JP2009096697A5 - - Google Patents

Description

A method for producing an alumina substrate for a zeolite membrane according to the present invention will be described.
(A) In the present invention, an Al ₂ O ₃ raw material having a purity of 99% by weight or more, preferably 99.5% by weight or more is used. In view of the mixing of impurities in the mixing / dispersing step, it is preferable to use an alumina raw material having a primary particle diameter of 6 to 12 μm, preferably 7 to 11 μm. As this Al ₂ O _3, a raw material powder produced by the Bayer method can be used. The Al ₂ O ₃ raw material manufactured by the Bayer method is preferable because it is cheaper than conventionally used alumina, and it is particularly preferable to use an alumina raw material fired at a high temperature in the manufacturing process. When the Al ₂ O ₃ purity is less than 99% by weight, the amount of impurities contained in the alumina substrate is increased, and the corrosion resistance is lowered. When the primary particle size is less than 6 μm, the particle size distribution after mixing / dispersion is narrowed, the average crystal particle size of the obtained substrate is reduced, which causes a decrease in corrosion resistance and an increase in the zeta potential of the substrate. Not . Hand, if the primary particle diameter exceeds 12μm, the pore diameter having the substrate is increased, undesirably zeolite seed crystal on the substrate surface during the zeolite membrane film formation is not uniformly responsible lifting.
(B) The component that forms the glass phase in the firing step is at least one selected from the group consisting of silica, feldspar, and clay in the form of raw material powder.
By using these raw material powders, a glass phase having a relatively uniform composition can be formed . The average particle diameter of the raw material powder is 0.5 to 5 [mu] m, Ru preferably 1~4μm der. When the average particle size is less than 0.5 μm, it is preferable because the powders are strongly aggregated and difficult to disperse uniformly, and the crystallinity of the zeolite membrane on the surface of the base tube becomes non-uniform when forming the zeolite membrane. Absent. Moreover, when exceeding 5 micrometers, since the uniform dispersibility of the glass phase in a baking process falls and it causes a mechanical characteristic to fall, it is unpreferable. These components change to the alkali metal oxide or alkaline earth metal oxide in the present invention by firing.
By using the raw material on more than _Al 2 _{O 3} content 85 to 95 wt%, SiO ₂ content is blended so that 3 to 13% by weight, using a ball mill or attrition mill in a wet, water Alternatively, mixing and dispersion are performed with an organic solvent. Note that the raw material treatment in the present invention may be only mixing and dispersion treatment without pulverization, whereby the change due to the treatment of the surface of the powder can be suppressed as much as possible, and the crystal grain size of the substrate can be easily controlled.
As the molding, extrusion molding or press molding is adopted.
In the case of extrusion molding, the obtained pulverized / dispersed slurry is dried and sized, and then a binder for extrusion molding (a known binder such as CMC, PVA, wax emulsion, etc. can be used) and water, and in some cases, pores are formed. An extrudate clay is obtained by adding an agent, mixing and kneading. Next, this molding clay is extruded to a predetermined shape.
In the case of press molding, a binder (wax emulsion, PVA, acrylic resin, etc.) is added to the obtained dispersion slurry and dried with a spray dryer (SD) to produce a molding powder. Into the mold and press-mold.
(C) The obtained molded body is fired in the atmosphere at 1200 to 1600 ° C, preferably 1250 to 1500 ° C. A calcination temperature of less than 1200 ° C. is not preferable because not only the mechanical properties deteriorate due to insufficient sintering, but also the crystallinity of the zeolite membrane on the surface of the substrate tube becomes nonuniform during the formation of the zeolite membrane. Moreover, when it exceeds 1600 degreeC, since sintering advances too much and a porosity falls, it is unpreferable.

Examples 1-7 and Comparative Examples 1-11
Using an alumina raw material with a purity of 99.7% by weight of silica, feldspar and clay with an average particle size of 0.3 to 4.7 μm, the content of SiO ₂ , oxides of alkali metal and / or alkaline earth metal It mix | blended so that content might become the composition of Table 1, mixed and disperse | distributed wet with water, and dried. In Comparative Example 7, the firing temperature was controlled so that the raw material having a small primary particle size had a predetermined average crystal particle size. To 100% by weight of these powders, 6% by weight of methylcellulose and 15% by weight of water were added as a binder, mixed and kneaded to obtain a clay for extrusion molding. Using the prepared clay for extrusion molding, a tube was extruded, and the obtained molded body was fired at 1140 ° C. to 1660 ° C. in the atmosphere to obtain a substrate having an outer diameter of Φ12 mm, an inner diameter of Φ9 mm, and a length of 100 mm. It was. The properties of the obtained substrate are shown in Table 1.
Examples 1 to 7 are substrates included in the scope of the claims of the present invention, and those having good crystallinity of the zeolite membrane were obtained by observation with a scanning electron microscope (SEM) of Example 2 (FIG. 1). It is apparent that the substrate for zeolite membrane has good film-forming properties. On the other hand, Comparative Examples 1 to 11 are substrates that do not satisfy at least one of the conditions of the present invention. For this reason, the formed zeolite membrane was found to have a non-uniform film thickness or a zeolite crystal aggregated. In particular, as shown in the portion surrounded by the dotted line in the SEM observation (FIG. 2) of Comparative Example 7, there were observed aggregates of zeolite membrane crystals.