Molecular sieve abstract
AMS-1B crystalline borosilicate molecular sieve is prepared by
reacting under crystallization conditions an aqueous mixture containing
sources for an oxide of silicon, an oxide of boron, a cation and
a lower alkyl primary or secondary amine.
Molecular sieve claims
What is claimed is:
1. A method to prepare AMS-1B crystalline borosilicate molecular
sieve containing a low sodium content comprising reacting under
crystallization conditions an aqueous mixture consisting essentially
of sources for a silicon oxide, a boron oxide, sodium cation and
an amine selected from the group consisting of methylamine and dimethylamine,
wherein the ratio of moles of amine to sodium cation is about 1
to about 10.
2. The method of claim 1 wherein the source of boron oxide is boric
acid.
3. The method of claim 1 wherein the source of sodium cation is
sodium hydroxide.
4. The method of claim 1 wherein the amine is methylamine.
5. The method of claim 1 wherein the molar ratio of sources for
silicon oxide to boron oxide is about 5 to about 50 the molar ratio
of water to silicon oxide is about 10 to about 35 and the molar
ratio of methyl amine to silicon oxide is about 1 to about 3.
6. The method of claim 1 wherein the pH of the crystallizing mixture
is maintained between about 10.5 and 13.
7. The method of claim 1 wherein the crystallizing mixture is maintained
at about 125.degree. C. to about 200.degree. C. for about one to
about ten days.
8. The method of claim 1 wherein the molecular sieve is incorporated
within a suitable matrix material.
9. The method of claim 8 wherein the matrix material is silica,
silica-alumina or alumina.
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to a new method to manufacture zeolites
and more particularly to a new method to manufacture crystalline
borosilicate AMS-1B molecular sieve.
Zeolitic materials, both natural and synthetic, are known to have
catalytic capabilities for many hydrocarbon processes. Zeolitic
materials typically are ordered porous crystalline aluminosilicates
having a definite structure with cavities interconnected by channels.
The cavities and channels throughout the crystalline material generally
are uniform in size allowing selective separation of hydrocarbons.
Consequently, these materials in many instances are known in the
art as "molecular sieves" and are used, in addition to
selective adsorptive processes, for certain catalytic properties.
The catalytic properties of these materials are affected to some
extent by the size of the molecules which selectively penetrate
the crystal structure, presumably to contact active catalytic sites
within the ordered structure of these materials.
Generally, the term "molecular sieve" includes a wide
variety of both natural and synthetic positive-ion-containing crystalline
zeolite materials. They generally are characterized as crystalline
alumino-silicates which comprise networks of SiO.sub.4 and AlO.sub.4
tetrahedra in which silicon and aluminum atoms are cross-linked
by sharing of oxygen atoms. The negative framework charge resulting
from substitution of an aluminum atom for a silicon atom is balanced
by positive ions, for example, alkali-metal or alkaline-earth-metal
cations, ammonium ions, or hydrogen ions.
Boron is not considered a replacement for aluminum or silicon in
a zeolite composition. However, recently a new crystalline borosilicate
molecular sieve AMS-1B was disclosed in U.S. Pat. Nos. 4268420
and 4269813 incorporated by reference herein. According to these
patents AMS-1B can be synthesized by crystallizing a source of an
oxide of silicon, an oxide of boron, an oxide of sodium and an organic
template compound such as a tetra-n-propylammonium salt. In order
to form a catalytically-active species of AMS-1B, sodium ion typically
is removed by one or more exchanges with ammonium ion followed by
calcination. Other methods to produce borosilicate molecular sieves
include using a combination of sodium hydroxide and aqueous ammonia
together with an organic template as disclosed in U.S. Pat. No.
4285919 incorporated herein by reference, and using high concentrations
of amine such as hexamethylenediamine as described in German Patent
Application No. 28 30 787. British Patent Application No. 2024790
discloses formation of a borosilicate using ethylenediamine with
sodium hydroxide. Aluminosilicates have been prepared with low sodium
content using diamines containing four or more carbon atoms as described
in European Published Patent Application Nos. 669 and 11 362. U.S.
Pat. Nos. 4139600 and 4151189 describe methods to produce aluminosilicate
sieves containing low sodium using diamines or C.sub.2 -C.sub.5
alkyl amines.
A method to produce AMS-1B crystalline borosilicate molecular sieve
which is low in sodium would be desirable in that an exchange procedure
to remove sodium would be unnecessary. Also a method to produce
AMS-1B crystalline borosilicate having a higher boron content than
usually prepared by conventional techniques would be very advantageous.
SUMMARY OF THE INVENTION
This invention is a method to prepare AMS-1B crystalline borosilicate
molecular sieve comprising reacting under crystallization conditions
an aqueous mixture containing sources for an oxide of silicon, an
oxide of boron, a cation and a lower alkyl primary or secondary
amine.
