JP3073258B2 - Porous inorganic 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 porous inorganic film having ultra-fine pores of several nm and having a porosity of more than 50%, and a method for producing the same. The present invention relates to a method typically used for producing a porous inorganic separation membrane capable of separating and removing ultra-fine particles, and a porous inorganic membrane produced by this method.

[0002]

2. Description of the Related Art Recently, a membrane separation operation performed by using an ultrafiltration membrane or a reverse osmosis membrane is taking an important position in the chemical industry, such as a seawater desalination system and a bioreactor. , Many actual devices at the plant level are already in operation.

An organic polymer membrane such as cellulose has been conventionally used as a separation membrane for such applications. However, as the field of application has expanded, application under more severe conditions has been required. I have. For example, in the fields of food industry and biotechnology, a separation membrane with high resistance to materials, which can withstand chemical cleaning and steam sterilization, is required. The polymer film has a problem that these requirements cannot be sufficiently satisfied.

On the other hand, apart from the above-mentioned organic polymer membrane, a separation membrane called a so-called ceramic filter has been conventionally known, and this separation membrane is subject to severe use conditions such as chemical resistance and high-temperature washing. It is expected to have a high resistance that can be used sufficiently even when required, and such ceramic filters conventionally known include, for example, a mixture of flammable substances such as ceramic raw material powder and carbon. There are known those which are formed and sintered, and those which use a porous material which is sintered while leaving a gap at the time of molding as a filter medium.

However, although the conventional ceramic filter can satisfy the above-mentioned requirements in terms of material such as chemical resistance and high temperature resistance, it has a drawback that it can only have a large pore diameter of several μm or more. In general, it is a general condition of the related art that there is no substitute for the ultrafiltration membrane or the reverse osmosis membrane polymer membrane of the organic polymer membrane described above.

Although not yet practically used in industry, recently, a porous material having a pore diameter of about 10 μm is immersed in a sol obtained by hydrolysis of a metal alkoxide to form a sol film on the surface of the porous material. Attempts have been made to form and sinter this to form a metal oxide film to obtain a filter having a fine pore size. For example, obtaining an alumina film from boehmite sol J. The method of Burggraaf et al.
J. Burggraafet. al. , Twente University, The Netherlands, 1984), a method of obtaining a silica-alumina composite film from aluminum isopropoxide and sodium silicate (Asaeda et al., Hiroshima University, 1985),
Obtaining a Titania Film from Titanium Isopropoxide
Anderson's method (University of Wisconsin, USA, 1985) has been reported. Since the particles obtained by the sol-gel method are as small as about 0.1 μm, a film having a considerably fine pore size can be produced by optimizing the sintering conditions.
For example, Asada et al. Have obtained a filter having a separation coefficient of 5 or more in water-alcohol separation.

However, the membrane obtained by the sol-gel method has a fatal problem that it shrinks with sintering and cracks occur on the surface. There is a drawback that it is difficult to produce a filter having a large area for use on a target scale, and thus solving the problem is a major problem.

Recently, ultrafine particles of silicon nitride synthesized by thermal CVD are electrostatically deposited on an alumina porous tube,
A method for producing an inorganic film having a pore size of about the same size has been proposed by Mr. Masuda et al. (JP-A-1-254212). According to this method, the particles generated by thermal CVD are extremely fine, about several tens of nanometers, and the formed film has a three-dimensional pearl chain-like structure peculiar to electrostatic deposition. Since it is considered that cracking is unlikely to occur, it is expected to be superior to the above-described sol-gel method.

