Development, characterization, and applications of a portable analyzer for continuous monitoring of H₂S in gas streams

A bench-scale analyzer for continuous monitoring of H₂S in gas streams was previously described (2012 Sens. Actuators B 162 377-83). The analyzer was based on the exothermic reaction between the scrubbed H₂S, in alkaline solution, with hydrogen peroxide. The analyzer offers several advantages but suffers from a relatively slow response time (i.e. 7 min) and a relatively low sensitivity (limit of detection = 100 ppm). In the present work, a substantially improved detector design and direct mixing of the gas with the liquid reagents are described. The improved detector, in the form of a coiled thin-walled stainless-steel (SS) tube also acts as a compartment for direct gas absorption and reaction with sodium hydroxide and hydrogen peroxide reagents, which eliminates the need for a gas scrubber based on microporous hollow fiber membranes (HFMs). The average temperature of the SS coil was measured by three thermocouples attached to the outer surface of the coil with thermally conductive epoxy. The improved detector design and the simplified scheme proved very successful in achieving six times faster response (i.e. 70 s) and ten times more sensitive response (i.e. 10 ppm) in the gas stream and improved repeatability (coefficient of variation = 0.55%). In addition, the previously reported advantages, such as excellent signal stability, wide dynamic range (up to 5% H₂S) and convenient tuning of the sensitivity and linearity by varying the ratio between the gas and reagent flow rates were perfectly retained. The improved detector is utilized to construct a compact portable version of the H₂S analyzer (∼6 kg), which provides a stand-alone operation for real-time monitoring of H₂S in the gas stream for up to 4 h prior to the need for reagent refill or battery recharge. The applications of the described portable analyzer in monitoring H₂S removal from H₂S-N₂ gas stream using an HFM contactor and absorption solvent, and in the determination of sulfide ions in liquid samples are presented. A comparison between the response of the present portable H₂S analyzer and a commercial analyzer is also presented.