Molecular sieve abstract
Problems on catalyst production and catalyst performance with respect
to conventional 8-oxygen-membered ring micropore-containing crystalline
silicoaluminophosphate molecular sieves as non-equilibrium methylamine
synthesis catalysts, are resolved. A chabazite type crystalline
silicoaluminophosphate molecular sieve having high purity and high
crystallinity and having, on a crystal grain surface, an amorphous
oxide layer whose Si/Al atomic ratio is greater than that of the
whole crystal grain can be stably produced with high yield with
the use of a small amount of structure directing agents by the present
method characterized in that hydrothermal treatment conducted in
the production of 8-oxygen-membered ring micropore-containing crystalline
silicoaluminophosphate sieves is controlled under specified treating
conditions. The thickness and composition of the amorphous oxide
layer, which exert marked influence on the yield of dimethylamine
synthesis, can be easily controlled and reproduced under the conditions
of catalyst synthesis according to the invention. Thus, the catalyst
of high performance can be stably supplied by the present invention
at a low cost with reduced output of waste.
Molecular sieve claims
1. A crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores, which comprises an amorphous
oxide layer on a crystal grain surface thereof, wherein the amorphous
oxide layer has a higher atomic ratio of silicon to aluminum than
the whole crystal grain thereof.
2. The crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores, according to claim 1 wherein
said whole crystal grain has an atomic ratio of silicon to aluminum
in a range of 0.05 to 0.30 and said amorphous oxide layer on the
crystal grain surface has an atomic ratio of silicon to aluminum
of 0.50 or more, as determined by X-ray photoelectron spectroscopy.
3. The crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores, according to claim 1 or 2 wherein
said amorphous oxide layer on the crystal grain surface has an atomic
ratio of silicon to phosphorus of 0.55 or more as determined by
X-ray photoelectron spectroscopy.
4. The crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores, according to any one of claims
1 to 3 wherein said amorphous oxide layer on the crystal grain
surface has a thickness in a range of 3 to 20 nm.
5. The crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores, according to any one of claims
1 to 4 which comprises at least one element selected from the group
consisting of magnesium, yttrium, titanium, zirconium, manganese,
iron, cobalt and tin.
6. The crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores, according to any one of claims
1 to 5 wherein said crystal grain has a rectangular parallelepiped
and/or cubic form, and an average grain diameter of 5 .mu.m or less.
7. The crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores, according to any one of claims
1 to 6 which has a crystal grain body portion that is the whole
crystal grain from which said amorphous oxide layer on the crystal
grain surface is excluded, said crystal grain body portion being
of chabazite structure.
8. The crystalline silicoaluminophosphate molecular sieve having
8-oxygen-membered ring micropores of chabazite structure, according
to claim 7 which has a ratio of peak intensity at (100) plane of
AFI structure to peak intensity at (100) plane of chabazite structure,
the ratio being 0.02 or less as determined by X-ray diffractometry.
9. A method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve defined in any
one of claims 1 to 8 by hydrothermally treating a starting mixture
composed of an organic amine and/or organic ammonium salt together
with an aluminum compound, phosphorus compound and silicon compound
and water to produce the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve having an amorphous
oxide layer on a crystal grain surface thereof, which comprises
a first step for producing at least a crystalline portion thereof
and a second step for conducting hydrothermal treatment to form
the amorphous oxide layer on the crystal grain surface.
10. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
claim 9 wherein said first step comprises two sub-steps for hydrothermal
treatment, one being a step for carrying out hydrothermal treatment
at 80 to 130.degree. C. for 1 hour or more, and the other being
a step for carrying out hydrothermal treatment at 150 to 200.degree.
C. for 1 to 10 hours.
11. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
claim 10 wherein said sub-step of the first step for carrying out
hydrothermal treatment at 80 to 130.degree. C. for 1 hour or more
includes a step in which temperature is increased from 80 to 130.degree.
C. in 1 hour or more, or a step in which temperature is kept at
a constant level in a range of 80 to 130.degree. C. for 1 hour or
more.
12. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 9 to 11 wherein said second step for hydrothermal
treatment includes a step for carrying out hydrothermal treatment
at 150 to 200.degree. C. for 10 hours or more.
13. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
claim 9 wherein said first step comprises two sub-steps, one being
a step for carrying out hydrothermal treatment at a constant temperature
in a range of 95 to 125.degree. C. for 3 to 24 hours and the other
being a step for carrying out hydrothermal treatment at 150 to 200.degree.
C. for 1 to 10 hours, and said second step for hydrothermal treatment
comprises a step for carrying out hydrothermal treatment at 150
to 200.degree. C. for 10 to 150 hours.
14. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 9 to 13 wherein said starting mixture composed
of an organic amine and/or organic ammonium salt together with an
aluminum compound, phosphorus compound, silicon compound and water
has a ratio of the total mole number of the organic amine and organic
ammonium salt to the mole number of the aluminum compound as Al.sub.2O.sub.3
the ratio being 0.4 to 0.98.
15. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 9 to 14 wherein said organic amine and/or organic
ammonium salt is tetraethyl ammonium hydroxide.
16. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 9 to 15 wherein said aluminum compound is pseudoboehmite.
17. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 9 to 16 wherein said phosphorus compound is phosphoric
acid.
18. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 1 to 17 wherein said silicon compound is silica
sol.
19. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 1 to 18 wherein a silicon compound is further
added before or during said second step.
20. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 9 to 19 wherein at least one element selected
from the group consisting of magnesium, yttrium, titanium, zirconium,
manganese, iron, cobalt and tin is further added.
21. The method for producing the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve, according to
any one of claims 9 to 20 wherein said 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve is of chabazite
structure.
22. A method for producing methylamines, comprising reacting methanol
and ammonia in the presence of the 8-oxygen-membered ring micropore-containing
crystalline silicoaluminophosphate molecular sieve defined in any
one of claims 1 to 8.
23. A method for producing methylamines, comprising reacting methanol
and monomethylamine in the presence of the 8-oxygen-membered ring
micropore-containing crystalline silicoaluminophosphate molecular
sieve defined in any one of claims 1 to 8.
24. A method for producing methylamines, comprising carrying out
disproportionation reaction of monomethylamine in the presence of
the 8-oxygen-membered ring micropore-containing crystalline silicoaluminophosphate
molecular sieve defined in any one of claims 1 to 8.
Molecular sieve description
TECHNICAL FIELD
[0001] The present invention relates to an 8-oxygen-membered ring
micropore-containing crystalline silicoaluminophosphate molecular
sieve (hereinafter referred to as 8-membered ring SAPO in principle),
a method for producing the same, and a method for producing methylamines
with the thus-produced 8-membered ring SAPO as a catalyst.
[0002] More specifically, the present invention relates to an 8-membered
ring SAPO having, on a crystal grain surface thereof, an amorphous
oxide layer that has a great effect on catalyst performance, the
amorphous oxide layer having an atomic ratio of silicon to aluminum
(Si/Al) higher than the whole crystal grain, a method for producing
the 8-membered ring SAPO which has the amorphous oxide layer, and
a method for producing methylamines with the thus-produced 8-membered
ring SAPO as a catalyst. Meanwhile, crystalline silicoaluminophosphate
molecular sieve of chabazite structure is one of the 8-membered
ring SAPOs that are mainly composed of silicon, aluminum, phosphorus
and oxygen and have a CHA structure according to the IUPAC structural
code specified by the International Zeolite Association (IZA).
[0003] Methylamines, in particular, dimethylamine, are important
starting materials for solvents represented by dimethylformamide,
rubber products, medicines and surfactants.
BACKGROUND ART
[0004] Methylamines are generally synthesized from methanol and
ammonia at around 400.degree. C. in the presence of a solid acid
catalyst, e.g., silica-alumina. As is well known, use of the silica-alumina
catalyst leads to predominant production of trimethylamine according
to thermodynamic equilibrium although trimethylamine is least demanded
among the three types of methylamines, namely, mono-, di- and tri-methylamines.
Since dimethylamine accounts for most of the demand for methylamines,
methods have been recently developed to selectively produce dimethylamine,
overcoming the thermodynamic equilibrium composition.
[0005] Some of these methods include those using zeolites (crystalline
aluminosilicate molecular sieves), e.g., Zeolite A (see, for example,
Patent Document 1), FU-1 (see, for example, Patent Document 2),
ZSM-5 (see, for example, Patent Document 3), ferrierite and erionite
(see, for example, Patent Document 4), ZK-5 Rho, chabazite and
erionite (see, for example, Patent Document 5) and mordenite (see,
for example, Patent Documents 6 7 8 and 9).
[0006] These methods deal with zeolites small in micropore channel
size, and try to improve selectivity for dimethylamine and catalytic
activity by subjecting them to ion exchanging, dealumination, doping
with a specific element or silylation in order to control micropore
channel size or modify acid sites on external surfaces thereof.
[0007] Also known is a method for production of monomethylamine
or the like at a higher proportion than the thermodynamically equilibrium
composition by use of a crystalline silicoaluminophosphate molecular
sieve (hereinafter referred to as SAPO in principle) as a non-zeolitic
molecular sieve (see, for example, Patent Document 10).
[0008] After having extensively studied selective dimethylamine
production techniques, the inventors of the present invention have
also found that SAPOs modified with silica or other various oxides
exhibit higher activity and dimethylamine selectivity than conventional
zeolite catalysts, and have already applied for patents (see, for
example, Patent Documents 11 12 and 13).
[0009] It is generally considered that crystalline molecular sieves,
e.g., zeolites and SAPOs, have a surface consisting of an exposed
crystal lattice surface. Therefore, the surface of zeolites and
SAPOs has strong acid sites which are characteristic of molecular
sieves that contain silicon and aluminum. In order to improve selectivity
for dimethylamine production, the surface acid sites are often subjected
to chemical vapor deposition using silicon compounds, liquid-phase
silylation, modification with a boron- or phosphorus-containing
compound, or the like (see, for example, Patent Documents 14 15
16 17 and 18). The techniques already described by the present
inventors in the patent publications (see Patent Documents 11 12
and 13) are also based on these concepts.
[0010] However, these conventional processes require lots of steps
since they require separation and washing by centrifugation or filtration
after synthesis of SAPOs and, in some cases, further modification
of calcined catalysts. In particular, silylation needs precise control
of moisture content of catalysts to be treated, and uses organic
solvents, e.g., ethanol or toluene, thereby causing problems of
disposal of waste fluid.
[0011] In this way, these conventional processes, in which synthesized
SAPOs are further modified to improve activity and selectivity,
involve problems to be solved both economically and environmentally.
There are demands for development of new methods which can control
activity and selectivity during steps for synthesis of SAPOs and
thus differently from the conventional processes that require the
post-treatment steps.
[0012] In order to solve these problems, the present inventors
have already found that an 8-membered ring SAPO of chabazite structure
having a rectangular parallelepiped or cubic crystal form of 5 .mu.m
or less in average grain diameter works as an excellent methylamine
production catalyst of high activity and dimethylamine selectivity,
and have already applied for patent (see Patent Document 19), in
addition to the above-described techniques.
[0013] This 8-membered ring SAPO of chabazite structure exhibits
excellent activity and selectivity without modification after synthesis.
However, the present inventors have further studied it and observed
a phenomenon of catalyst performance depending upon some synthesis
lots. Therefore, it involves technical problems that must be further
improved to obtain an optimum catalyst stably.
