Technical Field
[0001]
The present invention relates to an all-silicazeolite
separation membrane and a method for producing an
all-silicazeolite separation membrane without using
hydrofluoric acid. In particular, it can be favorably used
in zeolite separation membranes having an STT-type or CHA-type
zeolite crystal structure.
Background Art
[0002]
Zeolite has regularly arranged micropores, and in
general, many zeolites which have high heat resistance and are
also chemically stable are obtained, and therefore, it has been
used in various fields. Zeolite is generally an
aluminosilicate in which Si is partially substituted with Al
(having a three-dimensional network structure in which Si04
and Al04 are bonded by sharing oxygen as a basic framework
structure) , has pores of a molecular order (about 0. 3 to 1 nm)
of oxygen 8- to 14-membered ring, and has a stereoselective
l
adsorption ability. Therefore, zeolite is widely used in the
fields of, for example, liquid separation, vapor separation,
gas separation, membrane reactors, solid acid catalysts,
separation adsorbents, ion exchangers, and so on. Recently,
a membrane separation method using a zeolite membrane has been
proposed in place of a distillation method which requires much
heat energy for separation and collection of an organic
compound from a mixture containing the organic compound, and
there is also a case where the method has already been put into
practice.
[0003]
However, with respect to zeolite, it is known that the
hydrophilici ty or hydrophobicity of a zeolite membrane or the
selectivity or permeation performance for molecules passing
through the pores in the zeolite membrane varies depending on
the ratio of Si02 to Al20 3 (silica ratio: Si0,/Al20 3 ) to serve
as the constituent components. Further, it is also known that
the chemical resistance or the like differs depending on the
change in the ratio of Si02 to Al203.
[0004]
In general, as the silica ratio (the ratio of Si02 to
Al20 3 ) is increased, the hydrophobicity (lipophilicity) is
increased, and also the chemical resistance is increased, and
there is a tendency that a zeolite membrane having a high silica
ratio is demanded.
2
[0005]
Further, in natural gas such as methane mined from a
natural gas oil field, other than carbon dioxide, water having
a molecular diameter close to that of carbon dioxide and the
like are also contained. Therefore, when natural gas and
carbon dioxide are tried to be·separated, other than carbon
dioxide, also water molecules and the like penetrate into
zeolite membrane pores.
[0006]
In a conventional zeolite membrane having an
aluminosilicate crystal structure, aluminum atoms are present
in the crystal structure, and therefore, it has a problem that
water adsorption occurs on the aluminum atoms and carbon
dioxide hardly comes out from the pores, and thus, a desired
processing amount cannot be obtained.
[0007]
In order to achieve an object to improve this processing
amount, an all-silica zeolite membrane has been demanded. In
particular, STT-type and CHA-type zeolite separation
membranes for separating methane or the like or carbon dioxide
or the like could not be industrially realized due to a problem
related to the below-mentioned production method.
[0008]
That is, a zeolite separation membrane is synthesized
using a method of a thermal synthesis method from a raw material
3
composition, and this raw material composition contains a
silica source such as sodium silicate or colloidal silica, an
aluminum source such as aluminum hydroxide or sodium aluminate,
wate-r, a structure directing agent such as an organic template,
and a mineralizer such as an alkali metal hydroxide.
[0009]
This mineralizer has a function to dissolve a metal
component contained in the raw material composition in water.
[0010]
In the case where zeolite is an aluminosilicate, as the
mineralizer, NaOH (sodium hydroxide) is generally used.
However, when NaOH is used as the mineralizer for synthesizing
an all-silica STT-type or all-silica CHA-type zeolite membrane,
there is a problem that zeolite is not crystallized
(solidified) even if hydrothermal synthesis is performed, and
in order to solve this problem, there is a method using
hydrofluoric acid in place of NaOH.
[0011]
For example, PTL 1 to PTL 3 show a method for producing
a pure silica zeolite crystal in a particulate form (not a
zeolite membrane) of an STT type, a CHA type, or the like for
the purpose of separating carbon dioxide or the like by an
adsorption method, and hydrofluoric acid is used as a
mineralizer.
[0012]
4
' -
It is said that this hydrofluoric acid has a
crystallization acceleration effect of accelerating
dissolution or crystallization of a raw material composition
gel, a structure determination effect of synthesizing a
compound having a certain structure and composition by the
coexistence offluoride ions, and a template effect of
stabilizing the structure in the same manner as an organic
template by being incorporated into the framework of a
compound.
