JPH08299904A - Inorganic porous membrane and its production - Google Patents

Abstract

PURPOSE: To produce a porous inorg. membrane free of such defects as pinholes and cracks by using a colloidal particle formed from a sol wherein a metal polyoxide and the colloidal particle are dispersed and obtained by the hydrolysis of urea as a compositional component. CONSTITUTION: The coating soln. for forming an inorg. porous membrane consists of a sol wherein >=1 kind among the colloidal particles of metal polyoxide and metal polyhydroxide and dispersed, and the colloidal particle is obtained by the hydrolysis of urea in a metallic salt compd. soln. contg. urea. The colloidal particle has <=10nm diameter. Meanwhile, the inorg. porous membrane is formed by subjecting the coating soln. to gelation, drying the gel to form a film and calcining the film. The average pore diameter of the calcined body is preferably controlled to <=0.1μm and the amt. of pure water to be permeated to <=1×10<-4> l/min.M<2> Pa. The coating soln. is subjected to gelation, dried and calcined to produce the inorg. porous membrane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating solution for forming an inorganic porous film, an inorganic porous film and a method for producing the film. The inorganic porous membrane can be used for various membrane separation operations. In particular, those having an average pore diameter of less than 0.1 μm and those having a cut-off molecular weight of several hundred thousand or less are suitably used for various membrane separation operations.

[0002]

2. Description of the Related Art Among inorganic porous membranes, the average pore diameter is 0.1 μm.
Films of m or less are generally formed by the sol-gel method.

In this method, a sol composed of metal oxide particles is prepared by deflocculating a gel produced by hydrolysis of a metal alkoxide or the like with nitric acid or the like. A binder, a plasticizer and the like are added to this sol to prepare a sol liquid for coating a filtration membrane.

Using this sol solution for coating, a gel film is supported by forming a gel layer on a support having a single-layer or multi-layer structure by concentration polarization on the surface of the support.

A porous membrane can be obtained by drying and firing the thus-supported gel layer.
The above-described series of steps of drying and firing were repeated a plurality of times to manufacture a defect-free filtration membrane.

[Problems to be Solved by the Invention]

[0006] As a method for producing a filtration membrane by the above method,
There is one disclosed in Japanese Examined Patent Publication No. Sho 63-36808, but the particle size of the sol particles of the sol liquid for the filtration membrane coating used is not uniform, and defects such as cracks are likely to occur during the filtration membrane manufacturing process . The reason for this is considered that in this method, the metal alkoxide is hydrolyzed, and once gelled, it is deflocculated to form a sol.

Japanese Patent Publication No. 39652/1993 also shows a filtration membrane obtained by using a sol prepared by the same method, but defects are likely to occur for the same reason as above. It is noted in the same publication that the gel must be dried completely or partially under supercritical conditions in order to obtain a crack-free film.

Further, Japanese Patent Laid-Open No. 5-238845 discloses a method of obtaining uniform fine particle alumina sol by performing hydrolysis at a temperature of 80 ° C. or lower. However, after hydrolysis, the liquid is suspended. In this case, it can be said that there is still a problem in the uniformity of particles, as can be seen from the fact that a step of separating large particles partially generated by centrifugation is required.

In the conventional sol production method in which a metal alkoxide is hydrolyzed and then peptized with an acid or the like, hydrolysis occurs at the same time when water is added to the alkoxide. That is, it is difficult to carry out the hydrolysis uniformly over the entire reaction system, and it is difficult to suppress an undesirable phenomenon such as the formation of a gel precipitate in a part of the sol. Therefore, since the gel thus produced must be deflocculated with an acid to synthesize a sol, it is considered that the uniformity of the molecular weight, particle size, concentration, etc. of the sol is low.

