JP3128517B2 - Zeolite separation membrane and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zeolite separation membrane which can be used as a separation membrane, has a high withstand pressure and is suitable for a reverse osmosis membrane, and a method for producing the same.

[0002]

2. Description of the Related Art Zeolite crystals have pores of several angstroms in the crystals, and gas separation membranes and pervaporation separation membranes (hereinafter referred to as PV membranes) utilizing the molecular sieving characteristics and unique adsorption characteristics of these pores. It is expected to be applied to reverse osmosis separation membranes (hereinafter referred to as RO membranes), membrane reactors, gas sensors, and the like. In particular, RO membranes are highly stable against organic solvents, have a uniform pore size, have heat resistance and chemical resistance, and can be expected to have higher withstand pressure. Therefore, a zeolite separation membrane is a mixed solution of water and an organic solvent. As a separation membrane for separating an organic solvent from water, excellent separation performance and durability are expected as compared with an organic RO membrane or the like. In addition, zeolite membranes can selectively permeate water and organic solvents by utilizing the difference in adsorptivity depending on the type of zeolite, so select the type of zeolite and select a specific organic solvent from a mixture of organic solvents. Separation according to the purpose, such as separation, is possible.

According to the separation method using an RO membrane or a PV membrane, there is an advantage that the energy required for the separation is smaller and the running cost of the separation is lower as compared with the conventional distillation method. Is being actively conducted.

As a method for producing a zeolite separation membrane, a method of immersing a substrate in a suspension of a sol or a gel and hydrothermally synthesizing the same as disclosed in Japanese Patent Publication No. 4-80726 is disclosed. No. 89714, a method of synthesizing a zeolite membrane by hydrothermally treating a sol or gel coated on the surface of a substrate in steam.
A method is known in which a base material is immersed in a dilute sol of a synthetic raw material and a zeolite membrane is formed on the base material by hydrothermal synthesis as disclosed in Japanese Patent Application Laid-Open No. H11-163,078.

A conventional zeolite membrane is synthesized by hydrothermal treatment using high alkali alumino-silica gel or sol as a raw material. The process of forming the zeolite membrane is such that a gel attached to a substrate crystallizes from an amorphous state into a zeolite membrane. There is also a model in which zeolite crystals generated in a reaction solution are deposited on a substrate to form a film. These zeolite membranes produced by the hydrothermal synthesis method are usually as thick as several tens to several hundreds of micrometers, and have a bridge structure with large voids in the membrane as shown in FIG.

The reason that a zeolite membrane having a bridge structure is formed is that many crystal nuclei are generated in a reaction solution and settle on a substrate, and a large volume decrease occurs when a gel is crystallized. Conceivable. A zeolite membrane having a bridge structure (void) in the membrane has a drawback that the strength of the portion of the bridge structure is weak and the working pressure is inferior. Further, when the film thickness is as thick as several tens to several hundreds μm, there is a problem that the permeation flux is small. Such a zeolite membrane is not suitable for an RO membrane, and there is no report that a zeolite membrane was used for an RO membrane at present.

JP-A-7-109116 discloses a method for producing a zeolite membrane in which these disadvantages are improved. That is, a zeolite seed crystal is suspended in a dilute silica sol solution to form a slurry, and this slurry is impregnated into an alumina substrate to allow the zeolite crystal to adhere, and then the substrate is washed and dried if necessary. This substrate is immersed in a reaction solution containing a zeolite precursor and hydrothermally synthesized, and a zeolite film is formed on the substrate using the attached zeolite crystals as nuclei.

