Chemisorption of hydrogen sulphide and methanethiol by light expanded clay aggregates (Leca)

• Leca was studied with respect to sorption and chemisorption of H2S, MT and DMS.
• DMS is not degraded but H2S and MT are removed with variable efficiency.
• O2 is not necessary for chemisorption of H2S and MT.
• Moisture content has an influence on removal of H2S and MT.
• Dimethyl disulphide and dimethyl trisulphide are observed as gaseous by-products.

Removal of volatile sulphur compounds from livestock waste air by biological air filtration may be enhanced by application of packing materials with reactive properties. In this study, light expanded clay aggregates (Leca®) was tested with respect to sorption and potential chemical degradation of H2S, Methanethiol (MT) and Dimethyl sulphide (DMS). Leca was selected due to its content of minerals, including iron, and due to its high specific surface area. The performance of Leca was evaluated based on breakthrough curves and by comparing the difference between the inlet and outlet gas concentrations. Whereas DMS did not appear to be removed by Leca, both H2S and MT were removed with variable efficiency depending on the specific conditions. Dimethyl disulphide (DMDS) and dimethyl trisulphide (DMTS) were demonstrated to be produced during the degradation process in relatively high yields. A comparison between ambient air and nitrogen gas conditions showed that the chemisorption of H2S and MT did not necessarily need oxygen to be present. X-ray analysis of Leca showed an abundance of Fe2O3. It is therefore hypothesized that Fe2O3 in Leca can remove H2S and MT by chemisorption. Both air velocity and moisture content clearly affected the capacity of Leca for removal of H2S and MT. Lower removal is seen at higher air velocities, whereas higher moisture content enhances removal. However, chemisorption of MT by Leca appears to be limited above a threshold moisture level. Potential reaction mechanisms are discussed in relation to the observed effects. The results implicate that Leca can be used as a filter material with reactive properties provided that moisture content is controlled and that an adequate air velocity is used.