In Silico Discovery of New Materials for the Separation of Linear and Cyclic Siloxanes
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Chng, Jia Yuan
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Abstract
This thesis presents the use molecular modeling to inform and accelerate the implementation of adsorption-based separation strategies for the removal of cyclic siloxanes from silicone fluid. This work focuses on a back end adsorption system to separate cyclic and linear siloxane oligomers. We first introduced a newly developed transferable molecular force field (FF) for cyclic and linear siloxanes. This force field is used to calculate adsorption of siloxanes in Metal-Organic Frameworks (MOFs) using molecular simulations. We then used this FF to explore the kinetic separation of cyclic siloxanes from linear siloxanes using MOFs by detailed molecular dynamics simulations. We determined a range of pore-limiting diameters that only allows the diffusion of linear siloxanes. We developed a strategy and workflow to investigate the equilibrium separation of linear and cyclic siloxanes in MOFs. We showed that configurational entropy effects drive the preferential adsorption of linear siloxanes over
cyclic siloxanes. We also explored vacuum-temperature swing adsorption (VTSA) supercritical CO2 as a potential method for the recovery of adsorbed linear siloxanes. Finally, we extended the work to investigate the potential of pure-silica zeolites for separating linear and cyclic siloxanes. We developed a new FF for siloxanes in pure-silica zeolites. This FF is used to calculate adsorption of siloxanes in pure-silica zeolites using molecular simulations. Overall, the developed geometric principles and screening strategies efficiently narrowed down a list of candidate MOFs and pure-silica zeolites, and identified promising adsorbents for further experimentation in collaboration with experimental partners.
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Date
2025-08-22
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Dissertation (PhD)