Recovery of higher alcohols from dilute aqueous solutions

A method to recover a C3-C6 alcohol from a fermentation broth comprising microorganisms and the C3-C6 alcohol, comprising:

• a. decreasing the activity of water in a portion of the fermentation broth to at least at least that of saturation of the C3-C6 alcohol in the portion;
• b. forming a water-rich liquid phase and a C3-C6 alcohol-rich phase from the portion of the fermentation broth;
• and
• c. separating the water-rich phase and the C3-C6 alcohol-rich phase.

A method to produce a C3-C6 alcohol, comprising:

• a. culturing a microorganism in a fermentation medium to produce the C3-C6 alcohol;
• b. increasing the activity of the C3-C6 alcohol in a portion of the fermentation medium to at least that of saturation of the C3-C6 alcohol in the fermentation medium;
• c. forming a C3-C6 alcohol-rich liquid phase and a water-rich phase from the portion of the fermentation medium;
• d. separating the C3-C6 alcohol-rich phase from the water-rich phase;
• and
• e. conducting the water rich phase to the fermentation medium in the step a.

A method to produce a C3-C6 alcohol, comprising:

• a. hydrolyzing a feedstock comprising a polysaccharide and at least one other compound to produce fermentable hydrolysis products;
• b. fermenting a least a portion of the fermentable hydrolysis products in a fermentation medium to produce the C3-C6 alcohol, wherein the fermentation medium further comprises at least one non-fermented compound;
• c. increasing the activity of the C3-C6 alcohol from a portion of the fermentation medium to at lest that of saturation of the C3-C6 alcohol in the fermentation medium;
• d. forming a C3-C6 alcohol-rich phase and a water-rich phase from the portion of the fermentation medium;
• e. separating the C3-C6 alcohol-rich phase and a water-rich phase;
• and
• f. separating the at least one non-fermented compound from the fermentation medium, the water-rich phase or both.

A method to produce a C3-C6 alcohol, comprising:

• a. culturing a microorganism in a fermentation medium to produce the C3-C6 alcohol;
• b. increasing the activity of the C3-C6 alcohol in a portion of the fermentation medium;
• c. distilling the portion of the fermentation medium to produce a vapor phase comprising water and C3-C6 alcohol and a liquid phase, and
• d. conducting the liquid phase to the fermentation medium.

A method to operate a retrofit ethanol production plant comprising a pretreatment unit, multiple fermentation units, and a beer still to produce a C3-C6 alcohol, comprising:

• a. pretreating a feedstock to form fermentable sugars in the pretreatment unit;
• b. culturing a microorganism in a fermentation medium comprising the fermentable sugars in a first fermentation unit to produce the C3-C6 alcohol;
• c. treating a portion of the fermentation medium comprising the C3-C6 alcohol to remove a portion of the C3-C6 alcohol;
• d. returning the treated portion of the fermentation medium to the first fermentation unit;
• and
• e. transferring the fermentation medium from the first fermentation unit to the beer still.