Hoechst Aktiengesellschaft

Wilfried Bachmann

Theodor Papenfuhs

Eberhard Mundlos

Rolf Bader

Edgar Wetzel

Gerhard Waese

Horst Buttner

Christian Gnabs

Kurt Janecka

In the process for the purification of diemthyl terephthalate (DMT) by recrystallization from methanolic solution, the mother liquor containing the impurities, substantially the isomers DMI, DMO and aldehydes, is separated off and passed to a workup tank. The moist crystals are dried by melting with the evaporation of methanol. The mother liquor is then separated off by filtration, and the moist crystals obtained from the separation are washed before melting. The washing liquid is recycled together with a portion of the separated mother liquor into the recrystallization tank.

Process for the purification of dimethyl terephthalate

An improved process for isolating 2-hydroxynaphthalenecarboxylic acids from reaction mixtures of the alkali metal salts of the 2-hydroxynaphthalene with carbon dioxide had been found which comprises diluting with water the reaction mixture which contains the di-alkali metal salt of 2-hydroxynaphthalenecarboxylic acid and 2-hydroxynaphthalene, while keeping the mixture at a temperature of at least 80.degree. C, then adjusting the pH-value to about 6 to 7 by means of aqueous mineral acid, separating the lower phase at at least 80.degree. C, cooling the upper phase to about 15.degree. to 25.degree. C, separating the 2-hydroxynaphthalene, then adjusting the pH-value to about 1 to 2 by means of aqueous mineral acid and isolating the separated 2-hydroxynaphthalenecarboxylic acid. By this novel process, work intensive operations, expensive technical apparatuses which are suspectible to repairs, solvents which do not participate directly in the reaction and therewith complicated regenerations, as known from the present art, are completely avoided. It permits clear and very easy separation of the reaction products at only one and the same stage in the process and allows in advantageous manner continuous operation.

Process for isolating 2-hydroxynaphthalene carboxylic acids from

Growing community of inventors

Frankfurt am Main, Germany

Wilfried Bachmann