Destructive Adsorption of Chlorinated Volatile Organic Compounds on Calcium Oxide Powder under Air Flow

概要

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The destructive adsorption of dichloromethane (DCM), trichloroethylene (TCE), and perchloroethylene (PCE) on CaO powder under air flow was investigated. CaO pretreated at 823 K showed high activity (100% DCM conversion for 2 h) at 823 K under DCM (1 mol%)/air flow; 0.1 mol of CaO was used in this case. This amount was decided from the calculation data, according to which the amount of Ca2+ ions was equal to the total feed amount of Cl atoms in the reactant (DCM) during a 5-h reaction; CaCl2 was assumed to form in this reaction. During 100% DCM conversion, the main gaseous products formed were CO2, H2O, and CO, and no chlorinated product was formed. This implied that all the Cl atoms were captured in the CaO matrix to form CaCl2, as confirmed from XRD and XRF measurements. On the other hand, CaO was not useful for the destructive adsorption of PCE, and 100% PCE conversion was observed only for 5 min at 873 K under PCE (1 mol%)/air flow when 0.1 mol of CaO was used. When the amount of the reactant fed during a 10-h reaction was maintained at 0.2 mol, which corresponded to the CaO loading amount, the order of reactivity of the abovementioned chlorinated volatile organic compounds over CaO was TCE > DCM > PCE. This order could be explained on the basis of the H/Cl molar ratio in the reactant and the ease of thermal decomposition of the reactant because the destructive adsoption reaction proceeded via the reaction between the produced HCl and CaO.