Process for the separation of dimethyl-iso- and -orthophthalate from a mixture of these esters with dimethylterephthalate

摘要

The invention relates to a process for the separation of dimethyl isophthalate (DMI) and dimethyl orthophthalate (DMO) and other by-products from their mixture with dimethyl terephthalate (DMT), which is formed in the oxidation of p-xylene and subsequent esterification with methanol, by melt crystallization. The esterification product is first distilled one or more times. The DMT-rich fraction obtained is then wholly or partially subjected to one or more melt crystallizations, and the DMI-DMO fraction obtained in this way is at least partially discharged. Alternatively, the DMT-rich fraction is first recrystallized from methanol, then the methanol is evaporated from the mother liquor and the remaining residue is subjected to one or more melt crystallizations. The DMI-DMO fraction obtained is at least partially removed again.