The relevance of thermal effects during CO2 adsorption and regeneration in a geopolymer-zeolite composite: experimental and modelling insights

Low temperature adsorption of carbon dioxide in solid materials is a cost-effective option for implementing decarbonization in a retrofitting plant strategy. Among several natural and artificial sorbents, geopolymer-zeolite composites represent a valid alternative owing to the affinity and synergy between zeolite and the geopolymer binder. Thermal effects are usually associated to CO2 adsorption in solids: in particular zeolites exhibit values in the range 33 to 40 kJ/mol. The occurrence of the thermal effects (i.e. positive/negative variation of the bed temperature) impacts on the adsorption/desorption behavior and system performance. In this study, the relationship between adsorption/desorption and bed temperature has been studied in dynamic tests, complemented by thermogravimetric analysis and static sorption experiments. In dynamic tests, the maximum adsorption capacity was 1.40 mmol/g at 20% mol. of CO2 inlet concentration, whilst it resulted 0.80 mmol/g in a shorter breakthrough test. Correspondingly, the temperature peak during adsorption revealed an increase up to 20 °C. The thermal effect was exploited during desorption with a combined pressure-swing and temperature-swing strategy, leading to a shorter time for sorbent regeneration. A novel numerical model of the adsorption process well fitted the experimental results at different inlet CO2 concentration, providing insights for process design and optimization.