Co-production of bioethanol and biodiesel from corn stover pretreated with nitric acid

This research explores the application of glucose and xylose from corn stover pretreated with nitric acid (HNO3) for the co-production of bioethanol and biodiesel. Response surface methodology was employed to optimize HNO3 pretreatment condition including HNO3 concentration (0.2-1.0%), temperature (140-160 °C), and reaction time (1-10 min). The optimal reaction condition was 151.9 °C, 0.68% HNO3 and 2.5 min, which resulted in the highest xylose yield of 77.8% and glucan content of 57.1%. Quasi-simultaneous saccharification and fermentation (Q-SSF) of pretreated corn stover with Saccharomyces cerevisiae gave an ethanol concentration of 22.4 g/L, corresponding to 69.1% theoretical ethanol yield based on initial cellulose weight. In addition, Cryptococcus curvatus in hydrolysate medium showed the lipid yield (final cell weight × lipid content) of 1.04 g/L, which was higher than those in defined medium using pure xylose. Our work demonstrates that the simultaneous production of ethanol and lipid can be one potentially promising option for lignocellulose-derived fuel production.