In this hydrothermal synthesis method of zeolite, the generation of crystal nuclei in the reaction solution containing the zeolite precursor and the growth of zeolite crystals by-produced can greatly reduce the generation of zeolite crystals by-products. It is said that a dense zeolite membrane with few boundaries can be formed. The higher the degree of supersaturation of the reaction solution, the more easily the crystal nuclei are generated. If the degree of supersaturation of the reaction solution is high, the crystal growth of zeolite is suppressed. When the supersaturation degree of the reaction solution is lowered, the generation rate of crystal nuclei can be reduced by an order of magnitude, and zeolite can easily grow.Therefore, by growing a seed crystal previously attached to the base material, it is dense and has few crystal grain boundaries. It is stated that a zeolite membrane composed of a zeolite crystal layer can be hydrothermally synthesized.

[0009] However, there is no specific data in Examples or the like regarding the structure and characteristics of the zeolite membrane obtained in JP-A-7-109116. Although specific film forming conditions according to the examples are unknown,
It is stated that a film is formed in a reaction solution having a small degree of supersaturation. In this case, even if the degree of supersaturation is small, the reaction solution is supersaturated, and crystal nuclei are also generated in the reaction solution to grow zeolite crystals. This is apparent from the illustration of a flow sheet in which zeolite crystals generated in a reaction solution during hydrothermal synthesis are separated and used as seed crystals. Therefore, the formation of a bridge structure in the zeolite membrane cannot be sufficiently prevented by the method described in JP-A-7-109116.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a zeolite separation membrane which has a high withstand voltage, is excellent in separation performance, and can be used as an RO membrane, and a method for producing the zeolite membrane formed on a substrate. It is in.

[0011]

The zeolite separation membrane of the present invention comprises a dense zeolite crystal membrane having a thickness of 0.5 to 30 μm adhered on a porous substrate. Is characterized by having a withstand voltage of 1.0 MPa or more.

[0012] A zeolite membrane excellent in adhesion with a working pressure of 1.0 MPa or more has not been known so far. As described above, the zeolite membrane having excellent adhesiveness, that is, excellent working pressure,
It can be formed only by using a thin raw material solution for hydrothermal synthesis in which a part of the seed crystal disappears and another seed crystal grows at the beginning of hydrothermal synthesis. In the zeolite membrane synthesized under these conditions, the zeolite seed crystal grows on the porous substrate, and the zeolite crystals and the zeolite crystal and the porous substrate come into close contact with each other. Depending on the average pore size of the porous substrate used, if a zeolite seed crystal having a pore size of 8 times or less the average pore size of the porous substrate is used during hydrothermal synthesis, dense Zeolite crystal film.

If the thickness of the zeolite membrane is too large, it takes a long time to synthesize, and if the hydrothermal synthesis is performed for a long time or repeatedly, the cost of the zeolite separation membrane increases and the permeation performance decreases. Therefore, the thickness of the zeolite membrane is set to 30 μm or less. The thickness of the zeolite membrane is preferably 1 to 10 μm.

In the present invention, the working pressure of the zeolite separation membrane means the working pressure when a pressure is applied from the side where the zeolite membrane is formed toward the porous substrate. In order for the zeolite crystals of the zeolite membrane to cover the surface of the porous substrate without gaps, the zeolite seed crystal must be attached to one surface of the surface of the porous substrate.

When the zeolite membrane is thinner than 0.5 μm, the working pressure is inferior. However, in the zeolite membrane in which the zeolite crystal is formed thicker than 30 μm, a bridge (void) is easily formed in the zeolite membrane, and the zeolite membrane is formed. Pressure resistance may be impaired. By setting the thickness of the zeolite separation membrane in the range of 0.5 to 30 μm, it is possible to provide a zeolite separation membrane having relatively low cost and excellent separation performance. The thickness of the zeolite membrane is preferably 1 to 10 μm so that a good pressure resistance can be obtained stably. A dense zeolite membrane refers to a membrane in which no discernible void is found in the membrane when the cross section thereof is examined at a magnification of 500 times with a scanning electron microscope (SEM).

