The Study Of Dry Flue Gas Desulfurization Performance With Modified Palygorskite

Palygorskite, a2:1type clay mineral, a species of hydrated magnesium aluminumsilicate nonmetallic mineral commonly with a lathor fibrous morphology, are characterizedby a porous crystalline structure containing tetrahedral layers alloyed together alonglongitudinal sideline chains. Due to its unique structure, it possess moderate surfacecharge, certain ion exchange capacity, large specific surface area, high adsorption capacityand other physical and chemical properties. So, it has been widely used as adsorbent,catalyst and catalyst support. In addition, since there is vertical channel run through incrystal structure of palygorskite, making it have selective adsorption abilities for manysolar gaseous micro-molecules such as SO₂, H₂S and NH3etc. It has been widely approvedthat the adsorption performance, morphology, surface area, pore size distribution andsurface charge of palygorskite can be improved after appropriate modification.In this paper, palygorskite modified by heat treatment were used for the adsorption ofSO₂; the variations in its structure, morphology and adsorption capacity of SO₂wereinvestigated under diffrent heat treatment conditions. In addition, the effects of differentconcentrations of O₂and H₂O in flue gas on SO₂adsorption were studied under differentadsorption temperature.The structural transformation of Palygorskite desulfurizer duringthe heat treatment process was characterized by X-ray diffraction （XRD）,Brunauer–Emmett–Teller （BET） and Temperature Programmed Desorption（TPD）.An intrinsic correlation between structural properties and desulfurization performance ofpalygorskite adsorbent was discussed. Results indicated that, with the heat treatmenttemperature rising, the micro-crystal structures of palygorskite dispalyed significantly stepchanges which was suggested to be closely related to the removal of water in different formfrom palygorskite surface. The adsorption capacity of SO₂on Palygorskite firstly increasedand then decreased with the heat treatment temperature increasing. Based on these results,It can be deduced that the surface adsorbed water and zeolite water which occupy a largenumber of adsorption sites in palygorskite’s pores inhibiting the adsorption of SO₂, andthus the removal of surface adsorbed water and zeolite water of palygorskite after heattreatment led to the improvement of SO₂adsorption capacity. However, the existence ofcrystalline water is favorable for SO₂adsorption. Therefore adsorption capacity for SO₂ decreased significantly along with the removal of the part of crystallization water in hightemperature. Results showed that: the presence of O₂didn’t effect the SO₂adsorptioncapacity of palygorskite in the temperature range （50²00oC）, indicating that the purepalygorskite is unable for the catalytic oxidation of SO₂, and competitive adsorption wasnot occur between O₂and SO₂.While the presence of H₂O vapor drastically inhibited theabsorption of SO₂on palygorskite when the temperature was below100oC, suggesting theoccurrence of competitive adsorption between H₂O and SO₂. When the absorptiontemperature was higher than100oC, the presence of H₂O didn’t affect the SO₂adsorptioncapacity of palygorskite.In addition, based on the heat treatment of palygorskite, CuO/palygorskitedesulfurizer were prepared by means of pore volume impregnation. The influence of theconditions for preparation and reaction on SO₂removal activity were investigated. Thecharacterization of the CuO/palygorskite desulfurizer has been carried out by XRD、BET、Scanning Electron Microscope（SEM）、TPD and X-ray photoelectron spectroscopy （XPS）.The results showed that the desulfurizer calcinated at300oC was mostly active, calcinationat300oC enable the complete decomposition of the impregnated coppernitrate. TheCuO/palygorskite desulfurizer with10～12（wt）%CuO loading shows the highest activityfor SO₂removal, The decrease in catalytic activity of with the samples with the loading ofhigher than12w%Cu may be due to the sinterring of CuO Within the temperature range of200oC to250oC, the CuO/palygorskite desulfurizers showed highest activity. The O₂influe gas has neglectable influence on the desulfurizers’sulfur capacity. Results show thatthe loading of CuO significantly increase desulfurizers’sulfur capacity, the loading of CuOhas catalysed the oxidation of SO₂, which was confirmed by the analysis of collectedexhaust gas for SO3. The existence of O₂in the flue gas does not significantly improve theremoval of SO₂, indicating that the catalytic oxidation of SO₂due to lattice oxygen of CuO,and O₂in the flue gas can not timely reset the lattice oxygen.