Direct determination of permeability, diffusivity and solubility of gases in membrane based on simultaneous monitoring of pressure rise and decay in a single time-lag experiment

The time-lag method is the most common approach for evaluating the membrane gas permeability, diffusion and solubility coefficients in a single gas permeation experiment. However, only permeability and diffusivity are determined directly, while the solubility is evaluated from the ratio of permeability and diffusivity. Herein, we present how the conventional time-lag experiment can be used to determine all three transport coefficients directly when, in addition to monitoring the pressure rise in the constant volume downstream from the membrane, the corresponding pressure decay is also monitored in the constant volume upstream of the membrane. The new design of the upstream part of the constant volume (CV) system used in this study allowed pressure decay monitoring. We provide the mathematical fundamentals of the new methods enabled by the new CV system and demonstrate them experimentally using a commercial poly (dimethylsiloxane) PDMS membrane. • Novel design of the upstream part of a constant volume system. • Simultaneous monitoring of pressure decay and rise in the time lag experiments. • Monitoring of gas accumulation in membrane during the permeation tests. • Direct determination of the solubility coefficient in membrane. • Four independent S and D and three independent P from a single permeation test.