Patent ID: 7202380

Claim:
A method of producing pyromellitic acid, which comprises: a step of liquid-phase oxidizing 2,4,5-trimethylbenzaldehyde by molecular oxygen in water solvent; a step of separating the reaction liquid from the liquid-phase oxidation step into crude crystals of pyromellitic acid and a mother liquor; a step of recrystallizing the crude crystals of pyromellitic acid from water solvent to obtain a recrystallization mixture; a step of separating the recrystallization mixture into a recrystallized pyromellitic acid and a recrystallization mother liquor; a step of removing a part of the water solvent from the separated recrystallization mother liquor, thereby obtaining a condensed recrystallization mother liquor; and a step of recycling the condensed recrystallization mother liquor at least to the liquid-phase oxidation step, wherein a surplus water produced by at least one of the liquid-phase oxidation and the recycling of the recrystallization mother liquor is recovered by evaporation.