JPS623797B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to an aggregated molded body made of a linear extrudate of a porous inorganic substance and a method for producing the same. In recent years, the use of porous inorganic materials has been rapidly developed, and they are used in a wide range of fields, such as filtration materials, adsorbents, sound absorbing materials, heat insulating materials, and catalyst carriers.
As application to such a wide range of fields is being considered, problems arise in terms of ease of handling and influence on effects when using the raw shape of the material. It is increasingly being used by forming it into a honeycomb shape or the like. These molded bodies are selected optimally depending on their respective uses, and are used in reactions involving gaseous bodies and the like.
Honeycomb-shaped materials are often used in applications where pressure loss is a concern, such as catalyst carriers. However, honeycomb structures are subject to major restrictions from the viewpoint of manufacturing technology, and because there are limits to the processing technology of dies and forming rollers, it is not possible to obtain a fine structure beyond a certain level. For example, when molding means using dies, the cell wall thickness is limited to about 100μ, and when using roller molding means, it is difficult to achieve a thickness of less than 50μ.
After all, the limit for the number of cells is about 1,000 rooms per square inch. For these reasons, pellet-like or bead-like products are attracting renewed attention, and products obtained by adding a binder to these molded products and press-molding them are attracting attention. Such a press-formed product has extremely fine voids, and exhibits the advantage that, when used as a catalyst carrier, for example, the effective surface area is considerably larger than that of a honeycomb structure. However, it is necessary to use a binder twice: in the step of forming the pellet itself and in the step of secondary forming, and there is concern that this will not only cause a discrepancy in the porosity of the product, but also have an adverse effect on the mechanical strength. Furthermore, in the conventional method, the molded pellets are crushed and sieved before press molding, so the molding operation alone requires twice as much, and the processing cost increases. The present invention has been made with attention to these circumstances, and it is possible to complete the molding operation in one step, and to create a microporous structure that overrides the honeycomb structure and is comparable to the press-formed body described above. The purpose of the present invention is to provide a new molded article having the following properties and a method for producing the same. That is, the new molded article provided by the present invention is
It is a sintered body in which linear extrudates made of a porous inorganic substance are accumulated in a predetermined shape, and its overall shape, that is, its outer shape, may be arbitrarily designed. That is, the most suitable means for manufacturing the above-mentioned molded body is:
A binder is added and kneaded to a porous inorganic material powder, and this is extruded linearly from a nozzle provided in a discharge die and filled into a molding die of a predetermined shape.
Although the main idea is to dry and sinter, any shape can be used as the molding die, and an aggregate is formed according to the shape within the selected molding die. The sintered body thus provided is
Each linear extrudate itself contains many fine pores, and voids are also formed between the linear extrudates, giving it superior surface properties compared to honeycomb-shaped bodies, and It is not necessary to use a large amount of binder, and the manufacturing equipment is simple compared to any of the above methods, and the production cost can be kept low. The porous inorganic substance used as the material for the molded article of the present invention is an inorganic substance that has many small voids inside and/or on the surface of the solid, and as long as it satisfies these conditions, the source of the porous inorganic substance is It can be used regardless of origin or manufacturing method, but typical examples include zeolite (whether synthetic or natural), γ-alumina, silica gel, silica alumina, boehmite, activated titania, Examples include activated carbon and further molecular sieving carbon. Such porous inorganic materials are generally available in the form of powder or granules, and in order to extrude them into linear shapes, it is necessary to add a binder and knead them to make them viscous. There are no particular restrictions on the binder used here, and any binder can be used as long as it exhibits a caking function for powder and granules. Typical examples include MC, CMC, starch, and CMB.
Organic binders such as (carboxyl methyl starch), HEC (hydroxyethyl cellulose), HPC (hydroxypropyl cellulose), sodium lignin sulfonate, calcium lignin sulfonate, polyvinyl alcohol, acrylic ester, methacrylic ester, phenolic resin, melamine resin, etc. ; water glass, colloidal silica,
Examples include inorganic binders such as colloidal alumina, colloidal titanium, bentonite, and aluminum phosphate, and of course two or more of these may be used in combination. The content of the binder is preferably 35% by weight or less on a dry basis (based on the total kneaded material); if this value is exceeded, the strength of the sintered product will decrease and the porosity described below will decrease. Therefore, it cannot be recommended. There are no restrictions on these mixing and kneading means, and any known device or equipment may be used. However, if a screw type extrusion molding machine is used to extrude the linear material, the screw of the molding machine may be used. It can also be kneaded. The thus kneaded material is extruded into a linear product using the screw extruder, plunger extruder, or the like described above. In this case, a discharge die having one to several nozzles is used in the discharge section of the molding machine, and a linear object having a shape and thickness according to the cross-sectional shape or cross-sectional area of the nozzle is extruded. . Figure 1 shows a discharge die 2 in which a large number of nozzles 1 with a circular cross section are formed.
