U.S. patent application number 09/315419 was filed with the patent office on 2001-12-20 for new silicoaluminophosphates having an ael structure, and their preparation.
Invention is credited to STROHMAIER, KARL G., VAUGHAN, DAVID E. W..
Application Number | 20010053744 09/315419 |
Document ID | / |
Family ID | 22200172 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053744 |
Kind Code |
A1 |
STROHMAIER, KARL G. ; et
al. |
December 20, 2001 |
NEW SILICOALUMINOPHOSPHATES HAVING AN AEL STRUCTURE, AND THEIR
PREPARATION
Abstract
Disclosed are silicoaluminophosphates (SAPOs) having unique
silicon distributions and their preparation. More particularly, the
new SAPOs have a high silica:alumina ratio, and are prepared from
single phase synthesis solutions, or from microemulsions containing
surfactants.
Inventors: |
STROHMAIER, KARL G.; (PORT
MURRAY, NJ) ; VAUGHAN, DAVID E. W.; (FLEMINGTON,
NJ) |
Correspondence
Address: |
EXXONMOBILE CHEMICAL COMPANY
P.O. BOX 2149
BAYTOWN
TX
77520-9728
US
|
Family ID: |
22200172 |
Appl. No.: |
09/315419 |
Filed: |
May 20, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60086681 |
May 26, 1998 |
|
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Current U.S.
Class: |
502/214 ;
423/327.1; 423/DIG.30; 502/208 |
Current CPC
Class: |
B01J 29/85 20130101;
Y10S 423/30 20130101; C01B 39/54 20130101; B01J 29/06 20130101;
C01B 37/08 20130101; C10G 11/05 20130101; C10G 2400/20 20130101;
B01J 29/005 20130101; C10G 45/64 20130101 |
Class at
Publication: |
502/214 ;
502/208; 423/327.1; 423/DIG.030 |
International
Class: |
C01B 033/26; B01J
027/182 |
Claims
What is claimed is:
1. A composition comprising a molecular sieve with a framework
tetrahedra of silicon, aluminum, and phosphorus, and designated
ECR-42, the composition having a total silicon amount ranging from
above about 4 molar percent to about 20 molar percent, a total
aluminum amount ranging from about 40 molar percent to about 55
molar percent, and a total phosphorus amount ranging from about 30
molar percent to about 50 molar percent, the molar percents being
based on the total amount of aluminum, phosphorus, and silicon
present in the composition, and the molecular sieve having the
topology AEL and being isostructural with conventional SAPO-11,
wherein (a) the silicon present in the molecular sieve and the
conventional SAPO-11 is distributed among silicon sites in the
framework tetrahedra, each site having a first, a second, a third,
and a fourth next nearest neighbor position, and each next nearest
neighbor position being independently occupied by one atom selected
from silicon, and aluminum, and (b) the molecular sieve has a
substantially smaller number of silicon sites having silicon atoms
among all four next nearest neighbor positions than the
conventional SAPO-11 having the same total silicon amount.
2. A composition comprising a molecular sieve with a framework
tetrahedra of silicon, aluminum, and phosphorus, the composition
having a total silicon amount ranging from about 4 molar percent to
about 20 molar percent, a total aluminum amount ranging from about
40 molar percent to about 55 molar percent, and a total phosphorus
amount ranging from about 30 molar percent to about 50 molar
percent, the molar percents being based on the total amount of
aluminum, phosphorus, and silicon present in the composition, and
the molecular sieve having the topology AEL and being isostructural
with conventional SAPO-11, wherein (a) the molecular sieve has a
first number of Si atoms coordinated as Si(4Si), (b) the
conventional SAPO-11 with the Si amount has a second number of Si
atoms coordinated as Si(4Si), and (c) the first number of Si atoms
is substantially less than the second number of Si atoms.
3. A method for forming a molecular sieve composition, the method
comprising: (a) combining at least one water-dispersible phosphorus
source material, at least one template capable of structure
directing to AEL, water, and a water-soluble organic silicon source
material under gellation conditions in order to form a gel, and
then (b) reacting the gel under molecular sieve synthesis
conditions.
4. A molecular sieve product formed by (a) combining at least one
water-dispersible phosphorus source material, at least one template
capable of structure directing to AEL, water, and a
water-dispersible silicon source material under gellation
conditions in order to form a gel, and then (b) reacting the gel
under molecular sieve synthesis conditions.
5. A silicoaluminophosphate gel formed by combining under gellation
conditions at least one water-dispersible silicon source material,
at least one template capable of structure-directing to AEL, at
least one water-dispersible phosphorus source material, and water.
Description
FIELD OF THE INVENTION
[0001] This invention relates to silicoaluminates (SAPOs) having
unique silicon distributions, a method for their preparation and
their use as catalysts. More particularly, the new SAPOs,
designated ECR-42 herein, have a high silica:alumina ratio and a
beneficial silicon atom distribution.
BACKGROUND OF THE INVENTION
[0002] The preparation of crystalline silicoaluminophosphates is
well known. U.S. Pat. No. 4,480,871 describes the preparation of
crystalline, microporous silicoaluminophosphates by hydrothermal
crystallization of silicoaluminophosphate gels containing a
molecular structure forming template. SAPOs are members of a class
known as non-zeolitic molecular sieves. The SAPO molecular sieve
has a framework of AlO.sub.4, SiO.sub.4 and PO.sub.4 tetrahedra
linked by oxygen atoms. The negative change in the network is
balanced by the inclusion of exchangeable protons or cations such
as alkali or alkaline earth metal ions. The interstitial spaces of
channels formed by the crystalline network enables SAPOs to be used
as molecular sieves in a manner similar to crystalline
aluminosilicates such as zeolites.
[0003] Accordingly, numerous microporous framework structures
analogous to the aluminosilicate zeolites can be synthesized having
an AlPO.sub.4 composition and have been called ALPOs. A modified
family of materials has been made by the substitution of Si.sup.4+
for Al.sup.3+ and P.sup.5+ (SAPOs). Although the ALPO structures
are neutral frameworks, the substitution of Si.sup.4+ for P.sup.5+
imparts a negative charge on the framework. By suitable choice of a
cation, this can be translated into catalytic activity. However,
alternate substitutions may be possible that may result in a
disproportionately low exchange capacity. The exact nature of Si
substitution into ALPO structures is complex and highly variable
and may depend on both the topology of the ALPO/SAPO and the method
of preparation. The result is that preferred catalysts may be made
by a suitable choice of synthesis method. For example, SAPO-5 and
SAPO-11 may be conventionally prepared in an aqueous solution or
from microemulsions. The latter processes use hexanol and a
cationic or neutral surfactant to a two-phase gel leading to the
formation of a microemulsion.
[0004] The microemulsion process is a two-phase approach to
preparing SAPOs attempts to reduce the amount of undesirable silica
island formation by supplying the silicon from an organic phase to
the aqueous phase at a low concentration during crystallization.
The organic phase contains the organic solvent and organic silicon
source, tetraethylorthosilicate, which is only slightly soluble in
the aqueous phase. The aqueous phase is where crystallization
occurs and contains the phosphorous and aluminum. It has been
theorized that as the silicon is depleted from the aqueous phases
by the growing SAPO crystals, it will be replenished from the
organic phase, thereby forming a silicoaluminophosphate product
having a more uniform distribution of silicon in the framework.
