Abstract: In the process for preparing dimethyl terephthalate by oxydizing p-xylene and/or methyl p-toluate with molecular oxygen or a molecular oxygen-containing gas in the presence of a heavy metal catalyst, esterifying the resulting oxidation reaction mixture with methanol, followed by submitting the resulting esterification reaction mixture to distillation to separate dimethyl terephthalate and fractions of lower boiling point than dimethyl terephthalate, and thereafter recycling to said oxidation step (A) the distillation residue containing said heavy metal catalyst and/or (B) the extract portion containing said heavy metal catalyst obtained by further extraction treatment of said distillation residue (A), the improvement which comprises contact-treating said distillation residue (A) or said extract portion (B) with methanol prior to recycling same.

Abstract: A process for treating an aqueous solution containing organic compounds and having a high chemical oxygen demand (COD) by distilling the aqueous solution at a pH not lower than 9, and recovering the water of low chemical oxygen demand (COD) from said aqueous solution. The aqueous solution containing the organic compounds to be treated is derived from the reaction mixture of the oxidation system of methyl-substituted aromatic compound in the liquid phase with molecular oxygen or a molecular oxygen-containing gas, in the presence of a heavy metal catalyst but in the substantial absence of a lower aliphatic acid solvent, to form the corresponding aromatic acid.