Molecular sieve abstract
Disclosed are improved HAMS-1B crystalline molecular sieve-based
catalyst compositions made by impregnating such a sieve, which has
been incorporated in an inorganic matrix, with a small amount of
a magnesium compound, and a process for employing such catalyst
compositions for the methylation of a xylene in which the amount
of pseudocumene in the product is substantially enhanced compared
to that produced by the unimpregnated catalyst composition.
Molecular sieve claims
What is claimed is:
1. A process for making pseudocumene comprising methylating a xylene
in the presence of a catalyst composition comprising a HAMS-1B crystalline
borosilicate molecular sieve incorporated into an inorganic matrix,
said composition impregnated by a magnesium compound and subsequently
heated to substantially convert said compound to the oxide form.
2. A process for making pseudocumene comprising methylating a xylene
in the presence of the catalyst composition of claim 1 containing
between about 0.5 and about 25 weight percent magnesium.
3. A process for making pseudocumene comprising methylating a xylene
in the presence of the catalyst composition of claim 1 containing
between about 8 and about 15 weight percent magnesium.
4. A process for making pseudocumene comprising methylating a xylene
in the presence of the catalyst composition of claim 2 wherein said
HAMS-1B moleuclar sieve comprises from about 20 to about 80 wt.%
incorporated into an alumina, silica or silica-alumina matrix.
5. A process for making pseudocumene comprising methylating a xylene
in the presence of the catalyst composition of claim 3 wherein said
HAMS-1B molecular sieve comprises from about 20 to about 80 wt.%
incorporated into an alumina, silica or silica-alumina matrix.
6. A process for making pseudocumene comprising reacting methanol
or dimethylether with a xylene in the presence of the catalyst composition
of claim 4.
7. A process for making pseudocumene comprising reacting methanol
or dimethylether with a xylene in the presence of the catalyst composition
of claim 5.
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to improved AMS-1B crystalline molecular
sieve-based catalyst compositions, and particularly, to the use
of such compositions having improved ability to form pseudocumene
by the methylation of xylenes.
In U.S. Pat. Nos. 4504690 4128592 and 4086287 is taught
modifying a ZSM-5 aluminosilicate zeolite catalyst with P, Mg or
P/Mg oxides to obtain high proportions of the 14-dialkyl isomer.
Phosphorus or Mg modified ZSM-5 zeolite catalysts for the disproportionation
of toluene are shown in J. Appl. Polym. Sci. 36 209 (1981). Disproportionation
of toluene to produce benzene over a P, Mg modified crystalline
aluminosilicate zeolite catalyst is described in U.S. Pat. No. 4137195.
Alkylation or disproportionation of certain monosubstituted benzene
compounds to achieve nearly 100% selectivity to para-disubstituted
derivatives over magnesium compound-modified ZSM-5 aluminosilicate
zeolite catalysts is reported in J. Am. Chem. Sec. 101 6783 (1979).
Use of Mg alone or in combination with P to modify a ZSM-5 aluminosilicate
of zeolite catalyst is described in U.S. Pat. No. 4049573 and
the modified catalyst 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.
Catalyst compositions, generally useful for hydrocarbon conversion,
based upon AMS-1B crystalline borosilicate molecular sieve have
been described in U.S. Pat. Nos. 4268420 4269813 4285919
and Published European Application No. 68796.
As described in the references in the paragraph above, catalyst
compositions typically are formed by incorporating an AMS-1B crystalline
borosilicate molecular sieve material into a matrix such as alumina,
silica or silica-alumina to produce a catalyst formulation. In one
method of making AMS-1B crystalline borosilicate, sieve is formed
by crystallizing sources for silicon oxide and boron oxide with
sodium hydroxide and an organic compound. After crystallization,
the resulting sodium form is ion exchanged with an ammonium compound
and calcined to yield the hydrogen form of AMS-1B. In another more
preferred method, AMS-1B crystalline borosilicate is crystallized
in the hydrogen form from a mixture containing a diamine in place
of a metal hydroxide. AMS-1B borosilicates in hydrogen form are
designated HAMS-1B. Typically, the hydrogen form sieve is gelled
with an alumina sol, dried and calcined to yield a catalyst composition.