[0014] The 8-membered ring SAPO of chabazite structure having the
above-described particle size and shape is synthesized using organic
amines or organic ammonium salts, e.g., diethanolamine or tetraethyl
ammonium hydroxide in an amount of 1.5.+-.0.5 times the mole number
of the aluminum compounds as Al.sub.2O.sub.3. On the other hand,
the amount of the organic amine or organic ammonium salt incorporated
into the 8-membered ring SAPO of chabazite structure just after
synthesized but before calcined is an amount required to establish
the crystalline structure, namely, only about 0.37 times the mole
number as Al.sub.2O.sub.3. The surplus organic amines or organic
ammonium salts, which are not incorporated into the crystalline
structure, should be treated by activated sludge or the like. Therefore,
synthesis of a pure 8-membered ring SAPO with a reduced amount of
organic amines or organic ammonium salts would be a desirable process
both economically and environmentally.
[0015] Since 8-membered ring SAPOs exhibit relatively high selectivity
for dimethylamine in methylamine synthesis, various studies have
conventionally been made on the synthesis of methylamines using
such SAPOs (see, for example, Non-patent Document 4). As 8-membered
ring SAPOs, are known SAPO-14 -17 -18 -33 -34 -35 -39 -42
-43 -44 -47 and -56 (see, for example, Non-patent Documents 5
and 6). Among them, three types, namely, SAPO-34 SAPO-44 and SAPO-47
are known to have the chabazite structure. In particular, the SAPO-34
of chabazite structure has been extensively studied as a catalyst
for methylamine synthesis and methanol conversion (see, for example,
Patent Documents 10 and 21).
[0016] It is known that these 8-membered ring SAPOs can be synthesized
by hydrothermally treating a mixture of a silicon compound, aluminum
compound, phosphorus compound and water in the presence of a structure
directing agent such as tetraethyl ammonium hydroxide, morpholine,
cyclohexylamine and diethylethanolamine (see, for example, Patent
Document 20). It is not known, however, that these 8-membered ring
SAPOs have an amorphous oxide layer on their crystal grain surfaces,
and the amorphous oxide layer grows on crystal grain surfaces during
the hydrothermal synthesis and has a great effect on yield and selectivity
of the methylamine synthesis.
[0017] In general, the mixture to be hydrothermally treated to
synthesize 8-membered ring SAPOs is represented by the compositional
formula (1) shown below, and the structure directing agent R is
used in an amount of 1 to 3 times the mole number of Al.sub.2O.sub.3
in the mixture (a/c=1 to 3):
aR, bSiO.sub.2 cAl.sub.2O.sub.3 dP.sub.2O.sub.5 eH.sub.2O Formula
(1)
[0018] Survey of the amount of structure directing agents used
for synthesis of 8-membered ring SAPOs on various patent documents
and literatures reveals that structure directing agents are used
in an amount of at least one times the mole number of Al.sub.2O.sub.3
in the mixture to be hydrothermally treated, in order to produce
8-membered ring SAPOs of chabazite structure with high purity and
high degree of crystallinity, and it is mentioned that, when they
are used in a smaller amount, there occur impurities, e.g., a SAPO-5
structure which falls under the AFI structure according to the IUPAC
structural code specified by the International Zeolite Association
(IZA), as well as cristobalite or berlinite of aluminum phosphates.
[0019] A literature describes synthesis of SAPO-34 using tetraethyl
ammonium hydroxide (TEAOH) as a structure directing agent (see,
for example, Non-patent Document 1), and discusses that pure SAPO-34
is produced at a TEAOH/Al.sub.2O.sub.3 molar ratio of 2 to 3 SAPO-5
is produced at a ratio of 1 to 2 and a high-density phase is produced
at a ratio below 1. It is also mentioned that grains having a non-crystalline
amorphous structure are produced at a ratio above 3.
[0020] A literature describes synthesis of SAPO-34 using morpholine
as a structure directing agent (see, for example, Non-patent Document
2), and discusses that a mixture of aluminum phosphate cristobalite
and an amorphous compound is produced at a morpholine/Al.sub.2O.sub.3
molar ratio of 0.5 or less, a mixture of 80% SAPO-34 and 20% cristobalite
is obtained at a morpholine/Al.sub.2O.sub.3 molar ratio of 1.0
and pure SAPO-34 is obtained at a morpholine/Al.sub.2O.sub.3 molar
ratio of 2.0 or more.
[0021] In addition, a literature describes synthesis of SAPO-44
using cyclohexylamine as a structure directing agent (see, for example,
Non-patent Document 3), and discusses that contamination with SAPO-5
occurs at a cyclohexylamine/Al.sub.2O.sub.3 molar ratio of 1.9 or
less.
[0022] The above-cited references are as follows:
[0023] Patent Document 1: Japanese Patent Laid-Open No. S56-69846A,
[0024] Patent Document 2: Japanese Patent Laid-Open No. S54-148708A,
[0025] Patent Document 3: U.S. Pat. No. 4082805 specification,
[0026] Patent Document 4: Japanese Patent Laid-Open No. S56-113747A,
[0027] Patent Document 5: Japanese Patent Laid-Open No. S61-254256A,
[0028] Patent Document 6: Japanese Patent Laid-Open No. S56-46846A,
[0029] Patent Document 7: Japanese Patent Laid-Open No. S58-49340A,
[0030] Patent Document 8: Japanese Patent Laid-Open No. S59-210050A,
[0031] Patent Document 9: Japanese Patent Laid-Open No. A59-227841A,
[0032] Patent Document 10: Japanese Patent Laid-Open No. H02-734A,
[0033] Patent Document 11: Japanese Patent Laid-Open No. H11-35527A,
[0034] Patent Document 12: Japanese Patent Laid-Open No. H11-239729A,
[0035] Patent Document 13: Japanese Patent Laid-Open No. 2000-5604A,
[0036] Patent Document 14: Japanese Patent Laid-Open No. H03-262540A,
[0037] Patent Document 15: Japanese Patent Laid-Open No. H 11-508901A,
[0038] Patent Document 16: Japanese Patent Laid-Open No. H06-179640A,
[0039] Patent Document 17: Japanese Patent Laid-Open No. H07-2740A,
[0040] Patent Document 18: Japanese Patent Laid-Open No. S61-254256A,
[0041] Patent Document 19: Japanese Patent Laid-Open No. 2000-117114A,
[0042] Patent Document 20: U.S. Pat. No. 4440871 specification,
[0043] Patent Document 21: U.S. Pat. No. 5126308 specification,
[0044] Non-Patent Document 1: J. Liang, H. Li, S. Zhao, W. Guo,
R. Wang, and M. Ying, Appl. Catal., 1991 64 pp. 31 to 40
[0045] Non-Patent Document 2: A. M. Prakash, S. Unnikrishnan, J.
Chem. Soc. Faraday Trans., 1994 90 (15), pp. 2291 to 2296
[0046] Non-Patent Document 3: S. Ashtekar, S. V. V. Chilukuri,
D. K. Chakrabarty, J. Phys. Chem., 1994 98 pp. 4878 to 4883
[0047] Non-Patent Document 4: D. R. Corbin, S. Schwarz, and G.
C. Sonnichsen, Catalysis Today, 1997 37 pp. 71 to 102
[0048] Non-Patent Document 5: E. M. Flanigen, B. M. Lok, R. L.
Patton, and S. T. Wilson, New Developments in Zeolite Science and
Technology, Elsevier, 1986 pp. 103 to 112 and
[0049] Non-Patent Document 6: Structure Commission of the International
Zeolite Association, Atlas of Zeolite Framework Types, Elsevier,
2001 pp. 14 to 15.
[0050] As described above, the present inventors have found that,
among the SAPOs, an 8-membered ring SAPO of chabazite structure
having a rectangular parallelepiped or cubic crystal form of 5 .mu.m
or less in average grain diameter works as an excellent methylamine
production catalyst high in activity and dimethylamine selectivity
without any modification after synthesis, and have already applied
for patent (Japanese Patent Laid-Open No. 2000-117114A). However,
it has been observed that the SAPO having the above grain diameter
and shape still shows variation of catalyst performance depending
upon production lots.
[0051] The above-described 8-membered ring SAPO of chabazite structure
is obtained by hydrothermally treating a starting mixture that contains
organic amines or organic ammonium salts such as tetraethyl ammonium
hydroxide (TEAOH) and diethanolamine in an amount of 1.5.+-.0.5
times the mole number of aluminum compounds as Al.sub.2O.sub.3.
However, such a method as described above, in which an excessive
amount of organic amines or ammonium salts is required, produces
the catalyst at a low yield and needs treatment of the surplus organic
amines or ammonium salts by activated sludge or the like.
[0052] Therefore, the SAPO disclosed in Japanese Patent Laid-Open
No. 2000-117114A involves problems that must be further improved
concerning catalytic stability for amine synthesis, the excess amount
of structure directing agents, or the like.
[0053] Objects of the present invention are to solve the above
problems and provide an 8-membered ring SAPO having excellent catalytic
activity and dimethylamine selectivity, a method for stably producing
the SAPO at a low cost, and a method for producing methylamines
in the presence of the SAPO as a catalyst.
DISCLOSURE OF INVENTION
[0054] As a result of intensive researches for solving the above
problems, the present inventors have found that an 8-membered ring
SAPO having a body of a crystalline molecular sieve grain which
is formed therearound with an amorphous oxide layer having a silicon/aluminum
(Si/Al) atomic ratio higher than the crystalline portion is obtained
with the Si/Al atomic ratio of the amorphous oxide layer being higher
than the Si/Al atomic ratio of the whole crystal grain, during a
synthesis step of the 8-membered ring SAPO, and also have found
that the Si/Al atomic ratio or thickness of the amorphous oxide
layer has a great effect on catalytic activity and dimethylamine
selectivity, and can be precisely controlled by temperature and
time of the hydrothermal treatment conducted during a step for forming
the amorphous oxide layer. It is also found that a catalyst stable
in activity and dimethylamine selectivity can be produced by the
technique for controlling the Si/Al atomic ratio or thickness of
the amorphous oxide layer.
[0055] It is also found that the hydrothermal treatment comprising
a step for hydrothermal treatment at 80 to 130.degree. C. for 1
hour or more and then at 150 to 200.degree. C. for 1 to 10 hours
(first step) and a step for hydrothermal treatment at 150 to 200.degree.
C. for 10 hours or more (second step) produces a pure 8-membered
ring SAPO high in degree of crystallinity, and gives higher yield
of catalysts than conventional processes, even when the amount of
organic amines or organic ammonium salts used as structure directing
agents is reduced to below 1.0 in terms of molar ratio to Al.sub.2O.sub.3.
[0056] It is also found that the 8-membered ring SAPO thus produced
has higher catalytic activity and dimethylamine selectivity than
the SAPOs of chabazite structure obtained by conventional processes.
And, the present inventors have established a method for stably
producing a catalyst excellent in activity and dimethylamine selectivity
by combining the technique for producing the 8-membered ring SAPO
with the technique for controlling the Si/Al atomic ratio or thickness
of the amorphous oxide layer, thereby achieving the present invention.
[0057] That is, the present invention relates to an 8-membered
ring SAPO having an amorphous oxide layer on a crystal grain surface
thereof, the amorphous oxide layer having a higher Si/Al atomic
ratio than the whole crystal grain thereof, and to a method for
producing an 8-membered ring SAPO characterized in that thickness
of the amorphous oxide layer or surface composition of the crystal
grain is precisely controlled by temperature and time of hydrothermal
treatment conducted during a step for forming the amorphous oxide
layer. The present invention also relates to a method for producing
an 8-membered ring SAPO by hydrothermally treating a starting mixture
comprising an organic amine and/or organic ammonium salt as a structure
directing agent together with an aluminum compound, phosphorus compound,
silicon compound and water, wherein a ratio of the total mole number
of the organic amine and organic ammonium salt to the mole number
of the aluminum compound as Al.sub.2O.sub.3 is 0.4 to 0.98 and
the starting mixture is subjected to treatment which comprises a
first step of a hydrothermal treatment at 80 to 130.degree. C. for
1 hour or more followed by a further hydrothermal treatment at 150
to 200.degree. C. for 1 to 10 hours, and a second step of a hydrothermal
treatment at 150 to 200.degree. C. for 10 hours or more. The present
invention also relates to a method for producing methylamines, in
which the 8-membered ring SAPO produced by combination of the above-described
techniques for production of the 8-membered ring SAPO is used as
a catalyst.
