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Abstract:
Heteroatom doping is an effective method to modify carbonaceous sorbents and improve their chemical reactivity. In this study, P-doped biochars (PBCs) derived from one-step pyrolysis of H3PO4-laden biomass were developed for elemental mercury (Hg0) removal from coal-fired flue gas. Sample characterization showed that there were massive micropores and slit-shaped mesoporous in the PBCs. The specific surface area and pore volume of PBCs was obviously enhanced after P doping. In addition, more organic functional groups were generated on the PBCs surface, particularly the C-P=O and C=O groups. The PBCs presented far higher mercury removal efficiency compared with raw biochars (BCs). The influences of pyrolysis temperature (700 °C-1000 °C), adsorption temperature (25 °C-180 °C), and various flue gas components (NO, SO2, O2, HCl, and H2O) on mercury removal performance were also analyzed. At the optimum temperature (100 °C), the Hg0 adsorption capacity of PBC900 was increased by more than 400 times compared with BC900, which was also higher than that of a commercial brominated activated carbon. The mechanism responsible for Hg0 removal was further revealed. The results suggested that chemisorption dominated the Hg0 removal process, where the C-P=O, C=O, and O-C=O groups could serve as electron acceptors, accelerating the electron migration process for Hg0 oxidization.