The method for producing a zeolite separation membrane of the present invention comprises:
On the surface of the porous substrate, the average pore diameter of the porous substrate is 0.4.
A raw material solution in which a zeolite seed crystal having an average crystal grain size of ８8 times is adhered to one surface, and the porous substrate has a concentration of 1000 to 10000 ppm of a combination of Si and Al, and an alkali ion concentration of 10,000 to 60000 ppm. It is characterized in that it is immersed in and hydrothermally synthesized.

Prior to hydrothermal synthesis, zeolite seed crystals are
The average crystal grain size of the zeolite seed crystal is set to be 0.4 to 8 times the average pore diameter of the porous substrate because it is easy to uniformly adhere to the porous substrate over the entire surface. The average crystal grain size of the zeolite seed crystal is preferably 0.5 times the average pore size of the porous substrate.
Up to three times. When a seed crystal that is too fine is used, the seed crystal penetrates into the substrate, and the attachment of the seed crystal becomes uneven. If the seed crystal is too large, it is difficult to attach the seed crystal on the porous substrate. The method of attaching the seed crystal to the base material includes rubbing the dried zeolite crystal powder on the porous base material, applying a dispersion liquid in which the seed crystal is dispersed in water, or coating the base material in the dispersion liquid. There is a method such as immersion.

After the seed crystal is attached to the entire surface of the porous substrate, the porous substrate is immersed in a raw material solution to perform hydrothermal synthesis. For hydrothermal synthesis, the combined concentration of Si and Al is 10
A dilute raw material solution having an alkali ion concentration of 10,000 to 60,000 ppm is used. If the combined concentration of Si and Al is less than 1000 ppm, the growth rate of zeolite crystals is extremely slow, and it is difficult to form a zeolite film having a preferable thickness.

Further, when the combined concentration of Si and Al is 1000
If it exceeds 0 ppm, the raw material solution becomes supersaturated, crystal nuclei of zeolite are generated in the raw material solution, and the zeolite membrane formed by depositing zeolite crystals grown in the raw material solution on the base material is heterogeneous. Becomes a bridge in the film
And it is difficult to obtain a separation membrane having a high withstand voltage. As the alkali ion concentration increases, the combined concentration of Si and Al can be increased, and a practical zeolite crystal growth rate can be ensured.
0 ppm or more. However, if the alkali ion concentration is too high, the rate at which the zeolite crystals dissolve in the raw material solution increases, and crystal growth does not proceed.

The concentrations of silica, alumina and alkali in the raw material solution must be such that the growth of the seed crystal is given the highest priority. The raw material solution is used in the hydrothermal synthesis system in which the base material is placed. The zeolite crystals must be largely saturated. The composition of the raw material solution satisfies this condition, and no bridges (voids) are generated in the zeolite membrane formed by using the raw material solution having this configuration.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As the porosity of the porous substrate is small, the permeability of the separation membrane is reduced and the effective membrane area of the zeolite membrane is also reduced, so that the porosity of the porous substrate is 10% or more. Preferably it is. Further, if the porosity of the porous substrate is too large, the strength of the substrate itself is reduced and the withstand pressure of the zeolite membrane is reduced. Therefore, the porosity of the porous substrate is preferably 50% or less. The more preferable porosity of the substrate is 3
0 to 40%.

The shape of the porous substrate is not particularly limited as long as a zeolite membrane can be formed on the surface thereof, and may be a thin plate, a tube, a pellet, a hollow fiber, a honeycomb, or the like. As a method for producing these substrates, a press molding method, an extrusion molding method, a slurry casting method, or the like is employed according to a desired shape. It is of course possible to use a substrate having a multilayer structure. In this case, for example, a substrate obtained by laminating a second substrate layer on the first substrate layer by dip coating, spin coating, or the like may be used.

As the porous substrate, various ceramic substrates such as alumina, mullite, zirconia, and cordierite, and porous metals obtained by sintering stainless steel powder can be used. Since alumina is particularly excellent, alumina ceramics is preferred as the porous substrate. The average pore diameter of the porous substrate is
If it is too small, it is difficult to attach seed crystals, so 0.05 μm
It is preferable that this is the case. On the other hand, if the size is too large, the seed crystal enters the porous substrate and the attachment of the seed crystal becomes uneven, so that the average pore diameter of the porous substrate is preferably 10 μm or less. A more preferable average pore diameter is 0.1 to 5 μm.

