Production of water resisting, hard, porous metasepiolite

#1. Field of the Invention

#The present invention relates to a porous sepiolite and a process for producing the same. The invention specifically is concerned with a porous sepiolite which has an improved resistance to water, an improved resistance to thermal shock and a large specific surface area, and with a process for producing the same. This invention also relates to a catalyst composition for deodorization in which a catalyst component is supported on such a porous sepiolite.

#2. Description of the Prior Art

#In the accompanying drawings:

#FIGS. 1 to 3 are graph representations showing the pore-size distributions of a porous sepiolite obtained in Examples;

#FIG. 4 is a graph representation showing the residual rate of trimethylamine after treatment with an adsorptive decomposition catalyst composition of the present invention; and

#According to an embodiment of the present invention, a water-resisting porous sepiolite is prepared through the steps of grinding, moisture-controlling and molding sepiolite, and calcining it at a temperature in the range of about 650.degree. C. to about 800.degree. C. This sepiolite has a water-resisting property and keeps pores having a pore diameter of 1000 angstroms or larger at a similar extent as natural sepiolite has. This sepiolite has a peptizing resistance to water that it will not peptize or swell by soaking it in water. The sepiolite also has a high fracture strength at freezing that the sepiolite having been soaked in water and frozen is not destroyed when it is rapidly cooled. The sepiolite of the present invention also has a high resistance to thermal shock such that the sepiolite having been heated to an elevated temperature of 600.degree. C. will not become self-broken or damaged when it is put into cold water.

#The specific surface area of natural sepiolite is usually less than 400 m.sup.2 /g. The surface area of sepiolite that has been calcined at a temperature of 300.degree. C. is decreased to about 200 m.sup.2 /g. The area of sepiolite that has been calcined at a temperature in the range of 500.degree. C. to 800.degree. C. is decreased to the range of 200 to 120 m.sup.2 /g as the temperature is raised. It is well known in the art that sepiolite, when calcined at an elevated temperature of 800.degree. C. or higher, is transformed into steatite and that such a calcined sepiolite has a less surface area, a higher brittleness and a lower strength than non-calcined sepiolite. The firing at a temperature in the range of 300.degree. C.-800.degree. C. changes natural sepiolite into metasepiolite, and loses the crystalline structure of approximately 5-10 angstroms which is characteristic of sepiolite. Further, firing of the bundle of crystalline fibers (0.2 micrometers long, 100-300 angstroms wide, 50-100 angstroms thick) also decreases the surface area and crystallinity thereof. We have, however, found that the above-mentioned crystalline structure of 5-10 angstroms was not completely destroyed and that the pore openings and apertures in the structure were plugged and blocked due to dehydration, etc. We have also found that appropriate acid-treatment can recover the damaged crystalline structure and especially the zeolitic pores having a pore diameter of not more than 50 angstroms, which pores contribute largely to adsorption, and that the surface area is also increased. We have confirmed by an X ray diffraction method the fact that the crystalline structure was recovered near being a structure like the original natural sepiolite.

#As a result of further studying on the basis of the information described above, we have found out that the process including the steps of grinding, moisture-conditioning and molding sepiolite, calcining the sepiolite at a temperature in the range of about 650.degree. C. to about 800.degree. C., and further subjecting the calcined sepiolite to an acid treatment can provide a porous sepiolite that has a specific surface area in the range of 40-200 m.sup.2 /g with respect to the pores having a pore diameter of 50 angstroms or less, not less than 20% of the total surface area of the sepiolite being occupied with the pores having a pore diameter of 50 angstroms or less and the pore distribution curve of the sepiolite having a main peak at a pore diameter of no more than 50 angstroms. In view of its high adsorption and physical strength, a catalyst composition in which a catalyst component is supported on the porous sepiolite of the present invention can be used for adsorbing and removing foul odor or noxious components from the air in the storage compartment of a refrigerator.