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Asphaltene Precipitation in Paraffinic Froth Treatment – Effect of Solvent and Temperature Yuming Xu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03013 • Publication Date (Web): 28 Nov 2017 Downloaded from http://pubs.acs.org on December 1, 2017
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Asphaltene Precipitation in Paraffinic Froth Treatment – Effects of Solvent and Temperature Yuming Xu Natural Resources Canada, CanmetENERGY 1 Oil Patch Drive, Devon, Alberta, T9G 1A8
[email protected] Abstract In surface-mined oil sands operations bitumen is extracted from oil sand ore using a warm water extraction process that produces bitumen froth typically containing 60 wt% bitumen, 30 wt% water, and 10 wt% mineral solids. The bitumen froth is then cleaned in a froth treatment process in which the froth is diluted with solvent to enhance the separation of bitumen from water and solids. In paraffinic solvent froth treatment, light alkanes such as pentane or hexane are used as solvent, leading to precipitation of some of the asphaltenes in the bitumen. The precipitated asphaltenes form agglomerates with the solids and water and these agglomerates quickly settle, producing very clean diluted bitumen. In order to precipitate the required amount of asphaltenes, the solvent-tobitumen ratio used in commercial operations is typically high. In the present work we investigated asphaltene precipitation using other solvents such as butane, neopentane, and carbon dioxide at different temperatures. It was found that the solvent-to-bitumen mass ratio could be reduced significantly by using these solvents or combining them with a more commonly used solvent. The effect of the solvent on asphaltene precipitation can be explained in terms of the solubility parameters of the solvent. A general correlation was obtained between the asphaltene content in bitumen product and the solubility parameters of the solvent.
Keywords
Asphaltene precipitation; Froth treatment; Solubility parameters;
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2 1.
Introduction
Mined oil sand ore, typically containing about 8−12 wt% bitumen, is processed using a warm water extraction process (1). In this process the mined oil sand is mixed with hot water and the resulting slurry is pumped through a pipeline. During this hydrotransport the oil sand is conditioned, that is, the bitumen releases from the sand matrix as droplets, and these droplets engulf air bubbles. When the conditioned slurry enters the primary separation vessel, the bitumen-air droplets float to the top of the vessel to form the product called bitumen froth. Bitumen froth is a mixture of bitumen, water, and mineral solids with a typical composition of 60 wt% bitumen, 10 wt% mineral solids, and 30 wt% water. Water and mineral solids are removed in the subsequent froth treatment step in order to produce a clean bitumen product.
Since bitumen is viscous and the density difference between bitumen and water is small, the froth has to be diluted with an organic solvent to enhance the separation of the bitumen from the water and solids. There are two different froth treatment processes depending on the type of solvent used: traditional naphtha-based froth treatment (NFT) and the newer paraffinic solvent−based froth treatment (PFT). In NFT, naphtha is used to dilute the froth, after which the water and solids are separated from the diluted bitumen by gravity settling or under centrifugal force. The final diluted bitumen product still contains emulsified water (1−2 wt%) and mineral solids such as clay ( iso-pentane > n-pentane. Neopentane has an extremely high ability to precipitate asphaltenes. 2. Froth treatment tests using CO2 demonstrate that CO2 has a strong ability to precipitate asphaltenes when used in combination with paraffinic solvent; the effect of a given mass of CO2 is equivalent to that of about two unit masses of npentane. 3. The use of non-traditional solvents, such as neopentane or CO2 would significantly reduce the size requirement for the settler used in froth treatment plants and the required volume of solvent.
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26 4. Asphaltene precipitation by n-pentane, iso-pentane, and neopentane is slightly temperature dependent. The asphaltene content remaining in the bitumen increases with increasing temperature until reaching a maximum at around 75100 °C. 5. The effects of the solvent type and solvent concentration on asphaltene precipitation can be explained by the solubility parameters. The results illustrate that the asphaltene content in bitumen product is correlated with the solubility parameters of the effective solvent (solvent plus maltenes). A single curve fits all the solvents tested in this study, at various concentrations. This general curve can serve the oil sands industry as a guide for solvent selection in order to precipitate given percentages of asphaltenes. 5.
Acknowledgements
The author would like to thank Jianmin Pang, Surjit Thind, and Derek Chao for their assistance in experimental measurements, and Dr. Merouane Khammar for his assistance in providing the solubility parameter data for CO2. Financial support from the Canadian government’s interdepartmental Program of Energy Research and Development (PERD) is acknowledged.
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