 
have been reviewed extensively, e.g. by N. Y. Chen, W. E. Garwood and F. 
G. Dwyer, "Shape Selective Catalysis in Industrial Applications," 36, 
Marcel Dekker, Inc. (1989). Within a zeolite pore, hydrocarbon conversion 
reactions such as paraffin isomerization, olefin skeletal or double bond 
isomerization, oligomerization and aromatic disproportionation, alkylation 
or transalkylation reactions are governed by constraints imposed by the 
channel size. Reactant selectivity occurs when a fraction of the feedstock 
is too large to enter the zeolite pores to react; while product 
selectivity occurs when some of the products cannot leave the zeolite 
channels. Product distributions can also be altered by transition state 
selectivity in which certain reactions cannot occur because the reaction 
transition state is too large to form within the zeolite pores or cages. 
Another type of selectivity results from configurational diffusion where 
the dimensions of the molecule approach that of the zeolite pore system. A 
small change in dimensions of the molecule or the zeolite pore can result 
in large diffusion changes leading to different product distributions. 
This type of shape selective catalysis is demonstrated, for example, in 
toluene selective disproportionation to p-xylene. 
The synthesis of para-xylene is typically performed by methylation of 
toluene over a catalyst under conversion conditions. Examples are the 
reaction of toluene with methanol as described by Chen et al., J. Amer. 
Chem. Sec. 1979, 101, 6783, and toluene disproportionation, as described 
by Pines in "The Chemistry of Catalytic Hydrocarbon Conversions", Academic 
Press, N.Y., 1981, p. 72. Such methods typically result in the production 
of a mixture including para-xylene, ortho-xylene, and meta-xylene. 
Depending upon the para-selectivity of the catalyst and the reaction 
conditions, different percentages of para-xylene are obtained. The yield, 
i.e., the amount of feedstock actually converted to xylene, is also 
affected by the catalyst and the reaction conditions. 
Previously known toluene methylation reactions typically provide many 
by-products such as those indicated in the following formula: 
Thermodynamic Equilibria for Toluene Conversion to the Products Indicated 
##STR1## 
One method for increasing para-selectivity of zeolite catalysts is to 
modify the catalyst by treatment with "selectivating agents". Various 
silicon compounds have been used to modify catalysts to improve 
selectivity in hydrocarbon conversion processes. For example, U.S. Pat. 
Nos. 4,145,315, 4,127,616 and 4,090,981, describe the use of a silicone 
compound dissolved in an organic solvent to treat a zeolite. U.S. Pat. 
Nos. 4,465,886 and 4,477,583 describe the use of an aqueous emulsion of a 
silicone to treat a zeolite. U.S. Pat. Nos. 4,950,835 and 4,927,979 
describe the use of alkoxysilanes carried by gases or organic solvents to 
treat a zeolite. U.S. Pat. Nos. 4,100,215 and 3,698,157 describe the use 
of silanes in hydrocarbons, e.g., pyridine or ethers, to treat a zeolite. 
Some catalyst modification procedures, for example, U.S. Pat. Nos. 
4,477,583 and 4,127,616 have been successful in obtaining 
para-selectivity, i.e., para-xylene/all xylenes, of greater than about 90% 
but with commercially unacceptable toluene conversions of only about 10%, 
resulting in a yield of not greater than about 9%, i.e., 10%.times.90%. 
Such processes also produce significant quantities of ortho-xylene and 
meta-xylene thereby necessitating expensive separation processes in order 
to separate the para-xylene from the other isomers. 
Typical separation procedures comprise costly fractional crystallization 
and adsorptive separation of para-xylene from other xylene isomers which 
are customarily recycled. Xylene isomerization units are then required for 
additional conversion of the recycled xylene isomers into an equilibrium 
mixture comprising para-xylene. 
Those skilled in the art appreciate that the expense of the separation 
process is proportional to the degree of separation required. Therefore, 
significant cost savings are achieved by increasing selectivity to the 
para-isomer while maintaining commercially acceptable conversion levels. 
The activity of a zeolite is an important consideration in acid-type 
catalysis such as toluene disproportionation. Silicious zeolites may be 
considered to contain SiO.sub.4 --tetrahedra. Substitution for the 
tetravalent element by a trivalent element such as aluminum produces a 
negative charge which must be balanced. If this is done by a proton, the 
material is acidic and active. The activity of zeolite catalysts has been 
described in terms of its Alpha Value. 
Various methods have been devised for enhancing the catalytic activity, 
i.e., the alpha of zeolite materials. U.S. Pat. No. 4,871,702 describes 
ammonia activation of zeolites by contacting a zeolite and a solid source 
of aluminum with an aqueous ammonium solution under ammonia gas pressure. 
U.S. Pat. No. 4,665,248 describes treating a mixture of zeolite and a 
solid source of aluminum with liquid water in the presence of alkali metal 
cation. U.S. Pat. No. 4,568,787 discloses contacting a high silica zeolite 
with aluminum chloride vapor and hydrolyzing. U.S. Pat. No. 4,576,805 
describes enhancing catalytic activity of a zeolite by contacting with a 
volatile metal halide compound to incorporate the metal into the 
crystalline lattice of the zeolite. 
A method for simultaneous silicon modification for selectivity and activity 
enhancement of a catalyst would have important application in 
shape-selective catalysis. 
Accordingly, it would be highly advantageous to provide a shape selective 
hydrocarbon conversion process such as toluene disproportionation over a 
shape selective, highly active catalyst. 
SUMMARY OF THE INVENTION 
The invention is a process for shape selective hydrocarbon conversions such 
as the regioselective production of para-xylene. A reaction stream 
containing hydrocarbon feed such as toluene is contacted under hydrocarbon 
conversion conditions with a molecular sieve catalyst which has been 
concurrently pre-selectivated and activated by treating with a composition 
which includes a substantially aqueous solution of a water soluble 
organosilicon compound as a first silicon source. In toluene 
disproportionation, the reaction stream may also contain a second silicon 
source. These reaction conditions in toluene disproportionation are 
suitable to provide a single pass para-xylene product, relative to all 
C.sub.8 products, of at least about 90% and at least 15% toluene 
conversion. 