Therefore, when the film thickness of the coating sol liquid becomes too thick when forming the ultrafiltration membrane, defects such as cracks are likely to occur by the end of firing, so that a membrane sufficient as the ultrafiltration membrane is obtained. In order to obtain the thickness, a series of steps of coating a thin film of a sol liquid on a support, which does not cause cracks by the end of firing, gelling, drying and firing, is repeated three times or more. There was a need. In addition, it was necessary to strictly control the drying conditions (constant temperature and humidity), and this method was industrially low in completeness.

In short, in the conventional sol synthesis method utilizing hydrolysis of metal alkoxide, it is difficult to control hydrolysis and it is difficult to synthesize a sol having dispersed particles of uniform diameter. As a result, the maximum thickness of the porous film that can be produced without defects such as cracks and peeling was extremely thin, and defects such as pinholes were involved. Therefore, in order to eliminate defects such as pinholes, further cracks on the surface of the porous film,
It was necessary to stack two or more porous films without defects such as peeling to increase the film thickness. That is, the series of steps of coating the sol, gelling, drying and baking had to be repeated three times or more.

In addition, in some cases, it is necessary to strictly control the drying conditions (constant temperature and humidity) in order to prevent defects such as cracks in the film.

One of the objects of the present invention is to provide a novel coating solution for forming an inorganic porous film, an inorganic porous film and a method for producing an inorganic porous film.

Another object of the present invention is to provide a coating solution for forming an inorganic porous film, an inorganic porous film, and a method for producing an inorganic porous film, which solve the above-mentioned problems of the prior art.

[0015]

According to the present invention, the above problems can be solved by the following coating liquid for forming an inorganic porous film, an inorganic porous film and a method for producing an inorganic porous film.

A sol in which one or more colloidal particles of polymetal oxide and polymetal hydroxide are dispersed, and the colloidal particles are obtained by hydrolysis of urea in a metal salt compound solution containing urea. Coating liquid for forming an inorganic porous film, which is a particle (claim 1).

An inorganic sol characterized by being composed of a sol in which one or more colloidal particles of polymetal oxide and polymetal hydroxide are dispersed, and the colloidal particles are fine particles having an average particle diameter of 10 nm or less. Coating liquid for forming a porous film (claim 2).

An inorganic porous film which is a fired product of a dried film of a gelled product of the coating liquid for forming an inorganic porous film (claim 3).

The fired body preferably has an average pore diameter of less than 0.1 μm and a pure water permeation amount of 1 × 10 ⁻⁴ l / min.
・ M ² · Pa or less (claim 4).

A method for producing an inorganic porous film, wherein a coating film of the coating liquid for forming the inorganic porous film is gelled, dried and baked (claim 5).

Preferably, a series of steps of gelling, drying and baking the coating film is included twice or less (claim 6).

Preferably, the concentration of the colloidal particles in the coating solution is 0.5-0.5 in terms of metal oxide obtained by firing.
3% by weight (claim 7).

Preferably, the firing is carried out at a temperature of 400 to 1000 ° C. (claim 8).

[0024]

Preferred Embodiment

(Coating Liquid for Forming Inorganic Porous Film) The coating liquid of the present invention comprises a sol in which one or more of polymetal oxide colloidal particles and polymetal hydroxide colloidal particles are dispersed in a dispersion medium. The colloidal particles are particles obtained by hydrolysis of the urea in a metal salt compound solution containing urea, or fine particles having an average particle diameter of 10 nm or less.

The colloidal particles of polymetal oxide and polymetal hydroxide in the present invention are almost completely amorphous, but their crystallinity is not absent. That is, in general, the definitions of amorphous and crystalline are relative, and are classified according to the degree of amorphousness and crystallinity.
This is because there is no strict boundary based on numerical values. Further, the judgment is made by XRD (X-ray diffraction method), but even if it is judged from this result that it is amorphous, it cannot be absolutely asserted that it has no crystallinity.

Preferably, water such as pure water, a binder and a plasticizer are added to the sol. Thereby, the viscosity of the coating liquid and the concentration of the colloidal particles can be adjusted for coating.

