Patent ID: 7485747

Claim:
A process for reducing the content of 4-carboxybenzaldehyde and p-toluic acid in a benzene dicarboxylic acid composition comprising terephthlatic acid and containing less than a total of about 150 ppmw 4-carboxybenzaldehyde and p-toluic acid comprising: (1) feeding (i) paraxylene, (ii) aqueous acetic acid medium having an oxidation catalyst comprising a source of cobalt, a source of manganese, and a source of bromine dissolved therein, and (iii) an oxygen-containing gas to a first pressurized oxidation zone wherein liquid-phase, exothermic oxidation of paraxylene occurs, wherein the temperature and pressure within the first pressurized oxidation reactor are maintained at conditions of about 150 to 165° C. and about 3.5 to 13 bars absolute (bara) to produce an oxidizer composition comprising (i) dissolved terephthalic acid and terephthalic acid solids having the by-products 4-carboxybenzaldehyde and p-toluic acid, and (ii) an aqueous, acidic reaction medium having the oxidation catalyst composition dissolved therein; (2) removing from the upper portion of the first reactor a vapor comprising vaporized aqueous, acetic reaction medium and oxygen-depleted gas; (3) removing from the lower portion of the first reactor said oxidizer composition; (4) feeding (i) the oxidizer composition of step (3) and (ii) an oxygen-containing gas to a second pressurized oxidation zone wherein liquid-phase, exothermic oxidation of 4-carboxybenzaldehyde and p-toluic acid occurs, wherein the temperature and pressure within the second pressurized oxidation reactor are maintained at about 185 to 230° C. and about 4.5 to 18.3 bara, wherein the conditions in said first pressurized oxidation zone are effective to produce terephthalic acid solids containing said by-products that are accessible to further oxidation in said second pressurized oxidation reactor to provide a 4- carboxybenzaldehyde and p-toluic acid content of less than 150 ppmw in step (7) below; (5)removing from the upper portion of the second reactor a vapor comprising vaporized aqueous, acetic reaction medium and oxygen-depleted gas; (6)removing from the lower portion of the second reactor a second oxidizer composition comprising (i) solid and dissolved terephthalic acid and (ii) the aqueous, acetic acid reaction medium having the oxidation catalyst composition dissolved therein; and (7)separating terephthalic acid from the (ii) aqueous, acetic acid reaction medium of step (6) to a obtain terephthalic acid composition containing less than about 150ppmw 4-carboxybenzaldehyde and p-toluic acid.