The invention is also a method for modifying a molecular sieve catalyst 
having a Constraint Index of 1-12 by treating with a composition which 
includes a substantially aqueous solution of water soluble organosilicon 
compound as a first silicon source, and then calcining. The catalyst may 
be subsequently contacted with a mixture of a second silicon source which 
is a high-efficiency, para-xylene selectivating agent and toluene at 
reaction conditions for converting toluene to xylene. The molecular sieve 
thus treated has greatly enhanced activity and selectivity. The invention 
also includes the modified catalyst. 
Advantageously, a highly selective and highly active catalyst can be 
provided in the modification method. 
Furthermore, in the modification method, the use of aqueous solution of 
silicon sources is more cost efficient relative to organic solvent and 
aqueous emulsion procedures. The potentially hazardous distillation and 
condensation of organic solvents is avoided. Furthermore, improved 
deposition uniformity is provided using aqueous solutions compared to 
aqueous emulsions. 
In addition, a shape selective hydrocarbon conversion process over the 
modified catalyst shows enhanced product selectivity with good conversion.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is useful in shape selective hydrocarbon conversion 
processes such as in converting various aromatics, particularly toluene to 
commercially useful para-substituted benzenes, particularly para-xylene. 
Molecular sieves to be used in the process of the invention include 
intermediate pore zeolites. Such medium pore zeolites are considered to 
have a Constraint Index from about 1 to about 12. The method by which 
Constant Index is determined is described fully in U.S. Pat. No. 
4,016,218, incorporated herein by reference. Molecular sieves which 
conform to the specified values of Constraint Index for intermediate pore 
zeolites include ZSM-5, ZSM-11, ZSM-5/ZSM-11 intermediate, ZSM-12, ZSM-21, 
ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-50, MCM-22 and Zeolite Beta 
which are described, for example, in U.S. Pat. Nos. 3,702,886 and Re. No. 
29,949, 3,709,979, 3,832,449, 4,046,859, 4,556,447, 4,076,842, 4,016,245, 
4,229,424, 4,397,827, 4,954,325, 3,308,069, Re. 28,341 and EP 127,399 to 
which reference is made for details of these molecular sieves. These 
zeolites may be produced with differing silica:alumina ratios ranging from 
12:1 upwards. They have been, in fact, be produced from reaction mixtures 
from which aluminum is intentionally excluded, so as to produce materials 
having extremely high silica:alumina ratios which, in theory at least may 
extend up to infinity. Preferred intermediate pore zeolites include ZSM-5, 
ZSM-11, ZSM-12, ZSM-35 and MCM-22. Particularly preferred is ZSM-5. 
In the invention, the catalyst preferably has a silica-alumina ratio less 
than 100 preferably about 20-80 and an alpha value greater than 100, for 
example about 150-2000. 
The Alpha Value is an approximate indication of the catalytic cracking 
activity of the catalyst compared to a standard catalyst and it gives the 
relative rate constant (rate of normal hexane conversion per volume of 
catalyst per unit time.) It is based on the activity of the amorphous 
silica-alumina cracking catalyst taken as an Alpha of 1 (Rate 
Constant=0.016 sec.sup.-1). The Alpha Test is described in U.S. Pat. No. 
3,354,078 and in The Journal of Catalysis, Vol. 4, pp. 522-529 (August 
1965): Vol. 6, p. 278 (1966); and Vol. 61, p. 395 (1980), each 
incorporated herein by reference as to that description. It is noted that 
intrinsic rate constants for many acid-catalyzed reactions are 
proportional to the Alpha Value for a particular crystalline silicate 
catalyst (see "The Active Site of Acidic Aluminosilicate Catalysts, " 
Nature, Vol. 309, No. 5959, pp. 589-591, Jun. 14, 1984). The experimental 
conditions of the test used herein include a constant temperature of 
538.degree. C. and a variable flow rate as described in detail in the 
Journal of Catalysis, Vol. 61, p. 395. 
Since toluene disproportionation is an acid-type catalysis and requires a 
catalyst having inherent acid activity, i.e., an elevated alpha, a silicon 
modification of the catalyst which increases alpha is highly advantageous. 
A silicon modification using an aqueous solution of an organosilicon 
compound has been unexpectedly found to greatly increase alpha while 
concurrently yielding a catalyst with increased para-selectivity. 
The catalyst is modified, i.e., concurrently pre-selectivated and 
activated, by contact with an aqueous solution of an organosilicon 
compound. By "pre-selectivation" is meant pretreatment of the catalyst to 
lower non-shape selective surface acid activity and to increase the rate 
of subsequent selectivation using para-xylene selectivating agents. 
Organosilicon compounds useful herein are water soluble and may be 
described as organopolysiloxanes. The preferred compounds are polyalkylene 
oxide modified organopolysiloxanes. The organopolysiloxanes are preferably 
larger than the pores of the catalyst and do not enter the pores. 
The organopolysiloxanes include polysiloxanes having alkyl, alkoxy, aryl, 
aryloxy, arylalkyl or alkylaryl side groups. The amount of alkylene oxide 
groups in the organopolysiloxanes can be increased to overcome any 
hydrophobicity. Alkyl includes 1 to 12 carbons. Aryl includes 6 to 10 
carbons. Preferred organopolysiloxanes contained methyl and/or ethyl 
groups. 
Water soluble organosilicon compounds are commercially available as, for 
example, SAG-5300, manufactured by Union Carbide, conventionally used as 
an anti-foam, and SF 1188 manufactured by General Electric. 
The organosilicon compound is preferably dissolved in an aqueous solution 
in an organosilicon compound/H.sub.2 O weight ratio of from about 1/100 to 
about 1/1. 
A "solution" is intended to mean a uniformly dispersed mixture of one or 
more substances at the molecular or ionic level. The skilled artisan will 
recognize that solutions, both ideal and colloidal, differ from emulsions. 
The catalyst is contacted with a substantially aqueous solution of the 
organosilicon compound at a catalyst/organosilicon compound weight ratio 
of from about 100 to about 1, at a temperature of about 10.degree. C. to 
about 150.degree. C., at a pressure of about 0 psig to about 200 psig, for 
a time of about 0.1 hour to about 24 hours, the water is preferably 
removed, e.g., by distillation, or evaporation with or without vacuum, and 
the catalyst is calcined. 
Shape Selective Conversions 
Zeolites modified in accordance with the invention are generally useful as 
catalysts in shape selective hydrocarbon conversion processes including 
cracking reactions involving dewaxing of hydrocarbon feedstocks; 
isomerization of alkylaromatics; oligomerization of olefins to form 
gasoline, distillate, lube oils or chemicals; alkylation of aromatics; 
transalkylation of aromatics; conversion of oxygenates to hydrocarbons; 
rearrangement of oxygenates; and conversion of light paraffins and olefins 
to aromatics. 