BRIEF DESCRIPTION OF THE INVENTION
Conventionally, AMS-1B borosilicate molecular sieve is prepared
by crystallizing an aqueous mixture of sources for an oxide of boron,
an oxide of silicon, and an organic template compound in the presence
of an alkali metal hydroxide, usually sodium hydroxide. When such
a mixture is crystallized, the resulting AMS-1B molecular sieve
contains alkali metal, usually sodium, ions to balance the negative
framework charge caused by substitution of a boron atom for silicon
in the crystalline zeolite structure. However, when used for catalytic
purposes, presence of sodium ion usually is detrimental. Typically,
before a catalytic composition is made, the hydrogen form of AMS-1B
is prepared by exchange with ammonium ion followed by drying and
calcination.
This invention is a method of directly crystallizing AMS-1B molecular
sieve having a low sodium content which does not use expensive quatenary
ammonium template compounds which are used in conventional preparations.
Surprisingly, although an alkali metal hydroxide such as sodium
hydroxide is used in the preparation of this invention, the amount
of sodium in the resultant crystalline borosilicate molecular sieve
is low.
In another aspect of this invention, AMS-1B crystalline borosilicate
can be formed having higher boron contents than usually formed using
conventional techniques.
According to this invention, AMS-1B crystalline molecular sieve
is formed by crystallizing an aqueous mixture containing sources
for an oxide of boron, an oxide of silicon, a metal or ammonium
cation and a lower alkyl primary or secondary amine.
Typically, the mole ratios of the various reactants can be varied
to produce the crystalline borosilicates of this invention. Specifically,
the molar ratio of initial reactant concentration of silica to boria
can range from about 2 to about 400 preferably about 4 to about
150 and most preferably about 5 to about 50. The molar ratio of
water to silica can range from about 2 to about 500 preferably
about 5 to about 60 and most preferably about 10 to about 35. It
has been found that preparation using a water to silica molar ratio
of about 10 to about 15 can be especially preferable. The molar
ratio of lower alkylamine to silicon oxide used in the preparation
of AMS-1B crystalline borosilicate according to this invention should
be above about 0.05 typically below about 5 preferably about 0.5
to about 5.0 and most preferably about 1.0 to about 3.0. The molar
ratio of lower alkylamine to source of cation compound useful in
the preparation of this invention can range from 0.01 to about 100
preferably about 0.1 to about 20 and most preferably from about
1.0 to about 10.
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 of the present invention is prepared
by mixing in water (preferably distilled or deionized) lower alkylamine
template compound, a boron oxide source, and a cation source compound.
The order of addition usually is not critical although a typical
procedure is to dissolve boric acid and sodium hydroxide in water
and then add the lower alkylamine template compound. Generally,
the silicon oxide compound is added with intensive mixing such as
that performed in a Waring Blendor. 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 system falls within the range of about 8
to about 13.5 and most preferably between about 10 and about 12.5.
Examples of sources of silicon oxides useful in this invention
include silicic acid, sodium silicate, tetraalkyl silicates and
Ludox, a stabilized polymer of silicic acid manufactured by E. I.
du Pont 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.
Minor amounts of buffer compounds such as ammonium hydrogen phosphate
can be added to the crystallizing mixture.
Organic templates useful in preparing AMS-1B crystalline borosilicate
according to this invention include primary and secondary lower
alkylamines in which the alkyl group contain 1 to 3 carbon atoms,
preferably 1 to 2 carbon atoms. Examples of suitable amines are
methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine
and di-n-propylamine. Secondary alkylamines containing different
lower alkyl groups can be used. Preferable lower alkylamines are
methylamine, dimethylamine, ethylamine and diethylamine.
Useful cations in this invention include alkali- metal and alkaline-earth-metal
cations such as sodium, potassium, calcium and magnesium. Ammonium
cations may be used 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.
In a more detailed description of a typical preparation of this
invention, suitable quantities of lower alkylamine, boric acid (H.sub.3
BO.sub.3) and sodium hydroxide are dissolved in distilled or deionized
water. Preferably, the pH is adjusted between 10 and 13.5 using
a compatible base or acid such as sodium bisulfate or sodium hydroxide.
After sufficient quantities of silicic acid polymer (Ludox) are
added with intensive mixing, preferably the pH is again checked
and adjusted to a range of about 9 to about 14 preferably about
10 to about 13. 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 two 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 amine compound. Especially preferred
conditions are crystallizing at about 145.degree. C. for about two
to about four 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 washing. This material
can be mildly dried for anywhere from a few hours to a few days
at varying temperatures, typically about 25.degree.-200.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 amine 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, mildly dried product is calcined
at temperatures ranging from about 260.degree. to about 850.degree.