That is, the binder and the plasticizer control the viscosity of the coating liquid and the speed at which the solvent is absorbed into the support (the support coated with the coating liquid) by capillary condensation, and the film after coating is adjusted. The property of can be maintained. The viscosity of the coating liquid is preferably 5 to 200 mPa · s.

The particle concentration is adjusted to control the film thickness. As the binder, an organic binder (especially one that can be extinguished by heating), for example, PVA (polyvinyl alcohol), polyethylene glycol, methyl cellulose or the like can be appropriately used.

As the plasticizer, for example, glycerin can be used, and polyalkylene glycols,
Polyoxyalkylene glycols can also be used.

The concentration of the binder in the coating liquid is preferably 0.5 to 10% by weight, and the concentration of the plasticizer is preferably 1 to 10% by weight.

The above-mentioned specific sol in which one or more of the polymetal oxide colloidal particles and the polymetal hydroxide colloidal particles are dispersed in the dispersion medium can be prepared, for example, by the method disclosed in JP-A-4-220468. It can be manufactured.

The nitric acid-stabilized inorganic oxide amorphous sol disclosed in the above publication corresponds to the sol specified in the present invention, and its manufacturing method is as follows.

The sol is stopped before the precipitation of the metal hydroxide is caused by the neutralization reaction utilizing the hydrolysis of urea, which is one of the so-called uniform precipitation methods and is represented by the following reaction formula. At the very least, the sol is kept in a sol state, and then the sol thus obtained is manufactured by removing impurity ions in the sol by an ultrafiltration device. (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ NH ₃ + H ₂ O → NH ₄ ⁺ + OH ⁻

That is, urea is added to and dissolved in a nitrate aqueous solution of aluminum, titanium, zirconium, tin, yttrium or the like. Then, this aqueous solution is stirred while being heated to 90 ° C. or higher, and the neutralization reaction is continued while hydrolysis of urea is performed. The pH of this aqueous solution is usually 2 or less at the initial stage of the reaction, but gradually rises as the reaction proceeds, and the reaction is stopped when the pH before precipitation occurs is 6 or less, preferably 5 or less. The metal salt concentration of the aqueous nitrate solution at this time is 0.01 to 3 mol / liter, preferably 0.02 to
It is 2 mol / liter, and if it is 3 mol / liter or more, the sol viscosity becomes high and handling becomes difficult. Further, the amount of urea added is 0.3 to 5 mole times, preferably 0.5 to 3 mole times, relative to the metal.

After cooling the sol thus obtained, it is passed through an ultrafiltration membrane to discharge the impurity ions in the sol together with water out of the system to wash and concentrate. The pore diameter (average pore diameter) of the ultrafiltration membrane used at this time is preferably 3 nm to 50 nm. If the concentration of impurity ions in the sol is still high even after concentration, the pure water is added to the sol and the washing and concentration steps are repeated, or the impurity ions are removed using an ion exchange resin. The sol concentration obtained by washing and concentration with an ultrafiltration membrane was 10 in terms of metal salt oxide.
It is about 20% by weight. Since a higher sol concentration is easier to handle as a component of the coating solution, nitric acid is added to this sol and the sol is heated at a temperature of 80 ° C. or lower, preferably 60 ° C. or lower, so that about 50% by weight in terms of oxide. It is also possible to concentrate up to.

Although the kind of the metal salt is not limited, a zirconia sol is preferable in view of coating strength and chemical stability, and a nitric acid-stabilized amorphous zirconia sol is particularly preferable.

A more detailed example is as follows. As a zirconium oxide, 30 kg of an 18% by weight zirconyl nitrate aqueous solution and 3 kg of urea were added to 200 liters of pure water. Next, this aqueous solution was heated and boiled for 6 hours to obtain a transparent zirconia sol. After cooling this sol to room temperature, it was introduced into an ultrafiltration device to obtain 10 parts of zirconium oxide.
Concentrated to wt%. Further, pure water was added to the sol after concentration to adjust the zirconia concentration before concentration, and the sol was again concentrated and washed using an ultrafiltration device. This diluting / concentrating / washing operation was repeated 5 times, and nitric acid was added to 10% by weight of zirconia sol as zirconium oxide after the 5th washing, and then the sol was heated and concentrated under vacuum at 50 ° C.
A weight percent transparent nitric acid stabilized zirconia sol was obtained.

