Behavior of impregnated activated carbons heated to the point of oxidation Original Research Article

Activated carbons can be impregnated with metal oxides (Cr, Cu, Ag, Mo, Zn, Cc) and/or organic compounds (triethylenediamine (TEDA)) to help capture high vapor pressure substances. However, this process lowers the temperatures of initial oxidation and spontaneous ignition and affects both the CO and CO2 effluent concentrations upon heating. This study quantifies the depression of the point of initial oxidation (PIO) and attempts to find the cause of this depression for commercially available impregnated carbons. PIO and effluent CO and CO2 concentrations were determined with bed depths and linear flow rates specified by current military filtration parameters. The impregnated carbons were repeatedly raised to their oxidation points and cooled, upon which it was found that each subsequent reaction occurred at a slightly higher temperature with the PIO apparently asymptotically approaching a value that was unique to each impregnant formulation. In order (from lowest to highest initial PIO) the carbons tested were ASZM-T (Cu, Ag, Me, Zn, TEDA), ASC (Cr, Cu, Ag), ASZM (Cu, Ag, Mo, Zn), BPL-T (TEDA) and, as a reference, unimpregnated BPL carbon (all supplied by Calgon, Pittsburgh, PA). Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were applied to study the ignition mechanisms. Exothermic reduction of the chromium and copper oxides was found to initiate oxidation of ASC and ASZM, respectively. Thermal decomposition of TEDA, followed by copper oxide reduction, were found to be the initial steps in the ASZM-T ignition process.