| Popis: |
CO2 emissions are the main driver of different alarming scenarios of climate change, and thus actions to reduce them are forcefully required if we aim to avoid the most dramatic predictions. Among the actions proposed Direct Air Capture (DAC) has gained a rapidly increasing attention in the recent years. While it deals with the most diluted CO2 mixture, i.e. air, it allows to treat the emissions of any sector regardless of their source location. It has been proved that different species can trap CO2 from ambient air, the most promising so far are chemical filters made by coating a proper support with either amines or alkaline carbonates. In this work potassium carbonate (K2CO3) and sodium carbonate (Na2CO3), two alkaline carbonates, were investigated for DAC applications. The salts were deposited over the porosity of honeycombs, a type of structure that is well known for automotive applications, made of activated carbon. The resulting filters were set to different CO2 adsorption conditions representative of ambient air. Moreover, the regeneration of the adsorbents, which is coupled to the production of a CO2 stream of higher concentration than in air, was also studied parametrically aiming to determine its dependence with different thermodynamic variables. The results from the CO2 desorption tests were used to develop a lumped kinetic model to elucidate the influence of different process parameters on the CO2 enrichment achieved as well as the resulting energy consumption. The vast majority of the total energy consumption deals with the way that the CO2 desorption is performed. The results from the model were used to design a system for CO2 enrichment in a hypothetical greenhouse of one hectare of area and 7 meters tall. CO2 adsorbents made of K2CO3 are promising options provided that the amount of salt loaded over the honeycomb support can be increased substantially as this could considerably reduce the energy consumption. For this, the development of mechanically stronger support materials is required. Nevertheless, even with a rather low salt loading in the composite, about 6% wt. K2CO3, the adsorbent could fulfill the CO2 enrichment and climate control requirements of the hypothetical greenhouse. |