[0013]
However, this hydrofluoric acid has problems that it has
very high toxicity and is not suitable for the production of
a large structure such as a zeolite membrane complex, it takes
great time and effort to completely wash away hydrofluoric acid
adhered to the surface of a zeolite separation membrane also
after synthesis, and the production method is very complicated.
[0014]
Further, in the case where hydrofluoric acid remains in
a washing step after synthesis, there is a problem that the
purity of a zeolite separation membrane permeate or
non-permeate (product) is deteriorated.
Citation List
[0015]
Patent Literature
PTL 1: JP-A-2009-114007
5
PTL 2: JP-A-2009-214101
PTL 3: JP-A-2015-116532
Summary of Invention
Technical Problem
[0016]
In view of the above-mentioned problems of the prior art,
an object of the present invention is to provide an all-silica
zeolite separation membrane which does not cause a decrease
in the processing amount due to adsorption of water
molecules(which separates carbon dioxide or the like).
[0017]
Further, in view of the above-mentioned problems in the
production of the prior art, an object of the present invention
is to provide a safe method for producing an all-silica zeolite
separation membrane without using hydrofluoric acid.
Solution to Problem
[0018]
In order to achieve the above object, the present
invention provides the following zeolite separation membrane.,
a membrane synthesis raw material composition for producing
the zeolite separation membrane, and a method for producing
the zeolite separation membrane.
[0019]
( 1) A zeolite separation membrane, in which the framework
6
--- '
of a zeolite crystal structure formed on a porous support is
all silica, characterized in that the zeolite crystal structure
formed on the porous support is fluorine free.
[0020]
(2) The zeolite separation membrane according to the
above (l), characterized in that the zeolite crystal structure
is an STT type or a CHA type.
[0021]
(3) A raw material composition for producing the zeolite
separation membrane according to the above (1) or (2),
characterized in that the raw material composition contains
a silica source and an organic template and does not contain
a fluorine compound.
[0022]
( 4) A method for producing a zeolite separation membrane
having a zeolite crystal structure on a porous support,
characterized in that the method includes a step of producing
a seed crystal, a step of applying the seed crystal onto the
porous support, a step of producing a membrane synthesis raw
material composition, anda step of immersing the porous support
having the seed crystal applied thereon in the membrane
synthesis raw material composition, and performing
hydrothermal synthesis, and the membrane synthesis raw
material composition contains a silica source and an organic
template and does not contain a fluorine compound.
7
[0023]
(5) The method for producing a zeolite separation
membrane according to the above ( 4) , characterized in that the
hydrothermal synthesis temperature and time are from 140°C to
180°C and from 8 days to 12 days.
[0024]
In the present invention, the term "fluorine free" means
that in the hydrothermal synthesis of a zeolite membrane, the
synthesis is performed without using a fluorine-containing
mineralizer such as hydrofluoric acid, and therefore,
hydrofluoric acid does not remain in the zeolite membrane, and
fluorine is not present in the structure of the zeolite membrane
crystallized in the hydrothermal synthesis. Incidentally, a
fluorine-containing mineralizer used in the step of producing
a seed crystal may be contained in the zeolite membrane.
However, the amount thereof is much smallerthan the entire
synthesized zeolite membrane, and therefore, the zeolite
membrane can be said to be substantially fluorine free.
Advantageous Effects of Invention
[0025]
By using the all-silica STT-type or CHA-type zeolite
separation membrane of the present invention, when natural gas
such as methane or the like mined from a natural gas oil field
and carbon dioxide or the like are separated, carbon dioxide
8
or the like can be separated without causing a decrease in the
processing amount due to adsorption of water molecules or the
like contained in the natural gas.
[0026]
According to the production method of the present
invention, an all-silica zeolite separation membrane can be
safely produced without using a fluorine compound
(hydrofluoric acid or the like) .
Brief Description of Drawings
[0027]
[FIG. 1] FIG. 1 is an electron micrograph of an all-silica
STT-type zeolite membrane obtained in Example 1.
[FIG. 2] FIG. 2 showsan X-ray diffraction pattern of the
all-silica STT-type zeolite separation membrane obtained in
Example 1 and an X-ray diffraction pattern of an all-silica
STT-type zeolite particle.
[FIG. 3] FIG. 3 is an electron micrograph of a surface
of an all-silica zeolite membrane of Example 2 synthesized by
shortening the hydrothermal synthesis time.
[FIG. 4] FIG. 4 is acorrelation diagram between
temperature and a carbon dioxide permeation rate through the
all-silica STT-type zeolite separation membrane obtained in
Example 1 and a high silica (Si/Al ratio of 25) CHA-type zeolite
separation membrane.
