Catalytic conversion of toluene by biochar modified with KMnO4

Abstract

This study aims to investigate the effects of biomass species, modification treatment, experimental time and atmosphere on the catalytic conversion of toluene (tar model compound) by biochar from gasification of oak, wheat straw and Enteromorpha. The gas and liquid phase products are detected by GC and GC–MS, respectively. The physical and chemical characteristics of biochar samples are analyzed by SEM-EDS, BET, XRD and XPS. The results show that the catalytic activity of oak char modified by KMnO4 (Mn-OC) is higher than that of other biochar samples. The KMnO4 modification improves the pore structure, increases oxygen-containing groups and enhances the activity of oak char. The relatively high toluene conversion rate (53.96 %) and low carbon deposition rate (3.41 %) of Mn-OC indicates that KMnO4 is more suitable for the modification of oak char. H2 and aromatic hydrocarbons (especially biphenyl and their derivatives) are the main components of gas and liquid products, respectively. The proportion of H2 in the total volume of H2, CO, CH4 and CO2 of Mn-OC reaches 56.94 %. The addition of water vapor is helpful to the formation of oxygen-containing groups and the improvement of biochar surface structure. Thus, adding moderate water vapor is beneficial to promote the catalytic activity of biochar. The toluene conversion rate and the total volume fraction of four main gases decrease with the increase of experimental time. They reduce significantly when the experimental time is longer than 120 min, from 44.51 % (120 min) to 24.86 % (180 min), which might be due to the damage of pore structure and the consumption of oxygen-containing functional groups.