Molecular sieve abstract
Described are magnesium compound-impregnated catalyst compositions
comprising a gallium-modified, crystalline silica molecular sieve,
essentially free of aliminum, composited in an inorganic matrix.
Said compositions are useful fro hydrocarbon conversion, particularly
the selective ethylation of toluene in which they exhibit extremely
high paraselectivity at an excellent percent conversion.
Molecular sieve claims
What is claimed is:
1. A gas-phase process to form para-ethyltoluene in greater than
95 weight percent isomeric purity comprising contacting toluene
and ethylene at a temperature between about 250.degree. C. to about
400.degree. C. and in a mol ratio, toluene to ethylene, of about
2 to about 20 with a magnesium compound-impregnated catalyst composition
containing between about 4 and about 20 weight percent magnesium
comprising a crystalline silica molecular sieve, essentially aluminum-free
and containing between about 0.3 and about 4 weight percent nonexchangeable
gallium, composited in alumina or silica such that the composite
contains between about 20 to about 80 percent by weight of said
sieve, said sieve providing an X-ray pattern comprising the following
X-ray diffraction lines and assigned strengths:
2. A gas-phase process to form para-ethyltoluene in greater than
95 weight percent isomeric purity comprising contacting toluene
and ethylene at a temperature between about 250.degree. C. and about
400.degree. C. and in a mol ratio, toluene to ethylene, of about
2 to about 20 with a magnesium compound-impregnated catalyst composition
containing between about 4 and about 20 weight percent magnesium,
said catalyst composition comprising a crystalline silica molecular
sieve, essentially aluminum-free and containing between about 0.3
and about 4 weight percent nonexchangeable gallium, composited in
alumina or silica such that the composite contains between about
20 to about 80 percent by weight of said sieve, said sieve made
by crystallization from an aqueous solution containing a base, an
organic templating material, a gallium ion-affording material and
an oxide of silicon, and providing an X-ray pattern comprising the
following X-ray diffraction lines and assigned strengths:
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to the preparation of magnesium compound-impregnated
catalyst compositions comprising a crystalline gallosilicate molecular
sieve incorporated into an inorganic matrix and to processes for
selectively ethylating toluene accomplished by contacting toluene
and an ethylating agent under hydrocarbon conversion conditions
with said compositions. More particularly, the invention relates
to the preparation of magnesium compound-impregnated catalyst compositions
comprising high surface area, essentially free of aluminum, crystalline
gallosilicate-based molecular sieves incorporated into an inorganic
matrix, and toluene conversion processes using such catalyst compositions
comprising contacting ethylene and toluene under conversion conditions
to form an ethyltoluene product in which the paraselectivity is
nearly one hundred percent at excellent percent conversions.
In the commercial preparation of p-ethyltoluene for use to make
p-methylstyrene, it is economically important that the method used
to make the ethyltoluene makes a highly isomerically pure material.
Separation of similar-in-property isomers prior to dehydrogenation
of the ethyltoluene to the styrene compound is thus avoided. Paraselective
catalysts useful for the gas-phase ethylation of toluene which can
produce a product with greater than 95% isomeric purity are thus
a highly desirable commercial objective.
A number of recent patents have claimed the formation of gallosilicate-type
molecular sieves or gallium compound impregnated/exchanged sieves
of various structures which are said to be useful for a variety
of catalytic purposes. For example, U.S. Pat. Nos. 4372930 and
4450312 teach gallosilicate molecular sieves of Structure Types
Nu-3 and Nu-5 which are claimed to be useful for the selective alkylation
of alkanes and the isomerization of xylenes, respectively. U.S.
Pat. No. 4444652 teaches the formation of gallium compound impregnated/exchanged
sieves for upgrading low grade gasolines. In U.S. Pat. No. 4377502
the alkylation of toluene using a variety of crystalline aluminosilicate
sieves is set forth. The patent teaches that the aluminum may be
substituted by gallium. And in U.S. Pat. No. 4276437 ZSM-5 molecular
sieve catalyst compositions impregnated with gallium and phosphorus
compounds are taught for the selective paraethylation of toluene.
