Particulate Matter Formation in Post-combustion CO₂ Capture Columns: Insights from Molecular Dynamics Simulations

Abstract

The recent socio-political and climate changes have sparked tremendous interest in developing effective CO2 capture processes. Conventional post-combustion CO2 capture (PCCC) processes employ aqueous monoethanolamine (MEA) as a solvent; however, one of the major problems in the PCCC columns is the loss of a significant amount of the solvent in the form of particulate matter (PM). In spite of its importance, the formation of PM in a PCCC column has been overlooked, until recently. We herein analyze the process of the PM formation at a molecular level by underlining interactions between the participating components. Molecular dynamics (MD) simulations were performed on different systems consisting of CO2 and MEA, and also in the presence of other components and conditions that are typically present in a PCCC column. The simulation revealed the evolution of molecular clusters, which are in a separate phase than the gas present around, comprising all the gaseous MEA, SO2, and most of the CO2 and water vapor. We found the nucleation rate of the formed PM to be in the order of 1030 cm–3 s–1 for the studied systems. The presence of water vapor enhanced the growth of the clusters, although the structure remained largely unchanged. On the other hand, although SO2 was all absorbed in the cluster, it did not alter the growth rate or the structure of the formed cluster. Interestingly, the results also showed formation of large molecular clusters even at a low degree of supersaturation because of strong CO2–water interactions. Taken together, the results are the first of the efforts to understand PM formation in a typical PCCC column based on molecular simulations, and the findings led to certain practical suggestions to reduce PM formation.

Molecular Dynamics Simulations To Capture Nucleation and Growth of Particulates in Ethanolamine-Based Post-Combustion CO2 Capture Columns

“…Beyond this, saturation ratios of each case were calculated according to the procedure described in our preceding work. 13 Saturation ratio indicates the possibility for nucleation or particulate formation under the prevailing circumstances. The results of the calculations are displayed in Table S5 of the Supporting Information.…”

“…Analogous to the methodology developed formerly, the composition, temperature, and pressure of systems to be studied were derived from simulations and data taken from Khakharia et al , The molar fractions of MEA, water, CO 2 , nitrogen, and oxygen were set to 3.7 × 10 –5 , 0.183, 0.041, 0.729, and 0.041, respectively, which correspond to the molar fractions of the components at the top stage of a typical PCCC column.…”

“…In our previous work, we have studied the formation of particulate matter in a PCCC column using only aqueous MEA solutions under constant volume, examined their structure, and determined the nucleation rates . The results therein also revealed that the PM or aerosol formed consisted mainly of water vapor and CO 2 , and gaseous MEA was also absorbed in those particulates.…”

On Solvent Losses in Amine Absorption Columns

“…Recent studies estimated the nucleation rate of amine in PCCC plants using molecular dynamic (MD) simulation, which provides new insights into the nucleation process at the molecular levels. 34,35 However, implementation of the estimated nucleation rates using MD simulations in PCCC plants is lacking in the literature.…”

“…The simulation results mostly were not validated with experimental data, and none of them could predict the rate of nucleation and amine loss due to the nucleation process. Recent studies estimated the nucleation rate of amine in PCCC plants using molecular dynamic (MD) simulation, which provides new insights into the nucleation process at the molecular levels. , However, implementation of the estimated nucleation rates using MD simulations in PCCC plants is lacking in the literature.…”