Molecular sieve abstract
A crystalline, gallioaluminosilicate molecular sieve having the
offretite structure is synthesized by mixing a substantially gallia-free
aluminosilicate hydrogel containing a templating or directing agent
with a galliosilicate solultion substantially free of alumina to
form a mixture and then crystallizing the resultant mixture, usually
in 24 hours or less.
Molecular sieve claims
I claim:
1. A process for synthesizing a crystalline, gallioaluminosilicate
molecular sieve having the offretite structure which comprises:
(a) mixing a substantially gallia-free aluminosilicate hydrogel
having the following oxide mole ratios of components
with a galliosilicate solution substantially free of alumina and
dispersed particles, said solution having the following oxide mole
ratios of components
to form a mixture of said hydrogel and said solution, wherein M
is an alkali metal, N is an alkali metal other than M, Q is a cation
derived from an offretite selective templating agent and said mixing
is carried out by adding said galliosilicate solution to said aluminosilicate
hydrogel; and
(b) crystallizing said mixture to form a gallioaluminosilicate
molecular sieve having the offretite structure.
2. A process as defined by claim 1 wherein M is sodium and N is
potassium.
3. A process as defined by claim 2 wherein Q is a quaternary ammonium
cation.
4. A process as defined by claim 3 wherein said quaternary ammonium
cation is selected from the group consisting of a choline cation,
a tetramethylammonium cation, a tetrapropylammonium cation, a tetraethylammonium
cation and a tetrabutylammonium cation.
5. A process as defined by claim 3 wherein Q is a tetramethylammonium
cation.
6. A process as defined by claim 2 wherein said aluminosilicate
hydrogel is formed by dissolving sodium aluminate in an aqueous
solution of sodium hydroxide and potassium hydroxide and adding
a source of silica and said templating agent thereto.
7. A process as defined by claim 2 wherein said galliosilicate
solution is formed by dissolving gallium oxide in an aqueous solution
of sodium hydroxide and adding a source of silica thereto.
8. A process as defined by claim 1 wherein said mixture is crystallized
at a temperature between about 70.degree. C. and 250.degree. C.
9. A process as defined by claim 1 wherein said mixture is crystallized
at a temperature between about 90.degree. C. and 120.degree. C.
10. A process as defined by claim 1 wherein said crystallization
takes place in about 24 hours or less.
11. A process for synthesizing a crystalline, gallioaluminosilicate
molecular sieve having the offretite structure which comprises:
(a) mixing a source of alumina, a source of silica, a source of
potassium, a source of sodium, an offretite selective templating
agent and water to form an aluminosilicate hydrogel substantially
free of gallia, said hydrogel having the following oxide more ratios
of components
where Q is a cation derived from said templating agent;
(b) adding to said hydrogel a galliosilicate solution substantially
free of alumina and dispersed particles, said solution having the
following oxide mole ratios of components
to form a mixture of said solution and said hydrogel containing
between about 1 and 40 weight percent of said galliosilicate solution,
said mixture having the following oxide mole ratios of components
wherein said galliosilicate solution is prepared by mixing a source
of gallia, a source of silica, a source of sodium and water; and
(c) crystallizing said mixture at a temperature below about 250.degree.
C. to form a gallioaluminosilicate molecular sieve having the offretite
structure, wherein said crystallization takes place in less than
about 24 hours.
12. A process as defined by claim 11 wherein said source of gallia
comprises gallium oxide.
13. A process as defined by claim 11 wherein said source of sodium
comprises sodium hydroxide.
14. A process as defined by claim 11 wherein said source of potassium
comprises potassium hydroxide.
15. A process as defined by claim 11 wherein said source of silica
comprises a silica sol.
16. A process as defined by claim 11 wherein said source of alumina
comprises aluminum oxide or sodium aluminate.
17. A process as defined by claim 11 wherein Q is selected from
the group consisting of a quaternary ammonium cation and a protonated
amine.
18. A process as defined by claim 17 wherein said quaternary ammonium
cation is selected from the group consisting of a choline cation,
a tetramethylammonium cation, a tetrapropylammonium cation, a tetraethylammonium
cation and a tetrabutylammonium cation.
19. A process as defined by claim 17 wherein Q is a tetramethylammonium
cation.
20. A process as defined by claim 11 wherein step (c) is carried
out at a temperature between about 90.degree. C. and about 120.degree.
C. and said crystallization is essentially complete in less than
about 14 hours.