[0005] SAPOs have application for a wide variety of uses, for
example as catalysts. In this regard, it is known that increasing
Si concentration at first results in an increase in catalystic
activity. However, increasing Si content beyond about 0.04 mole
fraction in the framework, based on the total amount of silicon,
aluminum, and phosphorous in the framework, provides no increase in
activity, and may even lead to a decrease, depending on the
specific distribution and clustering of the Si.sup.4+
substituent.
[0006] In that the distribution of Si in the SAPO framework affects
catalytic activity, the catalytic activity of SAPOs therefore
depends on both the global composition and the Si distribution.
Accordingly, SAPOs are defined not only by chemical composition and
X-Ray Diffraction, but also by .sup.29Si MAS NMR spectra which
define the Si distributions. On the basis of this last technique,
it has been shown that when the SAPOs contain low amounts of Si,
the silicon atoms are mostly isolated. However, when the Si content
increases, Si islands start to appear, i.e., Si sites having
silicon atoms and no aluminum atoms in neighboring lattice
positions.
[0007] It would, therefore, be desirable to further increase
silicon content in SAPO molecular sieves without forming
undesirable silica islands in order to increase catalytic activity
and selectivity.
SUMMARY OF THE INVENTION
[0008] In one embodiment, the invention is a composition comprising
a molecular sieve with a framework tetrahedra of silicon, aluminum,
and phosphorus, and designated ECR-42, the composition having a
total silicon amount ranging from above about 4 molar percent to
about 20 molar percent, a total aluminum amount ranging from about
40 molar percent to about 55 molar percent, and a total phosphorus
amount ranging from about 30 molar percent to about 50 molar
percent, the molar percents being based on the total amount of
aluminum, phosphorus, and silicon present in the composition, and
the molecular sieve having the topology AEL and being isostructural
with conventional SAPO-11, wherein
[0009] (a) the silicon present in the molecular sieve and the
conventional SAPO-11 is distributed among silicon sites in the
framework tetrahedra, each site having a first, a second, a third,
and a fourth nearest neighbor position, and each next nearest
neighbor position being independently occupied by one atom selected
from silicon, and aluminum, and
[0010] (b) the molecular sieve has a substantially smaller number
of silicon sites having silicon atoms among all four nearest
neighbor positions than the conventional SAPO-11 with the total
silicon amount.
[0011] In another embodiment, the invention is a composition
comprising a molecular sieve with a framework tetrahedra of
silicon, aluminum, and phosphorus, the composition having a total
silicon amount ranging from above about 4 molar percent to about 20
molar percent, a total aluminum amount ranging from about 40 molar
percent to about 55 molar percent, and a total phosphorus amount
ranging from about 30 molar percent to about 50 molar percent, the
molar percents being based on the total amount of aluminum,
phosphorus, and silicon present in the composition, and the
molecular sieve having the topology AEL and being isostructural
with conventional SAPO-11, wherein
[0012] (a) the molecular sieve has a first number of Si atoms
coordinated as Si (4Si),
[0013] (b) the conventional SAPO-11 has a second number of Si atoms
coordinated as Si(4Si), and
[0014] (c) the first number of Si atoms is substantially less than
the second number of Si atoms.
[0015] In another embodiment, the invention is a method for forming
a molecular sieve composition, the method comprising:
[0016] (a) combining at least one water-dispersible phosphorus
source material, at least one template capable of structure
directing to AEL, water, and a water-soluble or dispersible organic
silicon source material under gellation conditions in order to form
a gel, and then
[0017] (b) reacting the gel under molecular sieve synthesis
conditions.
[0018] In another embodiment, the invention is a product formed in
accordance with such a process
[0019] In another embodiment, the invention is a
silicoaluminophosphate gel formed by combining under gellation
conditions at least one water-dispersible silicon source material,
at least one template capable of structure-directing to AEL, at
least one water-dispersible phosphorus source material, and
water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 schematically shows the type of silicon environments
in SAPO-type molecular sieves.
[0021] FIG. 2 shows a representative deconvolution of an .sup.29Si
NMR spectrum.
[0022] FIG. 3 shows the .sup.29Si NMR spectra of conventionally
prepared SAPO-11. Spectrum 3(a) shows a SAPO-11 of 5 molar percent
Si having about 1/3 of the Si atoms located in silicon islands.
Spectrum 3(b) is a SAPO-11 of 4 molar % Si having at most a small
amount of Si located in Si islands, and spectrum 3(c) shows a
SAPO-11 of 14 molar % Si having extensive Si island formation.
[0023] FIG. 4 shows powder x-ray diffraction data for the AEL-type
SAPOs prepared in examples 1 through 4.
[0024] FIG. 5-shows powder x-ray diffraction data from AEL-type
SAPOs of examples 5 through 8.
[0025] FIG. 6(a) shows scanning electron micrographs of an AEL-type
SAPO prepared in accordance with the method of Example (4), and
FIG. 6(b) shows an electron micrograph of conventionally-prepared
SAPO-11.
[0026] FIG. 7 shows the .sup.29Si NMR spectra of ECR-42 having
framework silicon in amounts ranging from about 5 molar % to about
13 molar %. Spectrum 7(a) shows ECR-42 with about 13 molar percent
Si and having about 9% of the Si atoms located in silicon islands,
representing a substantially reduced amount of framework Si in
islands compared to conventional SAPO-11 of about the same Si
content (FIG. 3(c). Spectrum 7(b) is of ECR-42 of example 6
containing about 7 molar % Si and having about 10% of the Si
located in Si islands, and spectrum 7(c) shows an ECR-42 of example
1 containing about 4 molar % Si having about 4% of the Si located
in Si islands.
DETAILED DESCRIPTION OF THE INVENTION
[0027] The invention is based in part on the discovery that SAPO
materials having the AEL topology and designated ECR-42 herein may
be prepared with high silicon concentration and without undesirable
silicon island formation. The invention is also based on the
discovery that a SAPO precursor gel such as a
silicoaluminophosphate gel may be formed from an aqueous synthesis
solution containing no added alcohol or surfactant provided the
co-solvent is a soluble species capable of maintaining a high
dispersion of silica in a synthesis solution. While not wishing to
be bound by any theory or model, the co-solvent is believed to
inhibit polymerization of the highly dispersed silica species. The
preferred methods therefore provide a SAPO molecular sieve
containing Si in the tetrahedral framework at a concentration above
about 0.04 molar fraction (based on the total amount of aluminum,
silicon, and phosphorous in the framework) and having a desirable
Si distribution in the framework, resulting in high catalytic
activity and selectivity.
[0028] In other words, it has been discovered that modifying the
synthesis of a silicon-substituted aluminophosphate by changing the
composition of the synthesis mixture, the synthesis conditions, or
both, modifies the silicon distribution in the
silicoaluminophosphate thus formed. This changed distribution of
silicon may have a major beneficial influence on the catalytic
activity of the silicoaluminophosphate.
