PhD Thesis Defense Notification – Ross J. Verploegh

Thesis Title:  Computational Assessment of Zeolitic Imidazolate Frameworks for Kinetic Gas Separations

Thesis Advisor:  David S. Sholl, ChBE

Committee Members:

            Sankar Nair, ChBE

            Krista S. Walton, ChBE

           Christopher W. Jones, ChBE

           Thomas M. Orlando, Chemistry and Biochemistry

Date:  July 13, 2017

Room:  Engineered Biosystems - EBB 5029

Time:  2:00 p.m.

ABSTRACT:  Industrial separations of light gases and hydrocarbons are currently performed with well-established energy and capital intensive distillations. Within the last decade, certain research advances have energy suppliers focused on novel separation techniques using metal-organic frameworks (MOFs) as a possible replacement for traditional distillation. Experimental groups at Georgia Tech have developed techniques for creating thin-film and mixed-matrix membranes that would perform these commodity fuel and reagent separations at ambient temperature and moderate pressures.  Zeolitic imidazolate frameworks (ZIFs), a family of MOFs, were shown experimentally to act as excellent molecular sieves for C1-C4 hydrocarbons and other light gases. Understanding diffusion properties of light gases and hydrocarbons in ZIFs was needed in determining which ZIFs have the most industrial promise, allowing for the direction of experimental focuses, and contributing to fundamental knowledge of diffusion processes. In this thesis, I established the utilization of a suite of computational methods that are suited to tackling four significant challenges facing the research community studying ZIFs. ZIFs are flexible materials and this inherent material property required the inclusion of fully flexible molecular dynamics calculations into classical transition state theory to explain adsorbate-ZIF framework interactions at infinite dilution. I extended the use of these computational methods to predict loading-dependent, single-component transport diffusion coefficients of hydrocarbons and membrane permeabilities. With no standard flexible force fields for ZIF frameworks, I developed a classical force field based on Density Functional Theory (DFT) calculations capable of accurately predicting small molecule diffusivities. In a joint experimental-computational collaboration, I aided in the development of a protocol for determining the local ordering of the organic linkers in binary mixed-linker ZIFs. This structural knowledge of mixed-linker ZIFs on the unit cell level prompted the creation of a lattice-diffusion model, which was used to qualitatively explain the impact of local ordering on diffusion as well as provide quantitative predictions of diffusion through binary mixed-linker ZIFs. This work enhances scientific knowledge on molecular transport in single and mixed-linker ZIFs and provides energy suppliers with the tools to engineer new separation alternatives for light gases.