A modelling study in harnessing metal-organic frameworks for challenging gas separations

  • Christopher Campbell

Student thesis: Doctoral Thesis

Abstract

The separation of gases is a complex and often expensive issue within industry,with energy-intensive distillation techniques often being the accepted solution. The discovery of tailorable Metal-Organic Frameworks (MOFs), however, is introducing an alternative route through separation techniques such as Pressure Swing Adsorption (PSA). Their tailorabiltiy promotes higher gas selectivities, the caveat is that experimentally assessing the full range of MOFs is unfeasible. Computational modeling could therefore be utilised to better evaluate the complete MOFpool. However, a unique subset of MOFs containing Coordinately Unsaturated Sites (CUS) are not well described computationally by standard forcefields. This work will therefore focus on developing a CUS model based off the work of Fischer et al.[1], which couples traditional modeling techniques with high level theory Quantum Mechanical (QM) methods, to tackle this challenging MOF class. This thesis outlined a refined CUS model which was capable of capturing ethylene adsorption in HKUST-1. Furthermore, the model was able to use the same CUS parameters from HKUST-1 and transfer them to model other copper-paddlewheel MOFs. This adsorbent transferability is of especial importance for large-scale screening applications, limiting the required number of QM calculations for modeling CUS-containing MOFs.The new model also demonstrated marked improvement in simulating the binary adsorption of ethylene/ethane in HKUST-1, compared with standard forcefields. This validation was key as the main focus of this workwas for application in multi-component systems, i.e gas separation.The CUS model was also successful expanded to carbon monoxide adsorption, which required further development of the CUS procedure. The updated CUS model showed a large improvement in describing carbon monoxide adsorption behaviour in HKUST-1, over currently available models. Importantly, the adsorbent transferability, demonstrated for ethylene adsorption in copper-paddlewheel MOFs, was also retained using the updated CUS procedure.The results of this computational study illustrate a new and exciting approach to capturing this complex CUS interaction. Furthermore, it highlights the great potential of MOFs in challenging gas separations.
Date of Award1 Apr 2018
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council) & University of Strathclyde
SupervisorAshleigh Fletcher (Supervisor) & Miguel Jorge (Supervisor)

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