Lyotropic Liquid Crystals: CO2 Capture and Phase Behavior
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The rising greenhouse gas emissions, in particular CO2, have contributed to an increase of the global temperature. In order to combat the severe effects of climate change, actions are being taken to favor a switch to low carbon technologies, such as renewable energy and carbon capture and storage (CCS). In the past years, research has focused on increasing the efficiency of existing CCS technologies, as well as developing new systems for CO2 capture. The motivation behind this work was to develop a new technology that can be used in the three stages involved in CCS, namely CO2 capture, transport, and storage. Specifically, the goal of this project was to select a polymer system to form lyotropic liquid crystals, and to characterize the liquid crystals in terms of CO2 absorption, microstructure, and rheology. Information about the physical properties of the liquid crystals is a valuable tool to assess the potential use of liquid crystals for CCS applications. Amphiphilic copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) were selected due to their commercial availability, and the extensive information available about the phase behavior and properties of these polymers. The phase behavior of polymer/monoethanolamine (MEA)/water systems was investigated by small angle X-ray scattering (SAXS). The ternary phase diagrams provided information about the microstructures formed at various compositions and the effect of CO2 on these microstructures. The most promising liquid crystalline phase for CO2 capture was selected from the phase behavior studies. Vapor-liquid equilibria (VLE) data of this liquid crystal with CO2 was obtained and the phase transition occurring during CO2 loading was investigated. Rheological measurements of samples with various CO2 loadings were performed, exhibiting an abrupt viscosity increase when MEA is loaded with CO2. Finally, VLE data of three different liquid crystals was obtained, including liquid crystals of an amine end-group modified polymer. The combination of VLE data with the viscosity of the samples showed that there is a strong correlation between the viscosity of the liquid crystals and the carbon dioxide absorption.