[0009] However, this film forming method is based on thermal CVD.
In addition to the high frequency alternating current for charging the ultrafine particles generated in the above, there is a disadvantage that an electrode of a special shape is required, and the porous tube itself for depositing the ultrafine particles must be used as an electrode, It is pointed out that the cost of the manufacturing apparatus and the produced film is higher than that of the sol-gel method. Also, in this method by electrostatic adsorption,
When this is used as a separation membrane, it is necessary to devise a method for uniformly obtaining fluid permeation throughout the membrane. For this reason, the same publication discloses a cylindrical porous sintered body on which the ultrafine particles are electrostatically deposited. The method of simultaneously moving in the axial direction while rotating in the circumferential direction is adopted. However, the control of the film thickness and the diameter of the fine pores depend on the size of the fine particles generated by CVD and the moving speed of the porous sintered body. Therefore, there is a disadvantage that it is not always easy to manufacture a filter having a large area used on an industrial scale.

[0010]

In view of the above-mentioned state of the prior art, the present inventor has developed a ceramic-based separation membrane, which is a material having excellent durability, which can be used on an industrial scale. We have intensively studied a method that has the functions described above, can reduce the load on the manufacturing equipment, and can reduce the cost of the produced film.

As a result, they have found that various problems which have been a problem to be solved by the prior art can be solved by forming a film using the above-mentioned fine particles produced by the CVD method using a film formation method completely different from the conventional method. Based on this, the present invention has been completed.

[0012] That is, one of the most fundamental problems aimed at by the present invention is that it can withstand use under high temperature and high pressure conditions, and is resistant to acid, base, and chemicals as compared with the conventional organic polymer film. It is an object of the present invention to provide a highly functional separation membrane which has excellent properties and can be subjected to membrane separation treatment on an industrial scale in various fields such as petroleum industry, pharmaceutical industry, food industry and the like.

Another object of the present invention is to have a fine ultra-fine hole of several nm, a large porosity, a low pressure loss, and no cracks even by sintering in the film forming process. It is another object of the present invention to provide a method for stably and efficiently producing a membrane and providing a porous inorganic membrane at low cost.

Another object which the present invention should particularly emphasize is:
Since the manufacturing method itself essentially has the function of homogenizing the film during the film formation process, it is easy to use a large-area film used on an industrial scale, in which the entire film is uniform in permeation resistance. An object of the present invention is to propose a manufacturing method having an excellent feature that it can be manufactured at a high speed.

[0015]

In order to solve the above-mentioned various problems, the present inventor has proposed a method in which a gas containing ceramic ultrafine particles having a particle size of several tens of nanometers produced by a CVD reaction is mixed together with a reaction gas. N2 the sheath gas such as a gas is conveyed gas <br/> flow Rutotomoni and suction filtered through end flow mode through a pore size 0.5μm or more, for example a ceramic porous pipe
It is, in the ceramic porous pipe surface by depositing the ceramic ultrafine particles as a layer, thereby completing the porous inorganic membrane production method of the present invention that firing the.

Further, according to the present invention, a substrate layer of a ceramic porous member having a pore diameter of 0.5 μm or more is formed by a CVD reaction.
Ultrafine ceramic particles with a particle size of several tens of nanometers are transported by airflow.
The present invention provides a porous inorganic film comprising a sintered body layer which is filtered and deposited by an end flow method using the above substrate layer as a filtering member and then sintered.

According to the method of the present invention, ultrafine particles generated by thermal CVD are collected by filtration on the surface of a porous tube or the like serving as a base material by the principle of filtration and dust collection to form a dense deposited layer. Is formed by sintering overheat to form a sintered film having ultra-fine pores on the surface of a porous tube or the like. Since the much weaker Van der Waals force is dominant, compared to the conventionally proposed electrostatic deposition method, it has a three-dimensional network structure while forming a dense film structure. There is no problem such as shrinkage or cracking during sintering.

From the characteristics of such a film structure, the porosity is 5
A large product of 0% or more can be produced, the pressure loss is low, and clogging due to filtration hardly occurs. Since the sedimentary layer can be formed based on the principle of filtration and dust collection, not only can the manufacturing apparatus be simple and the manufacturing cost be low, but also ultra-fine particles can be selectively deposited on low pressure loss parts, and as a whole A film with uniform transmission resistance is completed.

