Gas analyzer for continuous monitoring of carbon dioxide in gas streams

The construction and characterization of a simple and inexpensive gas analyzer setup for direct measurement of CO₂ concentration in gas streams are presented. The analyzer was based on a hollow fiber membrane (HFM) contactor which served as a mean for continuous gas sampling and preconcentration of CO₂ from the gas stream into a dilute buffer carrier solution. The resultant pH changes of the carrier solution were measured downstream by a pH flow-through detector. A Nernstian response of 55.5 mV/log[CO₂] was obtained over a wide dynamic range of 0.1-100% CO₂ in nitrogen. Moreover, the presented analyzer offered several favorable performance characteristics such as fast response (45 s) and recovery times (1-2 min), excellent signal stability and reproducibility (RSD = 1.2%) and intrinsic high selectivity in the presence of most common neutral gases (e.g., CH₄, N₂, O₂, CO, etc.). H₂S and SO₂ which are potentially interfering acidic gases were efficiently removed by a simple prior in-line treatment using acidified potassium permanganate bubbler. The analyzer was applied successfully to monitor the treatment process of CO₂ removal from CO₂-CH₄ gas mixtures. The merits of the developed analyzer suggest its reliable use in various applications requiring continuous carbon dioxide monitoring in gas streams for several hours.