SUMMARY OF THE INVENTION
Described herein are improved AMS-1B crystalline borosilicate molecular
sieve-based catalyst compositions made by impregnating such a sieve,
which has been incorporated in a matrix, with a small amount of
a suitable magnesium compound, and processes for employing such
catalyst compositions for the methylation of a xylene in which the
amount of pseudocumene in the product is substantially enhanced
compared to that produced by the unimpregnated composition.
DETAILED DESCRIPTION OF THE INVENTION
In the method of this invention a HAMS-1b crystalline molecular
sieve incorporated into an inorganic matrix is impregnated with
a small amount of magnesium oxide by treating with a solution of
a magnesium compound, drying, and calcining the resulting impregnated
catalyst composition at an elevated temperature. Impregnated compositions
when contacted at elevated temperature with a mixture of a xylene
and a methylating agent such as methanol or dimethylether can form
enhanced amounts of pseudocumene compared to unimpregnated catalyst
compositions.
To make an impregnated catalyst composition of this invention,
a composition comprising the acid form of the crystalline borosilicate,
HAMS-1B, 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 with the catalyst composition
should be from about 4% to 25% by weight, more preferably, from
about 8% to about 15% by weight, percents calculated as 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.
The catalyst compositions used in this invention are based on AMS-1B
crystalline borosilicate molecular sieve, which is described in
U.S. Pat. Nos. 4268420 4269813 and 4285919 and Published
European Patent Application No. 68796 all incorporated herein
by reference. AMS-1B crystalline borosilicate generally can be characterized
by the X-ray pattern listed in Table A and by the composition formula:
wherein R is an organic compound and M is at least one cation having
the oxidation state n, such as an alkali or an alkaline earth metal
cation or hydrogen. By regulation of the quantity of boron (represented
as B.sub.2 O.sub.3) in the reaction mixture, it is possible to vary
the SiO.sub.2 /B.sub.2 O.sub.3 molar ratio in the final product.
More specifically, the material useful in the present invention
is prepared by mixing a base, a boron oxide source, and an organic
template compound in water (preferably distilled or deionized).
The order of addition usually is not cirtical although a typical
procedure is to dissolve base and boric acid 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 Blendor
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. When alkali
metal hydroxides are used, the values of the ratio of OH.sup.- /SiO.sub.2
shown above should furnish a pH of the system that broadly falls
within the range of about 9 to about 13.5. Advantageously, the pH
of the reaction system falls within the range of about 10.5 to about
11.5 and most preferably between about 10.8 and about 11.2.
Examples of materials affording silicon oxide 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 boron source
is boric acid although equivalent species can be used such as sodium
borate and other boron-containing compounds.
Cations useful in formation of AMS-1B crystalline borosilicate
include alkali metal and alkaline earth metal cations such as sodium,
potassium, lithium, calcium and magnesium. Ammonium cations may
be used alone or in conjunction with such metal cations. Since basic
conditions are required for crystallization of the molecular sieve
of this invention, the source of such cation usually is a hydroxide
such as sodium hydroxide. Alternatively, AMS-1B can be prepared
directly in the hydrogen form by replacing such metal cation hydroxides
with an organic base such as ethylenediamine as described in Published
European Application No. 68796.
Organic templates useful in preparing AMS-1B crystalline borosilicate
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.
In a more detailed description of a typical preparation of this
invention, suitable quantities of sodium hydroxide and boric acid
(H.sub.3 BO.sub.3) are dissolved in distilled or deionized water
followed by addition of the organic template. The pH may be adjusted
between about 11.0.+-.0.2 using a compatible acid or base such as
sodium bisulfate or sodium hydroxide. After sufficient quantities
of a silica source such as a silicic acid polymer (Ludox) are added
with intensive mixing, preferably the pH is again checked and adjusted
to a range of about 11.0.+-.0.2.
