Author ORCID Identifier

http://orcid.org/0000-0002-7651-2032

Degree Year

2019

Document Type

Thesis

Degree Name

Bachelor of Arts

Department

Physics and Astronomy

Advisor(s)

Stephen FitzGerald

Keywords

Metal-organic frameworks, MOFs, Hydrogen, Deuterium, Gas separation

Abstract

In this thesis, we designed and built a gas flow-through system to study dynamic adsorption separation of hydrogen isotopes in metal-organic frameworks (MOFs). MOFs are porous, crystalline materials composed of metal complexes connected by organic linkers. They have been proposed as a cheaper, more energy efficient approach to hydrogen isotope separation than current industrial methods. We have previously found evidence of a zero-point energy-based separation mechanism for hydrogen isotopes in two MOFs: Co-MOF-74 and Cu(I)-MFU-4l. This mechanism, chemical affinity quantum sieving (CAQS), has been extensively studied under static equilibrium conditions. The system in this work was developed so that CAQS could be studied under dynamic conditions that more closely resemble those in industrial separation. Breakthrough analysis is an established technique for studying dynamic separation in porous materials. Generally, a breakthrough experiment involves flowing a gas mixture through a fixed bed of adsorbent material and measuring the composition of the effluent flow. In this work, a 1:1 mixture of common hydrogen and its isotope deuterium was flowed through 71 mg of Co-MOF-74 or 22 mg of Cu(I)-MFU-4l. A quadrupole mass spectrometer was used to monitor the composition of the effluent flow. We saw preferential adsorption of deuterium over common hydrogen in Co-MOF-74 at 77K and Cu(I)-MFU-4l at 170K, 140K, and 110K. This behavior was absent in Cu(I)-MFU-4l at 77K, a phenomenon that we would like to investigate further. Minimal adsorption occurred in both MOFs at room temperature, as expected. A selectivity of deuterium over common hydrogen was calculated for each temperature. These selectivities were approximately 30% lower than comparable literature values. Our goal is to make improvements to our system and methods to measure the selectivity more accurately and reproducibly. Notably, all measured selectivities were higher than the selectivity of the Girdler Sulfide method and cryogenic distillation, two industrial hydrogen isotope separation processes we are trying to improve on. This new system gives us the capability to study dynamic adsorption and kinetic separation of hydrogen isotopes in metal-organic frameworks going forward. We hope that our work will inform the development of efficient, environmentally sustainable separation processes.

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Physics Commons

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