U.S. patent application number 11/059945 was filed with the patent office on 2006-06-15 for synthesis of silicoaluminophosphate molecular sieves.
Invention is credited to Machteld Maria Mertens.
Application Number | 20060127296 11/059945 |
Document ID | / |
Family ID | 36584136 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060127296 |
Kind Code |
A1 |
Mertens; Machteld Maria |
June 15, 2006 |
SYNTHESIS OF SILICOALUMINOPHOSPHATE MOLECULAR SIEVES
Abstract
In a method of synthesizing a silicoaluminophosphate molecular
sieve comprising at least one intergrown phase of an AEI framework
type material and a CHA framework type material, a first synthesis
mixture is prepared comprising water and sources of phosphorus,
aluminum and optionally silicon. The first synthesis mixture is
then heated under agitation to a first temperature to form an
intermediate product mixture containing a silicoaluminophosphate or
aluminophosphate precursor material. The intermediate product
mixture is then cooled and stored at a second temperature lower
than the first temperature, whereafter a second synthesis mixture
is prepared comprising at least part of the intermediate product
mixture and at least one organic directing agent. The second
synthesis mixture is heated to a third temperature higher than the
second temperature to convert at least part of the precursor
material into the desired molecular sieve and the molecular sieve
is recovered.
Inventors: |
Mertens; Machteld Maria;
(Boortmeerbeek, BE) |
Correspondence
Address: |
EXXONMOBIL CHEMICAL COMPANY
5200 BAYWAY DRIVE
P.O. BOX 2149
BAYTOWN
TX
77522-2149
US
|
Family ID: |
36584136 |
Appl. No.: |
11/059945 |
Filed: |
February 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60634655 |
Dec 9, 2004 |
|
|
|
Current U.S.
Class: |
423/306 ;
502/214; 585/638; 585/639; 585/640 |
Current CPC
Class: |
C07C 1/20 20130101; Y10S
423/30 20130101; Y02P 30/20 20151101; C01B 37/08 20130101; B01J
29/005 20130101; B01J 29/85 20130101; Y02P 30/40 20151101; Y02P
30/42 20151101; C07C 1/20 20130101; C07C 11/02 20130101 |
Class at
Publication: |
423/306 ;
502/214; 585/638; 585/639; 585/640 |
International
Class: |
C07C 1/00 20060101
C07C001/00; B01J 27/182 20060101 B01J027/182; C01B 25/26 20060101
C01B025/26 |
Claims
1. A method of synthesizing a silicoaluminophosphate molecular
sieve comprising at least one intergrown phase of an AEI framework
type material and a CHA framework type material, the method
comprising: (a) preparing a first synthesis mixture comprising
water and sources of phosphorus, aluminum and optionally silicon;
(b) heating said first synthesis mixture under agitation to a first
temperature of from about 99.degree. C. to about 150.degree. C. to
form an intermediate product mixture containing a
silicoaluminophosphate or aluminophosphate precursor material; and
(c) cooling and storing the intermediate product mixture at a
second temperature less than 50.degree. C. (d) preparing a second
synthesis mixture comprising at least part of said intermediate
product mixture from (c) and at least one organic directing agent,
and, if necessary, a silicon source to provide a
SiO.sub.2:Al.sub.2O.sub.3 ratio within said second synthesis
mixture of from about 0.05 to about 0.3; (e) heating said second
synthesis mixture, under static conditions or with reduced
agitation in comparison with that used during heating of said first
synthesis mixture, to a third temperature higher than said first
temperature and from about 150.degree. C. to about 220.degree. C.
to convert at least part of said precursor material into said
molecular sieve; and (f) recovering said molecular sieve.
2. (canceled)
3. The method of claim 1, wherein the first temperature is about
115.degree. C. to about 125.degree. C.
4. (canceled)
5. The method of claim 1, wherein the second temperature is about
0.degree. C. to about 30.degree. C.
6. (canceled)
7. The method of claim 1, wherein the third temperature is about
165.degree. C. to about 190.degree. C.
8. The method of claim 1, wherein the pH of the first synthesis
mixture is less than 2.
9. The method of claim 1, wherein the pH of the first synthesis
mixture is between about 1.1 and about 1.5.
10. The method claim 1, wherein the P.sub.2O.sub.5:Al.sub.2O.sub.3
of the first synthesis mixture is between about 0.7 and about
1.0.
11. The method of claim 1, wherein the
P.sub.2O.sub.5:Al.sub.2O.sub.3 of the first synthesis mixture is
between about 0.75 and about 0.9.
12. The method of claim 1, wherein the first synthesis mixture
comprises said at least one organic directing agent.
13. The method of claim 12, wherein the second synthesis mixture
has the same composition as the intermediate product mixture.
14. The method of claim 1, wherein the molar ratio of organic
directing agent (R) to Al.sub.2O.sub.3 in the second synthesis
mixture is greater than that of the first synthesis mixture.
15. The method of claim 14, wherein the R:Al.sub.2O.sub.3 molar
ratio of the second synthesis mixture is greater than 0.6.
16. The method of claim 14, wherein the R:Al.sub.2O.sub.3 molar
ratio of the second synthesis mixture is about 0.65 to about 1.
17. The method of claim 14, wherein the R:Al.sub.2O.sub.3 molar
ratio of the first synthesis mixture is less than 0.7.