, a situation in which a large number of linear objects 3 are extruded is shown, and since a forming die 4 is arranged in front of the discharge die 2, the above-mentioned linear objects 3 are extruded by the forming die 4.
It is filled and stored inside. Since the forming die 4 is a finite mold, the extrudate 3 is accumulated while being bent in a free direction, and extrusion is stopped when the die 4 is filled. Furthermore, since a protruding rod 5 is formed in the center of the forming die 4 shown in the figure,
The formed aggregate 6 had a cylindrical shape, and its appearance after sintering was as shown in Reference Photo 1. In addition, in the forming device shown in the figure, the linear object 3 is extruded in the direction of gravity, but even when using a device that extrudes in the horizontal direction, it is difficult to ensure that the filling of the linear object 3 into the forming die 4 is completed. Since this is also the time to stop extrusion, there is practically no particular inconvenience. The obtained aggregate is dried by an appropriate method and further sintered to produce a product. However, the present invention does not place any restrictions on the conditions for drying and sintering, and the type of material, binder, and accumulation Optimal conditions may be determined by considering the shape and size of the lump. The sintered product thus obtained has both fine pores inherent in the material itself and voids formed between the linear extrudates, but as shown in Figure 4, the sintered products have It was found that as the area (after sintering) increases, the ventilation resistance (pressure drop) increases, and when the area exceeds 8 mm ² (after sintering), it exceeds the pressure drop level in the case of pellet filling. The reason for this is believed to be that linear objects with a large cross-sectional area are easily deformed when being filled into the molding die, and this deformation brings the linear objects into close contact with each other, reducing the void space. On the other hand, when looking at the clamping strength of the sintered product, there was almost no variation when the cross-sectional area was 8 mm ² or less, but it rapidly decreased when this was exceeded. The reason for this is thought to be that internal cracks occur in the sintered linear object due to deformation of the linear object, and a notch effect appears due to acute-angled deformation. The cross-sectional shape of the linear extrudate (circle, oval, semicircle, crescent, rectangle, diamond, petal, star, etc.), the size of the aggregate, the shape of the aggregate, and even the packing of the linear extrudate The optimum cross-sectional area should be selected depending on the density, etc. Furthermore, since the linear extrudate shrinks to some extent during drying and preheating, when designing the discharge die, it is better to make the nozzle diameter slightly larger. Incidentally, such a sintered product can be applied to any of the above-mentioned uses, but in this case, the product exhibits respective effects for each use due to the above-mentioned fine pores and the above-mentioned voids. However, if these volume ratios (hereinafter referred to as porocities) are too small, the surface area of the catalyst will be insufficient even when used as a catalyst carrier, making it difficult to obtain satisfactory results. Such porosity needs to be 0.2 cc/g or more when measured by the mercury intrusion method described below. The measurement of porosity is carried out as follows. The sintered product, which has been completely deaerated from the gas present in the micropores and voids, is immersed in pure mercury, sealed, and pressurized to inject mercury into the micropores and voids. , to measure the decrease in the apparent volume of mercury. This decrease value corresponds to porosity. In addition, in the present invention, the porosity is 0.2cc/
As will be made clear in the examples below, the reason for limiting the amount to be more than 100 g is due to consideration given to exhibiting better performance (in terms of water absorption, etc.) than at least conventional products. Extrusion of the above-mentioned linear objects can be carried out by installing only one nozzle in the discharge die, but in consideration of productivity, it is recommended to provide two or more nozzles to extrude multiple linear objects at the same time. is recommended, and in this case, it is possible to extrude linear objects with different cross-sectional shapes and/or cross-sectional areas for each nozzle, and the product configuration can be made according to the application. In addition, as for the shape of the accumulated mass, in FIG. 1, the linear extrudate was formed by bending it in the free direction, but as shown in FIG. , by cutting it to an appropriate length, or by extruding it while rotating either the discharge die 2 or the forming die 4 in Fig. 1, and bending the linear extrudate in the winding direction, as shown in Fig. 3. It may be shaped as shown. Since the present invention is configured as described above, a sintered product containing fine pores and voids can be produced extremely easily, and the handleability thereof is extremely good. The scope of application can be greatly expanded. Next, examples of the present invention will be shown. A kneaded material of a porous inorganic material and a binder was prepared with the composition shown in Table 1, and a linear extrudate was formed into a mass according to FIG. 1, followed by drying and sintering. The blending amounts each indicate parts by weight. Water absorption rate is 25℃ x 80%RH
It shows the water absorption rate after being left for 1 day, 3 days, and 6 days under the following conditions.