9
[FIG. 5] FIG. Sshowsan X-ray diffraction pattern of an
all-silica CHA-type zeolite separation membrane obtained in
Example 3 and an X-ray diffraction pattern of an all-silica
CHA-type zeolite particle.
[FIG. 6] FIG. 6showsan X-ray diffraction pattern of an
all-silica STT-type zeolite separation membrane obtained in
Example 4 and an X-ray diffraction pattern of an all-silica
STT-type zeolite particle.
[FIG. 7] FIG. 7shows a micrograph of the cross section
of the all-silica STT-type zeoliteseparation membrane
obtained in Example 1 and elemental analysis results.
Description of Embodiments
[0028]
Hereinafter, a zeolite separation membrane according to
one embodiment of the present invention will be described in
detail.

In theall-silica zeolite separation membrane of the
present invention, an all-silica zeolite membrane is formed
on the surface of a porous support.
[0029]
The crystal framework of the all-silica zeolite membrane
of the present invention does not substantially contain
aluminum and is composed of all silica (Si02). Aluminum in
10
pores of a general zeolite membrane has a strong adsorption
ability and serves as a resistance to a material to be separated
when multicomponent separation is desired to be performed.
Further, destruction of the zeolite membrane due to acidity
or high water content occurs in an aluminum portion in the
framework of the zeolite crystal structure. Therefore, the
all-silica zeolite membrane of the present invention which does
not contain aluminum has very high acid resistance and low
adsorption performance for water molecules or the like. The
phrase "not substantially contain aluminum" herein is used
because there is a possibility that aluminum contained in a
porous support may be contained in a very small amountduring
hydrothermal synthesis.
[0030]
On the other hand, it is said that there are two types
of separation methods by the zeolite separation membrane:
separation by a molecular sieving effect utilizing a difference
between a zeolite pore diameter and a molecular diameter and
separation by an adsorption effect utilizing a difference in
the adsorption property on the zeolite membrane of various
molecules. The all-silica zeolite separation membrane of the
present invention performs separation mainly by a molecular
sieving effect.
[0031]
Then, the STT-type zeolite membrane which is favorably
11
used in the present invention has two types of pores, and the
respective pores have sizes of 05. 3 x 3. 7'A, and 02. 4 x 3. 5A,
respectively. On the other hand, the CHA-type zeolite
membrane has a pore with a size of 03.8x 3.8 'A.
[0032]
Therefore, for example, molecules whose size is equal
to or larger than that of the pores of the zeolite membrane
such as methane ( 3. 8 A) , ethanol ( 4. 3 A) , acetic acid ( 4. 3 A) ,
sulfur hexafluoride (5.5 A), benzene (6.6A), p-xylene (6.6 x
3.8 'A), and o,m-xylene (7.3 x 3.9 A) cannot pass through the
pores, and molecules whose size is smaller than that of the
pores of the zeolite membrane such as hydrogen ( 2. 9 'A ) , water
( 3. 0 A) , argon ( 3. 4 A) , carbon dioxide ( 3. 3 A) , oxygen ( 3. 4 6A) ,
nitrogen ( 3. 64A) , and helium ( 2. 6 A) can pass through the pores
of the zeolite membrane, and therefore, the respective
molecules can be separated.
[0033]
Incidentally, the "STT" and "CHA" are classification
codes of zeolite specified based on the structure by the
International Zeolite Association (IZA).
[0034]
The thickness of the zeolite membrane is not particularly
limited, and may be any as long as the membrane can be produced
as thin as possible, and is preferably about 1.0 ~m to 10.0
~m.
12
[0035]
The porous support may be any as long as zeolite can be
crystallized as a thin membrane on the support, and includes
porous supports of alumina, silica, zirconia, titania,
stainless steel, and the like. Of course, the porous support
has holes larger than the pores of the zeolite membrane, and
molecular sieving is achieved by passing molecules having
passed through the zeolite membrane through the holes of the
porous support.
[0036]
The shape of the porous support is not particularly
limited, and a porous support having any of various shapes such
as a tubular shape, a plate shape, a honeycomb shape, a hollow
fiber shape, and a pellet shape can be used. For example, in
the case of a tubular shape, the size of the porous support
is not particularly limited, however, practically, the length
is about 2 to 200 em, the inner diameter is 0.5 to 2.0 em, and
the thickness lS about 0.5 to 4.0 mm.
[0037]

In a step of synthesizing a zeolite membrane, a seed
crystal of all-silica zeolite is applied onto the porous
support, and the porous support with the seed crystal is
immersed in a membrane synthesis raw material composition (gel) ,
and hydrothermal synthesis is performed, whereby an all-silica
13
zeolite membrane is formed.
