Lignocellulosic biomass conversion by sequential combination of organic acid and base treatments

Abstract

The purpose of this research is to explore a new hydrolysis approach using sequential two-step combinations of organic acid (oxalic acid) and base (tetramethylammonium hydroxide, TMAH) to convert lignocellulosic biomass at mild conditions using a spruce wood sample in a batch reactor. A sequential combination of oxalic acid followed by TMAH shows a strong synergistic conversion compared with single- or two-step reactions with either acid or base alone. Analytical characterization of products with several techniques suggests conversion of polysaccharides was enhanced. Examination of spruce residues by SEM suggests acid hydrolysis caused partial structural breakdown of cellulose that facilitates base reaction in the second step. Pre-swelling of spruce with water, oxalic acid, and TMAH showed no significant impact on conversion under the condition employed. Cellulose conversion exhibited synergy in the same trend as that in spruce. Loosening crystalline structure of cellulose lead to higher conversion of spruce, but did not contribute to the synergistic effect. Other chemical factor such as increase in cellulose reducing end could also contribute in part to the cause of the synergy.