Water Enhancement on CO2 adsorption: Equilibrium studies on an amine sorbent for Direct Air Capture

• Autor(a) principal: Amorim, Sara Rodrigues de
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/153102
• topic: CO2 capture; water vapor; direct air capture; co-adsorption; amine sorbent

This work aims to establish a relationship between CO2 adsorption capacity and water, in the context of CO2 removal directly from atmosphere (DAC). For this, experimental data was ob- tained for a broad range of humidity, temperatures and concentrations of CO2 , using a sup- ported amine sorbent. Subsequently, the CO2 adsorption results were fitted to equilibrium models from literature and compared with experimental trends. The Stampi-Bombelli and WADST models revealed the best fittings, being both values of SSR and R2 relatively close (SSR=0.338, R 2 =0.969 and SSR=0.360, R2 =0.968, respectively). The measurements were performed through the breakthrough method, on a pilot scale setup. These were featured with previous experimental work from SPT group for the same subject. After comparing both data sets, it was observed that the adsorbent had suffered ~20% degradation. Consequently, a correction factor was applied into previous values. Experimental results displayed some inconsistencies, which were attributed to the un- certainty of the correction factor and the complexity of co-adsorption mechanisms. The maxi- mum observed amount of CO2 adsorbed/kg of adsorbent was 2.25 kg.mol-1 (PCO2 =1000 Pa, T= 5ºC, RH= 84.97%), and ~2.7 mol.kg-1 after the correction factor, which is significantly close to values found in literature. The CO2 capacity under the presence of water in comparison with dry conditions (q/qdry ) was also considered to account its enhancement. At PCO2 = 40 Pa, the capacity adsorption nearly doubled in presence of high moisture content, while at the higher partial pressures (PCO2 =1000 Pa), humidity seemed to have a reduced impact. For DAC conditions, experimental trends were well characterized, which follows litera- ture remarks. Overall, the WADST and Stampi-Bombelli model represented the closest fits. In addition, an empirical model was proposed based on the observation of experimental trends. The model is described by a linear function, in which both values of slope and y-intercept were obtained through logarithmic equations.