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Title: Dielectric measurements and catalytic cracking of heavy oils using advanced microwave technologies
Author: Aldawsari, Afrah M. F.
ISNI:       0000 0004 6494 4246
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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The continuously growing world demands of petroleum to service the domestic and industrial electricity, transportation sectors, and its contribution to Climate Change, places onus on researchers to find more efficient methods for heavy oil (petroleum) processing. Given the enormous quantities of petroleum processed in the world, and the general prevalence of high energy cost and high carbon footprint processing technologies, there is strong interest in development of more efficient and improved unconventional processing methods. This thesis contributes to the field of unconventional processing methods for petroleum. We investigate the utility of microwave irradiation for efficient chemical activation for the processing of petroleum to useful products, and demonstrate that the selective and targeted dissipation of microwave energy has great potential to deliver shorter reaction times compared to conventional cracking processes driven by thermal energy. Heavy bunker oil, which is the starting feedstock for petroleum processing, is a thick and viscous material. Furthermore, it is not a good absorber of microwave energy due to the presence of nonpolar heavy fractions such as hydrocarbons, sulphur, and nitrogen compounds. Such characteristics make microwave processing of petroleum especially challenging. As the essential first step, the elucidation of microwave response properties of petroleum is one of the key outcomes of this thesis. This was accomplished by a systematic investigation of dielectric properties of model chemical compounds and oil samples using the cavity perturbation technique at 2.45 GHz. The zeolite HZSM-5 is widely recognized among the best catalysts for the production of high value light products from petroleum, and was employed for our studies. The dielectric properties of the zeolite were evaluated at room, and at higher temperatures up 500°C to gain insight into the behaviour of the sample (catalyst and oil) in a microwave energy driven catalytic cracking reaction. Generally, we found that the permittivity of the zeolite increases as the temperature increases. We attribute this to the enhancement in polarisation, as well as to a temperature dependent microwave conductivity, which occurs via proton hopping mechanism. We have systematically explored libraries of dielectric materials to understand the materials interaction with microwave energy. This has allowed us to investigate the variation of microwave energy dissipation and cracking reactions for various catalyst-petroleum systems. The optimisation of microwave applicator parameters using a model compound (decane) was performed. This indicated a clear diffierence in product distribution between thermal and microwave processing and an enhanced fraction of hydrogen and olefins were observed under microwave irradiation. We ascribe this observation to the difference in heat generation mechanism between the two modes. The microwave applicator was used to study heavy oil cracking it was found it is possible to conduct an efficient cracking reaction over appropriately modified zeolite. We should particularly highlight our results, whereby we demonstrate the production of large fraction of hydrogen over metal oxide doped HZSM-5 zeolite. It was found that the cracking reactions of the heavy oil over zeolite are influenced by the high electric field, which can result in highly localised superheating within the catalytic material. The heavy oil impregnated metal oxide-zeolite displayed significant temperature gradients between the catalyst particles hotspot and the surrounding domains compared to the non-modified zeolite. Thus, the dehydrogenation process and the release of hydrogen were found to be enhanced in the decomposition of metal oxide-HZSM-5 zeolite compared to the pure HZSM-5. Further enhancement of our system to a continuous flow reaction was performed in order to assess the potential for industrial applications of heavy oil cracking processes using microwave technology. This would be a critical step to demonstrate the scalability of our techniques. However, the results presented in this thesis reliably demonstrate that a significantly enhanced performance at lab scale system in shorter reaction times could be achieved through the cracking of heavy oil to hydrogen and high value light products.
Supervisor: Edwards, Peter Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available