Although common clathrates hydrates have long been considered as a method for gas storage, transportation and separation, some drawbacks including the need for very high pressures and/or very low subzero temperatures, and unfavourable formation kinetics have been a hurdle to their widespread use at industrial scale. During the last decade, after it was discovered that small gas molecules can be incorporated into the empty cages in semi-clathrate structures, semi-clathrate hydrates (SCH) attracted massive interest as an alternative means of gas storage and separation, taking into account the higher dissociation temperatures of these compounds. Despite the increasing number of publications on SCH, there is still a lack of data about these species of hydrates from both thermodynamic and kinetic points of view. In light of the emerging applications of SCH, this study examines the behaviour of semi-clathrates in ternary systems of ‘gas + SCH former + water’ using an experimental approach. After determining the phase diagram for tetra-n-butyl ammonium bromide (TBAB, as the most common SCH former) by differential thermal analysis, the stoichiometric concentration of TBAB is identified, its hydrate phase boundary under methane (as the rightful substitute of natural gas) pressure is measured and the stability of SCH at atmospheric conditions is monitored. Methane uptake capacity of TBAB and other SCH formers is measured and calculated both volumetrically and gravimetrically. In another part of the study, SCH are used to capture CO2 from syngas mixture in a process called pre-combustion capture in power plants. A unique glass micro model setup is utilized to visualize the SCH in a 2D porous medium. Moreover, the hydrate formation rate of SCH is studied by a kinetic model. Finally, the phase equilibria of hydrogen clathrates at high pressures are measured and compared with those of semi– clathrates formed in the system hydrogen + TBAB + water. The results of this work clarify some new features of SCH and enhance in-depth understanding of their behaviour which can ultimately lead to realizing the possible practical application of SCH in gas storage and separation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:575347 |
| Date | January 2012 |
| Creators | Gholinezhad, Jebraeel |
| Contributors | Tohidi, Bahman |
| Publisher | Heriot-Watt University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10399/2561 |
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