Molecular sieve abstract
Described are catalyst compositions comprising a high surface area,
zinc-modified, crystalline silica molecular sieve, essentially free
of aluminum, which has been incorporated into an inorganic matrix;
said compositions are useful for hydrocarbon conversion, particularly
the propylation of toluene in which they exhibit a very high paraselectivity
while making a product containing a high isopropyltoluene/n-propyl-toluene
isomer ratio. These catalyst compositions are made from an organic
base, a templating material, a zinc ion-affording compound, and
an oxide of silicon.
Molecular sieve claims
What is claimed is:
1. A process comprising contacting toluene and propylene under
alkylation conditions with a catalyst composition comprising a high
surface area, crystalline silica molecular sieve, essentially aluminum
free and containing between about 0.1 weight percent and about 5
weight percent nonexchangeable zinc, composited in an inorganic
matrix, said sieve made by crystallization from an aqueous solution
containing an organic base, an organic templating material, a zinc
ion-affording material and an oxide of silicon and providing an
X-ray pattern comprising the following X-ray diffraction lines and
assigned strengths:
2. The process of claim 1 wherein the amount of zinc in said crystalline
silica molecular sieve is between about 0.2 and about 4 weight percent.
3. The process of claim 1 wherein the amount of zinc in said crystalline
silica molecular sieve is between about 0.3 and about 3 weight percent.
10. The process of claim 7 wherein said catalyst composition is
made by a process comprising slurrying together said sieve and said
inorganic matrix in a liquid, removing said liquid and calcining
the result between about 350.degree. C. and about 700.degree. C.
11. The process of claim 8 wherein said catalyst composition is
made by a process comprising slurrying together said sieve and said
inorganic matrix in a liquid, removing said liquid and calcining
the result between about 350.degree. C. and about 700.degree. C.
12. The process of claim 9 wherein said catalyst composition is
made by a process comprising slurrying together said sieve and said
inorganic matrix in a liquid, removing said liquid and calcining
the result between about 350.degree. C. and about 700.degree. C.
13. A process comprising contacting toluene and propylene under
alkylation conditions with a catalyst composition comprising a high
surface area, crystalline silica molecular sieve, essentially aluminum
free and containing between about 0.2 weight percent and about 4
weight percent nonexchangeable zinc, composited in an inorganic
matrix, said sieve made by crystallization from a solution containing
ethylenediamine, tetrapropylammonium bromide, zinc acetate or nitrate,
and an oxide of silicon, and providing an X-ray pattern comprising
the following X-ray diffraction lines and assigned strengths:
14. The process of claim 13 wherein the amount of zinc in said
crystalline silica molecular sieve is between about 0.3 and about
3 weight percent.
15. The process of claim 13 wherein said inorganic matrix is silica,
silica-alumina or alumina.
16. The process of claim 14 wherein said inorganic matrix is silica,
silica-alumina or alumina.
17. The process of claim 13 wherein said inorganic matrix is alumina.
18. The process of claim 14 wherein said inorganic matrix is alumina.
19. The process of claim 17 wherein said catalyst composition is
made by a process comprising slurrying together said sieve and said
inorganic matrix in a liquid, removing said liquid and calcining
the result between about 350.degree. C. and about 700.degree. C.
20. The process of claim 18 wherein said catalyst composition is
made by a process comprising slurrying together said sieve and said
inorganic matrix in a liquid, removing said liquid and calcining
the result between about 350.degree. C. and about 700.degree. C.
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to the preparation of catalyst compositions
comprising a high surface area, zinc-modified, crystalline silica
molecular sieve, essentially free of aluminum, incorporated into
an inorganic matrix and to processes for propylating toluene accomplished
by contacting toluene and a propylating agent under hydrocarbon
conversion conditions with said compositions. More particularly,
the invention relates to the preparation without the use of alkali
metal ion or ammonia of high surface area, essentially free of aluminum,
crystalline silica molecular sieves which have been modified by
incorporation of a small amount of zinc, and toluene conversion
processes, using catalyst compositions made from the sieves by incorporating
such sieves in an inorganic matrix, involving the reaction of propylene
and toluene to form a product in which the isopropyltoluene-to-n-propyltoluene
isomer ratio is high and the ortho- and metacymene content of the
isopropyltoluene fraction is very small compared to the paracymene
content. This novel process offers a simple route from toluene to
a paracymene product having greatly reduced isomer purification
problems.
U.S. Pat. No. 4254296 describes a process for the preparation
of tertiary olefins employing a crystalline silica having a high
specific surface area, modified or unmodified with an oxide of certain
metals including zinc capable of entering the silica lattice as
a substitute for silicon or as a salt of polysilicic acids. Only
the modifying elements chromium, aluminum and beryllium are shown
in the Examples. In U.K. Patent Application No. 2024790A, high
specific surface area crystalline silicas are taught, wherein certain
elements, e.g. zinc, are said to have entered the crystal lattice
of the silica in place of silicon atoms or in the form of salts
of bisilicic or polysilicic acids. A zinc Example is given. These
acidic, thermally stable materials are suggested as catalysts for
a large number of reactions including the methylation of toluene
to xylenes, particularly paraxylene. U.S. Pat. Nos. 4423269 4423268
and 4417087 describe processes for oligomerization of gaseous
olefins over intermediate pore size crystalline silicas including
silicalite, chromia silicates (CZM) and U.S. Pat. No. Re. 29948
organosilicates as described in U.S. Pat. No. Re. 29948 or silicas
containing significant amounts of alumina. Zinc can be incorporated
into these materials for activity and stability using standard impregnation
and ion exchange techniques. U.S. Pat. No. 4329328 teaches the
synthesis of small pore "A type" zincosilicate or noncrystalline
sodium zincosilicates. U.S. Pat. No. 4291182 teaches a process
for the preparation of aromatic hydrocarbons and hydrogen from butane
over crystalline silicates promoted by zinc incorporated by impregnation
or ion exchange. In U.S. Pat. No. 3894104 use of a crystalline
aluminosilicate zeolite modified by incorporation (exchanged, impregnated
and/or vapor deposited) with one of a number of metals including
zinc to catalyze aromatization of a heteroatom-substituted hydrocarbon
is taught. In U.S. Pat. No. 1728732 materials made from a soluble
silicate, an alkali metal compound and a heavy metal salt (including
zinc salts) which, depending on the proportions used, resemble aluminosilicates
were synthesized, and some are said to be useful as catalysts.
