PRETREATMENT OF YELLOW-POPLAR SAWDUST BY PRESSURE COOKING IN WATER

The pretreatment of yellow poplar wood sawdust using liquid water at t emperatures above 220 degrees C enhances enzyme hydrolysis. This paper reviews our prior research and describes the laboratory reactor syste m currently in use for cooking wood sawdust at temperatures ranging fr om 220 to 260 degrees C. The wood sawdust at a 6-6.6% solid/liquid slu rry was treated in a 2 L, 304 SS, Parr reactor with three turbine prop eller agitators and a proportional integral derivative (PID) controlle r, which controlled temperature within +/-1 degrees C. Heat-up times t o the final temperatures of 220, 240, or 260 degrees C were achieved i n 60-70 min. Hold time at the final temperature was less than 1 min. A serpentine cooling coil, through which tap water was circulated at th e completion of the run, cooled the reactor's contents within 3 min af ter the maximum temperature was attained. A bottoms port, as well as p orts in the reactor's head plate, facilitated sampling of the slurry a nd measuring the pH, which changes from an initial value of 5 before c ooking to a value of approx 3 after cooking. Enzyme hydrolysis gave 80 -90% conversion of cellulose in the pretreated wood to glucose. Simult aneous saccharification and fermentation of washed, pretreated lignoce llulose gave an ethanol yield that was 55% of theoretical. Untreated w ood sawdust gave less than 5% hydrolysis under the same conditions.