18. The method of claim 14, wherein the R:Al.sub.2O.sub.3 molar
ratio of the first synthesis mixture is about 0.2 to about 0.6.
19. The method of claim 1, wherein the H.sub.2O:Al.sub.203 molar
ratio of the first synthesis mixture is at least 30.
20. The method of claim 1, wherein the H.sub.2O:Al.sub.2O.sub.3
molar ratio of the first synthesis mixture is about 30 to about
50.
21. The method of claim 1, wherein said precursor material
comprises at least one of ALPO-H3, variscite and metavariscite.
22. The method of claim 1 and also comprising reducing the water
content of the intermediate product mixture prior to storage
thereof.
23. The method of claim 22, wherein preparing the second synthesis
mixture in (d) also comprises adding water to said intermediate
product mixture from (c).
24. The method of claim 1, wherein the H.sub.2O:Al.sub.2O.sub.3
molar ratio of the second synthesis mixture is the same as that of
the first synthesis mixture.
25. The method of claim 1, wherein the heating in (b) is conducted
so as to raise the temperature of said first synthesis mixture at a
rate of at least 8.degree. C./hour.
26. The method of claim 1, wherein the heating in (b) is conducted
so as to raise the temperature of said first synthesis mixture at a
rate of from about 10.degree. C./hour to about 40.degree.
C./hour.
27. The method of claim 1, wherein the heating (e) is conducted
without agitation.
28. The method of claim 1, wherein the heating in (e) is conducted
so as to raise the temperature of said first synthesis mixture at a
rate of at least 8.degree. C./hour.
29. The method of claim 1, wherein the heating in (e) is conducted
so as to raise the temperature of said first synthesis mixture at a
rate of from about 10.degree. C./hour to about 40.degree.
C./hour.
30. The method of claim 1, wherein (c) comprises storing said
cooled intermediate product mixture for at least 2 hours before the
heating (e).
31. The method of claim 1, wherein (c) comprises storing said
cooled intermediate product mixture for about 30 hours to about 30
days before the heating (e).
32. The method of claim 1, wherein said at least one intergrown
phase has an AEI/CHA ratio of from about 5/95 to about 40/60 as
determined by DIFFaX analysis.
33. The method of claim 1, wherein said at least one intergrown
phase has an AEI/CHA ratio of from about 10/90 to about 30/70 as
determined by DIFFaX.
34. The method of claim 1, wherein said at least one intergrown
phase has an AEI/CHA ratio of from about 15/95 to about 20/80 as
determined by DIFFaX.
35. The method of claim 32, wherein said silicoaluminophosphate
molecular sieve has an X-ray diffraction pattern comprising at
least one reflection peak in each of the following ranges in the 5
to 25 (2.theta.) range: TABLE-US-00002 2.theta. (CuK.alpha.)
9.3-9.6 12.7-13.0 13.8-14.0 15.9-16.1 17.7-18.1 18.9-19.1 20.5-20.7
23.7-24.0.
36. The method of claim 1, wherein said silicoaluminophosphate
molecular sieve comprises first and second intergrown phases each
of an AEI framework type material and a CHA framework type
material.
37. The method of claim 36, wherein said first intergrown phase has
an AEI/CHA ratio of from about 5/95 to about 40/60 as determined by
DIFFaX analysis and said second intergrown phase has a different
AEI/CHA ratio from said first intergrown form.
38. The method of claim 37, wherein said second intergrown phase
has an AEI/CHA ratio of about 30/70 to about 55/45 as determined by
DIFFaX analysis.
39. The method of claim 37, wherein said second intergrown phase
has an AEI/CHA ratio of about 50/50 as determined by DIFFaX
analysis.
40. A silicoaluminophosphate molecular sieve produced by the method
of claim 1.
41. A process for making an olefin product from an oxygenate
feedstock comprising contacting said oxygenate feedstock with a
catalyst comprising the silicoaluminophosphate molecular sieve of
claim 40.
42. The process of claim 41, wherein the oxygenate-containing
feedstock comprises methanol, dimethyl ether, or mixtures thereof
and the olefin product comprises ethylene and propylene.
43. The process of claim 41 and further comprising converting the
olefin product to polymer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Provisional
Application No. 60/634,655 filed Dec. 9, 2004, the disclosure of
which is fully incorporated herein by reference.
FIELD OF INVENTION
[0002] This invention relates to the synthesis of
silicoaluminophosphate molecular sieves and to the use of the
resultant molecular sieves in the conversion of oxygenates,
particularly methanol, to olefins, particularly ethylene and
propylene.
BACKGROUND OF INVENTION
[0003] Light olefins, such as ethylene, propylene, butylenes and
mixtures thereof, serve as feeds for the production of numerous
important chemicals and polymers. Typically, C.sub.2-C.sub.4 light
olefins are produced by cracking petroleum refinery streams, such
as C.sub.3+ paraffinic feeds. In view of limited supply of
competitive petroleum feeds, production of low cost light olefins
from petroleum feeds is subject to waning supplies. Efforts to
develop light olefin production technologies based on alternative
feeds have therefore increased.
[0004] An important type of alternative feed for the production of
light olefins is oxygenates, such as C.sub.1-C.sub.4 alkanols,
especially methanol and ethanol; C.sub.2-C.sub.4 dialkyl ethers,
especially dimethyl ether (DME), methyl ethyl ether and diethyl
ether; dimethyl carbonate and methyl formate, and mixtures thereof.
