Study on desulfurization performance of MnO2-based activated carbon from waste coconut shell for diesel emissions control

Abstract

Increasing concern about the air pollution caused by sulfur dioxide (SO2) from diesel exhaust has resulted in the improvement of low-temperature desulfurization materials for the combined SO2 trap. In this study, coconut shell activated carbon (AC) is pretreated by nitric acid to prepare MnO2-based activated carbon materials for SO2 removal. The prepared materials are characterized intensively by SEM, TEM, BET, XRD, FTIR, and XPS. The SO2 capture capacity of these materials are measured at low temperature by thermogravimetry, and the SO2 equilibrium adsorption characteristic is also investigated. The results show that the concentrations of nitric acid do not significantly change the textural properties of MnO2-based AC materials. The content of surface-oxygenated groups (carbonyl carbon and transition) initially increases with the HNO3 concentration rising and reaches the maximum value when the HNO3 concentration is 10 mol/L, resulting in the enhancement of the SO2 capture capacity. SO2 capture capacity of MnO2-based activated carbon decreases after regeneration and keeps stable after several cycles of thermal regeneration. The experimental data for SO2 adsorption on MnO2-based AC composite can fit the Freundlich model well in comparison with Langmuir model.