Patent ID: 7732173

Claim:
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.