PURPOSE: To obtain a porous membrane having a high water flux, excelling in heat resistance, chemical resistance storage stability and handleability and suited for treatment of condensate, treatment of water for supercritical pressure boilers, comprising a polyether-imide having specified repeating units.
CONSTITUTION: A saturated vapor or mist-containing vapor of a poor solvent (C) which is miscible with component B and does not dissolve component A (e.g., water) is fed at a rate of 0.1W1,000mg/sec and forcibly contacted with at least either surface of a thin-film object formed from a 20W40wt.% concentration polymer solution formed by dissolving a polyether-imide (A) having repeating units of the formula (wherein n is 1W7), obtained by polycondensing phenoxyphenyldicarboxylic anhydride with phenylenediamine, in a good solvent (B) such as N-methylpyrrolidone to obtain a porous membrane of an average pore diameter ≤0.20μ, a thickness ≥50μ and a water flux ≥15ml/cm2.min.10psi.
TAKAHASHI HIROSHI
TAKEHATA KOJI