Many of these oxygenates may be produced from alternative sources
by fermentation, or from synthesis gas derived from natural gas,
petroleum liquids, carbonaceous materials, including coal, recycled
plastic, municipal waste, or any organic material. Because of the
wide variety of sources, alcohol, alcohol derivatives, and other
oxygenates have promise as economical, non-petroleum sources for
light olefin production.
[0005] The preferred process for converting an oxygenate feedstock,
such as methanol, into one or more olefin(s), primarily ethylene
and/or propylene, involves contacting the feedstock with a
crystalline molecular sieve catalyst composition. Crystalline
molecular sieves have a 3-dimensional, four-connected framework
structure of corner-sharing [TO.sub.4] tetrahedra, where T is any
tetrahedrally coordinated cation. Among the known forms of
molecular sieve are aluminosilicates, which contain a
three-dimensional microporous crystal framework structure of
[SiO.sub.4] and [AlO.sub.4] corner sharing tetrahedral units
silicoaluminophosphates (SAPOs), in which the framework structure
is composed of [SiO.sub.4], [AlO.sub.4] and [PO.sub.4] corner
sharing tetrahedral units.
[0006] Molecular sieves have been classified by the Structure
Commission of the International Zeolite Association according to
the rules of the IUPAC Commission on Zeolite Nomenclature.
According to this classification, framework-type zeolite and
zeolite-type molecular sieves, for which a structure has been
established, are assigned a three letter code and are described in
the Atlas of Zeolite Framework Types, 5th edition, Elsevier,
London, England (2001), which is herein fully incorporated by
reference.
[0007] Among the molecular sieves that have been investigated for
use as oxygenate conversion catalysts, materials having the
framework type of the zeolitic mineral chabazite (CHA) have shown
particular promise. For example, SAPO-34 is a crystalline
silicoaluminophosphate molecular sieve of the CHA framework type
and has been found to exhibit relatively high product selectivity
to ethylene and propylene, and low product selectivity to paraffins
and olefins with four or more carbon atoms.
[0008] The preparation and characterization of SAPO-34 have been
reported in several publications, including U.S. Pat. No.
4,440,871; J. Chen et al. in "Studies in Surface Science and
Catalysis", Vol. 84, pp. 1731-1738; U.S. Pat. No. 5,279,810; J.
Chen et al. in "Journal of Physical Chemistry", Vol. 98, pp.
10216-10224 (1994); J. Chen et al. in "Catalysis Letters", Vol. 28,
pp. 241-248 (1994); A. M. Prakash et al. in "Journal of the
Chemical Society, Faraday Transactions" Vol. 90(15), pp. 2291-2296
(1994); Yan Xu et al. in "Journal of the Chemical Society, Faraday
Transactions" Vol. 86(2), pp. 425-429 (1990).
[0009] According to the article entitled "Identification of a Key
Precursor Phase for Synthesis of SAPO-34 and Kinetics of Formation
Investigated by In Situ X-ray Diffraction" by O. B. Vistad et al.,
J. Phys. Chem. B, 2001, 105, pages 12437-12447, the synthesis of
SAPO-34 in the presence of HF and with morpholine as a structure
directing agent proceeds through the formation of a layered
crystalline precursor phase. The layered precursor is reported to
be formed at synthesis temperatures of 90.degree. C. to 150.degree.
C., whereas SAPO-34 is formed at temperatures of 170.degree. C. to
210.degree. C.
[0010] Similarly, the article entitled "Synthesis of AlPO.sub.4-11"
by N. J. Tapp et al., Zeolites, 1988, Vol. 8, 183-188 discloses
that the synthesis of AlPO.sub.4-11 free of condensed phase
impurities is aided by pretreatment of the synthesis gel at
90.degree. C. The pretreatment is reported to produce a poorly
crystalline metavariscite/variscite phase that is transformed to
AlPO.sub.4-11 on raising the temperature to 200.degree. C.
[0011] Regular crystalline molecular sieves, such as the CHA
framework type materials, are built from structurally invariant
building units, called Periodic Building Units, and are
periodically ordered in three dimensions. Disordered structures
showing periodic ordering in less than three dimensions are,
however, also known. One such disordered structure is a disordered
planar intergrowth in which the building units from more than one
framework type, e.g., both AEI and CHA, are present. One well-known
method for characterizing crystalline materials with planar faults
is DIFFaX, 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).
[0012] International Patent Publication No. WO 02/70407, published
Sep. 12, 2002 and incorporated herein by reference, discloses a
silicoaluminophosphate molecular sieve, now designated EMM-2,
comprising at least one intergrown form of molecular sieves having
AEI and CHA framework types, wherein said intergrown form 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. EMM-2 has
been found to exhibit significant activity and selectivity as a
catalyst for the production of light olefins from methanol
(MTO).
[0013] According to International Patent Publication No. WO
02/70407, EMM-2 can be synthesized by mixing reactive sources of
silicon, phosphorus and a hydrated aluminum oxide in the presence
of an organic directing agent, particularly a tetraethylammonium
compound. The resultant mixture is stirred and heated to a
crystallization temperature, preferably from 150.degree. C. to
185.degree. C., and then maintained at this temperature under
stirring for between 2 and 150 hours.
