Characterisation of metal-organic frameworks with inherent functionalisation for carbon capture methods

McAnally, Craig Alan

Thesis

Characterisation of metal-organic frameworks with inherent functionalisation for carbon capture methods

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Creator

McAnally, Craig Alan

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2017

Thesis identifier

T14617

Person Identifier (Local)

201365874

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Chemical and Process Engineering.

Abstract

Carbon Capture offers potential remediation for greenhouse gases from industrial point sources, and physical sorbents are an economically viable option, but one that requires optimisation. Here, materials were investigated to assess the effect of incorporation of functionalised ligands, which utilise a Lewis basic character, on the potential of such materials for Carbon Capture applications. Materials were investigated for their structural and adsorptive properties, allowing analysis and evaluation of the selective capture of carbon dioxide. Characterisation included single crystal X-ray diffraction, powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and elemental analysis. Adsorption properties were evaluated using volumetric nitrogen adsorption at 77 K, which showed all three materials experienced activated diffusion, and gravimetric carbon dioxide adsorption at 273 K. Further gravimetric adsorption analysis was performed at various temperatures using carbon dioxide, methane, and nitrogen gases, to analyse the performance of these materials under simulated conditions for carbon capture processes. Thermodynamic and kinetic properties were determined in order to provide an indication of the underlying processes governing diffusion and equilibration of adsorption.Three materials were investigated; Cu(bpetha)2SiF6 (bpetha = 1,2-bis(4-pyridyl)ethane), [Cu(TPT)]BF4.0.75H2O and [Cu(TPT)]NO3.MeOH (TPT = 1,3,5-tris(4-pyridyl)-2,4,6-triazine). Cu(bpetha)2SiF6 showed promising results for carbon dioxide adsorption (0.6 mmol g−1 at 100 kPa and 333 K), having kinetically selective behaviour for nitrogen and methane at timescales that are suitable for pressure swing adsorption processing (90 %/5 % of equilibrium uptake for carbon dioxide vs. nitrogen in under 3 min). The material also showed enhanced adsorption interactions towards carbonvdioxide as a consequence of electronegative fluorine atoms within the structure, and also exhibited flexibility of the framework towards carbon dioxide. [Cu(TPT)]BF4.0.75H2O showed poor adsorption capabilities for carbon dioxide (0.15 mmol g−1 at 100kPa and 333 K), which is ascribed to pore blocking effects of the anion within the structure. [Cu(TPT)]NO3.MeOH showed moderate uptakes for CO2 at low temperatures (1.96 mmol g−1 maximum capacity at 273 K), but demonstrated better adsorption capabilities for methane at higher temperatures (1.54 mmol g−1 at 100 kPa and 333 K). The framework experienced a large structural change upon adsorption, which was probed using methane at different temperatures.The results of this study showed that materials synthesised with inherent functionalisation could be developed to enhance carbon dioxide adsorption for Carbon Capture applications. However, other structural effects of the materials must be considered as the complexity of Metal-Organic Framework structures can influence the adsorption properties via a variety of mechanisms.

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