Study On The Fabrication Of MnO₂ Hydrophobic-catalytic Layer On Ceramic Membrane Surface By Hydrothermal Method

Wet flue gas desulfurization is an economical and efficient technology to control sulfur dioxide emission,in which the oxidation of sulfite formed after absorption is a key factor for the efficiency of desulfurization,and the harmless and resourceful treatment of waste water.A novel hydrophobic-catalysis bifunctional MnO₂@Al₂O₃composite membrane was prepared in this paper,to intensify the oxidation of sulfite by efficient loaded catalyst and membrane dispersion.The membrane reactor of sulfite oxidation could be constructed to realize the coupling of hydrophobic membrane dispersion and membrane catalytic process.The fabrication and hydrophobicity of MnO₂@Al₂O₃composite membrane were investigated in this paper.The superhydrophobic MnO₂@Al₂O₃composite membrane was fabricated via the hydrothermal combined with stearic acid impregnation modification method,using ceramic membrane as substrate.The role of roughness and surface energy in the construction of super-hydrophobicity was discussed in detail.The results indicated that the super-hydrophobicity of MnO₂@Al₂O₃composite membrane was collaboratively generated by micro-nano rough surface formed by sea urchins-like MnO₂with nano-thorns and low surface energy groups-CH₂-.The effect of membrane pore size,concentration of the reactants,reaction time,temperature on the morphology and hydrophobicity of MnO₂@Al₂O₃composite membranes was also studied.The results showed that MnO₂nanowires with a higher aspect ratio were formed at higher concentration or longer reaction time.Theγ-MnO₂was transformed toβ-MnO₂with the increase of reaction time.Small size crystals were formed at lower temperature,while,high roughness"mesh"structure was obtained due to anisotropic growth of crystals at higher temperature.The contact angle of composite membranes was raised with the increase of pore size,decreased with the increase of concentration,declined after an initial rise with the increase of reaction time,and decreased slightly after an initial rise with the increase of reaction temperature.The modification mechanisms of modified substances,including stearic acid,fluor silane and siloxane,were also investigated and discussed.Secondly,membrane dispersion&membrane catalytic reactor was constructed,the activity and stability of the superhydrophobic MnO₂@Al₂O₃composite membrane were investigated.The effects of pore size of substrate membrane,the crystal and hydrophilicity-hydrophobicity of MnO₂,as well as modified layers on the oxidation of Na₂SO₃were also studied.The loaded catalyst MnO₂in Na₂SO₃oxidation systems showed high catalytic activity and excellent stability.Its oxidation rate was increased by 37%compared with non-catalytic oxidation,and the initial oxidation rate was maintained consistent during five continuous catalytic oxidation tests.The higher Na₂SO₃oxidation rate of super-hydrophobic MnO₂@Al₂O₃membrane with smaller pore size can be attributed to the uniformly dispersed microbubbles,the higher gas holdup,and the faster mass transfer of O₂and SO₃^2-.Catalytic activity of theβ-MnO₂@Al₂O₃composite membrane was higher than that ofγ-MnO₂@Al₂O₃composite membrane due to its large amount of oxygen vacancies,which could accelerate oxygen migration and increase the oxidation reaction rate of Na₂SO₃.Higher oxidation activity of the super-hydrophobic of MnO₂@Al₂O₃composite membrane compared to hydrophilic surface was mainly because it could avoid the competition between water and oxygen for the active site.The active site of MnO₂was not covered by three modified layers,and steric effect was not occurred.The above results showed that MnO₂@Al₂O₃hydrophobic membrane dispersion and catalytic activity could efficiently enhance the oxidation rate of Na₂SO₃.The results could provide technical supports for catalytic oxidation and resource utilization of sulfite in flue gas desulfurization process.