[0038]
(Step of Producing Seed Crystal)
As the organic template and the silica_source for the
seed crystal, preferably, the same ones as used in the synthesis
of a desired zeolite crystal are used. As the zeolite seed
crystal, a seed crystal is produced by basically the same
procedure as the hydrothermal synthesis of the zeolite crystal
(separation membrane) except that hydrofluoric acid
(hereinafter sometimes referred to as "HF") is used, and the
porous support is not used.
The seed crystal for producing the all-silica STT-type
zeolite separation membrane is desirably produced, for example,
according to the formulation of Si02 : organic template : HF :
H20 = 1:0.2 to 1.5:0.5 to 1.5:5.0 to 15.0. In particular, it
is desirably produced according to the formulation of Si02 :
organic template : HF : H20 = 1:0.2 to 1.0:0.5 to 1.5:5.0 to
15.0.
[0039]
The seed crystal for producing the all-silica CHA-type
zeolite membrane is desirably produced, for example, according
to the formulation of Si02 : organic template : HF : HzO =
1:0.5to2.5:0.5 to2.0:2.5 to 8.0. In particular, the seed
crystal for producing the all-silica CHA-type zeolite membrane
is desirably produced according to the formulation of SiOz :
14
organic template HF H20 = 1: 1. Oto2. 5:0. 5 to 1. 5:2.5 to 8. 0.
[0040]
A seed synthesis raw material composition (gel) is
transferred to a pressure vessel, generally an autoclave, and
hydrothermal synthesis is performed. Thereafter, the
autoclave is cooled, and the gel is washed with ion exchanged
water, filtered, and dried under reduced pressure.
[0041]
The size of the seed crystal is preferably from 100 nm
to 1 ~m, more preferably from 100 to BOO nm. When the seed
crystal is larger than 1 ~' a dense zeolite layer may not be
able to be formedin relation to the pore diameter of the porous
support. Incidentally, the particle diameter of the seed
crystal can be measured using a particle diameter measuring
device (trade name: FPAR-1000) manufactured by Otsuka
Electronics Co., Ltd.
[0042]
In the hydrothermal synthesis of the seed crystal, it
is preferred to add the previously prepared seed crystal to
a synthesis liquid (synthesis gel). Crystallization of
zeolite can be accelerated, and the particle diameter can be
controlled.
[0043]
(Step of Applying Seed Crystal onto Porous Support)
First, with respect to the porous support, in the case
15
where a porous support having the zeolite membrane formed
thereon is used as a molecular sieve or the like, it is preferred
to set the average pore diameter or the like of the porous
support so as to satisfy the following conditions: (a) the
zeolite membrane can be rigidly supported, (b) the pressure
loss is made as small as possible, and (c) the porous support
has a sufficient
strength)
[0044]
self-supporting property (mechanical
The porous support is preferably subjected to a surface
treatment by a method such as water washing or ultrasonic
washing. For example, the surface of the support may be washed
by ultrasonic washing with water for 1 to 10 minutes. In order
to improve the surface smoothness, the surface thereof may be
polished using a sandpaper, a grinder, or the like.
[0045]
The particle diameter of the seed crystal is desirably
smaller, and the seed crystal may be crushed as needed and used.
In order to adhere the seed crystal onto the support, for
example, a dipping method in which the seed crystal is dispersed
in a solvent such as water, and the support is dipped in the
dispersion liquid, thereby adhering the seed crystal to the
support, a method in which a slurry-like material obtained by
mixing the seed crystal with a solvent such as water is rubbed
on the surface of the support, or the like can be used. The
16
application amount of the seed crystal is preferably set to,
for example, 1 X 10-4 to 1 X 10-3wt% with respect to the weight
of the support. Then, in order to enhance the adhesiveness,
the support after applying the seed crystal thereto is
preferably fired at, for example, 450°C to 700°C.
[0046]
(Step of Producing Membrane Synthesis Raw Material
Composition)
The silica source is not particularly limited, however,
preferred
colloidal
examples
silica,
thereof include amorphous silica,
silica gel, sodium silicate,
tetraorthosilicate (TEOS), and trimethylethoxysilane.
[0047]
As the organic template, an
N,N,N-trialkyl-1-adamantanammonium cationderived
from1-adamantanamine is preferred, and it is preferred to use
a hydroxide thereof. Among these,
N, N, N-trimethyl-adamantanammonium hydroxide ( TMAdaOH) is more
preferred. Additional examples thereof include
N, N, N-trialkylbenzylammonium hydroxide. It is considered
that a hydroxy group of such an organic template performs a
function as a mineralizer in the gel.
