Molecular sieve abstract
The present invention relates to a titanium-silicalite (TS-1) molecular
sieve and the method for preparation of the same, wherein each crystallite
of said titanium-silicalite molecular sieve has a hollow cavity
with a radial length of 5-300 nm. The benzene adsorption capacity
of the molecular sieve determined at 25.degree. C. and P/P.sub.0
=0.10 for 1 hour is at least 70 mg/g; and the method for preparation
of said molecular sieve comprises an acid-treatment and then an
organic-base treatment of the synthesized TS-1 molecular sieve,
or only an organic-base treatment. The TS-1 molecular sieve of the
present invention has a relatively high reactivity and activity
stability in the catalytic oxidation.
Molecular sieve claims
What is claimed is:
1. A titanium-silicalite molecular sieve with MFI structure, characterized
in that each crystallite of said molecular sieve has a hollow cavity.
2. A titanium-silicalite molecular sieve according to claim 1
wherein the radial length of said cavity in the hollow crystallite
is 5-300 nm.
3. A titanium-silicalite molecular sieve according to claim 1
wherein the benzene adsorption capacity of said molecular sieve
determined at 25.degree. C. and P/P.sub.0 =0.10 for 1 hour is at
least 70 mg/g.
4. A molecular sieve according to claim 1 wherein the grains of
said molecular sieve are composed of individual hollow crystallites
or aggregated crystallites resulting from aggregation of the hollow
crystallites.
5. A method for preparation of said molecular sieve claimed in
any one of claims 1-4 comprising mixing the synthesized MFI-type
titanium-silicalite molecular sieve with an aqueous organic base
solution homogenously, then subjecting the resultant mixture to
a base-treatment in an autoclave at 120-200.degree. C. under autogenous
pressure for 1-192 hours, and recovering the resultant product.
6. A method according to claim 5 wherein said organic base is
selected from a group consisting of aliphatic amines, alkylol amines,
quaternary ammonium bases or mixtures thereof.
7. A method according to claim 6 wherein said aliphatic amines
have a general formula of R.sup.2 (NH.sub.2).sub.n, wherein R.sup.2
represents a C.sub.1-6 -alkyl, and n is 1 or 2.
8. A method according to claim 7 wherein said aliphatic amine
is selected from the group consisting of ethylamine, n-butyl amine,
butanediamine and hexane diamine.
9. A method according to claim 6 wherein said alkylol amines have
a general formula of (HOR.sup.3).sub.m N, wherein R.sup.3 represents
a C.sub.1-4 -alkyl, and m is from 1 to 3.
10. A method according to claim 9 wherein said alkylol amine is
selected from monoethanolamine, diethanolamine or triethanolamine.
11. A method according to claim 6 wherein said quaternaryammonium
bases have a general formula of R.sup.4.sub.4 NOH, wherein R.sup.4
represents a C.sub.1-4 -alkyl.
12. A method according to claim 11 wherein said quaternaryammonium
base is tetrapropyl-ammonium hydroxide.
13. A method according to claim 5 wherein the ratio of molecular
sieve, organic base and water is: molecular sieve (g): organic base
(mol.): water (mol)=100: (0.0050-0.50): (5-200).
14. A method according to claim 13 wherein the ratio of molecular
sieve, organic base and water is: molecular sieve (g): organic base
(mol.): water (mol)=100: (0.010-0.15): (20-80).
15. A method according to claim 5 wherein the base-treatment is
carried out at 150-180.degree. C. under autogenous pressure for
2-120 h.
16. A method according to claim 5 further comprising repeating
said steps once or several times.
17. A method according to claim 5 further comprising mixing the
synthesized MFI-type of titanium-silicalite molecular sieve with
an acidic compound and water homogenously, and heating the mixture
at 5-95.degree. C. for 5-360 min, before the organic-base-treatment.
18. A method according to claim 17 wherein said acidic compound
is selected from organic aliphatic acids having a general formula
of R.sup.1 (COOH).sub.n, wherein R.sup.1 represents a C.sub.1-4
-alkyl, and n is 1 or 2.
19. A method according to claim 17 wherein said acidic compound
is selected from inorganic acid compounds including hydrochloric
acid, sulfuric acid, phosphoric acid, nitric acid and/or hydrofluoric
acid.
20. A method according to claim 17 wherein said acidic compound
is selected from acidic salt compounds including ammonium chloride,
ammonium phosphate, ammonium nitrate, ammonium sulfate and/or ammonium
fluoride.
21. A method according to claim 17 wherein the ratio of molecular
sieve, acidic compound and water is: molecular sieve (g): acidic
compound (mol): water (mol)=100: (0.010-2.0): (5-250).