The working pressure for applying a fluid pressure from the side of the zeolite separation membrane where the zeolite membrane is formed is 1.0 M
It can be used as a separation membrane at a pressure of Pa or more.
If the working pressure is 1.0MP or more, the zeolite separation membrane of the present invention can be used also for an RO membrane which was conventionally considered to be unusable because the working pressure was low. As the RO film, it is preferable to use a high withstand voltage.
Further, it is preferable to use a separation membrane having a working pressure of 2 MPa or more. Other applications of zeolite separation membranes include nanofiltration membranes, gas separation membranes, separation membranes such as PV membranes, and can be used for gas sensors. As the nanofiltration membrane, a membrane having a large working pressure is suitable.

The zeolite crystals include those having a large alumina / silica molar ratio such as A-type and Y-type, and ZSM-type.
-5, there are hydrophobic substances such as silicalite having a low alumina / silica molar ratio. There is also a zeolite crystal in which an element such as Fe, Cr, or Y is introduced at a location of Al in the zeolite crystal. For the zeolite membrane, it is preferable to select a zeolite crystal of a type suitable for the purpose of use from these. In this case, if the hydrothermal synthesis conditions are adjusted using a target type of zeolite seed crystal as the seed crystal,
A zeolite separation membrane composed of a single type of zeolite crystal can be manufactured.

In a preferred zeolite separation membrane of the present invention,
An alumina substrate is used as the porous substrate so that the adhesion strength of the zeolite membrane is increased. The reason why the adhesive strength of the zeolite membrane increases when using an alumina base material is as follows.
It is estimated that the interatomic distance in the alumina crystal is close to the interatomic distance in the zeolite crystal.

If the amount of seed crystals attached to the substrate surface is small, it is difficult to form a dense zeolite membrane, and if it is too large, voids are likely to be formed in the film. Is preferably 0.2 to 3 mg / cm ² . The more preferable amount of the zeolite seed crystal deposited on the substrate surface is 0.3 to 1 mg / cm ² .

As a starting material for the raw material solution, silica sol, water glass, and sodium silicate can be used as a silica source, sodium aluminate, aluminum nitrate, and aluminum hydroxide can be used as an alumina source, and sodium hydroxide and carbonate can be used as an alkali source. Sodium or the like can be used.
Further, a crystallization agent such as tetrapropylammonium bromide or tetrapropylammonium hydroxide may be mixed with the raw material solution.

In the hydrothermal synthesis of the zeolite membrane, the zeolite membrane is usually heated to 80 to 250 ° C. in a sealed state in a pressure vessel or in a vessel under normal pressure equipped with a cooler shown in FIG.
Hold for ~ 180 hours. After hydrothermal synthesis, the zeolite-formed substrate is washed with water and then dried. When a thermally decomposable component such as a crystallization accelerator is added, it is then heat-treated to remove it. When the hydrothermal synthesis of the zeolite membrane does not achieve the desired performance only once, the separation performance may be improved by repeating the hydrothermal synthesis a plurality of times to grow the zeolite crystals and fill the crystal grain boundaries.

[0030]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 In a room at about 20 ° C., sodium silicate, aluminum hydroxide, and sodium hydroxide were dissolved in water purified by a reverse osmosis method (hereinafter referred to as reverse osmosis water).
The molar ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ and H ₂ O is 9
0: 1: 9: 5760 raw material solution (Al 608 pp
m, Si 2710 ppm and Na 40300 ppm). Alumina base material (A) having a porosity of 38%, an average pore diameter of 1 μm (pore diameter having an integrated pore volume of 50% by a mercury porosimeter), a thickness of 3 mm and a diameter of 47 mm
(99.9% by weight of l ₂ O ₃ ) with an average crystal grain size of 1 μm
A type zeolite seed crystal was directly rubbed and adhered to the substrate surface.

