(532d) Pretreatment of Herbaceous Biomass by Sodium Carbonate in Batch and Percolation Reactors

Alkyl-aryl linkages in lignin are readily cleaved in alkaline conditions and the reaction is independent of [OH-] concentration, as long as pH is maintained in the alkaline region. For this reason, alkaline reagents generally show much higher selectively for reaction with lignin than carbohydrates in biomass. With this understanding, we have explored newer and cheaper reagents for alkaline pretreatment of biomass. Sodium Carbonate is among such candidates as it is 4-6 times cheaper than sodium hydroxide and also easier to recover than NaOH. In this study, sodium carbonate was used for pretreatment of Switchgrass and Corn stover in two different reactor systems. One was Soaking in Aqueous Alkali (SAAL) and the other was Sodium Carbonate Percolation (SCP). Both processes were effective in delignifying biomass. The SAAL process removed 65-70% lignin from Switchgrass while SCP process removed 70-75% lignin. With these treatments, the enzymatic glucan digestibility of 70% was obtained with Switchgrass, and 85% with Corn stover. The SCP process required higher temperature, but much less treatment time (20 min or less) than SAAL. Corn Stover was pretreated more effectively than Switchgrass by both processes, giving 10-15% higher digestibility than the latter. Optimum process conditions were determined considering the enzymatic digestibility and retention of carbohydrates. Effects of pretreatment conditions were further investigated over a broad range of temperature, time of treatment and solid/liquid ratio. TEM and SEM images were taken to examine the effects of pretreatment on both substrates. Increase in crystallinity index by XRD indicated that amorphous parts of biomass were lost during pretreatment, while there was no change in cellulose crystalline structure. FTIR reaffirmed the delignification of biomass after pretreatment.