Research On Solid-phase Catalytic Oxidation Of Magnesium Sulfite In Magnesia Flue Gas Desulfurization

Currently sulfur dioxide emitted from industrial boilers is the main primary pollutant in atmosphere and the vital precursor of haze weather. Magnesium-based desulfurization process has advantages of small occupied area, low investment, energy consumption and rare fouling, which is suitable for small and medium sized industrial boilers particularly. However, lonized catalyst is added to the magnesium sulfite catalytic oxidation mostly, which can’t be recovered effectively and needs to be replenished periodically, then it increases operating costs, the catalyst will be stranded in the mother liquor and the product, causing serious secondary pollution problems.Cobalt salt is used as the main active component of the catalyst, method of chemical oxidation and impregnation-calcinations are adopted to prepare solid catalyst EG/Co-1’ and EG/Co-2’,respectively. According to the result of orthogonal experiment, factors impacting the performance of catalyst EG/Co-1’,such as natural flake graphite, potassium permanganate mix acids, cobalt chloride and the reaction time are investigated and optimum preparation conditions are obtained. Quantity proportion of each material: C: KMnO4: mix acids: CoCl2=1.0:0.7:6.0:0.4, mass ratio of sulfuric acid and nitric acid in mix acids is 1:0,the reaction time is 40 minutes. Optimum preparation conditions of EG/Co-2’ is as follows: 10 mmol cobalt nitrate hexahydrate dissolve in 1 gram expanded graphite and hexyl alcohol as the dispersing agent, under which condition expanded graphite is adsorbed to saturated.Catalysts EG/Co-1’and EG/Co-2’ obtained in the best preparation conditions was used to study magnesium sulfite oxidation reaction kinetics. By changing pH, catalyst mass concentration, initial concentration of magnesium sulfite, oxygen partial pressure and temperature, orders of reagents and the apparent activation energy are achieved. The reaction orders for EG/Co-1’ mass concentration, initial concentration of magnesium sulfite and oxygen partial pressure are 0.3,0,0.65,respectively, and the apparent activation energy is 9.92 kJ.mol-1. Reaction orders for EG/Co-2’ mass concentration, the initial concentration of magnesium sulfite and oxygen partial pressure are 0.31,0,0.56, respectively, and the apparent activation energy is 11 kJ.mol-1. There’s a critical value 7.0 of pH to the oxidation rate of magnesium sulfite, below or above 7.0the rate will decrease. Combining the characterization results, three-phase reaction process model was established, and the total reaction rate of catalytic oxidation of magnesium sulfite was controlled by the mass transfer of oxygen in both presence of the two catalysts.According to the contrastive analysis of SEM and EDS characterization, cobalt capacity and secondary catalytic rate, EG/Co-1’is more effective for the oxidation and recycling of magnesium sulfate. Through studying magnesium sulfite solid-phase catalytic oxidation theory, The results show benefit and theory basis to recycling the residual product in magnesia desulfurization economically and efficiently.