In the present invention, the ultrafine ceramic particles produced by the CVD reaction tube are not particularly limited, and all the fine particles produced by a general method such as oxidation of chloride and thermal decomposition of metal alkoxide are used. And typically, alumina, zirconia, titania, silicon nitride and the like can be exemplified.

The substrate made of a ceramic sintered tube or the like on which such ceramic ultrafine particles are deposited is not particularly limited as long as it can withstand the sintering of the deposited layer, and is made of, for example, a conventionally known ceramic porous sintered body. Various materials such as pipes can be used selectively, and materials such as alumina, mullite,
A ceramic made of zirconia, titania, silicon carbide, silicon nitride, or the like, having a pore diameter of generally 0.5 μm or more, preferably 1 to 10 μm, and a thickness of about 1 to 10 mm is suitably employed.

When the above-mentioned substrate is used as a filtering member to deposit ceramic ultrafine particles on the surface thereof, the ultrafine particles, which are considerably smaller than the pore diameter of the substrate, have a small inertia due to their own weight. Due to its small size and the large adhesion between particles compared to its own weight,
Instead of entering the inside of the pores of the substrate, they are collected on the substrate surface. Therefore, the deposition pressure can be continued without increasing the permeation pressure loss of the sheath gas during the formation of the deposition layer. This also results in a much lower filtration resistance for the membranes produced than for membranes produced by conventional methods.

The porous inorganic membrane produced according to the present invention as described above can be suitably used for membrane separation treatment on an industrial scale in various fields such as petroleum industry, pharmaceutical industry and food industry. It can be used under high temperature and high pressure conditions and has excellent acid resistance, base resistance and chemical resistance. In addition, since the filtration resistance and pore distribution of the membrane are uniform throughout, separation on the membrane surface, for example, when used as a filter for separating ultrafine particles from a medium, is unlikely to cause clogging,
Also, the function as an excellent separation membrane that the transmittance can be easily recovered by back washing can be exhibited.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings.

FIG. 1 shows an apparatus for carrying out the method of the present invention, which is configured for manufacturing a titania film. The apparatus is entirely configured as follows.

That is, the whole apparatus has a cylindrical CVD reaction tube 5 made of quartz glass, and one end in the axial direction inside thereof (the left side in the figure which is the upstream side when viewed from the gas flow).
Is provided with a reaction gas supply pipe 4 having a double pipe structure.
The upstream of the double pipe of the reaction gas supply pipe 4 is connected to the reaction gas supply pipes 1 and 2, and in this example, the reaction gas A is supplied from the reaction gas supply pipe 1 connected to the inner pipe as (TiCl). _Four
+ N ₂ ) is supplied, and the reaction gas supply pipe 2 is connected to the outer pipe.
Is supplied with (O ₂ ) as a reaction gas B. Further, in order to transport the ultrafine TiO ₂ produced by reaction from the reaction gas supply pipe 4 by air flow, the CVD reaction pipe 5 is used.
A sheath gas supply pipe 3 is connected to the one end of the above, and in this example, a sheath gas (N ₂ ) is introduced into the CVD reaction pipe 5 as a carrier gas flow of fine particles. 6 is a water-cooled jacket, 7 is the above-mentioned reaction gas A, B in the CVD reaction tube 5.
Is an electric furnace 7 for heating to make the ultra-fine particles having a diameter of several tens of nanometers uniform. The above reaction gas A
(TiCl ₄ + N ₂ ) can be obtained, for example, by passing nitrogen gas through a titanium tetrachloride liquid.

Reference numeral 9 denotes a hollow cylindrical ceramic porous tube which is closed at one end and open at the other end, and is disposed at the other end (in the drawing) so as to face the reaction gas supply tube 4 in the CVD reaction tube 5. Right end) Suction tube 13 connected to open end
Is connected to the suction pump 11 via the waste gas treatment device 10 on the way.
, Thereby performing end-flow suction filtration using the ceramic porous tube 9 as a filtering member, thereby forming a membrane forming apparatus.