Alternatively, AMS-1B crystalline borosilicate molecular sieve
can be prepared by crystallizing a mixture of sources for an oxide
of silicon, an oxide of boron, an alky ammonium compound and ethylenediamine
such that the initial reactant molar ratios of water to silica range
from about 5 to about 25 preferably about 5 to about 20 and most
preferably from about 10 to about 15. In addition, preferable molar
ratios for initial reactant silica to oxide of boron range from
about 4 to about 150 more preferably from about 5 to about 80 and
most preferably from about 5 to about 20. The molar ratio of ethylenediamine
to silicon oxide should be above about 0.05 typically below 5
preferably between about 0.1 and about 1.0 and most preferably between
about 0.2 and 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 0.1 more preferably about 0.01 to about 0.1 and most
preferably about 0.2 to about 0.05.
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. C. to about 250.degree. C., preferably
about 125.degree. C. 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 five
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.-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 neccessary, if it is desired to remove this material
from the final product. Typically, mildly dried product is calcined
at temperatures ranging from about 260.degree. C. to about 850.degree.
C. and preferably about 425.degree. C. 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.
A catalytically active material can be placed onto the borosilicate
structure, either before or after incorporation into a matrix, by
ion exchange, impregnation, a combination thereof, or other suitable
contact means. Before placing a catalytically active metal ion or
compound on the borosilicate structure, the borosilicate should
be in the hydrogen form. If the sieve was prepared using a metal
hydroxide, such as sodium hydroxide, the hydrogen form typically,
is produced by exchange one or more times with ammonium ion, typically
using ammonium acetate, followed by drying and calcination as described
above.
The original cation in the AMS-1B crystalline borosilicate can
be replaced all or in part by ion exchange with other cations including
other metal ions and their amine complexes, alkylammonium ions,
ammonium ions, hydrogen ions, and mixtures thereof. Preferred replacing
cations are those which render the crystalline borosilicate catalytically
active, especially for hydrocarbon conversion. Typical catalytically
active ions include hydrogen, metal ions of Groups IB, IIA, IIB,
IIIA, VB, VIB and VIII, and of manganese, vanadium, chromium, uranium,
and rare earth elements.
Also, water soluble salts of catalytically active materials can
be impregnated onto the crystalline borosilicate of this invention.
Such catalytically active materials include metals of Groups IB,
IIA, IIB, IIIA, IIIB, IVB, VB, VIB, VIIB, and VIII, and rare earth
elements.
Examples of catalytically active elements include ruthenium, rhodium,
iron, cobalt, and nickel. Mixtures of elements can be used. Other
catalytic materials include ions and compounds of aluminum, lanthanum,
molybdenum, tungsten, and noble metals such as ruthenium, osmium,
rhodium, iridium, palladium, and platinum. Other additional catalytic
materials can be ions and compounds of scandium, yttrium, titanium,
zirconium, hafnium, vanadium, niobium, tantalum, chromium, cerium,
manganese, cobalt, iron, zinc and cadmium. Specific combinations
of non-noble metals of Group VIII and other catalytic materials
include ions or compounds of nickel and osmium, nickel and lanthanum,
nickel and palladium, nickel and iridium, nickel and molybdenum,
and nickel and tungsten.
Ion exchange and impregnation techniques are well-known in the
art. Typically, an aqueous solution of a cationic species is exchanged
one or more times at about 25.degree. C. to about 100.degree. C.
A hydrocarbon-soluble metal compound such as a metal carbonyl also
can be used to place a catalytically active material. Impregnation
of a catalytically active compound on the borosilicate or on a composition
comprising the crystalline borosilicate suspended in and distributed
throughout a matrix of a support material, such as a porous refractory
inorganic oxide like alumina, often results in a suitable catalytic
composition. A combination of ion exchange and impregnation can
be used. Presence of sodium ion in a composition usually is detrimental
to catalytic activity.