[0014] U.S. Pat. No. 6,334,994, incorporated herein by reference,
discloses a silicoaluminophosphate molecular sieve, referred to as
RUW-19, which is also said to be an AEI/CHA mixed phase
composition. In particular, RUW-19 is reported as having peaks
characteristic of both AEI and CHA 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. DIFFaX analysis of the X-ray diffraction
pattern of RUW-19 as produced in Examples 1, 2 and 3 of U.S. Pat.
No. 6,334,994 indicates that these materials are characterized by
single intergrown forms of AEI and CHA framework type molecular
sieves with AEI/CHA ratios of about 60/40, 65/35 and 70/30.
[0015] According to the '994 patent, RUW-19 can be synthesized by
initially mixing an Al-source, particularly Al-isopropoxide, with
water and a P-source, particularly phosphoric acid, and thereafter
adding a Si-source, particularly colloidal silica and an organic
template material, particularly tetraethylammonium hydroxide, to
produce a precursor gel. The gel is then put into a steel autoclave
and, after an aging period at room temperature, the autoclave is
heated to a maximum temperature between 180.degree. C. and
260.degree. C., preferably at least 200.degree. C., for at least 1
hour, with the autoclave being shaken, stirred or rotated during
the entire process of aging and crystallization. Factors which are
said to enhance the production of the mixed phase RUW-19 material
include maintaining the SiO.sub.2 content of the gel below 5%,
reducing the liquid content of the gel after addition of the
SiO.sub.2 source and crystallization at temperatures of 250.degree.
C. to 260.degree. C. Pure AEI and CHA phases are said to be favored
at temperatures of 200.degree. C. to 230.degree. C.
[0016] Study of the synthesis of EMM-2 has now shown that the
crystallization process to produce such AEI/CHA intergrowths
proceeds through the formation of a (silico)aluminophosphate
hydrate precursor, such as ALPO-H3 and/or variscite and/or
metavariscite, during heat-up of the mixture, followed by
dissolution of the precursor as the intergrown molecular sieve
nucleates. Moreover, it has been found that optimal conditions for
the formation of the precursor are different from the optimal
conditions for conversion of the precursor to the intergrown
molecular sieve. For example, whereas agitation of the synthesis
mixture seems to be important in initial precursor formation,
synthesis of the intergrown molecular sieve from the precursor
slurry can proceed with no or reduced agitation. In addition, the
presence of an organic directing agent seems to be more important
during nucleation of EMM-2 than during precursor formation. In
fact, the absence of an organic directing agent seems to allow the
precursor to crystallize under more mild conditions (for example at
lower temperature).
[0017] Accordingly, the present invention provides a method of
synthesizing a silicoaluminophosphate molecular sieve comprising at
least one intergrown phase of an AEI framework type and a CHA
framework type, in which the precursor formation stage and the
molecular sieve nucleation stage are decoupled whereby each stage
can be conducted under the most advantageous conditions.
SUMMARY
[0018] In one aspect, the invention resides in a method of
synthesizing a silicoaluminophosphate molecular sieve comprising at
least one intergrown phase of an AEI framework type material and a
CHA framework type material, the method comprising:
[0019] (a) preparing a first synthesis mixture comprising water and
sources of phosphorus, aluminum and optionally silicon;
[0020] (b) heating said first synthesis mixture under agitation to
a first temperature to form an intermediate product mixture
containing a silicoaluminophosphate or aluminophosphate precursor
material; and
[0021] (c) cooling and storing the intermediate product mixture at
a second temperature lower than said first temperature;
[0022] (d) preparing a second synthesis mixture comprising at least
part of said intermediate product mixture from (c) and at least one
organic directing agent;
[0023] (e) heating said second synthesis mixture to a third
temperature higher than said first temperature to convert at least
part of said precursor material into said molecular sieve; and
[0024] (f) recovering said molecular sieve.
[0025] Conveniently, said first temperature is from about
99.degree. C. to about 150.degree. C., such as about 115.degree. C.
to about 125.degree. C.
[0026] Conveniently, said second temperature is less than
50.degree. C., such as from about 0.degree. C. to about 30.degree.
C.
[0027] Conveniently, said third temperature is higher than said
first temperature, for example from about 150.degree. C. to about
220.degree. C., such as from about 165.degree. C. to about
190.degree. C.
[0028] Conveniently, the pH of the first synthesis mixture is less
than 2, such as between about 1.1 and about 1.5. Conveniently, the
pH of the second synthesis mixture is between about 5 and about 12,
such as between about 6 and about 8.
[0029] Conveniently, the P.sub.2O.sub.5:Al.sub.2O.sub.3 of the
first synthesis mixture is between about 0.7 and about 1.0, such as
between about 0.75 and about 0.9.
[0030] In one embodiment, the first synthesis mixture also
comprises said at least one organic directing agent (R), in which
case the second synthesis mixture conveniently has the same
composition as the intermediate product mixture. Typically,
however, the R:Al.sub.2O.sub.3 molar ratio of the second synthesis
mixture is greater than that of the first synthesis mixture.
Conveniently, the R:Al.sub.2O.sub.3 molar ratio of the second
synthesis mixture is greater than 0.6, such as about 0.65 to about
1, and the R:Al.sub.2O.sub.3 molar ratio of the first synthesis
mixture is less than 0.7, such as about 0.2 to about 0.6.