[0048]
The formulation of the all-silica STT-type zeolite
membrane synthesis raw material composition is composed of,
17
for example, only a silica source, an organic template, and
H20, and is, for example, preferably Si02 : TMAdaOH : H20 = 1: 0. 1
to 1.0:20 to 80, more preferably Si02 : TMAdaOH : H20 = 1:0.1
to 0.5:30 to 60.
[0049]
The formulation of the all-silica CHA-type zeolite
membrane synthesis raw material composition is composed of,
for example, only a silica source, an organic template, and
H20, and is, for example, preferably Si02 : TMAdaOH: H20 = 1:0.2
to 1.5:10 to 60, more preferably Si02 : TMAdaOH : H20 = 1:0.5
to 1.5:20 to 50.
[0050]
(Step of Hydrothermally SynthesizingZeolite Separation
Membrane)
In a method for hydrothermally synthesizing an
all-silica zeolite separation membrane, after the membrane
synthesis raw material composition (gel) which contains a
silica source and an organic template and does not contain a
fluorine compound is aged, the porous support having the
all-silica zeolite seed crystal applied thereon is inserted
into the membrane synthesis raw material composition, and
hydrothermal synthesis is performed using an airtight vessel,
generally, an autoclave. The aging temperature and time are
preferably room temperature and from 10 to 24 hours.
Specifically, the organic template and the silica source are
18
mixed, stirred, and heated, and generated water and ethanol
are removed by evaporation, and thereafter, ion exchanged water
is added to the residual solid and stirred while heating.
Thereafter, the porous support having the seed crystal applied
thereon is placed in a Teflon (registered trademark) inner
cylinder, which is filled with a secondary growth solution.
This is placed in an autoclave, and hydrothermal synthesis is
performed. Thereafter, the formed zeolite separation
membrane is washed by boiling with ion exchanged water, and
dried under reduced pressure, and then, fired so as to remove
the organic template remaining in the membrane. The firing
temperature and time are preferably from 450°C to 700°C and from
8 to 24 hours. Incidentally, ethanol is generated by
hydrolysis and condensation when TEOS is used as the silica
source.
[0051]
The hydrothermal synthesis temperature and time for
forming the all-silica STT-type zeolite membrane and the
all-silica CHA-type zeolite membrane are preferably from 140°C
to 180°C and from 6 days to 12 days, more preferably from 8
to 12 days.
[0052]
[Example 1: Production of All-Silica STT-type Zeolite
Separation Membrane]
(Preparation of Seed Crystal)
19
' --
In a beaker, TMAdaOH (organic template), TEOS (silica
source), and water were mixed, and stirred for 12 hours, whereby
TEOS was hydrolyzed. Thereafter, the mixture was heated to
150°C, whereby generated water and ethanol were completely
evaporated. To the solid remaining in the beaker,
hydrofluoric acid and ion exchanged water were added and
stirred. The molar formulation of the respective materials
is as follows: Si02 :TMAdaOH: HF: H20 ~ 1:0.5:0.5:7.5. After
stirring, the gel was transferred to an autoclave made of Teflon,
and hydrothermal synthesis was performed at 150°C for 3. 5 days.
The autoclave was cooled, and the gel in the Teflon inner
cylinder was washed with ion exchanged water, filtered, and
dried under reduced pressure.
[0053]
The thus prepared all-silica STT-type zeolite seed
crystal was applied onto the surface of a porous alumina support
(outer diameter: 3 mm, length: about 2 5 mm, pore diameter: 1. 5
~m) which is a test piece by rubbing the seed crystalthereon
in an amount of 3 X 10-4wt% with respect to the weight of the
support. Thereafter, the resulting material was fired at 7 0 0°C
for 12 hours.
[0054]
(Synthesis of Zeolite Membrane)
Subsequently, a membrane synthesis raw material
composition for membrane synthesis for producing a zeolite
20
membrane was prepared by the following procedure. First, in
a beaker, TMAdaOH which is an organic template and TEOS which
is a silica source were mixed and stirred for 12 hours. The
resulting mixture was heated to 150°C, whereby generated water
and ethanol were completely evaporated. To the solid
remaining in the beaker, ion exchanged water was added and
stirred while heating to 150°C. The molar formulation of the
respective materials is as follows: Si02 : TMAdaOH H,O =
1:0.25:44. Thereafter, the porous support having the seed
crystal applied thereon was placed in a Tefloninner cylinder,
which was filled with a secondary growth solution. This was
placed in an autoclave, and hydrothermal synthesis was
performed at 150°C for 8 days. The autoclave was cooled, and
the formed zeolite separation membrane .was taken out from the
Teflon inner cylinder, washed by boiling with ion exchanged
water, and dried under reduced pressure. Finally, in order
to remove TMAdaOH remaining in the membrane, firing was
performed at 500°C for 10 hours using an electric furnace.
