Material characterization and computational optimization of membrane technologies for applications in low-carbon energy systems [electronic resource]
Keywords: Energy Resources Engineering.

The current work investigates several membrane technologies aimed at addressing the gas separation needs in the transition to a more sustainable energy landscape. A main goal in this energy transition is to decarbonize the existing fossil fuel infrastructure. In the near future, electricity generation and many accompanying decarbonization pathways will continue to rely on fossil fuels. Low energy use and low greenhouse gas emissions are thus required for these decarbonization technologies to be effective. Future energy technologies will also be required to have operational flexibility to facilitate the integration of intermittent renewable energy. In this work, we use both experimental and computational methods to examine applications of membrane technologies in low-carbon energy systems. Specifically, we investigate carbon capture and hydrogen (H2) purification. The former falls under the broader concept of carbon capture, utilization, and storage (CCUS), which aims to mitigate carbon dioxide (CO2) emissions from the electricity sector. The latter is motivated by the use of hydrogen as an alternative fuel, tackling emissions from the transportation sector. Membrane technologies are considered particularly suitable for these two applications. Membrane separation is less energy-intensive compared to many other separation technologies and is advantageous in systems where low energy consumption is required. Membrane units are compact and modular and are especially attractive for many distributed and mobile applications often found in the transportation sector. Membrane operations are highly responsive to system changes and are thus compatible with intermittent renewable energy sources. The studies in this work are motivated by the concept of a metallic nitrogen-selective membrane. This membrane technology is currently in an early stage of development and would find promising applications in carbon capture, natural gas purification, and ammonia synthesis. In this work, we develop methodologies using several model membrane systems to address the research needs that have emerged from the development of metallic nitrogen-selective membranes. The first study investigates the effects of flue gas on metallic nitrogen-selective membranes in carbon capture applications using vanadium (V) as a candidate membrane material. We perform thermochemical exposure tests and material characterization to understand the chemical and morphological changes of the vanadium membrane. In the second study, we develop an experimental method to study the phase and structural changes of metallic membranes during gas permeation at high temperatures and elevated pressures using operando x-ray diffraction (XRD). This method is tested for hydrogen permeation in dense palladium membranes and can be tailored to the investigation of nitrogen permeation in metallic membranes. This study contributes to the fundamental understanding of hydrogen and nitrogen transport in metallic membranes. The third part of this work is a computational optimization study to investigate the techno-economic potential of membrane separation in flexible carbon capture. The model system in this study consists of a natural gas combined cycle (NGCC) plant and a CO2-selective membrane unit responding to varying electricity and carbon prices. We perform modeling and optimization to determine the optimal process design and time-varying operations of the overall system. The optimization framework developed in this study is robust and can be adapted to integrate nitrogen-selective membranes. The research efforts in this work offer methodologies for future experimental and computational studies of metallic nitrogen-selective membranes. The results obtained from the model systems will be able to serve as benchmarks for the development of such membranes.