(374k) Ethanol and Value-Added Chemicals Produced From Corn Stover Pretreated by Novel Methods

Corn (Zea mays L.) stover is among the most high-yielding agricultural residues, making it an important feedstock for biofuel production. Biochemical conversion of corn stover to fuels and value-added chemicals will open up new agricultural markets and provide significant societal benefits to the rural community and agro-industries. Acidic electrolyzed water (AEW) and alkaline electrolyzed water (ALEW) were used in this study as reagents in a one-step pretreatment, and the effectiveness was compared, using glucan conversion yield, with other pretreatment methods. In a second set of experiments, lignin was first removed with an ethanol-alkaline solution, followed by a hot-water pretreatment to deconstruct corn stover for the production of ethanol and value-added chemicals. In this study, these two methods were evaluated for conversion of corn stover into fermentable sugars. The fermentablility of the hydrolyzates obtained from the pretreatments was also examined. AEW and ALEW were used in the one-step pretreatment at three temperatures (165, 180, and 195°C) and 3 treatment times (10, 20, and 30min). A solid loading of 12.5% w/w was used (5g dry corn stover to make a 40g slurry). With an enzyme loading of 15FPU cellulase/ g glucan and 40U beta-glucosidase/ g glucan, the enzymatic hydrolysis was conducted in 100mL VITLAB flasks in a shaker water bath at 50°C and 200rpm for 120h with a solid loading of 6.25%. In the tests for the new two-step pretreatment, an organic alkaline solution of 1% NaOH in 70% ethanol was used for lignin removal in the 1st step of pretreatment. The slurry of 5g dry corn stover and 50mL organic alkaline solution was put into flasks incubated in a shaker water bath at 80°C for 2h. After incubation, the supernatant was removed for lignin recovery. The remaining solid was washed into tubular reactor with DI water for the 2nd step pretreatment at 120, 135, 150, and 165°C for 30min in a sandbath. The solid loading was controlled at 5g dry corn stover in 50mL DI water. The supernatant of the 2nd step was also removed for chemicals recovery, and the solid residue was subjected to hydrolysis. Except the hydrolysis time of 96h and the solid loading of 7.7%, the other conditions in the enzymatic hydrolysis remained the same as those in the one-step pretreatment experiments. In the electrolyzed water one-step pretreatment experiments, the highest glucan conversion yield (66%) was obtained with the AEW treatment at 195°C for 30min. The highest glucan conversion yield in the two-step pretreatment experiments was 83%, which was achieved for the pretreatment at 135°C for 30min. Besides, the hydrolyzates from samples pretreated with the two methods were tested for fermentability of ethanol.