[0055]
FIG. 1 shows an SEM image of a surface of the synthesized
all-silica zeolite separation membrane.
[0056]
FIG. 2 showsan X-ray diffraction pattern (XRD) of an
all-silica STT-type zeolite particle and an X-ray diffraction
pattern of the zeolite separation membrane produced by the
21
above-mentioned production method. The X-ray diffraction
pattern on the lower side is the X-ray diffraction pattern of
the all-silica STT-type zeolite particle. The X-ray
diffraction pattern on the upper side is the X-ray diffraction
pattern of the all-silica zeoliteseparation membrane produced
by the above-mentioned production method. Based on the two
X-ray diffraction patterns, the produced zeoliteseparation
membrane was identified to be an all-silica STT-type zeolite
membrane.
[0057]
(Example 2: Production of All-Silica STT-type Zeolite
Separation Membrane)
FIG. 3 shows an electron micrograph of a surface of an
all-silica zeolite membrane of Example 2 synthesized by
shortening the hydrothermal synthesis time.
[0058]
A membrane was synthesized using the same membrane
synthesis raw material composition (gel) as in Example 1 .. The
porous support having the seed crystal applied thereon was
placed in a Tefloninner cylinder, which was filled with a
secondary growth solution. This was placed in an autoclave,
and hydrothermal synthesis was performed at 150°C for 7 days.
The autoclave was cooled, and the formed zeolite separation
membrane was taken out from the Teflon inner cylinder, washed
by boiling with ion exchanged water, and dried under reduced
22
pressure. Finally, in order to remove TMAdaOH remaining in
the membrane, firing was performed at 500°C for 10 hours using
an electric furnace.
[0059]

With respect to the denseness of the all-silica STT-type
separation membrane, an evaluation experiment was performed
by pervaporation separation (PV) of an IPA (isopropyl alcohol)
aqueous solution (IPA: 90 wt%). The zeolite separation
membrane was immersed in the IPA aqueous solution at 75°C, and
the pressure inside was reduced using a vacuum pump. Then,
the permeated vapor separated by the zeolite separation
membrane was collected by liquid nitrogen, and the weight and
concentration thereof were measured by a Karl Fischer moisture
meter, and the permeation rate and the separation factor of
the zeolite separation membrane were obtained.
[0060]
In the evaluation test, in Example 2, the IPA permeation
rate was very large. That is, while the pore diameter of the
STT-type zeolite membrane is 0.37 nm, the molecular diameter
of IPA is 0. 4 7 nm, and the IPA molecule theoretically cannot
permeate into the pore of the membrane by a molecular sieving
effect. Therefore, it was considered that the IPA molecule
permeated from a defect at a crystal grain boundary or the like,
and it was concluded that a dense STT-type zeolite membrane
23
was not obtained when the synthesis time was set to 7 days.
On the other hand, in Example 1, the IPA permeation rate was
drastically decreased as compared with Example 2, and the
separation factor of 15 or less was obtained, and the
densification of the zeolite membrane could be confirmed.
Incidentally, in Example 2, although the membrane is not dense,
an STT~type zeolite membrane is formed.
[0061]
In FIG. 1 (Example 1) and FIG. 3 (Example 2), crystal
form change was observedaccording to the synthesis time. The
zeolite separation membrane of Example 2 was composed of
particles in an elliptical form with a size of about several
tens of micrometers. On the other hand, the surface of the
zeolite membrane of Example 1 was covered with very large
angular crystals, and a defect such as a pinhole or a crack
was not observed, and it was confirmed that a dense crystal
layer was obtained.
[0062]

FIG. 4 is adiagram showing a correlation between
temperature and a carbon dioxide permeation rate through the
all~silica STT~type zeolite separation membrane obtained in
Example 1 and a high silica (Si/Al ratio of 25) CHA~type zeolite
separation membrane.
[0063]
24
The high silica (Si/Al ratio of 25) CHA-type zeolite
separation membrane was synthesized by supporting a CHA-type
seed crystal on the outer surface of a porous alumina support
and performing a hydrothermal treatment in a membrane synthesis
raw material composition. The seed crystal was obtained by
preparing a gel using an FAU-type zeolite powder (manufactured
by Tosoh Corporation), sodium hydroxide, an organic template
(TMAdaOH), and ion exchanged water and performing a
hydrothermal treatment at a predetermined temperature for a
predetermined time.
