The catalytic oxidation of organic air pollutants. Part 3. Catalysts from manganese and copper sulphates

Manganese sulphate and copper sulphate were evaluated as the basis of catalysts for the control of organic air pollutants responsible for malodorous process emissions. Tests were made with low concentrations, 100 volumes × 10^?6 in air, (i.e. 100 parts × 10^?6 by volume), of methyl mercaptan or mercaptan + n-butanal as a function of temperature and time to determine efficiencies for destructive oxidation. The complex pattern of odorant removal and product formation observed using manganese sulphate is discussed in terms of active sites which convert mercaptan to SO₂ but are inhibited by the onset of dimethyl disulphide formation at higher temperatures; reactions between the odorants may also occur. Copper sulphate formed dimethyl disulphide at the lower temperatures but only SO₂, SO₃, CO and CO₂ were detected above 300°C; after a 100 h durability test at 400°C, the odour removal efficiency determined by dynamic dilution olfactometry was 99.9%. Hence copper sulphate is preferable to manganese sulphate and is equal in performance to the copper oxide tested previously (Part 1) but with the advantage of a stable performance from the outset under sulphating conditions.