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.