[0029] Accordingly, when AEL-type molecular sieve materials are
synthesized following the procedure described herein, the
distribution of Si and therefore the total number and strength of
acid sites in the molecular sieve framework is quite different, and
much higher than those of previously reported forms of SAPO
molecular sieves.
[0030] The preferred silicoaluminophosphate composition of this
invention, ECR-42, has the topology AEL which corresponds to
SAPO-11. The AEL topology is defined in the "Atlas of Zeolite
Structure Types," 4th Ed, by W. M. Meier, D. H. Olson and Ch.
Baerlocher, Elsevier, 1996. Although the composition is
isostructural with other AEL molecular sieve materials, it is a
distinct molecular sieve composition because the silicon, aluminum,
and phosphorus atoms are not arranged the same way as in
conventional SAPO-11 molecular sieve. Those skilled in the art will
recognize that two isostructural molecular sieves may be entirely
different compositions having entirely different properties,
depending on, for example, the nature and distribution of the
constituent atoms.
[0031] Preferred molecular sieve compositions are physically
different from other SAPO's having the AEL structure because the
silicon atoms are distributed differently in the molecular sieve
framework. The physical structure of the preferred composition (and
its silicon distribution) is illustrated schematically in FIG. 1.
While the actual structure is three dimensional and contains oxygen
in addition to silicon, aluminum and phosphorus, the figure's
atomic positions are represented on a two dimensional array and
oxygen atoms are omitted for clarity. As is shown in the figure,
each lattice site in the framework has four nearest neighbor
lattice sites. In the preferred compositions, as with all AEL-type
SAPOs, a lattice site occupied by a silicon 4+ cation, i.e., a
"silicon site", ordinarily may not have a phosphorous 5+ cation as
a nearest neighbor. The four nearest neighbor lattice sites may
therefore be occupied by one silicon and three aluminum cations,
two silicon and two aluminum cations, three silicon and one
aluminum cations, four silicon cations, or four aluminum cations.
As discussed, conventional AEL-type SAPOs with increased silicon
concentration, above about 4 molar %, contain undesirable silicon
islands, i.e., silicon atoms in the framework having four silicon
atom nearest neighbors. The silicon atoms in the preferred
composition are physically distributed so that the silicon island
concentration is greatly reduced compared with conventional SAPO-11
(i.e., SAPO-11 prepared in accordance with the methods disclosed in
the prior art) having the same total silicon concentration.
[0032] In a particularly preferred embodiment, the total molar
fraction of silicon in the ECR-42 framework is greater than about
0.05, and the number of Si atoms having no Si nearest neighbor
ranges from about 0 mol. % to about 100 mol. %, the number of Si
atoms having one Si nearest neighbor ranges from about 5 mol. % to
about 25 mol. %, the number of Si atoms having two Si nearest
neighbors ranges from about 0 mol. % to about 35 mol. %, the number
of Si atoms having three Si nearest neighbors ranges from about 0
mol. % to about 25 mol. %, and the number of Si atoms having four
Si nearest neighbors ranging from about 0 mol. % to about 25 mol.
%, the mol. % being based on the total silica in the ECR-42.
[0033] Preferably, the ECR-42 compositions have a Si content
ranging from above about 4 mol. % to about 20 mol. %, more
preferably from about 5 mol. % to about 15 mol. %, and still more
preferably from about 7 mol. % to about 15 mol. %, the silicon
content being based on the total amount of Si present in the
framework of the molecular sieve composition. Preferably, more than
about 50 molar %, and more preferably more than about 90 molar % of
the silicon atoms present in the framework do not have four silicon
atoms as nearest neighbors in the framework.
[0034] The preferred molecular sieve compositions have both a
desirably high silicon concentration and a desirable silicon atom
dispersion (i.e., a smaller number of silicon islands than would be
present in conventional SAPO-11 with the same silicon content) may
be formed in accordance with conventional molecular sieve synthesis
techniques. The preferred ECR-42 synthesis processes commence with
the formation of a silicoaluminophosphate gel having the
formula
X.sub.1SURF:X.sub.2TEMP:Al.sub.2O.sub.3:P.sub.2O.sub.5:X.sub.3SiO.sub.2:X.-
sub.4H.sub.2O:X.sub.5SOL
[0035] wherein SURF is a surfactant capable of forming a
microemulsion between synthesis solution's organic and aqueous
phases. While not wishing to be bound by any theory or model, it is
believed that the surfactant helps to solubilize the organic
tetraalkylorthosilicate silica source and also increases the
available interface between the organic species and inorganic
species in the synthesis gel resulting in an improvement in the
final silica distribution in the silicoaluminophosphate product.
Non-limiting examples of useful surfactants include one or more of
long chain alkylamines such as hexadecylamine, tetradecylamine,
dodecylamine, decylamine, or octylamine, or dimethyl alkylamine
compounds such as dimethylhexadecylammine or dimethyloctylamine, or
trimethylalkylammonium salts such as trimethylhexadecylammounium
chloride.
[0036] TEMP is a template capable of structure directing to AEL
such as di-n-propylamine, diisopropylamine, or diethylamine for
forming the preferred ECR-42 silicoaluminophosphate molecular
sieve.
[0037] SOL is a water-soluble organic co-solvent capable of
solubilizing the organic silicon source. While not wishing to be
bound, it is believed that solubilizing organic silicon sources
such as a tetraalkylorthosilicate silicon source into the aqueous
synthesis gel improves the final silicon distribution in the
silicoaluminophosphate product. Non-limiting examples of useful
water-soluble organic solvents include one or more of acetone,
1,2-propanediol, 1,3-propanediol, methanol, ethanol, propanol,
isopropanol, butanol, or ethylene glycol.
[0038] The silicon source material may be any silicon species
capable of being dispersed or dissolved in an aqueous synthesis
solution. As discussed, where an organic silicon species is
employed, a water-soluble organic solvent, SOL, is preferably
employed. While not wishing to be bound by any theory or model, it
is believed dispersing the silicon species in a low molecular
weight form in the silicoaluminophosphate synthesis gel improves
silicon distribution of the preferred ECR-42 material formed
therefrom. Non-limiting examples of useful silicon source materials
include one or more of tetraalkylorthosilicates such as
tetramethylorthosilicate, tetraethylorthosilicate,
tetrapropylorthosilicate, tetrabutylorthosilicate, and
silsesquisiloxanes having up to twelve Si centers.
[0039] X.sub.1 ranges from about 0 to about 0.5, X.sub.2 ranges
from about 0.1 to about 4, X.sub.3 ranges from about 0.01 to about
2, X.sub.4 ranges from about 10 to about 100, and X.sub.5 ranges
from about 0 to about 30. The silicoaluminophosphate gel may be
formed in accordance with the following processes.