In this sol, the pH was 1.5, the viscosity was 50 centipoise (cp), the colloidal particles were amorphous, the average particle size was 3 nm or less, and the sol was stable for a long time.

In the hydrolysis method from the urea-containing solution, the hydrolysis reaction of urea is utilized to synthesize the polymetal oxide or polymetal hydroxide, so that the reaction proceeds uniformly throughout the solution. Therefore, the synthesized sol is characterized in that the diameter of the dispersed colloidal particles is uniform and fine (10 nm or less). In particular, a nitric acid-stabilized amorphous sol, which has a transparent appearance and is composed of extremely fine amorphous particles having an average particle size of 3 nm or less, has an excellent binder effect and prevents the formation of precipitates.
It has the effect of preventing liquid phase separation and is preferably used.

When the coating solution of the present invention is used for producing an ultrafiltration membrane, the maximum particle size of colloidal particles is preferably 100 nm or less.

When a polyzirconium hydroxide sol (a sol in which colloidal particles of polyzirconium hydroxide are dispersed) is produced by the above method, it is as follows.

Urea is added and dissolved in a zirconyl nitrate solution which is a solution of a metal salt compound, and this aqueous solution is stirred while being heated to 90 ° C. or higher to carry out a neutralization reaction by hydrolysis of urea. The reaction is stopped before the pH at which hydroxide precipitation occurs. This makes it possible to obtain a polyzirconium hydroxide sol without going through a gel state.

A more detailed procedure for the synthesis of the sol is as follows.

Urea is added and dissolved in the zirconyl nitrate solution. Next, this aqueous solution is heated to 90 ° C. or higher and stirred,
Neutralization reaction is performed by hydrolysis of urea. The reaction is stopped before the precipitation of the metal hydroxide occurs (pH = 6 or less, preferably pH = 5 or less) to synthesize the sol.

After cooling the sol thus obtained, the impurities in the sol are removed by washing with an ultrafiltration membrane for washing and concentration. The sol is concentrated to 10% by weight (converted to zirconia), nitric acid is added, and then concentrated at 50 ° C. under vacuum.
By the above method, an aqueous dispersion of amorphous fine particles having a concentration of 25 to 30% by weight (converted to zirconia), a pH of 1 to 3, and an average particle size of 10 nm or less can be obtained.

Instead of the zirconyl nitrate solution, a solution (for example, an aqueous solution) of a metal salt (for example, nitrate) such as aluminum, titanium, tin, or yttrium is used. A substance or a hydroxide can be obtained.

(Inorganic porous film) The inorganic porous film of the present invention is a fired product of a dried film of a gelled product of the coating liquid for forming the inorganic porous film.

The inorganic porous film of the present invention has no cracks or pinholes and has a uniform pore size.

The fired body is preferably a metal oxide, for example, zirconia, titania, alumina or the like.

(Method for Producing Inorganic Porous Membrane) The coating film can be formed by applying the coating liquid of the present invention onto a support.

The coating amount of the coating liquid of the present invention on the support is preferably 3.8 × 10 ⁻⁴ g / per firing.
cm ² or less (more preferably 1.5 × 10 ⁻⁴ g / cm ²
The coating amount is such that an inorganic porous film (for example, a zirconia porous film) can be obtained with a density of (about).

As the support, a ceramic support having a single-layer or multi-layer structure can be used.

A preferred embodiment for producing an inorganic porous membrane that can be used as an ultrafiltration membrane is as follows.

