The Effect of Lignin Content and Freeness of Pulp on the Bioethanol Productivity of Jabon Wood

Abstract

This research was intended to evaluate the potential of bioethanol production from Jabon wood. Kraft pulping was conducted to achieve pulp with kappa number of 0, 10, 20, 30, 40, and 80. Fully bleached pulp was prepared from pulp with kappa number of 15. The resulted pulps were beaten with PFI mill to achieve the freeness level of 400, 300, 200, and 100 mL CSF. Ethanol was produced through SSF process. Reducing sugars and ethanol concentration were determined by Nelson-Somogyi method and gas chromatography (GC), respectively. Significant increase of reducing sugar was achieved by pulp beating to 100 mL CSF. Pulp with Klason lignin of 12 % produced the highest total and residual reducing sugar (11.5 and 9.4 %, respectively), but with the lowest fermented reducing sugar (2.2 %). Pulp with 0 % Klason lignin resulted in the lowest residual reducing sugar (2.7 %) and the highest fermented reducing sugar (8.4 %). Pulp with Klason lignin of 0.0 and 1.5 % at the freeness level of 100 mL CSF resulted in the highest ethanol yield (16.4 and 14.4 %, respectively) and cellulose conversion (24.2 and 22.1 %, respectively). Above 4.5 % concentration, lignin hampered reducing sugar fermentation. Promising performance of enzymatic hydrolysis was achieved when pulp was at least 50 % delignified and relatively high ethanol yield was gained with at least 94 % lignin removal. In view of delignification and increasing beating intensity of pulp increased sugar and ethanol production, the present results support the possibility of repurposing kraft mills for the production of cellulose-based bioethanol.