Enhancing enzymatic hydrolysis of corn cob, corn stover and sorghum stalk by dilute aqueous ammonia combined with ultrasonic pretreatment

Ultrasound-assisted dilute aqueous ammonia pretreatment under mild operating conditions has been investigated for intensification of enzyme hydrolysis for corn cob, corn stover and sorghum stalk. The effect of the pretreatment temperature (40-70 °C), time (1-4 h) and aqueous ammonia concentration (1.0-4.0 wt%) on the enzymatic hydrolysis sugar yield (EH sugar yield) were investigated. After that, a series of comparative experiments were conducted using ultrasonic, aqueous ammonia and ultrasonic combined with aqueous ammonia pretreatments for the three materials respectively. In addition, X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) of the samples before and after pretreatment were performed in order to investigate the change of the microscopic structures of the biomass. Finally, the main components of the raw materials and the samples after pretreatment by aqueous ammonia or ultrasound-assisted aqueous ammonia were analyzed by van Soest method, indicating the delignification by the pretreatment. It was found that dilute aqueous ammonia combined with ultrasonic pretreatment can improve the accessibility of cellulose in the biomass and improve the enzymatic hydrolysis sugar yield. The largest EH sugar yield was 80.6%, 66.2% and 56.9% for corn cob, corn stover and sorghum stalk, respectively, after the combined pretreatment.