Molecular sieve abstract
A crystalline material substantially free of framework phosphorus
and comprising a CHA framework type molecular sieve with stacking
faults or at least one intergrown phase of a CHA framework type
molecular sieve and an AEI framework type molecular sieve, wherein
said material, in its calcined, anhydrous form, has a composition
involving the molar relationship: (n)X.sub.2O.sub.3:YO.sub.2 wherein
X is a trivalent element; Y is a tetravalent element; and n is from
0 to about 0.5. The material exhibits activity and selectivity in
the conversion of methanol to lower olefins, especially ethylene
and propylene.
Molecular sieve claims
We claim:
1. A crystalline material substantially free of framework phosphorus
and comprising a CHA framework type molecular sieve with stacking
faults or at least one intergrown phase of a CHA framework type
molecular sieve and an AEI framework type molecular sieve, wherein
said material, in its calcined, anhydrous form, has a composition
involving the molar relationship: (n)X.sub.2O.sub.3:YO.sub.2 wherein
X is a trivalent element; Y is a tetravalent element; and n is from
0 to about 0.5.
2. The crystalline material of claim 1 wherein n is from about
0.001 to about 0.1.
3. The crystalline material of claim 1 wherein n is from about
0.0017 to about 0.02.
4. The crystalline material of claim 1 wherein said material, in
its calcined form, contains from about 1 to about 100 ppm by weight
of a halide.
5. The crystalline material of claim 1 wherein said material, in
its calcined form, contains from about 5 to about 50 ppm by weight
of a halide.
6. The crystalline material of claim 1 wherein said material, in
its calcined form, contains from about 10 to about 20 ppm, by weight
of a halide.
7. The crystalline material of claim 4 wherein said halide comprises
fluoride.
8. The crystalline material of claim 1 wherein Y is silicon, tin,
titanium germanium or a combination thereof.
9. The crystalline material of claim 1 wherein Y is silicon.
10. The crystalline material of claim 1 wherein X is aluminum,
boron, iron, indium, gallium or a combination thereof.
11. The crystalline material of claim 1 wherein X is aluminum.
12. A crystalline material which comprises at least a CHA framework
type molecular sieve and which, in its as-synthesized form, contains
in its intra-molecular framework a first directing agent for directing
the synthesis of a CHA framework-type molecular sieve and a second
directing agent for directing the synthesis of a AEI framework-type
molecular sieve, said first and second directing agents being different
and the first directing agent comprising a multi-cyclic amine or
ammonium compound.
13. The crystalline material of claim 12 wherein the first directing
agent comprises a tricyclic or tetracyclic amine or ammonium compound.
14. The crystalline material of claim 12 wherein the first directing
agent comprises at least one of an N-alkyl-3-quinuclidinol, an N,N,N-trialkyl-exoaminonorbornane,
an N,N,N-trimethyl-1-adamantammonium compound, an N,N,N-trimethyl-2-adamantammonium
compound, an N,N,N-trimethylcyclohexylammonium compound, an N,N-dimethyl-33-dimethylpiperidinium
compound, an N,N-methylethyl-33-dimethylpiperidinium compound,
an N,N-dimethyl-2-methylpiperidinium compound, a 13366-pentamethyl-6-azonio-bicyclo(3.2.1)octane
compound and N,N-dimethylcyclohexylamine.
15. The crystalline material of claim 12 wherein the first directing
agent comprises an N,N,N-trimethyl-1-adamantylammonium compound.
16. The crystalline material of claim 12 wherein the second directing
agent comprises a monocyclic amine or ammonium compound.
17. The crystalline material of claim 12 wherein the second directing
agent comprises a substituted piperidine or piperidinium compound.
18. The crystalline material of claim 12 wherein the second directing
agent comprises a tetraalkylpiperidinium compound.
19. The crystalline material of claim 12 wherein the second directing
agent comprises an N,N-dimethyl-26-dimethylpiperidinium compound
or an N,N-diethyl-26-dimethylpiperidinium compound.
20. The crystalline material of claim 12 wherein the molar amount
of second directing agent retained in the as-synthesized material
to the total molar amount of first and second directing agents retained
in the as-synthesized material is between 0.1 and 0.3.
21. The crystalline material of claim 12 wherein said material
is substantially free of framework phosphorus.
22. A method of synthesizing a crystalline material comprising
a CHA framework type molecular sieve and having a composition involving
the molar relationship: (n)X.sub.2O.sub.3:YO.sub.2 wherein X is
a trivalent element; Y is a tetravalent element; and n is from 0
to about 0.5 the method comprising: (a) preparing a reaction mixture
capable of forming said material, said mixture comprising a source
of water, a source of an oxide of a tetravalent element Y and optionally
a source of an oxide of a trivalent element X; (b) maintaining said
reaction mixture under conditions sufficient to form crystals of
said crystalline material comprising stacking faults or at least
one intergrown phase of a CHA framework type molecular sieve and
an AEI framework type molecular sieve; and (c) recovering said crystalline
material from (b).
23. The method of claim 22 wherein said reaction mixture also comprises
at least one organic directing agent (R) for directing the formation
of said crystalline material.
24. The method of claim 22 wherein said reaction mixture also comprises
a plurality of different organic directing agents for directing
the formation of said crystalline material.
25. The method of claim 22 wherein said reaction mixture comprises
at least one first organic directing agent for directing the formation
of a CHA framework type material and at least one second organic
directing agent for directing the formation of an AEI framework
type material.
26. The method of claim 25 wherein the first directing agent comprises
a multi-cyclic amine or ammonium compound.
27. The method of claim 25 wherein the first directing agent comprises
a tricyclic or tetracyclic amine or ammonium compound.
28. The method of claim 25 wherein the first directing agent comprises
at least one of an N-alkyl-3-quinuclidinol, an N,N,N-trialkyl-exoaminonorbornane,
an N,N,N-trimethyl-1-adamantammonium compound, an N,N,N-trimethyl-2-adamantammonium
compound, an N,N,N-trimethylcyclohexylammonium compound, an N,N-dimethyl-33-dimethylpiperidinium
compound, an N,N-methylethyl-33-dimethylpiperidinium compound,
an N,N-dimethyl-2-methylpiperidinium compound, a 13366-pentamethyl-6-azonio-bicyclo(3.2.1)octane
compound and N,N-dimethylcyclohexylamine.
29. The method of claim 25 wherein the first directing agent comprises
an N,N,N-trimethyl-1-adamantylammonium compound.
30. The method of claim 25 wherein the second directing agent
comprises a monocyclic amine or ammonium compound.
31. The method of claim 25 wherein the second directing agent
comprises a substituted piperidine or piperidinium compound.
32. The method of claim 25 wherein the second directing agent
comprises a tetraalkylpiperidinium compound.
33. The method of claim 25 wherein the second directing agent
comprises an N,N-dimethyl-26-dimethylpiperidinium compound or an
N,N-diethyl-26-dimethylpiperidinium compound.
34. The method of claim 25 wherein the molar ratio of the first
organic directing agent to the second organic directing agent in
the reaction mixture is between about 0.01 and about 100.
35. The method of claim 22 wherein said reaction mixture also
comprises a halide or a halide-containing compound.
36. The method of claim 22 wherein said reaction mixture also
comprises a fluoride or fluoride-containing compound.
37. The method of claim 22 wherein the conditions in (b) include
a temperature of from about 50.degree. C. to about 300.degree. C.
38. The method of claim 22 wherein the conditions in (b) include
a temperature of from about 135.degree. C. to about 185.degree.
C.
39. The method of claim 22 wherein said reaction mixture also
comprises seed crystals.
40. The method of claim 39 wherein said seed crystals are added
to said reaction mixture as a colloidal suspension in a liquid medium.
41. The method of claim 39 wherein said seed crystals are homostructural
with said crystalline material comprising at least one intergrown
phase of a CHA framework type and an AEI framework type.
42. The method of claim 39 wherein said seed crystals comprise
a crystalline material having an AEI, OFF, CHA or LEV framework-type.
43. The method of claim 39 wherein said seed crystals comprise
a crystalline material having an AEI framework type.
44. The method of claim 23 wherein said reaction mixture has the
following molar composition: TABLE-US-00009 H.sub.2O/YO.sub.2 0.1
to 20 Halide/YO.sub.2 0 to 2 R/YO.sub.2 0.01 to 2; X.sub.2O.sub.3/YO.sub.2
0 to 0.5.
45. The method of claim 23 wherein said reaction mixture has the
following molar composition: TABLE-US-00010 H.sub.2O/YO.sub.2 2
to 10; Halide/YO.sub.2 0.01 to 1; R/YO.sub.2 0.1 to 1; X.sub.2O.sub.3/YO.sub.2
0 to 0.1.
46. A method of synthesizing a crystalline material comprising
at least a CHA framework type molecular sieve and comprising YO.sub.2
wherein Y is a tetravalent element, and optionally X.sub.2O.sub.3
wherein X is a trivalent element, the method comprising: (a) preparing
a reaction mixture comprising a source of water, a source of the
tetravalent clement Y, optionally a source of the trivalent element
X, and an organic directing agent (R) comprising at least one first
organic directing agent for directing the formation of a CHA framework
type material and at least one second organic directing agent for
directing the formation of an AEI structure type material, said
first and second directing agents being different and the first
directing agent comprising a multi-cyclic amine or ammonium compound;
(b) maintaining said reaction mixture under conditions sufficient
to form crystals of said material; and (c) recovering said crystalline
material from step (b).