22. A method according to claim 18 wherein the ratio of molecular
sieve, acidic compound and water is: molecular sieve (g): acidic
compound (mol): water (mol)=100: (0.080-0.80): (10-100).
23. A method according to claim 17 wherein said acid-treatment
is carried out at 15-60.degree. C. for 10-180 min.
Molecular sieve description
FIELD OF THE INVENTION
The invention relates to a titanium-silicalite molecular sieve
and the method for the preparation of the same, specifically to
a five-member ring titanium-silicalite molecular sieve with MFI
structure (TS-1) and the method for preparation of the same.
BACKGROUND OF THE INVENTION
A crystalline titanium-silicalite molecular sieve is a novel heteroatom
substituted silicalite molecular sieve, which was first reported
in 1980s'. Now, a variety of titanium-silicalites have been reported,
including TS-1 with MFI structure, TS-2 with MEL structure and TS-48
with a larger pore system. These molecular sieves can be applied
to catalytic oxidation of different organic substrates, for example,
epoxidation of olefins, hydroxylation of aromatics, oximation of
cyclohexanol and oxidation of alcohols, and exhibit an excellent
reactivity and selectivity in these catalytic oxidations. These
crystalline titanium-silicalites used as redox molecular sieve catalysts
have a prosperous future for applications in some industrial processes.
TS-1 molecular sieve is a synthetic, crystalline porous material
having a structure similar to ZSM-5 obtained by substituting titanium
for a partial silicon in the skeleton, which exhibits an excellent
catalytic reactivity and selectivity in different oxidations attributed
to coordination of the catalytic oxidation property in titanium
and shape selectivity effects in ZSM-5 structure. Compared with
the traditional oxidation reactions, H.sub.2 O.sub.2 as the oxidant
in all the oxidations catalyzed by TS-1 has the advantage of giving
environmentally benign water as its by-product and operating simply.
Hence, TS-1 makes it possible to develop new industrial processes.
Marco Taramasso et al first disclosed a process for synthesizing
TS-1 in 1981 (GB 2071071A, U.S. Pat. No. 4410501). In their
report, the preparation of TS-1 is based on the initial formation
of a reaction mixture containing a silica source, a titanium source,
an organic base (RN+) and/or an alkaline oxide(Me.sub.n/2 O), followed
by hydrothermal crystallization in an autoclave at 130-200.degree.
C. for 6-30 days. The final product TS-1 is obtained after filtration,
washing, drying and calcination. The silicon source used is selected
from tetra-alkyl ortho-silicate, or colloidal SiO.sub.2 or an alkali
metal silicate, and the titanium source used is selected from hydrolyzable
titanium compounds, preferably Ti(OC.sub.2 H.sub.5).sub.4. The organic
base used is preferably tetra-propyl ammonium hydroxide. The reaction
mixtures generally show a composition range in mol % as follows:
Generally Preferably SiO.sub.2 /TiO.sub.2 : 5.about.200 35.about.65
OH.sup.- /SiO.sub.2 : 0.1.about.1.0 0.3.about.0.6 H.sub.2 O/SiO.sub.2
: 20.about.200 60.about.100 Me/SiO.sub.2 : 0.about.0.5 0 RN.sup.+
/SiO.sub.2 : 0.1.about.2.0 0.4.about.1.0
Thangaraj et al. indicated that titanium-content in the skeleton
of the TS-1 molcular sieve synthesized by the above process was
very low, and disclosed a TS-1 molecular sieve synthesis method
for effectively increasing titanium content in the skeleton of the
synthesized TS-1 molecular sieve(Zeolite, 1992 Vol. 12 p943-950).
It was said that, by this method, the value of Si/Ti in the molecular
sieve prepared by Taramasso's method could be reduced from 39 to
20. Thangaraj's method comprises: adding an appropriate amount of
an aqueous solution of tetrapropyl ammonium hydroxide (TPAOH) into
a tetraethyl silicate solution with stirring for a certain period
of time to get the solution dissolved throughly, then adding an
isopropanol solution of tetrabutyl titanate slowly under viogrous
stirring to obtain a clear liquid mixture(said solution must be
added slowly dropwise to prevent the formation of white TiO.sub.2
precipitate due to quick hydrolysis of tetrabutyl titanate); after
stirring for 15 minutes, adding another appropriate amount of an
aqueous TPAOH solution slowly, then displacing alcohol in the reaction
mixture under 75-80.degree. C. for 3-6 hours, and afterwords transferring
the mixture into an autoclave to undergo hydrothermal crystallization
under 170.degree. C. for 3-6 days, and after drying to obtain the
TS-1 molecular sieve. In the process, the reaction mixture shows
a composition in molecular ratio as follows;
Du et al in CN1167082A discloses a method for preparation of a
TS-1 molecular sieve, comprising: dissolving a titanium source in
an aqueous TPAOH solution, and mixing with solid silica gel pellets
homogeneously to obtain a reaction mixture, then undergoing hydrothermal
crystallization in an autoclave under 130-200.degree. C. for 1-6
days, and afterwards filtrating, washing, drying and calcining the
mixture by conventional processes.