Dewaxing 
The subject catalysts have good cracking and hydrocracking activity and may 
be used to convert paraffins from high to low molecular weight substances 
in dewaxing processes. The catalysts of the invention may be used in 
processes such as those described, for example, in U.S. Pat. Nos. 
3,700,585, Re. 28,398, 3,968,024 and 4,181,598 which are incorporated 
herein by references. The term dewaxing means the removal of those 
hydrocarbons which will readily solidify (waxes) from petroleum stocks. 
Hydrocarbon feeds which can be treated include lubricating oil stocks as 
well as those which have a freeze point or pour point problem, i.e., 
petroleum stocks boiling above 350.degree. F. The dewaxing can be carried 
out at either cracking or hydrocracking conditions. 
In U.S. Pat. No. 3,700,585 and Re. 28,398 to Chen et al., typical cracking 
conditions include a liquid hourly space velocity (LHSV) between about 0.5 
and 200, a temperature between about 288.degree. C. (550.degree. F.) and 
590.degree. C. (1100.degree. F.), a pressure between about subatmospheric 
and several hundred atmospheres over ZSM-5 type catalysts. Typical 
hydrocracking conditions include a liquid hourly space velocity between 
about 0.1 and 10, a temperature between about 340.degree. C. (650.degree. 
F.) and 538.degree. (1000.degree. F.), a pressure between about 100 and 
3000 psig, and a hydrogen to hydrocarbon mole ratio between about one and 
20. U.S. Pat. No. 3,968,024 describes similar conversions using ZSM-5 of 
small crystal size. U.S. Pat. No. 4,181,598 describes shape selective 
cracking to produce lubes. 
Isomerization of alkylaromatics 
The modified catalysts of the invention are also advantageously used in the 
isomerization of alkylaromatics in conversion reactions of the type 
described, for example, in U.S. Pat. Nos. 3,856,872, 3,856,873, Re. 
30,157, 4,101,595, 4,101,597, 4,312,790, Re. 31,919 and 4,224,141 which 
are herein incorporated by reference. 
In U.S. Pat. No. 3,856,872 to Morrison, there is described a process for 
converting C.sub.8 aromatics xylene and ethylbenzene to para-xylene 
(octafining) at a temperature of 550.degree. F. (288.degree. C.) to 
900.degree. F. (482.degree. C.), a pressure of 150 to 300 psig, and a 
liquid hour space velocity (LHSV) of 1 to 200 over an acid form catalyst 
containing metal such as platinum or nickel and hydrogen. 
In U.S. Pat. No. 3,856,873 to Burress, mixtures of C.sub.8 aromatic 
hydrocarbons are isomerized to para-xylene by contact in vapor phase with 
zeolite at a temperature of 500.degree. F. (260.degree. C.) to 
1000.degree. F. (538.degree. C.), a pressure of 0 (atmospheric) to 1,000 
psig, and a WHSV of 0.5 to 250 with no added hydrogen. The catalyst is an 
acid ZSM-5, ZSM-12 or ZSM-21. 
U.S. Pat. No. 4,101,595 to Chen et al. describes the production of 
para-xylene from aromatics of 8 to 10 carbons over a dual function 
catalyst with a shape selective acid catalyzed step at a temperature of 
650.degree. F. (343.degree. C.) to 1000.degree. F. (538.degree. C.), a 
pressure of 50 to 500 psig, a LHSV of 0.1 to 100 and a molar of 
hydrogen/hydrocarbon of 0.1 to 15. The acid form catalyst has a Constraint 
Index of 1 to 12, a silica/alumina ratio of at least 12, a crystal density 
of not less than 1.6 g/cc, may be pre-coked, and includes Group VIII noble 
metal. 
In U.S. Pat. No. 4,101,597 to Breckenridge, a C.sub.8 feed is first 
isomerized at 550.degree. F. (288.degree. C.) to 700.degree. F. 
(371.degree. C.) over a zeolite having a Constraint Index of 1 to 12, a 
silica/alumina ratio of at least 12 and containing a metal having a 
hydrogenation/dehydrogenation function. A C.sup.9+ fraction produced 
during isomerization of C.sub.8 is separated from the other isomerization 
products, blended with hydrogen and toluene and contacted with a porous, 
acidic catalyst such as ZSM-5 at 750.degree. F. (399.degree. C.) to 
900.degree. F. (482.degree. C.). The catalyst has a Constraint Index of 1 
to 12, a silica/alumina ratio of at least 12, and a metal providing 
hydrogenation/dehydrogenation function. 
In U.S. Pat. No. 4,224,141 to Morrison, C.sub.8 aromatics are isomerized to 
benzene, toluene and xylenes over a ZSM-5 which is reduced in activity by 
dilution with inert matrix, steaming or thermal treatment, very high 
silica/alumina ratio, base exchange with alkali metal, coking or the like. 
The conversion is at a temperature of 800.degree. F. (427.degree. C.) to 
1000.degree. F. (538.degree. C.) in a low pressure isomerization unit at a 
pressure only sufficient to overcome pressure drop through downstream 
processing equipment, e.g. below 100 psig, and a WHSV of 1 to 200. 
In U.S. Pat. No. 4,312,790 and Re. 31,919 to Butter et al., a zeolite is 
incorporated with noble metal subsequent to zeolite crystallization but 
prior to catalyst extrusion. The catalyst is used for xylene isomerization 
at a temperature of 500.degree. F. (260.degree. C.) to 1000.degree. F. 
(540.degree. C.), a pressure between 50 and 1000 psig, a WHSV of 1 to 50 
and a hydrogen/hydrocarbon male ratio of 1 to 20. 
Conversion of oxygenates to hydrocarbons 
U.S. Pat. No. 4,476,330 to Kerr et al., herein incorporated by reference, 
describes the conversion of aliphatic oxygenates to a higher molecular 
weight compound by contacting with a zeolite having a silica/alumina ratio 
substantially greater than 10 at a temperature of 70.degree. F. 