21. A process as defined by claim 11 wherein said Na.sub.2 O/Ga.sub.2
O.sub.3 ratio in the galliosilicate solution of step (b) is between
about 8 and about 15.
22. A process as defined by claim 11 wherein the aluminosilicate
hydrogel formed in step (a) has the following oxide mole ratios
of components
23. A process as defined by claim 22 wherein the galliosilicate
solution of step (b) has the following oxide mole ratios of components
24. A process as defined by claim 23 wherein the mixture of said
aluminosilicate hydrogel and said galliosilicate solution has the
following oxide mole ratios of components
25. A process as defined by claim 24 wherein said gallioaluminosilicate
molecular sieve having the offretite structure has the following
composition expressed in terms of oxide mole ratios in the anhydrous
state
wherein a equals 0.5 to 0.99 b equals (1-a), c equals 5.5 to 30
d equals 0.1 to 0.9 z equals 0.1 to 0.9 t equals 0.1 to 0.06 and
d+z+t equals about 1.0.
26. A process as defined by claim 25 wherein c equals 6 to 15.
27. A process for synthesizing a crystalline, gallioaluminosilicate
molecular sieve having the offretite structure which consists essentially
of:
(a) mixing a substantially gallia-free aluminosilicate hydrogel
having the following oxide mole ratios of components
with a galliosilicate solution substantially free of alumina and
dispersed particles, said solution having the following oxide mole
ratios of components
to form a mixture of said hydrogel and said solution, wherein said
mixing is carried out by adding said galliosilicate solution to
said aluminosilicate hydrogel so that said mixture has the following
oxide mole ratios of components
where Q is a quaternary ammonium cation or a protonated amine;
and
(b) crystallizing said mixture at a temperature between about 70.degree.
C. and about 250.degree. c. to form a gallioaluminosilicate molecular
sieve having the offretite structure.
28. A process as defined by claim 27 wherein said gallioaluminosilicate
molecular sieve having the offretite structure has the following
composition expressed in terms of oxide mole ratios in the anhydrous
state
wherein a equals 0.5 to 0.99 b equals (1-a), c equals 5.5 to 30
d equals 1.0 to 0.9 z equals 0.1 to 0.9 t equals 0.1 to 0.6 and
d+z+t equals about 1.0.
29. A process as defined by claim 27 wherein step (b) is carried
out at a temperature between about 90.degree. C. and about 120.degree.
C. for a period of time not exceeding about 24 hours.
30. A process as defined by claim 1 wherein said gallioaluminosilicate
molecular sieve having the offretite structure has the following
composition expressed in terms of oxide mole ratios in the anhydrous
state
wherein a equals 0.5 to 0.99 b equals (1-a), c equals 5.5 to 30
d equals 1.0 to 0.9 z equals 0.1 to 0.9 t equals 0.1 to 0.6 and
d+z+t equals about 1.0.
31. A process as defined by claim 1 wherein a sufficient amount
of said galliosilicate solution is added to said aluminosilicate
hydrogel so that the mixture of said solution and said hydrogel
contains between about 1 and 40 weight percent of said solution.
32. A process as defined by claim 1 wherein the crystallization
of said gallioaluminosilicate molecular sieve in step (b) is essentially
complete in less than about 18 hours.
33. A process as defined by claim 11 wherein the SiO.sub.2 /(Al.sub.2
O.sub.3 +Ga.sub.2 O.sub.3) mole ratio in the mixture of said galliosilicate
solution and said aluminosilicate hydrogel equals 8 to 15.
34. A process as defined by claim 11 wherein the SiO.sub.2 /(Al.sub.2
O.sub.3 +Ga.sub.2 O.sub.3) mole ratio in the mixture of said galliosilicate
solution and said aluminosilicate hydrogel equals 8 to 11.
35. A process as defined by claim 27 wherein the crystallization
of said gallioaluminosilicate molecular sieve in step (b) is essentially
complete in less than about 24 hours.
36. A process as defined by claim 27 wherein a sufficient amount
of said galliosilicate solution is added to said aluminosilicate
hydrogel so that the mixture of said solution and said hydrogel
contains between about 1 and 40 weight percent of said solution.
37. A process as defined by claim 1 wherein said crystalline, gallioaluminosilicate
molecular sieve contains between about 13 and 17 weight percent
alumina.
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to crystalline molecular sieves containing
both aluminum and gallium and is particularly concerned with a method
for synthesizing a crystalline gallioaluminosilicate having the
offretite structure.