In Japanese Patent Application Kokai 60-19726 a gallosilicate of
the ZSM-5 structure impregnated with a phosphorus oxide is used
to improve alkylation paraselectivity when the sieve is used for
the ethylation of toluene.
In U.S. Pat. Nos. 4504690 4128592 and 4086287 the modifying
of a ZSM-5 aluminosilicate zeolite catalyst with P, Mg, or P/Mg
oxides to obtain high proportions of the 14-dialkyl isomer during
alkylation is taught. Phosphorus or Mg-modified ZSM-5 zeolite catalysts
for the disproportionation of toluene are described in J. Appl.
Polym. Sci. 36 209 (1981). Disproportionation of toluene to produce
benzene over P, Mg-modified crystalline aluminosilicate zeolite
catalysts is described in U.S. Pat. No. 4137195. Alkylation or
disproportionation of certain monosubstituted benzene compounds
to achieve nearly 100% selectivity to paradisubstituted derivatives
over magnesium compound-modified ZSM-5 aluminosilicate zeolite catalysts
is reported in J. Am. Chem. Soc. 101 6783 (1979). Use of Mg alone
or in combination with P to modify a ZSM-5 aluminosilicate zeolite
catalyst is described in U.S. Pat. No. 4049573 and the modified
catalyst is used for converting alcohols and ethers to hydrocarbons.
Again, Mg is used to modify ZSM-5 zeolite catalysts in U.S. Pat.
No. 4002698 which can be used for selective production of p-xylene
from charge stocks of toluene and a C.sub.3 -C.sub.10 olefin.
SUMMARY OF THE INVENTION
Described herein are magnesium compound-impregnated catalyst compositions
comprising a high surface area, crystalline, gallosilicate molecular
sieve, essentially aluminum free, incorporated into an inorganic
matrix; said compositions when used to catalyze the ethylation of
toluene are nearly one hundred percent paraselective at an excellent
percent conversion. These magnesium compound-impregnated gallosilicate
catalyst compositions are made in such a way that the gallium content
of the sieve, while small, is incorporated differently in the crystalline
lattice than gallium-containing sieves made by ion exchange or impregnation
processes.
More specifically, the material useful in the present invention
is prepared by mixing a base, a gallium ion-affording substance,
an oxide of silicon, and an organic template compound in water (preferably
distilled or deionized). The order of addition usually is not critical
although a typical procedure is to dissolve the organic base and
the gallium ion-affording substance in water and then add the template
compound. Generally, the silicon oxide compound is added with mixing
and the resulting slurry is transferred to a closed crystallization
vessel for a suitable time. After crystallization, the resulting
crystalline product can be filtered, washed with water, dried, and
calcined.
During preparation, acidic conditions should be avoided. Advantageously,
the pH of the reaction mixture falls within the range of about 9.0
to about 13.0; more preferably between about 10.0 and about 12.0
and most preferably between about 10.5 and 11.5.
Examples of oxides of silicon useful in this invention include
silicic acid, sodium silicate, tetraalkyl silicates, and Ludox,
a stabilized polymer of silicic acid manufactured by E. I. DuPont
de Nemours & Co. Typically, the oxide of gallium source is a
water-soluble gallium compound such as gallium nitrate or gallium
acetate or another gallium compound, the anion of which is easily
removed during sieve calcination prior to use. Water insoluble gallium
compounds such as the oxide can be used as well.
Cations useful in formation of the gallosilicate sieves include
the sodium ion and the ammonium ion. The sieves also can be prepared
directly in the hydrogen form with an organic base such as ethylenediamine.
The acidity of the gallosilicate sieves of this invention is high
as measured by the Hammett H.sub.o function which lies in the neighborhood
of about -3 to about -6.
Organic templates useful in preparing the crystalline gallosilicate
include alkylammonium cations or precursors thereof such as tetraalkylammonium
compounds, especially tetra-n-propylammonium compounds. A useful
organic template is tetra-n-propylammonium bromide. Diamines, such
as hexamethylenediamine, can be used.
