Examination of sulfur-functionalized, copper-doped iron nanoparticles for vapor-phase mercury capture in entrained-flow and fixed-bed systems

The use of copper-doped Fe nanoaggregates silanized with organic sulfur as bis-(triethoxy silyl propyl)-tetra sulfide has been investigated for the capture of elemental mercury (Hg⁰) from the vapor phase for potential power plant applications. Silanization procedures resulted in 70% deposition of the targeted sulfur level, with particles containing approximately 4 wt % S. The addition of copper was found to increase the fixed-bed (total) capacity of this type of sorbent from 170 ± 20 μg Hg·g sorbent^-1 with no copper doping to 2730 ± 80 μg Hg·g sorbent^-1 at 1.2 wt % Cu. When no S is deposited, the capacity of Fe/Cu nanoaggregates was only 180 μg Hg·g sorbent^-1. These findings suggest that a combined Cu-S mechanism is responsible for Hg capture. Moving-bed (injection) testing of the Fe-based sorbents in a simulated flue gas stream showed that the 1.2 wt % Cu sample was able to achieve significant removal of the Hg. At a modest sorbent injection rate of 3.6 × 10^-3 g·L^-1·h^-1, this material showed a steady-state removal capacity of 107.5 μg Hg·g sorbent^-1 for an inlet concentration of 17.8 μg·m^-3. On the basis of only 4% usage of the total capacity during single-pass injection, it might be beneficial to develop methods to separate and recycle these materials to reduce power plant operation costs for Hg emissions control.