On the surface of this substrate, about 0.6 mg
/ Cm ² of seed crystal was attached. Next, this base material was inserted into a hydrothermal synthesis vessel having the structure shown in FIG. 3 filled with the raw material solution, immersed in the raw material solution, heated to 80 ° C. under normal pressure while stirring at 100 rpm, and held for 5 hours. A zeolite membrane was formed on an alumina substrate. Next, the substrate was taken out of the container, washed and dried to obtain a zeolite separation membrane.
After 5 hours from the start of the hydrothermal synthesis, a part of the raw material solution was taken out and analyzed. As a result, Al553 ppm, Si28
70 ppm and Na 42200 ppm. Further, the raw material solution after the hydrothermal synthesis was filtered, but almost no filtrate remained on the filter paper.

When the surface of the obtained zeolite separation membrane was observed with a scanning electron microscope (SEM), cubic crystals were formed uniformly on the surface of the substrate. As a result of examination by X-ray diffraction, it was found that the zeolite membrane was composed only of A-type zeolite. Cross section of zeolite membrane by SEM
As a result, the bridge structure (void) was not found in the zeolite membrane, and the zeolite membrane was dense. Further, the thickness of the zeolite membrane was about 6.3 μm. FIG. 1 is a schematic view of a cross section of a dense zeolite separation membrane having a large working pressure and manufactured in Example 1. The working pressure of this zeolite membrane was 6 MPa or more as described later.

Example 2 Using the same raw materials as in Example 1, a suspension having a molar ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ and H ₂ O of 3.2: 1: 2.5: 156 was used. A turbid solution was prepared, and a filtered solution (610 ppm of Al, 2720 pp of Si)
(including 38,400 ppm of m, Na) was used for the raw material solution, and hydrothermal synthesis was performed under the same conditions as in Example 1 except for the above. S
As a result of examination by EM and X-ray diffraction, the synthesized zeolite membrane was composed of only A-type zeolite crystals, was dense, had a thickness of about 6.5 μm, and had a withstand pressure of 5 MPa. After 5 hours from the start of the hydrothermal synthesis, a part of the raw material solution was taken out and analyzed.
ppm and 35700 ppm of Na. In addition, the raw material solution after the hydrothermal synthesis was filtered, but the filtrate hardly remained on the filter paper, and could not be examined by X-ray diffraction.

[Examples 3 and 4] A zeolite separation membrane (Example 3) was obtained by hydrothermal synthesis under the same conditions as in Example 1 except that the hydrothermal synthesis conditions were 90 ° C. for 5 hours in Example 1. Was.
Further, the operation of applying a seed crystal in the same manner on the zeolite separation membrane obtained in Example 3 and performing hydrothermal synthesis under the same conditions is added twice (total of three times) to obtain a zeolite separation membrane (Example 3). 4) was obtained. As a result of examining these by SEM and X-ray diffraction,
A dense zeolite membrane consisting of only A-type zeolite crystals was formed on the substrate. The thicknesses of the zeolite membranes formed on the substrate were about 7.7 μm and about 8.9 μm, respectively, and the working pressure was 6 MPa or more.

Example 5 In Example 1, SUS304 powder was sintered on a porous substrate, and a porous metal having a porosity of 30% and an average pore diameter of 15 μm was used. Hydrothermal synthesis was performed under the same conditions to obtain a zeolite separation membrane having a zeolite membrane thickness of 5.3 μm. The working pressure of this zeolite separation membrane was 6 MPa or more as described later.

