Development of organic modified zeolites and metal organic frameworks (MOFs) for carbon dioxide (CO₂) capture from humid flue gas streams

Research Doctorate - Doctor of Philosophy (PhD)Low cost technologies are needed for capturing the carbon dioxide generated from large scale point sources, most notably coal-fired power plants. Current carbon dioxide capture technologies are expensive, both in terms of capital and operating costs, and as such significant research and development efforts are being resourced in order to improve the economic viability of these technologies. The main challenge remains to discover an adsorbent which can capture in the presence of moisture, as this scenario realistically mimics conditions for capture of carbon dioxide in flue gas streams. The overall objective of the current investigation is to develop solid adsorbents to capture and separate carbon dioxide (CO₂) from a humid of carbon dioxide gas stream using a regenerable amine modified sorbent. This research presents a targeted investigation on solid adsorbents which have been produced by modification of microporous and mesoporous materials including zeolites and Metal Organic Frameworks (MOFs) with various organic amines. These amines are shown, in a number of cases, to enhance carbon dioxide capture capacity in the dry as well as humid conditions. The investigation was also focussed on measuring and then understanding the chemical and physical properties of modified materials and to undertake this task, a number of characterisation techniques including nitrogen physisorption, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscopy and in-situ Fourier transform infrared (FTIR) spectroscopy analyses were employed. Functionalisation of Na-β zeolite was performed using post synthesis impregnation with melamine. The dynamic CO₂ adsorption capacity of modified adsorbent (3.69 mmolg^-1) was enhanced significantly from its original unmodified capacity (2.20 mmol/g). Zeolite Na-Y was modified with triethylenetetramine (TETA), with the aim of synthesising a hybrid material with enhanced CO2 adsorption capacity and selectivity, especially where the adsorption takes place in the presence of water vapour. A mechanism describing the interaction of CO2 on the surface functional groups on TETA was presented. Multicyclic use of NaY-TETA may be an ideal future sorbent for CO₂ capture from flue gases. Guanidine was used to modify 13X zeolite to enhance CO₂ adsorption capacity of feed streams with various humidity levels. The rapid adsorption and desorption of CO₂ adsorption demonstrated by modified adsorbent shows approximately 50% enhancement in adsorption capacity under humid conditions. The lower regeneration temperature (150 °C) required for the modified material and its higher CO₂ capacity in the presence of moisture suggests 13XGnd20 is a potential candidate for large scale CO₂ adsorption application. Metal-Organic Frameworks (MOFs) Cu-BTC porous material, synthesized by solvothermal method, demonstrated high CO₂ adsorption capacity along with good selectivity of CO₂ over N₂. Cu-BTC was further modified with melamine and guanidine using pre-synthesis as well as post-synthesis methods which resulting an excellent carbon dioxide capture capacity