[0064]
Subsequently, the porous support having the seed crystal
supported thereon by dipping or rubbing and the membrane
synthesis raw material composition were placed in an autoclave,
and a polycrystalline layer was formed by performing a
hydrothermal treatment at a predetermined temperature for a
predetermined time. After washing, TMAdaOH was removed by
firing, whereby the high silica CHA-type zeolite separation
membrane was obtained.
[0065]
The method for producing this high silica CHA-type
zeolite membrane is the same as the production method described
in "Synthesis of high silica CHA membrane using zeolite as
starting material and separation property thereofu reported
by Imasaka et al. in the 80th annual meeting of the Society
25
of Chemical Engineers, Japan (see "Synthesis of high silica
CHA membrane using zeolite as raw material and separation
property thereof" in the BOth annual meeting of the Society
of Chemical Engineers, Japan")
disclosed in WO 2016/006564.
[0066]
Further, the method is also
FIG. 4 shows the relationship between the measurement
temperature and the C02 permeation rate for the above-mentioned
high silica CHA-type zeolite membrane and the all-silica
STT-type zeolite membrane synthesized in Example 1. The
measurement was performed in a temperature range from 40 to
120°C, and the flow amount of C02 gas permeating through the
zeolite membrane was measured, and the permeation rate was
calculated.
[0067]
As the measurement temperature was increased, a decrease
in the C02 permeation rate through the high silica CHA-type
zeolite separation membrane was observed. By increasing the
temperature to 120°C, the permeation rate was decreased to about
50%. On the other hand, in the case of the all-silica STT-type
zeolite separation membrane synthesized in Example 1, even if
the measurement temperature was increased, almost no change
was observed in the C02 permeation rate. Cationic species such
as Na + exist for an Al atom of the high silica CHA-type zeolite
separation membrane, and it is presumed that when these are
26
exposed to high temperature conditions, the molecular motion
thereof becomes active, and therefore, C02 permeation is
inhibited. On the other hand, it is considered that in the
all-silica zeolite separation membrane, an Al atom itself is
not present, and C02 smoothly permeates in the pores, and
therefore, a decrease due to temperature was not observed.
[0068]
[Example 3: Production of All-Silica CHA-type Zeolite
Separation Membrane]
(Preparation of Seed Crystal)
In a beaker, TMAdaOH (organic template) and colloidal
silica (silica source) were mixed, and hydrofluoric acid was
added thereto. Thereafter, the mixture was heated while
stirring, whereby water was completely removed. The solid was
crushedin an agate mortar and ion exchanged water was added
thereto. The molar formulation of the respective materials
is as follows: Si02 :TMAdaOH: HF: H20 = 1:1.4:1.4:6.0. The
gel was transferred to an autoclavemade of Teflon, and
hydrothermal synthesis was performed at 150°C for 24 days. The
autoclave was cooled, and the gel in the Teflon inner cylinder
was washed with ion exchanged water, filtered, and dried under
reduced pressure.
[0069]
The thus prepared all-silica CHA-type zeolite seed
crystal was applied onto the surface of a porous alumina support
27
(outer diameter: 16 mm, length: about 40 mm, pore diameter:
1. 0 ).J.m) which is a test piece by rubbing the seed crystal thereon
in an amount of 3 X 10-4wt% with respect to the weight of the
support. Thereafter, the resulting material was fired at 7 00°C
for 12 hours.
[0070]
(Synthesis of Zeolite Membrane)
Subsequently, a membrane synthesis raw material
composition for membrane synthesis for producing a zeolite
membrane was prepared by the following procedure. First, in
a beaker, TMAdaOH which is an organic template and TEOS which
is a silica source were mixed and stirred for 12 hours. The
resulting mixture was heated to l50°C, whereby generated water
and ethanol were completely evaporated. To the solid
remaining in the beaker, ion exchanged water was added and
stirred while heating to 150°C. The molar formulation of the
respective materials is as follows: Si02 : TMAdaOH
1:0.5:44. Thereafter, the porous support having the seed
crystal applied thereon was placed in a Tefloninner cylinder,
which was filled with a secondary growth solution. This was
placed in an autoclave, and hydrothermal synthesis was
performed at 150°C for 8 days. The autoclave was cooled, and
the formed zeolite separation membrane was taken out from the
Teflon inner cylinder, washed by boiling with ion exchanged
water, and dried under reduced pressure. Finally, in order
28
to remove TMAdaOH remaining in the membrane, firing was
performed at 500°C for 10 hours using an electric furnace.