47. The method of claim 46 wherein the crystalline material comprises
a composition involving the molar relationship: (n)X.sub.2O.sub.3:YO.sub.2
wherein n is from 0 to about 0.5.
48. A process for producing olefins comprising the step of contacting
an organic oxygenate compound under oxygenate conversion conditions
with a catalyst comprising a porous crystalline material substantially
free of framework phosphorus and comprising a CHA framework type
molecular sieve with stacking faults or at least one intergrown
phase of a CHA framework type molecular sieve and an AEI framework
type molecular sieve, wherein said material, in its calcined, anhydrous
form, has a composition involving the molar relationship: (n)X.sub.2O.sub.3:YO.sub.2
wherein X is a trivalent element; Y is a tetravalent element; and
n is from 0 to about 0.5.
49. The process of claim 48 wherein n is from about 0.001 to about
0.1.
50. The process of claim 48 wherein wherein n is from about 0.0017
to about 0.02.
51. The process of claim 48 wherein said organic oxygenate compound
comprises methanol, dimethyl ether or a mixture thereof.
Molecular sieve description
FIELD OF INVENTION
This invention relates to a novel chabazite-containing molecular
sieve, its synthesis and its use in the conversion of oxygenates,
particularly methanol, to olefins, particularly ethylene and propylene.
BACKGROUND OF INVENTION
The conversion of oxygenates to olefins (OTO) is currently the
subject of intense research because it has the potential for replacing
the long-standing steam cracking technology that is today the industry-standard
for producing world scale quantities of ethylene and propylene.
The very large volumes involved suggest that substantial economic
incentives exist for alternate technologies that can deliver high
throughputs of light olefins in a cost efficient manner. Whereas
steam cracking relies on non-selective thermal reactions of naphtha
range hydrocarbons at very high temperatures, OTO exploits catalytic
and micro-architectural properties of acidic molecular sieves under
milder temperature conditions to produce high yields of ethylene
and propylene from methanol.
Current understanding of the OTO reactions suggests a complex sequence
in which three major steps can be identified: (1) an induction period
leading to the formation of an active carbon pool (alkyl-aromatics),
(2) alkylation-dealkylation reactions of these active intermediates
leading to products, and (3) a gradual build-up of condensed ring
aromatics. OTO is therefore an inherently transient chemical transformation
in which the catalyst is in a continuous state of change. The ability
of the catalyst to maintain high olefin yields for prolonged periods
of time relies on a delicate balance between the relative rates
at which the above processes take place. The formation of coke-like
molecules is of singular importance because their accumulation interferes
with the desired reaction sequence in a number of ways. In particular,
coke renders the carbon pool inactive, lowers the rates of diffusion
of reactants and products, increases the potential for undesired
secondary reactions and limits catalyst life.
Over the last two decades, many catalytic materials have been identified
as being useful for carrying out the OTO reactions. Crystalline
microporous materials are the preferred catalysts today because
they simultaneously address the acidity and morphological requirements
for the reactions. Particularly preferred materials are eight-membered
ring aluminosilicates, such as those having the chabazite and AEI
framework types, and their silicoaluminophosphate counterparts,
such as SAPO-34 and SAPO-18. These molecular sieves have cages that
are sufficiently large to accommodate aromatic intermediates while
still allowing the diffusional transport of reactants and products
into and out of the crystals through regularly interconnected window
apertures. By complementing such morphological characteristics with
appropriate levels of acid strength and acid density, working catalysts
are produced. Extensive research in this area indicates that silicoaluminophosphates
are currently more effective OTO catalysts than aluminosilicates.
In particular, the control of the silica to alumina molar ratio
is a key requirement for the use of aluminosilicates in OTO reactions.
Nevertheless, aluminosilicate zeolites continue to be explored for
use in OTO and appear to have yet undiscovered potential.
Chabazite is a naturally occurring zeolite with the approximate
formula Ca.sub.6Al.sub.12Si.sub.24O.sub.72. Three synthetic forms
of chabazite are described in "Zeolite Molecular Sieves",
by D. W. Breck, published in 1973 by John Wiley & Sons, the
complete disclosure of which is incorporated herein by specific
reference. The three synthetic forms reported by Breck are Zeolite
"K-G", described in J. Chem. Soc., p. 2822 (1956), Barrer
et al; Zeolite D, described in British Patent No. 868846 (1961);
and Zeolite R, described in U.S. Pat. No. 3030181 (1962). Zeolite
K-G zeolite has a silica:alumina mole ratio of 2.3:1 to 4.15:1
whereas zeolites D and R have silica:alumina mole ratios of 4.5:1
to 4.9:1 and 3.45:1 to 3.65:1 respectively.
U.S. Pat. No. 4544538 incorporated herein by reference, describes
the synthesis of another synthetic form of chabazite, SSZ-13 using
N-alkyl-3-quinuclidinol, N,N,N-tri-alkyl-1-adamantylammonium cations
and/or N,N,N-trialkyl-exoaminonorbornane as a directing agent in
a conventional OH.sup.- medium. According to the '538 patent, SSZ-13
typically has a silica to alumina molar ratio of 8 to 50 but it
is stated that higher molar ratios can be obtained by varying the
relative ratios of the reactants in the synthesis mixture and/or
by treating the zeolite with chelating agents or acids to remove
aluminum from the zeolite lattice. However, attempts to synthesize
SSZ-13 in OH.sup.- media at silica to alumina molar ratios in excess
of 100 have been unsuccessful and have produced ITQ-1 or SSZ-23
depending on the alkali metal cation present. Moreover, increasing
the silica to alumina molar ratio of SSZ-13 by dealumination has
met little or no success.
Significant work has been conducted on the use of SSZ-13 as a catalyst
for MTO reactions. However, investigations to date have shown that
the performance of SSZ-13 is always inferior to that of its silicoaluminophosphate
analog, SAPO-34. See, for example, Yuen, L.-T., Zones, S. I., Harris,
T. V., Gallegos, E. J., and Auroux, A., "Product Selectivity
in Methanol to Hydrocarbon Conversion for Isostructural Compositions
of AFI and CHA Molecular Sieves", Microporous Materials 2
105 117 (1994) and Dahl, I. M., Mostad, H., Akporiaye, D., and Wendelbo,
R., "Structural and Chemical Influences on the MTO Reaction:
A Comparison of Chabazite and SAPO-34 as MTO Catalysts", Microporous
and Mesoporous Materials 29 185 190 (1999).
A silica crystalline molecular sieve having the CHA framework type
has been hydrothermally synthesized using N,N,N-trimethyladamantylammonium
in hydroxide form as the structure-directing agent at nearly neutral
pH in the presence of fluoride. See Diaz-Cabanas, M-J, Barrett,
P. A., and Camblor, M. A. "Synthesis and Structure of Pure
SiO.sub.2 Chabazite: the SiO.sub.2 Polymorph with the Lowest Framework
Density", Chem. Commun. 1881 (1998).
More recently, an aluminosilicate with the CHA framework type and
having a silica to alumina molar ratio in excess of 100 such as
from 150 to 2000 has been synthesized again in the presence of
fluoride ions. See U.S. Patent Application Publication No. 2003/0176751
published Sep. 18 2003 and incorporated herein by reference.
Molecular sieves of the AEI framework-type do not exist in nature.
However, a number of aluminophosphates and silicoaluminophosphates
having the AEI framework type have been synthesized, including SAPO-18
ALPO-18 and RUW-18. In addition, U.S. Pat. No. 5958370 incorporated
herein by reference, discloses an aluminosilicate zeolite having
an AEI framework-type and a silica to alumina molar ratio of 10
to 100. Aluminosilicates having a silica to alumina ratio greater
than 100 and all-silica molecular sieves with an AEI framework-type
have so far not been reported.
Regular crystalline molecular sieves, such as the AEI and CHA framework
types, are built from structurally invariant building units, called
Periodic Building Units, and are periodically ordered in three dimensions.
However, disordered structures showing periodic ordering in less
than three dimensions are also known. One such disordered structure
is a disordered planar intergrowth in which the repeated building
units from more than one framework type, e.g., both AEI and CHA,
are present. In addition, for certain molecular sieves, the building
units can exist in mirror image forms, which can result in stacking
faults where a sequence of building units of one mirror image form
intersects a sequence of building units of the opposite mirror image
form.
U.S. Pat. No. 6334994 incorporated herein by reference, discloses
a silicoaluminophosphate molecular sieve, referred to as RUW-19
which is said to be an AEI/CHA mixed phase composition. In particular,
RUW-19 is reported as having peaks characteristic of both CHA and
AEI framework type molecular sieves, except that the broad feature
centered at about 16.9 (2.theta.) in RUW-19 replaces the pair of
reflections centered at about 17.0 (2.theta.) in AEI materials and
RUW-19 does not have the reflections associated with CHA materials
centered at 2.theta. values of 17.8 and 24.8.
