(355c) Optimization of Process Parameters for Alkaline Pretreatment of Switchgrass

Sodium hydroxide, aqueous ammonia, and sodium carbonate were investigated as pretreatment reagents for Switchgrass. The effect of reagent concentration, size of substrate, temperature and time of treatment on enzymatic hydrolysis was analyzed and optimum conditions were found for the best enzymatic digestibility. The effect of type of alkali on the pretreatment conditions was also studied. A different feedstock (corn stover) was treated in a similar manner for comparison. Switchgrass used in this study was locally grown. It has higher lignin content (26.5% as opposed to 18-22% in other species). It therefore requires pretreatment under high severity conditions as compared to that on the other species of Switchgrass. Each of the alkaline reagents selected has its own merits- they selectively remove lignin, the non-digestible part of the biomass to improve the enzymatic hydrolysis. Ammonia is easily recoverable; NaOH is a strong base, proven delignifying reagent, and Na2CO3 is weaker alkali, but much less expensive than NaOH. Various concentrations of the reagent were used for the treatment and additives like hydrogen peroxide and surfactants were added in small quantities to improve the yields on enzymatic hydrolysis. It was found that the treatment removes 45-75% of lignin. The data were further analyzed to identify the specific effects of particle size, alkalinity, composition of biomass, and liquid/solid ratio on the enzymatic hydrolysis. Representative treated substrates were further studied for surface structure by SEM, BET surface area, and crystallinity by XRD.