[0058] More specifically, the present invention relates to an 8-membered
ring SAPO, methods for producing the SAPO, and methods for producing
methylamines by use of the 8-membered ring SAPO as a catalyst, as
described in (1) to (24) below.
[0059] (1) An 8-membered ring SAPO which comprises an amorphous
oxide layer on a crystal grain surface thereof, wherein the amorphous
oxide layer has a higher atomic ratio of silicon to aluminum than
the whole crystal grain thereof.
[0060] (2) The 8-membered ring SAPO as defined in (1), wherein
the whole crystal grain has an atomic ratio of silicon to aluminum
in a range of 0.05 to 0.30 and the amorphous oxide layer on the
crystal grain surface has an atomic ratio of silicon to aluminum
of 0.50 or more, as determined by X-ray photoelectron spectroscopy.
[0061] (3) The 8-membered ring SAPO as defined in any one of (1)
and (2), wherein the amorphous oxide layer on the crystal grain
surface has an atomic ratio of silicon to phosphorus of 0.55 or
more as determined by X-ray photoelectron spectroscopy.
[0062] (4) The 8-membered ring SAPO as defined in any one of (1)
to (3), wherein the amorphous oxide layer on the crystal grain surface
has a thickness in a range of 3 to 20 nm.
[0063] (5) The 8-membered ring SAPO as defined in any one of (1)
to (4), which further comprises at least one element selected from
the group consisting of magnesium, yttrium, titanium, zirconium,
manganese, iron, cobalt and tin.
[0064] (6) The 8-membered ring SAPO as defined in any one of (1)
to (5), wherein the crystal grain has a rectangular parallelepiped
and/or cubic form, and an average grain diameter of 5 .mu.m or less.
[0065] (7) The 8-membered ring microporous SAPO as defined in any
one of (1) to (6), which has a crystal grain body portion that is
the whole crystal grain from which the amorphous oxide layer on
the crystal grain surface is excluded, said crystal grain body portion
being of chabazite structure.
[0066] (8) The 8-membered ring SAPO of chabazite structure as defined
in (7), which has a ratio of peak intensity at (100) plane of AFI
structure to peak intensity at (100) plane of chabazite structure,
this ratio being 0.02 or less as determined by X-ray diffractometry.
[0067] (9) A method for producing the 8-membered ring SAPO defined
in any one of (1) to (8) by hydrothermally treating a starting mixture
composed of an organic amine and/or organic ammonium salt together
with an aluminum compound, phosphorus compound, silicon compound
and water to produce the 8-membered ring SAPO having an amorphous
oxide layer on a crystal grain surface thereof, which comprises
a first step for producing at least a crystalline portion thereof
and a second step for conducting hydrothermal treatment to form
the amorphous oxide layer on the crystal grain surface.
[0068] (10) The method for producing the 8-membered ring SAPO,
as defined in (9), wherein the first step comprises two sub-steps
for hydrothermal treatment, one being a step for carrying out hydrothermal
treatment at 80 to 130.degree. C. for 1 hour or more, and the other
being a step for carrying out hydrothermal treatment at 150 to 200.degree.
C. for 1 to 10 hours.
[0069] (11) The method for producing the 8-membered ring SAPO,
as defined in (10), wherein the sub-step of the first step for carrying
out hydrothermal treatment at 80 to 130.degree. C. for 1 hour or
more includes a step in which temperature is increased from 80 to
130.degree. C. in 1 hour or more, or a step in which temperature
is kept at a constant level in a range of 80 to 130.degree. C. for
1 hour or more.
[0070] (12) The method for producing the 8-membered ring SAPO,
as defined in any one of (9) to (11), wherein the second step for
hydrothermal treatment includes a step for carrying out hydrothermal
treatment at 150 to 200.degree. C. for 10 hours or more.
[0071] (13) The method for producing the 8-membered ring SAPO,
as defined in (9), wherein the first step comprises two sub-steps,
one being a step for carrying out hydrothermal treatment at a constant
temperature in a range of 95 to 125.degree. C. for 3 to 24 hours
and the other being a step for carrying out hydrothermal treatment
at 150 to 200.degree. C. for 1 to 10 hours, and the second step
for hydrothermal treatment comprises a step for carrying out hydrothermal
treatment at 150 to 200.degree. C. for 10 to 150 hours.
[0072] (14) The method for producing the 8-membered ring SAPO,
as defined in any one of (9) to (13), wherein the starting mixture
composed of an organic amine and/or organic ammonium salt together
with an aluminum compound, phosphorus compound, silicon compound
and water has a ratio of the total mole number of the organic amine
and organic ammonium salt to the mole number of the aluminum compound
as Al.sub.2O.sub.3 this ratio being 0.4 to 0.98.
[0073] (15) The method for producing the 8-membered ring SAPO,
as defined in any one of (9) to (14), wherein the organic amine
and/or organic ammonium salt is tetraethyl ammonium hydroxide.
[0074] (16) The method for producing the 8-membered ring SAPO,
as defined in any one of (9) to (15), wherein the aluminum compound
is pseudoboehmite.
[0075] (17) The method for producing the 8-membered ring SAPO,
as defined in any one of (9) to (16), wherein the phosphorus compound
is phosphoric acid.
[0076] (18) The method for producing the 8-membered ring SAPO,
as defined in any one of (1) to (17), wherein the silicon compound
is silica sol.
[0077] (19) The method for producing the 8-membered ring SAPO,
as defined in any one of (1) to (18), wherein a silicon compound
is further added before or during the second step.
[0078] (20) The method for producing the 8-membered ring SAPO,
as defined in any one of (9) to (19), wherein at least one element
selected from the group consisting of magnesium, yttrium, titanium,
zirconium, manganese, iron, cobalt and tin is further added.
[0079] (21) The method for producing the 8-membered ring SAPO,
as defined in any one of (9) to (20), wherein the 8-membered ring
SAPO is of chabazite structure.
[0080] (22) A method for producing methylamines, comprising reacting
methanol and ammonia in the presence of the 8-membered ring SAPO
defined in any one of (1) to (8).
[0081] (23) A method for producing methylamines, comprising reacting
methanol and monomethylamine in the presence of the 8-membered ring
SAPO defined in any one of (1) to (8).
[0082] (24) A method for producing methylamines, comprising carrying
out disproportionation reaction of monomethylamine in the presence
of the 8-membered ring SAPO defined in any one of (1) to (8).
[0083] Hereinafter, the present invention is described in more
detail. The SAPO of the present invention is an 8-membered ring
SAPO having an amorphous oxide layer on a surface thereof, the oxide
layer having a higher Si/Al atomic ratio than the whole crystal
grain.
[0084] SAPO means a crystalline and microporous compound having
a three-dimensional, microporous, crystalline framework structure
that is composed of a tetrahedron unit of PO.sub.2.sup.+, AlO.sub.2.sup.-
and SiO.sub.2 as described in U.S. Pat. No. 4440871 specification.
[0085] Moreover, a compound containing a tetrahedron unit having
metal(s) other than silicon, aluminum and phosphorus in its three-dimensional,
microporous, crystalline framework structure is disclosed in EP
159624 or the like. It is referred to as ELAPSO molecular sieve.
However, these patent documents are silent on SAPOs having an amorphous
oxide layer on the surface thereof as provided by the present invention.
[0086] The 8-membered ring SAPO of the present invention may contain
a metallic component other than silicon, aluminum and phosphorus.
It preferably contains an element selected from magnesium, yttrium,
titanium, zirconium, manganese, iron, cobalt and tin, of which titanium
and zirconium are particularly preferable for their effects of improving
catalytic activity and life. These elementary components may be
present in and/or outside the three-dimensional, microporous, crystalline
framework structure. Content of these elements is not limited, but
their total content is preferably in an atomic ratio of 0.0001 to
0.1 to aluminum. The 8-membered ring SAPO containing these elements
can be prepared by hydrothermally treating a mixture comprising
a structure directing agent, silicon compound, aluminum compound,
phosphorus compound, water, and nitrate, sulfate, chloride, oxide
sol, oxide powder, alkoxide and/or complex of the above-described
element(s).
[0087] The SAPO preferably has an effective micropore size in a
range from 0.3 to 0.6 nm, in order to produce methylamines, in particular,
produce dimethylamine selectively, by the reaction of methanol and
ammonia. Such micropores prevent trimethylamine molecules from passing
therethrough, but allow smaller monomethylamine and dimethylamine
molecules to pass therethrough, thereby finally slanting reaction
selectivity towards monomethylamine and dimethylamine (D. R. Corbin,
S. Schwarz, and G. C. Sonnichsen, Catalysis Today, 37 (1997), pp.
71 to 102). The above-described effective micropore size corresponds
to those of 8-oxygen- to 10-oxygen-membered ring SAPOS, of which
the 8-membered ring SAPO is necessary to further decrease trimethylamine
selectivity.
[0088] Examples of 8-membered ring SAPOs include SAPO-14 -17
-18 -33 -34 -35 -39 -42 -43 -44 -47 and -56. The relationship
between the number attached to each of these SAPOs and IUPAC structural
code specified by the Structure Commission of the International
Zeolite Association (IZA), is described in, for example, "Atlas
of Zeolite Framework Types" edited by Structure Commission
of the International Zeolite Association, published by Elsevier.
The above-described SAPOs correspond to the IUPAC structural codes
of AFN, ERI, AEI, ATT, CHA, LEV, ATN, LTA, GIS, CHA, CHA and AFX,
respectively. Of these SAPOs, SAPO-17 -18 -34 -35 -44 -47 and
-56 are preferable, and SAPO-34 of chabazite structure is particularly
preferable.
[0089] The 8-membered ring SAPO of chabazite structure according
to the present invention is a crystalline molecular sieve of CHA
structure according to the IUPAC structural code specified by the
International Zeolite Association (IZA) and mainly composed of silicon,
aluminum, phosphorus and oxygen. More specifically, it is a compound
having a structure represented by CHA, among the SAPOs described
in U.S. Pat. No. 4440871 specification. As SAPOs having such CHA
structure, known are three types of SAPOS, namely, SAPO-34 SAPO-44
and SAPO-47 as described in M. Flanigen, R. L. Patton, and S. T.
Wilson, Studies in Surface Science and Catalysis, Innovation in
Zeolite Materials Science, pp. 13 to 27 1988.
[0090] The 8-membered ring SAPO of the present invention is most
featured in that it has, on a surface thereof, an amorphous oxide
layer having a higher Si/Al atomic ratio than the whole crystal
grain. The amorphous oxide layer can be observed by FIB-STEM analysis.