The crystalline gallosilicate molecular sieve can be prepared by
crystallizing a mixture of sources for an oxide of silicon, an oxide
of gallium, an alkylammonium compound, and a base such as sodium
hydroxide, ammonium hydroxide or ethylenediamine such that the initial
reactant molar ratios of water to silica range from about 5 to about
80 preferably from about 10 to about 50 and most preferably from
about 20 to about 40. In addition, preferable molar ratios for initial
reactant silica to oxide of gallium range from about 4 to about
200 more preferably from about 10 to about 150 and most preferably
from about 20 to about 100. The molar ratio of base to silicon oxide
should be about above about 0.5 typically below about 5 preferably
between about 0.05 and about 1.0 and most preferably between about
0.1 and about 0.5. The molar ratio of aklylammonium compound, such
as tetra-n-propylammonium bromide, to silicon oxide can range from
0 to about 1 or above, typically above about 0.005 preferably about
0.01 to about 0.2 most preferably about 0.02 to about 0.1.
The resulting slurry is transferred to a closed crystallization
vessel and reacted usually at a pressure at least the vapor pressure
of water for a time sufficient to permit crystallization which usually
is about 0.25 to about 25 days, typically is about one to about
ten days and preferably is about one to about seven days, at a temperature
ranging from about 100.degree. to about 250.degree. C., preferably
about 125.degree. to about 200.degree. C. The crystallizing material
can be stirred or agitated as in a rocker bomb. Preferably, the
crystallization temperature is maintained below the decomposition
temperature of the organic template compound. Especially preferred
conditions are crystallizing at about 165.degree. C. for about three
to about seven days. Samples of material can be removed during crystallization
to check the degree of crystallization and determine the optimum
crystallization time.
The crystalline material formed can be separated and recovered
by well-known means such as filtration with aqueous washing. This
material can be mildly dried for anywhere from a few hours to a
few days at varying temperatures, typically about 50.degree. to
about 225.degree. C., to form a dry cake which can then be crushed
to a powder or to small particles and extruded, pelletized, or made
into forms suitable for its intended use. Typically, materials prepared
after mild drying contain the organic template compound and water
of hydration within the solid mass and a subsequent activation or
calcination procedure is necessary, if it is desired to remove this
material from the final product. Typically, the mildly dried product
is calcined at temperatures ranging from about 260.degree. to about
850.degree. C. and preferably from about 425.degree. to about 600.degree.
C. Extreme calcination temperatures or prolonged crystallization
times may prove detrimental to the crystal structure or may totally
destroy it. Generally, there is no need to raise the calcination
temperature beyond about 600.degree. C. in order to remove organic
material from the originally formed crystalline material. Typically,
the molecular sieve material is dried in a forced draft oven at
165.degree. C. for about 16 hours and is then calcined in air in
a manner such that the temperature rise does not exceed 125.degree.
C. per hour until a temperature of about 540.degree. C. is reached.
Calcination at this temperature usually is continued for about 4
hours. The gallosilicate sieves thus made generally have a surface
area greater than about 300 sq. meters per gram as measured by the
BET procedure.
The gallosilicate sieve useful in this invention is admixed with
or incorporated within various binders or matrix materials depending
upon the intended process use. The crystalline gallosilicates are
combined with active or inactive materials, synthetic or naturally
occurring zeolites, as well as inorganic or organic materials which
would be useful for binding the gallosilicate. Well-known materials
include silica, silica-alumina, alumina, magnesia, titania, zirconia,
alumina sols, hydrated aluminas, clays such as bentonite or kaolin,
or other binders well known in the art. Typically, the gallosilicate
is incorporated within a matrix material by blending with a sol
of the matrix material and gelling the resulting mixture or slurrying
the sieve with the matrix material and drying. Also, solid particles
of the gallosilicate and matrix material can be physically admixed.