(21.degree. C.) to 1400.degree. F. (760.degree. C.). The feeds include 
lower aliphatic organic oxygenates up to C.sub.6, acetals, ketals, acid 
halides, alcohols, carboxylic acids, aldehydes, acid anhydrides, epoxides, 
ethers, esters, hemiacetals, gem diols, hydroxy acids, ketones, ketenes, 
lactones, peracids, peroxides, sugars, and especially alcohols, ethers and 
esters. Oligomerization of olefins 
The modified catalysts of the invention are advantageously used in the 
oligomerization of olefins to form gasoline, distillate, lube oils or 
chemicals in conversion reactions of the type described, for example, in 
U.S. Pat. Nos. 4,517,399, 4,520,221, 4,547,609 and 4,547,613 which are 
herein incorporated by reference. 
U.S. Pat. No. 4,517,399 to Chester et al. describes the conversion of 
olefins of 3 to 18 carbons, e.g. propylene, to high viscosity, low pour 
point lubricating oils by contacting with ZSM-5 type zeolites having large 
crystals of at least two microns. The conversion conditions include a 
temperature of 350.degree. F. (177.degree. C.) to 650.degree. F. 
(343.degree. C.) a pressure of 100 to 5000 psig, and a WHSV of 0.1 to 10. 
U.S. Pat. No. 4,520,221 to Chen describes the polymerization of olefins of 
2 to 8 carbons, e.g. propylene, butylene, to high viscosity lubes, e.g. 
linear hydrocarbons, over highly siliceous, acidic ZSM-5 type catalysts 
with surface acidity inactivated by treatment with base, e.g. bulky amines 
with a cross-section larger than about 5 Angstroms. The conversion 
involves a one or two stage process with the polymerization of lower 
olefins to linear materials, e.g. at about 200.degree. C. over a surface 
poisoned zeolite, and oligomerization of the product over a modified or 
unmodified catalyst at a temperature of 50.degree.-75.degree. lower than 
the first stage, e.g. 150.degree. C. Therefore, the temperatures range 
from 25.degree. C. to 400.degree. C., with a pressure of atmospheric to 
1500 psi and a WHSV of 0.04 to 1.0. 
U.S. Pat. No. 4,547,609 to Dessau describes a two stage process whereby in 
the first stage, light olefins of 2 to 6 carbons are oligomerized to 
gasoline and distillate liquids including aliphatics of 10 to 20 carbons 
over a zeolite having a crystal size greater than 0.5 micron at conditions 
including at a temperature of 500.degree. F. (260.degree. C.) or higher, 
e.g. a range of 500.degree. F. (260.degree. C.) to 800.degree. F. 
(437.degree. C.), a pressure of atmospheric to 2000 psig and a WHSV of 0.1 
to 20. In the second stage, the distillate fraction is converted to high 
viscosity lubes by contact with a zeolite of smaller crystal size under 
milder conditions of a temperature about 200.degree. F. (100.degree. C.) 
to 500.degree. F. (260.degree. C.), a pressure of atmospheric to 650 psig, 
and a WHSV less than one. 
U.S. Pat. No. 4,547,613 to Garwood et al. describes converting olefins of 2 
to 16 carbons to high viscosity lube oil. A ZSM-5 type catalyst is 
pre-conditioned by contact with light olefins of 2 to 16 carbons, e.g. 
propylene at 400.degree. .F (204.degree. C.) to 1000.degree. F. 
(538.degree. C.), at a pressure of 0 to 100 psig for 1 to 70 hours. 
Conversion conditions include a temperature of 350.degree. F. (177.degree. 
C.) to 650.degree. F. (343.degree. C.), a pressure of 400 to 5000 psig and 
a WHSV of 0.1 to 10. The lube fraction may be subjected to a hydrogenation 
step to stabilize. 
Conversion of aromatics to dialkyl-substituted benzene 
The modified zeolite catalysts of the invention are advantageously used in 
the conversion of aromatics compounds to provide dialkyl-substituted 
benzene products which are highly enriched in the para-dialkyl substituted 
benzene isomer. Conversion reactions of this type include aromatics 
alkylation, transalkylation and disproportionation. Aromatics alkylations 
in which the catalysts of the invention can be used are described, for 
example, in U.S. Pat. Nos. 3,755,483, 4,086,287, 4,117,024 and 4,117,026 
which are herein incorporated by reference. 
As described in U.S. Pat. No. 3,755,483 to Burress, aromatic hydrocarbons 
such as benzenes, naphthalenes, anthracenes and substituted derivatives 
thereof, e.g. toluene and xylene, may be alkylated with alkylating agents 
such as olefins ethylene, propylene, dodecene, and formaldehyde, alkyl 
halides, and alkyl alcohols with 1 to 24 carbons under vapor phase 
conditions including a reactor inlet temperature up to about 900.degree. 
F. (482.degree. C.), with a reactor bed temperature up to about 
1050.degree. F. (566.degree. ), at a pressure of about atmospheric to 
about 3000 psig, a ratio of aromatic/alkylating agent of about 1:1 to 
about 20:1 and a WHSV of 20 to 3000 over ZSM-12. 
As described in U.S. Pat. No. 4,086,287 to Kaeding et al., 
monoalkylbenzenes having alkyls of 1-2 carbons, such as toluene and 
ethylbenzene, may be ethylated to produce a para-ethyl derivative, e.g. 
para-ethyltoluene at a temperature of from about 250.degree. C. to about 
600.degree. C., a pressure of 0.1 atmospheres to 100 atmospheres, a weight 
hourly space velocity (WHSV) of 0.1 to 100, and a ratio of feed/ethylating 
agent of 1 to 10 over a catalyst having an acid activity, i.e., alpha, of 
2 to 5000, modified by precoking or combining with oxides of phosphorus, 
boron or antimony to attain a catalyst with a xylene sorption capacity 
greater than 1 g/100 g of zeolite and an orthoxylene sorption time for 30% 
of said capacity of greater than 10 minutes, where sorption capacity and 
sorption time are measured at 120.degree. C. and a xylene pressure of 
4.5.+-.0.8 mm of mercury. 
U.S. Pat. No. 4,117,024 to Kaeding describes a process for the ethylation 
of toluene or ethylbenzene to produce p-ethyltoluene at a temperature of 
350.degree. C. to 550.degree. C., a critical pressure of greater than one 
atmosphere and less than 400 psig, with hydrogen/ethylene ratio of 0.5 to 
10 to reduce aging of the catalyst. The zeolite described in U.S. Pat. No. 
4,117,024 has a crystal size greater then one micron, and is modified as 
the catalyst in U.S. Pat. No. 4,086,287 to attain the sorption capacity 
described in U.S. Pat. No. 4,086,287. 