COMPARATIVE EXAMPLE 1 Using the same raw material as in Example 1, a suspension having a molar ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ and H ₂ O of 3.2: 1: 2.5: 78 was used. A turbid solution was prepared, and a filtered solution (752 ppm of Al, 10200 pp of Si)
m, Na was used for the raw material solution, and hydrothermal synthesis was performed under the same conditions as in Example 1 except for the above. S
As a result of examination by EM and X-ray diffraction, A
The type zeolite seed crystal hardly grows, the formed film having a thickness of about 15 μm is not dense, and the working withstand voltage is 0.
It was 8 MPa or less. It was confirmed that a small amount of faujasite was mixed in this film. Further, when the raw material solution after the hydrothermal synthesis was filtered, faujasite was detected in the filtrate remaining on the filter paper.

Comparative Examples 2 and 3 In Comparative Example 1, the conditions for hydrothermal synthesis were 10 hours at 80 ° C. (Comparative Example 2) and 5 hours at 100 ° C. (Comparative Example 3). Hydrothermal synthesis was performed under the same conditions as in Example 1 to form a zeolite membrane on the substrate. As a result of examination by SEM and X-ray diffraction, the A-type zeolite crystal applied to the surface of the substrate hardly grew in any case, and the formed zeolite membrane having a thickness of about 15 μm was not dense, and the withstand voltage in use was It was 0.8 MPa or less. It was confirmed that a small amount of faujasite crystals were mixed in this film. Further, when the raw material solution after the hydrothermal synthesis was filtered, faujasite crystals were detected in the filtrate remaining on the filter paper.

[Comparative Examples 4 and 5] Using the same raw materials as in Example 1, supersaturated raw materials having a molar ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ and H ₂ O of 2: 1: 2: 120 Solution (Al 25
000 ppm, 25900 ppm of Si, 426 ppm of Na
And the hydrothermal synthesis conditions were adjusted to 100
The hydrothermal synthesis was performed under the same conditions as in Example 1 except that the temperature was 3.5 hours at 5 ° C. (Comparative Example 4) and the temperature was 100 hours at 100 ° C. (Comparative Example 5). As a result of examining the obtained separation membrane by SEM and X-ray diffraction, the A-type zeolite crystal applied to the surface of the substrate hardly grew in any case, and the thickness of the formed membrane was about 70 μm. The zeolite membrane was not dense, and it was recognized that a gel-like substance was present in the gaps between the seed crystals. The working pressure of this zeolite membrane was 0.8 MPa or less. Further, the raw material solution after the hydrothermal synthesis was filtered, and the filtrate after washing and drying was examined by X-ray diffraction. As a result, the presence of A-type zeolite and faujasite was recognized.

Comparative Example 6 Hydrothermal synthesis was performed under the same conditions as in Comparative Example 5 except that the hydrothermal synthesis conditions were set to 80 ° C. As a result of examining the obtained separation membrane by SEM and X-ray diffraction, in each case, the A-type zeolite crystals applied to the surface of the substrate hardly grew, and the formed zeolite membrane was about 50 μm in thickness. It was not dense and it was recognized that a gel-like substance was present in the gaps between the seed crystals. The working pressure of this zeolite membrane was 0.8 MPa or less.
Further, the raw material solution after the hydrothermal synthesis was filtered, and the filtrate after washing and drying was examined by X-ray diffraction. As a result, the presence of A-type zeolite and faujasite was recognized.

Comparative Example 7 A supersaturated material having the same molar ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ and H ₂ O as 1: 0.5: 1: 60 using the same raw material as in Example 1. Solution (Al 25
000 ppm, 25900 ppm of Si, 426 ppm of Na
And hydrothermal synthesis conditions at a temperature of 10
Hydrothermal synthesis was carried out under the same conditions as in Example 1 except that the temperature was changed to 0 ° C. for 3 hours to obtain an A-type zeolite separation membrane having a zeolite membrane thickness of 30 μm. This separation membrane, as described below,
The working pressure was 0.8 MPa.

