Hoogrenderende Post-combustie CO2-afvang met Amineoplossingen: Vanuit een Katalytisch Perspectief

With growing concern over global warming and extreme climate changes, the Paris Agreement has established a clear objective to limit the global temperature increase to below 1.5 to 2.0°C compared to pre-industrial levels. Significant efforts have been made worldwide, including the expansion of renewable energy and the replacement of fossil fuels with more sustainable sources like biomass. However, it is widely accepted that fossil resources will not be completely replaced for at least a century. Furthermore, certain industries, such as cement production, cannot entirely eliminate CO2 emissions due to the inherent nature of their processes. Post-combustion CO2 capture is regarded as a crucial method for addressing point CO2 emission sources, typically achieving a capture ratio of 90% to 99% with minimal impact on the original process. Among the various post-combustion CO2 capture technologies, CO2 absorption with amine solutions is the most 'ready-to-use' technology, having been utilized in natural gas sweetening for decades. However, unlike natural gas, which contains more than 40% CO2, emission sources from power plants, cement, and steel industries have much lower CO2 content (3%-30%) and lower gas pressure (1-1.5 bar). These factors present new challenges in achieving rapid CO2 absorption while maintaining economic efficiency. Primary amines like monoethanolamine (MEA) and tertiary amines like methyl diethanolamine (MDEA) are the two main solvents used in industry, each operating via different mechanisms. Primary amines absorb CO2 through a zwitterion mechanism, forming carbamate. This exothermic reaction has a high heat of absorption (89 kJ/mol for MEA), and high absorption kinetic, but resulting in high energy consumption for amine regeneration (CO2 desorption). In contrast, tertiary amines convert CO2 into bicarbonate, which has a much lower heat of absorption, making desorption easier. However, the formation of bicarbonate is slower, requiring larger absorption towers. Given the distinct mechanisms and challenges of CO2 absorption with primary and tertiary amines, this thesis investigates the use of various catalysts to enhance reaction efficiency. The goal is to develop a more effective and economically balanced next-generation CO2 capture process. For CO2 desorption in primary amines, solid Brønsted acids such as zeolites (e.g., HZSM-5) and acid-treated metal oxides (e.g., SO42-/ZrO2) were initially thought to serve as active sites. However, we uncovered an overlooked stoichiometric effect from zeolites, which had been previously misinterpreted as a catalytic enhancement of CO2 desorption. By critically reassessing the Brønsted acid mechanism through a series of kinetic and spectroscopic studies, we confirmed that the Brønsted acid sites of zeolites function as stoichiometric agents, similar to sulfuric acid, rather than true catalysts like some oxides, such as TiO(OH)2. Building on this discovery, we developed a novel, highly efficient, and stable ZrOxHy catalyst that enhances CO2 desorption in the primary amine regeneration process. This catalyst outperforms state-of-the-art systems in both batch and continuous fixed-bed reactors, achieving up to an 85% reduction in regeneration time in continuous fixed-bed setups. This indicates a significant potential to reduce stripper dimensions and mitigate the costly degradation of amine solvents. The high catalytic activity is attributed to its unique, well-balanced dual active sites with appropriate acidity and basicity, as demonstrated by in situ ATR-FT-IR experiments and intensive material characterisation such as surface potential and 1H MAS NMR spectroscopy. To address the slow CO2 hydration kinetics in tertiary amine absorption, we developed a carbonic anhydrase (CA) enzyme mimic catalyst by creating local linker defects in MOFs material. These defects, analogous to active Zn-OH2 sites in the enzyme, were confirmed through IR and NMR spectroscopy. The reaction rate is 5-fold higher than the normal defect-free MOFs with a TOF of 272 min-1, while maintaining stable activity after five cycles. A linear structure-activity relationship between the reaction rate constant and the defect amount further confirmed the defects as the active sites. Based on an operando attenuated total reflection infrared spectroscopic study, we proposed a bio-mimicking of the catalytic absorption mechanism occurring at the active Zn-OH2 sites. In conclusion, this thesis introduces potential low-cost CO2 amine capture methods utilizing high-efficiency catalysts: ZrOxHy for CO2 desorption and defect-MOF for CO2 absorption. Further exploration of the catalytic mechanisms behind these reactions provides valuable insights for future catalyst design in this field.