Upcycling coal liquefaction residue into sulfur-rich activated carbon for efficient Hg0 removal from coal-fired flue gas

Abstract

Recent, carbon-based adsorption technology, especially activated carbon with element-doping treatment, has been considered an effective approach to capture elemental mercury (Hg0) from coal-fired flue gas. In this study, a novel sulfur-rich activated carbon (S/AC) was in-situ derived from coal liquefaction residue (CLR) with KOH activation, which can make full use of the sulfur in CLR and simplify the preparation process. The effects of KOH to CLR weight ratios and activation temperatures on Hg0 removal performance were discussed. The S/AC was characterized by N2 adsorption/desorption, XRD, SEM, TEM-EDS, XPS and Hg-TPD techniques. A fixed-bed reactor was used to estimate the Hg0 removal performance of sorbents. The effects of adsorption temperatures and flue gas components on Hg0 removal performance were also evaluated. The sorbent exhibited excellent Hg0 removal performance with the KOH to CLR weight ratio of 1:2 and the activation temperature of 800 °C. The Hg0 removal efficiency was stabilized at 97% at 60–120 °C with a gas hourly space velocity (GHSV) of 7.5 × 104 h−1. Both SO2 and NO exhibited positive influences on S/AC sorbents for Hg0 capture. The XPS and Hg-TPD results indicated that sulfur is primary active site for Hg0 removal, and the mercury adsorbed on S/AC sorbent was HgS. The research indicated that CLR is a potential raw material for synthesizing high efficient S/AC sorbents for Hg0 removal from flue gas.