Effects of reduced severity ammonia pretreatment on pelleted corn stover

Biomass densification impacts pretreatment efficacy and subsequent biochemical conversion to biofuels and other biobased chemicals. Pelleted corn stover was used to evaluate the soaking in aqueous ammonia (SAA) pretreatment efficacy at high solid loadings with reductions ammonia concentration, temperature, and pretreatment time. Pretreatment resulted in 70% greater delignification of stover pellets than loose stover. Glucose yields from enzymatic hydrolysis were 49% higher for the pelleted stover and yields did not change with a twofold increase in pretreatment solid loadings. Hydrolysis yields were modeled as a function of pretreatment conditions and the developed model predicted a maximum 24-h hydrolysis glucose yield of 96% at a pretreatment temperature of 60 °C, for 4 h, with 18% ammonia. Pretreatment severity can still be reduced while maintaining 90% or higher yields with different combinations of temperature, time, and ammonia concentration. Temperature was the most important pretreatment parameter within the design space for achieving high glucose yields. FTIR and SEM analysis of SAA-pretreated corn stover pellets illustrated that the pelleting process increases pretreatment efficacy by modifying the biomass structure, disrupting the lignin-hemicellulose linkages, and partially removing lignin. Using pelleted biomass can reduce the required severity of SAA-pretreatment while still producing glucose yields above 90%. Using pelleted corn stover as a biorefinery feedstock has potential to lower pretreatment costs in addition to the improved handling and transportation.