Enzymatic post-hydrolysis of water-soluble cellulose oligomers released by chemical hydrolysis for cellulosic butanol production

A process consisting of regeneration of crystalline cellulose, dilute-phosphoric acid hydrolysis of regenerated cellulose to soluble oligomers, and enzymatic post-hydrolysis of soluble oligomers in the absence of disturbing solid particles was evaluated as a process alternative for upgrading the obtainable sugar concentration and facilitating the long-term enzymatic hydrolysis of cellulose by utilizing soluble oligomers instead of insoluble particles. Cellulose was regenerated though phosphoric acid-acetone process, i.e., dissolution into 21g/g acid at 50 degrees C for 60min and precipitation by adding 41g/g acetone. Regenerated cellulose was hydrolyzed at 120, 150 or 180 degrees C for 30 or 60min using 0.5 or 1% phosphoric acid. After filtration, the hydrolysates were subjected to 10 or 15 FPU/g cellulase. Dilute-acid hydrolysis of regenerated cellulose with 0.5% acid at 180 degrees C, 30min, and 10% solid loading resulted in an oligomeric hydrolysate with 44.6g/L soluble oligomers. Enzymatic post-hydrolysis of soluble oligomers resulted in a monomeric hydrolysate containing as high as 47g/L glucose and cellobiose. In the hydrolysis, 429g sugar was released at high concentration from one kg crystalline cellulose. The hydrolysates were subjected to fermentation by Clostridium acetobutylicum, where oligomeric hydrolysates showed poor fermentability. The fermentation of monomeric hydrolysates obtained by dilute-acid hydrolysis (120 degrees C, 60min, and 0.5% acid) and post-hydrolysis (15 filter paper unit/g) resulted in 6.1g/L acetone-butanol-ethanol. Besides other potential advantages, this hydrolysis approach resulted in relatively high concentration of glucose which may facilitate cellulosic butanol production. [GRAPHICS] .