Kinetics and Mechanism of Delignification of Switchgrass During Niobium Oxide Pretreatment

Abstract

<abstract> Pretreatment is one of the most challenging and expensive steps in using biomass for fuel production. Hence, there is growing interest in exploring alternate pretreatment techniques. Recently it was suggested that biomass could be pretreated via solid acid catalysts. Hence, in this work, we used niobium oxide as a solid catalyst for pretreatment of switchgrass to understand the mechanism and kinetics of the delignification process. Alamo switchgrass was pretreated with 0.25 g g^-1 of niobium oxide at 60°C, 75°C, and 90°C for 20 to 120 min in a 150 mL batch reactor. Subsequently, switchgrass samples were characterized using scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and BET surface area analysis. SEM indicated that niobium oxide pretreatment was able to disrupt the external structure of switchgrass, which was corroborated by BET data. XPS of the pretreated surface indicated an increase in surface oxygen content, suggesting that niobium oxide was able to delignify switchgrass via oxidation. In addition, delignification of switchgrass ranged from 47.65% ±2.04% to 59.03% ±3.28% (60°C to 90°C). After enzymatic hydrolysis, a glucan conversion of 86.62% ±0.26% to 95.87% ±1.3% was also observed. Our results indicate that niobium oxide offers an effective and reusable pretreatment alternative to harsh chemicals that require significant downstream processing.