Polyester production system employing horizontally elongated esterification vessel

1. A process comprising:

subjecting a reaction medium comprising terephthalic acid to esterification in an esterification zone defined within a horizontally elongated substantially empty esterification vessel,

wherein said esterification vessel has a length-to-diameter (L:D) ratio less than 10:1,

wherein said reaction medium enters said esterification vessel via a fluid inlet and is subjected to esterification to produce a liquid product and a vapor by-product,

wherein said liquid product exits said esterification vessel via a liquid outlet, said liquid outlet is horizontally spaced from said fluid inlet by 1.25 D or more, said reaction medium is agitated and flows substantially horizontally through said esterification vessel,

and further wherein the vapor by-product flows through said esterification vessel generally above said reaction medium and exits said esterification vessel via a vapor outlet that is horizontally spaced from said fluid inlet by 1.25 D or more,

and wherein the reaction medium in the esterification vessel undergoes little or no mechanical agitation inside the esterification vessel.

2. The process of claim 1 , wherein 0 percent of the agitation is provided by mechanical agitation.

3. The process of claim 1 , further comprising adding heat to said reaction medium in said esterification vessel, wherein the amount of heat added to said reaction medium in said esterification vessel is 20 BTU/pound or less.

4. The process of claim 1 , wherein said esterification vessel has an L:D ratio ranging from 1.25:1 to 8:1.

5. The process of claim 1 , wherein the average depth of said reaction medium in said esterification vessel is 0.75 D or less.

6. The process of claim 1 , wherein said esterification vessel has an L:D ratio ranging from 1.5:1 to 6:1, and wherein the average depth of said reaction medium in said esterification vessel is 0.5 D or less.

7. The process of claim 1 , wherein said vapor outlet is vertically spaced from said liquid outlet by 0.5 D or more.

8. The process of claim 7 , wherein said esterification vessel comprises a downwardly extending baffle around which said vapor by-product must flow before exiting said vapor outlet.

9. The process of claim 7 , wherein foam is generated in said esterification vessel, wherein substantially no foam exits said esterification vessel through said vapor or liquid outlets.

10. The process of claim 1 , wherein said reaction medium enters said esterification vessel having a conversion of 50 percent or more.

11. The process of claim 1 , wherein the residence time of said reaction medium in said esterification vessel is 45 minutes or less.

12. The process of claim 1 , further comprising heating said reaction medium in a heat exchanger before introduction into said esterification vessel, wherein the conversion of said reaction medium increases by 5 percentage points or more in said heat exchanger.

13. The process of claim 12 , wherein said reaction medium exits said heat exchanger and enters said esterification vessel having a conversion of 50 percent or more.

14. The process of claim 13 , wherein the conversion of said reaction medium increases by 2 percentage points or more in said esterification vessel.

15. The process of claim 12 , wherein the temperature of said reaction medium increases by 50° F. or more in said heat exchanger.

16. The process of claim 12 , wherein the residence time of said reaction medium in said heat exchanger is 60 minutes or less.

17. The process of claim 12 , wherein said heat exchanger comprises tubes at least partly surrounded by a heat transfer medium, wherein said reaction medium flows through said tubes.

18. The process of claim 17 , wherein the volume of said esterification vessel is greater than the aggregate internal volume defined by all the tubes of said heat exchanger.

19. The process of claim 1 , further comprising transporting at least a portion of a liquid phase of said reaction medium from a liquid outlet of said esterification vessel to a fluid inlet of said esterification vessel via a recirculation loop.

20. The process of claim 19 , wherein the total volume of said esterification vessel is 50 percent or more of the total internal volume defined by said recirculation loop.

21. The process of claim 19 , wherein the total volume of said esterification vessel is 75 percent or more of the total internal volume defined by said recirculation loop.

22. The process of claim 19 , wherein said recirculation loop includes a heat exchanger for heating said reaction medium before introduction into said esterification vessel and a recirculation pump for pumping at least a portion of said liquid phase.

23. The process of claim 19 , further comprising withdrawing a product portion of said liquid phase from said recirculation loop and subjecting at least a fraction of said product portion to further esterification in a downstream esterification zone, subjecting said product portion to polycondensation in a downstream polycondensation zone, or both.

24. The process of claim 19 , further comprising introducing an acid into said recirculation loop.

25. The process of claim 24 , wherein said acid is a solid when introduced into said recirculation loop, and wherein said liquid phase aids in the dissolution of said acid.

26. The process of claim 24 , further comprising introducing an alcohol into said recirculation loop.

27. The process of claim 1 , wherein said reaction medium comprises an acid and an alcohol.

28. The process of claim 27 , wherein said alcohol comprises ethylene glycol.

29. The process of claim 1 , wherein the reaction medium in the esterification vessel undergoes no mechanical agitation inside the esterification vessel.