Reference numeral 8 denotes a firing electric furnace for sintering the ceramic porous tube 9 having ultrafine particles deposited on the surface thereof by the above film forming apparatus after forming the film.

Example 1 Using the apparatus shown in FIG. 1, a titania film was produced under the following conditions.

That is, as the reaction gas A, 0.5
One liter (room temperature) of nitrogen gas is passed through the titanium tetrachloride liquid kept at 30 ° C., and is blown out from the inner tube of the reaction gas supply pipe 4 (inner tube tip diameter 8 mm) set at 800 ° C. Oxygen gas as the reaction gas B is 0.05
Reaction gas supply pipe 4 (outer pipe diameter 1
Ultrafine particles of 50 nm or less were produced by blowing out between the outer tube and the inner tube (2 mm tapered shape). Further, nitrogen gas was supplied from the sheath gas supply pipe 3 at a rate of 1 liter / minute.

On the other hand, an alumina tube having an outer diameter of 10 mm, a length of 100 mm, a thickness of 1.5 mm and an average pore diameter of 10 μm was installed as a ceramic porous tube 9 at the other end of the reaction tube 5.
Suction was performed at a rate of about 2 liters / minute or more by the suction pump 11 to form a deposited layer of titania ultrafine particles on the surface of the alumina porous tube 9.

After this operation was continued for 20 minutes, supply and suction of gas were stopped, and the alumina porous tube 9 was fired at 1200 ° C. for 2 hours in an electric furnace 8 for sintering.

As described above, a porous inorganic film having a sintered layer of ultrafine titania (layer thickness: about 70 μm) on the surface of the alumina porous tube 9 was obtained.

The obtained titania film was a high-temperature phase rutile type and its cross section was shown by an electron micrograph in FIG. In this electron micrograph, the layer of relatively large particles on the left is the above-described alumina porous tube, and the dense layer on the right is the titania film. FIG. 3 shows a surface electron micrograph of the titania film. These photographs show that the titania film is sintered to form a three-dimensional network structure.

Measurement of Porosity The porosity ε _m of the porous inorganic film produced as described above is calculated as follows.
It was determined from the following Kozeny-Carman equation. The pressure loss ΔP is determined by measuring the pressure difference when a gas flows through the membrane with a differential pressure gauge, the gas flow rate Q is measured by a flow meter, the viscosity coefficient μ of the gas is determined from a table of physical property constants, and the filtration area is determined by: Measured.
The true densities ρ _b and ρ _m of the material were measured with a pycnometer, the specific surface areas S _b and S _m were measured by a BET method, and ε _b was determined from the weight and size of the substrate.

[0035]

(Equation 1)

As a result, the porosity of the titania film of the above example was 84%.

Examples 2 and 3 Examples 2 and 3 except that the flow rate of nitrogen gas for obtaining the reaction gas A, the flow rate of nitrogen gas from the sheath gas supply pipe 3, and the sintering temperature were changed as shown in Table 1 below. In the same manner as in Example 1, a porous inorganic film was obtained.

[0038]

[Table 1]

[0039] In order to confirm the separation performance of the titania film is porous inorganic membrane obtained as separate transparently test above microparticle suspension, following the separation efficiency when the suspension was filtered polyethylene latex I examined it as follows.

That is, 0.05 to 1 shown in Table 2 below
Suspensions (about 400 ppm) of five types of polyethylene latex up to μm were prepared, and each suspension was adjusted to 0.02% by weight with distilled water passed through a 0.2 μm filter. Approximately 50 cc of the suspension thus prepared was taken, and each was put into the suspension tank 20 of the test apparatus shown in FIG. 4, sucked up by the microtube pump 21, and filtered through the above-mentioned porous inorganic membrane. The solution was supplied to the module 22 for filtration, and the filtrate was collected in the collection tank 23.