U.S. Patent Application Publication No. 2002/0165089 published
Nov. 7 2002 and incorporated herein by reference, discloses a silicoaluminophosphate
molecular sieve comprising at least one intergrown phase of molecular
sieves having AEI and CHA framework types, wherein said intergrown
phase has an AEI/CHA ratio of from about 5/95 to 40/60 as determined
by DIFFaX analysis, using the powder X-ray diffraction pattern of
a calcined sample of said silicoaluminophosphate molecular sieve.
Phosphorus-free molecular sieves, such as aluminosilicates and
silicas, comprising CHA/AEI intergrowths have so far not been reported.
SUMMARY
In one aspect, the invention resides in a crystalline material
substantially free of framework phosphorus and comprising a CHA
framework type molecular sieve with stacking faults or at least
one intergrown phase of a CHA framework type molecular sieve and
an AEI framework type molecular sieve, wherein said material, in
its calcined, anhydrous form, has a composition involving the molar
relationship: (n)X.sub.2O.sub.3:YO.sub.2 wherein X is a trivalent
element, such as aluminum, boron, iron, indium, and/or gallium;
Y is a tetravalent element such as silicon, tin, titanium and/or
germanium; and n is from 0 to about 0.5 conveniently from 0 to
about 0.125 for example from about 0.001 to about 0.1 such as
from about 0.0017 to about 0.02.
Conveniently, the calcined crystalline material contains from about
1 to about 100 ppm, for example from about 5 to about 50 ppm, such
as from about 10 to about 20 ppm, by weight of a halide, preferably
fluoride.
In a further aspect, the invention resides in a crystalline material
which comprises at least a CHA framework type molecular sieve and
which, in its as-synthesized form, contains in its intra-molecular
structure a first directing agent for directing the synthesis of
a CHA framework-type molecular sieve and a second directing agent
for directing the synthesis of a AEI framework-type molecular sieve,
said first and second directing agents being different.
In one embodiment, each of the first and second directing agents
comprises a cyclic amine or ammonium compound. More particularly,
the first directing agent comprises a multi-cyclic amine or ammonium
compound and the second directing agent comprises a monocyclic amine
or ammonium compound. Conveniently, the multi-cyclic amine or ammonium
compound comprises a tricyclic or tetracyclic amine or ammonium
compound, such as at least one of an N-alkyl-3-quinuclidinol, an
N,N,N-trialkyl-exoaminonorbornane and an adamantylamine or ammonium
compound, for example an N,N,N-trialkyl-1-adamantylammonium compound;
typically an N,N,N-trimethyl-1-adamantylammonium compound. Conveniently,
the monocyclic amine or ammonium compound comprises a substituted
piperidine or piperidinium compound, for example a tetraalkylpiperidinium
compound, typically an N,N-diethyl-26-dimethylpiperidinium compound.
In yet a further aspect, the invention resides in a method of synthesizing
a crystalline material comprising a CHA framework type molecular
sieve and having a composition involving the molar relationship:
(n)X.sub.2O.sub.3:YO.sub.2 wherein X is a trivalent element, Y
is a tetravalent element and n is from 0 to about 0.5 the method
comprising: (a) preparing a reaction mixture capable of forming
said material, said mixture comprising a source of water, a source
of an oxide of a tetravalent element Y, and optionally a source
of an oxide of a trivalent element X; (b) maintaining said reaction
mixture under conditions sufficient to form crystals of said crystalline
material comprising stacking faults or at least one intergrown phase
of a CHA framework type molecular sieve and an AEI framework type
molecular sieve; and (c) recovering said crystalline material from
(b).
Conveniently, said reaction mixture also comprises a halide or
a halide-containing compound, such as a fluoride or a fluoride-containing
compound.
Conveniently, said reaction mixture also comprises a first directing
agent for directing the synthesis of a CHA framework-type molecular
sieve and a second directing agent for directing the synthesis of
a AEI framework-type molecular sieve.
Conveniently, said reaction mixture also comprises seed crystals.
The seed crystals can be homostructural or heterostructural with
said intergrown phase. In one embodiment, the seed crystals comprise
a crystalline material having an AEI, CHA, OFF or LEV framework-type.
In still a further aspect, the invention resides in a process for
producing olefins comprising the step of contacting an organic oxygenate
compound under oxygenate conversion conditions with a catalyst comprising
a porous crystalline material substantially free of framework phosphorus
and comprising at least one intergrown phase of a CHA framework
type and an AEI framework type.
It is to be understood that the term "in its calcined, anhydrous
form" is used herein to refer to a material which has been
heated in air at a temperature in excess of 400.degree. C. for 0.1
to 10 hours without allowing the material to rehydrate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a and 1b are DIFFaX simulated diffraction patterns for intergrown
CHA/AEI zeolite phases having varying CHA/AEI ratios.
FIG. 2 is the X-ray diffraction pattern of the calcined product
of Example 1.
FIG. 3 is an overlay of part of the X-ray diffraction pattern of
FIG. 2 with the DIFFaX simulated trace obtained as the sum of 56%
of phase (a), a random intergrown AEI/CHA phase having an AEI/CHA
ratio of 15/85 and 44% of phase (b), a random intergrown AEI/CHA
phase having an AEI/CHA ratio of 75/25. The weighted average AEI/CHA
ratio for example 1 is calculated as 41/59.
FIG. 4 is a high resolution transmission electron micrograph of
the product of the 175.degree. C. synthesis of Example 2.
FIG. 5 is a high resolution transmission electron micrograph of
the product of Example 3. The inset is a Fourier Transform of the
high resolution transmission electron micrograph.
FIG. 6 is a bright-field transmission electron micrograph of the
product of Comparative Example 5.
FIG. 7 is a bright-field transmission electron micrograph of the
natural chabazite of Comparative Example 6.
FIG. 8 is the X-ray diffraction pattern of the calcined product
of Example 7.
FIG. 9 is a high resolution transmission electron micrograph of
the product of Example 7.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The present invention relates to a novel crystalline material that
is substantially free of framework phosphorus and that comprises
a CHA framework type molecular sieve with stacking faults or at
least one intergrown phase of a CHA framework type molecular sieve
and an AEI framework type molecular sieve. The invention also relates
to the synthesis of this novel crystalline material in a halide,
and particularly a fluoride, medium and to use of the material,
such as in a process for the conversion of oxygenates, particularly
methanol, to olefins, particularly ethylene and propylene.
Intergrown molecular sieve phases are disordered planar intergrowths
of molecular sieve frameworks. Reference is directed to the "Catalog
of Disordered Zeolite Structures", 2000 Edition, published
by the Structure Commission of the International Zeolite Association
and to the "Collection of Simulated XRD Powder Patterns for
Zeolites", M. M. J. Treacy and J. B. Higgins, 2001 Edition,
published on behalf of the Structure Commission of the International
Zeolite Association for a detailed explanation on intergrown molecular
sieve phases.
Regular crystalline solids are built from structurally invariant
building units, called Periodic Building Units, and are periodically
ordered in three dimensions. Structurally disordered structures
show periodic ordering in dimensions less than three, i.e. in two,
one or zero dimensions. This phenomenon is called stacking disorder
of structurally invariant Periodic Building Units. Crystal structures
built from Periodic Building Units are called end-member structures
if periodic ordering is achieved in all three dimensions. Disordered
structures are those where the stacking sequence of the Periodic
Building Units deviates from periodic ordering up to statistical
stacking sequences.
In the case of regular AEI and CHA framework type molecular sieves,
the Periodic Building Unit is a double six ring layer. There are
two types of layers "a" and "b", which are topologically
identical except "b" is the mirror image of "a".
When layers of the same type stack on top of one another, i.e. aaaaaaaa
or bbbbbbbb, the framework type CHA is generated. When layers "a"
and "b" alternate, ie, abababab, the framework type AEI
is generated. Intergrown AEI/CHA molecular sieves comprise regions
of CHA framework type sequences and regions of AEI framework type
sequences. Each change from a CHA to an AEI framework type sequence
results in a stacking fault. In addition, stacking faults can occur
in a pure CHA phase material when a sequence of one mirror image
layers intersects a sequence of the opposite mirror image layers,
such as for example in aaaaaabbbbbbb.
Analysis of intergrown molecular sieves, such as AEI/CHA intergrowths,
can be effected by X-ray diffraction and in particular by comparing
the observed patterns with calculated patterns generated using algorithms
to simulate the effects of stacking disorder. DIFFaX is a computer
program based on a mathematical model for calculating intensities
from crystals containing planar faults (see M. M. J. Tracey et al.,
Proceedings of the Royal Chemical Society, London, A [1991], Vol.
433 pp. 499 520). DIFFaX is the simulation program selected by
and available from the International Zeolite Association to simulate
the XRD powder patterns for randomly intergrown phases of zeolites
(see "Collection of Simulated XRD Powder Patterns for Zeolites"
by M. M. J. Treacy and J. B. Higgins, 2001 Fourth Edition, published
on behalf of the Structure Commission of the International Zeolite
Association). It has also been used to theoretically study intergrown
phases of AEI, CHA and KFI, as reported by K. P. Lillerud et al.
in "Studies in Surface Science and Catalysis", 1994 Vol.
84 pp. 543 550.
FIGS. 1a and 1b show the simulated diffraction patterns calculated
by DIFFaX for single intergrown zeolite phases having various AEI/CHA
ratios. These patterns were calculated using the input file given
in Table 1 below, with each pattern being normalized to the highest
peak of the entire set of simulated patterns, i.e. the peak at about
9.6 degrees 2.theta. for the 0/100 AEI/CHA pattern. Normalization
of intensity values allows the intensity of an X-ray diffraction
peak at a certain 2.theta. value to be compared between different
diffraction patterns.