The above-metioned methods in the prior art for synthesizing the
TS-1 molecular sieves have drawbacks mainly in that, in the course
of process, a relatively large portion of stagnant Ti is formed
as ex-skeleton Ti remaining in the pore channels of the molecular
sieves, this portion of ex-skeleton Ti cannot play an effective
role in the catalytic oxidation, but will cause decomposition of
the oxidant(H.sub.2 O.sub.2). Consequently, the TS-1 molecular sieves
prepared by the above methods exhibit low catalytic oxidation activity,
and moreover, due to unstable content of ex-skeleton Ti, TS-1 molecular
sieves having good catalytic oxidation activity can hardly be obtained
steadily, so the TS-1 molecular sieves obtained are generally inferior
in activity stability, which handicaps the industrial application
of the TS-1 molecular sieve in the prior art.
DISCLOSURE OF THE INVENTION
The object of this invention is to provide a novel titanium-silicalite
molecular sieves (TS-1) with MFI structure, particularly having
a unique morphology of crystallite and showing good catalytic reactivity
and stability in oxidations. Another object of the invention is
to provide a method for the preparation of the said titanium-silicalite
molecular sieve.
The titanium-silicalite molecular sieve provided by the invention
is characterized by crystallites with hollow struture, in which
the hollow cavity of each crystallite has a radial length in the
range of 5.about.300 nm, preferable 10.about.200 nm. The benzene
adsorption capacity of said titanium-silicalite sample tested at
25.degree. C. and P/P.sub.0 =0.10 for 1 h is at least 70 mg/g, preferably
at least 80 mg/g.
Said titanium-silicalite molecular sieve provided by the invention
is also characterized by that the cavity shape of said titanium-silicalite
crystallite can be varied, such as in circular, or rectangular,
or irregularly polygonal, or irregularly circular, or a combination
of these shapes.
The grains of the titanium-silicalite molecular sieve with MFI
structure provided by the invention are composed of individual hollow
crystallites or aggregated crystallites as a result of aggregation
of the hollow crystallites.
Said titanium-silicalite molecular sieve provided by the invention
is also characterized by that there is an obvious hysteresis loop
between the low-temperature N.sub.2 adsorption isotherm and desorption
isotherm of said molecular sieve, while generally there is not any
hysteresis loop between those isotherms of the conventional titanium-silicalite.
The applicants in their research found that the hysteresis loop
is related to the hollow cavity structure in the crystallites of
said titanium-silicalite molecular sieve. The bigger the hollow
cavity in the crystallites, the larger the said hysteresis loop.
The SiO.sub.2 : TiO.sub.2 molar ratio of said titanium-silicalite
molecular sieve of the invention ranges from 5 to 500 preferably
from 10 to 200.
The first method for the preparation of said titanium-silicalite
molecular sieve provided by the invention comprises the following
steps: (1) Mixing a sythesized TS-1 with an acidic compound and
water homogenously, and letting the mixture react at 5-95.degree.
C. for 5-360 min., preferably at 15-60.degree. C. for 10-180 min.
to obtain an acid-treated TS-1; (2) Mixing the acid-treated TS-1
obtained in step 1 with an organic base and water homogenously,
then transferring the mixture to a autoclave to react at 120-200.degree.
C. under autogenous pressure for 1-192 hr., preferably at 150-180.degree.
C. under antogenous pressure for 2-120 hr, then filtrating, washing,
drying and calcining the resultant to obtain the TS-1.
In the first method according to the present invention, step 1
and step 2 may be repeated once or several times respectively, or
only step 2 is repeated once or several times, so as to further
enlarge the hollowness in the crystallites, reduce the amount of
ex-skeleton TiO.sub.2 and improve the catalytic reactivity of the
TS-1 molecular sieve.
Said TS-1 used in step 1 of the first method of the present invention
can be a synthesized TS-1 prepared by any method of the prior art,
which can be as-synthesized or calcined, i.e. with or without an
organic template, preferably calcined and with the organic template
removed.