Typically, such gallosilicate compositions can be pelletized or
extruded into useful shapes. The crystalline gallosilicate content
can vary anywhere from a few up to 100 weight percent of the total
composition. Catalytic compositions can contain about 0.1 weight
percent to about 100 weight percent crystalline gallosilicate material
and preferably contain about 10 weight percent to about 95 weight
percent of such material and most preferably contain about 20 weight
percent to about 80 weight percent of such material.
More specifically, catalytic compositions comprising the crystalline
gallosilicate material and a suitable matrix material can be formed
by adding a finely divided crystalline gallosilicate sieve to an
aqueous sol or gel of the matrix material, such as PHF Alumina made
by American Cyanamid Co. The resulting mixture is thoroughly blended
and gelled, typically by adding a material such as ammonium hydroxide.
The resulting gel is dried below about 200.degree. C., more preferably
between about 100.degree. C. and about 150.degree. C. and calcined
between about 350.degree. C. and about 700.degree. C. to form a
catalyst composition in which the crystalline gallosilicate sieve
is distributed throughout the matrix material.
Alternatively, the sieve and a suitable matrix material like alpha-alumina
monohydrate such as Conoco Catapal SB Alumina can be slurried with
a small amount of a dilute weak acid such as acetic acid, dried
at a suitable temperature under about 200.degree. C., preferably
about 100.degree. to about 150.degree. C. and then calcined at between
about 350.degree. and about 700.degree. C., more preferably between
about 400.degree. to about 650.degree. C.
Silica-supported catalyst compositions can be made by dry mixing
the gallosilicate sieve with a silica source such as Cab-O-Sil,
adding water and stirring. The resulting solid is then dried below
about 200.degree. C. and finally calcined between about 350.degree.
C. and 700.degree. C.
To make an impregnated catalyst composition of this invention,
a composition comprising the crystalline gallosilicate molecular
sieve in an inorganic matrix is contacted with a magnesium compound-containing
solution. The resulting mass is dried at temperatures up to about
150.degree. C., driving off in this step essentially all of the
impregnation solvent. The resulting composition is then activated
by calcination for about 1 hour to about 24 hours at temperatures
between about 300.degree. C. and about 800.degree. C., more preferably
about 4 hours to about 24 hours at a temperature between about 400.degree.
C. to about 600.degree. C.
The amount of magnesium incorporated within the catalyst composition
should be from about 2 percent to 25 percent by weight, more preferably
from about 4 percent to about 20 percent by weight, weight percents
calculated as weight percent magnesium. The incorporated magnesium
is believed to be present substantially in the oxide form.
Preferred magnesium compounds include most soluble magnesium salts,
more preferably magnesium nitrate or acetate is used.
The solutions of magnesium compounds used in impregnation may be
made from polar or nonpolar solvents, including water and organic
solvents generally. Solvents that are destructive of either the
zeolite or matrix should be avoided. Water and alcohol are preferred
solvents.
Catalyst compositions of this invention are useful in hydrocarbon
conversion reactions. A particularly useful reaction is alkylation
of aromatics and especially the selective para-ethylation of toluene.
Ethylation of toluene in the presence of the above-described catalyst
compositions is effected by contact of the toluene with ethllene,
preferably in the gas phase, at a temperature between about 200.degree.
and about 600.degree. C. and preferably between about 250.degree.
and about 400.degree. C. The reaction generally takes place at atmospheric
pressure, but the pressure may be within the approximate range of
about 1 atmosphere to about 2000 psig. The molar ratio of toluene
to ethylene employed is within the approximate range of about 0.5
to about 50 more preferably about 2 to about 20. Reaction is suitably
accomplished utilizing a weight hourly space velocity of between
about 0.1 and about 100 and preferably between about 0.5 and about
50. The reaction product, consisting selectively of paraethyltoluene
with comparatively smaller amounts of the other ethyl isomers, generally
need not be separated for further use.
The following Examples will serve to illustrate certain specific
embodiments of the hereindisclosed invention. These Examples should
not, however, be construed as limiting the scope of the novel invention
as there are many variations which may be made thereon without departing
from the spirit of the disclosed invention, as those of skill in
the art will recognize. |