When forming an inorganic porous membrane that can be used as an ultrafiltration membrane, the average pore diameter of the support (lower layer) on which the inorganic porous membrane (upper layer) is to be formed is preferably
It is 0.1 μm or less, and the coating liquid of the present invention is applied only to the portion of the support where the ultrafiltration membrane is to be formed, and the gel layer is supported by a known method.

After drying this gel layer in air,
By firing at 1000 ° C. to oxidize the binder, the deplasticizer and the gel, a ceramic ultrafiltration membrane, which is an inorganic porous membrane, can be obtained.

In this way, the pore diameter is 5 to several tens nm.
Thus, an ultrafiltration membrane having a thickness of at least several 100 nm can be formed.

The molecular weight cutoff (pore diameter) of the membrane can be controlled by adjusting either or both of the firing temperature and the firing time. By increasing the firing temperature, particles grow (the particle size increases) and the pore size can be increased. By increasing the firing time, particles grow (particle size increases), and the pore size can be increased.

[0058]

Example 30 g of an 18 wt% aqueous zirconyl nitrate solution as zirconia and 3 g of urea were added to 200 ml of pure water. Then, this aqueous solution was heated and boiled for 6 hours to obtain a transparent polyzirconium hydroxide sol. After cooling this sol to room temperature, it was introduced into an ultrafiltration device to obtain 10% by weight of zirconia.
Concentrated to. Further, pure water was added to the sol after the concentration to make the zirconia concentration before the concentration, and the sol was again concentrated and washed using an ultrafiltration device. This diluting / concentrating / washing operation was repeated 5 times, and nitric acid was added to the polyzirconium hydroxide sol concentrated to 10% by weight as zirconia after the 5th washing, and then the sol was heated under vacuum at 50 ° C., Concentration gave a 25% by weight transparent polyzirconium hydroxide sol.

PVA as a binder and glycerin as a plasticizer were added to this polyzirconium hydroxide sol,
1% by weight calculated by adding pure water and converting to the amount of zirconium oxide,
PVA was 3.5% by weight and glycerin was 5% by weight to obtain an ultrafiltration membrane coating solution (sol solution).

An alumina tubular support having an average pore diameter of 10 μm and an alumina membrane having an average pore diameter of 1 μm and 0.1 μm formed in this order were used as a support for coating the sol solution. After the outer surface was temporarily covered so that the coating solution (sol solution) did not touch the outer wall, the support was dipped in the coating solution and pulled up at a constant speed to carry a gel layer on the inner surface of the support. After drying this in air at room temperature for 24 hours, the temperature was raised in the air at a heating rate of 5 ° C./min using an electric furnace to 60
The mixture was kept at 0 ° C. for 2 hours for calcination to convert the deorganized component, zirconium hydroxide, to zirconium oxide to obtain a tubular filter medium having a zirconia ultrafiltration membrane formed on the inner wall of the tube.

The amount of pure water permeated through the alumina membrane of the support having the average pore diameter of 0.1 μm was 5 × 10 ^−5.
Since it is 1 / min · m ² · Pa, the pure water permeation amount of the tubular filtration material obtained after firing does not exceed the above value.

When the obtained filtration membrane was observed by SEM (scanning electron microscope), cracks and pinholes were not confirmed, and the membrane thickness was about 300 nm. The cut-off molecular weight of the tubular filter medium is polyethylene glycol (PE
It was about 15,000 in G). The fractionation performance was measured by filtering a mixed solution of PEG having various molecular weights and measuring the molecular weight at which the blocking rate was 95%.

The tubular filter material obtained by forming a zirconia-based ultrafiltration membrane by changing the sol particle concentration (concentration of colloidal particles in the sol), the number of coatings (the number of firings), and the firing temperature Table 1 shows the change in molecular weight cutoff and the presence or absence of defects (pillholes or cracks) in the zirconia ultrafiltration membrane. Even if this sol is used, if the particle concentration is too high, cracks occur, and if it is too low, film defects such as pinholes tend to occur, but the sol particle concentration should be within the proper range. Therefore, the occurrence of defects could be prevented. The appropriate range is about 0.5 to 3 in terms of weight concentration in terms of zirconia.
It was in the wt% range. The thickness of the coating film of the coating liquid was 0.7 μm or less.