For example, FIGS. 1 and 2 show the SAPO-34 where a cubic SAPO-34
grain was scraped off on both sides by focused ion beams (FIB, FB-2100
manufactured by Hitachi Ltd.) and the cross section of the remaining
80 nm thick flake was observed by a scanning transmission electron
microscope (STEM, thin film evaluation device HD-2000 manufactured
by Hitachi Ltd.). FIG. 1 shows a 3-layered structure, where the
outermost layer is of carbon, platinum and tungsten deposited to
fix the sample grain and increase its electroconductivity. The central
portion is the crystal grain body, and a thin film between them
is the amorphous oxide layer. FIG. 2 shows the grain of FIG. 1 magnified
for the portion of around 100 nm deep from the surface. The portion
with a check pattern corresponds to the crystal grain body stripped
of the amorphous oxide layer, and the white layer having no check
pattern corresponds to the amorphous oxide layer. The check pattern
indicates that the grain has a regular structure, and the clear
Laue spots observed by electron beam diffractometry indicate that
the crystal grain body portion is crystalline (FIG. 3). On the other
hand, the white layer showing no check pattern indicated no Laue
spots according electron beam diffraction analysis, and thus it
lacks a regular structure and is amorphous (FIG. 4). Moreover, the
amorphous layer is a silicon-rich oxide layer having a higher Si/Al
atomic ratio than the crystal grain body, as confirmed by the compositional
analysis using an energy dispersive X-ray (EDX) analyzer.
[0091] Existence of the amorphous oxide layer and its thickness
greatly affect reactivity and dimethylamine selectivity in the production
of methylamines by the reaction of methanol and ammonia, or disproportionation
reaction of monomethylamine. Taking the above-described SAPO-34
as an example, the SAPO-34 having an amorphous oxide layer thinner
than 3 nm achieves a reaction at a high reactivity but produces
trimethylamine at a selectivity of 10% or higher, and thus shows
insufficient dimethylamine selectivity. The SAPO-34 having an amorphous
oxide layer thicker than 20 nm, on the other hand, shows a low trimethylamine
selectivity of 1% or less but insufficient reactivity. These results
can be explained by considering that the thin amorphous oxide layer
does not sufficiently cover active acid sites that exist on the
crystal grain surface and have no molecular sieve effect, and the
remaining active acid sites produce trimethylamine that is most
stable thermodynamically, whilst the excessively thick amorphous
oxide layer sufficiently covers active acid sites, but retards the
diffusion of reacting species towards active sites of the crystal
grain body or the dissociation of the produced species from the
crystal body, thereby lowering reactivity. Since the amorphous oxide
layer is mainly composed of oxides of silicon, aluminum and phosphorus
and contains silicon as a major component, it lacks strong acidity
unlike silica-alumina and thus shows little reactivity.
[0092] Therefore, preferable thickness of the amorphous oxide layer
in the present invention is 3 to 20 nm, more preferably 3.5 to 16
nm.
[0093] Composition of the amorphous oxide layer can be analyzed
by the above-described energy dispersive X-ray analyzer, and more
simply determined by analysis of the surface composition of the
crystal grain according to X-ray photoelectron spectroscopy (XPS,
ESCA). The X-ray photoelectron spectroscopy can determine the composition
of a depth of 1.5 to 4.0 nm from the outermost surface of crystal
grains.
[0094] Composition of the crystal grain body, on the other hand,
can be considered to be almost the same as that of the whole crystal
grain, because the amorphous oxide layer is very thin. For example,
it can be determined by completely dissolving SAPO grains in a mineral
acid or the like and using inductively coupled plasma emission spectroscopy
(ICP).
[0095] The surface composition according to the present invention
was determined by the ESCALAB MKII analyzer manufactured by VG Scientific
Ltd. with Al-K.alpha. ray as the X-ray source (1486.7 eV) using
Scofield correction factors as described in J. H. Scofield, Journal
of Electron Spectroscopy and Related Phenomena, 8 (1976), pp. 129
to 137. Composition of the whole crystal grain was determined by
dissolving SAPOs in a low-concentration hydrofluoric acid solution
using the SPS-1200VR analyzer manufactured by Seiko Instruments
Inc.
[0096] Surface composition of the crystal grain, determined by
X-ray photoelectron spectroscopy, changes with thickness of the
amorphous oxide layer, and Si/Al and Si/P atomic ratios increase
with the thickness of the amorphous oxide layer. In the case of
the SAPO-34 for example, the Si/Al and Si/P atomic ratios determined
by X-ray photoelectron spectroscopy are respectively 0.49 and 0.53
when thickness of the amorphous oxide layer is 2.5 nm; the Si/Al
and Si/P atomic ratios are respectively 1.61 and 2.45 when the thickness
is 7 nm; and the Si/Al and Si/P atomic ratios are respectively 1.98
and 2.92 when the thickness is 13 nm.
[0097] The increase in Si/Al and Si/P atomic ratios with the increase
in the thickness of the amorphous oxide layer results from the silicon
component that preferentially deposits onto the crystal grain surface
from the synthesis solution containing silicon, aluminum and phosphorus
components, during the amorphous oxide layer forming process described
later. This is supported by the fact that concentration of silicon
components in the synthesis solution selectively decreases when
the solution is analyzed by ICP during the amorphous oxide layer
forming process.
[0098] In other words, surface composition of the crystal grain
corresponds to thickness of the amorphous oxide layer. An 8-membered
ring SAPO exhibiting excellent reactivity and dimethylamine selectivity
has, on the surface thereof, a Si/Al atomic ratio in a range from
0.50 to 2.20 when no silicon compound is added in the below-described
second step. Similarly, the surface Si/P atomic ratio is in a range
from 0.55 to 3.10. When a silicon compound is added in the second
step, silicon components are present in the synthesis solution at
a fairly higher concentration than the aluminum and phosphorus components.
In this case, an 8-membered ring SAPO exhibiting excellent performance
has, on the surface thereof, Si/Al and Si/P atomic ratios of 0.50
or more and 0.55 or more, respectively.
[0099] The whole 8-membered ring SAPO generally has an ICP-determined
Si/Al atomic ratio in a range from 0.05 to 0.30 although the atomic
ratio varies depending on synthesis conditions.
[0100] As discussed above, the Si/Al atomic ratio of the crystal
grain surface of the 8-membered ring SAPO of the present invention,
which is determined by X-ray photoelectron spectroscopy with Al-K.alpha.
ray (1486.7 eV) as the X-ray source, is higher than the Si/Al atomic
ratio of the whole crystal grain, which is determined by the ICP
analysis, and the former Si/Al atomic ratio is preferably 0.50 or
more, more preferably 0.50 to 2.20. On the other hand, the Si/P
atomic ratio of the crystal grain surface, determined by X-ray photoelectron
spectroscopy, is preferably 0.55 or more, more preferably 0.55 to
3.10. The Si/Al atomic ratio of the whole crystal grain of the 8-membered
ring SAPO of the present invention is preferably in a range from
0.05 to 0.30.
[0101] In the present invention, the amorphous oxide layer is mainly
composed of oxides of silicon, aluminum and phosphorus, but may
contain elements other than silicon, aluminum and phosphorus.
[0102] The amorphous oxide layer is formed after crystallization
of the SAPO crystal grain body is almost completed. In other words,
the SAPO of the present invention with an amorphous oxide layer
on a surface thereof is synthesized by way of two steps, namely,
a first step in which a starting mixture comprising an organic amine
and/or organic ammonium salt together with an aluminum compound,
a phosphorus compound, a silicon compound and water is hydrothermally
treated to produce at least crystalline portions of the SAPO, and
a second step wherein a further hydrothermal treatment is carried
out to form the amorphous oxide layer on a surface of the crystal
grain.
[0103] More specifically, the first step is a step for crystallizing
most of the starting mixture in the very commonly-known production
process of 8-membered ring SAPOs, and the second step is a step
in which the 8-membered ring SAPO thus crystallized in the first
step is further treated hydrothermally in a silicon-containing solution.
[0104] In the present method for producing an 8-membered ring SAPO
as described later, the first step corresponds to the process in
which hydrothermal treatment is carried out at 80 to 130.degree.
C. for 1 hour or more while crystallization does not proceed substantially,
and then further hydrothermal treatment is carried out at 150 to
200.degree. C. for 1 to 10 hours so as to allow crystallization
to notably proceed. On the other hand, the second step corresponds
to the subsequent process in which further hydrothermal treatment
is carried out at 150 to 200.degree. C. after 8-membered ring SAPOs
have been crystallized by the hydrothermal treatment carried out
at 150 to 200.degree. C. for 1 to 10 hours.
[0105] Thickness and surface composition of the amorphous oxide
layer can be controlled by conditions of hydrothermal treatment
in the second step. Thickness of the amorphous oxide layer increases
as time of hydrothermal treatment increases, e.g., 2.5 nm in 5 hours,
7 nm in 50 hours, 13 nm in 100 hours and 25 nm in 175 hours in the
case of the above-described SAPO-34 hydrothermally treated at 170.degree.
C. Rate at which the amorphous oxide layer is formed also depends
on temperature of hydrothermal treatment. By utilizing such characteristics,
e.g., by changing temperature and/or time of hydrothermal treatment,
thickness and surface composition of the amorphous oxide layer can
be controlled. Moreover, thickness or surface composition of the
amorphous oxide layer may be analyzed with lapse of time, so that
the thickness or surface composition is controlled to suit a reaction,
e.g., the reaction of methanol and ammonia for producing methylamines.
[0106] The temperature and time of hydrothermal treatment in the
second step is not limited, because once the 8-membered ring SAPO
crystal grains are formed by hydrothermal treatment in the first
step, formation of the amorphous oxide layer proceeds even at room
temperature, although slowly, by keeping these grains in the synthesis
solution even after the solution is cooled to room temperature.
However, the hydrothermal treatment in the second step is preferably
carried out at 150 to 200.degree. C. for 10 hours or more from practical
viewpoint.
[0107] The rate at which the amorphous oxide layer is formed can
be controlled by concentration of silicon compounds in the synthesis
solution, besides the above-described temperature and time of hydrothermal
treatment. In the present invention, therefore, a silicon compound
may be further added before or during the second step. The addition
of a silicon compound is particularly preferable when the amorphous
oxide layer is formed slowly. The silicon compound that can be used
includes powdered silica, silica sol, orthosilicate or the like,
of which silica sol is particularly preferable. Moreover, a compound
containing another element, e.g., yttrium, titanium, zirconium,
iron or tin, may be used, as required, in addition to a silicon
compound.
[0108] As described in Background Art, crystalline molecular sieves
having a pure silica layer around the SAPO body are well known,
which include, for example, ammonium type mordenite treated with
tetrachlorosilane in gas phase as disclosed in Japanese Patent Laid-open
No. H11-508901A, and mordenite or SAPO silylated with an organic
silicon compound in liquid phase as disclosed in Japanese Patent
Laid-open Nos. H07-2740A and H11-35527A.
[0109] However, the structure of the surface silica layer of these
SAPOs has been little investigated. M. Niwa and Y. Murakami (J.
of Chem. Soc. of Japan, pp. 410 to 419 1989) consider that tetrahedral
structures of silica are regularly arranged on an exposed regular
structure of SAPO so that a structure similar to a crystalline molecular
sieve body is formed (epitaxy growth of silica). More recently,
D. Lu, J. Nomura, K. Domen, H. A. Begum, N. Katada and M. Niwa (Shokubai-shi,
Vol. 44 pp. 483 to 485 2002) have observed a vapor-deposited silica
layer by transmission electron microscopy and have mentioned that
the silica layer is not amorphous but has a regular structure growing
under limitation by an external surface structure of zeolite. These
known silica layers growing by modification with silicon compounds
are considered to be crystalline, and different from the amorphous
oxide layer of the present invention.
[0110] Moreover, in these conventionally-known methods, particularly,
those employing a gas-phase process, the silica layer is produced
by way of a number of steps and complicated precise control, e.g.,
drying of crystalline molecular sieves under restricted conditions,
treatment with tetrachlorosilane under specific conditions and washing
and elimination of chlorine components resulting from the treatment.