Where the crystalline material of the invention comprises an intergrowth
of a CHA framework type molecular sieve and an AEI framework type
molecular sieve, the material can possess a widely varying AEI/CHA
ratio of from about 99:1 to about 1:99 such as from about 98:2
to about 2:98 for example from about 95:5 to 5:95. In one embodiment,
where the material is to be used a catalyst in the conversion of
oxygenates to olefins, the intergrowth is preferably CHA-rich and
has AEI/CHA ratio ranging from about 5:95 to about 30:70. In addition,
in some cases the intergrown material of the invention may comprise
a plurality of intergrown phases each having a different AEI/CHA
ratio. The relative amounts of AEI and CHA framework-type materials
in the intergrowth of the invention can be determined by a variety
of known techniques including transmission electron microscopy (TEM)
and DIFFaX analysis, using the powder X-ray diffraction pattern
of a calcined sample of the molecular sieve.
Where the crystalline material of the invention comprises a CHA
framework type molecular sieve but with stacking faults, the presence
of these stacking faults can readily be determined by transmission
electron microscopy. It is to be appreciated that stacking faults
may not be present in every crystal of the CHA material but generally
will be present in at least 5%, such as at least 10%, of the crystals.
In its calcined and anhydrous form, the crystalline material of
the present invention has a composition involving the molar relationship:
(n)X.sub.2O.sub.3:YO.sub.2 wherein X is a trivalent element, such
as aluminum, boron, iron, indium, and/or gallium, typically aluminum;
Y is a tetravalent element, such as silicon, tin, titanium and/or
germanium, typically silicon; and n is from 0 to about 0.5 conveniently
from 0 to about 0.125 for example from about 0.001 to about 0.1
such as from about 0.0017 to about 0.02. Where a halide-containing
compound has been used in the synthesis of the material, the calcined
form of the material of the present invention is normally found
to contain trace amounts, typically from about 1 to about 100 ppm,
for example from about 5 to about 50 ppm, such as from about 10
to about 20 ppm, by weight of the halide, preferably fluoride.
In its as-synthesized form, the crystalline material of the present
invention typically has a composition involving the molar relationship:
(n)X.sub.2O.sub.3:YO.sub.2:(m)R:(x)F:z H.sub.2O, wherein X, Y and
n are as defined in the preceding paragraph, R is at least one organic
directing agent and wherein m ranges from about 0.01 to about 2
such as from about 0.1 to about 1 z ranges from about 0.5 to about
100 such as from about 2 to about 20 and x ranges from about 0
to about 2 such as from about 0.01 to about 1. The R and F components,
which are associated with the material as a result of their presence
during crystallization, can be at least partly removed by post-crystallization
methods hereinafter more particularly described. Typically, in its
as-synthesized form, the intergrowth of the present invention contains
only low levels of alkali metal, generally such that the combined
amount of any potassium and sodium is less than 50% of the X.sub.2O.sub.3
on a molar basis. For this reason, after removal of the organic
directing agent (R), the material generally exhibits catalytic activity
without a preliminary ion-exchange step to remove alkali metal cations.
As will be discussed below, the least one organic directing agent
(R) typically comprises at least one first organic directing agent
for directing the synthesis of a CHA framework-type material and
at least one second organic directing agent for directing the synthesis
of an AEI framework-type material. It is found that these directing
agents are typically retained intact in the intra-molecular structure
of the molecular sieve product. Depending on the composition of
the directing agents it will normally possible to determine the
relative amounts of the different directing agents retained in the
as-synthesized molecular sieve by analytical techniques, such as
.sup.13C MAS (magic-angle spinning) NMR. Thus, in a preferred embodiment,
where the first organic directing agent is an N,N,N-trimethyl-1-adamantylammonium
compound (TMAA) and the second organic directing agent is an N,N-diethyl-26-dimethylpiperidinium
compound (DEDMP), the DEDMP exhibits peaks corresponding to the
C nuclei in the CH.sub.3 moieties in the 0 to 20 ppm range of the
.sup.13C MAS NMR spectrum, which peaks are not present in the .sup.13C
MAS NMR spectrum of the TMAA. This, by measuring the peak heights
in the 0 to 20 ppm range of the .sup.13C MAS NMR spectrum, the relative
amounts of TMAA and DEDMP in the as-synthesized material can be
determined. Preferably, the molar amount of AEI directing agent
retained in the as-synthesized material to the total molar amount
of AEI and CHA directing agent retained in the as-synthesized material
is between 0.1 and 0.3.
To the extent desired and depending on the X.sub.2O.sub.3/YO.sub.2
molar ratio of the material, any cations in the as-synthesized intergrowth
can be replaced in accordance with techniques well known in the
art, at least in part, by ion exchange with other cations. Preferred
replacing cations include metal ions, hydrogen ions, hydrogen precursor,
e.g., ammonium ions, and mixtures thereof. Particularly preferred
cations are those which tailor the catalytic activity for certain
hydrocarbon conversion reactions. These include hydrogen, rare earth
metals and metals of Groups IIA, IIIA, IVA, VA, IB, IIB, IIIB, IVB,
VB, VIIB, VIIB and VIII of the Periodic Table of the Elements.
The intergrowth of the invention can be prepared from a reaction
mixture containing a source of water, a source of an oxide of the
tetravalent element Y, optionally a source of an oxide of the trivalent
element X, at least one organic directing agent I as described below,
and typically a halide or a halide-containing compound, such as
a fluoride or a fluoride-containing compound, said reaction mixture
having a composition, in terms of mole ratios of oxides, within
the following ranges:
Where the tetravalent element Y is silicon, suitable sources of
silicon include silicates, e.g., tetraalkyl orthosilicates, fumed
silica, such as Aerosil (available from Degussa), and aqueous colloidal
suspensions of silica, for example that sold by E.I. du Pont de
Nemours under the tradename Ludox. Where the trivalent element X
is aluminum, suitable sources of aluminum include aluminum salts,
especially water-soluble salts, such as aluminum nitrate, as well
as hydrated aluminum oxides, such as boehmite and pseudoboehmite.
Where the halide is fluoride, suitable sources of fluoride include
hydrogen fluoride, although more benign sources of fluoride such
as alkali metal fluorides and fluoride salts of the organic directing
agent are preferred.
The at least one organic directing agent R used herein conveniently
comprises a mixture of a plurality of different organic directing
agents. Preferably, the mixture comprises at least one first organic
directing agent for directing the synthesis of a CHA framework-type
material and at least one second organic directing agent for directing
the synthesis of an AEI framework-type material.
Suitable first organic directing agents for directing the synthesis
of a CHA framework-type material include N,N,N-trimethyl-1-adamantammonium
compounds, N,N,N-trimethyl-2-adamantammonium compounds, N,N,N-trimethylcyclohexylammonium
compounds, N,N-dimethyl-33-dimethylpiperidinium compounds, N,N-methylethyl-33-dimethylpiperidinium
compounds, N,N-dimethyl-2-methylpiperidinium compounds, 13366-pentamethyl-6-azonio-bicyclo(3.2.1)octane
compounds, N,N-dimethylcyclohexylamine, and the bi- and tri-cyclic
nitrogen containing organic compounds cited in (1) Zeolites and
Related Microporous Materials: State of the Art 1994 Studies of
Surface Science and Catalysis, Vol. 84 p 29 36; in (2) Novel Materials
in Hetrogeneous Catalysis (ed. Terry K. Baker & Larry L. Murrell),
Chapter 2 p 14 24 May 1990 in (3) J. Am. Chem. Soc., 2000 122
p 263 273 and (4) in U.S. Pat. Nos. 4544538 and 6709644. Suitable
compounds include hydroxides and salts, such as halides, especially
chlorides and fluorides.
Suitable second organic directing agents for directing the synthesis
of an AEI framework-type material include N,N-diethyl-26-dimethylpiperdinium
compounds (mixture or either of the cis/trans isomers), N,N-dimethyl-26-dimethylpiperdinium
compounds (mixture or either of the cis/trans isomers), and the
directing agents cited in J. Am. Chem. Soc., 2000 122 p 263 273
and U.S. Pat. No. 5958370. Suitable compounds include hydroxides
and salts, such as halides, especially chlorides and fluorides.
Conveniently, the molar ratio of the first organic directing agent
to the second organic directing agent in the reaction mixture is
from about 0.01 to about 100 such as from about 0.02 to about 50
for example from about 0.03 to about 33 such as from about 0.03
to about 3 for example from about 0.05 to about 0.3.
In one embodiment, the organic directing agent comprises a mixture
of cyclic amines or ammonium compounds, particularly a mixture where
one component is a multi-cyclic amine or ammonium compound and more
particularly a mixture where one component is a multi-cyclic amine
or ammonium compound and another component is a monocyclic amine
or ammonium compound. Conveniently, the monocyclic amine or ammonium
compound comprises a substituted piperidine or piperidinium compound,
for example a tetraalkylpiperidinium compound, typically an N,N-diethyl-26dimethylpiperidinium
compound. Conveniently, the multi-cyclic amine or ammonium compound
comprises a tetracyclic amine or ammonium compound, such as an adamantylamine
or ammonium compound, for example an N,N,N-trialkyl-1-adamantylammonium
compound; typically an N,N,N-trimethyl-1-adamantylammonium compound.
