NH4Br-Modified Biomass Char for Mercury Removal in a Simulated Oxy-fuel Atmosphere: Mechanism Analysis by X-ray Photoelectron Spectroscopy

Abstract

Mercury from recycled oxy-fuel gas needs to be removed because it can damage the aluminum devices in the system. In this work, low-cost NH4Br-modified rice husk char (RHCBr) was prepared as the biosorbent for mercury removal in an oxy-fuel atmosphere. RHCBr was characterized by scanning electron microscopy, Brunauer–Emmett–Teller, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS) technologies to study the physical and chemical properties of the prepared sorbents. Effects of O2, HCl, SO2, and HCl/SO2 synthesis on mercury removal in a simulated oxy-fuel atmosphere were investigated in a fixed-bed reactor. XPS technology was applied to explore the mercury adsorption species and deduce the potential mercury heterogeneous oxidation mechanism in an oxy-fuel atmosphere. It was found that enriched CO2 in an oxy-fuel atmosphere could facilitate the mercury removal process. Generally, O2 and HCl could promote the mercury removal efficiency in an oxy-fuel atmosphere, while SO2 could inhibit it. However, a low concentration of SO2 could promote it with the presence of HCl and O2. The mercury adsorption species on RHCBr were mainly HgSO4, HgCl2, and HgBr2 in the presence of acid gas components (HCl and SO2). HCl could actively facilitate the generation of C–Cl groups, which were also active sites for mercury removal, while SO2 could generate active site cover NH4HSO4, causing the deactivation of active sites. When HCl/SO2 synthesis was added, active site cover HSO4– would be removed by HCl, facilitating the mercury removal process. Meantime, HgCl2 species could be further converted to the strong-bonded species HgSO4 in the presence of O2 and SO2, which was also beneficial for mercury removal.