[0064]

[Table 1]

The colloidal particles in the sol of the above embodiment are X
Although it can be judged as amorphous by RD (X-ray diffraction method),
It cannot be said that there is no crystallinity.

[0066]

The coating liquid for forming an inorganic porous film according to claims 1 and 2 comprises a sol in which one or more colloidal particles of polymetal oxide and polymetal hydroxide are dispersed. Is particles obtained by hydrolysis of the urea in a metal salt compound solution containing urea, or fine particles having an average particle size of 10 nm or less,
An inorganic porous film can be produced by gelating a coating film, drying it, and baking it. The produced inorganic porous membrane can be suitably used for various membrane separation operations.

That is, it is possible to produce an inorganic porous film free from defects such as pinholes and cracks even under the condition that a series of steps of coating, gelation, drying and firing of a coating film is performed only once.

For example, even under the above conditions, it became possible to form a film having a thickness of up to several hundreds of nanometers (nm) without defects. In particular, since the maximum thickness of the inorganic porous film obtained without defects such as cracks is large, even when producing an inorganic porous film having a thickness exceeding the maximum thickness, it is possible to reduce the number of times of repeating the series of steps. Can be manufactured.

Therefore, it is possible to save the energy consumed in the series of steps for manufacturing, for example, the energy during firing, and to shorten the manufacturing time.

Since the inorganic porous membranes of claims 3 to 4 are calcined bodies of dried membranes of the gelled product of the coating liquid for forming the inorganic porous membrane, they can be suitably used for various membrane separation operations.

In the method for producing an inorganic porous membrane according to claims 5 to 8, since the coating film of the coating liquid for forming the inorganic porous membrane is gelled, dried and baked, it can be suitably used for various membrane separation operations. It is possible to produce an inorganic porous membrane capable of Further, since strict control of drying conditions such as critical drying and constant temperature and constant humidity drying is not essential, it is suitable for industrial production.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C01B 13/32 C01B 13/32 C04B 35/622 C04B 35/00 D (72) Inventor Seiji Yamada Nagoya City, Aichi Prefecture Noritake Company Limited 1-336, Noritake Shinmachi, Nishi-ku

Claims (8)

[Claims] 1. A sol in which at least one of colloidal particles of polymetal oxide and polymetal hydroxide is dispersed, wherein the colloidal particles are hydrolyzed of urea in a metal salt compound solution containing urea. A coating liquid for forming an inorganic porous film, which is a particle obtained by 2. A sol in which at least one kind of colloidal particles of polymetal oxide and polymetal hydroxide is dispersed, and the colloidal particles are fine particles having an average particle size of 10 nm or less. A coating liquid for forming an inorganic porous film. 3. An inorganic porous film, which is a fired product of a dry film of a gelled product of the coating liquid for forming an inorganic porous film according to claim 1 or 2. 4. The fired body has an average pore size of less than 0.1 μm and a pure water permeation amount of 1 × 10 ⁻⁴ l / min · m ² · Pa.
The inorganic porous membrane according to claim 3, wherein: 5. A method for producing an inorganic porous film, which comprises gelling, drying and baking the coating film of the coating liquid for forming an inorganic porous film according to claim 1. 6. The method for producing an inorganic porous film according to claim 5, comprising a series of steps of gelling, drying and baking the coating film twice or less. 7. The inorganic porous film according to claim 5, wherein the concentration of colloidal particles in the coating liquid is 0.5 to 3% by weight in terms of metal oxide obtained by firing. Manufacturing method. 8. The method for producing an inorganic porous membrane according to claim 5, 6 or 7, wherein the firing is performed at a temperature of 400 to 1000 ° C.