Thus the term multi-cyclic amine is used herein to include multi-cyclic
compounds in which the N atom is external to the rings. Suitable
ammonium compounds include hydroxides and salts, such as halides,
especially chlorides.
Conveniently, the reaction mixture has a pH of about 4 to about
14 such as about 4 to about 10 for example about 6 to about 8.
Crystallization can be carried out at either static or stirred
conditions in a suitable reactor vessel, such as for example, polypropylene
jars or Teflon.RTM.-lined or stainless steel autoclaves, at a temperature
of about 50.degree. C. to about 300.degree. C., such as about 135.degree.
C. to about 185.degree. C., for a time sufficient for crystallization
to occur. Formation of the crystalline product can take anywhere
from around 30 minutes up to as much as 2 weeks, such as from about
45 minutes to about 240 hours, for example from about 1.0 to about
120 hours. The duration depends on the temperature employed, with
higher temperatures typically requiring shorter hydrothermal treatments.
Synthesis of the new intergrowth may be facilitated by the presence
of at least 0.1 ppm, such as at least 10 ppm, for example at least
100 ppm, conveniently at least 500 ppm of seed crystals based on
total weight of the reaction mixture. The seed crystals can be homostructural
with the crystalline material of the present invention, for example
the product of a previous synthesis, or can be a heterostructural
crystalline material, such as an AEI, LEV, OFF, CHA or ERI framework-type
molecular sieve. Conveniently, the seed material is an AEI-type
molecular sieve, and particularly an AEI-type aluminosilicate. The
seeds may be added to the reaction mixture as a colloidal suspension
in a liquid medium, such as water. The production of colloidal seed
suspensions and their use in the synthesis of molecular sieves are
disclosed in, for example, International Publication Nos. WO 00/06493
and WO 00/06494 published on Feb. 10 2000 and incorporated herein
by reference.
Typically, the crystalline product is formed in solution and can
be recovered by standard means, such as by centrifugation or filtration.
The separated product can also be washed, recovered by centrifugation
or filtration and dried.
As a result of the crystallization process, the recovered crystalline
product contains within its pores at least a portion of the organic
directing agent used in the synthesis. In a preferred embodiment,
activation is performed in such a manner that the organic directing
agent is removed from the molecular sieve, leaving active catalytic
sites within the microporous channels of the molecular sieve open
for contact with a feedstock. The activation process is typically
accomplished by calcining, or essentially heating the molecular
sieve comprising the template at a temperature of from about 200.degree.
C. to about 800.degree. C. in the presence of an oxygen-containing
gas. In some cases, it may be desirable to heat the molecular sieve
in an environment having a low or zero oxygen concentration. This
type of process can be used for partial or complete removal of the
organic directing agent from the intracrystalline pore system. In
other cases, particularly with smaller organic directing agents,
complete or partial removal from the sieve can be accomplished by
conventional desorption processes.
Once the intergrown crystalline material of the invention has been
synthesized, it can be formulated into a catalyst composition by
combination with other materials, such as binders and/or matrix
materials, that provide additional hardness or catalytic activity
to the finished catalyst.
Materials which can be blended with the intergrown crystalline
material of the invention can be various inert or catalytically
active materials. These materials include compositions such as kaolin
and other clays, various forms of rare earth metals, other non-zeolite
catalyst components, zeolite catalyst components, alumina or alumina
sol, titania, zirconia, quartz, silica or silica sol, and mixtures
thereof. These components are also effective in reducing overall
catalyst cost, acting as a thermal sink to assist in heat shielding
the catalyst during regeneration, densifying the catalyst and increasing
catalyst strength. When blended with such components, the amount
of intergrown crystalline material contained in the final catalyst
product ranges from 10 to 90 weight percent of the total catalyst,
preferably 20 to 80 weight percent of the total catalyst.
The intergrown crystalline material described herein can be used
to dry gases and liquids; for selective molecular separation based
on size and polar properties; as an ion-exchanger; as a chemical
carrier; in gas chromatography; and as a catalyst in organic conversion
reactions. Examples of suitable catalytic uses of the intergrown
crystalline material described herein include (a) hydrocracking
of heavy petroleum residual feedstocks, cyclic stocks and other
hydrocrackate charge stocks, normally in the presence of a hydrogenation
component selected from Groups 6 and 8 to 10 of the Periodic Table
of Elements; (b) dewaxing, including isomerization dewaxing, to
selectively remove straight chain paraffins from hydrocarbon feedstocks
typically boiling above 177.degree. C., including raffinates and
lubricating oil basestocks; (c) catalytic cracking of hydrocarbon
feedstocks, such as naphthas, gas oils and residual oils, normally
in the presence of a large pore cracking catalyst, such as zeolite
Y; (d) oligomerization of straight and branched chain olefins having
from about 2 to 21 preferably 2 to 5 carbon atoms, to produce medium
to heavy olefins which are useful for both fuels, i.e., gasoline
or a gasoline blending stock, and chemicals; (e) isomerization of
olefins, particularly olefins having 4 to 6 carbon atoms, and especially
normal butene to produce iso-olefins; (f) upgrading of lower alkanes,
such as methane, to higher hydrocarbons, such as ethylene and benzene;
(g) disproportionation of alkylaromatic hydrocarbons, such as toluene,
to produce dialkylaromatic hydrocarbons, such as xylenes; (h) alkylation
of aromatic hydrocarbons, such as benzene, with olefins, such as
ethylene and propylene to produce ethylbenzene and cumene; (i) isomerization
of dialkylaromatic hydrocarbons, such as xylenes, (j) catalytic
reduction of nitrogen oxides and (k) synthesis of monoalkylamines
and dialkylamines.
In particular, the intergrown crystalline material described herein
is useful as a catalyst in the conversion of oxygenates to one or
more olefins, particularly ethylene and propylene. As used herein,
the term "oxygenates" is defined to include, but is not
necessarily limited to aliphatic alcohols, ethers, carbonyl compounds
(aldehydes, ketones, carboxylic acids, carbonates, and the like),
and also compounds containing hetero-atoms, such as, halides, mercaptans,
sulfides, amines, and mixtures thereof. The aliphatic moiety will
normally contain from about 1 to about 10 carbon atoms, such as
from about 1 to about 4 carbon atoms.
Representative oxygenates include lower straight chain or branched
aliphatic alcohols, their unsaturated counterparts, and their nitrogen,
halogen and sulfur analogues. Examples of suitable oxygenate compounds
include methanol; ethanol; n-propanol; isopropanol; C.sub.4 C.sub.10
alcohols; methyl ethyl ether; dimethyl ether; diethyl ether; di-isopropyl
ether; methyl mercaptan; methyl sulfide; methyl amine; ethyl mercaptan;
di-ethyl sulfide; di-ethyl amine; ethyl chloride; formaldehyde;
di-methyl carbonate; di-methyl ketone; acetic acid; n-alkyl amines,
n-alkyl halides, n-alkyl sulfides having n-alkyl groups of comprising
the range of from about 3 to about 10 carbon atoms; and mixtures
thereof. Particularly suitable oxygenate compounds are methanol,
dimethyl ether, or mixtures thereof, most preferably methanol. As
used herein, the term "oxygenate" designates only the
organic material used as the feed. The total charge of feed to the
reaction zone may contain additional compounds, such as diluents.
In the present oxygenate conversion process, a feedstock comprising
an organic oxygenate, optionally with one or more diluents, is contacted
in the vapor phase in a reaction zone with a catalyst comprising
the molecular sieve of the present invention at effective process
conditions so as to produce the desired olefins. Alternatively,
the process may be carried out in a liquid or a mixed vapor/liquid
phase. When the process is carried out in the liquid phase or a
mixed vapor/liquid phase, different conversion rates and selectivities
of feedstock-to-product may result depending upon the catalyst and
the reaction conditions.
When present, the diluent(s) is generally non-reactive to the feedstock
or molecular sieve catalyst composition and is typically used to
reduce the concentration of the oxygenate in the feedstock. Non-limiting
examples of suitable diluents include helium, argon, nitrogen, carbon
monoxide, carbon dioxide, water, essentially non-reactive paraffins
(especially alkanes such as methane, ethane, and propane), essentially
non-reactive aromatic compounds, and mixtures thereof. The most
preferred diluents are water and nitrogen, with water being particularly
preferred. Diluent(s) may comprise from about 1 mol % to about 99
mol % of the total feed mixture.
The temperature employed in the oxygenate conversion process may
vary over a wide range, such as from about 200.degree. C. to about
1000.degree. C., for example from about 250.degree. C. to about
800.degree. C., including from about 250.degree. C. to about 750.degree.
C., conveniently from about 300.degree. C. to about 650.degree.
C., typically from about 350.degree. C. to about 600.degree. C.
and particularly from about 400.degree. C. to about 600.degree.
C.