C. and preferably about 525.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.
Materials which can enhance or modify catalytic activity can be
incorporated with the crystalline zeolite by ion exchange, impregnation,
a combination thereof, or other suitable contact means. Preferred
replacing cations are those which render the crystalline borosilicate
catalytically more active, especially for hydrocarbon conversion.
Typical catalytically active ions include hydrogen, metal ions of
Groups IB, IIA, IIB, IIIA, 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 hydrogen, metals of
Groups IB, IIA, IIB, IIIA, IVB, VIB, VIIB, and VIII, and rare earth
elements.
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. to about 100.degree. C. 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 such as 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. AMS-1B-based catalyst compositions useful
in xylene isomerization can be prepared by ion exchange with nickelous
nitrate or by impregnation with ammonium molybdate.
The amount of catalytically active material placed on the AMS-1B
borosilicate can vary from less than one weight percent to about
thirty weight percent, typically from about 0.005 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 may
be used as a pure material as a catalyst or adsorbent, or may be
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, alumina sols, hydrated
aluminas, clays such as bentonite or kaoline, 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 typically contain about 2 wt. % to about 65 wt. % of
such material.
Catalytic compositions comprising the crystalline borosilicate
material of this invention and a suitable matrix material can be
formed by adding a finely-divided crystalline borosilicate and a
catalytically active metal compound to an aqueous sol or gel of
the matrix material. The resulting mixture is thoroughly blended
and gelled typically by adding a material such as ammonium hydroxide.
The resulting gel can be dried and calcined to form a composition
in which the crystalline borosilicate and catalytically active metal
compound are distributed throughout the matrix material.
Specific details of catalyst preparations are described in U.S.
Pat. No. 4268420.
The crystalline borosilicates prepared according to this invention
are useful as catalysts for various hydrocarbon conversion processes
and are suitable for chemical adsorption. Some of the hydrocarbon
conversion processes for which the borosilicate appear to have useful
catalytic properties are fluidized catalytic cracking; hydrocracking;
isomerization of normal paraffins and naphthenes; reforming of naphthas
and gasoline-boiling-range feedstocks; isomerization of alkylaromatics,
such as xylenes; disproportionation of aromatics, such as toluene,
to form mixtures of other more valuable products including benzene,
xylene, and other higher methyl substituted benzenes; hydrotreating;
alkylation, including (a) alkylation of benzene with ethylene, ethanol
or other ethyl carbocation precursor to yield ethylbenzene, (b)
alkylation of benzene or toluene with methanol or other methanol
or carbocation precursor to yield xylenes, especially p-xylene,
or pseudocumene, (c) alkylation of benzene with propylene and (d)
alkylation of C.sub.3 to C.sub.5 paraffins with C.sub.5 to C.sub.3
olefins; hydrodealkylation; hydrodesulfurization; and hydrodenitrogenation.
They are particularly suitable for the isomerization of alkylaromatics,
such as xylenes, and for the conversion of ethylbenzene. Such borosilicates,
in certain ion-exchanged forms, can be used to convert alcohols,
such as methanol, to hydrocarbon products, such as aromatics or
olefins, or for hydroformylation and syngas conversion. Borosilicates
prepared according to this invention which have higher boron content
than those prepared according to conventional techniques are useful
particularly in xylene isomerization and conversion of methanol.
This invention is demonstrated but not limited by the following
Examples and Comparative Runs.
EXAMPLES I-V
A series of reaction mixtures were prepared by dissolving a lower
alkylamine, boric acid, sodium hydroxide and ammonium hydrogen phosphate
as a buffer in distilled water. This solution was added to a stirred
colloidal silica solution (Ludox HS-40 40 wt. % SiO.sub.2); stirring
was continued for about five minutes. The resulting mixture was
charged to a 0.3 liter rocking autoclave and digested at an elevated
temperature. After the mixture was crystallized, the resulting product
was filtered, washed with distilled water, dried overnight at 150.degree.
C., and calcined at 540.degree. C. for four hours preceded by a
programmed preheating at a temperature increase of no more than
125.degree. C./hour. The products were analyzed by X-ray diffraction
and elemental analysis. Products characterized as AMS-1B had an
X-ray diffraction pattern similar to that contained in Table I and
elemental analysis showing incorporation of boron. Details of these
preparations and analyses are summarized in Table II.
Some preparations were exchanged with ammonium acetate before calcination.
Such exchanges were performed in a one-liter kettle equipped with
baffles and an air-driven stirrer. Ten to thirty grams of sieve
were reacted with 25 grams of ammonium acetate in 300 milliliters
of water and heated to 100.degree. C. with stirring for 2 to 16
hours. Solids were filtered and washed with hot distilled water.
After one to four such exchanges, the resulting solids were dried
in a vacuum oven at 155.degree. C. before calcination. |