Enhancing Hemicellulose Recovery and the Enzymatic Hydrolysis of Cellulose by Adding Lignosulfonates during the Two-Stage Steam Pretreatment of Poplar

Abstract

To enhance overall sugar recovery, poplar was steam pretreated in two stages. First, under mild pretreatment conditions (160 degrees C, 15 min) using various acid catalysts (H2SO4, SO2, oxalic, citric) to assess optimum hemicellulose recovery, followed by an uncatalyzed, second pretreatment (200 degrees C, 5 min), to facilitate enzymatic hydrolysis of the cellulose. The first stage solubilized and recovered about 50% of the xylan, as compared to the 30% obtained in the more severe, single-stage pretreatment. As surfactants are known to increase hemicellulose accessibility during pretreatments, lignosulfonates were added to birch xylan and poplar, increasing xylose yields and retaining 60 mmol/kg strong acid groups, even after the second pretreatment stage and extensive washing, suggesting that lignosulfonates adsorbed to the substrate and enhanced cellulose accessibility. This was confirmed by the increased water retention values and Direct Orange dye adsorption. A two-stage steam pretreatment, incorporating lignosulfonate addition, increased cellulose hydrolysis from 75 to 92%.