A novel oxidative method for the absorption of Hg⁰ from flue gas of coal fired power plants using task specific ionic liquid scrubber

A simple continuous process is described for the removal of mercury from gas streams (such as flue gas of a coal fired power stations) using imidazolium based Task Specific Ionic Liquids [TSILs] with the general structure ([RMIM][XI₂^-]) where X=Cl, Br or I. The latter are formed by blending dialkylimidazolium halide salts with iodine. When applied in a gas/liquid scrubber, these salts were shown to absorb >99% of elemental mercury originally present in a gas stream in concentration of 75-400ppb. The mercury abatement is attained by oxidating the mercury to HgI₂ which is bound as a stable IL complex ([RMIM⁺][XHgI₂^-]. The novel absorption system exhibits a remarkable mercury concentration factor of seven orders of magnitude. The final solution obtained contains up to 50% (w/w) mercury in the IL. Upon exposure to sodium formate, directly added to the saturated IL at 45°C, reduced metallic mercury swiftly precipitated from the solution and could be quantitatively separated and collected. The free IL could be fully recycled.