JPH0335970B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a porous membrane for gas diffusion separation used for gas separation or concentration by a gas diffusion method. [Prior art] When separating or concentrating gases using a porous membrane, for example, when separating H ₂ and CO or H ₂ and N ₂ , the fine particles of the porous membrane are separated so that Knutsen diffusion dominates. It is necessary to use a material whose pore diameter is adjusted to about several tens of angstroms to several hundreds of angstroms. As a specific conventional gas separation membrane, inorganic porous Vycor glass having a pore diameter of about 40 Å is known. This Vycor glass has excellent heat resistance and contact resistance due to its high silicate content, but due to its strength, it is difficult to reduce the film thickness to 0.5 mm or less, so The drawback was that the gas permeation rate per membrane area was low. Therefore, in order to create a separation membrane with a high gas permeation rate, the pore diameter of the porous membrane should be set to several tens of angstroms so that Knutsen diffusion is dominant.
It is desirable to adjust the film thickness to ~ several hundred Å and make the film thickness as thin as possible, but if the film thickness is extremely thin, it will not be able to maintain mechanical strength and will be impractical. Attempts have been made in various fields to adopt a so-called multilayer structure in which the membrane is reinforced by coating it on a porous support with a relatively large pore diameter of about 1 mm. Such porous membranes are usually used in a tubular shape for ease of handling or strength. Therefore, the manufacturing method is to first manufacture a porous support tube with a thickness of about 1 mm using commonly used powder metallurgy methods, sintering methods, etc., and then coat this with a thin film having micropores using various methods. ing. Thin film coating methods include vacuum evaporation and sputtering to form an ultra-thin film of around 1 μm, but these methods are impractical because it is difficult to control uniform pore diameters and there is a limit to the equipment capacity. A method is used in which fine powder is deposited to a thickness of several tens of microns. There are two methods for forming this fine powder layer: a dry method and a wet method, but the dry method has poor particle fluidity and is extremely difficult to form a layer of uniform thickness, so the wet method is the mainstream. . This wet method includes a centrifugal molding method in which a porous support tube is rotated, a fine powder slurry is supplied inside the support tube, and the powder is adhered by centrifugal force, and a centrifugal molding method in which a porous support tube is rotated, and the powder is adhered by centrifugal force. There are electrophoresis methods in which a slurry is deposited on a porous support tube, and commonly used coating methods.The fine powder has good fluidity because it is used as a slurry by adding water, alcohol, or an organic solvent such as acetone. , a layer of uniform thickness can be easily formed. In this way, it is possible to form a uniform thin film using the wet method, but the pore diameter that can be easily formed is several thousand Å or more, and in order to obtain a pore diameter of several tens of Å to several hundred Å, it is possible to form a uniform thin film. When using ultrafine powder, there is a drawback that cracks occur when the slurry layer is formed and then dried by evaporating the liquid. In order to prevent this cracking, there is a method of adding a binder to the slurry, but it is difficult to remove the binder afterwards and obtain micropores. In addition, as one method for obtaining micropores, a method for manufacturing porous materials has been proposed in which fine particles are filled in a coarse porous substrate by immersion (Japanese Patent Laid-Open No. 57
−182964). However, this method has the disadvantage that the entire coarsely porous matrix is filled with fine particles. [Problems to be Solved by the Invention] The present inventors previously proposed a method for solving the above-mentioned drawbacks of the prior art, which consists of a dense layer and a support layer composed of particles larger than the particles in the dense layer. A porous material for gas diffusion separation is prepared by immersing a porous material with a multilayer structure in a slurry in which particles for the active layer smaller than the particles in the dense layer are separated in a dispersion medium, and then removing the dispersion medium after pulling up the slurry. Found a manufacturing method (Japanese Patent Application No. 58-203630) When using this method, a porous material for gas diffusion separation with a good permeability coefficient ratio and a large permeability coefficient can be obtained, but the yield of particles for the active layer is low. There was a problem in that the slurry concentration was not very good and the slurry concentration had to be increased, or if the slurry concentration was low, the number of treatments had to be increased. [Means to Solve the Problems] The present inventors further investigated the above method, and found that the porous material was concentrated in the slurry, and after the slurry was pulled up, the dispersion medium was removed and then removed from the dense layer side. The present invention has been achieved by discovering that the above problems can be solved by doing the following. That is, when a porous material with a multilayer structure with different pore diameters is immersed in a slurry in which fine particles are dispersed under reduced pressure, and the dispersion medium is removed from the dense layer side of the porous