Ethanol recovery process

1. A process for producing a light alcohol, comprising the following steps:

(a) fermenting a sugar to form a fermentation broth comprising the alcohol and water;

(b) performing a first membrane separation step, comprising:

(i) providing a first membrane having a first feed side and a first permeate side;

(ii) passing at least a portion of the fermentation broth as a first feed stream across the first feed side under first conditions that provide a first driving force for transmembrane permeation;

(iii) withdrawing from the first feed side a residue stream depleted in the alcohol compared with the first feed stream;

(iv) withdrawing from the first permeate side a first permeate stream enriched in the alcohol compared with the first feed stream;

(c) performing a dephlegmation step, comprising:

(i) providing a dephlegmator adapted for partial condensation of a gas stream by providing countercurrent flow between the rising gas stream and a falling condensate stream;

(ii) passing at least a portion of the first permeate stream into the dephlegmator as the gas stream;

(iii) withdrawing from the dephlegmator an overhead stream enriched in the alcohol compared with the gas stream;

(iv) withdrawing from the dephlegmator a condensate stream depleted in the alcohol compared with the gas stream;

(d) performing a second membrane separation step comprising:

(i) providing a second membrane having a second feed side and a second permeate side;

(ii) passing at least a portion of the overhead stream across the second feed side under conditions that provide a second driving force for transmembrane permeation;

(iii) withdrawing from the second feed side an alcohol product stream enriched in the alcohol compared with the overhead stream;

(iv) withdrawing from the second permeate side a second permeate stream depleted in the alcohol compared with the overhead stream.

2. The process of claim 1 , wherein the sugar has been prepared by conversion of a plant biomass that comprises a starch or a cellulose.

3. The process of claim 2 wherein the biomass is derived from a plant selected from the group consisting of corn, rice, grapes and trees.

4. The process of claim 1 , wherein the sugar is from a cheese whey.

5. The process of claim 1 , wherein step (a) is carried out as part of a simultaneous saccharification and fermentation process.

6. The process of claim 1 wherein step (a) is carried out using a microorganism.

7. The process of claim 1 , wherein step (a) is carried out using an enzymatic fermentation agent.

8. The process of claim 1 , wherein step (a) is carried out using a yeast.

9. The process of claim 1 , wherein the alcohol is ethanol.

10. The process of claim 1 , wherein the alcohol comprises a mixture of ethanol, iso-propanol and a butanol.

11. The process of claim 1 , wherein the alcohol comprises a mixture of ethanol, acetone and a butanol.

12. The process of claim 1 , further comprising performing a filtration step selected from the group consisting of ultrafiltration, microfiltration, nanofiltration and reverse osmosis between steps (a) and (b).

13. The process of claim 1 , wherein step (b) is carried out as pervaporation.

14. The process of claim 1 , wherein step (b) is carried out using a first membrane selected from the group consisting of polymeric membranes and inorganic membranes.

15. The process of claim 1 , wherein the first conditions that provide the first driving force comprise heating the first feed stream before step (b).

16. The process of claim 1 , wherein the dephlegmator has a length and is further adapted to provide heat exchange between the gas stream and a coolant stream over at least a part of the length.

17. The process of claim 1 , wherein the dephlegmator includes at least a section containing structured packing.

18. The process of claim 1 , wherein heat energy supplied to step (c) by the first permeate stream is supplemented by heating at least a portion of the condensate stream to form a return vapor stream and returning the return vapor stream to the dephlegmator to provide supplemental heat energy.

19. The process of claim 18 , wherein a total heat energy is supplied to step (c) by the first permeate stream and the return vapor stream, and wherein at least 80% of the total heat energy is supplied by the first permeate stream.

20. The process of claim 18 , wherein a total heat energy is supplied to step (c) by the first permeate stream and the return vapor stream, and wherein at least 90% of the total heat energy is supplied by the first permeate stream.

21. The process of claim 1 , wherein a total heat energy is supplied to step (c) and the total heat energy is supplied solely by the first permeate stream.

22. The process of claim 1 , wherein the overhead stream is condensed and then heated before step (d).

23. The process of claim 1 , wherein the overhead stream is compressed before step (d).

24. The process of claim 1 , wherein step (d) is carried out using a second membrane selected from the group consisting of polymeric membranes and inorganic membranes.

25. The process of claim 1 , wherein the condensate stream is recirculated within the process.

26. The process of claim 1 , wherein the condensate stream is recirculated to step (b).

27. The process of claim 1 , wherein the second permeate stream is recirculated within the process.

28. The process of claim 1 , wherein the second permeate stream is recirculated to step (c).

29. The process of claim 1 , wherein the first residue stream is recirculated to step (a).

30. The process of claim 1 , further comprising passing the alcohol product stream to a molecular sieve and withdrawing from the molecular sieve a high-purity alcohol product stream.

31. The process of claim 1 , wherein step (b) is carried out in two sub-steps.

32. The process of claim 1 , wherein step (d) is carried out in two sub-steps.

33. The process of claim 1 , wherein step (a) is carried out on a batch basis.

34. The process of claim 1 , wherein step (a) is carried out on a continuous basis.

35. A process for producing ethanol, comprising the following steps:

(a) fermenting a sugar to form a fermentation broth comprising ethanol and water;

(b) filtering at least a portion of the fermentation broth to produce a filtrate stream;

(c) performing a first membrane separation step, comprising:

(i) providing a first membrane having a first feed side and a first permeate side;

(ii) passing the filtrate stream as a liquid feed stream across the first feed side under first conditions that provide a first driving force for transmembrane permeation;

(iii) withdrawing from the first feed side a residue stream depleted in ethanol compared with the liquid feed stream;

(iv) withdrawing from the first permeate side a first permeate stream enriched in ethanol compared with the liquid feed stream;

(d) performing a dephlegmation step, comprising:

(i) providing a dephlegmator having a coolant flow side and a gas stream flow side and adapted for partial condensation of a gas stream by providing countercurrent flow between the rising gas stream and a falling condensate stream;

(ii) passing at least a portion of the first permeate stream into the dephlegmator as the gas stream;

(iii) flowing a coolant across the coolant flow side in heat-exchanging relationship with the gas stream;

(iv) withdrawing from the dephlegmator an overhead stream enriched in ethanol compared with the gas stream;

(v) withdrawing from the dephlegmator a condensate stream depleted in ethanol compared with the gas stream;

(e) performing a second membrane separation step comprising:

(i) providing a second membrane having a second feed side and a second permeate side;

(ii) passing at least a portion of the overhead stream across the second feed side under conditions that provide a second driving force for transmembrane permeation;

(iii) withdrawing from the second feed side an ethanol product stream enriched in ethanol compared with the overhead stream;

(iv) withdrawing from the second permeate side a second permeate stream depleted in ethanol compared with the overhead stream.

36. The process of claim 35 , wherein heat energy supplied to step (d) by the first permeate stream is supplemented by heating at least a portion of the condensate stream to form a return vapor stream and returning the return vapor stream to the dephlegmator.

37. The process of claim 35 , wherein a total heat energy is supplied to step (d) and at least 80% of the total heat energy is supplied by the first permeate stream.

38. The process of claim 35 , wherein the overhead stream is condensed and then heated before step (e).

39. The process of claim 35 , wherein the overhead stream is compressed before step (e).