Zeolites are well known natural and synthetic molecular sieves
that can be defined as crystalline, three-dimensional aluminosilicates
consisting essentially of alumina and silica tetrahedra which interlock
to form discrete polyhedra. The polyhedra are interconnected to
form a framework which encloses cavities or voids that are interconnected
by channels or pores. The size of the cavities and pores will vary
depending on the framework structure of the particular zeolite.
Normally, the cavities are large enough to accommodate water molecules
and large cations which have considerable freedom of movement, thereby
permitting sorption, reversible dehydration and ion exchange. The
dimensions of the cavities and pores in a zeolite are limited to
a small number of values and can vary from structure to structure.
Thus, a particular zeolite is capable of sorbing molecules of certain
dimension while rejecting those of dimensions larger than the pore
size associated with the zeolite structure. Because of this property
zeolites are commonly used as molecular sieves.
In addition to their molecular sieving properties, zeolites show
a pronounced selectivity toward polar molecules and molecules with
high quadrupole moments. This is due to the ionic nature of the
crystals which gives rise to a high nonuniform electric field within
the micropores of the zeolite. Molecules which can interact energetically
with this field, such as polar or quadrupolar molecules, are therefore
sorbed more strongly than nonpolar molecules. This selectivity toward
polar molecules is the unique property of zeolites which allows
them to be used as drying agents and selective sorbents.
The pore size of a zeolite can vary from about 2.6 Angstroms for
analcime to about 10.0 Angstroms for zeolite omega. The term "pore
size" as used herein refers to the diameter of the largest
molecule that can be sorbed by the particular zeolite or other molecular
sieve in question. The measurement of such diameters and pore sizes
is discussed more fully in chapter 8 of the book entitled "Zeolite
Molecular Sieves," written by D. W. Breck and published by
John Wiley & Sons in 1974 the disclosure of which book is hereby
incorporated by reference in its entirety. The pore size range of
2.6 to 10.0 Angstroms is particularly suited for molecular separation
and catalytic processing. Analcime will sorb ammonia while excluding
larger molecules whereas zeolite omega will sorb perfluorotributyl
amine [(C.sub.4 F.sub.9).sub.3 N] while excluding any molecule having
a diameter greater than about 10.0 Angstroms. All of the other approximately
150 zeolites now known have pore sizes falling within the range
between 2.6 and 10.0 Angstroms.
In addition to their use as drying agents and selective sorbents,
zeolites are widely used as components of chemical conversion catalysts.
As found in nature or as synthesized, zeolites are typically inactive
because they lack acid sites. In general, acid sites are created
by subjecting the zeolite to an ion exchange with ammonium ions
followed by some type of thermal treatment which creates acid sites
by decomposing the ammonium ions into gaseous ammonia and protons.
Activated zeolites have been used in many types of chemical conversion
processes with the smaller pore zeolites being used to selectively
sorb and crack normal and moderately branched chain paraffins.
Because of the unique properties of zeolitic molecular sieves,
there have been many attempts at synthesizing new molecular sieves
by either substituting an element for the aluminum or silicon present
in zeolitic molecular sieves or adding another element in addition
to the aluminum and silicon. The term "zeolite" or "zeolitic"
as used herein refers to molecular sieves whose frameworks are formed
of substantially only silicon and aluminum atoms in tetrahedral
coordination with oxygen atoms. One such class of new molecular
sieves that has been created is that in which a portion of the framework
aluminum has been replaced by gallium. Specifically, it has been
reported in Canadian Patent No. 1182096 that gallioaluminosilicate
molecular sieves having a structure similar to that of offretite
have been synthesized. The synthesis process, as illustrated in
Examples 1 through 3 of the patent, involves mixing a colloidal
silica gel with gallium (III) oxide, sodium hydroxide, potassium
hydroxide, sodium aluminate or aluminum hydroxide, water and tetramethylammonium
chloride to form a mixture which is stirred and then heated in a
closed vessel at 95.degree. C. or above. According to the examples,
crystallization times ranged between 72 and 120 hours. Although
such times are not excessive, shorter crystallization times will
result in substantial savings in the energy required for crystallization.
Accordingly, it is one of the objects of the present invention
to provide a relatively simple and rapid process for synthesizing
a crystalline, gallioaluminosilicate molecular sieve having the
offretite structure, which sieve may be useful in many types of
chemical conversion processes, particularly hydrocarbon conversion
processes. This and other objects of the invention will become more
apparent in view of the following description of the invention.
