(354d) Molecular Dynamics Simulations Probe Greenhouse Gas Sorption Capabilities of Metal-Organic Framework-Based Membrane for Efficient Gas Separation Processes

The implementation of scalable, sustainable gas separation technologies that simultaneously mitigate the emission of greenhouse gases and meet global energy and material demands is paramount in ongoing global efforts to curtail the harmful impacts of global warming. Whereas widely in use separations technologies like distillation columns, strippers, and absorbers have been shown to be economically viable only at large time-scales and throughputs for well-defined processes, metal-organic framework (MOF)-based membranes have been researched recently for their modular nature, tunable physical and chemical properties, and angstrom-level resolution of their pore structures that make them ideal candidates in the next generation of efficient gas separations processes. However, the full potential of MOF-based membrane gas separations is yet to be realized due to the significant dependence of inherent framework properties like hydrophilicity, aperture size, and structural flexibility on the selective adsorption and permeation capabilities of the materials and how they are to interact with the gases or mixtures to be used during the separation processes.

Herein, we contend that both the evaluation of MOF materials and the intensive analysis of MOF-gas molecule interactions is necessary to determine the chemical and physical phenomena that lay the foundation of critical separation criteria associated with MOF materials and to ascribe proper gas separation suitability for respective MOF-membrane systems and their implementation units. To test our hypothesis, we employed atomistic molecular dynamics (MD) simulations for the intensive examination of the interactions between various greenhouse gases—carbon dioxide (CO₂), methane (CH₄), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and nitric oxide (NO)—and a hydrophilic, Al-based MIL-160 membrane, which was chosen for its hydrothermal stability and selective uptake of water vapor, as well as for the chemically mild conditions in which it can be synthesized. In our analysis, the respective gravimetric solubility, permeability, and diffusivity of each gas species was calculated at varying pressures spanning vacuum-, atmospheric-, and high-pressure conditions respectively. We found that a MIL-160 membrane had excellent applicability in the separation of gas species that exhibit significant differences in electronegativity leading to advantageous differences in gas molecule binding affinity to the MIL-160 membrane; further, our computational strategy demonstrated that the separation capabilities of MIL-160 are dependent on simulation pressure, thus suggesting that a MIL-160 membrane has potential extended applicability in selective adsorption-based gas separations processes. Our strategy to identify and capitalize on respective MOF-gas molecule interactions provided a beneficial framework that can help design and optimize the next generation of gas separations technologies that meet increasingly stringent sustainability benchmarks while simultaneously reducing the emission of anthropogenic greenhouse gases.