Evaluating the performance of Cr-Soc-MOF Super-Adsorbents for CO2 capture from flue gas under humid condition through molecular simulation

Abstract

One of the major criticisms for gas separation by utilizing Metal Organic Framework (MOF) porous material for all classes of adsorbents is their very poor performance under humidified gas streams. Very few MOFs show better CO2 separation from N2 mixture in the presence of moisture. Conversely, plenty of MOFs demonstrated good CO2 capture from dry gas streams. In order to explore the potential characteristics of gas separation under humid conditions by coordinatively unsaturated metal organic framework (CUS-MOF) with square octahedral (Soc) topology were exercised single component (CO2, N2) adsorption and co-adsorption (CO2/N2) in the presence of moisture at 298 K with pressure ranging from 0 to 10 bar. Herein, we investigated five exceptional Cr-Soc-MOFs similar to the experimentally established iso-structural topology by differing the polynuclear aromatic ring size and N-heteroatom to their pore wall. The specific interaction of guest molecules to the coordinatively unsaturated metal site (CUS), i.e., rigid μ3-oxygen-centered tri-nuclear metal carboxylate, of Cr-Soc-MOF-n series were identified with Density Functional Theory (DFT) calculations, this energy profile was used to derive specific force field. Further, Grand canonical Monte Carlo (GCMC) simulation was employed with DFT-derived force field to identify suitable CO2 capture for Cr-Soc-MOFs in the presence of moisture. Interestingly, the Cr-Soc-MOFs with larger pore volume were retained not only CO2 uptake in the range of 23 – 35 wt% but also selectivity about 20 – 50 range even up to 70% of RH. Importantly, we introduced a mathematical tool to theoretically analyze the dynamic co-adsorption in the form of breakthrough curve measurement from CO2/N2 simulated co-adsorption by mimicking the real flue gas condition, also working capacity (ΔN), Regenerability (R%) and Adsorbent Performance Indicator (API) of Cr-Soc-MOF-n series were investigated. The CO2 separation performances of Cr-Soc-MOF-n series suggested that the polynuclear aromatic ring to their pore wall withstand CO2 uptake in the presence of humidity rather than N-heteroatom decorated Cr-Soc-MOF due to its high pore volume and the accommodation of extra aromatic ring in their pore channels.