SUMMARY OF THE INVENTION
In accordance with the invention it has now been found that a crystalline,
gallioaluminosilicate molecular sieve comprising silicon, aluminum,
gallium and oxygen and having the offretite crystal structure can
be synthesized by mixing a source of alumina, a source of silica,
a source of one alkali metal, a source of a different alkali metal,
an offretite selective templating or directing agent and water to
form a hydrogel substantially free of gallia in which the components
have the following oxide mole ratios:
where M is an alkali metal, N is an alkali metal other than M and
Q is a cation derived from the templating agent. After the above-described
hydrogel is formed, it is mixed with a galliosilicate solution substantially
free of alumina prepared by mixing a source of gallia, a source
of silica, a source of one of the alkali metals used to form the
aluminosilicate hydrogel and water. The mole ratio of alkali metal
oxide-to-gallia in the galliosilicate solution is sufficiently large
to prevent gel formation, or, if a gel does form, to facilitate
dissolution of the gel upon vigorous stirring. The components comprising
the solution are typically present in the following oxide mole ratios:
After the alumina-free solution is added to the gallia-free aluminosilicate
hydrogel, the mixture is crystallized, normally with gentle agitation,
at a temperature below about 250.degree. C., preferably below 150.degree.
C., to form a crystalline, gallioaluminosilicate molecular sieve
having the offretite structure. This molecular sieve typically has
the composition, expressed in terms of oxide mole ratios in the
anhydrous state, of:
where a equals 0.5 to 0.99 b equals (1-a), c equals 5.5 to 30
d equals 0.1 to 0.9 z equals 0.1 to 0.9 t equals 0.1 to 0.6 and
z+d+t equals about 1.0. The X-ray powder diffraction pattern of
the molecular sieve contains at least the d-spacings set forth in
Table 1 below, which d-spacings are characteristic of a zeolite
with the offretite structure.
In a preferred gallioaluminosilicate molecular sieve, M is sodium,
N is potassium, and Q is a quaternary ammonium cation.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 in the drawing shows the X-ray powder diffraction pattern
of a zeolite with the offretite structure; and
FIG. 2 depicts the X-ray powder diffraction pattern of a molecular
sieve synthesized in accordance with the process of the invention
as exemplified in Example 1.
DETAILED DESCRIPTION OF THE INVENTION
A crystalline, gallioaluminosilicate molecular sieve having the
offretite structure is prepared by crystallizing a mixture of an
aluminosilicate hydrogel and a galliosilicate solution essentially
free of alumina and particulates. The aluminosilicate hydrogel is
formed separately from the galliosilicate solution by mixing a source
of alumina, a source of silica, a source of two different alkali
metals and an offretite selective templating agent with water under
conditions such that the various components react to form the desired
hydrogel. The galliosilicate solution is formed by mixing a source
of gallia, a source of silica and a source of one of the alkali
metals used to form the aluminosilicate hydrogel with water in the
absence of an organic templating or directing agent to form the
desired solution. The gallioaluminosilicate molecular sieve formed
upon crystallization of the mixture will normally contain between
about 10 weight percent and about 20 weight percent alumina, preferably
between about 13 and 17 weight percent, and between about 0.5 weight
percent and about 10.0 weight percent gallia, preferably between
about 1.0 and 6.0 weight percent.
The silica used in forming the aluminosilicate hydrogel and the
galliosilicate solution may be in the form of sodium silicate, silica
hydrosols, silica gels, silica salts, silicic acid sols, silicic
acid gels, aerosils, organic silica salts such as tetramethylammonium
silicate and methyltriethoxysilane, and reactive amorphous solid
silicas. The source of the silica can be in either the liquid or
solid state. Examples of reactive, amorphous solid silicas that
may be used include fumed silicas, chemically precipitated silicas,
and precipitated silica sols usually having a particle size of less
than 1 micron in diameter. The preferable sources of silica are
sodium silicates (water glass) and aqueous colloidal dispersions
of silica particles.
The alumina used to produce the aluminosilicate hydrogel may be
in the form of aluminum oxide with or without waters of hydration,
aluminum hydroxide, an inorganic aluminum salt such as aluminum
nitrate, sulfate, chloride or acetate, sodium aluminate or aluminum
alkoxydes. The use of sodium aluminate is normally preferred.
