Method for purification of alcohols

1. A method to recover a C3-C6 alcohol from a stream comprising C3-C6 alcohol, ethanol and water in a recovery system, comprising:

a. separating a water-rich liquid phase from a C3-C6 alcohol-rich liquid phase;

b. conducting the water-rich liquid phase to a column to produce a vapor stream comprising water and ethanol;

c. conducting the vapor stream to a rectification column to produce a liquid distillate comprising water and ethanol, wherein the liquid distillate is not reintroduced to the recovery system; and

d. recovering C3-C6 alcohol from the alcohol-rich liquid phase.

2. The method of claim 1 , wherein the vapor stream is enriched in low molecular weight alcohols.

3. The method of claim 2 , wherein the low molecular weight alcohols comprise C2 and C3 alcohols.

4. The method of claim 1 , further comprising conducting the C3-C6 alcohol-rich liquid phase to a dehydration column to dehydrate the C3-C6 alcohol and produce a C3-C6 dehydrated alcohol comprising less than about 1 wt % water and greater than about 96 wt. % of a single C3-C6 alcohol.

5. The method of claim 4 , further comprising conducting the greater than about 96 wt. % C3-C6 alcohol to a purification column to purify the C3-C6 alcohol to solvent grade C3-C6 alcohol.

6. The method of claim 5 , wherein the solvent grade C3-C6 alcohol comprises greater than about 99.1 wt. % of a single C3-C6 alcohol.

7. The method of claim 1 , wherein the stream is a portion of a fermentation broth.

8. The method of claim 1 , further comprising:

conducting a bottom liquid produced in the rectification column to a distillation column to remove ethanol and produce a distilled bottom liquid; and

conducting the distilled bottom liquid to the step of separating a water-rich liquid phase from a C3-C6 alcohol-rich liquid phase.

9. The method of claim 1 , further comprising sub-cooling a vapor distillate produced in the rectification column to recover a substantial portion of the vapor distillate and recycle the substantial portion of the vapor distillate to the recovery system.

10. The method of claim 1 , wherein the method to recover the C3-C6 alcohol from the feed stream is conducted in a retrofit ethanol production plant, wherein the retrofit ethanol production plant comprised an ethanol recovery system, wherein the column in step (b) is a column from the ethanol recovery system.

11. The method of claim 10 , wherein the column in step (b) is a first partition portion of a column from the ethanol recovery system.

12. The method of claim 10 , wherein the recovery system further comprises a dehydration column.

13. The method of claim 10 , wherein the column is a stripping column from the ethanol recovery system.

14. The method of claim 12 , wherein the dehydration column is a retrofit rectification column of the ethanol recovery system.

15. The method of claim 11 , wherein the recovery system further comprises a dehydration column and wherein the dehydration column is a second partition portion of the column from the ethanol recovery system.

16. The method of claim 10 , wherein the method to recover a C3-C6 alcohol in the retrofit ethanol production plant does not require a molecular sieve.

17. The method of claim 10 , wherein the method to recover a C3-C6 alcohol in the retrofit ethanol production plant does not use a molecular sieve.

18. The method of claim 1 , wherein the C3-C6 alcohol is selected from the group consisting of propanol, butanol, pentanol, and hexanol.

19. The method of claim 18 , wherein the C3-C6 alcohol is butanol.

20. The method of claim 19 , wherein the butanol is selected from the group consisting of 1-butanol, 2-butanol, tert-butanol (2-methyl-2propanol), and isobutanol (2-methyl-1-propanol).

21. The method of claim 19 , wherein the butanol is isobutanol (2-methyl-1-propanol).