Said acidic compound used in step 1 of the first method is selected
from organic acid compounds, such as an aliphatic acid R.sup.1 (COOH).sub.n,
wherein R.sup.1 is a C.sub.1-4 -alkyl, and n is 1 or 2; or inorganic
mineral acids; such as hydrochloric acid, sulfuric acid, phosphoric
acid, nitric acid and hydrofluoric acid; or acidic salt compounds,
such as ammonium chloride, ammonium phosphate, ammonium nitrate,
ammonium sulfate and ammonium fluoride; preferably inorganic acid.
The ratio of molecular sieve to acidic compound to water used in
step 1 of the first method is: molecular sieve (g): acidic compound
(mol): water (mol)=100:(0.010-2.0):(5-250), preferably 100:(0.080-0.80):(10-100).
The organic base used in step 2 of the first method of the present
invention is selected from the group consisting of aliphatic amines,
alkylol amines, quaternary ammonium bases, or mixtures of these
compounds, preferably alkylol amines, or quaternary ammonium bases
or mixtures of these compounds; most preferably quaternary ammonium
bases or mixtures of the organic base and quaternary ammonium bases.
Said aliphatic amines have a general formula of R.sup.2 (NH.sub.2).sub.n,
wherein R.sup.2 is a C.sub.1-6 -alkyl, and n is 1 or 2 preferably
ethyl amine, n-butyl amine, butanediamine, or hexanediamine.
Said alkylol amine compounds have a general formula of (HOR.sup.3).sub.m
N, wherein R.sup.3 is a C.sub.1-4 -alkyl, and m is from 1 to 3
preferably mono ethanolamine, diethanolamine or triethanolamine.
Said quaternary ammonium bases have a general formula of R.sup.4.sub.4
NOH, wherein R.sup.4 is a C.sub.1-4 -alkyl, preferably a C.sub.2-4
-alkyl, more preferably propyl.
The ratio of molecular sieve to organic base to water used in step
2 of the first method is: molecular sieve (g): organic base (mol.):
water (mol)=100:(0.005-0.50):(5-200), preferably 100:(0.010-0.15):(20-80).
The second method for the preparation of said titanium-silicalite
(TS-1) molecular sieve according to the present invention is characterized
in that the method comprises that a synthesized TS-1 molecular sieve
having a MFI structure prepared by conventional method is mixed
with an organic base and water homogenously, then the mixture is
transferred to a sealed reaction vessel to react at 120-200.degree.
C. under autogenous pressure for 1-192 h, preferably at 150-180.degree.
C. for 2-120 h, and then the reaction product is recovered. Compared
with the first method, the second method is different in that it
saves the step of acid treatment and treats the above-said synthesized
TS-1 molecular sieve having a MFI-structure with an organic base
directly, wherein said organic base and its amount used are the
same as the afore-mentioned. In the second method, the organic base
treatment can be repeated once or several times.
The hollow cavity in the crystallite of said TS-1 molecular sieve
product obtained by the first method is larger than that produced
by the second method, while the second method can also achieve the
object of the invention.
DESCRIPTION OF THE DRAWING
FIG. 1 shows the XRD crystalline phase diagram of the sample obtained
in example 1.
FIGS. 2-13 are transmission electron microscopic (TEM) images of
the samples taken from comparative example 1 and examples 1-11
respectively.
FIGS. 14-25 are low-temperature N.sub.2 adsorption-desorption isotherms
of samples taken from comparative example 1 and examples 1-11 respectively.
According to the methods of this invention, the adoption of acid-base
treatment and/or organic base treatment has enabled the ex-skeleton
Ti to re-enter the skeleton of the TS-1 molecular sieve, thus the
amount of ex-skeleton TiO.sub.2 is reduced, while the amount of
effective Ti in the skeleton is increased, and as a result, the
reactivity of the titanium-silicalite molecular sieve in catalytic
oxidation is obviously higher than that prepared by the prior art
(see Example 12) and its activity stability is better (see Example
13). Besides, the thin-wall and hollow -cavity structure of the
crystallites of said TS-1 molecular sieve of the invention favors
the diffusion of the molecules, particularty the larger molecules
among the reactants (e.g. the aromatic compounds) and reaction products
in the catalytic reactions, especially in the catalytic oxidations
of the aromatic or cyclic compounds.
The invention will be further described in combination with various
specific Examples. In the following examples, TPAOH was the product
of Tokyo Kasei Organic Chemicals, the other regents were all the
commercial products. The transmission electron microscopic images
of the titanium-silicalites were taken with a JEM-2000 FX-II transmission
electron microscope (TEM) of Japan Electron Corporation. Benzene
adsorption capacity was measured by the routine static adsorption
method. Determination of the low-temperature N.sub.2 adsorption-desorption
isotherms was carried out according to ASTM D4222-98 standard method.
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