The source of alkali metals used in forming the aluminosilicate
hydrogel and the galliosilicate solution may be any alkali metal
salt or hydroxide. Although any combination of two different alkali
metal sources may be utilized in forming the hydrogel, it is preferable
that a source of sodium and a source of potassium be employed. A
source of one of the alkali metals used to form the hydrogel is
normally used to prepare the galliosilicate solution with a source
of sodium being preferred. It is possible for the source of alkali
metal used to prepare the galliosilicate solution to also be the
source of gallia utilized to form the solution. Alkali metal gallates
are examples of materials which serve as a source of both an alkali
metal and gallia.
The gallia used to produce the galliosilicate solution may be in
the form of gallium oxide, gallium hydroxide, an alkali metal gallate
or an inorganic gallium salt, such as gallium nitrate, gallium sulfate,
or gallium acetate. As mentioned above, the source of the gallia
may also be the source of the alkali metal required to form the
galliosilicate solution. In fact, a preferred source of gallia is
prepared by dissolving gallium oxide in an aqueous solution of sodium
hydroxide to form sodium gallate which is then used as a component
to form the galliosilicate solution.
The templating agent used to form the aluminosilicate hydrogel
is normally any organic compound which, when in solution, yields
cations, such as quaternary ammonium cations and protonated amines,
that direct crystallization of the hydrogel toward the offretite
structure, i.e., are offretite selective. Typically, the templating
agent is either an amine or a quaternary ammonium compound. Examples
of amines useful as the templating agent include ethylene diamine,
diethyl triamine, triethylene tetraamine, and alkanolamines. The
preferred templating agents are quaternary ammonium compounds, such
as tetramethyl, tetrapropyl, tetraethyl or tetrabutylammonium halide
or hydroxide, choline chloride, and benzyltrimethylammonium chloride
or hydroxide. The most preferred templating agents for use in making
the aluminosilicate hydrogel of the invention are tetramethylammonium
halides.
The aluminosilicate hydrogel used to form the mixture from which
the gallioaluminosilicate molecular sieve having the offretite structure
is crystallized is normally prepared first dissolving the source
of alumina in a solution containing a mixture of two alkali metal
hydroxides, preferably potassium and sodium hydroxide. The resulting
solution is then mixed with an offretite selective templating agent
and a source of silica to form the gel which is then vigorously
stirred. A sufficient amount of the alumina source, the silica source,
the sources of alkali metals, the templating agent and water is
used so that the resultant hydrogel contains the following oxide
mole ratios of components:
where M is an alkali metal, preferably sodium, N is another alkali
metal, preferably potassium, and Q is a cation derived from the
templating agent, preferably a quaternary ammonium cation.
The galliosilicate solution that is added to the hydrogel to form
the crystallization mixture is substantially free of alumina and
dispersed particles and is typically prepared by dissolving a source
of gallia in an aqueous alkali metal hydroxide and mixing the resulting
solution with a silica source. A sufficient amount of the gallia
source, the silica source, the alkali metal source and water is
used so that the resultant mixture contains the following oxide
mole ratios of components:
Generally, a sufficient amount of the alkali metal source is used
so that the alkali metal/gallia ratio is such that a gel is not
formed when the components are mixed together or, if a gel is formed
upon the mixing of the components, it can be forced into solution
by stirring at ambient temperature.
After the aluminosilicate hydrogel and the galliosilicate solution
have been separately prepared, a sufficient amount of the solution
is added to the hydrogel so that the resultant mixture, which remains
in a gel form, contains between about 1 and about 40 weight percent
of the solution, preferably between about 10 and 30 weight percent.
Normally, the oxide mole ratios of components in the resultant mixture
will fall within the following ranges:
The mixture is then stirred at atmospheric pressure and at a temperature
between about 20.degree. C. and about 60.degree. C., preferably
at about ambient temperature, for from about 1 hour to about 2 days,
preferably between about 1 hour and about 10 hours. After stirring,
the mixture is crystallized by heating, with or without stirring
or agitation, for between about 8 hours and 48 hours, usually in
less than about 24 hours and preferably in less than about 15 hours,
at a temperature in the range between about 70.degree. C. and 250.degree.
C., preferably between about 90.degree. C. and 175.degree. C., and
most preferably between about 90.degree. C. and 120.degree. C. The
temperature is normally controlled within the above ranges to avoid
the formation of phase impurities. After the hydrogel has been crystallized,
the resulting slurry is passed to a filter, centrifuge or other
separation device to remove the excess reactants or mother liquor
from the crystallized molecular sieve. The crystals are then washed
with water and dried at a temperature between about 50.degree. C.
and about 200.degree. C. to remove surface water.
