Prevention of Physical Aging within Carbon Molecular Sieve Membranes for Gas Separations
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Carbon molecular sieve membranes (CMSMs) are a subclass of porous materials with the ability to perform molecular sieving. Controlling the jump lengths from one pore to another allows for enhanced permselectivity of such membranes. This control makes CMS materials extraordinarily attractive for gas separations, in comparison to state-of-the-art polymeric membranes that separate molecules based primarily on sorption-diffusion. This work considers the recent progress in the development of carbon membranes as well as limitations that prevent their commercialization, in particular the rapid onset of aging that occurs with CMSMs. Various aspects of how properties of a CMSM may change over time and how important it is to find the optimum starting materials and process conditions to minimize aging are addressed within. Conditions which affect the performance of CMSMs and current preparation methods are explored and aligned with future research needed to achieve commercially viable CMSMs. Chapter 1 summarizes the history and applicability of CMSMs along with their ability to surpass commercially used polymeric membranes for gas separations. A focus on their limitations, primarily physical aging, is addressed along with current endeavors to mitigate it. Chapter 2 explicates the novel use of metal nanoparticles in CMSMs to scaffold membranes’ inherent pore structure to minimize aging. The in-situ formation of copper nanoparticles within polymer of intrinsic microporosity-1 (PIM-1) was studied via transmission electron microscopy and gas permeation. Chapter 3 describes the synthesis of tailored metal pillars which can be used for various polymeric precursors, including Matrimid® 5218 and PIM-1. The tunability of the size of the metal nanoparticles provides a more universal approach to reduce physical aging within CMSMs that can be monitored by means of gas permeation.