Conditioning of so2-ethanol-water spent liquor for fermentation by clostridia

Abstract

The present invention relates to producing chemicals and biofuels from wood material, e.g. mixed forest biomass. Specifically, the invention concerns a process for conditioning spent liquor produced by SO 2 -ethanol-water (SEW) fractionation of wood chips for fermentation to butanol, ethanol and acetone/isopropanol (so called ABE process) by Clostridia bacteria.

1 - 5 . (canceled) 
     
     
         6 . A method for conditioning of a biomass-derived liquor containing sulfur dioxide, said method comprising:
 (a) obtaining a liquor derived from cooking and washing a biomass feedstock, wherein said liquor comprises sulfur dioxide, water, hemicelluloses, and lignin; and   (b) exposing said liquor to catalytic oxidation in the presence of a ferrous sulfate-based catalyst and an oxidant under effective reaction conditions to oxidize said sulfite anions to sulfate anions, thereby generating a conditioned liquor.   
     
     
         7 . The method of  claim 6 , wherein said biomass is selected from hardwoods, softwoods, annual plant fibers, or combinations thereof. 
     
     
         8 . The method of  claim 6 , wherein said liquor further comprises ethanol. 
     
     
         9 . The method of  claim 6 , wherein said ferrous sulfate-based catalyst is ferrous sulfate heptahydrate, FeSO 4 .7H 2 O. 
     
     
         10 . The method of  claim 6 , said method further comprising evaporating and stripping said liquor to remove an amount of sulfur dioxide. 
     
     
         11 . The method of  claim 10 , wherein said stripping is steam stripping. 
     
     
         12 . The method of  claim 10 , said method further comprising separating a lignin-containing precipitate. 
     
     
         13 . The method of  claim 6 , said method further comprising increasing the pH of said liquor to precipitate and remove an amount of sulfur dioxide, in the form of lignosulfonate. 
     
     
         14 . The method of  claim 13 , wherein said pH of said liquor is increased by addition of lime, and wherein said lignosulfonate is calcium lignosulfonate that precipitates from said liquor. 
     
     
         15 . The method of  claim 6 , said method further comprising fermenting said conditioned liquor with Clostridia bacteria. 
     
     
         16 . The method of  claim 15 , wherein said Clostridia bacteria are of species  Clostridium acetobutylicum.    
     
     
         17 . The method of  claim 6 , said method further comprising fermenting said conditioned liquor to a mixture of 1-butanol, ethanol, and acetone. 
     
     
         18 . The method of  claim 6 , said method further comprising fermenting said conditioned liquor to a mixture of 1-butanol, ethanol, and isopropanol.