Light olefin products will form, although not necessarily in optimum
amounts, at a wide range of pressures, including but not limited
to autogenous pressures and pressures in the range of from about
0.1 kPa to about 10 MPa. Conveniently, the pressure is in the range
of from about 7 kPa to about 5 MPa, such as in the range of from
about 50 kPa to about 1 MPa. The foregoing pressures are exclusive
of diluent, if any is present, and refer to the partial pressure
of the feedstock as it relates to oxygenate compounds and/or mixtures
thereof. Lower and upper extremes of pressure may adversely affect
selectivity, conversion, coking rate, and/or reaction rate; however,
light olefins such as ethylene still may form.
The process should be continued for a period of time sufficient
to produce the desired olefin products. The reaction time may vary
from tenths of seconds to a number of hours. The reaction time is
largely determined by the reaction temperature, the pressure, the
catalyst selected, the weight hourly space velocity, the phase (liquid
or vapor) and the selected process design characteristics.
A wide range of weight hourly space velocities (WHSV) for the feedstock
will function in the present process. WHSV is defined as weight
of feed (excluding diluent) per hour per weight of a total reaction
volume of molecular sieve catalyst (excluding inerts and/or fillers).
The WHSV generally should be in the range of from about 0.01 hr.sup.-1
to about 500 hr.sup.-1 such as in the range of from about 0.5 hr.sup.-1
to about 300 hr.sup.-1 for example in the range of from about 0.1
hr.sup.-1 to about 200 hr.sup.-1.
A practical embodiment of a reactor system for the oxygenate conversion
process is a circulating fluid bed reactor with continuous regeneration,
similar to a modern fluid catalytic cracker. Fixed beds are generally
not preferred for the process because oxygenate to olefin conversion
is a highly exothermic process which requires several stages with
intercoolers or other cooling devices. The reaction also results
in a high pressure drop due to the production of low pressure, low
density gas.
Because the catalyst must be regenerated frequently, the reactor
should allow easy removal of a portion of the catalyst to a regenerator,
where the catalyst is subjected to a regeneration medium, such as
a gas comprising oxygen, for example air, to burn off coke from
the catalyst, which restores the catalyst activity. The conditions
of temperature, oxygen partial pressure, and residence time in the
regenerator should be selected to achieve a coke content on regenerated
catalyst of less than about 0.5 wt %. At least a portion of the
regenerated catalyst should be returned to the reactor.
In one embodiment, prior to being used to convert oxygenate to
olefins, the catalyst is pretreated with dimethyl ether, a C.sub.2
C.sub.4 aldehyde composition and/or a C.sub.4 C.sub.7 olefin composition
to form an integrated hydrocarbon co-catalyst within the porous
framework of the intergrown molecular sieve. Desirably, the pretreatment
is conducted at a temperature of at least 10.degree. C., such as
at least 25.degree. C., for example at least 50.degree. C., higher
than the temperature used for the oxygenate reaction zone and is
arranged to produce at least 0.1 wt %, such as at least 1 wt %,
for example at least about 5 wt % of the integrated hydrocarbon
co-catalyst, based on total weight of the molecular sieve. Such
preliminary treating to increase the carbon content of the molecular
sieve is known as "pre-pooling" and is further described
in U.S. application Ser. Nos. 10/712668 10/712952 and 10/712953
all of which were filed Nov. 12 2003 and are incorporated herein
by reference.
The invention will now be more particularly described with reference
to the following Examples and the accompanying drawings. In the
Examples, the X-ray diffraction data were collected with several
types of instruments: Philips XRD shall hereinafter refer to X-ray
diffraction data collected with a Philips powder X-Ray Diffractometer,
equipped with a scintillation detector with graphite monochromator,
using copper K-alpha radiation. The diffraction data were recorded
by step-scanning at 0.02 degrees of two-theta, where theta is the
Bragg angle, and a counting time of 1 second for each step. The
interplanar spacings, d's, were calculated in Angstrom units, and
the relative intensities of the lines, I/I.sub.o, where I.sub.o
is the intensity of the strongest line, above background were determined
by integrating the peak intensities.
Synchrotron XRD shall hereinafter refer to powder X-ray diffraction
data collected at Brookhaven National Labs on beamline X10B with
a monochromatic radiation wavelength of 0.8695 .ANG. using Debye-Scherrer
geometry. Samples were first calcined in air at 600.degree. C. for
3 hours to remove the template. The calcined samples were then sealed
in 2 mm outside diameter quartz capillary tubes while out-gassing
at 300.degree. C. under vacuum (<0.1 torr). The diffraction data
were recorded by step-scanning at 0.01 degrees two-theta, where
theta is the Bragg angle. The counting time was automatically adjusted
for each step during the measurement so that a separate beam monitor
detector registered 30000 counts (typically 5.2 5.4 seconds). The
interplanar spacings, d's, were calculated in Angstrom units, and
the relative intensities of the lines, I/Io, where Io is the intensity
of the strongest line, above background were determined by integrating
the peak intensities.
Scintag XRD shall hereinafter refer to X-ray diffraction data collected
with a Scintag X2 X-Ray Diffractometer equipped with a Peltier-cooled
solid state detector, using copper K-alpha radiation. The diffraction
data were recorded by step-scanning at 0.02 degrees two-theta, where
theta is the Bragg angle, and a counting time of 0.3 second for
each step. The interplanar spacing, d's, were calculated in Angstrom
units, and the relative intensities of the lines, I/Io, where Io
is the intensity of the strongest line, above background were determined
by integrating the peak intensities.
X-ray diffraction data for the calcined samples was obtained by
subjecting the as-synthesized product to the following calcination
procedure. About 2 grams of the as-synthesized product were heated
from room temperature to 200.degree. C. under a flow of nitrogen
at a rate of 2.degree. C. per minute. The temperature was held at
200.degree. C. for 30 minutes and then the sample was heated from
200.degree. C. to 650.degree. C. under nitrogen again at a rate
of 2.degree. C. per minute. The sample was held at 650.degree. C.
under nitrogen for 5 8 hours, whereafter the nitrogen was then replaced
by air and the sample was kept at 650.degree. C. under air for 3
hours. The sample was then cooled to 200.degree. C. and kept at
200.degree. C. to prevent hydration. The hot sample was then transferred
into the XRD sample cup and was covered by Mylar foil to prevent
hydration.
DIFFaX analysis was used to determine the AEI/CHA ratio of the
molecular sieves. For DIFFaX analysis, powder XRD diffraction patterns
for varying ratios of AEI/CHA were generated using the DIFFaX program
available from the International Zeolite Association (see also M.
M. J. Treacy et al., Proceedings of the Royal Chemical Society,
London, A (1991), Vol. 433 pp. 499 520 "Collection of Simulated
XRD Powder Patterns for Zeolites" by M. M. J. Treacy and J.
B. Higgins, 2001 Fourth Edition, published on behalf of the Structure
Commission of the International Zeolite Association). Table 1 gives
the DIFFaX input file used to simulate the XRD diffraction pattern
of a 50/50 intergrowth. For the purposes of this analysis, calculations
were based on a random distribution of the layers. Such calculations
are used for statistical purposes only, and do not mean that the
true nature of the material is necessarily random.
FIGS. 1a and 1b show the simulated diffraction patterns calculated
by DIFFaX for single intergrown zeolite phases having various AEI/CHA
ratios, normalized to the highest peak of the entire set, i.e. the
peak at about 9.6 2.theta. for the 100% CHA case which was set to
100. The diffractograms were simulated using the following parameter
settings: all Si AEI_CHA .lamda.=1.54056 PSEUDO-VOIGT 0.1 0.036;
line broadening: 0.009: 0.6. A non-linear least-squares procedure
("DIFFaX Analysis") was then used to refine the contribution
of one or more phases, and of the background and the 2.theta. shift
required to fit the experimental profile. An intergrowth sensitive
region (see e.g. FIG. 3) was always chosen in order to maximize
the sensitivity of the calculations. Alternatively, a manual trial-and-error
fit can be performed for identifying the type and magnitude of the
contributing phases, the background counts and the 20 shift. For
materials characterized by the presence of more than one intergrown
phase, the contribution of AEI and CHA was calculated by a least
squares analysis method, summing the AEI and CHA contribution of
each intergrown phases. For Synchrotron XRDs, the comparison with
the DIFFaX simulated patterns was done by converting the experimental
XRD patterns to CuK.alpha.1 (.lamda.=1.54056 A).
In addition, the .sup.13C MAS (magic-angle spinning) NMR spectra
were obtained using a Chemagnetics.RTM. CMXII-200 spectrometer operating
at a static field of 4.7 T (199.9 MHz .sup.1H, 50.3 MHz .sup.13C).
The as-synthesized samples were loaded in MAS ZrO.sub.2 NMR rotors
(5-mm o.d.) and spun at the magic angle. The .sup.13C MAS NMR (or
Bloch decay) experiments were performed using a doubly-tuned probe
by applying a (90.degree.) .sup.13C pulse followed by .sup.13C data
acquisition. A .sup.1H-.sup.13C dipolar-decoupling field of about
62-kHz was used during .sup.13C data acquisition. The .sup.13C Bloch
decay spectra were obtained at 8-kHz MAS using a pulse delay of
about 60-sec. The free-induction decays thus obtained were Fourier
transformed (with a 25 Hz exponential line broadening filter). The
.sup.13C chemical shifts are referenced with respect to an external
solution of tetramethyl silane (TMS .delta..sub.C=0.0 ppm), using
hexamethyl benzene as a secondary standard. One or more of the none-overlapping
regions can be taken and its relative intensity determined. This
can in turn be converted into mole ratio of the specific template
whereby the relative contribution of one template versus the other
can be calculated. All solid-state NMR measurements were done at
room temperature.
