Patent ID: 8231789
Filing Date: 2012-07-31
Classification: B01D,C25D

Abstract:
1. A method of cross-flow filtration using a membrane filter, comprising: feeding a fluid to be filtered across a membrane surface of a porous alumina membrane filter serving as the membrane filter so that the fluid flows parallel to the membrane surface to separate material to be filtered with the porous alumina membrane filter, wherein the porous alumina membrane filter is made of an aluminum anodized film and includes micropores having a degree of ordering as defined by formula (1): (wherein A represents a total number of micropores in a measurement region, and B represents a number of specific micropores in the measurement region for which, when a circle is drawn so as to be centered on a center of gravity of a specific micropore and so as to be of a smallest radius that is internally tangent to an edge of another micropore, the circle includes centers of gravity of six micropores other than the specific micropore) of at least 50%, a porosity as defined by formula (2): (wherein C represents a sum of opening areas of all the micropores in the measurement region; and D represents an area of the measurement region) of at least 40%, and a percentage of a pore size standard deviation to an average pore size of up to 10%, and wherein the aluminum anodized film is obtained by anodizing treatment including the following operations (1) to (4) in this order: (1) subjecting a surface of an aluminum substrate to a first anodizing treatment to form a micropore-bearing anodized film on the surface of the aluminum substrate; (2) partially dissolving the anodized film using an aqueous solution comprising at least one selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, sodium hydroxide, potassium hydroxide, and lithium hydroxide; (3) performing a second anodizing treatment to grow the micropores in a depth direction of the micropores; and (4) removing a part of the anodized film above inflection points in cross section of the micropores.