Design and optimization of processes with novel adsorbent materials for CO₂ capture by a combined molecular simulations-experimental approach

In this contribution, we present two examples where molecular simulations, combined with experiments and/or process calculations, are used to gain fundamental understanding of the underlying phenomena of CO2 capture by adsorption in bare and amine-functionalized materials and to complement data for process design and optimize their performance. Several adsorbent materials with promising performance for CO2 capture have been used for this purpose. First, an adsorption screening for pure CO2 was carried out by means of the Grand Canonical Monte Carlo technique to evaluate several families of MOFs, zeolites and some mesoporous materials. Among these materials, mesoporous MCM-41 and silica gel structures were subsequently selected in order to gain microscopic insights into their adsorption behavior and their performance difference upon functionalization. The computational results were compared with experimental results, showing that the predictive models were able to accurately capture the increased CO2 capture due to the chemisorption phenomena induced by the grafted aminosilane molecules. It was found that this increased uptake at low partial pressures arise only when the average distance between nitrogen atoms of the amines is similar to the size of the CO2 molecules. However, although adsorption is improved at low pressures for these two functionalized materials, the total uptake at higher pressures is not so high and makes them less attractive than other structures for their application in post-combustion CO2 separation. The most promising materials found in the screening process were further investigated considering multi-component mixtures (CO2/N2), also including impurity traces. Working capacities and energetic performances for Swing Adsorption processes at industrial conditions were calculated. Results show that Mg-MOF-74 stands up as one of the most promising material to be used in Pressure and Vacuum Swing Adsorption processes; however, considering its current availability to large scale and its cost, the zeolite 13X still remains as the preferred candidate for the industrial process (with especial attention in VSA systems). This work reinforces the validity of molecular simulations for optimizing environmental related processes, with special focus on CO2 capture and separation, bridging the fundamental knowledge of the materials performance to their industrial applications.