U.S. Pat. No. 4,117,026 to Haag and Olson describes the production of 
para-dialkyl benzenes having alkyls of 1 to 4 carbons under conditions 
which vary according to the feed. When the feed includes monoalkyl 
substituted benzenes having an alkyl of 1 to 4 carbons, olefins of 2 to 
15, or paraffins of 3 to 60 carbons or mixtures thereof, conversion 
conditions include a temperature of 250.degree. C. to 750.degree. , a 
pressure of 0.1 to 100 atmospheres and a WHSV of 0.1 to 2000. For the 
disproportionation of toluene, the conditions include a temperature of 
400.degree. C. to 700.degree. C., a pressure of 1 to 100 atmospheres and a 
WHSV of 1-50. When the feed includes olefins of 2 to 15 carbons including 
cyclic olefins, the conversion conditions include a temperature of 
300.degree. C. to 700.degree. C., a pressure of 1 to 100 atmospheres and a 
WHSV of 1 to 1000. When the feed includes paraffins of 3 to 60 carbons, 
conditions include a temperature of 300.degree. C. to 700.degree. C., a 
pressure of 1 to 100 atmospheres and a WHSV of 0.1 to 100. However for 
lower paraffins of 3 to 5 carbons, the temperature should be above 
400.degree. C. When the feed includes mixed aromatics such as ethylbenzene 
and toluene, and also optionally olefins of 2 to 20 carbons or paraffins 
of 5 to 25 carbons, conversion conditions includes a temperature of 
250.degree. C. to 500.degree. C. and a pressure greater than 200 psig. In 
the absence of added aromatics, the olefins and higher paraffins are more 
reactive and require lower severity of operation, e.g. a temperature of 
250.degree. C. to 600.degree. C., preferably 300.degree.-550.degree. C. 
The catalyst described in U.S. Pat. No. 4,117,026 is modified as in U.S. 
Pat. No. 4,086,287. 
Conversion of light paraffins and olefins to aromatics 
The modified catalysts of the invention may also be used in the conversion 
of light paraffins and olefins to aromatics in processes of the type 
described, for example, in U.S. Pat. Nos. 3,760,024 and 3,756,942 which 
are herein incorporated by reference. 
U.S. Pat. No. 3,760,024 to Cattanach describes a process for the conversion 
of paraffins of 2 to 4 carbons and/or olefins to aromatics of 6 to 10 
carbons over a ZSM-5 type catalyst with or without 
hydrogenation/dehydrogenation component. Conversion conditions include a 
temperature of 100.degree. C. to 650.degree. C., a pressure of 0 to 1,000 
psig, a WHSV of 0.1 to 500 and a hydrogen/hydrocarbon ratio of 0 to 20. 
U.S. Pat. No. 3,756,942 to Cattanach describes the conversion of paraffins, 
olefins and naphthenes to aromatics over ZSM-5 type catalysts. If the feed 
contains at least 35 wt. % olefins, conversion is at 650.degree. F. 
(363.degree. C.) to 1400.degree. F. (760.degree. C.). If the feed contains 
less than 35 wt. % olefins, the temperature is 900.degree. F. (482.degree. 
C.) to 1400.degree. F (760.degree. C.) with the absence of substantial 
added hydrogen. For both types of feed, the pressure is atmospheric to 35 
atmospheres and the WHSV 1 to 15. 
Pyridine synthesis 
The modified catalysts of the invention are also advantageously used in the 
synthesis of pyridine. Pyridine bases may be produced through the 
reactions of aldehydes and ketones with ammonia. The reaction of 
acetaldehyde with ammonia in the presence of heterogenous catalysts at 
about 350.degree. C. to about 550.degree. C. yields 2- and 
4-methylpyridine. Acetaldehyde, formaldehyde and ammonia react to yield 
pyridine and 3-methylpyridine. Pyridine synthesis is described, for 
example, in U.S. Pat. No. 4,675,410 to Feitler and U.S. Pat. No. 4,220,783 
to Chang et al. which are herein incorporated by reference. 
Caprolactam synthesis 
Caprolactam is used in the commercial production of nylon. Caprolactam may 
be produced by Beckmann rearrangement of cyclohexane oxime over acid 
catalysts including zeolites. The synthesis of caprolactam is described, 
for example, in U.S. Pat. No. 4,359,421 which is herein incorporated by 
reference. 
Therefore, the modified catalysts of the present invention are suitable for 
use in a variety of shape selective hydrocarbon conversion processes 
including as non-limiting examples, cracking hydrocarbons with reaction 
conditions including a temperature of from about 300.degree. C. to about 
700.degree. C., a pressure of from about 0.1 atmosphere (bar) to about 30 
atmospheres and a weight hourly space velocity of from about 0.1 hr.sup.-1 
to about 20 hr.sup.-1 ; dehydrogenating hydrocarbon compounds with 
reaction conditions including a temperature of from about 300.degree. C. 
to about 700.degree. C., a pressure of from about 0.1 atmosphere to about 
10 atmospheres and weight hourly space velocity of from about 0.1 to about 
20; converting paraffins to aromatics with reaction conditions including a 
temperature of from about 300.degree. C. to about 700.degree. C., a 
pressure of from about 0.1 atmosphere to about 60 atmospheres, a weight 
hourly space velocity of from about 0.5 to about 400 and a 
hydrogen/hydrocarbon mole ratio of from about 0 to about 20; converting 
olefins to aromatics, e.g. benzene, toluene and xylene, with reaction 
conditions including a temperature of from about 100.degree. C. to about 
700.degree. C., a pressure of from about 0.1 atmosphere to about 60 
atmospheres, a weight hourly space velocity of from about 0.5 to about 400 
and a hydrogen/hydrocarbon mole ratio of from about 0 to about 20; 
converting alcohols, e.g. methanol, or ethers, e.g. dimethylether, or 
mixtures thereof to hydrocarbons including olefins and/or aromatics with 
reaction conditions including a temperature of from about 275.degree. C. 
to about 600.degree. C., a pressure of from about 0.5 atmosphere to about 
50 atmospheres and a liquid hourly space velocity of from about 0.5 to 
about 100; isomerizing xylene feedstock components with reaction 
conditions including a temperature of from about 230.degree. C. to about 
510.degree. C., a pressure of from about 3 atmospheres to about 35 
atmospheres, a weight hourly space velocity of from about 0.1 to about 200 
and a hydrogen/hydrocarbon mole ratio of from about 0 to about 100; 
disproportionating toluene with reaction conditions including a 
temperature of from about 200.degree. C. to about 760.degree. C., a 
pressure from about atmospheric to about 60 atmospheres and a weight 
hourly space velocity of from about 0.08 to about 20; alkylating aromatic 
hydrocarbons, e.g. benzene and alkylbenzenes in the presence of an 
alkylating agent, e.g. olefins, formaldehyde, alkyl halides and alcohols, 
with reaction conditions including a temperature of from about 250.degree. 