[0031] Conveniently, the H.sub.2O:Al.sub.2O.sub.3 molar ratio of
the first synthesis mixture is at least 30, such as about 30 to
about 50.
[0032] Conveniently, the method also comprises reducing the water
content of the intermediate product mixture prior to storage
thereof. In such a case, preparing the second synthesis mixture in
(d) conveniently also comprises adding water to said intermediate
product mixture from (c). In one embodiment, the
H.sub.2O:Al.sub.2O.sub.3 molar ratio of the second synthesis
mixture is the same as that of the first synthesis mixture.
[0033] Conveniently, said precursor material comprises at least one
of ALPO-H3, variscite and metavariscite.
[0034] Conveniently, the heating in (b) is conducted so as to raise
the temperature of said first synthesis mixture at a rate of at
least 8.degree. C./hour, such as at a rate of from about 10.degree.
C./hour to about 40.degree. C./hour. Conveniently, the heating in
(e) is also conducted so as to raise the temperature of said second
synthesis mixture at a rate of at least 8.degree. C./hour, such as
at a rate of from about 10.degree. C./hour to about 40.degree.
C./hour. In one embodiment, the heating (e) is conducted without
agitation.
[0035] Conveniently, (c) comprises storing said cooled intermediate
product mixture for at least 2 hours, such as for about 30 hours to
about 30 days, before the heating (e).
[0036] In one embodiment, said at least one intergrown phase has an
AEI/CHA ratio of from about 5/95 to about 40/60, for example from
about 10/90 to about 30/70, such as from about 15/85 to about
20/80, as determined by DIFFaX analysis. In a further embodiment,
the silicoaluminophosphate molecular sieve comprises first and
second intergrown phases each of an AEI framework type material and
a CHA framework type material, the first intergrown phase having an
AEI/CHA ratio of from about 5/95 to about 40/60 as determined by
DIFFaX analysis, and the second intergrown phase having a different
AEI/CHA ratio from said first intergrown form, such as an AEI/CHA
ratio of about 50/50 as determined by DIFFaX analysis.
[0037] In further aspects, the invention resides in a
silicoaluminophosphate molecular sieve produced by the method
described herein and to use of the molecular sieve in a process for
converting an oxygenate-containing feedstock to a product
comprising olefins.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIGS. 1a and 1b are DIFFaX simulated diffraction patterns
for intergrown AEI/CHA phases having varying AEI/CHA ratios.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0039] The present invention relates to the synthesis of a
crystalline silicoaluminophosphate molecular sieve comprising at
least one intergrown form of an AEI framework type material and a
CHA framework type material, and to the use of the resultant
molecular sieve in the conversion of oxygenates, particularly
methanol, to olefins, particularly ethylene and propylene.
[0040] According to the invention, it has been found that the
synthesis of AEI/CHA intergrowths proceeds through the formation,
and subsequent dissolution, of certain (silico)aluminophosphate
hydrate precursors, such as ALPO-H3, variscite and/or
metavariscite. Moreover, it has been found that the optimal
conditions for precursor formation are different from those for
precursor dissolution/molecular sieve nucleation. The synthesis
method of the invention therefore seeks to decouple the initial
formation of the precursor from the subsequent dissolution of the
precursor and nucleation of the intergrown molecular sieve. In this
way, it is possible to independently optimize the conditions
employed in each stage of the synthesis.
Molecular Sieve
[0041] 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.
[0042] 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.
[0043] The intergrown silicoaluminophosphate molecular sieves
described herein are disordered planar intergrowth of end-member
structures AEI and CHA. For AEI and CHA structure types, 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. . . . aaa . . . or . . . bbb . .
. , the framework type CHA is generated. When layers "a" and "b"
alternate, e.g. . . . abab . . . , a different framework type,
namely AEI, is generated. The intergrown molecular sieves described
herein comprise stackings of layers "a" and "b" containing regions
of CHA framework type and regions of AEI framework type. Each
change of CHA to AEI framework type is a stacking disorder or
planar fault.
[0044] In the case of crystals with planar faults, the
interpretation of X-ray diffraction patterns requires an ability 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 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.
[0045] FIGS. 1a and 1b show the simulated diffraction patterns
obtained for intergrowths of a CHA framework type molecular sieve
with an AEI framework type molecular sieve having various AEI/CHA
ratios. FIG. 1a shows the diffraction patterns in the 15 to 35
(2.theta.) range simulated by DIFFAX for intergrown phases with
AEI/CHA ratios of 0/100 (CHA end-member), 10/90 AEI/CHA=0.11),
20/80 (AEI/CHA=0.25), 30/70 (AEI/CHA=0.41), 40/60 (AEI/CHA=0.67),
50/50 (AEI/CHA=1.00) and 60/40 (AEI/CHA=1.50). FIG. 1b shows the
diffraction patterns in the range of 5 to 20 (2.theta.) simulated
by DIFFaX for intergrown phases with AEI/CHA ratios of 0/100 (CHA
end-member), 10/90 (AEI/CHA=0.11), 20/80 (AEI/CHA=0.25), 50/50
(AEI/CHA=1.0), 70/30 (AEI/CHA=2.33), 80/20 (AEI/CHA=4.0), 100/0
(AEI end-member). All XRD diffraction patterns are normalized to
the highest peak of the entire set of simulated patterns, i.e. the
peak at about 9.5 degrees 20 for pure CHA (AEI/CHA ratio of 0/100).
