Experimental characterization of a specific chemisorbent and a physisorbent for direct air capture application : Analyzing the effect of parameters such as desorption temperature, humidity and varying CO2 partial pressure on the performance of the adsorbe

Abstract: Climate change has become an indisputable threat to the planet with global warming being at the forefront. With continuous usage and combustion of fossil fuels, the atmospheric CO2 concentration has kept on increasing leading to higher average temperatures globally. With humanity’s reliance on fossil fuels for energy increasing due to the constant rise in global population, the current mitigation measures are not enough. Slowing the rate of increase in the concentration of carbon dioxide in the atmosphere through traditional carbon capture methods from point source emissions is not enough anymore. There is a need to directly remove CO2 from the air to reduce the carbon dioxide concentration from the atmosphere to further prevent the rise in global average temperatures. This is achieved by Negative Emission Technologies such as Direct Air Capture, which directly captures CO2 from the atmosphere. For direct air capture processes, certain adsorbent materials that captures CO2 from the atmosphere are more favourable than the others due to their surface chemistry, their affinity towards CO2 and the way they respond in different conditions such as humidity, desorption temperature and varying partial pressures of carbon dioxide in the gas mixture. CO2 adsorption measurements for Lewatit VP OC 1065, a chemisorbent, and for an activated carbon Carbotech D55/1.5, a physisorbent, were conducted using the mixsorb L gas analyzer by 3P Instruments. Experiments with varying design conditions such as desorption temperature, humidity levels and partial pressures were conducted to analyze their effect on the equilibrium loading of the adsorbent. High desorption temperature of 125 ℃ over a period of time had a negative effect on the stability of Lewatit whereas at slightly lower desorption temperature of 90℃, the adsorbent showed stability and repeatability of equilibrium loading, over a period of time, was seen. Humidity had a positive effect on the adsorption capacity of amine containing Lewatit due to the formation of bi-carbonates whereas the effect wasn’t as prominent in activated carbons. Moreover, with Lewatit further divided into different batches based on its performance and its particle size, sieved Lewatit showed the highest CO2 adsorption capacity, in dry and humid conditions, due to its small particle size, high affinity for CO2 and a higher surface area available for adsorption amongst all the experiments conducted within this thesis.