[0041]

[Table 2]

Separately from the above-mentioned operations, pipettes are used to accurately remove 20 cc from the suspension tank 20 and the recovery tank 23, put into weighing bottles, and dry all day and night in a dryer (105 ° C.). By weighing, the concentration Ci of the feed solution and the concentration Co of the permeate solution were obtained, respectively.

From the above results, the separation efficiency η was determined by the following equation.

[0044]

(Equation 2)

FIG. 5 shows the separation efficiencies of the above five types of suspensions obtained in Examples 1 to 3 in which the horizontal axis represents the particle diameter and the vertical axis represents the particle rejection efficiency. In the figure, b indicates the first embodiment, c indicates the second embodiment, and d indicates the third embodiment.

As a comparative example, a similar separation efficiency test was performed using only the alumina porous tube 9 in which no ultrafine particles were deposited and fired, and the results are shown in FIG.

As can be seen from the results shown in FIG. 4, each of the examples shows an excellent separation efficiency as compared with the case where the alumina porous tube 9 is used as it is.
It can be seen that 100% rejection can be achieved up to μm, and that even at several tens of nm, the rejection is still 70% or more.

[0048]

According to the present invention, compared to the conventional organic polymer film, it can withstand use under high temperature and high pressure conditions and has acid resistance, base resistance and chemical resistance. There is an effect that an excellent and highly functional porous inorganic separation membrane which can be used for membrane separation treatment on an industrial scale in various fields such as the pharmaceutical industry and the food industry can be provided.

Also, it has dense ultra-fine pores of several nm,
In addition, since the porosity is large, the pressure loss is low, and cracks are not generated even by the sintering process in the film forming process, the film can be manufactured stably and efficiently, so that the porous inorganic film can be provided at low cost.

Furthermore, the production method of the present invention essentially has the function of homogenizing the membrane during the membrane production process, and the membrane is produced on the same principle as the final application of filtration. There is an excellent effect that a film in which the entire film is uniform in transmission resistance can be easily produced even if the film has a large area to be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a configuration outline of an apparatus for carrying out a method of the present invention.

FIG. 2 is a photograph showing a particle structure, and is an electron micrograph showing a cross section of a porous inorganic film having a titania film produced according to Example 1.

FIG. 3 is a photograph showing a particle structure, and is a surface electron micrograph of the titania film.

FIG. 4 shows an apparatus for testing separation and permeation of a fine particle suspension.

FIG. 5 is a diagram showing a result of separation of a polyethylene latex suspension using the porous inorganic membrane having a titania membrane of Examples 1 to 3, and a result of a comparative example.

[Explanation of symbols]

1, 2: reaction gas supply pipe, 3: sheath gas supply pipe, 4:
Reaction gas supply pipe, 5: quartz glass CVD reaction pipe, 6: water cooling jacket, 7: electric furnace, 8: firing electric furnace, 9: ceramic perforated pipe, 10: waste gas treatment device, 11: suction pump , 13: suction tube, 20: suspension tank, 21: microtube pump, 22: filtration module, 23: collection tank.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 38/00 304 B01D 67/00 B01D 71/02

Claims (3)

(57) [Claims] 1. Particles of several tens of nm produced by a CVD reaction
The gas containing the diameter of the ceramic ultrafine particles, together with the reaction gas
The air flow is conveyed by the sheath gas and the hole diameter is 1-10.
to the ceramic porous member surface by <br/> suction filtered through end flow mode through the ceramic porous member μm depositing the ceramic ultrafine particles as a layer, a porous inorganic membrane, characterized by firing the Production method. Wherein Oite to claim 1, porous inorganic membrane manufacturing methods ceramic porous member, characterized in that a tube. 3. A substrate layer of a ceramic porous member having a pore size of 0.5 μm or more, and a substrate layer of several tens nm produced by a CVD reaction .
A porous inorganic film, comprising: a sintered body layer which is obtained by carrying an ultra-fine ceramic particle having a particle size by air flow, filtering and depositing the substrate layer by an end flow method using the substrate layer as a filtering member, and then sintering.