Comparative Example 8 Using the same raw materials as in Example 1, a raw material solution having a molar ratio of Na ₂ O, Al ₂ O ₃ , SiO ₂ and H ₂ O of 1: 0.5: 1: 120 ( 12500 Al
ppm, Si 13000ppm, Na 21000p
pm), and the hydrothermal synthesis was performed under the same conditions as in Example 1 except that the hydrothermal synthesis was performed at a temperature of 100 ° C. for 3 hours, and the zeolite membrane had a 30 μm-thick A-type zeolite separation membrane. I got The working pressure of this separation membrane was 0.9 MPa as described later.

From the results of the above hydrothermal synthesis test, Si and A
l is 1,000 to 10,000 ppm, and the alkali ion concentration is 10,000 to 60,000 pp.
When a porous substrate coated with a seed crystal on one side is immersed in a raw material solution of m and hydrothermal synthesis is performed, a zeolite separation membrane in which a dense zeolite membrane adheres to the surface of the porous substrate can be manufactured. I understand. Further, in the embodiment of the zeolite membrane according to the present invention, Al and Si concentrations in the raw material solution hardly change at least at the initial stage of hydrothermal synthesis, and Al and Si in the raw material solution are consumed to form the zeolite membrane. Therefore, it is considered that the seed crystal mainly applied to the substrate was used for forming the zeolite membrane.

Test Example 1 An RO separation test was performed using the zeolite separation membrane produced in Example 1 stored in reverse osmosis water. That is, using the apparatus having the configuration shown in FIG.
Was used as a feed solution, and the effect of concentration polarization on the membrane surface was suppressed while stirring at 100 rpm. The operating pressure was increased to a maximum of 8 MPa, the evaporation of ethanol was prevented using a cold trap on the permeate side, and the concentrations of the feed solution and the permeate were measured by gas chromatography.

The concentration of ethanol on the supply side was changed to Cf (% by weight).
When the ethanol concentration on the permeation side is Cp (% by weight), the apparent rejection ratio Robs is expressed as Robs = (Cf−C
p) / Cf. The results of the RO test at an operating pressure of 1.5 MPa are shown in FIG. As shown in FIG. 5-a, immediately after the start of the test, the rejection was high due to the mixing of water contained in the base material, but it gradually decreased and reached a steady state after 60 hours. With this zeolite separation membrane, it was found that RO separation was possible with a rejection of 40% or more from a 10% by weight aqueous ethanol solution at an operating pressure of 1.5 MPa. FIG. 5-b shows the change over time of the permeation flux, but no change over time was observed.

FIG. 6 shows the change over time of the permeation flux (Flux) and the rejection when the operating pressure was increased to 4, 6, and 8 MPa.
Shown in As can be seen from FIG.
Even when the pressure was increased to Pa, the membrane structure was stable, and the permeation flux and rejection did not change over time even after 50 hours, and a rejection of about 20% was obtained with a 10% by weight aqueous ethanol solution. This R
The O-separation membrane exhibited stable performance up to 10 hours even at an operating pressure of 8 MPa, but after 20 hours, the permeation flux increased sharply, impairing the blocking performance. This R after the test
Cracks having a width of about 0.2 μm were observed on the surface of the O-separation membrane, and cracks were also observed on the cross section of the membrane.

Further, the zeolite separation membrane produced in Example 5 and the zeolite separation membrane produced in Comparative Examples 7 and 8 were each subjected to an RO separation test. The zeolite separation membrane produced in Example 5 showed stable separation performance similarly to the zeolite separation membrane of Example 1 even when the pressure of 6 MPa was applied for 50 hours. On the other hand, when the zeolite separation membranes produced in Comparative Examples 7 and 8 were respectively increased in pressure to 0.8 MPa and 0.9 MPa, the transmittance increased sharply and the separation membranes were broken. Cracks were observed in each of the damaged zeolite separation membranes by SEM observation.

