Method and apparatus for drying carboxylic acid

Abstract

Disclosed is a method and apparatus for drying a wet cake in a carboxylic acid production process. The method comprises employing a contact dryer for drying solid particles of carboxylic acid, where the solid particles can have a residence time of less than about 7 minutes in the dryer and an exit temperature of less than about 250° C. upon exiting the dryer.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A preferred embodiment of the present invention is described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a process flow diagram illustrating a system for the production, purification, and drying of carboxylic acid constructed in accordance with the present invention, particularly illustrating a configuration where the crude slurry from the oxidation reactor is subjected to purification, the resulting purified slurry is subjected to product isolation, and the wet cake from the product isolation zone is subjected to drying in a drying zone;

FIG. 2 is a side view of a dryer that may be used in one embodiment of the present invention with certain sections being cut away to more clearly illustrate the operation of the dryer;

FIG. 3 is a sectional view of the dryer taken along line 3-3 in FIG. 2, particularly illustrating a rotor having a plurality of radial arms affixed thereto and paddles attached to each individual radial arm;

FIG. 4 is a weight percent vs. time plot depicting the thermal gravimetric analyses of purified terephthalic acid (PTA) in air, PTA in nitrogen, crude terephthalic acid (CTA) in air, and CTA in nitrogen, determined in accordance with the procedure described in Example 5; and

FIG. 4 a is a magnified view of the plot depicted in FIG. 4, particularly illustrating the weight percent range from 95 to 100 and the time range from 185 to 285 of the weight percent vs. time plot depicted in FIG. 4.

Claims

1. A method for drying solid particles comprising a carboxylic acid, said method comprising: (a) introducing a wet cake comprising said solid particles into a contact dryer comprising an inner surface; and(b) drying said wet cake in said contact dryer to thereby produce a substantially dry product comprising at least a portion of said solid particles, wherein at least about 10 percent of said solid particles form a layer over at least a portion of said inner surface, wherein said layer has an average thickness of less than about 1.5 inches, wherein said solid particles have an exit temperature of less than about 250° C. upon exiting said dryer.

2. The method of claim 1, wherein said particles have an average residence time of less than about 7 minutes in said dryer.

3. The method of claim 1, wherein said particles have an average residence time of less than about 5 minutes in said dryer.

4. The method of claim 1, wherein at least about 40 percent of said solid particles form a layer over at least a portion of said inner surface, wherein said layer is less than about 1 inch thick.

5. The method of claim 1, wherein said exit temperature is in the range of from about 105 to about 240° C.

6. The method of claim 1, wherein said wet cake is fed to said dryer at a feed rate of at least about 20 lbs/hour per square foot of heated surface area during said drying.

7. The method of claim 1, wherein said wet cake is fed to said dryer at a feed rate in the range of from about 40 to about 175 lbs/hour per square foot of heated surface area during said drying.

8. The method of claim 1, wherein said wet cake has a temperature in the range of from about 20 to 120° C. immediately prior to entering said dryer.

9. The method of claim 1, wherein said substantially dry product comprises less than about 2 weight percent liquid.

10. The method of claim 1, wherein said wet cake comprises in the range of from about 2 to about 25 weight percent liquid.

11. The method of claim 1, wherein said carboxylic acid is terephthalic acid.

12. The method of claim 1, wherein said carboxylic acid is crude terephthalic acid.

13. The method of claim 1, wherein said carboxylic acid is purified terephthalic acid.

14. The method of claim 1, wherein said dryer comprises a jacketed cylinder presenting said inner surface, wherein said inner surface is heated.

15. The method of claim 14, wherein the jacket temperature of said dryer is maintained in the range of from about 120 to about 280° C. during said drying.

16. The method of claim 14, wherein said dryer further comprises a paddle rotor disposed substantially coaxially within said jacketed cylinder.

