Pretreatment and Enzymatic Hydrolysis of Kenaf as a Potential Source for Lignocellulosic Biofuel and Green Chemicals

Abstract

This study focuses on the conversion of cellulose and hemicelluloses present in kenaf stalks into fermentable sugars using sulfuric acid pretreatment followed by enzymatic hydrolysis. The first step prior to pretreatment was to determine the compositions of hexose, pentose sugars and lignin in pulverized kenaf stalks. Pretreatment on kenaf was performed by varying three independent parameters: 1) reaction temperatures (150 -160 °C); 2) reaction time (10 - 30 min) and 3) diluted sulfuric acid concentration (0.5 – 2.0 %). Regression analysis was employed to examine the effects of these parameters on two responses: 1) the solubility of hemicelluloses in liquid fraction (Y1); and 2) the yield of cellulose digestibility (Y2). The observed R2 values were 0.99 and 0.97 implying the statistical significance of the model equations. The optimum conditions of the factors were 153 °C for 20 min at 1.55% acid concentration. The maximum experimental cellulose digestibility (87%) was observed at 160 °C for 20 min at a 2% acid concentration. The model predicted maximum digestibility was 89% at the same reaction conditions. The results showed that kenaf biomass pretreatment at a low acid concentration (0.5% sulfuric acid) led to limited hemicellulose solubility and therefore resulted in limited cellulose digestibility. The maximum concentrations of fermentable inhibitors were 4.21 g L-1 for acetic acid at 2.29 combined severity factor, 2.29 g L-1 furfural, and 0.71g L-1 Hydroxymethylfurfural (HMF) at 1.75 combined severity factor (CSF). Keywords: Kenaf, Dilute acid pretreatment, Enzymatic hydrolysis, Hemicellulose and cellulose.