The amount of catalytically active material placed on the AMS-1B
borosilicate can vary from about 0.01 weight percent to about 30
weight percent, typically from about 0.05 to about 25 weight percent,
depending on the process use intended. The optimum amount can be
determined easily by routine experimentation.
The AMS-1B crystalline borosilicate useful in this invention is
admixed with or incorporated within various binders or matrix materials
depending upon the intended process use. The crystalline borosilicate
can be 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 borosilicate. 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 borosilicate
is incorporated within a matrix material by blending with a sol
of the matrix material and gelling the resulting mixture. Also,
solid particles of the borosilicate and matrix material can be physically
admixed. Typically, such borosilicate compositions can be pelletized
or extruded into useful shapes. The crystalline borosilicate 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 borosilicate 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.
Catalyst compositions treated with a magnesium compound according
to this invention can be in powder form or already in extrudate
form.
Methylation of xylene in the presence of the above described catalyst
is effected by contact of a xylene with a methylating agent, preferably
methanol or dimethylether, 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. The reaction generally takes place at
atmospheric pressure, but the pressure range may be within the approximate
range of about 1 atmosphere to about 2000 psig. The molar ratio
of methylating agent to xylene is generally between about 0.5 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
about 0.1-1 mols of methanol per mol of toluene. With the use of
other methylating agents, such as methylchloride, methylbromide,
dimethylether, methylcarbonate, 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 1000 and preferably between
about 5 and about 500. The reaction product consisting predominantly
of xylene and tri and tetramethyl benzenes may be separated by any
suitable means, such as by passing the same through a distillation
column.
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.
EXAMPLES
General
All methylation reactions in Examples 3 and 4 below were carried
out in a stainless steel reactor of plug flow design. A mixture
of the appropriate xylene and methanol (4:1 mol ratio) was introduced
at atmospheric pressure into a preheater packed with inert Denstone
packing. Reactants were then passed into a 1/2" O.D..times.5"
reactor tube filled with approximately 5 g of catalyst. The entire
reactor and preheater assembly was supported in a fluidized-bed
sand bath maintained at reaction temperature. Product was collected
in a cooled vessel as it dripped from the reactor and was analyzed
by gas chromatography on a 60-meter fused silica capillary column.
Magnesium contents are given in weight percent of the element.
COMPARATIVE EXAMPLE 1
The catalyst composition of this Example was made from 40% HAMS-1B
crystalline borosilicate and 60% alumina. A 118 g portion of HAMS-1B
was gelled with a 1810 g portion of American Cyanamide PHF alumina
sol that has a 9.47% by weight content of alumina, using 171 ml
of concentrated ammonium hydroxide (29% NH.sub.3) and 236 g of water.
The gel was dried at 165.degree. C. for 18 hours. The dried sample
was ground to 18-40 mesh then calcined at 538.degree. C. for 12
hours.
EXAMPLE 2
A 6.0 g portion of the catalyst composition of Example 1 in the
form of 1/16" extrudates was placed in a solution of 8.27 g
Mg(NO.sub.3).sub.2 .multidot.6H.sub.2 O dissolved in 15 ml of water.
The mixture was heated in a water bath at 92.degree. C. for one
hour, cooled and stirred for an additional two hours, and then left
undisturbed overnight. After 11/2 hours in a drying oven at 110.degree.
C. to remove bulk water, the catalyst was placed in a calcining
oven. The temperature of the oven was slowly increased at 1/2 hour
intervals until 500.degree. C. was reached, and held at this temperature
overnight. Upon cooling the catalyst composition was ready for use
and contained about 10% by weight magnesium.
COMPARATIVE EXAMPLE 3
A catalyst composition charge of 4 g of the catalyst composition
of Example 1 was placed in the reactor and heated to 400.degree.
C. under a stream of argon. The appropriate xylene/methanol mixture
was fed at a rate of 0.21 ml/min. for a period of 90 minutes whereupon
the sampling was completed. The temperature was raised to 500.degree.
C. and sampling continued for a further 90 minutes. In the Table
below are recorded selectivity data and other conditions for runs
1-8 carried out as in this Example.
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