Such normalization of intensity values allows a quantitative
determination of mixtures of intergrowths
[0046] As the ratio of AEI increases relative to CHA in the
intergrown phase, one can observe a decrease in intensity of
certain peaks, for example, the peak at about 2.theta.=25.0 and an
increase in intensity of other peaks, for example the peak at about
2.theta.=17.05 and the shoulder at 2.theta.=21.2. Intergrown phases
with AEI/CHA ratios of 50/50 and above (AEI/CHA.gtoreq.1.0) show a
broad feature centered at about 16.9 (2.theta.).
[0047] In a preferred embodiment, the intergrown
silicoaluminophosphate molecular sieve employed in the catalyst
composition of the invention is at least one intergrowth of an AEI
framework type and a CHA framework type, wherein said at least one
intergrowth has an AEI/CHA ratio of from about 5/95 to about 40/60,
for example from about 10/90 to about 30/70, such as from about
15/85 to about 20/80, as determined by DIFFAX analysis. Such a
CHA-rich intergrowth is characterized by a powder XRD diffraction
pattern (obtained from a sample after calcination and without
rehydration after calcination) having at least the reflections in
the 5 to 25 (2.theta.) range as shown in Table 1 below:
TABLE-US-00001 TABLE 1 2.theta. (CuK.alpha.) 9.3-9.6 12.7-13.0
13.8-14.0 15.9-16.1 17.7-18.1 18.9-19.1 20.5-20.7 23.7-24.0
[0048] The X-ray diffraction data referred to herein are collected
with a SCINTAG X2 X-Ray Powder Diffractometer (Scintag Inc., USA),
using copper K-alpha radiation. The diffraction data are 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. Prior
to recording of each experimental X-ray diffraction pattern, the
sample must be in the anhydrous state and free of any template used
in its synthesis, since the simulated patterns are calculated using
only framework atoms, not extra-framework material such as water or
template in the cavities. Given the sensitivity of
silicoaluminophosphate materials to water at recording
temperatures, the molecular sieve samples are calcined after
preparation and kept moisture-free according to the following
procedure.
[0049] About 2 grams of each molecular sieve sample are heated in
an oven from room temperature under a flow of nitrogen at a rate of
3.degree. C./minute to 200.degree. C. and, while retaining the
nitrogen flow, the sample is held at 200.degree. C. for 30 minutes
and the temperature of the oven is then raised at a rate of
2.degree. C./minute to 650.degree. C. The sample is then retained
at 650.degree. C. for 8 hours, the first 5 hours being under
nitrogen and the final 3 hours being under air. The oven is then
cooled to 200.degree. C. at 30.degree. C./minute and, when the XRD
pattern is to be recorded, the sample is transferred from the oven
directly to a sample holder and covered with Mylar foil to prevent
rehydration. Recording under the same conditions immediately after
removal of the Mylar foil will also provide a diffraction pattern
suitable for use in DIFFaX analysis.
[0050] In an alternative embodiment, the intergrown
silicoaluminophosphate molecular sieve produced by the synthesis
method of the invention comprises a plurality of intergrown forms
of the CHA and AEI framework types, typically with a first
intergrown form having an AEI/CHA ratio of from about 5/95 to about
40/60, as determined by DIFFAX analysis, and a second intergrown
form having a different AEI/CHA ratio from said first intergrown
form. The second intergrown form typically has an AEI/CHA ratio of
about 30/70 to about 55/45, such as about 50/50, as determined by
DIFFAX analysis, in which case the XRD diffraction pattern exhibits
a broad feature centered at about 16.9 (2.theta.) in addition to
the reflection peaks listed in Table 1.
[0051] Preferably, the CHA framework type molecular sieve in the
intergrowth of the invention is SAPO-34 and the AEI framework type
molecular sieve is selected from SAPO-18, ALPO-18 and mixtures
thereof. In addition, the intergrown silicoaluminophosphate
preferably has a framework silica to alumina molar ratio
(Si/Al.sub.2) greater than 0.16 and less than 0.19, such as from
about 0.165 to about 0.185, for example about 0.18. The framework
silica to alumina molar ratio is conveniently determined by NMR
analysis.
Molecular Sieve Synthesis
[0052] The molecular sieve synthesis method of the invention
comprises three stages; namely a first stage in which a
silicoaluminophosphate or aluminophosphate precursor material is
produced, a second storage stage, and a third stage in which the
precursor material is converted into the desired intergrown AEI/CHA
framework type molecular sieve.
[0053] In the first synthesis stage, water is initially combined
with reactive sources of phosphorus, aluminum and optionally
silicon, to form a first synthesis mixture having a molar
composition within the following ranges:
[0054] P.sub.2O.sub.5:Al.sub.2O.sub.3=about 0.7 to about 1.0, such
as about 0.75 to about 0.9;
[0055] H.sub.2O:Al.sub.2O.sub.3=at least 30, such as from about 30
to about 50; and
[0056] SiO.sub.2:Al.sub.2O.sub.3=0 to about 0.3, such as about 0.1
to about 0.2.
