Direct Air Carbon Dioxide Capture Using Supported In-situ Polymerized Amines
Creators: name: Al-Absi, Akram Abdulhakeem
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: Engineering--Chemical

description: One of the most promising negative emission technologies is direct air capture (DAC). However, it is still in the early stages of development, and the cost per ton of CO2 captured remains high. DAC faces various challenges, primarily due to the ultra-low concentration of CO2 in the atmosphere. The choice of sorbent materials is a critical factor limiting the implementation of DAC. Ideal DAC sorbent materials shall exhibit high CO2 capacity, high selectivity, rapid kinetics, low energy requirements, high stability, cost-effective and environmentally friendly synthesis. Most importantly, they should function effectively under different adsorption conditions. Yet, further research is required to synthesize such sorbents. Therefore, this thesis aims to investigate the synthesis and development of efficient sorbents for DAC with high capacity, high selectivity, and high stability that work under various adsorption conditions. In this study, new series of novel in-situ cationic ring opening polymerized (CROP) amines were synthesized by utilizing different initiators (IPTMS and CPTMS) and different monomers (MeOX, EtOX, and PhOX) onto various supports, namely MSF, PE-SBA-15, and LPAlSi. The porosity of the support was found to play a major role in the quantity of amines being loaded, while the CPTMS initiator demonstrating greater activity than IPTMS. The EtOX monomer exhibited the best performance, attributed to optimal diffusion limitations and amine loadings. To fully exploit the location-independent nature of DAC, this thesis investigated the potential of DAC across wide range of adsorption conditions, spanning from -20 to 60°C and 0-83% relative humidity. Adsorption temperature and relative humidity positively affected adsorption uptake up to a certain point, after which it started to decline. The optimum adsorption conditions were found to be 20°C and 62% RH, resulting in a CO2 uptake of 2.45 mmol/g-sorbent over MSF-C-EtOX sorbent. Furthermore, this thesis evaluated the durability and sustainability challenges of amine-supported sorbents, especially in terms of maintaining CO2 capture performance during extended use or storage. Class I (impregnated), Class II (grafted), and Class III (in-situ polymerized) amine-supported sorbents were synthesized, followed by a systematic investigation of their stability under various conditions, including thermal degradation, hydrothermal treatment, and extended operational cycles. The thesis also examined the impact of prolonged storage on Class III sorbents. While Class I sorbents demonstrated the highest capacity, Class III sorbents exhibited significant stability and resulted in the highest CO2 uptakes after different harsh treatments. A comparison of cycle performance among the three classes revealed the remarkable stability of in-situ polymerized amines, exhibiting only a 0.3% drop at the end of the 50th cycle, as opposed to around 6% for impregnated amines. Lastly, the extended aging of the novel in-situ polymerized amines for three years demonstrated substantial maintenance of CO2 uptake, with only an 11% drop compared to impregnated counterparts, which exhibited a larger decrease over a shorter duration. Overall, this thesis contributes to the advancement of DAC by developing novel sorbents. The findings presented here provide the fundamental direction necessary and are significant in engaging researchers in the development of efficient and sustainable materials for DAC applications, offering solutions to address carbon emissions and tackle the challenge of climate change.