Test Example 2 A PV separation test was performed using the zeolite separation membranes produced in Examples 3 and 4. That is, using a device having the configuration shown in FIG. 7, in a thermostat at 30 ° C., the supply liquid was a 0 to 90% by weight aqueous ethanol solution, and the concentrations of the supply liquid and the permeate were measured by gas chromatography. When the molar concentrations of ethanol and water on the supply side are X ₁ mol% and X ₂ mol%, respectively, and the molar concentrations of ethanol and water on the permeation side are Y ₁ mol% and Y ₂ mol%, respectively, the separation coefficient α is α = (X ₁ · Y ₂ ) / (X ₂ · Y ₁ ). FIG. 8 shows the obtained results. FIG.
As can be seen from -a, in the PV separation test using the zeolite separation membrane of Example 4, a high separation performance of about 400 was obtained when a 90% by weight aqueous ethanol solution was used as a feed solution. FIG. 8-b shows the permeation flux.

[0049]

According to the present invention, it is possible to provide a zeolite separation membrane that is dense, thin, and has a high working pressure. Since the zeolite separation membrane according to the present invention has a high working pressure, it is also suitable for use in RO membranes and nanofiltration membranes that were not suitable with conventional zeolite separation membranes. Such a zeolite membrane having a high withstand pressure has a seed crystal adhered to the entire surface of the porous substrate, and at least at the initial stage of hydrothermal synthesis, the seed crystal is mainly used for forming the zeolite membrane. It can be formed by using a thin raw material solution.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of a zeolite separation membrane according to the present invention.

FIG. 2 is a schematic view showing a cross section of a conventional zeolite separation membrane.

FIG. 3 is a sectional view showing an outline of a hydrothermal synthesis apparatus used in an example of the present invention.

FIG. 4 is a schematic diagram of a reverse osmosis separation device used in a test example of the present invention.

FIG. 5 is a graph showing the change over time of the permeation flux and the apparent rejection ratio Robs when the zeolite separation membrane of the present invention is used for reverse osmosis separation.

FIG. 6 shows the permeation flux and apparent rejection Rob when the pressure is changed using the zeolite separation membrane of the present invention for reverse osmosis separation.
Graph showing change over time of s

FIG. 7 is a schematic diagram of a pervaporation separation apparatus used in a test example of the present invention.

FIG. 8 is a graph showing permeation flux and separation coefficient α when the zeolite separation membrane of the present invention is used for pervaporation separation.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-59-213615 (JP, A) JP-A-61-107902 (JP, A) JP-A-6-321530 (JP, A) JP-A-5-213 105420 (JP, A) JP-A-7-109116 (JP, A) JP-A-6-99044 (JP, A) JP-A-7-89714 (JP, A) JP 4-80726 (JP, B2) (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 67/00-71/82 510 C02F 1/44 C01B 33/20-39/54

Claims (6)

(57) [Claims] 1. A dense zeolite crystal film having a thickness of 0.5 to 30 .mu.m is formed on a porous substrate in close contact with each other, and has a withstand pressure of 1.0 MPa or more as a separation film. Zeolite separation membrane. 2. The zeolite separation membrane according to claim 1, wherein the porosity of the porous substrate is 10 to 50%, and the average pore diameter is 0.05 to 10 μm. 3. The zeolite separation membrane according to claim 1, wherein the porous substrate is made of alumina. 4. The zeolite separation membrane according to claim 1, wherein the zeolite separation membrane is for a reverse osmosis membrane or a nanofiltration membrane. 5. After a zeolite seed crystal having an average crystal grain diameter of 0.4 to 8 times the average pore diameter of the porous substrate is adhered to the entire surface of the porous substrate, the porous substrate Materials are Si and A
l is 1,000 to 10,000 ppm, and the alkali ion concentration is 10,000 to 60,000 pp.
A method for producing a zeolite separation membrane, characterized in that it is immersed in a raw material solution of m and hydrothermally synthesized. 6. The method for producing a zeolite separation membrane according to claim 5, wherein a zeolite seed crystal of 0.2 to 3 mg / cm ² is attached to the surface of the substrate.