[0040] (I) Processes using surfactant and water-soluble
co-solvent
[0041] Silicoaluminophosphate gels having the formula
X.sub.1SURF:X.sub.2TEMP:Al.sub.2O.sub.3:P.sub.2O.sub.5:X.sub.3SiO.sub.2:X.-
sub.4H.sub.2O:X.sub.5SOL
[0042] may be prepared by combining a phosphorus source such as
H.sub.3PO.sub.4, ammonium phosphate, and mixtures thereof; water;
and an aluminum source such as hydrated alumina, organo alumina,
pseudo-boehmite, aluminum hydroxide, colloidal alumina, and
mixtures thereof, and then adding the template in order to form a
homogeneous alumino phosphate mixture. The
P.sub.2O.sub.5:Al.sub.2O.sub.3 molar ratio in the alumino phosphate
mixture preferably ranges from about 0.7 to about 1.3, and more
preferably ranges from about 0.9 to about 1.1. The
TEMP:Al.sub.2O.sub.3 molar ratio in the alumino phosphate mixture
preferably ranges from about 0.1 to about 5, and more preferably
from about 0.5 to about 3. A surfactant solution of the surfactant,
the water-soluble organic solvent, and water may then be added to
the alumino phosphate mixture along with the organic silicon source
and water (if necessary to obtain the desired value of X.sub.4) in
order to form a synthesis solution having a SURF:Al.sub.2O.sub.3
molar ratio preferably ranging from about 0 to about 0.5, and more
preferably ranging from about 0.05 to about 0.3. The relative
amounts of the ingredients for the synthesis solution may be
calculated from the desired values of X.sub.1 through X.sub.5. The
SOL:Al.sub.2O.sub.3 molar ratio in the synthesis solution
preferably ranging from about 0 to about 30, and more preferably
ranging from about 4 to about 20, and the SiO.sub.2:Al.sub.2O.sub.3
molar ratio preferably ranging from about 0.01 to about 2.0, and
more preferably ranging from about 0.1 to about 0.8. The synthesis
solution may then be subjected to gel formation conditions in order
to provide the silicoaluminophosphate gel. The ingredients of the
synthesis solution, surfactant solution, and alumino phosphate
mixture may be mixed in any order. For example, in an alternative
embodiment the organic silicon source may be added to a mixture of
phosphoric acid and the water-soluble organic solvent. The template
and the surfactant may then be added, with the water and aluminum
source being added last.
[0043] Preferred silicoaluminophosphate crystallization conditions
for forming the ECR-42 molecular sieve from the gel include heating
the gel in a microwave autoclave for a time sufficient to
crystallize the gel. Lower temperature and shorter crystallization
times are preferred because such conditions may prevent the
formation of undesirable products. Accordingly, the preferred
heating times range from about 1 minute to about 5 days, at a
temperature ranging from about 100.degree. C. to about 250.degree.
C., and at a pressure ranging from about 0 bar to about 70 bar. In
cases where other products, unreacted gel, or a mixture thereof is
present at the conclusion of the reaction, the molecular sieve may
be recovered by a separation process such as centrifugation. The
process may also include conventional product washing and drying
such as an ethanol rinse, followed by a water rinse, followed by
air oven drying at a temperature ranging from about ambient
temperature to about 200.degree. C. It should be noted that
conventional heating, in for example an air oven or an externally
heated autoclave, may be substituted for microwave heating in this
process, and that a substantially pure ECR-42 molecular sieve
composition having the AEL-topology will result with either heating
method. When conventional heating is used, the temperature
preferably ranges from about 100.degree. C. to about 250.degree.
C., and more preferably from 150.degree. C. to about 200.degree.
C.
[0044] (II) Processes using surfactant, hexanol co-solvent and
microwave heating
[0045] Silicoaluminophosphate gels having the formula
X.sub.1SURF:X.sub.2TEMP:Al.sub.2O.sub.3:P.sub.2O.sub.5:X.sub.3SiO.sub.4:X.-
sub.2H.sub.2O:X5SOL'
[0046] wherein SOL'is a relatively water insoluble organic solvent
including solvent mixtures capable forming a microemulsion with
water and a surfactant, and including mixtures thereof, may be
prepared by according to the method (I) above, except that the
water insoluble organic solvent SOL'is substituted for the
water-soluble solvent SOL. But for the solvent substitution, the
molar ratios of the ingredients in the alumino phosphate mixture
and the synthesis solution are as set forth in method (I), and as
in that method, the mixing order is not critical.
[0047] The preferred ECR-42 molecular sieve composition may be
formed from the gel in accordance with the steps set forth in
process (I). It should be noted that conventional heating may
result in the presence of SAPO-41 material in the molecular sieve
composition.
[0048] (III) Processes using ethanol with water-soluble cosolvnet
and no added surfactant
[0049] Silicoaluminophosphate gels of stoichiometry:
X.sub.2TEMP:Al.sub.2O.sub.3:P.sub.2O.sub.5:X.sub.3SiO.sub.2:X.sub.4H.sub.2-
O:X.sub.5SOL
[0050] may be prepared by a method identical to method (I), above,
except that no surfactant solution is used. An aqueous solution of
water, the water-soluble organic solvent, and the silicon source is
used instead of the surfactant solution. But for the absence of the
surfactant, the molar ratios of the ingredients in the alumino
phosphate mixture and the synthesis solution are as set forth in
method (I), and as in that method, the mixing order of the
ingredients is not critical.
[0051] The preferred ECR-42 molecular sieve composition may be
formed from the gel in accordance with the steps set forth in
process (I).
[0052] (IV) Processes using an organic silicon source and no added
surfactant or water-soluble organic cosolvent.
[0053] Silicoaluminophosphate gels of stoichiometry:
X.sub.2TEMP:Al.sub.2O.sub.3:P.sub.2O.sub.5:X.sub.3SiO.sub.2:X.sub.4H.sub.2-
O
[0054] may be prepared by a method identical to method (I), above,
except that no surfactant and no co-solvent are employed. An
aqueous dispersion of water, and an organic silicon source such as
TEOS, including mixtures thereof, is used instead of the surfactant
solution.
[0055] But for the absence of the surfactant, the molar ratios of
the ingredients in the alumino phosphate mixture and the synthesis
solution are as set forth in method (I), and as in that method, the
mixing order of the ingredients is not critical.
[0056] The preferred ECR-42 molecular sieve composition may be
formed from the gel in accordance with the steps set forth in
process (I). The product may contain SAPO-31.
[0057] (V) Processes for forming SAPO-11 using colloidal silica
with no added surfactant and no added solvent.
[0058] Silicoaluminophosphate gels of stoichiometry:
X.sub.2TEMP:Al.sub.2O.sub.3:P.sub.2O.sub.5:X.sub.3SiO.sub.2:X.sub.4H.sub.2-
O
[0059] may be prepared by a method identical to method (I), above,
except that no surfactant solution is used. An aqueous dispersion
of water and the colloidal or fumed silica is used instead of the
organic silicon source and surfactant solution. But for the absence
of the surfactant and co-solvent, the molar ratios of the
ingredients in the alumino phosphate mixture and the synthesis
solution are as set forth in method (I), and as in that method, the
mixing order of the ingredients is not critical.
[0060] A SAPO-11 molecular sieve composition may be formed from the
gel in accordance with the steps set forth in process (I). The
product may contain SAPO-31.
[0061] The preferred ECR-42 molecular sieve compositions are
crystalline, and may be prepared with crystal sizes ranging from
about 0.001 micrometers to about 1.0 micrometers. Preferably,
crystal size ranges from about 0.01 micrometers to about 0.5
micrometers. The synthesis may be adjusted to prepare crystals of
decreased size by diluting the synthesis solution with surfactant,
co-solvent, and mixtures thereof. Small crystals may also be
prepared by conventional methods such as seeding and high shear
agitation rates.
