Collaborative Research: Quantifying the Role of Interfaces in Liquid Separation Membranes based on Carbon Molecular Sieves

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Fuels, chemicals, pharmaceuticals, water, and many other daily-use consumer products are manufactured from natural resources by a series of refining processes. The desired chemical compounds must then be separated and purified from the raw materials, which represents a significant technological challenge. Liquid-phase separations are particularly challenging and, as a result, have a large environmental and energy footprint that continues to grow. For instance, more than 1 trillion gallons of organic-loaded water are treated each year in produced water applications alone. This volume is expected to increase along with global energy production and continues to include growing contributions from biorefineries and biochemical plants. Carbon molecular sieves (CMS) are rigid solid materials with holes that are comparable in size to molecules of liquid compounds. The CMS materials can be used as sieves to separate and purify liquid compounds in an energy-efficient way to address these new challenges. However, the performance of CMS in separations can be less than desirable. CMS separation performance limitations are often attributed to various effects related to molecular transport at the CMS surfaces and interfaces. In this research project, the investigators will combine advanced experimental techniques to measure and understand the motion of liquid molecules within the CMS materials at different relevant length scales. The fundamental knowledge created during this project will enable the design of CMS materials for targeted chemical separations. The research program is integrated with an educational and outreach plan that focuses on increasing interest among and retention of underrepresented students in STEM. The goal of this research is to quantify and understand deviations from the desired separation performance often exhibited by freestanding CMS membranes and hybrid CMS membranes formed by dispersing CMS particles in a polymer. These deviations are often attributed to various non-ideal effects related to small molecule transport at CMS surfaces and interfaces. The investigators will combine advanced diffusion nuclear magnetic resonance (NMR) spectroscopy and macroscopic transport measurements to quantify transport at interfaces, including transport through CMS surface barriers and along low-density defects at the polymer-CMS interfaces in hybrid membranes. These findings will be used to create verifiable structure-transport relations, leading to new design principles of CMS-based membranes for liquid separations. The project will develop important fundamental knowledge of the role of interfaces in CMS-based membranes on liquid transport across an entire range of relevant length scales below and above one micrometer.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.