Method for oxidizing a slurry composition in a post oxidation zone in the presence of added steam

1. A process to produce a crystallized post oxidation composition said process comprising the following steps in the order named:

(a) oxidizing an aromatic feedstock at a temperature of about 110° C. to about 200° C. in a primary oxidation zone in the presence of a catalyst system to form a crude carboxylic acid composition; wherein said catalyst system comprises cobalt;

(b) routing said crude carboxylic acid composition in a solid liquid displacement zone to form a slurry composition and a mother liquor; wherein at least a portion of said catalyst system in the crude carboxylic acid composition is removed in the mother liquor; wherein additional solvent is fed to said solvent liquid displacement zone;

(c) oxidizing at a temperature of about 180° C. to about 280° C. in a post oxidation zone said crude carboxylic acid composition or said slurry composition in said post oxidation zone in the presence of added steam to form a post oxidation composition and an offgas stream; wherein said post oxidation zone comprises at least one post oxidation device; wherein said post oxidation composition comprises 4-carboxybenzaldehyde; and wherein said post oxidation zone results in at least 70% by weight conversion of said 4-carboxybenzaldehyde to terephthalic acid; and

(d) crystallizing in a crystallization zone said post oxidation composition to form said crystallized post oxidation composition; wherein said crystallization zone comprises at least one crystallizer.

2. The process according to claim 1 wherein said crystallized post oxidation composition has a b* color of less than 3.5.

3. The process according claim 1 wherein said carboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof.

4. The process according to claim 1 wherein said carboxylic acid is terephthalic acid.

5. The process according to claim 4 wherein said added steam is used to heat the post oxidation device to a temperature in a range from about 180° C. to about 280° C.

6. The process according to claim 5 wherein said post oxidation device is operated at a pressure of about 10 barg to about 50 barg.

7. The process according to claim 4 wherein said crystallizer is operated at a temperature between about 140° C. and 190° C.

8. The process according to claim 1 wherein said aromatic feedstock comprises para-xylene.

9. The process according to claim 1 wherein said solvent is acetic acid.

10. The process according to claim 9 wherein said aromatic feed stock comprises para-xylene.

11. A process to produce a purified post oxidation composition comprising the following steps in the order named:

(a) oxidizing an aromatic feedstock at a temperature of about 110° C. to about 200° C. in a primary oxidation zone in the presence of a catalyst system to form a crude carboxylic acid composition; wherein said catalyst system comprises cobalt;

(b) routing said crude carboxylic acid composition in a solid liquid displacement zone to form a slurry composition; and a mother liquor; wherein at least a portion of said catalyst system in the crude carboxylic acid composition is removed in the mother liquor; wherein additional solvent is fed to said solvent liquid displacement zone;

(c) oxidizing at a temperature of about 180° C. to about 280° C. in a post oxidation zone said crude carboxylic acid composition or said slurry composition in the presence of added steam to form a post oxidation composition; wherein said post oxidation zone comprises at least one post oxidation device; wherein said crude carboxylic acid composition comprises at least one carboxylic acid; wherein said post oxidation composition comprises 4-carboxybenzaldehyde; and wherein said post oxidation zone results in at least 70% by weight conversion of said 4-carboxybenzaldehyde to terephthalic acid and

(d) purifying said post oxidation composition in a purification zone to form said purified post oxidation composition having b* color of less than said post oxidation composition; and wherein said b* is less than 4.5.

12. The process according to claim 11 where said purified post oxidation composition has a b* color less than 3.5.

13. The process according to claim 1 wherein said carboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof.

14. The process according to claim 1 wherein said carboxylic acid is terephthalic acid.

15. The process according to claim 14 wherein said added steam is used to heat said post oxidation device to a temperature in a range from about 180° C. to about 280° C.

16. The process according to claim 15 wherein said post oxidation device is operated at a pressure of about 10 barg to about 50 barg.