[0062] Molecular sieve materials prepared in accordance with these
methods are useful as catalytic materials. A non-limiting
description of the catalytic nature and some catalytic uses of such
materials is as follows.
[0063] As is known to those skilled in the art, molecular sieve
materials may possess an intrinsic or added catalytic
functionality, and such materials are frequently referred to as
"molecualr sieve catalysts". Additional catalytic functionalities
may be provided for molecular sieve materials by conventional
methods. Such methods are applicable to the preferred molecular
sieves, and may be summarized as follows.
[0064] Accordingly, the molecular sieve material formed from the
gel as set forth above may be calcined to remove the template. The
sample may then be allowed to cool, preferably in the presence of a
dessicator, and then loaded with a catalytically active species
such as Pt by conventional techniques such as incipient
wetness.
[0065] The preferred catalytic molecular sieve compositions are
useful for at least hydrocarbon isomerization, hydrotreating, and
cracking such as hydrocracking and fluid catalytic cracking,
especially naphtha cracking. The preferred ECR-42 molecular sieve
compositions have a dramatically increased catalytic activity for
such processes over AEL type SAPO molecular sieves prepared by
conventional techniques.
[0066] More specifically, the preferred ECR-42 molecular sieves may
be used in applications including, but not limited to, catalytic
dewaxing, isodewaxing/isomerization, hydrocracking, alkylation of
aromatic hydrocarbons (e.g., benzene) with long chain olefins
(e.g., C.sub.14 olefin), alkylation of aromatic hydrocarbons (e.g.,
benzene and alkylbenzenes) in presence of an alkylating agent
(e.g., olefins, formaldehyde, alkyl halides and alcohols having 1
to about 20 carbon atoms), alkylation of aromatic hydrocarbons
(e.g., benzene) with light olefins to produce short chain aromatic
compounds (e.g., alkylation of benzene with propylene to give
cumene), transalkylation of aromatic hydrocarbons in the presence
of polyalkylaromatic hydrocarbons, isomerization of aromatic
feedstock components (e.g., xylene), naphtha cracking to make
olefins, oligomerization of straight and branched chain olefins
having from about 2 to 5 carbons atoms, diproportionation of
aromatics (e.g., the disproportionation of toluene to make benzene
and paraxylene), and conversion of naphtha (e.g., C6-C10) and
similar mixtures to highly aromatic mixtures.
[0067] In summary, it has been discovered that when AEL-type
molecular sieves are preferably synthesized in accord with the
methods described herein, that the distribution of Si and therefore
the total number and strength of acid sites is quite different, and
much higher, than those of conventional SAPO-11 . It has also been
discovered that the preferred molecular sieves are extremely active
and selective for carrying out reactions of hydrocarbon such as
alkylation, disproportionation, oligomerization, naphtha cracking
and other reactions known to involve molecular sieve catalysts,
especially the catalytic dewaxing and isodewaxing of hydrocarbon
feeds containing paraffins.
[0068] The invention is further exemplified by the following
non-limiting examples.
EXAMPLES
[0069] I. Preparation of the Preferred ECR-42 Molecular Sieves
Example 1
Preparation of ECR-42 using surfactant, ethanol co-solvent, and
microwave heating
[0070] A silicoaluminophosphate gel of stoichiometry:
0.16CA:DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.2SiO.sub.2:50.3H.sub.2O:7.3eth-
anol
[0071] (where CA is hexadecylamine) was prepared by mechanically
mixing together 28.6 grams of H.sub.3PO.sub.4(85%), 25 grams of
water and 17 grams of Catapal B alumina (Vista Chemical Co.,
Houston, Tex. 74%Al.sub.2O.sub.3, 26% H.sub.2O for 45 min. in a 500
ml Teflon bottle until homogenous. To this mixture was added 12.7
grams of DPA, and the mixture was then stirred for 30 minutes. A
surfactant solution was prepared by mixing 2.4 grams of
hexadecylamine in 20.8 grams of ethanol and 12.5 grams of water.
This solution was added to half of the
di-n-propylamine/aluminophosphate mixture along with 2.6 grams of
TEOS and 11.2 grams of water. The resulting mixture was stirred for
about 3 min. in a 125 ml blender. This gel was divided between
three CEM XP-1500 Teflon microwave autoclaves (about 28.5 grams
each), available from CEM Corp., Matthews, NC. The three autoclaves
were heated for 5 min. in a microwave oven to a pressure of 485
psi. After 5,30 and 60 min. at 485 psi the samples were removed
from the oven. The ECR-42 products were recovered by centrifugation
and washed twice with ethanol and then twice with de-ionized water.
The resulting products were dried in an air oven at 115.degree. C.
and the powder X-ray diffraction pattern measured which showed the
products to be pure SAPO-11, see FIG. 4(a). Elemental analysis of
the 60 min. sample gave: 17.3% Al; 17.0% P; 1.68% Si, representing
a product stoichiometry of Si.sub.0.05Al.sub.0.51P.sub.0.44.
Example 2
Preparation of ECR-42 using surfactant, hexanol co-solvent, and
microwave heating.
[0072] A silicoaluminophosphate gel of stoichiometry:
0.16CA:DPA:A.sub.2O.sub.3:P.sub.2O.sub.5:0.4SiO.sub.2:39H.sub.2O:4.5hexano-
l
[0073] (where CA is hexadecylamine) was prepared by mechanically
mixing together 28.6 grams of H.sub.3PO.sub.4(85%), 25 grams of
water and 17 grams of Catapal B alumina (Vista, 74%Al.sub.2O.sub.3,
26% H.sub.2O) for 2 hr. in a 500 ml Teflon bottle until homogenous.
To this mixture was added 12.7 grams of DPA and the mixture was
then stirred for 30 minutes. A surfactant solution was prepared by
mixing 4.8 grams of hexadecylamine in 56.9 grams of hexanol and 25
grams of water. This solution was added to the
di-n-propylamine/aluminophosphate mixture along with 10.3 grams of
TEOS and 22.3 grams of water. The resulting mixture was stirred for
about 3 min. in a 125 ml blender. This gel was divided between two
125 ml Teflon-lined autoclaves and a CEM XP-1500 Teflon microwave
autoclave (about 28.5 grams).
[0074] The two autoclaves were heated at 195.degree. C. for 24 and
40 hrs. in a conventional oven. The microwave autoclave was heated
for 5 min. in a microwave oven to a pressure of 485 psi. After 60
min. at 485 psi the sample was removed from the oven. The products
were recovered by centrifugation and washed twice with ethanol and
then twice with de-ionized water. The resulting ECR-42 products
were dried in an air oven at 115.degree. C. and the powder X-ray
diffraction pattern measured showed that the product of the
microwave heating was pure SAPO-11 (FIG. 4(c)) and the product of
the conventionally heated samples to be SAPO-11 and SAPO-41 (FIG.