C. to about 500.degree. C., a pressure of from about atmospheric to about 
200 atmospheres, a weight hourly space velocity of from about 2 to about 
2000 and an aromatic hydrocarbon/alkylating agent mole ratio of from about 
1/1 to about 20/1; and transalkylkating aromatic hydrocarbons in the 
presence of polyalkylaromatic hydrocarbons with reaction conditions 
including a temperature of from about 340.degree. C. to about 500.degree. 
C., a pressure of from about atmospheric to about 200 atmospheres, a 
weight hourly space velocity of from about 10 to about 1000 and an 
aromatic hydrocarbon/polyalkylaromatic hydrocarbon mole ratio of from 
about 1/1 to about 16/1. 
In general, therefore, catalytic conversion conditions over a catalyst 
comprising the modified zeolite include a temperature of from about 
100.degree. C. to about 760.degree. C., a pressure of from about 0.1 
atmosphere (bar) to about 200 atmospheres (bar), a weight hourly space 
velocity of from about 0.08 hr.sup.-1 to about 2000 hr.sup.-1 and a 
hydrogen/organic, e.g. hydrocarbon compound of from 0 to about 100. 
Toluene Disproportionation 
Toluene Disproportionation will be used as a representative shape selective 
conversion. A catalyst treated in the manner described herein yields a 
para-selective product in toluene disproportionation. Reaction conditions 
in the disproportionation include temperatures ranging from about 
100.degree. C. to about 600.degree. C., preferably from about 300.degree. 
C. to about 500.degree. C.; pressures ranging from about 0 to about 2000 
psig, preferably from about 15 to about 800 psig; a mole ratio of hydrogen 
to hydrocarbons from about 0 (i.e. no hydrogen is present) to about 10, 
preferably from about 1 to about 4; at a weight hourly space velocity 
(WHSV) from about 0.1 to about 100 hr.sup.-1, preferably from about 0.1 to 
about 10 hr.sup.-1. 
Normally a single pass conversion of a toluene stream results in a product 
stream which includes dimethylbenzenes having alkyl groups at all 
locations, i.e., ortho-, meta-, and para-xylenes. Furthermore, the xylenes 
are known to proceed in a reaction which produces unwanted ethylbenzenes 
(EB) by the following reaction: 
##STR2## 
Previously, the purity of p-xylene with respect to all of the C.sub.8 
products in a single pass has been limited to less than 90% when 
isomerization is permitted. This efficiency is reduced somewhat by the 
production of ethylbenzene. 
The present invention, however, provides high efficiency conversion which 
reduces production of ortho- and meta-isomers to the benefit of the 
desired para-isomer. The resulting product stream contains greater than a 
90% purity of para-xylene. For example, the ortho-xylene isomer can be 
reduced to not more than about 0.5% of the total xylenes content while the 
meta-xylene isomer can be reduced to less than about 5% of the total 
xylene content. Moreover, when the reaction system is properly treated, 
such as by deposition of platinum on the molecular sieve, the presence of 
ethylbenzene can be reduced to less than about 0.3% of the C.sub.8 
product. 
As explained in greater detail herein, the present invention provides a 
method for obtaining para-xylene at conversion rates of at least about 
15%, preferably at least about 20-25%, and with para-xylene purity of 
greater than 90%, preferably at least 95%, and most preferably about 99%. 
Therefore, higher para-xylene purity at commercially acceptable conversion 
rates than previously disclosed processes. The present invention thus 
allows for a significant reduction in process costs previously associated 
with the separation of unwanted by-products. Processes of the prior art 
typically require expensive secondary and tertiary treatment procedures in 
order to obtain these efficiencies. 
The present invention includes the regioselective conversion of toluene to 
para-xylene by methylating toluene in a reaction stream containing a 
toluene feed with a trim selectivated catalytic molecular sieve which has 
been pre-selectivated and activated, with conversion reaction conditions 
to provide a single pass, para-xylene purity of at least about 90% based 
on the C.sub.8 products. The trim selectivation methods are described 
below. As used herein, the term "para-xylene purity" means the percentage 
of para-xylene in all of the C.sub.8 products which include ethylbenzene, 
para-xylene, ortho-xylene, and meta-xylene. Those skilled in the art will 
appreciate that the proximity of the boiling points of these C.sub.8 
products necessitates more expensive separation processes whereas 
para-xylene may be more readily separated from other components in the 
product stream such as benzene, toluene, and para-ethyltoluene. 
As used herein, the term "xylene-conversion product" indicates the total 
amount of xylenes resulting from the disproportionation reaction. The word 
"para-xylene" in this term is not intended to limit the scope of the 
present invention to the production of xylenes since other 
para-substituted aromatics may be produced. 
In a preferred embodiment, the invention also includes a method for the 
regioselective production of para-xylene by passing a reaction stream 
which contains an aromatic feedstock, e.g., toluene, in a single pass, 
over a trim-selectivated catalytic molecular sieve, which is 
pre-selectivated, the single pass in the presence of hydrogen at reaction 
conditions suitable to provide para-xylene purity of greater than about 
90%. The product stream may also include small amounts of ortho- and 
meta-xylene and trace amounts of impurities such as ethylbenzene. 
The toluene may be fed simultaneously with a high-efficiency selectivating 
agent and hydrogen at reaction conditions until the desired p-xylene 
selectivity, e.g., 90% or 95%, is attained, whereupon the feed of 
selectivating agent is discontinued. This co-feeding of selectivating 
agent with toluene will be termed "trim selectivation". Reaction 
conditions for this trim-selectivation step generally include a 
temperature of about 350.degree.-540.degree. C. and a pressure of about 
atmospheric--5000 psig. The feed is provided to the system at a rate of 
about 0.1-20 WHSV. The hydrogen is fed at a hydrogen to hydrocarbon molar 
ratio of about 0.1-20. 
