Direct air capture (DAC): capturing CO2 from the air – design of a lab-scale PVSA system and the development of a carbon-based adsorbent material for atmospheric CO2 capture

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Dineen, Cormac P.J.
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University College Cork
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Mankind faces huge economic, technological and societal challenges if we are to meet the climate targets set out in the Paris Climate Agreement of limiting global warming to 2°C and avoid the most devastating effects of climate change. Research carried out by the IPCC in 2018 on emissions mitigations pathways compatible with our climate targets shows that commercial-scale deployment of Carbon Dioxide Removal (CDR) technologies will be almost certainly be required if we are to limit warming to 2°C. This research focuses on Direct Air Capture (DAC), an emerging CDR technology designed to remove CO2 directly from the atmosphere using sorbent materials. Building on a rapidly expanding body of work, this research has two primary goals. Firstly, it aims to create a laboratory scale, Pressure Vacuum Swing Adsorption (PVSA) system, designed for the testing of the CO2 adsorption isotherms of new adsorbent materials. The second goal is the development and testing of a new adsorbent material for CO2 capture.Having reviewed the relevant literature, a dual-column PVSA system was designed to operate a Skarstrom cycle for atmospheric CO2 adsorption. The cycle was modified to include a vacuum pump, which provides further testing capabilities in the system. The designed system can assess adsorption-desorption isotherms at sub-atmospheric conditions of pressure, as well as atmospheric conditions of pressure. Following the build phase, the system was tested at a variety of different inlet pressures and it was found that the PVSA Skarstrom cycle operated successfully and as designed. A biopolymer adsorbent material was developed by expanding the surface area of a native Irish seaweed, Ascophyllum Nodosum. The adsorbent powder product was shown, using SEM and BET analysis, to have a vastly expanded surface area when compared with that of the initial biopolymer material. The adsorbent powder was then pelletized using different techniques, and the structural properties of the pellets, which are key performance parameters for PVSA systems, were analysed and described. On the basis of the work carried out in this research, and the current global GHG emissions profile, further opportunities for research exist, and are necessary, in the development of new adsorbent materials for atmospheric CO2 capture. As a result of this research, it is recommended that research be carried out in the development of new, carbon-based adsorbents, which exhibit good structural and chemical properties for CO2 adsorption but have not yet been widely analysed for suitability within DAC systems.
DAC , CCS , Ascophyllum nodosum , PSA , Atmospheric CO2 removal , Direct air capture , Greenhouse gas removal , Pressure swing adsorption
Dineen, C. P. J. 2020. Direct air capture (DAC): capturing CO2 from the air – design of a lab-scale PVSA system and the development of a carbon-based adsorbent material for atmospheric CO2 capture. MRes Thesis, University College Cork.