4(b)). Elemental analysis of the microwave heated sample gave:
14.5% Al; 16.4% P; 2.84% Si, representing a product stoichiometry
of Si.sub.0.09Al.sub.0.46P.sub.0.45 and the conventionally heated
sample (40 hrs.) gave 15.4% Al; 16.4% P; 3.36% Si, representing a
product stoichiometry of Si.sub.0.10Al.sub.0.47P.sub.0.43.
Example 3
Preparation of ECR-42 using surfactant, ethanol co-solvent, and
microwave heating
[0075] A silicoaluminophosphate gel of stoichiometry:
16CA:DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.2SiO.sub.2:39.1H.sub.2O:7.3ethan-
ol
[0076] (where CA is hexadecylamine) was prepared by mechanically
mixing together 71.5 grams of H.sub.3PO.sub.4(85%), 62.5 grams of
water and 42.4 grams of Catapal B alumina (Vista,
74%Al.sub.2O.sub.3, 26% H.sub.2O) for 45 min. in a 1000 ml Teflon
bottle until homogenous. To this mixture was added 31.7 grams of
DPA and the mixture was then stirred for 30 minutes. A surfactant
solution was prepared by mixing 12 grams of hexadecylamine in 104
grams of ethanol and 62.5 grams of water. This solution was added
to the di-n-propylamine/aluminophosphate mixture along with 13
grams of TEOS and 56 grams of water. The resulting mixture was
stirred for about 3 min. in a 250 ml blender. One half of this gel
was divided between five CEM XP-1500
[0077] Teflon microwave autoclaves (about 42.5 grams each). The
five autoclaves were heated for 10 min. in a microwave oven to a
pressure of 485 psi. After 30 min. at 485 psi the samples were
removed from the oven. The ECR-42 products were combined and then
recovered by centrifugation and washed twice with ethanol and then
twice with de-ionized water. The resulting product was dried in an
air oven at 115.degree. C. and the powder X-ray diffraction pattern
measured which showed the product to be pure SAPO-11. See FIG.
4(d). Elemental analysis gave: 15.96% Al; 17.3% P; 1.638% Si,
representing a product stoichiometry of
Si.sub.0.05Al.sub.0.49P.sub.0.46.
Example 4
Preparation of ECR-42 using surfactant, ethanol co-solvent and
microwave heating
[0078] A silicoaluminophosphate gel of stoichiometry:
0.16CA:DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.4SiO.sub.2:39.1H.sub.2O:7.3eth-
anol
[0079] (where CA is hexadecylamine) was prepared by adding 6.5
grams more of TEOS to the second half of the gel prepared in
Example 3. After thoroughly homogenizing in a blender this gel was
divided between five CEM XP-1500 Teflon microwave autoclaves (about
42.5 grams each. The five autoclaves were heated for 10 min. in a
microwave oven to a pressure of 485 psi. After 30 min. at 485 psi
the samples were removed from the oven. The ECR-42 products were
combined and then recovered by centrifugation and washed twice with
ethanol and then twice with de-ionized water. The resulting product
was dried in an air oven at 115.degree. C. and the powder X-ray
diffraction pattern measured which showed the product to be pure
SAPO-11. See FIG. 4(e). Elemental analysis gave: 15.23% Al;17.2%
P;2.795% Si, representing a product stoichiometry of
Si.sub.0.08Al.sub.0.46P.sub.0.46.
Example 5
Preparation of ECR-42 using surfactant, ethanol co-solvent, and
conventional heating
[0080] A silicoaluminophosphate gel of stoichiometry:
16
CA:2DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.4SiO.sub.2:40H.sub.2O:7.5ethan-
ol
[0081] (where CA is hexadecylamine) was prepared by mixing together
25.4 grams of H.sub.3PO.sub.4(85%), 35 grams of water, and 15.2
grams of Catapal A alumina (Vista, 74%Al.sub.2O.sub.3, 26%
H.sub.2O) for 2 min. in a 250 ml plastic beaker. To this mixture
was added 22.3 grams of DPA and the mixture was then stirred for 3
minutes. A surfactant solution was prepared by mixing 4.25 grams of
hexadecylamine in 38.1 grams of ethanol for thirty minutes. This
solution was added to the di-n-propylamine/aluminophosphate mixture
along with 9.18 grams of TEOS and 30.6 grams of water. The
resulting mixture was homogenized for about 5 min. in a 250 ml
blender. About 80 g of this gel was placed in a 125 Teflon lined
autoclave. The autoclave was heated for 24 hours in an air oven at
195.degree. C. After cooling, the ECR-42 product was recovered by
centrifugation and washed twice with ethanol and then twice with
de-ionized water. The resulting product was dried in an air oven at
115.degree. C. and the powder X-ray diffraction pattern measured
which showed the product to be pure SAPO-11, see FIG. 5(a).
Elemental analysis gave: 17.2% Al; 17.1% P;3.052% Si, representing
a product stoichiometry of Si.sub.0.084Al.sub.0.491P.sub.0.425.
Example 6
Preparation of ECR-42 using TEOS, ethanol co-solvent and
conventional heating
[0082] A silicoaluminophosphate gel of stoichiometry:
2DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.4SiO.sub.2:40H.sub.2O:7.5ethanol
[0083] was prepared by mixing together 28.9 grams of
H.sub.3PO.sub.4(85%), 40 grams of water and 17.3 grams of Catapal A
alumina (Vista, 74%Al.sub.2O.sub.3, 26% H.sub.2O) for 2 min. in a
250 ml plastic beaker. To this mixture was added 25.4 grams of DPA
and the mixture stirred for 3 minutes. To the
di-n-propylamine/aluminophosphate mixture was added 43.3 grams of
ethanol with 10.4 grams of TEOS and 34.7 grams of water. The
resulting mixture was homogenized for about 5 min. in a 250 ml
blender. About 80 g of this gel was placed in a 125 Teflon lined
autoclave. The autoclave was heated for 24 hours in an air oven at
195.degree. C. After cooling, the ECR-42 product was recovered by
centrifugation and washed once with ethanol and then three times
with de-ionized water. The resulting product was dried in an air
oven at 115.degree. C. and the powder X-ray diffraction pattern
measured which showed the product to be pure SAPO-11. See FIG.
5(b). Elemental analysis gave: 17.94% Al; 20.1% P; 2.56% Si,
representing a product stoichiometry of Si.sub.0.065Al.sub.0.47-
3P.sub.0.462.
Example 7
Preparation of ECR-42 using TEOS and conventional heating
[0084] A silicoaluminophosphate gel of stoichiometry:
1.5DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.4SiO.sub.2:50H.sub.2O
[0085] was prepared by mixing together 25.1 grams of
H.sub.3PO.sub.4(85%), 36 grams of water and 15 grams of Catapal A
alumina (Vista, 74%Al.sub.2O.sub.3, 26% H.sub.2O) for 2 min. in a
250 ml plastic beaker. To this mixture was added 16.5 grams of DPA,
and the mixture was stirred for 3 minutes. To the
di-n-propylamine/aluminophosphate mixture was added 9.1 grams of
TEOS (tetraethylorthosilicate) and 48.4 grams of water. The
resulting mixture was homogenized for about 5 min. in a 250 ml
blender. One half of this gel was placed in a 125 Teflon-lined
autoclave. The autoclave was heated for 24 hours in an air oven at
220.degree. C. After cooling, the ECR-42product was recovered by
centrifugation and washed four times with de-ionized water. The
resulting product was dried in an air oven at 115.degree. C. and
the powder X-ray diffraction pattern measured which showed the
product to be SAPO-11 and SAPO-41. See FIG. 5(c). Elemental
analysis gave: 18.8% Al; 19.7% P; 2.70% Si, representing a product
stoichiometry of Si.sub.0.067Al.sub.0.49P.sub.0.455.