Also, the silylation in liquid phase needs fine control techniques
and a number of steps for controlling moisture content of crystalline
molecular sieves and surface-treating crystalline molecular sieves
based on hydrolysis of organic silicon compounds. In contrast, since
the present invention forms the amorphous oxide layer during the
8-membered ring SAPO synthesis process, it needs a much smaller
number of steps than conventional methods, and thus can control
catalyst performance very simply and hence is economical.
[0111] In other words, it has not been known at all that an amorphous
oxide layer is present on a surface of a synthesized 8-membered
ring SAPO grain, existence and thickness of the amorphous oxide
layer have a great effect on catalyst performance, and the thickness
of the amorphous oxide layer can be precisely controlled by conditions
of hydrothermal treatment in the course of formation of the amorphous
oxide layer in the 8-membered ring SAPO synthesis process. The 8-membered
ring SAPO of the present invention, which has the amorphous oxide
layer on a surface thereof, is completely different, both in concept
and essence, from the silica-modified crystalline molecular sieves
such as silica-modified SAPOs that have been silylated in liquid
phase.
[0112] Referring to conditions of hydrothermal treatment according
to the present invention, the hydrothermal treatment as the first
step is carried out by hydrothermally treating a starting mixture
at 80 to 130.degree. C. for 1 hour or more under which no crystallization
of the 8-membered ring SAPO proceeds substantially, and then hydrothermally
treating it at 150 to 200.degree. C. so as to allow the crystallization
to notably proceed, and the hydrothermal treatment as the second
step is subsequently carried out by performing hydrothermal treatment
at 150 to 200.degree. C. This make it possible to stably produce
an 8-membered ring SAPO which is high in purity and degree of crystallinity,
has an amorphous oxide layer of controlled Si/Al molar ratio and
thickness, and is excellent in catalytic activity and dimethylamine
selectivity even when a structure directing agent is used in an
amount lower than conventional processes, for example, in an amount
of less than 1.0 times the mole number of Al.sub.2O.sub.3. In other
words, since the first step comprises a step of hydrothermal treatment
conducted under relatively mild temperature conditions of 80 to
130.degree. C. for 1 hour or more so as to effectively utilize the
structure directing agent, it has been made possible to reduce the
amount of the structure directing agent close to the minimum amount
that will be actually incorporated into the crystal.
[0113] The production method of the present invention is further
featured in that catalyst yield increases as the addition amount
of structure directing agents decreases. Because of the two advantages,
namely, the reduced amount of the structure directing agent and
the increased yield of catalyst, the method of the present invention
increases catalyst production drastically compared with conventional
methods, and thus greatly lowers costs for production of catalyst
and is quite advantageous in terms of industrial production. Therefore,
compared with conventional processes requiring an excessive amount
of structure directing agents, the production method of the present
invention is greatly improved from economical viewpoints since it
reduces not only costs for consumption and disposal of structure
directing agents but also costs for catalyst production thanks to
the increased yield of catalyst.
[0114] The reason why the present method improves the catalyst
yield can be explained as follows. That is, conventional methods
need a large amount of structure directing agent which is alkaline
and invariably increases the pH level of the starting mixture. This
increases solubility of the SAPO components, e.g., silicon, aluminum
and phosphorus compounds, and thus decreases catalyst yield. The
pH level after hydrothermal treatment was 8 or more according to
conventional methods, but is generally 5.5 to 7.5 according to the
present production method.
[0115] The 8-membered ring SAPO is generally synthesized by using
a compound such as tetraethyl ammonium hydroxide, morpholine, cyclohexylamine
and diethylethanolamine as a structure directing agent, mixing the
structure directing agent together with a silicon compound, an aluminum
compound, a phosphorus compound and water uniformly, and subjecting
the mixture to hydrothermal treatment in an autoclave at a temperature
of 150 to 200.degree. C. for several to 200 hours.
aR, bSiO.sub.2 cAl.sub.2O.sub.3 dP.sub.2l O.sub.5 eH.sub.2O
Formula (1)
[0116] The structure directing agent is generally used in an amount
of one to three times the mole number of Al.sub.2O.sub.3 provided
that the starting mixture to be hydrothermally treated is represented
by the above compositional formula (1).
[0117] As described in Background Art, it was considered to be
difficult to synthesize a pure 8-membered ring SAPO using a structure
directing agent in an amount of less than one times the mole number
of Al.sub.2O.sub.3 and no successful synthesis has been known.
In addition to the patent documents cited before, a method for synthesis
of a SAPO for use in production of olefins from methanol is described,
for example, in U.S. Pat. No. 5126308 where the total addition
amount of tetraethyl ammonium hydroxide and di-n-propylamine as
structure directing agents is 1.0 or more times the mole number
of Al.sub.2O.sub.3. U.S. Pat. No. 5663471 describes a SAPO production
method, where the addition amount of tetraethyl ammonium hydroxide
as a structure directing agent is 2.0 times the mole number of Al.sub.2O.sub.3.
[0118] The 8-membered ring SAPO includes molecules of structure
directing agents in its micropores before being calcined. Amount
of the structure directing agent present in the micropores can be
determined by subjecting the SAPO to compositional analysis such
as ICP, gravimetric analysis such as TG or LOI (loss on ignition)
analysis, before the SAPO is calcined. L. Marchese, A. Frache, E.
Gianotti, G. Marta, M. Causa and S. Coluccia (Microporous, and Mesoporous
Materials, 30 1999 pp. 145 to 153) describe synthesis of SAPO-34
in the presence of morpholine as a structure directing agent, and
mention that SAPO-34 includes 1.5 molecules of the structure directing
agent in the cage thereof before being calcined. This corresponds
to a molar ratio of 0.49 to Al.sub.2O.sub.3. It is desirable to
synthesize a pure 8-membered ring SAPO using the structure directing
agent in this molar ratio of 0.49 but no example thereof has been
known.
[0119] If synthesis is carried out as in Comparative Examples 1
to 3 in the below-described Examples section using a structure directing
agent in a reduced amount of less than 1.0 times the mole number
of Al.sub.2O.sub.3 under the conventional hydrothermal conditions
in place of the present hydrothermal treatment carried out at 80
to 130.degree. C. for 1 hour or more, there are produced not only
an 8-membered ring SAPO but also non-8-membered ring ones such as
SAPO-5 having an AFI structure and a structure falling under an
aluminum phosphate of JCPDS card No. 20-0045 specified by International
Centre for Diffraction Data. As a result, the produced 8-membered
ring SAPO is decreased in purity and degree of crystallinity.
[0120] It is not clear why an 8-membered ring SAPO of high purity
and crystallinity can be stably produced using a structure directing
agent in a molar ratio of below 1.0 to Al.sub.2O.sub.3 when the
first step includes a hydrothermal treatment carried out at 80 to
130.degree. C. for 1 hour or more. For example, in case of 8-membered
ring SAPOs of chabazite structure, it may be considered as follows.
[0121] When the hydrothermal treatment is carried out at 80 to
130.degree. C. for 1 hour or more in the first step, there are formed
double-six-ring-structure units constituting the framework of the
8-membered ring SAPO of chabazite structure, and nuclei of the 8-membered
ring SAPO of chabazite structure in the synthesis solution. Thus,
it is considered that crystallization of the 8-membered ring SAPO
of chabazite structure proceeds fast when the subsequent hydrothermal
treatment is carried out at 150 to 200.degree. C.
[0122] In contrast, it is considered that, when the step of carrying
out the hydrothermal treatment at 80 to 130.degree. C. for 1 hour
or more is omitted, the double-six-ring-structure units and the
nuclei of the 8-membered ring SAPO of chabazite structure are formed
insufficiently in the synthesis solution, and thus non-8-membered
ring SAPOs such as a SAPO having the AFI structure is formed, or
crystallization does not proceed completely, even when the solution
is hydrothermally treated at 150 to 200.degree. C. Such a phenomenon
would hardly occur in the presence of a sufficient amount of the
structure directing agent, but will become more noted as the amount
of the structure directing agent is decreased.
[0123] Purity of the 8-membered ring SAPO can be determined by
X-ray diffractometry. For example, purity of an 8-membered ring
SAPO of chabazite structure can be estimated by the ratio of peak
intensity at (100) plane of AFI structure to peak intensity at (100)
plane of chabazite structure, determined by X-ray diffractometry.
The peaks of chabazite structure and AFI structure at the (100)
plane respectively appear at around 9.5.degree. and around 7.4.degree.
in terms of 2.theta. according to the scanning axis 2.theta./.theta.
method with CuK.alpha. ray.
[0124] The 8-membered ring SAPO has an effective micropore diameter
of around 4 .ANG., and thus trimethylamine whose molecular size
is 6.3.times.5.8.times.4.1 .ANG. cannot pass through the micropores
in the synthesis of methylamines by the reaction of methanol and
ammonia. Therefore, the 8-membered ring SAPO has a characteristic
of selectively producing dimethylamine which is useful as a starting
material for solvents, medicines, surfactants and so on. By contrast,
SAPO-5 which is not of 8-membered ring but AFI structure, has an
effective micropore diameter of around 7 .ANG. and can pass the
trimethylamine molecules. For example, in case of the 8-membered
ring SAPO of chabazite structure, when a SAPO whose ratio of peak
intensity at (100) plane of AFI structure to peak intensity at (100)
plane of chabazite structure exceeds 0.02 is used for reaction,
trimethylamine is more produced, thereby decreasing dimethylamine
selectivity. For this reason, the present 8-membered ring SAPO of
chabazite structure preferably has a ratio of peak intensity at
(100) plane of AFI structure to peak intensity at (100) plane of
chabazite structure in a range of 0.02 or less.
[0125] The 8-membered ring SAPO produced by the method of the present
invention has a high purity and degree of crystallinity, and has
an amorphous oxide layer of controlled thickness or surface composition
in the preferable ranges described earlier. As a result, it exhibits
excellent catalytic activity and dimethylamine selectivity in the
production of methylamines by the reaction of methanol and ammonia,
reaction of methanol and monomethylamine, and disproportionation
reaction of monomethylamine.
[0126] In the present invention, the method for controlling temperature
of hydrothermal treatment comprises the first step of carrying out
hydrothermal treatment at 80 to 130.degree. C. for 1 hour or more
followed by hydrothermal treatment at 150 to 200.degree. C. for
1 to 10 hours, and the second step of carrying out hydrothermal
treatment at 150 to 200.degree. C. for 10 hours or more.
[0127] In particular, it is a preferable condition of the temperature
controlling method for hydrothermal treatment that hydrothermal
treatment is carried out at a constant temperature in a range from
95 to 125.degree. C. for 3 to 24 hours during the first step, and
subsequent hydrothermal treatment is carried out at 150 to 200.degree.
C. for 10 to 150 hours as part of crystallization step of the first
step and hydrothermal treatment of the second step since it stably
provides crystalline silicoaluminophosphate molecular sieves which
have 8-oxygen-membered ring micropores of chabazite structure and
are pure and high in crystallinity.
[0128] Catalysts excellent in activity and dimethylamine selectivity
can be stably produced when hydrothermal treatment is carried out
at 80 to 130.degree. C. for 1 hour or more followed by subsequent
hydrothermal treatment at 150 to 200.degree. C. during the first
step. However, if the former hydrothermal treatment is, for example,
carried out at above 130.degree. C. for 1 hour or more, an AFI structure,
which is not of an 8-membered ring SAPO, is notably formed, thereby
decreasing dimethylamine selectivity. On the other hand, if it is
carried out at below 80.degree. C. for 1 hour or more, crystalline
silicoaluminophosphate molecular sieves that have 8-oxygen-membered
ring micropores are, as a whole, decreased in silicon content, thereby
lowering catalytic activity.