material by drying or other means, the dense layer first The amount of liquid in the small pores decreases, and the resulting capillary action causes the slurry in the large pores to move into the small pores and remove the liquid. As a result, the fine particles in the porous multilayer structure undergo redistribution, and the large pores are filled with low density, and the small pores in the dense layer are filled with high density. In addition, because the porous material has a multilayer structure, there is almost no effect of fine particles remaining in the large pores. The present invention was made with attention to the above phenomenon, and it is possible to extremely easily and effectively produce a porous gas separation membrane with a multilayer structure having a uniform thin film with a pore diameter of several tens of Å to several hundreds of Å. can. Furthermore, according to the present invention, fine particles are embedded in the pores of the dense layer of the porous material with a multilayer structure by immersion in the slurry and subsequent removal of the dispersion medium, so there is no need to add a binder. It can be firmly held and has sufficient strength. Next, the manufacturing method of the present invention will be explained in detail. Metals such as Fe, Ni, Al, Al ₂ O ₃ , SiO ₂ ,
A multilayer structure is created by dispersing microparticles of several tens of Å to several hundred Å for forming an active layer made of metal oxides such as TiO ₂ , Fe ₂ O ₃ , and ZrO ₂ in water or an organic liquid such as alcohol or acetone. porous material is immersed under reduced pressure. The term “active layer” here refers to H ₂ and CO.
A diffusion separation layer effective for separating or concentrating a mixed gas such as H ₂ and N ₂ refers to a porous layer having a pore diameter of several tens of angstroms to several hundreds of angstroms in which gas flow is dominated by Knutsen diffusion. The porous materials with a multilayer structure used here include metals such as Fe, Ni, and Al, Al ₂ O ₃ ,
It is made of metal oxides, metal carbides, etc. such as SiO ₂ , TiO ₂ , Fe ₂ O ₃ , ZrO _{2 ,} etc., and has a dense layer with pore diameters of several hundred Å to several μ and at least one support layer in the outermost or innermost layer. It has body layers. Further, the support layer in the present invention is a layer having a thickness of about 0.2 mm to 5 mm and is composed of particles having a diameter 5 to 100 times larger than that of the fine particles constituting the dense layer. When the support layer consists of two or more layers, each layer is composed of particles with different particle sizes, and the particles in the layer closer to the dense layer are composed of particles with smaller particle sizes. . Further, as the material used for the particles of the support layer, metals such as Ni, Al, Fe, and various metal compounds are used, similar to the fine particles and active layer particles used for the dense layer and active layer. Such a single-layer or multi-layer porous support can be easily produced by a sintering method or the like. In particular, when the support layer is made up of multiple layers, the outer layer or inner layer (the layer farthest from the dense layer) can be formed of relatively large particles, allowing the layer thickness to be increased without sacrificing gas permeability. Therefore, the strength of the support can be improved. In addition, in order to provide a dense layer on such a support layer, for example, fine particles for the dense layer may be supplied to the inner surface of the porous support tube made as described above (if necessary, the tube body may be rotated). (The fine particles may be supplied while drying, or a slurry of the fine particles may be supplied to the tube.) A flexible tube is inserted into the tube, and a fluid is applied to the tube to pressure the fine particles. It can be provided by pressing the support member from the inside onto the inner surface of the support member and, if necessary, sintering the support member. The porous membrane for gas diffusion separation in the present invention preferably has a tubular shape, but may have a plate shape or other shapes. Therefore, in the present invention, the expression "outermost layer" or "innermost layer" mainly refers to a tubular body. However, in the case of a plate, etc., it also refers to one side and the other side. The concentration of fine particles in the slurry is a concentration at which the particles are sufficiently dispersed, and is determined by the type of particles, particle size, and type of dispersion medium. Furthermore, if the particles are difficult to disperse, a dispersion aid such as acetic acid or a surfactant may be added. As shown above, in the present invention, when the dispersion medium is removed, the fine particles are packed in the dense layer at a high density, so even a dilute concentration is sufficiently effective. In the immersion method, it is preferable to completely replace the gas in the porous pores with the slurry in order to produce a membrane with uniform pore diameters, so during the immersion, use a vacuum pump etc. under moderately reduced pressure. It is preferable to hold it or apply ultrasonic waves or the like. After the porous material is immersed in the slurry in this manner, the porous material is pulled up from the slurry and the dispersion medium is removed from the outer surface of the dense layer. The dispersion medium can be removed by heating or vacuum drying the outer surface of the dense layer. In addition, after removing it to a dispersion medium,