[Table] As shown in Table 1, as the amount of binder increases, the porosity tends to decrease, and at the same time, the water absorption capacity also decreases. However, in Experiment No. 1, which used a standard binder, the water absorption rate reached 18% after being left for 6 days, whereas with conventional products (packed with pellets) it was estimated to be around 10% at most. A comparison shows that there is a significant improvement. Also, it is clear from Table 1 that the porosity is
It is understood that those with a water absorption capacity of 0.2 cc/g or more (Experiment Nos. 1 to 4) have a water absorption ability superior to that of conventional products.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the manufacturing method, Fig. 2 is a sectional view of the main part, Fig. 3 is a perspective view showing an example of the product, and Fig. 4 is a sectional view showing the manufacturing method.
The figure is a graph showing the relationship between the cross-sectional area and physical properties of a linear extrudate. 1... Nozzle, 2... Discharge die, 3... Linear extrudate, 4... Molding die.

Claims (1)

[Scope of Claims] 1. A porous molded product obtained by forming a linear extrudate made of a porous inorganic substance into an aggregate of a predetermined shape, drying and sintering, and which has fine pores inherent in each linear extrudate itself. , has voids formed between the linear extrudates, and has a porosity of 0.2 cc, which is measured from the degree of decrease in mercury volume when the degassed product is immersed in sealed mercury and the mercury is pressurized. /g or more. 2. The porous molded article according to claim 1, wherein the linear extrudate has a cross-sectional area of 8 mm ² or less. 3. A porous molded article according to claim 1 or 2, which is formed as an aggregate consisting of linear extrudates with different cross-sectional shapes and/or cross-sectional areas. 4. A porous molded article according to any one of claims 1 to 3, wherein the aggregate is a bundle of linear extrudates. 5. A porous molded article according to any one of claims 1 to 3, wherein the aggregate is formed by bending a linear extrudate in a free direction. 6. A porous molded article according to any one of claims 1 to 3, wherein the aggregate is formed by bending a linear extrudate in the winding direction. 7. A porous molded article according to any one of claims 1 to 6, wherein the aggregate is cylindrical. 8 Adding and kneading a binder to powder of porous inorganic material, extruding it linearly from a nozzle provided in a discharge die, filling it into a molding die of a predetermined shape, and accumulating it according to the shape in the die. A method for producing a porous molded body, which comprises forming a lump, followed by drying and sintering. 9. The method for producing a porous molded article according to claim 8, wherein the binder content in the entire kneaded material is 35% by weight or less on a dry basis. 10. A method for producing a porous molded body according to claim 8 or 9, in which a large number of linear extrudates are simultaneously extruded through a large number of nozzles. 11. A method for producing a porous molded body according to claim 10, wherein extrusion is carried out through nozzles having different cross-sectional shapes and/or cross-sectional areas. 12. A method for producing a porous molded body according to claim 10 or 11, in which a linear extrudate is bundled and accumulated in a molding die. 13. A method for producing a porous molded body according to any one of claims 8 to 11, in which a linear extrudate is filled into a molding die space while being bent in a free direction. 14. A method for producing a porous molded body according to any one of claims 8 to 11, in which a linear extrudate is filled into a molding die while rotating a discharge die. 15. A method for producing a porous molded body according to any one of claims 8 to 11, in which a linear extrudate is filled into a molding die while the molding die is rotated.