[0057] In addition, an organic structure directing agent (R) can be
incorporated in the first synthesis mixture, in which case the
R:Al.sub.2O.sub.3 ratio of the first synthesis mixture is typically
below 0.7, such as from about 0.2 to about 0.6.
[0058] The reactive source of phosphorus used in the first
synthesis mixture is conveniently phosphoric acid. Examples of
suitable reactive aluminum sources include hydrated aluminum oxides
such as boehmite and pseudoboehmite. Preferably, pseudoboehmite is
used. Where present, the reactive source of silicon may be a
silicate, e.g., fumed silica, such as Aerosil (available from
Degussa), a tetraalkyl orthosilicate, or an aqueous colloidal
suspension of silica, for example that sold by E.I. du Pont de
Nemours under the tradename Ludox. The organic structure directing
agent conveniently includes a tetraethyl ammonium compound, such as
tetraethyl ammonium hydroxide (TEAOH), tetraethyl ammonium
phosphate, tetraethyl ammonium fluoride, tetraethyl ammonium
bromide, tetraethyl ammonium chloride or tetraethyl ammonium
acetate. Typically, the directing agent includes tetraethyl
ammonium hydroxide. In some cases, more than one organic structure
directing agent may be employed, such as a combination of a
tetraethyl ammonium compound and dipropylamine.
[0059] The pH of the first synthesis mixture is preferably arranged
to be less than 2, such as between about 1.1 and about 1.5, and
can, if necessary, be adjusted to be within the desired range by
addition of acid or base to the first synthesis mixture.
[0060] The first synthesis mixture is then heated so as to raise
its temperature at a rate of at least 8.degree. C./hour, such as at
a rate of from about 10.degree. C./hour to about 40.degree.
C./hour, to a first temperature of about 99.degree. C. to about
150.degree. C., such as about 115.degree. C. to about 125.degree.
C. During heating, the first synthesis mixture is continuously
agitated (i.e. by mixing, stirring, tumbling, shaking, swinging or
any other mode of agitation) with an intensity that avoids
precipitation of the mixture components. The first synthesis
mixture is then maintained at said first temperature, preferably
with the agitation being continued, for a time, typically from
about 0.5 hours to about 120 hours, to form an intermediate product
mixture containing a slurry of a silicoaluminophosphate or
aluminophosphate precursor material. The precursor material is
different from the final intergrown AEI/CHA framework type
molecular sieve and generally comprises at least one of ALPO-H3,
variscite and metavariscite.
[0061] After precursor formation, the intermediate product mixture
is cooled from the first temperature to a second, lower
temperature, typically less than 50.degree. C., such as from about
0.degree. C. to about 30.degree. C., and is then stored at this
lower temperature until it is desired to produce the final
intergrown molecular sieve. Typically, the storage time is at least
2 hours, such as from about 30 hours to about 30 days. In addition,
prior to storage, it may be desirable to at least partially dry the
precursor slurry to reduce its H.sub.2O:Al.sub.2O.sub.3 ratio.
[0062] Following storage, additional water can be added to the
precursor material, especially where the precursor slurry is dried
before storage, optionally together with a reactive silica source
or additional reactive silica source and an organic directing agent
or additional organic directing agent to produce a second synthesis
mixture having a molar composition within the following ranges:
[0063] P.sub.2O.sub.5:Al.sub.2O.sub.3=about 0.7 to about 1.0, such
as about 0.75 to about 0.9; [0064] H.sub.2O:Al.sub.2O.sub.3=at
least 30, such as from about 30 to about 50;
[0065] SiO.sub.2:Al.sub.2O.sub.3=about 0.05 to about 0.3, such as
about 0.1 to about 0.2; and
[0066] R:Al.sub.2O.sub.3=at least 0.6, such as about 0.65 to about
1.0.
[0067] It is, however, to be appreciated that, where an organic
directing agent is present in the first synthesis mixture, the
intermediate product mixture can be used as-is to produce the
desired AEI/CHA intergrowth. In other words, the second synthesis
mixture can have the same composition as the intermediate product
mixture.
[0068] The pH of the second synthesis mixture is generally not
critical, but typically is arranged to between about 5 and about
12, such as between about 6 and about 8.
[0069] The second synthesis mixture is then heated so as to raise
its temperature at a rate of at least 8.degree. C./hour, such as at
a rate of from about 10.degree. C./hour to about 40.degree.
C./hour, to a third temperature higher than the first temperature
and generally from about 150.degree. C. to about 220.degree. C.,
such as about 165.degree. C. to about 190.degree. C. This second
heating step can be conducted under static conditions or with
reduced agitation as compared with the first heating step. The
second synthesis mixture is then maintained at said third
temperature until the intergrown molecular sieve crystallizes from
the mixture, which generally takes from 2 to 150 hours; such as
from about 5 to about 100 hours, for example from about 10 to about
50 hours.
[0070] The crystalline product can then be recovered by any
standard means, such as by centrifugation or filtration. The
separated product can also be washed, recovered by centrifugation
or filtration and dried. The crystalline product is typically in
the form of plates, platelets, stacked platelets or cubes.
Typically the crystals have a d.sub.50 (50% by volume of crystals
is smaller than the d.sub.50 value) particle size from about 0.1 to
about 3 .mu.m, such as about 0.5 to about 2.0 .mu.m, for example
about 1.3 to about 1.9 .mu.m.