The water content of the crystalline, gallioaluminosilicate molecular
sieve will depend on the method used for drying the particles formed
upon crystallization. The amount of cations derived from the templating
agent present in the dried molecular sieve will depend upon the
silica-to-(gallia+alumina) mole ratio and the alkali metal content
of the gallioaluminosilicate crystals. In general, the moles t of
Q.sub.2 O present, as shown in formula (1) above, will equal about
1.0 minus the sum of the moles of the two different alkali metal
oxides present, z+d.
After the synthesized gallioaluminosilicate crystals have been
washed and dried, they are typically treated in order to render
them active for acid catalyzed reactions. This procedure normally
comprises calcining the washed and dried crystals in air at a temperature
between about 400.degree. C. and about 700.degree. C., preferably
between about 500.degree. C. and about 600.degree. C., for between
about 5 hours and about 15 hours to decompose the cations derived
from the templating agent into gaseous products. After this calcination,
the gallioaluminosilicate molecular sieve is exchanged with ammonium
ions, hydrogen ions, polyvalent cations such as rare earth-containing
cations, magnesium cations or calcium cations, or a combination
of ammonium ions, hydrogen ions, and polyvalent cations, thereby
lowering the sodium content to below about 2.0 weight percent, preferably
below about 1.0 weight percent and most preferably below about 0.05
weight percent, calculated as Na.sub.2 0. When reducing the sodium
content using an ammonium ion exchange technique, the molecular
sieve is typically slurried for 1 to 5 hours at a temperature above
ambient temperature but less than about 100.degree. C. in an aqueous
solution containing a dissolved ammonium salt, such as ammonium
nitrate, ammonium sulfate, ammonium chloride and the like. Ordinarily,
to achieve extremely low levels of alkali metal cations, the ion
exchange procedure will be repeated at least twice, and occasionally
several times. After the ammonium exchange or other treatment to
reduce alkali metal content, the molecular sieve is again calcined
in air, preferably at a temperature between about 350.degree. C.
and 550.degree. C. to decompose the ammonium cations into ammonia,
which is driven off during the calcination step, and thereby produce
the catalytically active hydrogen form of the gallioaluminosilicate
molecular sieve.
A crystalline, gallioaluminosilicate molecular sieve produced in
accordance with the process of the invention and activated as described
above may be used as a component of a catalyst for converting hydrocarbons
and other organic compounds into more valuable reaction products
by acid catalyzed reactions, such as alkylation, transalkylation,
dealkylation, isomerization, dehydrocyclization, dehydrogenation,
hydrogenation, cracking, hydrocracking, dewaxing, hydrodewaxing,
oligomerization, aromatization, alcohol conversion reactions, the
conversion of syngas to mixtures of hydrocarbons and the like. A
preferred oligomerization reaction in which a catalyst containing
such a sieve may be used is the conversion of low molecular weight
olefins into cycloparaffins and/or aromatic compounds.
In utilizing a gallioaluminosilicate molecular sieve produced in
accordance with the process of the invention as a catalyst component
in conversion processes as described above, it will normally be
combined with a porous, inorganic refractory oxide component, or
a precursor thereof, such as alumina, silica, titania, magnesia,
zirconia, beryllia, silica-alumina, silica- magnesia, silica-titania,
a dispersion of silica-alumina in gamma alumina, a clay such as
kaolin, hectorite, sepiolite or attapulgite, combinations of the
above and the like. The preferred porous, inorganic refractory oxide
component will depend upon the particular conversion process involved
and will be well known to those skilled in the art. Examples of
precursors that may be used include peptized alumina, alumina gels,
hydrated alumina, silica-alumina gels, hydrogels, Ziegler-derived
aluminas and silica sols. The exact amounts of crystalline gallioaluminosilicate
and porous, inorganic refractory oxide used in the catalyst will
again depend upon the particular conversion process in which the
catalyst is to be used.
It will be understood that, although the primary use of the catalyst
of the invention will be in hydrocarbon conversion processes to
convert hydrocarbon feedstocks into desirable reaction products,
the catalyst can also be used to convert feedstocks or organic compounds
other than hydrocarbons into desired reaction products. For example,
the catalyst can be used to convert alcohols into transportation
fuels and to convert gaseous mixtures of carbon monoxide and hydrogen
into hydrocarbons.
