An examination of the efficacy of aqueous ammonia pretreatment at different scales

Aqueous ammonia soaking has gained attention as a relatively mild form of lignocellulose pretreatment, capable of fractionating lignin at moderate temperatures (below or close to 100 °C). To test the scalability of the pretreatment process, corn stover was subjected to aqueous ammonia pretreatment at the 45-ml, 250-ml, 1-liter and 75-liter scales. Pretreatment was carried out at 110 °C for 6 hours. Partially milled corn stover was mixed with 15% w/w aqueous ammonia, the resulting slurry having a dry solids loading of 15% w/w. Following pretreatment, solids were washed and their composition determined through NREL analytical procedures. Using the composition data, a material balance was developed around the carbohydrates and the fractionation examined at the different scales. Washed pretreated solids were then subjected to SSF for 48 hours at 10% w/w solids loading using cellulase, ß-glucosidase and xylanase and S. cerevisiae. As with the pretreatment, SSF was repeated at the 200-ml and 30-liter scales. Liquid samples (1-5 ml) drawn throughout the process were analyzed through HPLC to generate concentration data, through which sugar release was tracked. Using the sugar data, the feasibility of large-scale ammonia pretreatment was examined.