Catalytic microwave-assisted torrefaction of sugarcane bagasse with calcium oxide optimized via Taguchi approach: Product characterization and energy analysis

Abstract

The production of biochar, bio-oil, and biogas from sugarcane bagasse (SB) is investigated via catalytic microwave-assisted torrefaction where calcium oxide is employed as a microwave absorber. Using the Taguchi approach, three parameters of microwave power, holding time, and catalyst concentration are considered. The optimal combination of the three parameters provides the highest energy yield of 77.64%. The highest calorific value is recorded at 24.66 MJ⋅kg−1, demonstrating a 46.96% improvement compared to the dry-basis raw feedstock. The results from ANOVA indicate that microwave power significantly affects the energy yield, followed by the holding time and catalyst concentration. Scanning electron microscopy shows severe degradation of SB surfaces while XRD curves demonstrate the retention of the crystalline structures of the torrefied SB samples. The main compounds identified in the bio-oil are phenolic compounds. FTIR results show no significant changes in the functional groups after acid-washing and catalyst impregnation. The upgrading energy index profiles portray that light torrefaction conditions lead to higher energy efficiencies, rendering higher energy yields while consuming less energy inputs. Overall, catalytic microwave-assisted torrefaction with calcium oxide is a feasible technique to transform SB into bioenergy products such as biochar, bio-oil, and biogas. More importantly, attaining a balance between product quality and energy efficiency is crucial for the feasible production of fuels that are ready for industrialization.