The high efficiency para-xylene selectivating agent for trim selectivation 
preferably comprises a silicon containing compound discussed in greater 
detail below. For example, organic silicons such as phenylmethyl silicone, 
dimethyl silicone, and mixtures thereof are suitable. According to one 
embodiment of the present invention, a silicone containing 
phenylmethylsilicon and dimethylsilicon groups in a ratio of about 1:1 is 
co-fed to the system, while the other components, e.g., toluene and 
hydrogen, are fed in the amounts set forth above. The high-efficiency 
para-xylene selectivating agent is fed in an amount of about 0.1%-50% of 
the toluene according to this preferred embodiment. Depending upon the 
percentage of selectivating agent used, the trim selectivation will 
preferably last for about 50-300 hours, most preferably less than 170 hrs. 
The catalyst is pre-selectivated ex situ with a water soluble organosilicon 
compound, then calcined and subsequently may be trim selectivated with a 
high efficiency para-xylene selectivating agent. After pre-selectivation, 
the catalytic molecular sieves for the present invention are preferably 
converted to the hydrogen form. The crystal size of zeolites used herein 
is preferably greater than 0.1 micron. 
As used herein, the term "high efficiency, p-xylene selectivating agent" as 
used for trim selectivation is used to indicate substances which will 
increase the para-selectivity of a catalytic molecular sieve to the stated 
levels while maintaining commercially acceptable toluene to xylene 
conversion levels. Such substances include, for example, organic silicon 
compounds such as phenylmethyl silicone, dimethylsilicone, and blends 
thereof which have been found to be suitable. 
The trim selectivation of the catalyst is preferably performed with a 
silicone containing compound. An example of silicone compounds which can 
be used in the present invention can be characterized by the general 
formula: 
##STR3## 
where R.sub.1 is hydrogen, fluorine, hydroxy, alkyl, aralkyl, alkaryl or 
fluoro-alkyl. The hydrocarbon substituents generally contain from 1 to 10 
carbon atoms and preferably are methyl or ethyl groups. R.sub.2 is 
selected from the same group as R.sub.1, and n is an integer of at least 2 
and generally in the range of 3 to 1000. The molecular weight of the 
silicone compound employed is generally between about 80 and about 20,000 
and preferably within the approximate range of 150 to 10,000. 
Representative silicone compounds include dimethylsilicone, 
diethylsilicone, phenylmethylsilicone, methylhydrogensilicone, 
ethylhydrogensilicone, phenylhydrogensilicone, methylethylsilicone, 
phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone, 
ethyltrifluoropropylsilicone, polydimethylsilicone, 
tetrachlorophenylmethyl silicone, tetrachlorophenylethyl silicone, 
tetrachlorophenylhydrogen silicone, tetrachlorophenylphenyl silicone, 
methylvinylsilicone and ethylvinylsilicone. The silicone compound need not 
be linear but may be cyclic as for example hexamethylcyclotrisiloxane, 
octamethylcyclotetrasiloxane, hexaphenylcyclotrisiloxane and 
octaphenylcyclotetrasiloxane. Mixtures of these compounds may also be used 
as well as silicones with other functional groups. Other 
silicon-containing compounds, such as silanes and siloxanes, may also be 
utilized. 
Preferably, the kinetic diameter of the high efficiency, p-xylene 
selectivating agent is larger than the zeolite pore diameter, in order to 
avoid reducing the internal activity of the catalyst. 
Before trim-selectivation, the catalyst is preselectivated, and a silicon 
compound is deposited on the external surface of the catalyst. 
Following deposition of the silicon-containing compound in 
pre-selectivation, the catalyst is calcined. For example, the catalyst may 
be calcined in an oxygen-containing atmosphere, preferably air, at a rate 
of 0.2.degree. to 5.degree. C./minute to a temperature greater 300.degree. 
C. but below a temperature at which the crystallinity of the zeolite is 
adversely affected. Generally, such temperature will be below 600.degree. 
C. Preferably the temperature of calcination is within the approximate 
range of 350.degree. to 550.degree. C. The product is maintained at the 
calcination temperature usually for 1 to 24 hours. 
While not wishing to be bound by theory, it is believed that the advantages 
of the present invention are obtained, in part, by rendering acid sites on 
the external surfaces of the catalyst substantially inaccessible to 
reactants while increasing catalyst tortuosity. Acid sites existing on the 
external surface of the catalyst are believed to isomerize the para-xylene 
exiting the catalyst pores back to an equilibrium level with the other two 
isomers thereby reducing the amount of para-xylene in the xylenes to only 
about 24%. By reducing the availability of these acid sites to the 
para-xylene exiting the pores of the catalyst, the relatively high level 
of para-xylene can be maintained. It is believed that the high-efficiency, 
p-xylene selectivity agents of the present invention block or otherwise 
render these external acid sites unavailable to the para-xylene by 
chemically modifying said sites. 
In line with this theory, it is also believed that the presence of hydrogen 
in the reaction zone during the trim selectivation is important in order 
to maintain the desired high yields of para-xylene when a silicone 
compound is used as the high-efficiency para-xylene selectivating agent. 
The importance of the hydrogen may be reduced in alternative embodiments 
by using a high efficiency para-xylene selectivating agent comprising 
silane or some other compound which effectively renders the isomerizing 
acid sites on the external surface of the catalyst inaccessible. 
The invention may utilize a high efficiency para-xylene selectivating agent 
which includes a silicon compound wherein the silicon compound is 
introduced by co-feeding, for example, at least one silicon compound with 
the toluene feedstock over a conversion catalyst at reaction conditions 
until the desired degree of selectivation is achieved, at which time the 
feed of selectivating agent may be discontinued. 
The toluene feedstock preferably includes about 50% to 100% toluene, more 
preferably at least about 80% toluene in the toluene feedstock. Other 
compounds such as benzene, xylenes, and trimethylbenzene may also be 
present in the toluene feedstock without adversely affecting the present 
invention. 
The toluene feedstock may also be dried, if desired, in a manner which will 
minimize moisture entering the reaction zone. Methods known in the art 
suitable for drying the toluene charge for the present process are 
numerous. These methods include percolation through any suitable 
desiccant, for example, silica gel, activated alumina, molecular sieves or 
other suitable substances, or the use of liquid charge dryers. 
