Membrane gas separation at low temperatures and high activity levels

• Membran-Gastrennung bei tiefen Temperaturen und hohem Aktivitätsniveau

Alders, Michael Theo; Wessling, Matthias (Thesis advisor); Favre, Eric (Thesis advisor)

Aachen : RWTH Aachen University (2020, 2021)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik series - AVT.CVT - chemical process engineering 19 (2021)
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

Membranes represent an energy-saving separation process for the treatment of gas mixtures and are increasingly established in commercial gas treatment. Commonly, mass transport through membranes is described using a simple solution diffusion model (SDM). However, this model implicitly contains many simplifications and assumptions, whereby the SDM is often applied far beyond the admissibility of these simplifications. In the past, new materials for gas permeation membranes have been evaluated primarily according to their pure gas selectivity at ≈ 35℃. However, it is known that many materials show a higher selectivity at low temperatures. In a first step, published permeation data of hundreds of polymers is collected and evaluated. The aggregation of these data allows the systematic analysis of temperature sensitive material properties of gas permeation membranes. Material system specific properties are also investigated. The aggregation of this data reveals general trends in temperature dependence as well as specific properties depending on the type of polymer. The resulting data is then used to improve classical gas treatment processes by reducing the operating temperature. For this purpose, a techno-economic process model is created and linked to the membrane parameters. Through non-linear global optimization, the optimal operating temperature of a process can be determined specifically for each material system. In the case of rubber-like membranes, an increase in membrane selectivity can also be caused by swelling effects. A semi-empirical permeation model is used to systematically predict these effects. As an example, the model is used to determine parameters for PDMS as the most ideal membrane material. With the help of this model it is now possible for the first time to predict the membrane behaviour in the presence of higher hydrocarbons qualitatively and quantitatively for different temperatures. These mixing effects also raise the question of the basic physical behavior of polar and non-polar vapors in PDMS membranes, which is subsequently investigated. For hydrocarbons the results correspond to the expected behaviour, but for polar vapors effects are observed which cannot be conclusively clarified. However, possible causes are described and discussed intensively. Finally, an outlook is given on further applications and separation tasks that can benefit from the knowledge gained in this work.

Institutions

• Chair of Chemical Process Engineering and Institute of Process Engineering [416110]