SUMMARY OF THE INVENTION
Described herein are catalyst compositions comprising a high surface
area, zinc-modified, crystalline silica molecular sieve, essentially
aluminum free, incorporated into an inorganic matrix; said compositions
when used to catalyze the propylation of toluene are very paraselective
at a high isopropyltoluene/n-propyltoluene isomer ratio. These zincosilicate
catalyst compositions are made in such a way that the zinc content
of the sieve, while small, is incorporated differently in the crystalline
lattice than zinc-containing sieves made by ion exchange or impregnation
processes.
DETAILED DESCRIPTION OF THE INVENTION
The zincosilicate crystalline molecular sieves of this invention
are characterized by the representative X-ray pattern listed in
Table A below and by the composition formula:
wherein M is at least one cation, n is the valence of the cation,
y is between 4 and about 600 and z is between 0 and about 160. It
is believed that the small zinc content of the sieves is at least
in part incorporated in the crystalline lattice. Various attempts
to remove the zinc from the zincosilicate sieves by exhaustive exchange
with sodium, ammonium and hydrogen ions were unsuccessful and therefore,
the zinc content is considered nonexchangeable in the instant sieves.
By regulation of the quantity of zinc (represented as ZnO) in the
reaction mixture, it is possible to vary the SiO.sub.2 /ZnO molar
ratio in the final product. In general it is desirable to have the
zinc content of the zincosilicate sieve of this invention between
about 0.1 and about 5 percent by weight of zinc. More preferably,
the amount of zinc should be between about 0.2 and about 4 weight
percent zinc and, most preferably, between about 0.3 and about 3
weight percent of zinc. Too much zinc in the reaction mixture appears
to reduce the sieve crystallinity which reduces the catalytic usefulness
of the sieve.
More specifically, the material useful in the present invention
is prepared by mixing an organic base, a zinc 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 zinc ion-affording substance in water and then add the template
compound. Generally, the silicon oxide compound is added with intensive
mixing such as that performed in a Waring Blender 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 8.0
to about 12.0; more preferably between about 9.0 and about 11.0
and most preferably between about 9.5 and 10.5.
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 zinc source is a water-soluble
zinc compound such as zinc nitrate or zinc acetate or another zinc
compound, the anion of which is easily removed during sieve calcination
prior to use.
Cations useful in formation of the zincosilicate sieves include
the zinc ion and the hydrogen ion. The sieves are prepared directly
in the hydrogen form with an organic base such as ethylenediamine.
In the case of the instant zincosilicates, some of the zinc may
be present in part as a substitute counter ion for the hydrogen
ion. The acidity of these sieves is low as measured by the Hammett
Ho function which lies in the neighborhood of about +3 to about
+6.
Organic templates useful in preparing the crystalline zincosilicate
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 zincosilicate molecular sieve can be prepared by
crystallizing a mixture of sources for an oxide of silicon, an oxide
of zinc, an alkylammonium compound and 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 zinc 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 ethylenediamine
to silicon oxide should be about above about 0.05 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 alkylammonium
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 20 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
to 16 hours. The zincosilicate sieves thus made, generally have
a surface area greater than about 300 sq. meters per gram as measured
by the BET procedure.
The zincosilicate sieve useful in this invention is admixed with
or incorporated within various binders or matrix materials depending
upon the intended process use. The crystalline zincosilicates 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 zincosilicate. 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 zincosilicate 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 zincosilicate
and matrix material can be physically admixed. Typically, such zincosilicate
compositions can be pelletized or extruded into useful shapes. The
crystalline zincosilicate content can vary anywhere from a few up
to 100 wt. % of the total composition. Catalytic compositions can
contain about 0.1 wt. % to about 100 wt. % crystalline zincosilicate
material and preferably contain about 10 wt. % to about 95 wt. %
of such material and most preferably contain about 20 wt. % to about
80 wt. % of such material.
More specifically, catalytic compositions comprising the crystalline
zincosilicate material of this invention and a suitable matrix material
are formed by adding a finely-divided crystalline zincosilicate
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 zincosilicate
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. C. to about 150.degree. C. and then calcined at
between about 350.degree. C. and about 700.degree. C., more preferably
between about 400.degree. C. to about 650.degree. C.
The catalyst compositions of this invention appear to be more paraselective
for the propylation of toluene when matrixed by the slurry technique
rather than the gel technique, both of which are described immediately
above.
Catalyst compositions of this invention are useful in hydrocarbon
conversion reactions. A particularly useful reaction is alkylation
of aromatics and especially propylation of toluene.
Propylation of toluene in the presence of the above-described catalyst
compositions is effected by contact of the toluene with propylene,
preferably in the gas phase, at a temperature between about 200.degree.
C. and about 600.degree. C. and preferably between about 250.degree.
C. 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 propylene 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
paracymene with comparatively smaller amounts of other isopropyltoluenes
and n-propyltoluenes may be separated, if required, by any suitable
means such as fractionation. |