Microporous materials with tailored structural properties for enhanced gas separation

• Main Author: Chuah, Chong Yang
• Other Authors: Bae Tae Hyun
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2019
• Subjects: DRNTU::Engineering::Bioengineering
• Online Access: https://hdl.handle.net/10356/90277; http://hdl.handle.net/10220/48516
• Institution: Nanyang Technological University

Extensive research on the gas separation process has been conducted in view of the current industrial gas separation processes which uses cryogenic distillation and liquefaction are energy-intensive. In this regard, adsorbents and membranes which demonstrate favourable interaction with the desired gases were selected in view of their capability in performing effective separation at a lower energy penalty together with smaller plant footprint. Hence, the main objective of this thesis is to investigate and develop novel nanoporous materials and membranes that are capable in providing effective separation and capture of desired gas components. The study begins with the development of hierarchical zeolite MFI for its feasibility in SF6 adsorption. Clear enhancement in overall SF6 adsorption kinetics was observed with the creation of hierarchical structure, thus indicating its usefulness in rapid SF6 adsorption-desorption cycling. Under similar strategy, hierarchical HKUST-1 and PPN were developed for its potential in SF6 capture and recovery. HKUST-1 possess open metal sites allows reversible interaction with SF6. Therefore, hierarchical structures were created to allow an increased accessibility of SF6 to the active sites, as the kinetic diameter of SF6 is larger as compared to CO2. Besides, PPN which demonstrates better resistance towards chemical degradation and humidity was created by the variation of porosity properties. The incorporation of an optimal amount of tertiary amine allows an improvement in SF6/N2 selectivity in both equilibrium and dynamic condition, together with sharp segregation between SF6 and N2 peaks in chromatographic separation. Nonetheless, enhancement in SF6 adsorption kinetics is limited by its large micropore size. Besides, the facilitation the overall adsorption-desorption cycling of adsorbate was verified by the creation hollow-structured nanomaterial. Based on the study conducted, creation of hollow structure (Co-MOF-74hollow nanorods) allows the shaper CO2 breakthrough curve together with sharper chromatographic separation between CO2 and N2. On the other hand, the investigation of nanoporous materials was further conducted with the utilization as filler in mixed-matrix membrane (MMM). Permeability-selectivity trade-off in polymeric membrane has been well reported as solution-diffusion mechanism is the main transport mechanism of gases in membranes. The incorporation of nanoporous materials into polymeric membrane has been the most technical viable option to improve the gas separation performance. In general, MOFs has attracted vast research interest as the fillers in MMM in view of its large surface area and pore volume, where the functionalities can be tuned via pre- or post-synthetic functionalization. In this work, HKUST-1 nanocrystals were incorporated into polymeric membrane for O2/N2, CO2/CH4 and CO2/N2 separation. It has been observed that the utilization of HKUST-1 nanocrystal as the filler materials has demonstrated an increase in gas (O2, CO2) permeability, without compromising the mixed-gas selectivity. Besides, amine-functionalized HKUST-1 nanocrystals is feasible in improving CO2/N2 selectivity without compromising CO2 permeability. In conclusion, this thesis presents the development of nanoporous materials and membranes in the field of gas separation. Considering that the potential of nanoporous materials and membranes in other gas separation processes is immense, future work will be generally focussed on the application of nanoporous materials and membranes in terms of the plausible potentials in other separation process (e.g. olefin/paraffin). Besides, other factors that hamper the practicability of nanoporous materials in industrial gas separation process such as the presence of water in the feed will be conducted. It has been observed that the presence of water molecules can compete with the desired test gases, which in general limits the overall gas separation performance.