[0129] Preferable heating patterns for the hydrothermal treatment
carried out at 80 to 130.degree. C. during the first step by elevating
the temperature include heating from room temperature to 170.degree.
C. at a constant rate in 6 hours; heating from room temperature
to 80.degree. C. in 1 hour and from 80 to 170.degree. C. at a constant
rate in 3 hours; and heating from room temperature to 110.degree.
C. in 2 hours, keeping the temperature at 110.degree. C. for 5 hours,
and then heating up to 170.degree. C.
[0130] On the other hand, it is not preferable to heat from 80
to 130.degree. C. at a rate of 70.degree.2 C./hour or more, because
the AFI structure is notably produced. Also, it is not preferable
to heat to 80.degree. C. at a rate of 100.degree. C./hour or more,
because the starting mixture is often solidified. Meanwhile, there
is no limitation to the condition of heating carried out between
the hydrothermal treatment at 80 to 130.degree. C. and the hydrothermal
treatment at 150 to 200.degree. C. in the first step.
[0131] Preferable time for the hydrothermal treatment at 150 to
200.degree. C. during the second step varies depending upon hydrothermal
treatment temperature and silicon content of the starting mixture,
but is acceptable when it is 10 hours or more for which formation
of the amorphous oxide layer sufficiently proceeds. It is preferably
10 to 150 hours for which the amorphous oxide layer of adequate
thickness or surface composition can be stably formed on the crystal
grain surface, and is more preferably 20 to 120 hours because an
8-membered ring SAPO having an amorphous oxide layer of thickness
or surface composition sufficient for excellent catalytic activity
and dimethylamine selectivity can be stably produced.
[0132] The hydrothermal treatment is carried out preferably with
stirring rather than being allowed to stand, and more preferably,
in such a manner that the mixture to be hydrothermally treated is
sufficiently mixed uniformly.
[0133] The silicon compound useful as a starting material for production
of the 8-membered ring SAPO of the present invention includes powdered
silica, silica sol, orthosilicate, tetraethoxysilane and the like,
of which silica sol is particularly preferable. Amount of the silica
compound to be used is not limited, but preferably it is used in
a SiO.sub.2/Al.sub.2O.sub.3 molar ratio of 0.1 to 0.6 assuming
that the starting mixture is represented by the ratio of oxides.
The aluminum compound useful as the starting material includes pseudoboehmite,
boehmite, gibbsite, bayerite, aluminum oxide such as .gamma.-alumina,
aluminum hydroxide, hydrated aluminum oxide, aluminum alkoxide such
as aluminum triisopropoxide, and the like, of which pseudoboehmite
is particularly preferable in consideration of material cost, availability
and reactivity. On the other hand, aluminates, e.g., sodium aluminate,
are not desirable because they normally need not only a usually-required
calcination step but also ion exchange of cation, e.g., sodium ion,
thereby requiring troublesome post-treatment.
[0134] The particularly preferable phosphorus compound useful as
the starting material is orthophosphoric acid, although not limited
thereto. Amount of phosphoric acid to be used is not limited, but
preferably it is incorporated in a P.sub.2O.sub.5/Al.sub.2O.sub.3
molar ratio of 0.7 to 1.1 assuming that the starting mixture is
represented by the ratio of oxides. Aluminum phosphate may be used
in replace of the aluminum compound and the phosphorus compound,
or in combination with the aluminum compound or the phosphorus compound.
Amount of water to be used is not limited, so long as it gives a
slurry having a concentration that allows it to be stirred uniformly.
However, it is preferably used in a water/Al.sub.2O.sub.3 molar
ratio of 100 or less in consideration of industrial productivity.
[0135] The organic amine and organic ammonium salt used as the
structure directing agent include primary, secondary and tertiary
amines, quaternary ammonium salts, aminoalcohols and diamines. The
organic amine and organic ammonium salt with which an 8-membered
ring SAPO is easily synthesized include tetraethyl ammonium hydroxide,
triethylmethyl ammonium hydroxide, diethanolamine, diethylethanolamine,
morpholine, methylbutylamine, diisopropylamine, di-n-propylamine,
quinuclidine, cyclohexylamine, and N,N,N',N'-tetramethyl-16-hexanediamine.
These organic amines and organic ammonium salts may be used either
singly or as a mixture of two or more of them. An alkyl ammonium
hydroxide may contain a chloride or bromide originating from its
raw material. These impurities, however, are not considered to cause
serious problems. Of these structure directing agents, tetraethyl
ammonium hydroxide is more preferable for production of an 8-membered
ring SAPO of chabazite structure, considering its average grain
diameter and shape.
[0136] Amount of the organic amine and/or organic ammonium salt
to be used for synthesizing an 8-membered ring SAPO is not limited.
However, an 8-membered ring SAPO of high purity and crystallinity
can be produced even when a ratio of the total mole number of the
organic amine and organic ammonium salt to the mole number of the
aluminum compound as Al.sub.2O.sub.3 is within a range of 0.4 to
0.98 and hence this range of ratio is preferable. For synthesis
of an 8-membered ring SAPO of chabazite structure, the ratio of
the total mole number of the organic amine and organic ammonium
salt to the mole number of the aluminum compound as Al.sub.2O.sub.3
is preferably 0.4 to 0.98 since SAPOs of high purity and crystallinity
can be produced. Even when the molar ratio of the total of the organic
amine and organic ammonium salt to Al.sub.2O.sub.3 exceeds 0.98
an 8-membered ring SAPO of chabazite structure can be produced,
but undesirably shaped grains, namely, plate grains are produced,
or the use of excessive amines or ammonium salts causes increase
in cost of raw materials or decrease in catalyst yield. Also, these
surplus amines and ammonium salts are discharged as a waste liquid
in separation/washing step after the hydrothermal treatment, and
are not desirable considering additional cost for disposal and environmental
load. When the molar ratio of the total of the organic amine and
organic ammonium salt is below 0.40 a structure falling under an
aluminum phosphate of JCPDS card No. 20-0045 is formed, thereby
decreasing catalytic activity and dimethylamine selectivity.
[0137] In general, the 8-membered ring SAPO has a shape of cube,
rectangular parallelepiped, plate, rod, needle, sphere or a combination
thereof. Of these shapes, preferable ones for the present 8-membered
ring SAPO of chabazite structure are cube and rectangular parallelepiped
having an average crystal grain diameter of 5 .mu.m or less, particularly
preferably cube and rectangular parallelepiped having an average
crystal grain diameter of 1 to 4 .mu.m. On the other hand, the plate
shape having an average crystal grain diameter of 1 .mu.m or less,
and aggregates of plate-shaped grains are not desirable, because
the 8-membered ring SAPO of chabazite structure having an average
crystal grain diameter of 5 .mu.m or less and cubic or rectangular
parallelepiped shape exhibits excellent catalytic activity, dimethylamine
selectivity and catalyst life in production of methylamines by the
reaction of methanol and ammonia. The average grain diameter can
be easily determined by laser-aided diffraction type particle size
distribution analyzer, and grain shape can be determined by scanning
electron microscopy.
[0138] The 8-membered ring SAPO synthesized under hydrothermal
treatment conditions is subjected to filtration, decantation or
centrifugal separation, and washing. Then, it is dried at 80 to
150.degree. C., and calcined. The calcination is normally carried
out in a flow of air or air/nitrogen mixture at 400 to 1000.degree.
C., particularly preferably 500 to 900.degree. C.
[0139] The 8-membered ring SAPO of the present invention is used
as a catalyst for reaction of methanol and ammonia, reaction of
methanol and monomethylamine, or disproportionation reaction of
monomethylamine, as it is or after it is molded by compression,
tableting or extrusion molding. It is also applicable to other catalytic
reactions, e.g., for production of lower olefins from methanol (MTO
reaction).
[0140] When the 8-membered ring SAPO of the present invention is
used as a catalyst to produce methylamines by the reaction of methanol
and ammonia, the reaction of methanol and monomethylamine, or the
disproportionation reaction of monomethylamine, these reactions
may be carried out in a fixed or fluidized bed. Reaction temperature
is preferably in a range from 200 to 400.degree. C., particularly
preferably 250 to 350.degree. C. Reaction pressure is not limited,
but normally preferably in a range from 0.1 to 10 MPa.
[0141] Hereinafter, the present invention is described by way of
Examples and Comparative Examples which by no means limit the present
invention. The drawings are explained below.
BRIEF DESCRIPTION OF DRAWINGS
[0142] FIG. 1 shows a scanning transmission electron microscopic
image (magnification: 80000) of the catalyst prepared in Example
14;
[0143] FIG. 2 shows a magnified image (magnification: 1000000)
of the portion enclosed by the white frame appearing on the left
side of FIG. 1;
[0144] FIG. 3 shows an electron beam diffraction image of the portion
with check pattern of FIG. 2; and
[0145] FIG. 4 shows an electron beam diffraction image of the white
layer free of check pattern of FIG. 2.
EXAMPLES
[0146] Methods for measurement of physical and chemical properties,
and synthesis procedures for methylamines, employed in the Examples,
are described below. (1) Catalyst yield was expressed in weight
percent by converting the weight each of silica, aluminum, phosphorus,
titanium and zirconium compounds in the starting material charged
in the autoclave into respective weights of SiO.sub.2 Al.sub.2O.sub.3
P.sub.2O.sub.5 TiO.sub.2 and ZrO.sub.2 dividing the weight of
the synthesized and calcined solid product by the total of the above
converted weights, and then multiplying the quotient by 100. The
weight of the synthesized solid product was measured as it was sufficiently
dried (calcined powder) by drying at 110.degree. C. for 8 hours
after calcination.
[0147] (2) Purity of the 8-membered ring SAPO of chabazite structure
in the synthesized solid product was determined by subjecting the
calcined powder to X-ray diffractometry, and expressed as abundance
ratio of AFI structure. The abundance ratio of AFI structure was
obtained by dividing X-ray diffraction peak intensity at (100) plane
of AFI structure by X-ray diffraction peak intensity at (100) plane
of chabazite structure.
[0148] (3) Degree of crystallization was determined by subjecting
calcined powders to X-ray diffractometry, and obtaining a ratio
of peak intensity at (100) plane of chabazite structure of each
of the calcined powders to peak intensity at (100) plane of the
chabazite structure that was synthesized in Comparative Example
8 following the procedure described in the Catalyst Preparation
Example 1 of Japanese Patent Laid-Open No. 2000-117114A.
[0149] (4) Shape of grain was determined by scanning transmission
electron microscopic analysis (FE-SEM analysis).
[0150] (5) Average grain diameter was determined by a laser diffraction
particle size analyzer.
[0151] (6) X-ray photoelectron spectroscopic analysis was carried
out for calcined powders, so that surface composition was obtained
based on the narrow spectral peak areas of the Si(2p), Al(2p) and
P(2p) bands, corrected by Scofield correction factors.
[0152] (7) Reaction tests were carried out using catalysts prepared
from the calcined powder which was tableted or compressed and granulated
into the grains of 1 to 2 mm in size, in a flow type reactor system
equipped with a feed tank, feed supply pump, inert gas charging
unit, reactor tube (inner diameter: 13 mm, length: 300 mm, SUS 316),
cooler, sampling tank, back pressure valve, and so on.
[0153] (8) Composition of reaction products was analyzed by gas
chromatography for a sample collected for 30 minutes.