Example 8
Preparation of SAPO-11 using colloidal silica
[0086] A silicoaluminophosphate gel of stoichiometry:
1.5DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.4SiO.sub.2:50H.sub.2O
[0087] was prepared by mixing together 31.4 grams of
H.sub.3PO.sub.4(85%), 80 grams of water and 18.8 grams of Catapal B
alumina (Vista, 74%Al.sub.2O.sub.3, 26% H.sub.2O) and mechanically
stirring for 0.5 hour in a 500 ml Teflon bottle. To this mixture
was added 20.7 grams of DPA (di-n-propylamine) and 8.19 g solution
of aqueous colloidal silica (duPont Ludox AS-40, 40% SiO.sub.2) and
stirred for 1.5 hours. Finally, 20.9 grams of water were added, and
the resulting mixture was homogenized for about 5 min. in a 250 ml
blender. This gel was divided between two 125 Teflon lined
autoclaves. The autoclaves were heated for 24 hours in an air oven
at 195.degree. C. After cooling, the products were combined and
then recovered by centrifugation and washed four times with
de-ionized water. The resulting product was dried in an air oven at
115.degree. C. and the powder X-ray diffraction pattern measured
which showed the product to be SAPO-11 and SAPO-31. See FIG. 5(d).
Elemental analysis gave a product stoichiometry of
Si.sub.0.056Al.sub.0.502P.sub.0.- 442.
Examples 9
Preparation of ECR-42 using various alcohol co-solvents and
tetraalkylorthosilicates
[0088] A series of silicoaluminophosphate gels of
stoichiometry:
X.sub.1CA:2DPA:Al.sub.2O.sub.3:P.sub.2O.sub.5:0.4SiO.sub.2:40H.sub.2O:X.su-
b.5SOL
[0089] where CA is hexadecylamine and DPA is di-n-propylamine) were
prepared by mixing together the appropriate amounts of
H.sub.3PO.sub.4(85%), water and Catapal A alumina (Vista,
74%Al.sub.2O.sub.3, 26% H.sub.2O) for 2 min. in a 250 ml plastic
beaker. To this mixture was added the appropriate amount of DPA
(di-n-propylamine) and the mixture stirred for 3 minutes. Then the
appropriate amount of alcohol, tetraalkylorthosilicate and water
were added to obtain the stoichiometry as indicated in Table 1. The
resulting mixtures were homogenized for about 5 min. in a 250 ml
blender. One half of this mixture was transferred to 125
Teflon-lined autoclave. To the other half was mixed in 1.5 grams of
hexadecylamine and also transferred to 125 Teflon-lined autoclave.
The autoclaves were heated for 24 hours in an air oven at
195.degree. C. After cooling the product was recovered by
centrifugation and washed twice with ethanol and then twice with
de-ionized water. The resulting products were dried in an air oven
at 115.degree. C. and the powder X-ray diffraction patterns
measured which showed the products to be pure ECR-42. Elemental
analyses and product stoichiometries are listed in Table 2.
1TABLE 1 Experiment Si Number X.sub.1 X.sub.5 SOL Source 9 0 11.5
methanol tetraethylorthosilicate 10 .16 11.5 methanol
tetraethylorthosilicate 11 0 6.1 n-propanol tetraethylorthosilicate
12 .16 6.1 n-propanol tetraethylorthosilicate 13 0 6.1 i-propanol
tetraethylorthosilicate 14 .16 6.1 i-propanol
tetraethylorthosilicate 15 0 5.0 n-butanol tetraethylorthosilicate
16 .16 5.0 n-butanol tetraethylorthosilicate 17 0 8 ethanol
tetramethylorthosilicate 18 .16 8 ethanol tetramethylorthosilicate
19 0 8 ethanol tetrapropylorthosilicate 20 .16 8 ethanol
tetrapropylorthosilicate
[0090]
2TABLE 2 Experiment Molar Molar Molar Number % Si % Al % P Si Al P
9 3.213 18.40 19.37 0.080 0.480 0.440 10 3.870 17.63 13.68 0.112
0.530 0.358 11 2.813 20.73 22.22 0.063 0.484 0.452 12 3.542 18.27
15.00 0.098 0.526 0.376 13 3.147 18.09 19.42 0.080 0.476 0.445 14
3.550 18.65 15.23 0.097 0.528 0.376 15 2.668 18.60 19.70 0.067
0.485 0.448 16 3.360 19.38 15.78 0.089 0.533 0.378 17 3.148 18.31
19.35 0.079 0.479 0.441 18 4.194 18.35 12.98 0.120 0.545 0.336 19
3.124 18.00 19.24 0.079 0.477 0.444 20 3.730 19.52 15.90 0.097
0.528 0.375
Example 10
[0091] The materials of experiments 1-20 were subject to .sup.29Si
MAS NMR to determine the relative amounts of silicon in the five
different environments, i.e., Si(4Si), Si(3Si), Si (2Si), Si(1Si),
Si(0Si). The .sup.29Si Magic-angle spinning (MAS) nuclear magnetic
resonance (NMR) spectra with proton decoupling were recorded on a
Chemagnetics CMXII500 spectrometer at 99.3 MHz using a 7.5 mm probe
spinning at 6 kHz. Typical run conditions were: 800 to 10000
acquisitions; 4 or 5 sec. pulse width; 60 to 120 sec. relaxation
delay. Chemical shifts were measured relative to tetramethylsilane
(TMS). The spectra were then deconvoluted into the five silicon
environments. The molar fractions of each silicon environment are
given in Table 3.
3TABLE 3 Example 4 Al, 0 Si 3 Al, 1 Si 2 Al, 2 Si 1 Al, 3 Si 0Al, 4
Si 1 54 21 13 9 4 2 3 4 5 49 19 16 11 5 6 33 22 22 13 10 7 8 36 17
7 17 23 9 24 31 18 18 9 10 24 44 15 14 3 11 12 13 32 32 22 5 9 14
41 31 6 12 10 15 16 17 35 15 10 18 22 18 19 20
[0092] II. Discussion
[0093] A. Crystallite Size and Shape
[0094] It is well known that zeolite morphology has a major
influence on the reactivities of zeolites. Such effects become more
important with smaller pores and larger molecules. At very small
crystal sizes, the exterior surface may play a major role in
processes using such zeolites, especially the location of exterior
pore openings with respect to the catalytically active site(s).