[0071] Synthesis of the desired AEI/CHA 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, CHA or ERI structure-type molecular sieve. The seed
crystals can have the same composition as, or can have a different
composition (e.g., the seeds can be an aluminosilicate) from, the
crystalline material of the present invention. The seeds can be
added to the first synthesis mixture, the second synthesis mixture
or to both mixtures.
[0072] The crystalline product recovered from the second synthesis
mixture 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.
Molecular Sieve Catalyst Compositions
[0073] The intergrown molecular sieve produced by the synthesis
method of the invention can be used in a wide variety of catalytic
and non-catalytic applications, but is particularly intended for
use as a catalyst in the conversion of oxygenates to olefins.
Before use in such a process, the intergrown molecular sieve will
normally be formulated into a catalyst composition by combination
with other materials, such as binders and/or matrix materials,
which provide additional hardness or catalytic activity to the
finished catalyst.
[0074] 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.
Use of the Molecular Sieve
[0075] The silicoaluminophosphate molecular sieves produced by the
method of the invention are useful as catalysts in a variety of
processes including cracking of, for example, a naphtha feed to
light olefin(s) or higher molecular weight (MW) hydrocarbons to
lower MW hydrocarbons; hydrocracking of, for example, heavy
petroleum and/or cyclic feedstock; isomerization of, for example,
aromatics such as xylene; polymerization of, for example, one or
more olefin(s) to produce a polymer product; reforming;
hydrogenation; dehydrogenation; dewaxing of, for example,
hydrocarbons to remove straight chain paraffins; absorption of, for
example, alkyl aromatic compounds for separating out isomers
thereof; alkylation of, for example, aromatic hydrocarbons such as
benzene and alkyl benzene, optionally with propylene to produce
cumene or with long chain olefins; transalkylation of, for example,
a combination of aromatic and polyalkylaromatic hydrocarbons;
dealkylation; dehydrocyclization; disproportionation of, for
example, toluene to make benzene and paraxylene; oligomerization
of, for example, straight and branched chain olefin(s); and the
synthesis of monoalkylamines and dialkylamines.
[0076] In particular, the intergrown molecular sieves described
herein are useful in the catalytic conversion of oxygenates to
olefins. 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.
[0077] 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.
[0078] 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.
[0079] When present, the diluent(s) is (are) 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] Using the various oxygenate feedstocks discussed above,
particularly a feedstock containing methanol, the catalyst
composition of the invention is effective to convert the feedstock
primarily into one or more olefin(s). The olefin(s) produced
typically have from 2 to 30 carbon atoms, preferably 2 to 8 carbon
atoms, more preferably 2 to 6 carbon atoms, still more preferably 2
to 4 carbons atoms, and most preferably are ethylene and/or
propylene. The resultant olefins can be separated from the
oxygenate conversion product for sale or can be fed to a downstream
process for converting the olefins to, for example, polymers.
[0087] The invention will now be more particularly described with
reference to the following Example.
[0088] In the Example, DIFFaX analysis was used to determine the
AEI/CHA ratio of the molecular sieves. Simulated 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. Tracey 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). The DIFFaX input file used to simulate the XRD
diffraction patterns is given in Table 2 of U.S. Patent Application
Publication No. 2002/0165089, incorporated herein by reference. In
order to obtain best fitting between the DIFFaX simulated patterns
and the experimental patterns, two sets of simulated XRD patterns
were generated using a line broadening of 0.009 (as described in
U.S. Patent Application No. 2002/0165089) and a line broadening of
0.04 (FIGS. 1a and 1b). The simulated diffraction patterns were
then compared with the experimental powder XRD diffraction
patterns. In this respect, a very sensitive range is the 15 to 19.5
2.theta. range.
EXAMPLE 1
[0089] A mixture of 381.81 g of phosphoric acid (85% in water,
Acros), 371.88 g of demineralized water and 25.64 g Ludox AS 40
(40% silica) was prepared. To this mixture 695.85 g of a
tetraethylammonium hydroxide solution (35% in water) was added. To
the resultant mixture was added 224.86 g of alumina (Condea Pural
SB-1). A slurry was produced and was transferred to a 2 liter Parr
stainless steel autoclave. The composition of the mixture in terms
of molar ratios was as follows:
[0090]
0.10SiO.sub.2/Al.sub.2O.sub.3/P.sub.2O.sub.5/TEAOH/35H.sub.2O
[0091] The autoclave was heated at 20.degree. C./hour to
150.degree. C. and then maintained at this temperature for 112
hours, with the mixture being stirred with a laboratory mixer at
600 rpm (tip speed of 3.1 m/s) during the whole hydrothermal
treatment. After cooling to room temperature, a sample of the
slurry was washed and dried and an X-ray diffraction pattern of the
crystalline product was taken and was identified as AlPO--C, a
partial dehydrated form of AlPO--H3.
[0092] The rest of the synthesis mixture was stored for 20 days at
room temperature without agitation. After the storage, part of the
slurry was transferred to a 300 ml stainless steel autoclave and
re-heated, without agitation, in 8 hrs to 175.degree. C. and then
maintained at this temperature for 48 hrs. After cooling the slurry
was washed and dried and a sample was taken for calcination and XRD
analysis. The DIFFaX ratio of the sample was 20/80. The yield of
the dried product was 21.3 wt % and the Si/Al2 was 0.15.
[0093] 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.
* * * * *