SIMULTANEOUS PRODUCTION OF DIMETHYL TEREPHTHALATE AND DIMETHYL ISOPHTHALATE

PROBLEM TO BE SOLVED: To efficiently and simultaneously produce the subject compounds useful as raw materials, etc., for polyesters by oxidizing a raw material composition containing p-xylene, m-xylene, etc., then esterifying the resultant oxidation product with methanol, recrystallizing the prepared reactional solution, subsequently dissolving a mixture, containing a reaction intermediate and consisting essentially of dimethyl isophthalate and dimethyl terephthalate in the recrystallization mother liquor, subsequently concentrating the mother liquor, distilling the prepared residue, providing a fraction at a high concentration of dimethyl isophthalate, heat-treating the fraction in the presence of a catalyst and then distilling the resultant heat- treated product. SOLUTION: A raw material composition comprising p-xylene, m-xylene or an oxidation derivative thereof is oxidized with a molecular oxygen-containing gas in the liquid phase in the presence of a heavy metallic oxidation catalyst and the resultant oxidation product is then esterified with methanol. The prepared esterification reactional product is subsequently distilled to remove low-boiling and high-boiling components. A main fraction consisting essentially of dimethyl esters is obtained and then recrystallized in a lower alkyl alcohol to recover dimethyl terephthalate from the recrystallized cake. A mixture, containing a reactional intermediate and consisting essentially of dimethyl isophthalate and dimethyl terephthalate is dissolved in the recrystallization mother liquor to afford a solution, which is then concentrated to remove the lower alkyl alcohol. The resultant residue is distilled to provide a fraction at a high concentration of dimethyl isophthalate and the prepared fraction is subsequently heat- treated in the presence of a catalyst and further distilled to simultaneously produce the high-purity objective compounds.