Determination of sulfide and mercaptans in caustic scrubbing liquor

Abstract

Sulfides and mercaptans, which are important in industrial operations involving the removal of acidic gases by caustic alkali scrubbing, are determined by injecting 10 μl of a simulated scrubber liquid into a water carrier and mixing sequentially with strongly acidic solutions of N,N-dimethyl-p-phenylenediamine and ferric chloride. Both sulfide and mercaptans react; the respective colored products absorb maximally at 670 nm and 500 nm. Simultaneous determination is made possible by using dual wavelength detection. The deliberate use of a short reaction time that results in less than 10% extent of completion of the reaction, and a small sample volume, permits a determination range of 0.1–10 mM (3–320 μg ml−1 S) for each analyte, suitable for the intended application.