Two-stage continuous process for producing a solvent

Abstract

The present invention relates to a two stage continuous microbiological process for the production of solvents such as acetone, butanol and ethanol. Preferably, the process involves the use of a solventogenic bacteria such as clostridia. In the first (acidogenic) stage, the culture vessel is fed with fresh growth media at dilution rates that support fast growth and acid production. The culture flows into the second (solventogenic) stage, which is a separate culture vessel or vessels, designed to provide the culture with sufficient residence time to convert acids into solvents. Preferably this vessel is tubular or a series of linked batch vessels.

1 .- 13 . (canceled) 
     
     
         14 . A system for the production of a solvent, the system comprising:
 (i) a first culture vessel which contains or is adapted to contain a liquid medium suitable for acidogenic growth of an acid- and solvent-producing micro-organism,   (ii) one or more second culture vessels which contain or are adapted to contain a liquid medium suitable for solventogenic growth of the acid- and solvent-producing micro-organism, and   (iii) a pH auxostat,   
       wherein the pH auxostat is arranged to control the pH of the liquid medium in the first culture vessel, and 
       wherein the first and second culture vessels are in liquid communication. 
     
     
         15 . A system as claimed in  claim 14 , wherein the pH auxostat comprises a pH sensor, a pump or pumps, and electronic means capable of operating the pump(s) when the pH in the first culture vessel falls below a predetermined level. 
     
     
         16 . A system as claimed in  claim 14 , wherein the system additionally comprises a vessel which contains or is adapted to contain an alkali; and/or a vessel which contains or is adapted to contain fresh culture media. 
     
     
         17 . A system as claimed in  claim 14 , wherein the second culture vessel(s) are in the form of a long tubular vessel (with or without baffles), a series of linked batch vessels or a single batch vessel. 
     
     
         18 . A system as claimed in  claim 14 , wherein the system additionally comprises a cell separator which is arranged to act on a portion of the liquid media which been removed from the second culture vessel(s); to separate cells from the liquid media in that portion; and optionally to return the cells to the second culture vessel(s). 
     
     
         19 . A system as claimed in  claim 14 , wherein the system additionally comprises means for separating one or more solvents from liquid medium. 
     
     
         20 . A system as claimed in  claim 19 , wherein the solvent(s) are recovered from the liquid medium by liquid extraction means, gas stripping means and/or distillation means.