Process for production of a carboxylic acid/diol mixture suitable for use in polyester production

1. A process for producing a carboxylic acid/diol mixture, said process comprising adding a decolorized carboxylic acid solution comprising a carboxylic acid and water in an esterification reactor zone and adding a diol to said decolorized carboxylic acid solution in said esterification zone; wherein said diol is added to remove at least 5% by weight of said water vaporization from said decolorized carboxylic acid solution to form said carboxylic acid/diol mixture.

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

3. A process for producing a carboxylic acid/diol mixture, said process comprising the following steps:

(a) mixing a crude carboxylic acid powder with water in a mixing zone to form a crude carboxylic acid solution; wherein said carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof;

(b) decolorizing said crude carboxylic acid solution in a reactor zone to produce a decolorized carboxylic acid solution;

(c) optionally, flashing said decolorized carboxylic acid solution in a flashing zone to remove a portion of the water from said decolorized carboxylic acid solution; and

(d) adding said decolorized carboxylic acid solution comprising a carboxylic acid and water in an esterification reactor zone and adding a diol to said decolorized carboxylic acid solution in said esterification zone; wherein said diol is added to remove at least 5% by weight of the said water by vaporization from said decolorized carboxylic acid solution to form said carboxylic acid/diol mixture.

4. A process according to claim 3 wherein said decolorizing is accomplished by reacting said crude carboxylic acid solution with hydrogen in the presence of a catalyst in a reactor zone to produce said decolorized carboxylic acid solution; wherein said catalyst comprises a group VIII metal or combination thereof.

5. A process according to claim 1 or 3 wherein said diol is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof.

6. A process for producing a terephthalic acid/diol mixture, said process comprising the following steps:

(a) mixing a crude terephthalic acid powder with water in a mixing zone to form a crude terephthalic acid solution;

(b) decolorizing said crude terephthalic acid solution in a reactor zone to form a decolorized terephthalic acid solution;

(c) optionally, flashing said decolorized terephthalic acid solution in a flashing zone to remove a portion of the water from said decolorized terephthalic acid solution; and

(d) adding a diol to said decolorized terephthalic acid solution comprising terephthalic acid and water in an esterification reactor zone; wherein said diol is added to remove at least 5% of said water by vaporization from said decolorized terephthalic acid solution to form said terephthalic acid/diol mixture; and wherein said terephthalic acid and diol subsequently reacts in said esterification zone to form a hydroxy alkyl ester stream.

7. A process according to claim 6 wherein said decolorizing is accomplished by reacting said crude terephthalic acid solution with hydrogen in the presence of a catalyst in said reactor zone to produce said decolorized terephthalic acid solution; wherein said catalyst comprises a group VIII metal or combination thereof.

8. A process according to claim 6 wherein said crude terephthalic acid powder contains a concentration of p-toluic acid and 4-carboxybenzaldehyde less than about 900 ppm by weight.

9. A process according to claim 6 wherein said diol is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4 butanediol, cyclohexanedimethanol, and mixtures thereof.

10. A process according to claim 6 wherein said diol is ethylene glycol.

11. A process according to claim 8 wherein said crude terephthalic powder has a b* color less than about 7.

12. A process according to claim 6 wherein said mixing occurs at a pressure between about 900 psia to about 1400 psia.

13. A process according to claim 6 wherein the concentration of crude terephthalic acid in said crude terephthalic acid solution is in a range between about 15% to about 35% by weight.

14. A process according to claim 7 wherein said reacting occurs at a temperature greater than about 230° C.

15. A process according to claim 7 wherein said reacting occurs at a pressure between about 900 psia to about 1400 psia.

16. A process according to claim 7 wherein said reacting occurs at a hydrogen flow rate of about 1.5 times the molar ratio necessary to convert 4-carboxybenzaldehyde to p-toluic acid in said crude terephthalic acid solution.

17. A process according to claim 6 wherein said flashing occurs at a temperature greater than about 150° C.

18. A process according to claim 6 wherein said flashing occurs at a pressure between about 75 psia to about 1400 psia.

19. A process according to claim 6 wherein said adding occurs at a temperature greater than about 240° C.

20. A process according to claim 6 wherein said diol is introduced into said esterification reactor zone at a temperature between about 150° C. to about 300° C.

21. A process according to claim 6 wherein said adding occurs at a pressure between about 40 psia to about 100 psia.

22. A process for producing a terephthalic acid/ethylene glycol mixture, said process comprising the following steps:

(a) mixing a crude terephthalic acid powder with water in a mixing zone to form a crude terephthalic acid solution wherein said mixing zone is operated at a temperature greater than about 230° C., wherein the pressure in said mixing zone is in a range of about 900 psia to about 1400 psia; wherein the concentration of said crude terephthalic acid in said crude terephthalic acid solution is in a range of about 15% to about 35% by weight; wherein the color of said crude terephthalic acid powder is less than about 7 measured by b*; wherein the total concentration of p-toluic and 4-carboxybenzaldehyde in said crude terephthalic acid powder is less than about 900 ppm by weight;

(b) decolorizing said crude terephthalic acid solution with hydrogen in a reactor zone in the presence of a catalyst to form a decolorized terephthalic acid solution; wherein said catalyst comprises a group VIII metal or combination thereof; wherein said hydrogen is introduced into said reactor zone at a flow rate of about 1.5 times the molar ratio necessary to convert 4-carboxybenzaldehyde to p-toluic acid in said crude terephthalic acid solution; wherein said reacting occurs at a temperature greater than about 230° C., wherein said reacting occurs at a pressure between about 900 psia to about 1400 psia;

(c) optionally, flashing said decolorized terephthalic acid solution in a flashing zone to remove a portion of water from said decolorized terephthalic acid solution wherein said flashing zone comprises at least one flash vessel operated at a pressure in the range of about 75 psia to about 1400 psia; and wherein said vessel is operated at a temperature in a range greater than about 150° C.; and

(d) adding a diol to said decolorized terephthalic acid solution comprising terephthalic acid and water in an esterification reactor zone; wherein said diol is added to remove at least 5% by weight of water by vaporization to form said terephthalic acid/ethylene glycol mixture; and wherein said carboxylic acid and diol subsequently reacts to form a hydroxy alkyl ester stream; wherein said diol is ethylene glycol at a temperature in a range of about 150° C. to about 300° C.