TEM analysis included both Bright-Field TEM imaging (BF-TEM) and
High-Resolution TEM imaging (HR-TEM).
TEM data were obtained by crushing individual as-calcined samples
into fines (<100 nm thick) using an agate mortar and pestle.
The fines were transferred into a flat bed mold, embedded in a standard
mix of LR White hard grade resin (Polysciences, Inc., USA), and
cured under ambient conditions. The resin blocks were removed from
the flat bed molds and placed "end on" into polyethylene
BEEM capsules. Each BEEM capsule was filled with a standard mix
of LR White hard grade embedding resin and cured under ambient conditions.
The cured resin blocks were removed from the BEEM capsules and placed
into a Reichert-Jung Ultracut E microtome. Electron transparent
sections (.about.100 nm thick) were ultramicrotomed at ambient temperature
from the resin blocks using a diamond knife. The microtomy process
fractured the samples into many small sections, which were floated
off on water and collected onto standard, 200 mesh carbon-coated
TEM grids. After air-drying, the grids were examined in the bright
field TEM imaging mode of a Philips CM200F TEM/STEM at an accelerating
voltage of 200 kV. Each small section of material was identified
as a chard in the TEM analysis. In order to quantify the number
of faulted crystals, 500 chards of each sample were examined at
low magnification, and the presence of stacking faults or twins
was noted by visual inspection. The number of faulted crystals is
expressed as the number of chards that show one or more faults or
twins in a total of 500 chards.
HR-TEM data were obtained by embedding the calcined samplez in
LR White hard grade resin (The London Resin Co., UK). Then, without
adding the curing accelerator; the resin was thermally cured at
80.degree. C. for at least 3 hours in a nitrogen atmosphere. Electron
transparent thin sections were cut at ambient temperature using
a Boeckeler Powertome XL ultra-microtome equipped with a diamond
knife. The thin sections were collected on lacey carbon TEM grids.
HR-TEM analysis was done in a Philips CM12T transmission electron
microscope at an accelerating voltage of 120 kV. The crystals were
carefully oriented with the appropriate zone axis parallel to the
electron beam and high-resolution TEM images were recorded on photographic
plate at a nominal magnification of 100000.times..
EXAMPLE 1
0.286 ml of a 23.5 mg/ml aqueous solution of Al(NO.sub.3).sub.3.9H.sub.2O
was added to a mixture of 8.060 ml of an aqueous solution of N,N-diethyl-26-dimethylpiperidinium
hydroxide, DEDMP.sup.+ OH.sup.-, (0.6008 molar) and 1.000 ml of
an aqueous solution of N,N,N-tri-methyl-1-adamantylammonium hydroxide,
TMAA.sup.+ OH.sup.-, (0.5379 molar). 2.400 ml of tetraethylorthosilicate
was then added to this composition and the resultant mixture was
continuously stirred in a sealed container for at least 2 3 hours
at room temperature until all the tetraethylorthosilicate was completely
hydrolyzed. To the resultant clear solution was added 0.234 ml of
a 48 wt % aqueous solution of hydrofluoric acid which immediately
resulted in the production of a slurry. This slurry was further
homogenized by stirring and exposure to air for evaporation of water
and ethanol until a thick slurry mixture was obtained. Extra water
was further evaporated from the slurry mixture under static conditions
to give 2672 mg of a dry gel solid having the following molar composition:
SiO.sub.2:0.00083Al.sub.2O.sub.3:0.45DEDMP:0.05TMAA:0.6F:5.0H.sub.2O
To this solid was added with mechanical mixing 10 mg (0.37 wt %
based on the dry gel solid) of a seeding material, AEI having a
Si/Al atomic ratio of 8.9 and Si/Na atomic ratio of 26.4. The resulting
mixture of solids was transferred to a Teflon.RTM.-lined 5 ml pressure
reactor and crystallized at 150.degree. C. for 65 hours under slow
rotation (about 60 rpm). After cooling, the resultant solid was
recovered by centrifuging, washed with distilled water, and dried
at 100.degree. C. to give 775 mg of a white microcrystalline solid
(29.0% yield based on the weight of the dry gel). The as-synthesized
product had the X-ray diffraction pattern summarized in Table 2
below. The calcined product had the Scintag X-ray diffraction pattern
shown in FIG. 2.
DIFFaX analysis was conducted on the X-ray pattern of FIG. 2 and
the results are summarized in FIG. 3. FIG. 3 shows that the product
of Example 1 is characterized by the presence of more than one random
intergrown AEI/CHA phase. Least squares analysis shows that the
product of Example 1 is composed of about 56 wt % of a first intergrown
AEI/CHA phase having an AEI/CHA ratio of 15/85 and about 44 wt %
of a second intergrown AEI/CHA phase having an AEI/CHA ratio of
75/25 such that the weighted average AEI/CHA ratio of the material
was about 41/59.
SEM analysis of the calcined product showed particles having a
thick plate morphology and a size of about 1 2 micron. Chemical
analysis showed the silica/alumina molar ratio of the product to
be 1200.
EXAMPLE 2
The synthesis of Example 1 was repeated in two separate experiments
using the same starting materials in the same proportions as Example
1 but with the crystallization temperatures being 135.degree. C.
and 175.degree. C. respectively. DIFFaX analysis was conducted as
described in example 1 on the Synchrotron X-ray diffraction pattern
of the calcined product of the 175.degree. C. synthesis and showed
the presence of two intergrown AEI/CHA phases, namely about 78 wt
% of a first intergrown phase having an AEI/CHA ratio of 5/95 and
and about 22 wt % of a second intergrown phase having an AEI/CHA
ratio of 95/5 which corresponds to a weighted average AEI/CHA ratio
of about 25/75.
.sup.13C MAS NMR analysis of the product of the 175.degree. C.
synthesis showed the presence of DEDMP (the AEI directing agent)
and TMAA (the CHA directing agent) in a molar ratio of 50/50 in
the as-synthesized product. This contrasts with a DEDMP:TMAA molar
ratio of 90/10 in the synthesis mixture.
A high resolution transmission electron micrograph of the product
of the 175.degree. C. synthesis is shown in FIG. 4 and confirms
the presence of twinned/faulted CHA crystals with intercalated regions
of faulted AEI phase material.
EXAMPLE 3
The synthesis of Example 1 was repeated with the molar ratio of
DEDMP/TMAA in the synthesis mixture being 1.0. DIFFaX analysis on
the Synchrotron X-ray diffraction pattern of the as-calcined product
showed the product to be pure CHA. In addition, .sup.13C MAS NMR
analysis showed the presence of only TMAA (the CHAdirecting agent)
in the as-synthesized product. A HR-TEM transmission electron micrograph
of the product is shown in FIG. 5. No presence of faulting is apparent
in the HR-TEM image. The Fourier Transform of the HR-TEM image shows
sharp spots and no streaks, which is indicative of a regular stacking
and of the absence of stacking faults or twins. No faults were observed
in the 500 chards produced for the TEM analysis.
EXAMPLE 4
The synthesis of Example 1 was repeated with the molar ratio of
DEDMP/TMAA in the synthesis mixture being 5.67 and the crystallization
temperature being 175.degree. C. DIFFaX analysis on the Synchrotron
X-ray diffraction pattern of the as-calcined product showed the
presence of three phases, namely about 73.5 wt % of a first intergrown
phase having an AEI/CHA ratio of 5/95 about 5.2 wt % of a second
intergrown phase having an AEI/CHA ratio of 90/10 and about 21.3
wt % of a third phase having an AEI/CHA ratio of 0/100 which corresponds
to a weighted average AEI/CHA ratio of about 8.5/91.5. .sup.13C
MAS NMR analysis showed the presence of DEDMP (the AEI directing
agent) and TMAA (the CHA directing agent) in a molar ratio of 23/77
in the as-synthesized product.
EXAMPLE 5 (COMPARATIVE)
The process described in U.S. Pat. No. 4544538 was repeated to
produce SSZ-13 as follows. 2.00 g 1N NaOH, 2.78 g 0.72 molar N,N,N-trimethyladamantammonium
hydroxide, and 3.22 g deionized water were added sequentially to
a 23 ml Teflon lined Parr autoclave. To the resultant solution 0.05
g of aluminum hydroxide (Teheis F-2000 dried gel, 50% Al.sub.2O.sub.3)
was added and the solution was mixed until it cleared. 0.60 g fumed
silica (Cab-O-Sil, M5 grade, 97% SiO.sub.2) was then added to the
autoclave and the solution was mixed until uniform.
The autoclave was sealed and heated without agitation at 160.degree.
C. for 4 days. The autoclave was then cooled to room temperature
and the solid product recovered by filtration. The product was washed
repeatedly with deionized water and then dried in a vacuum oven
at 50.degree. C.
X-ray diffraction analysis showed the product to be pure CHA framework
type molecular sieve. A transmission electron micrograph of the
product is shown in FIG. 6. No presence of faulting is apparent
in the TEM and no faults were observed in the 500 chards produced
for the TEM analysis.
