METHOD OF LOWERING LEVEL OF CARBOXYBENZALDEHYDE ISOMERS IN TEREPHTHALIC OR ISOPHTHALIC ACID Russian patent published in 2004 - IPC

FIELD: industrial organic synthesis.

SUBSTANCE: improved method of lowering 4-carboxybenzaldehyde in production of terephthalic acid or 3-carboxybenzaldehyde in production of isophthalic acid comprises: (i) dissolving crude terephthalic or isophthalic acid in solvent at 50 to 250^оС to give a solution; (ii) crystallizing purified acid from mentioned solvent at lower temperature and/or lower pressure; (iii) separating crystallized terephthalic or isophthalic acid from solution; (iv) adding oxidant into carboxybenzaldehyde oxidation reactor to oxidize solution filtered in step (iii) resulting in conversion of 4-carboxybenzaldehyde or 3-carboxybenzaldehyde into, respectively, terephthalic or isophthalic acid; (v) evaporating solvent from solution obtained in step (iv); (vi) cooling concentrated solution from step (v) to crystallize additional purified terephthalic or isophthalic acid and filtering resulting suspension, while major portion of mother liquor from step (vi) is recycled into dissolution apparatus in step (i) and its minor portion is discarded. It is also possible to add oxidant to the crude terephthalic or isophthalic acid solution after step (i) in order to eliminate step (iv).

EFFECT: enhanced purification efficiency under moderate temperature and pressure conditions.

40 cl, 2 dwg, 6 tbl, 3 ex