[0071]
FIG. Sshowsan X-ray diffraction pattern (XRD) of an
all-silica CHA-type zeolite particle and an X-ray diffraction
pattern of the zeolite separation membrane produced by the
above-mentioned production method. The X-ray diffraction
pattern on the lower side is the X-ray diffraction pattern of
the all-silica CHA-type zeolite particle. The X-ray·
diffraction pattern on the upper side is the X-ray diffraction
pattern of the zeoliteseparation membrane produced by the
above-mentioned production method. Based on the two X-ray
diffraction pat terns, the produced zeoli teseparation membrane
was identified to be an all-silica CHA-type zeolite membrane.
[0072]
[Example 4: Production of All-Silica STT-type Zeolite
Separation Membrane]
The all-silica STT-type zeolite seed crystal synthesized
in Example 1 was applied onto the surface of a porous alumina
support having an outer diameter of 16 mm, a length of 40 mm,
and a pore diameter of 1. 0 ~tm by rubbing the seed crystal thereon
in an amount of 6 X 10-'wt% with respect to the weight of the
support. Thereafter, the resulting material was fired at 700°C
for 12 hours.
[0073]
29
' -- ----------------
Subsequently, a membrane synthesis raw material
composition for membrane synthesis was prepared by the
following procedure. First, in a beaker, TMAdaOH which is an
organic template and TEOS which is a silica source were mixed
and stirred for 12 hours. The resulting mixture was heated
to 150°C, whereby generated water and ethanol were completely
evaporated. To the solid remaining in the beaker, ion
exchanged water was added and stirred while heating to 150°C.
The molar formulation of the respective materials is as
'
follows: Si02 :TMAdaOH H20 = 1:0.25:54. Thereafter, the
porous support having the seed crystal applied thereon was
placed in a Tefloninner cylinder, which was filled with a
secondary growth solution. This was placed in an autoclave,
and hydrothermal synthesis was performed at 150°C for 8 days.
The autoclave was cooled, and the formed zeolite separation
membrane was taken out from the Teflon inner cylinder, washed
by boiling with ion exchanged water, and dried under reduced
pressure. Finally, in or.der to remove TMAdaOH remaining in
the membrane, firing was performed at 500°C for 10 hours using
an electric furnace.
[.0074]
FIG. 6showsan X-ray diffraction pattern (XRD) of an
all-silica STT-type zeolite particle and an X-ray diffraction
pattern of the zeolite separation membrane produced by the
above-mentioned production method. The X-ray diffraction
30
pattern on the lower side is the X-ray diffraction pattern of
the all-silica STT-type zeolite particle. The X-ray
diffraction pattern on the upper side is the X-ray diffraction
pattern of the zeoliteseparation membrane produced by the
above-mentioned production method. Based on the two X-ray
diffraction patterns, the produced zeoliteseparation membrane
was identified to be an all-silica STT-type zeolite membrane.
[0075]
FIG. 7 shows an electron micrograph of the cross section
of the all-silica STT-type zeolite membrane obtained in Example
1.
[0076]
An elemental analysis was performed byEDX measurement
(trade name: EMAXENERGYEX-350, manufacturedbyHORIBA, Ltd.)
for respective portions in FIG. 7. As a result, fluorine atoms
were not detected in any portion, and it was found that fluorine
is not present in the zeolite membrane synthesized by the method
of the present invention. Incidentally, the detection limit
of the EDX measurement is 0.00 atom%.

CLAIMS
[Claim 1]
A zeolite separation membrane, in which the framework of
a zeolite crystal structure formed on a porous support is all
silica, characterized in that
thezeoli te crystal structure formed on the porous
support is fluorine free.
[Claim 2]
The zeolite separation membrane according to claim 1,
characterized in that the zeolite crystal structure is an STT
type or a CHA type.
[Claim 3]
A raw material composition for producing the zeolite
separation membrane according to claim 1 or 2, characterized
in that
the raw material composition contains a silica source
and an organic template and does not contain a fluorine
compound.
[Claim 4]
A method for producing a zeolite separation membrane
having a zeolite crystal structure on a porous support,
characterized in that
the method comprises:
a step of producing a seed crystal;
a step of applying the seed crystal onto theporous
32
support;
a step of producing a membrane synthesis raw
material composition; and
a step of immersing the porous support having the
seed crystal applied thereon in the membrane synthesis raw
material composition,and performing hydrothermal synthesis,
and
the membrane synthesis raw material composition contains
a silica source and an organic template and does not contain
a fluorine compound.
[Claim 5]
The method for producing a zeolite separation membrane
according to claim 4, characterized in that
thehydrothermal synthesis temperature and time are from
140°C to l80°C and from 8 days to 12 days.