Depending on the particular type of conversion process in which
the catalyst containing a gallioaluminosilicate molecular sieve
with the offretite structure is to be used, it may be desirable
that the catalyst also contain a metal promoter or combination of
metal promoters selected from Group IB, Group IIB, Group IIIA, Group
IVA, Group VA, Group VIB, Group VIIB and Group VIII of the Periodic
Table of Elements. As used herein "Periodic Table of Elements"
refers to the version found in the inside front cover of the "Handbook
of Chemistry and Physics," 65th edition, published in 1984
by the Chemical Rubber Company, Cleveland, Ohio. Specific metal
components which may be used as promoters include components of
copper, silver, zinc, aluminum, gallium, indium, thallium, lead,
tin, antimony, bismuth, chromium, molybdenum, tungsten, manganese,
iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum,
rhenium, thorium and the rare earths. These metal promoters may
be ion exchanged into the crystalline gallioaluminosilicate itself,
they may be incorporated into the mixture of the crystalline gallioaluminosilicate
and the porous, inorganic refractory oxide, or they may be added
by impregnation after the catalyst particles have been formed.
The catalyst is normally prepared by mulling the activated form
of the crystalline gallioaluminosilicate molecular sieve produced
in accordance with the process of the invention with the porous,
inorganic refractory oxide component. If desired, a binder such
as peptized Catapal alumina may be incorporated into the mulling
mixture, as also may be one or more active promoter metal precursors.
After mulling, the mixture is extruded through a die having openings
of a cross sectional size and shape desired in the final catalyst
particles. For example, the die may have circular openings to produce
cylindrical extrudates, openings in the shape of three-leaf clovers
so as to produce an extrudate material similar to that shown in
FIGS. 8 and 8A of U.S. Pat. No. 4028227 the disclosure of which
is hereby incorporated by reference in its entirety, or openings
in the shape of four-leaf clovers. Among preferred shapes for the
die openings are those that result in particles having surface-to-volume
ratios greater than about 100 reciprocal inches. If the die opening
is not circular in shape, it is normally desirable that the opening
be in a shape such that the surface-to-volume ratio of the extruded
particles is greater than that of a cylinder. After extrusion, the
extruded catalyst particles are broken into lengths of from 1/16
to 1/2 inch and calcined in air at a temperature of at least 750.degree.
F., usually between about 800.degree. F. and about 1200.degree.
F., and preferably in the range between about 900.degree. F. and
1050.degree. F.
As mentioned previously, metal promoter components may be mulled,
either as a solid or liquid, with a gallioaluminosilicate prepared
in accordance with the process of the invention and the porous,
inorganic refractory oxide component to form the catalyst extrudates
prior to the calcination step. Alternatively, the metal promoter
component or components may be added to the catalyst by impregnation
after the calcination step. The metal promoter component or components
may be impregnated into the calcined extrudates from a liquid solution
containing the desired metal promoter component or components in
dissolved form. In some cases, it may be desirable to ion exchange
the calcined extrudates with ammonium ions prior to adding the metal
promoter component or components. After the calcined extrudates
have been impregnated with the solution containing the metal promoter
component or components, the particles are dried and calcined in
the air at a temperature normally ranging between about 800.degree.
F. and about 1100.degree. F. to produce the finished catalyst particles.
In addition to the crystalline, gallioaluminosilicate molecular
sieve having the offretite structure, the catalyst may also contain
other molecular sieves such as aluminosilicates, borosilicates,
aluminophosphates, silicoaluminophosphates, naturally occurring
zeolites, pillared clays and delaminated clays. Suitable aluminosilicates
for combining with the crystalline gallioaluminosilicate include
Y zeolites, ultrastable Y zeolites, X zeolites, zeolite beta, zeolite
L, faujasite and zeolite omega. The actual molecular sieve used
in combination with the crystalline gallioaluminosilicate will depend
upon the particular conversion process in which the resultant catalyst
is to be used. The molecular sieve of choice is normally incorporated
into the catalyst by mixing the molecular sieve with a crystalline
gallioaluminosilicate and porous, inorganic refractory oxide prior
to mulling and extrusion.
It is typically preferred to use catalysts containing the crystalline
gallioaluminosilicate molecular sieve synthesized in accordance
with the process of the invention as a cracking or oligomerization
catalyst in the absence of added hydrogen or in hydroconversion
processes such as hydrocracking, isomerization and hydrodewaxing.
