Study On Characteristics Of Mn_xO_y/Al₂O₃ Regenerable Mercury Adsorbent

The influence of mercury and its compounds on human health and environmental protect has become the focus of the world attention due to their acute toxicity.The mercury emission pollution from coal-fired power units also has been increasingly concerned because of coal is the dominant fuel in the energy consumption structure.Although mercury adsorbents injection is considered to be the most promising among the existing mercury removal technologies,the used mercury adsorbents would bring collateral contamination and resource waste,and most of the mercury adsorbents in present studies can not realize reuse.Therefore,to carry out research on regenerable mercury adsorbents is particularly important.In this paper,Mn element was taken for oxygen element matrix,porous alumina material was taken as carrier and impregnation method was adopted to prepare Mn_xO_y/Al₂O₃ adsorbents.The purpose is to research mercury removal characteristic and regenerate characteristic of the adsorbent.Adsorbents modified in different concentration solutions or different activation temperatures were investigated in a fixed-bed reactor to explore the optimal preparation condition.Results showed that Hg0 removal efficiency increased with concentration of modified solution increasing due to the increase of the load of active component,while Hg0 removal efficiency declined with activation temperature increasing due to the decline of the load of effective active components,and the adsorption process was mainly depenedent on mesoporous.Experiments were conducted in different reaction temperatures and different mercury initial concentrations.Results showed that Hg0 removal efficiency increased with reaction temperature increasing due to the fact that higher temperature could reduce the active energy in chemical reaction,Hg0 removal efficiency increased at first then decreased with mercury initial concentration increasing,because the increase of mercury initial concentration would increase the chance of reaction while efficiency declined at higher concentration due to a certain number of active sites.Experiments were also conducted in different concentrations of O₂,SO₂ and NO,and temperature programmed desorption?TPD?and energy dispersive X-ray?EDX?were taken to study the mechanism of mercury adsorption.Results showed that Hg0 removal efficiency had a significant amount in the existence of O₂ condition compared with anaerobic condition,and the efficiency increased slightly with the concentration of O₂,O₂ could promote the mercury adsorption through forming HgO and the reaction followed Mars-Masessen mechanism.Hg0 removal efficiency decreased with the concentration of SO₂ increasing and higher concentration may cause adsorbent sulfur poisoning,SO₂ presented inhibitive effect in reaction overall while SO₂ promoted slightly through forming HgSO4 and ng2SO4.Hg0 removal efficiency increased with the concentration of NO increasing due to NO₂ was produced to form HgO and reaction also promoted by forming Hg?NO3?2 and HgNO3,and the former was dominated.Used adsorbents were treated with TPD or non-thermal plasma to study the mechanisms of thermal regeneration and non-thermal plasma regeneration.Results showed that used adsorbent lose its activity after thermal desorption,for one reason was the ratio of Mn⁴⁺/(Mn⁴⁺+Mn³⁺)on adsorbent surface declined obviously and another was higher temperature caused low-temperature sintering of adsorbent.Hg0 removal efficiency could have a partial rise after non-thermal plasma treatment,while structural damage was irreversible.Used adsorbent had Hg0 removal efficiency from 40%up to 75%after non-thermal plasma treatment,due to the increase of ratio of Mn⁴⁺.The influences of plasma discharge power,plasma discharge time and regeneration frequencies were also discussed.Results showed that active sites could not recover activity due to lower regeneration power and shorter regeneration time,and pore structure would be damaged due to higher regeneration power and longer regeneration time,so the optimal regeneration power and the optimal regeneration time should be considered.Hg0 removal efficiency of the primary adsorbent declined to 80%from 91.70%and remained above 80%after three times of regeneration,therefore,non-thermal plasma treatment was proved to be feasible and effective.