[0095] Powder X-ray diffraction may be used for determining
crystallite size (and often shape) of materials less than about
1000.ANG. by the relative broadening of peaks in the X-ray
diffraction pattern. When the shape of the crystallites is
anisotrophic (different dimensions in different directions), then
the resulting powder diffraction pattern may have both broad and
sharp peaks if one or two of the dimensions of the crystals are
small enough to show peak broadening. Those reflections coming from
Miller planes in the crystals corresponding to the short dimension
will have broader peaks than those coming from Miller planes
corresponding to the longer dimension will have sharper peaks.
[0096] SAPO-11 has an orthorhombic crystal structure, a structure
which is frequently associated with spatial anisotropies. The
dimensions of the unit cell are a=8.4.ANG., b=18.5.ANG. and
c=13.5.ANG., and the structure is such that the 10-ring channels
run along the a dimension [100]. If the shape of the crystallites
was platelet in shape such that the a dimension was significantly
smaller than the b and c dimensions, one would expect the X-ray
diffraction pattern to show the peaks corresponding to the (h00)
reflections to be broader than those of the (0kl) reflections. This
would result in those peaks corresponding to the (h00) reflections
to have shorter peak height relative to the (0kl) peaks, not due to
a reduction on peak intensity, but to an increase in the peak
width.
[0097] While not wishing to be bound by any model or theory, it is
believed that an increased catalytic activity for a molecular sieve
catalyst would result when a large number of channel openings are
available to allow for efficient transportation of the reacting
species and products to and from the active sites inside of, or at
the pore mouth of, the molecular sieve crystal. The preferred
ECR-42 molecular sieve catalysts have this desirable spatial
anisotropy (preferred orientation), as shown in the powder x-ray
diffraction results in FIGS. 4 and 5. The (200) reflections are
clearly broader in width and shorter in height than surrounding
(0kl) reflections as the reactants are changed from TEOS (Example
7) to TEOS and ethanol co-solvent (Example 6) to TEOS, surfactant,
and ethanol co-solvent (Example 5). The SEM micrograph of FIG. 6(a)
clearly shows the preferred thin platelets present in the product
of Example 4. The platelets have a thickness less than 50 nm, well
within the threshold for seeing X-ray diffraction peak broadening,
and consistent with the diffraction patterns in FIGS. 4 and 5. FIG.
6(b) on the other hand, shows the undesirable thick platelet
morphology that results in conventionally prepared SAPO-11.
[0098] B. Silicon Distribution by .sup.29Si NMR
[0099] As discussed, while the preferred molecular sieve materials
have an X-ray diffraction pattern with line positions corresponding
to the AEL topology, they are physically and chemically distinct
from known SAPO-11 materials because of differences in the local
atomic arrangement of the component atoms. Conventional powder
x-ray diffraction analysis not a sufficient analytical tool to
determine the structural differences between SAPO-11 and the
preferred ECR-42 molecular sieves partially because of x-ray line
broadening, as discussed above. Consequently, in order to determine
the above-noted structural differences, it is necessary to use an
analytical tool which can discriminate between the atomic
environment in the overall crystal structure such as .sup.29Si MAS
NMR, which is well known in the art. An example of how the number
or Si nearest neighbors may be derived from NMR data is shown in
FIG. 5 and Table 3.
[0100] As discussed, it is believed that is the silicon
distribution with the crystal is one important characteristic
influencing catalytic activity in SAPO materials. Since silicon is
responsible for the acidity in SAPO materials, it is desirable that
silicon be well dispersed in the aluminophosphate framework for
high catalytic activity. It is known that increasing silicon
concentration in conventionally prepared SAPO-11 results in the
formation of large silicon islands as shown in FIG. 3(b) (low Si
concentration, some island formation) and FIG. 3(c) (high Si
concentration, with extensive island formation). FIG. 3(a) shows
that still lower Si concentration results in undesirable isolated
silicon atoms. Although large silicon islands are undesirable
because those silicon atoms at the interior of the islands are
catalytically inactive, small silicon-rich regions present in the
preferred ECR-42 material are desirable because the strongest acid
sites are believed to form at the borders of the Si -rich regions
and the aluminophosphate domains. This is because those silicons at
the borders have fewer aluminum atoms as nearest neighbors, which
leads to decreasing acidity resulting from aluminum's lower
electronegativity.
[0101] The distribution of silicon in SAPOs may be measured by
.sup.29Si NMR spectroscopy. For example, in SAPO-11, it is known
that those silicon atoms having 4 aluminums and 0 silicons (4Al,
0Si) as nearest neighbors show as NMR resonance at -90 to -93 ppm
chemical shift relative to tetramethylsiliane (TMS). Therefore, the
molar percent of Si atoms with zero, one, two, three, and four Si
atom nearest neighbors may be obtained, for example, by
deconvoluting the integrated intensities from .sup.29Si NMR
measurements. The Si (4Al,0Si) and the other silicon environments
are illustrated schematically in FIG. 1 and listed in
4TABLE 4 Si Environment 4Al, O Si 3 Al, 1 Si 2 Al, 2 Si 1 Al, 3 Si
0 Al, 4 Si Chemical -86 to -95 to -100 to -106 to -109 to shift in
ppm -94 ppm -99 ppm -105 ppm -108 ppm -115 ppm from TMS
[0102] It is clear from the above chart that for well dispersed
silicon, a .sup.29Si NMR spectra would have high intensity for the
(4Al, 0Si) resonance at -86 to -94 ppm, while a poorly dispersed
silicon would have high intensity at the (0Al, 4Si) resonance at
-109 to -115 ppm. Those silicons located at the border of the
silicon atoms having the highest acid strength would show high
relative intensity for the (3Al, 1Si), (2Al, 2Si), and (1Al, Si)
resonances. FIG. 7 shows .sup.29Si NMR spectra of the preferred
ECR-42 molecular sieve with framework Si contents of 4, 8, and 13
molar %. The spectra show the excellent silicon dispersion in the
preferred ECR-42 material. By way of comparison, FIG. 3 shows that
Si islanding is avoided in conventional SAPO-11 at very low Si
concentrations only. See FIG. 3(b). At Si content above about 0.04
mole fraction, substantial Si islanding occurs. See FIG. 3(a) and
(c). In particular, FIG. 7-B, shows that the preferred ECR-42
molecular sieve does not show undesirable Si island formation at
higher Si concentrations than in the conventionally prepared sample
shown in FIG. 3(a).
[0103] It should be noted that due to the characteristic of the
experimental NMR spectra, the deconvolutions shown in FIG. 2 are
not unique, but should be chosen with chemical sense. Therefore,
the simulation results constitute an estimation of the different
structural units contributing to the spectra, and may be used to
illustrate Si atom coordination differences that are evident from
the experimental data.
[0104] Moreover, the preferred molecular sieve, ECR-42, may contain
Si concentrations as low as about 1 wt. %, and it is often
difficult to obtain high quality NMR data from samples of such a
low concentration over the whole range of chemical shifts.
Consequently, some degree of uncertainty may be introduced into the
deconvolutions required to determine the number of Si atoms with
zero, one, two, three and four Si nearest neighbors. Nevertheless,
the intensity of the -109 to -115 ppm region is sufficient in
molecular sieve materials of even 1 wt. % to determine the
approximate molar percent of Si framework atoms having four Si atom
nearest neighbors, i.e., Si atoms located in Si islands.
* * * * *