EXAMPLE 6 (COMPARATIVE)
A sample of a light brown colored natural chabazite was obtained
from western US. It was analyzed to have Si/Al=3.70 0.28 wt % Na,
0.33 wt % K, 0.03 wt % Ca, 0.28 wt % Mg, and 1.50 wt % Fe. The sample
was subjected to transmission electron microscopy without any prior
treatment and the results are shown in FIG. 7. No presence of faulting
was apparent in the BF-TEM and no faults were observed in the 500
chards produced for the BF-TEM analysis.
EXAMPLE 7
0.239 ml of a 23.5 mg/ml aqueous solution of Al(NO.sub.3).sub.3.9H.sub.2O
was added to a mixture of 5.597 ml of an aqueous solution of N,N-diethyl-26-dimethylpiperidinium
hydroxide, DEDMP.sup.+ OH.sup.-, (0.6008 molar) and 1.959 ml of
an aqueous solution of N,N,N-tri-methyl-1-adamantylammonium hydroxide,
TMAA.sup.+ OH.sup.-, (0.5721 molar). 2.000 ml of tetraethylorthosilicate
was then added to this composition and the resultant mixture was
continuously stirred in a sealed container for 15 hours at room
temperature until all the tetraethylorthosilicate was completely
hydrolyzed. To the resultant clear solution was added 0.195 ml of
a 48 wt % aqueous solution of hydrofluoric acid which immediately
resulted in the production of a slurry. This slurry was further
homogenized by stirring and exposure to air for evaporation of water
and ethanol until a thick slurry mixture was obtained. To this thick
slurry, 0.058 ml (0.37 wt. % based on the weight of the dry gel)
of LEV colloidal seeds (SiO.sub.2/Al.sub.2O.sub.3=12) suspension
slurry (14.1 wt. %) containing 4478 wt. ppm of sodium and 18000
wt. ppm of potassium was added and stirring was continued for another
10 minutes. Extra water was further evaporated from the slurry mixture
under static conditions to give 2242 mg of a dry gel solid having
the following molar composition: SiO.sub.2:0.00083Al.sub.2O.sub.3:0.375DEDMP:0.125TMAA:0.6F:5.0H.sub.2O
The resulting mixture of solids was transferred to a Teflon.RTM.-lined
5 ml reactor and crystallized at 175.degree. C. for 65 hours under
slow rotation (about 60 rpm). After cooling, the resultant solid
was recovered by centrifuging, washed with distilled water, and
dried at 100.degree. C. to give 634 mg of a white microcrystalline
solid (28.3% yield based on the weight of the dry gel). The Synchrotron
X-ray diffraction pattern of as-synthesized product is shown in
Table 3 whereas the X-ray diffraction pattern of the as-calcined
product is shown in FIG. 8.
DIFFaX analysis on the calcined Synchrotron X-ray pattern of FIG.
8 suggests the material of Example 7 is a pure CHA phase material.
However, .sup.13C MAS NMR analysis showed the presence of DEDMP
(the AEI directing agent) and TMAA (the CHA directing agent) in
a molar ratio of 13/87 in the as-synthesized product. The HR-TEM
of the product is shown in FIG. 9 and clearly shows the crystal
is faulted. To quantify the amount of faulting, 500 chards were
analyzed in BF-TEM and 10% of the chards showed faults.
.sup.13C MAS NMR analysis showed the presence of DEDMP (the AEI
directing agent) and TMAA (the CHA directing agent) in a molar ratio
of 13/87 in the as-synthesized product. SEM analysis of the calcined
product showed particles having a thick plate morphology and a size
of about 0.5 micron. Chemical analysis showed the silica/alumina
molar ratio of the product to be 1200.
EXAMPLE 8
The as-synthesized materials from Examples 1 and 2 were individually
pressed to pellets at 30000 psig (2.07.times.10.sup.5 kPa) and then
ground and sieved to between 80 and 125 .mu.m. Two separate samples
of each of the sized materials were weighed between 21 and 22 mg
and mixed separately with 90 mg of 100 .mu.m silicon carbide. These
mixtures were loaded into separate 1.9 mm internal diameter tubes
sealed at the bottom with a quartz frit. The tubes were sealed into
heated reactor blocks and the catalysts were then calcined at 540.degree.
C. under flowing air for 2 hours to effect organic template removal.
The calcined catalysts were then subjected to a mixture of 85% methanol
in N.sub.2 at 500.degree. C., approximately 100 weight hourly space
velocity (WHSV), and 40 psia (276 kPa) methanol partial pressure
for 25 minutes. During the methanol reactions the reactor effluents
were collected and stored at timed intervals for analysis by gas
chromatography. Following the methanol reaction the catalysts were
subjected to a flow of 50% oxygen in nitrogen at 550.degree. C.
for approximately 90 minutes to burn off deposited coke. The reactor
effluents were analyzed by infrared spectroscopy with quantitation
of both carbon monoxide and carbon dioxide to determine the amounts
of coke deposition.
Selectivities to hydrocarbon products were calculated. The values
given below are averages of each individual selectivity over the
entire reaction. Each value represents an average of the selectivities
obtained from the two individual repeats.
EXAMPLE 9
The synthesis of Example 3 was repeated with the molar ratio of
DEDMP/TMAA in the synthesis mixture varying between 0.33 and 19.
The results of .sup.13C MAS NMR analysis for detecting the presence
of DEDMP (the AEI directing agent) and TMAA (the CHA directing agent),
expressed in molar ratios, in the as-synthesized products, as well
as the percentage of faulted chards observed in 500 chards by BF-TEM
analysis are shown in the following table, together with the results
for the as-synthesized material from Example 3.
TABLE-US-00006 DEDMP/TMAA in synthesis gel 1 3 5.67 13 C NMR analysis
0/100 8/92 30/70 DEDMP/TMAA in as- synthesized crystals Faulted
Chards by TEM 0 3 27 (% in 500 chards)
The as-synthesized products of Example 9 together with the as-synthesized
material from Example 3 were individually pressed to pellets at
30000 psig (2.07.times.10.sup.5 kPa) and then ground and sieved
to between 80 and 125 .mu.m. Two separate samples of both of the
sized materials were weighed between 21 and 22 mg and mixed separately
with 90 mg of 100 .mu.m silicon carbide. These mixtures were loaded
into separate 1.9 mm internal diameter tubes sealed at the bottom
with a quartz frit. The tubes were sealed into heated reactor blocks
and the catalysts were then calcined at 540.degree. C. under flowing
air for 2 hours to effect organic template removal. The calcined
catalysts were then subjected to a mixture of 85% methanol in N.sub.2
at 540.degree. C., approximately 100 weight hourly space velocity
(WHSV), and 40 psia (276 kPa) methanol partial pressure. During
the methanol reactions the reactor effluents were collected and
stored at timed intervals for analysis by gas chromatography. Following
the methanol reaction the catalysts were subjected to a flow of
50% oxygen in nitrogen at 550.degree. C. for approximately 90 minutes
to burn off deposited coke. The reactor effluents were analyzed
by infrared spectroscopy with quantitation of both carbon monoxide
and carbon dioxide to determine the amounts of coke deposition.
Selectivities to hydrocarbon products were calculated for each
reaction. The values given below are the individual point selectivities
obtained 30 seconds after the start of the methanol reaction for
each catalyst. These values represent the points of maximum olefin
selectivity for each catalyst. Each value represents an average
of the selectivities obtained from the two individual repeats.
EXAMPLE 10
The as-synthesized material from Example 7 was pressed to a pellet
at 30000 psig (2.07.times.10.sup.5 kPa) and then ground and sieved
to between 80 and 125 .mu.m. Two separate samples of the sized material
were weighed between 21 and 22 mg and mixed separately with 90 mg
of 100 .mu.m silicon carbide. These mixtures were loaded into separate
1.9 mm internal diameter tubes sealed at the bottom with a quartz
frit. The tubes were sealed into heated reactor blocks and the catalysts
were then calcined at 540.degree. C. under flowing air for 2 hours
to effect organic template removal. The calcined catalysts were
then subjected to a mixture of 85% methanol in N.sub.2 at 540.degree.
C., approximately 100 weight hourly space velocity (WHSV), and 40
psia (276 kPa) methanol partial pressure for 25 minutes. During
the methanol reaction the reactor effluents were collected and stored
at timed intervals for analysis by gas chromatography. Following
the methanol reaction the catalysts were subjected to a flow of
50% oxygen in nitrogen at 550.degree. C. for approximately 90 minutes
to burn off deposited coke. The reactor effluents were analyzed
by infrared spectroscopy with quantitation of both carbon monoxide
and carbon dioxide to determine the amounts of coke deposition.
Selectivities to hydrocarbon products were calculated. The values
given below are averages of each individual selectivity over the
entire reaction. Each value represents an average of the selectivities
obtained from the two individual repeats.
TABLE-US-00008 Product Selectivity C.sub.1 2.9 C.sub.2.sup.0 0.3
C.sub.2.sup.= 41.6 C.sub.3.sup.0 0.1 C.sub.3.sup.= 36.0 C.sub.4
13.7 C.sub.5.sup.+ 3.9 Coke 1.3
While the present invention has been described and illustrated
by reference to particular embodiments, those of ordinary skill
in the art will appreciate that the invention lends itself to variations
not necessarily illustrated herein. For this reason, then, reference
should be made solely to the appended claims for purposes of determining
the true scope of the present invention. |