MnOx-TiO2吸附剂对燃煤烟气中汞的脱除

以锐钛矿型TiO_2为载体,采用浸渍法对其进行MnO_x改性制备脱汞吸附剂,探究了负载量、焙烧温度、反应温度及烟气组分等参数对吸附剂脱汞性能的影响。利用N_2吸附-脱附、TG/DTG、XRD、FT-IR、Hg-TPD、XPS等方法对吸附剂的理化性质进行了表征。结果表明,Mn的最佳负载量为12%,最佳焙烧温度和反应温度分别为450和300℃,在实验条件下MnO_x-TiO_2吸附剂可达到的最佳脱汞效率为98.46%。烟气中少量的O_2及微量的HCl对吸附剂的脱汞有较强的促进作用;SO_2对吸附剂的脱汞有较强的抑制作用,SO_2与Hg~0存在的竞争吸附作用以及脱汞反应中产生的硫酸盐覆盖活性位点表面,是导致脱汞效率下降的主要原因。烟气中的CO_2和NO也会对汞的脱除产生轻微的抑制作用。负载在吸附剂上的MnO_x存在Mn~(4+)、Mn~(3+)两种价态,其中,Mn~(4+)将Hg~0氧化为Hg~(2+),自身被还原为Mn~(3+)。结合实验和分析结果发现,Hg~0的吸附和氧化基本遵循Mars-Maessen和Langmuir-Hinshelwood机理。

Removal of elemental mercury (Hg0) from simulated flue gas over MnOx-TiO2 sorbents

A series of MnO_x modified TiO₂ based sorbents were synthesized using wet impregnation method and its performance on elemental mercury (Hg⁰) removal was studied. The effects of loading amount, calcination temperature, reaction temperature, and flue gas compositions on mercury removal efficiency were investigated. The sorbents were characterized by TGA, N₂ adsorption-desorption, XRD, FT-IR, XPS and Hg-TPD. It was shown that the optimum MnO_x loading value was 12%, and the optimal calcination and reaction temperature were 450 and 300 ℃, respectively. The highest mercury removal efficiency of MnO_x-TiO₂ sorbent was 98.46%. O₂ and HCl in flue gas played a positive role in mercury removal. SO₂ had a strong inhibitory effect on mercury removal, which may be due to the competition adsorption between SO₂ and Hg⁰. At the same time, the manganese sulfate produced during the reaction covered the surface of the active site, resulting in the decrease in mercury removal efficiency. CO₂ and NO in flue gas also slightly inhibited mercury removal. Mn⁴⁺ participated in oxidizing Hg⁰ to Hg²⁺, accompanied with its reduction to Mn³⁺. The adsorption and oxidation process of Hg⁰ over MnO_x-TiO₂ basically conformed to the Mars-Maessen mechanism and Langmuir-Hinshelwood mechanism.