17. The method of claim 16, wherein said paddle rotor comprises a plurality of radial arms extending from said rotor.

18. The method of claim 17, wherein each of said radial arms comprises a paddle that is rotatable relative to said radial arms.

19. The method of claim 17, wherein said arms and said paddles extend at least about 80 percent of the distance of the annular space created between the outer surface of said paddle rotor and said heated inner surface.

20. The method of claim 17, wherein said radial arms form a substantially helical pattern along the length of said paddle rotor.

21. The method of claim 14, wherein said jacket allows for a heat transfer medium to be circulated therethrough, wherein said heat transfer medium comprises a fluid.

22. The method of claim 21, wherein said jacket comprises a heat transfer medium inlet for introducing said heat transfer medium into said jacket, wherein said heat transfer medium has an inlet temperature in the range of from about 120 to about 280° C.

23. The method of claim 16, wherein during said drying said paddle rotor is operable to facilitate contact of said solid particles with said heated inner surface and to facilitate movement of said solid particles through said jacketed cylinder.

24. The method of claim 16, wherein during said drying said paddle rotor rotates to impart centrifugal force on said solid particles, wherein said centrifugal force is sufficient to overcome the force of gravity thereby forming said layer of said solid particles over at least about 20 percent of said heated inner surface.

25. The method of claim 18, wherein said paddle rotor rotates at a speed such that the tips of said paddles travel at a speed of at least about 10 cm/s.

26. The method of claim 14, wherein said heated inner surface has a temperature in the range of from about 115 to about 265° C. during said drying.

27. The method of claim 1, said method further comprising introducing a drying gas into said dryer to aid in drying at least a portion of said wet cake, wherein said drying gas has an inlet temperature of at least about 100° C.

28. The method of claim 1, wherein said dryer comprises an inert atmosphere during said drying.

29. The method of claim 1, wherein said dryer further comprises a vacuum seal device through which said solid particles exit said dryer.

30. The method of claim 29, wherein said vacuum seal device comprises a rotary air lock valve.

31. A method for producing a substantially dry crude terephthalic acid (CTA) particulate product, said method comprising: (a) oxidizing an aromatic compound in an oxidation zone to thereby produce a slurry comprising solid CTA particles;(b) treating at least a portion of said slurry in a product isolation zone to thereby produce a wet cake comprising at least a portion of said solid CTA particles; and(c) drying at least a portion of said wet cake in a contact dryer comprising an inner surface to thereby produce said substantially dry CTA particulate product, wherein at least about 10 percent of said solid CTA particles form a layer over at least a portion of said inner surface, wherein said layer has an average thickness of less than about 1.5 inches, wherein said solid CTA particles have an exit temperature of less than about 250° C. upon exiting said dryer.

32. The method of claim 31, wherein said particles have an average residence time of less than about 7 minutes in said dryer.

33. The method of claim 31, wherein said particles have an average residence time of less than about 5 minutes in said dryer.

34. The method of claim 31, wherein said substantially dry CTA particulate product comprises less than about 2 weight percent liquid.

35. The method of claim 31, wherein said exit temperature is in the range of from about 105 to about 240° C.

36. The method of claim 31, further comprising using a common vacuum source to create a vacuum in said product isolation zone and said dryer during said treating and said drying.

37. The method of claim 31, wherein said dryer comprises a jacketed cylinder presenting said inner surface, wherein said inner surface is heated, wherein said dryer further comprises a paddle rotor disposed substantially coaxially within said jacketed cylinder.

38. The method of claim 37, wherein said paddle rotor comprises a plurality of radial arms extending from said rotor, wherein each of said radial arms comprises a paddle that is rotatable relative to said radial arms.

39. The method of claim 37, wherein said jacket allows for a heat transfer medium to be passed therethrough, wherein said jacket comprises a heat transfer medium inlet for introducing said heat transfer medium into said jacket, wherein said heat transfer medium has an inlet temperature in the range of from about 120 to about 280° C.