[0154] 1. Synthesis of 8-Membered Ring SAPO (Relationship with
Amount of Structure Directing Agent and Conditions of Hydrothermal
Treatment)
[0155] Examples 1 to 9 and Comparative Examples 1 to 9 show synthesis
examples of 8-membered ring SAPOs, in which the amount of tetraethyl
ammonium hydroxide as a structure directing agent and the heating
condition of hydrothermal treatment were varied. Table 1 summarizes
catalyst yield, abundance ratio of AFI structure, degree of crystallization,
and grain shape and size observed in the Examples and the Comparative
Examples. Table 2 summarizes the reaction test results. The reaction
test was carried out using a reactor tube charged with 2.5 g (3.5
mL) of granulated catalysts, feeding thereto a methanol/ammonia
mixture (1:1 by weight) at a rate of 8.62 g/hour and a space velocity
(GHSV) of 2500 hour.sup.-1 and conducting reaction at a temperature
of 305.degree. C. and a pressure of 2 MPa.
Example 1
[0156] A uniform mixture of 85% by weight phosphoric acid (46.12
g) and pure water (191.16 g) was cooled to 30.degree. C. or lower,
to which pseudoboehmite (26.32 g: PURAL SB from SASOL GERMANY GmbH,
Al.sub.2O.sub.3 content: 77.5%) was added with stirring. The resulting
mixture was stirred for 30 minutes, and then 35% by weight aqueous
solution of tetraethyl ammonium hydroxide (79.94 g) was added thereto
while it was cooled to 30.degree. C. or lower under stirring. The
resulting mixture was stirred for 1 hour, and then silica sol (18.04
g: SNOWTEX N from Nissan Chemical Industries Ltd., SiO.sub.2 content:
20% by weight) was added thereto, and further stirred for 30 minutes.
The resulting mixture had a composition in terms of oxide molar
ratio as follows: 0.95 TEAOH:1.0 Al.sub.2O.sub.3:1.0 P.sub.2O.sub.5:0.3
SiO.sub.2:75 H.sub.2O (TEAOH: tetraethyl ammonium hydroxide). The
resulting mixture was hydrothermally treated with stirring at 400
rpm in a stainless steel autoclave of 0.6 L in inner volume. In
the hydrothermal treatment, temperature as of the contents was elevated
at 25.degree. C./hour from 25 to 170.degree. C. in the first step,
and kept at 170.degree. C. for 35 hours in part of crystallization
step of the first step and in the second step, where hydrothermal
treatment pressure was self-generated. The autoclave was cooled
to room temperature and opened. The product slurry was centrifugally
separated to obtain the precipitate, which was washed and centrifugally
separated using 200 mL of pure water 3 times, and then dried at
80.degree. C. for 12 hours. It was then calcined under air flow
at 600.degree. C. for 4 hours, to obtain white powder (40.35 g).
Catalyst yield was 77%. The product powder was a pure 8-membered
ring SAPO of chabazite structure, as confirmed by X-ray diffractometry,
which detected no peak for AFI structure or the compound of JCPDS
card No. 20-0045. It had a high degree of crystallization of 1.00
and was composed of crystal grains which were cubic and highly uniform
both in size and shape. It had an average grain diameter of 1.8
.mu.m. It exhibited reaction performance 6 hours after the beginning
of feed of raw materials as follows: 92 wt % in methanol conversion,
39 wt % in monomethylamine selectivity, 54 wt % in dimethylamine
selectivity and 7 wt % in trimethylamine selectivity, as shown in
Table 2.
Example 2
[0157] A white calcined powder (40.50 g) was prepared in the same
manner as in Example 1 except that temperature as of the contents
under hydrothermal treatment was elevated at 73.degree. C./hour
from 25 to 115.degree. C., kept at 115.degree. C. for 5 hours, and
then elevated at 73.degree. C./hour from 115 to 170.degree. C. in
the first step, and then kept at 170.degree. C. for 35 hours in
part of crystallization step of the first step and in the second
step. Table 1 shows catalyst yield, abundance ratio of AFI structure,
degree of crystallization, grain shape and average grain diameter.
Table 2 shows reaction performance 6 hours after the beginning of
feed of raw materials.
Example 3
[0158] A white calcined powder (46.15 g) was prepared in the same
manner as in Example 2 except that the addition amount of 35% by
weight aqueous solution of tetraethyl ammonium hydroxide was changed
to 63.14 g, and the addition amount of pure water was changed to
202.07 g. The hydrothermally treated mixture had a composition in
terms of oxide molar ratio as follows: 0.75 TEAOH:1.0 Al.sub.2O.sub.3:1.0
P.sub.2O.sub.5:0.3 SiO.sub.2:75 H.sub.2O. Table 1 shows catalyst
yield, abundance ratio of AFI structure, degree of crystallization,
grain shape and average grain diameter. Table 2 shows reaction performance
6 hours after the beginning of feed of raw materials.
Example 4
[0159] A white calcined powder (46.05 g) was prepared in the same
manner as in Example 3 except that temperature as of the contents
under hydrothermal treatment was elevated at 73.degree. C./hour
from 25 to 80.degree. C., at 50.degree. C./hour from 80 to 130.degree.
C. and at 70.degree. C./hour from 130 to 170.degree. C. in the first
step, and kept at 170.degree. C. for 35 hours in part of crystallization
step of the first step and in the second step. Table 1 shows catalyst
yield, abundance ratio of AFI structure, degree of crystallization,
grain shape and average grain diameter. Table 2 shows reaction performance
6 hours after the beginning of feed of raw materials.
Example 5
[0160] A white calcined powder (45.94 g, catalyst yield: 88%) was
prepared in the same manner as in Example 2 except that the addition
amount of 35% by weight aqueous solution of tetraethyl ammonium
hydroxide was changed to 42.10 g, and the addition amount of pure
water was changed to 215.74 g. The hydrothermally treated mixture
had a composition in terms of oxide molar ratio as follows: 0.50
TEAOH:1.0 Al.sub.2O.sub.3:1.0 P.sub.2O.sub.5:0.3 SiO.sub.2:75 H.sub.2O.
The resulting calcined powder was subjected to X-ray diffractometry
which detected a small peak of the compound of JCPDS card No. 20-0045
in addition to the peak of chabazite structure, but no peak of AFI
structure observed in the catalyst prepared in Comparative Example
3 at the same TEAOH/Al.sub.2O.sub.3 molar ratio. The powder had
a degree of crystallization of 0.65 which was higher than Comparative
Example 3. Shape of crystal grains was cubic, and average grain
diameter was 1.1 .mu.m. This example indicates that an 8-membered
ring SAPO of chabazite structure having higher purity and degree
of crystallization can be obtained even at the same TEAOH/Al.sub.2O.sub.3
molar ratio of 0.50 as Comparative Example 3 by keeping the temperature
at 115.degree. C. for 5 hours when hydrothermal treatment is carried
out in the first step.
Example 6
[0161] A uniform starting mixture of 85% by weight phosphoric acid
(46.12 g), pure water (108.99 g) and 35% by weight aqueous solution
of tetraethyl ammonium hydroxide (63.14 g) was cooled to 30.degree.
C. or lower, to which pseudoboehmite (26.32 g: PURAL NF from SASOL
GERMANY GmbH, Al.sub.2O.sub.3 content: 77.5%) was added with stirring.
The resulting mixture was stirred for 1 hour, and then silica sol
(18.04 g: SNOWTEX N from Nissan Chemical Industries Ltd., SiO.sub.2
content: 20% by weight) and titania sol (4.04 g: STS-01 from Ishihara
Sangyo Kaisha, Ltd., TiO.sub.2 content: 29.5% by weight) were added
thereto, and further stirred for 30 minutes. The resulting mixture
had a composition in terms of oxide molar ratio as follows: 0.75
TEAOH:1.0 Al.sub.2O.sub.3:1.0 P.sub.2O.sub.5:0.3 SiO.sub.2:0.075
TiO.sub.2:50 H.sub.2O. The resultant starting mixture was hydrothermally
treated with stirring at 500 rpm in a stainless steel autoclave
of 0.6 L in inner volume. In the hydrothermal treatment, temperature
as of the contents was elevated at 65.degree. C./hour from 25 to
110.degree. C., kept at 110.degree. C. for 5 hours, and then elevated
at 65.degree. C./hour from 110 to 160.degree. C. in the first step,
and kept at 160.degree. C. for 35 hours in part of crystallization
step of the first step and in the second step, where hydrothermal
treatment pressure was self-generated. The autoclave was cooled
to room temperature and opened. The product slurry was centrifugally
separated to obtain the precipitate, which was washed and centrifugally
separated using 200 mL of pure water 3 times, and then dried at
80.degree. C. for 12 hours. It was then calcined under air flow
at 800.degree. C. for 4 hours, to obtain white powder (48.30 g).
Catalyst yield was 90%. The product powder was a pure 8-membered
ring SAPO of chabazite structure, as confirmed by X-ray diffractometry,
which detected no peak of AFI structure or the compound of JCPDS
card No. 20-0045. It had a high degree of crystallization of 1.10
and was composed of crystal grains which were cubic and highly uniform
both in size and shape. It had an average grain diameter of 1.7
.mu.m.
[0162] It exhibited reaction performance 6 hours after the beginning
of feed of raw materials as follows: 94 wt % in methanol conversion:
37 wt % in monomethylamine selectivity, 60 wt % in dimethylamine
selectivity and 3 wt % in trimethylamine selectivity, as shown in
Table 2.
Example 7
[0163] A white calcined powder (47.81 g) was prepared in the same
manner as in Example 6 except that temperature as of the contents
under hydrothermal treatment was elevated at 65.degree. C./hour
from 25 to 125.degree. C., kept at 125.degree. C. for 24 hours,
and then elevated at 65.degree. C./hour from 125 to 170.degree.
C. in the first step, and kept at 170.degree. C. for 35 hours in
part of crystallization step of the first step and in the second
step. Table 1 shows catalyst yield, abundance ratio of AFI structure,
degree of crystallization, grain shape and average grain diameter.
Table 2 shows reaction performance 6 hours after the beginning of
feed of raw materials.
Example 8
[0164] A white calcined powder (47.09 g) was prepared in the same
manner as in Example 6 except that temperature as of the contents
under hydrothermal treatment was elevated at 65.degree. C./hour
from 25 to 90.degree. C., kept at 90.degree. C. for 5 hours and
then elevated at 65.degree. C./hour from 90 to 165.degree. C. in
the first step, and kept at 165.degree. C. for 12 hours in part
of crystallization step of the first step and in the second step.
Table 1 shows catalyst yield, abundance ratio of AFI structure,
degree of crystallization, grain shape and average grain diameter.
Table 2 shows reaction performance 6 hours after the beginning of
feed of raw materials.
Example 9
[0165] A white calcined powder (50.43 g, catalyst yield: 92%) was
prepared in the same manner as in Example 6 except that the addition
amount of 35% by weight aqueous solution of tetraethyl ammonium
hydroxide was changed to 42.09 g, the addition amount of pure water
was changed to 118.0 g, and the addition amount of silica sol was
changed to 24.05 g, and temperature as of the content under hydrothermal
treatment was elevated at 20.degree. C./hour from 25 to 115.degree.
C., kept at 115.degree. C. for 5 hours and then elevated at 20.degree.
C./hour from 115 to 170.degree. C. in the first step, and kept at
170.degree. C. for 50 hours in part of crystallization step of the
first step and in the second step. The hydrothermally treated mixture
had a composition in terms of oxide molar ratio as follows: 0.50
TEAOH:1.0 Al.sub.2O.sub.3:1.0 P.sub.2O.sub.5:0.4 SiO.sub.2:0.075
TiO.sub.2:50 H.sub.2O. Table 1 shows catalyst yield, abundance ratio
of AFI structure, degree of crystallization, grain shape and average
grain diameter. Table 2 shows reaction performance 6 hours after
the beginning of feed of raw materials.