When used in hydroconversion processes, the catalyst will normally
contain hydrogenation components comprising metals selected from
Group VIII and/or Group VIB of the Periodic Table of Elements. These
hydrogenation metal components are incorporated into the catalyst
extrudates either prior to or after extrusion. Examples of Group
VIII and Group VIB metal components that may be used include nickel,
cobalt, tungsten, molybdenum, palladium and platinum components.
In some cases, it may be desirable that the catalyst contain at
least one Group VIII metal component and at least one Group VIB
metal component. When this is the case, the preferred combination
is a nickel and/or cobalt component with a molybdenum and/or tungsten
component.
If the hydrogenation metal component consists essentially of one
or more noble metals such as platinum or palladium or compounds
thereof, it is generally desired that the finished catalyst particles
contain between about 0.05 and about 10 weight percent of the hydrogenation
metal component, preferably between about 0.10 weight percent and
about 3.0 weight percent, calculated as the metal. If on the other
hand, the hydrogenation metal component consists essentially of
one or more non-noble metals, such as nickel or nickel and tungsten
or compounds thereof, it is normally desired that the finished catalyst
particles contain between about 1.0 and about 40 weight percent
of the hydrogenation metal components, preferably between about
3 weight percent and about 30 weight percent, calculated as the
metal oxide.
Feedstocks that may be subjected to hydroconversion processes using
a catalyst containing a gallioaluminosilicate synthesized in accordance
with the process of the invention include mineral oils, synthetic
oils, such as shale oil, oil derived from tar sands and coal liquids,
and the like. Examples of appropriate feedstocks for hydroconversion
processes include straight run gas oils, vacuum gas oils and catalytic
cracker distillates. Preferred hydroconversion feedstocks include
gas oils and other hydrocarbon fractions having at least about 50
weight percent of their components boiling above about 700.degree.
F.
In general, the temperature at which the hydroconversion process
takes place is between about 450.degree. F. and about 850.degree.
F., preferably between about 600.degree. F. and about 800.degree.
F. The pressure will normally range between about 750 and about
3500 p.s.i.g., preferably between about 1000 and about 3000 p.s.i.g.
The liquid hourly space velocity (LHSV) is typically between about
0.3 and about 5.0 reciprocal hours, preferably between about 0.5
and about 3.0 reciprocal hours. The ratio of hydrogen gas to feedstock
utilized will usually range between about 1000 and about 10000
scf/bbl, preferably between about 2000 and about 8000 scf/bbl as
measured at 60.degree. F. and one atmosphere.
Since a crystalline, gallioaluminosilicate molecular sieve produced
in accordance with the process of the invention has the offretite
structure, its pore size will be about 6.0 Angstroms, a pore size
which makes such a gallioaluminosilicate particularly suited for
use as a component of a catalyst employed in dewaxing or hydrodewaxing
processes. Dewaxing and hydrodewaxing differ from hydrocracking
in that these processes involve the selective cracking of molecules
and produce a product having a boiling point range similar to that
of the feedstock because essentially only the straight and slightly
branched chain paraffin molecules in the feedstock are cracked while
essentially all the highly branched chain paraffins, aromatic and
cyclic molecules in the feedstock remain unchanged. Hydrocracking,
on the other hand, involves the indiscriminate or nonselective cracking
of molecules in the presence of added hydrogen and always results
in a product having a boiling point range significantly different
from that of the feedstock because a substantial proportion of all
types of molecules comprising the feedstock are converted into lower
boiling components. Hydrodewaxing differs from dewaxing in that
the former is carried out in the presence of added hydrogen while
the latter is not. When catalysts containing a crystalline gallioaluminosilicate
with the offretite structure are used in dewaxing or hydrodewaxing
processes, the boiling point of the effluent from the dewaxing or
hydrodewaxing zone will be approximately the same as the boiling
point of the feedstock. In the case of maximum conversion in the
dewaxing or hydrodewaxing zone, the boiling point of the effluent
will be no more than about 20.degree. F. lower than that of the
feedstock.
The nature and objects of the invention are further illustrated
by the following examples, which are provided for illustrative purposes
only and not to limit the invention as defined by claims. The examples
demonstrate a simple and rapid method of synthesizing a crystalline
gallioaluminosilicate molecular sieve with the offretite structure
and illustrate that the amount of gallia in the sieve can be controlled
by the amount of gallia used in the hydrogel from which the sieve
is crystallized. |