40. The method of claim 37, wherein during said drying said paddle rotor is operable to facilitate contact of said solid particles with said heated inner surface and to facilitate movement of said solid particles through said jacketed cylinder.

41. A method for producing a substantially dry purified terephthalic acid (PTA) particulate product, said method comprising: (a) oxidizing an aromatic compound in an oxidation zone to thereby produce a first slurry comprising solid crude terephthalic acid (CTA) particles;(b) subjecting at least a portion of said CTA particles to purification in a purification zone to thereby produce a second slurry comprising solid PTA particles;(c) treating at least a portion of said second slurry in a product isolation zone to thereby produce a wet cake comprising at least a portion of said PTA particles; and(d) drying said wet cake in a contact dryer to thereby produce said substantially dry PTA particulate product, wherein at least about 10 percent of said solid PTA particles form a layer over at least a portion of said inner surface, wherein said layer has an average thickness of less than about 1.5 inches, and wherein said solid PTA particles have an exit temperature of less than about 250° C. upon exiting said dryer.

42. The method of claim 41, wherein said particles have an average residence time of less than about 7 minutes in said dryer.

43. The method of claim 41, wherein said particles have an average residence time of less than about 5 minutes in said dryer.

44. The method of claim 41, wherein said substantially dry PTA particulate product comprises less than about 1 weight percent liquids.

45. The method of claim 41, wherein said exit temperature is in the range of from about 105 to about 240° C.

46. The method of claim 41, further comprising using a common vacuum source to create a vacuum in said product isolation zone and said dryer during said treating and said drying.

47. The method of claim 41, wherein said dryer comprises a jacketed cylinder presenting said inner surface, wherein said inner surface is heated, wherein said dryer further comprises a paddle rotor disposed substantially coaxially within said jacketed cylinder.

48. The method of claim 47, wherein said jacket allows for a heat transfer medium to be passed therethrough, wherein said jacket comprises a heat transfer medium inlet for introducing said heat transfer medium into said jacket, wherein said heat transfer medium has an inlet temperature in the range of from about 120 to about 280° C.

49. The method of claim 47 wherein said paddle rotor comprises a plurality of radial arms extending from said rotor, wherein each of said radial arms comprises a paddle that is rotatable relative to said radial arms.

50. The method of claim 47, wherein during said drying said paddle rotor is operable to facilitate contact of said solid particles with said heated inner surface and to facilitate movement of said solid particles through said jacketed cylinder.

51. A method for drying a wet cake comprising terephthalic acid (TPA), said method comprising: (a) introducing said wet cake into a contact dryer; and(b) drying said wet cake in said dryer to thereby produce a dry TPA product, wherein during said drying at least a portion of said TPA in said wet cake forms a thin layer on the inside surface of said dryer, wherein said dry TPA product has a temperature in the range of from about 105 to about 240° C. upon exiting said dryer.

52. The method of claim 51, wherein said TPA has an average residence time in said dryer of less than about 7 minutes.

53. The method of claim 51, wherein said dry TPA product has a temperature in the range of from about 125 to about 200° C. upon exiting said dryer.

54. The method of claim 51, wherein said wet cake comprises in the range of from 1 to about 35 weight percent moisture, and wherein said dry TPA product comprises less than 1 weight percent moisture.

55. The method of claim 51, wherein said dryer comprises a jacketed cylinder presenting a heated inner surface.

56. The method of claim 55, wherein said wet cake is fed to said dryer at a feed rate of at least about 35 lbs/hour per square foot of said heated inner surface during said drying.

57. The method of claim 55, wherein said dryer further comprises a paddle rotor having a plurality of blades.

58. The method of claim 56, wherein at least a portion of said blades are angled, shaped, and/or oriented so as to impart centrifugal and axially forward forces on said TPA.

59. The method of claim 55, wherein the jacket temperature of said dryer is maintained in the range of from about 120 to about 270° C. during said drying.

60. The method of claim 51, wherein said contact dryer is a thin layer contact dryer.