It can also be fired if necessary. When fired, interactions occur between the particles and the porous material and between the particles, further increasing the strength. In addition, the adjustment method between several tens of angstroms and several hundreds of angstroms can be carried out by changing the packed particle diameter, slurry concentration, and the number of repetitions of immersion and removal of the dispersion medium. In addition, when there is a significant difference between the pore diameter of the dense layer of the porous material and the packed particle diameter, for example, when the pore diameter of the dense layer is several microns and the packed particle diameter is several tens of angstroms, it is necessary to ~several thousand Å
It is also possible to carry out the treatment by immersion and removal of the dispersion medium using a packed particle size of several tens of angstroms, and then perform the same treatment using a packed particle size of several tens of angstroms. [Example] Hereinafter, the present invention will be illustrated by examples. Example 1 Three-layer Al 2 O 3 porous material with an inner diameter of 7 mm, an outer diameter of 10 mm, and a length of 750 mm, which has a dense layer with an average pore diameter of 2000 Å and a thickness of 20 μ on the inside, and is composed of supports with average pore diameters of _1.5 μ and ₁₀ μ. Tube 1wt of _SiO2 ultrafine particles with average particle size 80Å
%, and immersed in the slurry solution for 30 minutes while keeping it under reduced pressure with a vacuum pump. After that, the slurry was removed from the solution, dried by circulating air at about 80℃ for 30 minutes inside the porous tube, and then placed in an electric furnace at 500℃ for 3 hours.
Baked for an hour. The average pore diameters in the dense layer were 120 Å, 80 Å, and 66 Å when the dipping, drying, and firing operations were repeated once, twice, and three times, respectively. In addition, the permeability coefficients and permeability coefficient ratios of H ₂ and N ₂ gases measured at 25°C were as shown in Table-1. Example 2 The same Al ₂ O ₃ porous tube as in Example 1 was prepared with an average particle diameter of
The samples were immersed in slurries of 80 Å SiO ₂ ultrafine particles at various concentrations for 30 minutes while being kept under reduced pressure using a vacuum pump.
After that, it is removed from the slurry solution, dried by flowing air at about 80℃ for 30 minutes inside the porous tube, and then
It was fired for 3 hours in an electric furnace at 500°C. This immersion,
The slurry concentration, average pore diameter in the dense layer, and 25
The relationship between the permeability coefficients and permeability coefficient ratios of H ₂ and N ₂ gases measured at °C was as shown in Table 2. Example 3 The same Al ₂ O ₃ porous tube as in Example 1 was prepared with an average particle diameter of
It was immersed in a 1 wt% slurry solution of 150 Å SiO ₂ ultrafine particles for 30 minutes while maintaining reduced pressure with a vacuum pump. After that, it is removed from the slurry solution, dried by flowing air at about 80℃ for 30 minutes inside the porous tube, and then
It was fired for 3 hours in an electric furnace at 500°C. This immersion,
Drying and firing operations were performed once, twice, and three times.
The average pore diameters in the dense layer were 115 Å, 90 Å, and 75 Å, respectively, after repeated experiments. 25 again
The permeability coefficients and permeability coefficient ratios of H ₂ and N ₂ gases measured at °C were as shown in Table 3. Example 4 A porous membrane prepared by repeating the dipping, drying, and baking operations three times in Example 1 was heated at 25°C.
The permeability coefficients of H ₂ , He, CH ₄ , N ₂ , CO, and CO ₂ gases were measured. The results are shown in Figure 1, and it can be seen that the permeability coefficient has a clear direct relationship with the reciprocal of the root of the molecular weight of each gas, indicating that gas permeation is dominated by Knutsen diffusion. Example 5 The same Al ₂ O ₃ porous tube as in Example 1 was prepared with an average particle diameter of
Ultrafine Al ₂ O ₃ particles with a diameter of 200 Å were immersed in a 1 wt % slurry solution prepared by suspending the slurry in water using acetic acid as a dispersing agent for 30 minutes while maintaining the reduced pressure using a vacuum pump. Then take it out of the slurry solution and store it inside a porous tube at about 80℃.
It was dried by passing air through it for 30 minutes, and then fired in an electric furnace at 500°C for 3 hours. The average pore diameter in the dense layer of the porous membrane obtained by repeating this dipping, drying, and baking operation three times was 75 Å, and the permeability coefficient of H ₂ measured at 25°C was
77NCC/cm ² min atm, the permeability coefficient of N ₂ is
22 NCC/cm ² min atm was obtained, and the permeability coefficient ratio of H ₂ and N ₂ was 3.5. The permeability coefficient and permeability coefficient ratio measured at 25°C using a Vycor glass tube with an inner diameter of 8 mm, an outer diameter of 10 mm, and an average pore diameter of 40 Å are shown in Table 4. As is clear from the results of the above examples, the method for producing a porous membrane for gas diffusion separation according to the present invention has a high permeability coefficient ratio (separability) and a very large permeation coefficient (gas permeation amount). It can be seen that the gas separation membrane can be manufactured extremely easily. The manufacturing method of the present invention has been explained above using the case of manufacturing a tubular multilayered porous gas separation membrane as an example, but the present invention is not limited to this case, and can be applied to other shapes such as a plate shape. It can also be applied to the production of porous gas separation membranes.

