Cao, Zheng2025-10-162025-10-162025-10-16http://hdl.handle.net/10393/50931https://doi.org/10.20381/ruor-31456The field of membrane science has experienced remarkable advancements in gas separation technologies recently. A key challenge in enhancing membrane performance is exceeding the "upper bound" limit, which requires simultaneously high permeability and selectivity. To meet this goal, reliable and swift membrane characterization techniques are critical in the process of developing new materials for gas separation membranes. The time-lag method is the most widely used technique for determining the gas transport coefficients in gas separation membranes, which allows evaluating membrane permeability (P), diffusivity (D), and solubility (S) coefficients in a single permeation experiment. However, the conventional time-lag method is limited by the accuracy of the monitoring system, and when applied to more complex cases or more advanced materials. The objective of this thesis is to explore more efficient and reliable membrane characterization techniques to overcome these challenges. In this project, we developed and employed a novel constant-volume (CV) system that enables simultaneous monitoring of dynamic upstream pressure decay and the downstream pressure rise. This innovative CV system allowed us to leverage both upstream pressure decay and downstream pressure rise to propose new membrane characterization methods for a more robust determination of P, D, and S. The resolution and the accuracy of the system were significantly improved by splitting the upstream into the working volume and the reference volume. A new experiment protocol was also presented to minimize the impact of the adiabatic expansion during the initiation of the test. Thanks to the advantage of the system, we proposed and validated a series of new methods using a rubbery membrane, namely polydimethylsiloxane (PDMS). The transport properties obtained through these new methods yielded transport coefficients that were very close to those determined using the conventional time-lag method. To better calibrate the system, this work also studied some potential artifacts in the system. The effect of using a porous support disc on estimating the membrane's effective transport parameters was explored by numerical simulations. The results show that relative diffusivity and relative permeability are strictly a function of the porosity of the porous disc and the ratio of the pore diameter to the membrane thickness, which can be used to correct the impact of the porous plate and recover the intrinsic membrane properties. Based on the improved experimental system and analytical protocol, we investigated the influence of the applied pressure on membrane transport properties due to the phenomenon known as the membrane compaction effect. To systematically evaluate this effect, we first measured the thickness of the compressed membranes under different loads in a high-precision testing machine. Next, we utilized our novel CV system to characterize the membrane transport properties under different pressure conditions. The experimental results revealed an apparent reduction in the transport properties of the PDMS membrane as it underwent compression due to gas pressure differentials. To determine the most probable values of the transport, a data reconciliation technique was employed, considering both methods and measurement deviation. This approach minimizes an objective function that integrates all sources of variation. A gradient descent optimization algorithm was then applied to converge on the best estimates of P, D, and S. The reconciled results improve the consistency and precision in estimating transport properties compared to the original results. In parallel with our experimental work, we conducted numerical simulations, including the finite difference (FD) method, electrical analogy networks, and the Monte Carlo (MC) technique, to complement and enhance our findings. These simulations generated upstream and downstream pressure-time profiles corresponding to membrane behavior, providing valuable insight into the actual experimental data. To examine the effect of a porous support disc on the membrane's effective transport parameters under ideal conditions, we solved Fick's second law of diffusion using the finite difference method. The results clearly showed that the membrane thickness, the pore size, and the disc porosity can significantly influence the estimation of the diffusivity and permeability of the membrane when using the time-lag method. These findings not only help calibrate our new CV system more accurately but also offer theoretical support for characterizing more complex materials, such as glassy polymers and mixed-matrix membranes.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/Membrane characterizationConstant volume systemsTime-lag methodPorous support plateMixed matrix membranesPDMS membraneData reconciliationThesis