Upgrading of pyrolysis bio-oil using WO3/ZrO2 and Amberlyst catalysts: Evaluation of acid number and viscosity

Tungstated zirconia (WO3/ZrO2 with WO3 loadings of 9.9 (WZ9.9), 15.5 (WZ15.5), and 15.7 wt% (WZ15.7)) and Amberlyst (15, 35, 36, 39 and 45) catalysts were employed to upgrade pyrolysis bio-oil of acacia sawdust through an esterification reaction using methanol at atmospheric pressure and room temperature or 80 °C. The upgrading efficiency was evaluated by measuring the total acid number (TAN) and viscosity. The viscosity and TAN of the resulting upgraded bio-oil were found to be dependent on the calcination temperature of the WO3/ZrO2 catalysts. At room temperature, the largest decrease in viscosity and TAN of the bio-oil and methanol mixture was obtained using WZ9.9 tungstated zirconia calcined at 900 °C. An increase in reaction temperature to 80 °C improved the flowability and TAN of the methanol-added bio-oil using WZ9.9 activated at 900 °C. The product distribution of the bio-oil upgraded using methanol revealed esterification to be the dominant reaction pathway under the reaction conditions of this study. When the ether extracted bio-oil was upgraded at 80 °C using methanol over catalysts, the Amberlyst catalysts were found more effective than tungstated zirconia catalysts in enhancing the esterification reaction and reducing TAN.