Portable dual-channel gas analyzer for continuous monitoring of carbon dioxide in gas streams

Abstract

Abstract Development, characterization and application of a portable dual-channel analyzer based on gravity driven flow for continuous monitoring of CO2 in gas streams are presented. The analyzer is constructed from (i) a carrier/stripping solution reservoir, (ii) a diffusion scrubber (DS) in the form of a hollow fiber membrane (HFM) module integrated with a custom-designed flow-through pH-detector cell, and (iii) a waste solution reservoir. The analyzer is designed in such a way that the dilute sodium bicarbonate carrier/stripping solution flows downward by gravity into the lumen side of the hollow fibers in the HFM module which allows efficient contact with the gas stream. Absorption of CO2 into the carrier solution produces pH changes that constituted the analytical signal. Flat-bottom glass electrode and solid-state IrO2 electrodes were used as pH detectors in two types of custom-built flow cells, respectively. Under the optimized conditions, the measured pH signal showed Nernstian response to the CO2 concentration (59.6 and 62.0 mV/log[CO2] and r2 = 0.9992 and 0.9984 for the glass and IrO2 pH detectors, respectively) in the gas stream over a wide dynamic range (0.1-100 % CO2 in balance of nitrogen). Moreover, the presented analyzer based on either detector offered several favorable performance characteristics such as reasonably short response and recovery times; excellent signal stability and reproducibility and high selectivity in the presence of non-ionogenic gases, e.g., CH4, N2, O2, CO, etc. The suggested analyzer was applied successfully in the dual-channel monitoring of CO2 absorption from CO2-CH4 binary feed gas mixtures.