A process for isolating 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine (DIOPAT) from an aqueous alkaline mixture M having a pH of 10 or more and comprising
- (i) the 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine;
- (ii) 2,4-dihydroxybenzophenone;
- (iii) aluminum salts;
- wherein the process comprises the steps of
- a) separating the 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine from the aluminum salts and the 2,4-dihydroxybenzophenone by nanofiltration of the alkaline mixture M, wherein the 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine is obtained in the form of an alkaline aqueous solution S as the retentate;
- b) precipitating the 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine by modifying the pH of the aqueous solution S to a value of 9.5 or lower;
- c) separating the precipitated 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine from the aqueous solution S by filtration, wherein the 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine is obtained in the form of an aqueous suspension SP as the retentate;
- wherein the nanofiltration step a) is performed at a pressure of from 10 to 30 bar and at a temperature in the range of from 20 to 60° C.