Patent ID: 8631946

Claim:
A composite semipermeable membrane comprising a porous support membrane on which a separating functional polyamide layer is formed by a polycondensation reaction of a polyfunctional aromatic amine with a polyfunctional acid halide, wherein the separating functional polyamide layer has carboxy groups, amino groups, phenolic hydroxyl groups, and azo groups, wherein X A is the ratio of the amino groups (molar equivalent of amino groups)/(molar equivalent of azo groups+molar equivalent of phenolic hydroxyl groups+molar equivalent of amino groups) on a feed water contact “A” surface of the separating functional polyamide layer, and X A is in the range 0.5 or less, and X B is the ratio of the amino groups (molar equivalent of the amino groups)/(molar equivalent of azo groups+molar equivalent of phenolic hydroxyl groups+molar equivalent of amino groups) on a permeate-side “B” surface of the separating functional polyamide layer, and X B is in the range of 0.5 to 1, the A and B surfaces being on opposite sides of the composite semipermeable membrane.