Gas permeation is increasingly considered for high capacity applications. This contribution discusses the commonly employed membrane module types for flat sheet membranes and suggests a new module concept. The applications considered are the separation of CO 2 from flue gas and hydrocarbon dewpointing of natural gas. Rigorous models for predicting the operating performance of the module types are described. Pilot plant experiments were conducted to validate the model for envelope type modules. Simulation studies were carried out to predict the performances of the different module types for the two examples and assess their advantages and disadvantages.

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On the way toward a carbon-neutral economy, a rise in the demand for separation technologies can be expected. This holds especially for membranes, which are energy efficient and thus very promising technologies. However, this challenges membrane researchers to consider the sustainability and scalability of their membrane fabrication processes. At our institute, we employ a roll-to-roll coating process for the production of thin film composite membranes. This procedure is relatively easy to scale up and can be adapted for different polymers/solvents and thus applications. To increase the production efficiency and optimize the process for any polymer of interest, it is necessary to develop a solid understanding of the physics of this production system. Therefore, we would like to present a numerical model based on computational fluid dynamics that can predict the film thickness of a polydimethylsiloxane-based polymer coated in a roll-to-roll setup. In the future, this model should improve the production efficiency and fine-tuning of process parameters. We verify the numerical procedure with a mesh refinement study and validate the predicted film thicknesses with experimental results for different roll speeds and polymer concentrations. The predicted variability of the thickness is assessed by a design of experiments study and compares relatively well to the measured variations of the coated membrane thickness.

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The PolyActive™ thin film composite membrane (TFCM) has already been successfully applied for CO2 separation tasks at feed pressures up to 10 bar. To investigate the applicability at higher pressures, measurements were undertaken with C2H4 containing gas mixtures with a composition comparable to the product stream of the oxidative coupling of methane process, as well as single gases up to a feed pressure of 30 bar. Furthermore, the permeances of the conducted gas mixture experiments were simulated. The results show a strong swelling influence of CO2 on the used membrane depending on the CO2 fugacity. This swelling effect leads to a pronounced decrease in selectivity. The observed membrane behavior at high pressures could not be predicted by the Free Volume Model (FVM). Two different simulations were conducted: one based on parameters calculated from single gas data measured at pressures up to 2 bar; and a second based on parameters calculated from single gas data measured at pressures from 2 to 30 bar. The two simulations differ in their prediction accuracy. However, they confirm that it is possible to predict the measured permeances in the pressure range up to an average CO2 fugacity of 6 bar.

Porous, porous/gutter layer and porous/gutter layer/selective layer types of membranes were investigated for their gas transport properties in order to derive an improved description of the transport performance of thin film composite membranes (TFCM). A model describing the individual contributions of the different layers’ mass transfer resistances was developed. The proposed method allows for the prediction of permeation behaviour with standard deviations (SD) up to 10%. The porous support structures were described using the Dusty Gas Model (based on the Maxwell–Stefan multicomponent mass transfer approach) whilst the permeation in the dense gutter and separation layers was described by applicable models such as the Free-Volume model, using parameters derived from single gas time lag measurements. The model also accounts for the thermal expansion of the dense layers at pressure differences below 100 kPa. Using the model, the thickness of a silicone-based gutter layer was calculated from permeation measurements. The resulting value differed by a maximum of 30 nm to the thickness determined by scanning electron microscopy.