NOVELTY - Controlling (M1) the concentration of butanol at or below predetermined level in at least one fermentation broth comprising butanol and water and contained in at least one fermentation vessel involves: continuously removing a portion of the fermentation broths from fermentation vessel to form a removed fermentation broth; and feeding the removed fermentation broth into a stripping section of an apparatus in which the stripping section is in gaseous communication, but not liquid communication, with an associated absorption section.    USE - For controlling the concentration of butanol at or below a predetermined level in at least one fermentation broth comprising butanol and water in a fermentation vessel (claimed), for the production of butanol by fermentation of sugar and which is useful as a fuel.    ADVANTAGE - The process is economical and does not require a limitation on sugar loading. The process solves the problem of toxic butanol levels which can destroy microorganisms in a fermentation process by ensuring that butanol concentration is maintained below the tolerance level of the fermentation microorganisms and allowing for subsequent recycle of the microorganisms back to the fermentation vessel, thereby enhancing the efficiency of the process.    DETAILED DESCRIPTION - Controlling (M1) the concentration of butanol at or below a predetermined level in at least one fermentation broth comprising butanol and water and contained in at least one fermentation vessel involves:    (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 (22) of an apparatus in which the stripping section is in gaseous communication, but not liquid communication, with an associated absorption section (20), 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 a gaseous mixture comprising butanol and the inert gas and 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 absorbing 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 controlling the concentration of butanol in the fermentation broth.    INDEPENDENT CLAIMS are included for the following:    (1) recycling at least one fermentation broth comprising fermentation microorganisms from a fermentation process where butanol is produced in at least one fermentation vessel, involving: (a) removing a portion of the fermentation broth comprising fermentation microorganisms where the butanol is produced from its respective fermentation vessel to form a removed fermentation broth comprising fermentation microorganisms; (b) feeding the removed fermentation broth comprising fermentation microorganisms into a stripping section; (c) simultaneously feeding an inert gas into the stripping section, thereby causing a portion of the butanol to leave the removed fermentation broth comprising fermentation microorganisms and form (i) a gaseous mixture comprising butanol and the inert gas, and (ii) a reduced-butanol fermentation broth comprising fermentation microorganisms; and (d) returning the reduced-butanol fermentation broth comprising fermentation microorganisms to its respective fermentation vessel; and    (2) an intermediate composition comprising a butanol-rich absorbent phase comprising about 5-15% butanol and an organic liquid absorbent having a lower vapor pressure than butanol.    DESCRIPTION OF DRAWING(S) - The figure shows an apparatus having stripping and absorption sections for removing butanol from a fermentation broth.    Column (10)    Compression equipment (14)    Absorption section (20)    Stripping section (22)    Lines (32, 34, 36, 38)