Catalytic oxidation of gaseous reduced sulfur compounds using coal fly ash

Abstract

Activated carbon has been shown to oxidize reduced sulfur compounds, but in many cases it is too costly for large-scale environmental remediation applications. Alternatively, we theorized that coal fly ash, given its high metal content and the presence of carbon could act as an inexpensive catalytic oxidizer of reduced sulfur compounds for “odor” removal. Initial results indicate that coal fly ash can catalyze the oxidization of H 2S and ethanethiol, but not dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) at room temperature. In batch reactor systems, initial concentrations of 100–500 ppmv H 2S or ethanethiol were reduced to 0–2 ppmv within 1–2 and 6–8 min, respectively. This was contrary to control systems without ash in which concentrations remained constant. Diethyl disulfide was formed from ethanethiol substantiating the claim that catalytic oxidation occurred. The presence of water increased the rate of adsorption/reaction of both H 2S and ethanethiol for the room temperature reactions (23–25 °C). Additionally, in a continuous flow packed bed reactor, a gaseous stream containing an inlet H 2S concentration of 400–500 ppmv was reduced to 200 ppmv at a 4.6 s residence time. The removal efficiency remained at 50% for approximately 4.6 h or 3500 reactor volumes. These results demonstrate the potential of using coal fly ash in reactors for removal of H 2S and other reduced sulfur compounds.