METHOD FOR LOWERING SALT CONTENT OF AQUEOUS SOLUTION OF STILBENE DERIVATIVE AND PRODUCTION OF CONCENTRATED AQUEOUS SOLUTION OF STILBENE DERIVATIVE

摘要

PURPOSE:To lower effectively the content of salts in an aq. soln. of a stilbene derivative, by filtering an aq. soln. of a crude stilbene derivative through a semipermeable membrane mainly composed of polybenzimidazolone under pressure. CONSTITUTION:An aq. soln. contg. 5-10% stilbene derivative (A) of formula I (wherein X1, X2 are each a group of formula II or III, etc. ; Y1, Y2 are each a group of formula IV or V, etc. ; M is hydrogen ion, sodium ion, a quaternary ammonium salt ion, etc.) and 1.5-4% inorg. salts and/or org. amines dissolved therein is filtered under pressure. Namely, said aq. soln. is passed through a semipermeable membrane mainly composed of polybenzimidazolone under pressure to pass the inorg. salts and/or the org. amines together with water through the semipermeable membrane, thus removing them. The stilbene derivative is left on the membrane behind to obtain an aq. stilbene derivative soln. having a low salt content.