Investigation of biomass degradation mechanism in pretreatment of switchgrass by aqueous ammonia and sodium hydroxide

Pretreatment of switchgrass using aqueous ammonia or NaOH was investigated as a means to enhance the enzymatic digestibility. To increase the effectiveness of pretreatment, H2O2 was supplemented with the alkaline reagents. Since H2O2 is unstable at high temperature, low-to-high step-change of temperature was applied, and this scheme was found to be effective in the case of NH3/H2O2 treatment. The composition of pretreatment liquid indicates that hemicellulose solubilized during alkaline treatment exists either in the form of oligomers or as lignin–carbohydrate complex (LCC). LCC formation was prominent in ammonia treatment and in NaOH/H2O2 treatment, and that LCC formation protects the hemicelluloses sugars from degradation. Lignin in the pretreatment liquor was precipitated and subjected to TGA and FTIR analyses. TGA data indicate that NaOH–lignin has more uniform structure and higher O/C ratio than ammonia–lignin. FTIR analysis indicates that NaOH–lignin has lower aromatic content but higher guaiacyl type structure than ammonia–lignin.