Molecular Simulation of Carbon Dioxide Capture on Elastic Layered Metal-Organic Framework Adsorbents

The likelihood of fossil fuel power plants being targeted for future CO2 emissions regulation creates a motivation for developing an alternative CO2 capture method that is more sustainable and less energy intensive than the current approach using amine solvents. A special class of metal-organic framework adsorbents known as elastic layered metal-organic frameworks (ELM) exhibit a step-like CO2 adsorption isotherm that offers intriguing advantages for CO2 capture applications in comparison to other proposed carbon capture adsorbents with Langmuir-like adsorption isotherms.;Molecular simulations and experiments were therefore carried out to explain the adsorption phenomena observed for ELM material and assess the suitability of ELM adsorbents for CO2 capture from flue gas and synthesis gas mixtures. The hybrid osmotic Monte Carlo (HOMC) simulation methodology developed as a part of this work, for the first time has provided atomistic insights into the mechanism leading to the expansion of the material and CO2 isosteric heat of adsorption profiles. The adsorption-induced expansion was shown to depend on the CO2 orientation transition and the interplay of the CO2-framework configuration, to increase CO2-CO 2 interaction energy by 1.6 kJ/mol compared to the pre-expansion state. Predicted CO2 selectivities (from 44 to 600 with different temperatures and pressures) are comparable to those typically observed with other microporous materials that have been proposed for use as carbon capture adsorbents (typically from 3 – 1000). In addition, the CO2 isosteric heat of adsorption of ELMs are moderate (23 – 28 kJ/mol) compared to other current adsorbents (30 – 45 kJ/mol). Structure-function relationships established for this series of ELM adsorbents shows that the gate pressure is to follow the metal vertex trend Cu2+ < Co2+ < Ni2+ from lowest to highest gate pressure for ELM framework series investigated in this work, containing BF4- and CF3SO 3- as the anions.;Results of the study show that ELM materials possess important features of an effective carbon capture adsorbent such as high CO2 selectivity, moderate CO2 heat of adsorption. Broadly speaking, the simulation results and experimental studies reported in this work support the conclusion that ELM adsorbents have the requisite material properties to merit further consideration as carbon capture adsorbents.