Research On Seawater Flue Gas Desulfurization By Modified Clinoptilolite Catalyst

With the increasing requirements of the environmental protection, SO₂dischargedecreased by12.45%than before until2010, which achieved the binding indicator ofthe eleventh five-year plan. Summing up the experience of the reduction of SO₂emission, the contribution of technological progress was up to66%. Therefore, facingthe new challenge of twelfth five-year plan, we should improve and optimize theexisting desulfurization technologies, and come up with innovative ideas in order toincrease the removal efficency of SO₂.With advantages such as no secondary pollution and low cost, seawater gasdesulfurization technology has been applied in the coastal areas. However, due to theabsorption balance of SO₂and the restriction of aeration tank areas, this method hasnot been widely applied widely yet, especially for the high SO₂concentration fluegas.This paper mainly focuses on the preparation and evaluation of the zeolitecatalysts by the methods of impregnation and precipitation for the purpose ofdesulfurization by seawater. After the process of modifyng the zeolite catalysts, thezeolite catalyst was expected to own relatively higher ability to oxidize S（IV） andimprove their removal efficiency of SO₂, and decrease the concentration of S（IV） inthe outlet seawater in order to ease the burden of the seawater recovery stage. Finnaly,these catalyst could be applied for removing SO₂in the condition that theconcentration of SO₂is higher in the flue gas, which is to provide data and theoreticalbasis for removal of high concentration of SO₂by seawater flue gas desulfurizationtechnology.Using different kinds of iron and manganese salts as the precursor, the catalystsare prepared by the methods of impregnation and precipitation. In order to inspect theinfluences of the temperature and atmosphere of baking, the activities of modified catalysts are estimated at different temperatures of reactions. With the help of somecharacterization methods such as XRD, SEM, TG-DTA, BET, TPD and TPR, thereaction pathway between seawater and SO₂in the presence of the catalysts isspeculated.Referring to the relevant experimental results, the desulfurization efficiency ofmodified zeolite catalysts were improved to some extent, while the oxidative abilitywas unsatisfied through the methods of impregnation and precipitation. But if the ironand manganese salts were impregnated simultaneously, the desulfurization efficiencyand oxidative ability would be improved.From the results of350-Fe-Clin in liquid phase, it could be concluded that theoxidation of S（IV） was mainly non-catalytic when pH was approximately at6. Withthe decrease of pH, the oxidative rate decreased correspondingly. And once pHreached3or lower, the modified zeolite catalyst would possess much better catalyticoxidation ability.By the methods of XRD and BET, it showed that the structure of zeolite wouldkeep stable no matter whether the zeolite was modified or the active component wassupported in the pores or on the surface of zeolite. The results of TG-DTA showedthat the modified zeolite catalyst exhibited much stronger absorption for crystal waterand certain amount of stereotypes matter had transformed. The result of SEM-EDSshowed that the content of Fe was4%（wt%） for the modified clin catalyst.The results of temperature-programmed desorption indicated that SO₂absorptioncapacity with350-Fe-Clin was the strongest, which was consistent with the results ofactivity evaluation, among impregnated iron modified zeolite catalysts. Whenconsidering the influence of different absorptive gas conditions, the interactionbetween SO₂and O2contributed to the absorptive suqence.In the absence of theinfluence of internal diffusion and external diffusion, the desorption activation energyof350-Fe-Clin to SO₂was19.85kJ/mol. When conducting TPR in H2atmosphere,with increases calcination temperature, the modified zeolite catalysts in lowcalcination temperature contains some hydroxylation ferric oxides and the amount of them would decrease or disappear.Considering the results of both characterization and activity evaluation, thereaction of SO₂absorped in seawater was analyzed in the presence of catalyst. Theapparent activation energy of350-Fe-Clin is-6.1kJ/mol, which was calculated bysub-liner fitting and integral reactor equation. Refering to the reaction mechanism, thecorresponding activated energy was the difference between the activated energy ofcontrol step and the whole reaction heat.