Facile synthesis of phosphorus-doped porous biochars for efficient removal of elemental mercury from coal combustion flue gas

Abstract

• An efficient sorbent was synthesized for Hg 0 removal through heteroatom doping. • More pore networks and functional groups were formed on the biochar after P doping. • The Hg 0 adsorption capacity of biochar was increased by 411 times after P doping. • The C-P = O, C = O, and O-C = O groups served as active sites for Hg 0 removal. 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 H 3 PO 4 -laden biomass were developed for elemental mercury (Hg 0 ) 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, SO 2 , O 2 , HCl, and H 2 O) on mercury removal performance were also analyzed. At the optimum temperature (100 °C), the Hg 0 adsorption capacity of PBC 900 was increased by more than 400 times compared with BC 900 , which was also higher than that of a commercial brominated activated carbon. The mechanism responsible for Hg 0 removal was further revealed. The results suggested that chemisorption dominated the Hg 0 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 Hg 0 oxidization.