【table】

【table】

【table】

[Table] Comparative Example 2 The same porous pipe made of Al ₂ O ₃ as in Example 1 was manufactured in a patent application filed in 1983.
203630, it was immersed in a 30% slurry solution of 80 Å SiO ₂ ultrafine particles for 30 minutes while being kept under reduced pressure with a vacuum pump. Thereafter, it was taken out from the slurry, dried in a dryer at 100°C for 1 hour, and fired in an electric furnace at 500°C for 3 hours. The permeability coefficients and permeability coefficient ratios of H ₂ and N ₂ gases measured at 25° C. after repeating the immersion, drying, and firing operations twice were as shown in Table 5. Additionally, Table 5 also shows the results of the repeated treatment two times as shown in Example 1.

[Table] As can be seen from this result, by removing the fractional medium from the outer surface of the dense layer side, it is possible to produce a slurry having substantially the same permeability coefficient and permeation coefficient ratio at a significantly lower concentration. Comparative Example 2 The same porous tube made of Al ₂ O ₃ as in Example 1 was immersed in a 1 wt % slurry solution of 80 Å SiO ₂ ultrafine particles for 30 minutes while maintaining the tube under reduced pressure using a vacuum pump. The slurry was taken out and dried in a dryer at 100°C for 1 hour without removing the dispersion medium (Japanese Patent Application No. 58-203630), and then calcined in an electric furnace at 500°C for 3 hours.
The average pore diameter and permeation of H ₂ and N ₂ gases measured at 25°C were obtained by repeating the immersion, drying, and firing operations twice, and by performing the same operation with a 30wt% slurry solution. The coefficients and permeability coefficient ratios were as shown in Table-5. In addition, Table 5 also shows the results of the two repeated treatments shown in Example 1.

【table】

〔Effect of the invention〕

According to the present invention, a porous gas separation membrane having a high-strength porous structure having a uniform thin active layer with micropores of several tens of Å to several hundreds of angstroms is extremely simple and has a good yield of particles for the active layer. It has the advantage that it can be manufactured effectively and that a slurry with a relatively low concentration of particles for the active layer can be used to provide the active layer.

[Brief explanation of the drawing]

Figure 1 shows the porous membrane obtained in Example 1.
It is a graph showing the results of measuring the permeability coefficients of various gases at 25°C.

Claims (1)

[Claims] 1. A multilayer structure comprising a dense layer made of fine particles as the outermost or innermost layer, and at least one support layer made of particles larger than the particles in the dense layer. A gas characterized in that the porous material is immersed in a slurry in which active layer particles smaller than the particles of the dense layer are dispersed in a dispersion medium, the slurry is pulled up, and the dispersion medium is removed from the outer surface on the side of the dense layer. A method for manufacturing a porous membrane for diffusion separation. 2. A method for producing a porous membrane for gas diffusion separation, which comprises repeating the method described in claim 1 a plurality of times.