SO2 crossover flux of Nafion® and sFS-PBI membranes using a chronocoulometric (CC) monitoring technique
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A chronocoulometric electrochemical measuring technique was used to evaluate the gas flux and permeation properties of sulphuric acid dissolved SO2 across various polymeric membranes, using an in-house assembled permeation setup. This was done in the temperature and differential pressure range of 298–353 K and 0–2 bar respectively. The sulphuric acid concentration was varied between 30 and 90 wt%. The electrochemically measured current due to SO2 oxidation at the platinum electrode was converted to molar gas flux using Faraday's law. The flux was found to decrease as the temperature increased for all the evaluated membranes for example from 2.16×10−8±0.15 mol s−1 cm−2 at 298 K to 1.46×10−8±0.15 mol s−1 cm−2 at 353 K for Nafion® 112. The flux was found to increase with increasing Δp across the membrane and decrease with increasing acid concentration. From the flux data we were able to calculate the SO2 permeation, diffusion and solubility parameters for the various membranes.The measured and calculated values were compared to existing literature values. The lowest SO2 crossover was observed at high temperatures, low differential pressures and high H2SO4 concentrations.