For the improved disproportionation process of this invention, the suitable 
molecular sieve may be employed in combination with a support or binder 
material such as, for example, a porous inorganic oxide support or a clay 
binder. While the preferred binder is silica, other non-limiting examples 
of such binder materials include alumina, zirconia, magnesia, thoria, 
titanic, boria and combinations thereof, generally in the form of dried 
inorganic oxide gels or gelatinous precipitates. Suitable clay materials 
include, by way of example, bentonite and kieselguhr. The relative 
proportion of suitable crystalline molecular sieve to the total 
composition of catalyst and binder or support may be about 30 to about 90 
percent by weight and is preferably about 50-80 percent by weight of the 
composition. The composition may be in the form of an extrudate, beads or 
fluidizable microspheres. 
Operating conditions employed in the improved process of the present 
invention may be adjusted to affect the para-selectivity and toluene 
conversion rate. Such conditions include the temperature, pressure, space 
velocity, molar ratio of the reactants, and the hydrogen to hydrocarbon 
mole ratio. One preferred embodiment of the present invention includes 
contacting a catalytic molecular sieve with a toluene feedstock which 
includes a silicone compound under conditions for effecting vapor-phase 
disproportionation. Conditions effective for accomplishing the high 
para-selectivity and acceptable toluene disproportionation conversion 
rates include a reactor inlet temperature of about 350.degree.-540.degree. 
C., preferably greater than about 400.degree. C., a pressure of about 
atmospheric--5000 psig, preferably about 100 to 1000 psig, a WHSV of about 
0.1-20, preferably about 2-4, and a hydrogen to hydrocarbon mole ratio of 
about 0.1-20, preferably about 2-4. This process may be conducted in 
either batch or fluid bed operation with attendant benefits of either 
operation readily obtainable. 
The effluent is separated and distilled to remove the desired product, 
i.e., para-xylene, plus other by-products. 
The catalyst may be further modified in order to reduce the amount of 
undesirable by-products, particularly ethylbenzene. The state of the art 
is such that the reactor effluent from standard toluene disproportionation 
typically contains about 0.5% ethylbenzene by-product. Upon distillation 
of the reaction products, the level of ethylbenzene in the C.sub.8 
fraction often increases to about 3-4 percent. This level of ethylbenzene 
is unacceptable for polymer grade p-xylene since ethylbenzene in the 
C.sub.8 product, if not removed, degrades the quality of fibers ultimately 
produced from the p-xylene product. Consequently, ethylbenzene content 
must be kept low. The specification for ethylbenzene in the C.sub.8 
product has been determined by industry to be less than 0.3%. Ethylbenzene 
can be substantially removed by isomerization or by superfractionation 
processes. Removal of the ethylbenzene by conventional isomerization would 
be impractical with the present invention since the xylene stream, which 
includes greater than 90% para-xylene, would be concurrently isomerized to 
equilibrium xylenes reducing the amount of para-xylene in this xylene 
stream to about 24%. It is known in the art that the alternative procedure 
of removing the ethylbenzene by superfractionation is extremely expensive. 
In order to avoid the need for downstream ethylbenzene removal, the level 
of ethylbenzene by-product is advantageously reduced by incorporating a 
hydrogenation-dehydrogenation function in the catalyst, such as by 
addition of a metal compound such as platinum. While platinum is the 
preferred metal, other metals such as palladium, nickel, copper, cobalt, 
molybdenum, rhodium, ruthenium, silver, gold, mercury, osmium, iron, zinc, 
cadmium, and mixtures thereof may be utilized. The metal may be added by 
cation exchange, in amounts of about 0.01-2%, typically about 0.5%. The 
metal must be able to enter the pores of the catalyst in order to survive 
a subsequent calcination step. For example, a platinum modified catalyst 
can be prepared by first adding the catalyst to a solution of ammonium 
nitrate in order to convert the catalyst to the ammonium form. The 
catalyst is subsequently contacted with an aqueous solution of tetraamine 
platinum(II) nitrate or tetraamine platinum(II) chloride. The metallic 
compound advantageously enters the pores of the catalyst. The catalyst can 
then be filtered, washed with water and calcined at temperatures of about 
250.degree. to 500.degree. C. The hydrogenation-dehydrogenation metal ions 
are preferably introduced into the catalyst before pre-selectivation. 
By the present process, toluene can be converted to aromatic concentrates 
of high value, e.g., about 99% para-xylene based on all C.sub.8 products. 
In a typical embodiment of the present process, optimum toluene conversion 
is found to be about 20-25 weight percent with a para-xylene purity of 
about 90-99%. 
The following non-limiting examples illustrate the invention: 
EXAMPLE 1 
Silica-modified HZSM-5 was prepared by adding 2.5 g silica bound HZSM-5 to 
0.29 g organopolysiloxane, a dimethyl silicone fluid modified to render it 
water soluble (SAG-5300, Union Carbide). The water was distilled off and 
the residue was air calcined at 2.degree. C. per minute to 538.degree. C., 
then six hours at 538.degree. C. The silica-modified HZSM-5 product 
contained 8.5% added silica. 
The alpha value of the silica-modified catalyst was 1622 compared to 731 
for the parent zeolite. 
COMATIVE EXAMPLES 
Silica-modified HZSM-5 catalysts having similar silica loading and prepared 
by aqueous emulsion and organic solvent procedures decreased the alpha 
value of HZSM-5 from 180 to 52 and from 199 to 67 respectively. 
EXAMPLE 2 
The catalyst prepared in Example 1 was tested for toluene 
disproportionation at 400.degree. C., 4.0 WHSV, 500 psig and a 2/1 
hydrogen/hydrocarbon ratio. Conversion was 28% indicating a very active 
catalyst. Xylene equilibrium was 22% p-, 55% m- and 23% o-. 
EXAMPLE 3 
The catalyst prepared in Example 1 was trim selectivated using 1% 
phenylmethyl silicone in toluene feed at 446.degree. C., 500 psig, 4.0 
WHSV, and hydrogen/hydrocarbon ratio=2. The following table shows toluene 
conversion and p-xylene selectivity as a function of time on stream. The 
trim selectivation substantially increased p-xylene selectivity from 24% 
to 90% at a commercially attractive 23% toluene conversion. 
TABLE 1 
______________________________________ 
Time on Toluene p-Xylene in 
Stream, Hrs. 
Conversion, 10+ % 
Xylenes, Wt % 
______________________________________ 
2 51 24 
6 51 26 
24 40 47 
48 35 68 
72 32 78 
96 29 83 
165 23 90 
______________________________________