Patent ID: 8460439

Claim:
A method for controlling the concentration of butanol at or below a predetermined level in one or more fermentation broths comprising butanol and water and contained in one or more respective fermentation vessels, said method comprising: (a) continuously removing a portion of at least one of the fermentation broths from its respective fermentation vessel to form a removed fermentation broth; (b) feeding the removed fermentation broth into a stripping section of an apparatus in which said stripping section is in gaseous communication, but not liquid communication, with an associated absorption section, the apparatus having at least one stripping section with an associated absorption section; (c) simultaneously feeding an inert gas into the stripping section, thereby causing a portion of the butanol to leave the fermentation broth and form (i) a gaseous mixture comprising butanol and the inert gas and (ii) a reduced-butanol fermentation broth; (d) returning the reduced-butanol fermentation broth to its respective fermentation vessel, and allowing the gaseous mixture to enter the absorption section of the apparatus that is associated with the stripping section of step (b); (e) continuously feeding into the absorption section of step (d) an organic liquid absorbent having a lower vapor pressure than that of butanol and an ability to absorb butanol, thereby forming a liquid mixture comprising the liquid absorbent and at least a portion of the butanol from the gaseous mixture, thereby reducing the butanol content in the gaseous mixture to form a reduced-butanol gaseous mixture; (f) returning the reduced-butanol gaseous mixture to a stripping section of the apparatus; and (g) recovering butanol from the liquid mixture and returning the liquid absorbent to an absorption section of the apparatus; thereby, as a result of the method, controlling the concentration of butanol in the fermentation broth.