Tuesday, May 3, 2011
Use of sodium carbonate as a reagent for pretreatment of corn stover and switchgrass was investigated. Sodium carbonate was chosen because it is inexpensive and can easily be recovered using a part of the Kraft pulping process. It is a mild alkaline reagent which can delignify biomass while conserving cellulose and hemicellulose in the solid. This offers an economic benefit since the need for detoxification of liquid stream is eliminated in the bioconversion stage. Biomass was treated in a flow through reactor system at 110 - 180ºC for 10 - 30 min. The pretreatment removed 65% - 75% lignin and 10% - 35% hemicellulose from the biomass, while leaving most of the cellulose intact. The treated substrates yielded 70% glucan digestibility with switchgrass and 80% with corn stover at an enzyme loading of 30mg/glucan. Biomass undergoes many physical and chemical changes after pretreatment. The results of enzymatic hydrolysis of biomass correlated well with pretreatment severity factor, weight loss, and percentage delignification of biomass after pretreatment. SEM images show that pretreatment increases surface area and porosity of the substrate. XRD analysis of biomass indicated an increase in average crystallinity of biomass, but no significant change in the cellulose crystalline structure. Changes in cellulose crystallite size were also detected. FTIR showed changes in the Syringyl/Guaiacyl ratios of the remaining lignin and changes in the bond structure of remaining biomass after pretreatment. TGA showed significant differences in decomposition profiles between the treated and untreated substrate reflecting the chemical changes occurring due to pretreatment.