Schwefeltrioxidbestimmung in Abgasen nach der Isopropanolmethode : Eine kritische Betrachtung

A careful reexamination of the method based on 80% isopropyl alcohol for the determination of SO 3 in flue gases has shown that the results obtained are systematically too low. In the experiments presented these deviations amounted up to 80%; they are especially pronounced at high SO 3 -concentrations and low concentrations of water in the sample. There is strong evidence that under the conditions of absorption SO 3 may react with isopropyl alcohol thereby forming the mono- or di-ester of sulfuric acid. This reaction would therefore be responsible for the low results. To avoid this systematic error the absorption procedure has been modified: The sample gas is first brought in contact with pure water and immediately after with pure isopropyl alcohol. In this way the ester formation is suppressed and all the SO 3 in the sample is found. It has also been shown that the presence of NO X does not lead to the formation of new SO 3 from SO 2 .