Comparative Example 1
[0166] A white calcined powder (40.32 g) was prepared in the same
manner as in Example 1 except that temperature as of the contents
under hydrothermal treatment was elevated at 79.degree. C./hour
from 25 to 170.degree. C. in the first step, and kept at 170.degree.
C. for 42 hours in part of crystallization step of the first step
and in the second step. The product powder was subjected to X-ray
diffractometry which detected the peak of AFI structure which is
not of an 8-memberded ring SAPO, in addition to the peak of chabazite
structure which is of an 8-membered ring SAPO. It had an abundance
ratio of AFI structure of 0.03. No peak for the compound of JCPDS
card No. 20-0045 was detected. However, it had a low degree of crystallization
of 0.89. Shape of crystal grains was cubic, but there were found
some hexagonal columnar crystals which are considered to be of AFI
structure. They had an average grain diameter of 1.8 .mu.m. Table
2 shows reaction performance 6 hours after the beginning of feed
of raw materials.
Comparative Example 2
[0167] A white calcined powder (43.30 g) was prepared in the same
manner as in Example 3 except that temperature as of the contents
under hydrothermal treatment was elevated at 78.degree. C./hour
from 25 to 170.degree. C. in the first step, and kept at 170.degree.
C. for 35 hours in part of crystallization step of the first step
and in the second step. The product powder was subjected to X-ray
diffractometry, which detected the peak of AFI structure which is
not of an 8-membered ring SAPO, and the peak of the compound of
JCPDS card No. 20-0045 in addition to the peak of chabazite structure
which is of an 8-membered ring SAPO. It had an abundance ratio of
AFI structure of 0.03 and a low degree of crystallization of 0.79.
Shape of crystal grains was rectangular parallelepiped, but there
were found some hexagonal columnar crystals which are considered
to be of AFI structure and some amorphous grains which are considered
to be of an amorphous compound. They had an average grain diameter
of 1.5 .mu.m. Table 2 shows reaction performance 6 hours after the
beginning of feed of raw materials.
Comparative Example 3
[0168] A white calcined powder (43.40 g) was prepared in the same
manner as in Example 5 except that temperature as of the contents
under hydrothermal treatment was elevated at 78.degree. C./hour
from 25 to 170.degree. C. in the first step, and kept at 170.degree.
C. for 35 hours in part of crystallization step of the first step
and in the second step. The product powder was subjected to X-ray
diffractometry, which detected the peak of AFI structure which is
not of an 8-membered ring SAPO, and the peak of the compound of
JCPDS card No. 20-0045 in addition to the peak of chabazite structure
which is of an 8-membered ring SAPO. It had an abundance ratio of
AFI structure of 0.10 and a low degree of crystallization of 0.32.
Comparative Example 4
[0169] A white calcined powder (45.51 g) was prepared in the same
manner as in Example 2 except that the addition amount of 35% by
weight aqueous solution of tetraethyl ammonium hydroxide was changed
to 21.05 g, and the addition amount of pure water was changed to
229.43 g. The hydrothermally treated mixture had a composition in
terms of oxide molar ratio as follows: 0.25 TEAOH:1.0 Al.sub.2O.sub.3:1.0
P.sub.2O.sub.5:0.3 SiO.sub.2:75 H.sub.2O. The product calcined powder
was subjected to X-ray diffractometry, which confirmed it to be
the compound of JCPDS card No. 20-0045 and detected no peak of
chabazite or AFI structure.
Comparative Example 5
[0170] A white calcined powder (47.65 g) was prepared in the same
manner as in Example 6 except that temperature as of the contents
under hydrothermal treatment was elevated at 65.degree. C./hour
from 25 to 135.degree. C., kept at 135.degree. C. for 5 hours and
then elevated at 65.degree. C./hour from 135 to 170.degree. C. in
the first step, and kept at 170.degree. C. for 35 hours in part
of crystallization step of the first step and in the second step.
The product powder was subjected to X-ray diffractometry, which
detected the peak of AFI structure, in addition to the peak of chabazite
structure, but no peak of the compound of JCPDS card No. 20-0045.
It had an abundance ratio of AFI structure of 0.04 and a degree
of crystallization of 0.98. Shape of crystal grains was cubic, and
there were also found some needle-shaped crystals which are considered
to be of AFI structure. They had an average grain diameter of 1.9
.mu.m. Table 2 shows reaction performance 6 hours after the beginning
of feed of raw materials.
Comparative Example 6
[0171] A white calcined powder (45.65 g) was prepared in the same
manner as in Example 6 except that temperature as of the contents
under hydrothermal treatment was elevated at 65.degree. C./hour
from 25 to 70.degree. C., kept at 70.degree. C. for 5 hours and
then elevated at 65.degree. C./hour from 70 to 170.degree. C. in
the first step, and kept at 170.degree. C. for 35 hours in part
of crystallization step of the first step and in the second step.
The product powder was subjected to X-ray diffractometry, which
detected the peak of AFI structure, in addition to the peak of chabazite
structure which is of an 8-membered ring SAPO, but no peak of the
compound of JCPDS card No. 20-0045. It had an abundance ratio of
AFI structure of 0.03 and a degree of crystallization of 0.90. Shape
of crystal grains was thick plate. They had an average grain diameter
of 1.5 .mu.m. Table 2 shows reaction performance 6 hours after the
beginning of feed of raw materials.
Comparative Example 7
[0172] A white calcined powder (36.40 g, catalyst yield: 66%) was
prepared in the same manner as in Example 9 except that the addition
amount of 35% by weight aqueous solution of tetraethyl ammonium
hydroxide was changed to 105.23 g, and the addition amount of pure
water was changed to 76.93 g, and the hydrothermal treatment was
carried out while stirring was made at 200 rpm. The hydrothermally
treated mixture had a composition in terms of oxide molar ratio
as follows: 1.25 TEAOH:1.0 Al.sub.2O.sub.3:1.0 P.sub.2O.sub.5:0.4
SiO.sub.2:0.075 TiO.sub.2:50 H.sub.2O. The product calcined powder
was subjected to X-ray diffractometry, which confirmed it to be
of pure chabazite structure, but detected no peak of AFI structure
or the compound of JCPDS card No. 20-0045. It had a low degree of
crystallization of 0.65. Shape of crystal grains was thin plate.
They had an average grain diameter of 0.6 .mu.m. Table 2 shows reaction
performance 6 hours after the beginning of feed of raw materials.
Comparative Example 8
[0173] Zirconia-modified SAPO-34 was prepared in the same manner
as in the Catalyst Preparation Example 1 described in Japanese Patent
Laid-Open No. 2000-117114A. A uniform mixture of 35% by weight aqueous
solution of tetraethyl ammonium hydroxide (151.41 g) and pure water
(84.60 g) was cooled to 5.degree. C., to which aluminum isopropoxide
(81.80 g: from Nacalai Tesque, Inc.) was added, and the mixture
was stirred at a high speed for 15 minutes. Then, silica sol (18.04
g) and powdered zirconium oxide (2.40 g: RC-100 from Daiichi Kigenso
Kagaku Kogyo Co., Ltd.) were added thereto, and the mixture was
stirred at a high speed for 15 minutes until it became uniform.
The resulting mixture was then supplemented with 85% by weight phosphoric
acid (46.20 g), stirred in a similar manner for 5 minutes, and then
ground for 1 hour. The resulting mixture had a composition in terms
of oxide molar ratio as follows: 1.80 TEAOH:1.0 Al.sub.2O.sub.3:1.0
P.sub.2O.sub.5:0.3 SiO.sub.2:0.097 ZrO.sub.2:57 H.sub.2O. The resulting
mixture was hydrothermally treated with stirring at 200 rpm in a
stainless steel autoclave of 0.6 L in inner volume. In the hydrothermal
treatment, temperature as of the contents was elevated at 75.degree.
C./hour from 25 to 200.degree. C., and kept at 200.degree. C. for
4 hours, where hydrothermal treatment pressure was self-generated.
The autoclave was cooled to room temperature and opened. The product
slurry was centrifugally separated to obtain the precipitate, which
was washed and centrifugally separated using 200 mL of pure water
4 times, and then dried at 80.degree. C. for 12 hours. It was then
calcined under air flow at 600.degree. C. for 4 hours, to obtain
white powder (34.21 g). Catalyst yield was 62%. The product powder
was subjected to X-ray diffractometry, which confirmed it to be
of pure chabazite structure, and detected no peak of AFI structure
or the compound of JCPDS card No. 20-0045. Shape of crystal grains
was cubic, and they were uniform both in size and shape. They had
an average grain diameter of 1.4 .mu.m. It exhibited reaction performance
6 hours after the beginning of feed of raw materials as follows:
90 wt % in methanol conversion, 41 wt% in monomethylamine selectivity,
54 wt % in dimethylamine selectivity, and 5 wt % in trimethylamine
selectivity, as shown in Table 2.
Comparative Example 9
[0174] A zirconia-modified SAPO-34 was prepared in the same manner
as in Comparative Example 8 to yield white calcined powder (32.55
g, catalyst yield: 59%). This powder was subjected to X-ray diffractometry,
which confirmed it to be of pure chabazite structure, and detected
no peak of AFI structure or the compound of JCPDS card No. 20-0045.
Shape of crystal grains was cubic, and they were highly uniform
both in size and shape. They had an average grain diameter of 1.6
.mu.m. Table 2 shows reaction performance 6 hours after the beginning
of feed of raw materials.
1TABLE 1 Heating rate in Temperature and Temperature and TEAOH/
H.sub.2O/ hydro- time for which time for which Cata- Abundance Al.sub.2O.sub.3
Al.sub.2O.sub.3 thermal the temperature the temperature lyst ratio
Degree of Grain molar molar treatment is kept during is kept during
yield of AFI crystalli- diameter Examples ratio ratio (.degree.
C./h) the first step the second step*1) (%) structure zation Grain
shape (.mu.m) Ex. 1 0.95 75 25 -- 170.degree. C., 35 h 77 0 1.00
Cubic 1.8 Ex. 2 0.95 75 73 115.degree. C., 5 h 170.degree. C., 35
h 77 0 1.00 Cubic 1.7 Ex. 3 0.75 75 73 115.degree. C., 5 h 170.degree.
C., 35 h 88 0 1.15 Rectangular 1.7 parallelepiped Ex. 4 0.75 75
73 *2 170.degree. C., 35 h 88 0 1.04 Cubic 1.5 Ex. 5 0.50 75 73
115.degree. C., 5 h 170.degree. C., 35 h 88 0 0.65 Cubic 1.1 Ex.
6 0.75 50 65 110.degree. C., 5 h 160.degree. C., 35 h 90 0 1.10
Cubic 1.7 Ex. 7 0.75 50 65 125.degree. C., 24 h 170.degree. C.,
35 h 89 0 1.09 Cubic 1.7 Ex. 8 0.75 50 65 90.degree. C., 5 h 165.degree.
C., 12 h 88 0 1.04 Rectangular 1.6 parallelepiped Ex. 9 0.50 50
20 115.degree. C., 5 h 170.degree. C., 50 h 92 0 1.05 Cubic 1.8
C. Ex. 1 0.95 75 79 -- 170.degree. C., 42 h 77 0.03 0.89 Cubic 1.8
C. Ex. 2 0.75 75 78 -- 170.degree. C., 35 h 83 0.03 0 |