Asphaltene Precipitation from Bitumen/Multicomponent Solvent Mixtures
Date
2021-03-01
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Abstract
Bitumen is sometimes diluted with multicomponent solvents in oilfield processes and it is useful to predict if and how much asphaltenes may precipitate from these mixtures. The Modified Regular Solution (MRS) approach was adapted for these applications. For this purpose, the onset and yield of asphaltene precipitation from heavy oil diluted with multicomponent solvents were determined at temperatures from 21 to 180°C and pressures up to 10 MPa. The solvents considered include: 1) mixtures of n-pentane, n-heptane, cyclohexane, and toluene; 2) petroleum solvents such as condensates, diesel, and kerosene. The asphaltene yields at ambient conditions and high pressures were measured gravimetrically in a bench top apparatus and in a blind cell apparatus, respectively. The onset of asphaltene precipitation was extrapolated from asphaltene yield data at ambient conditions and determined optically at higher pressures with titrations performed in a high-pressure microscope. Temperature dependent binary interaction parameters (BIP) were introduced to a previously developed MRS approach to model asphaltene precipitation from heavy oil diluted with blended pure solvents. BIP for the cyclohexane/asphaltene and toluene/asphaltene pseudo-component pairs were sufficient to match all of the data collected with binary solvent blends. All other BIP were set to zero. The model with the BIP obtained from the binary solvent blends predicted the asphaltene onsets and yields from heavy oil with ternary solvent blends, generally to within the error of the measurements. A methodology to characterize petroleum solvents based on their GC assays to predict their molecular weight, density, and solubility parameters was developed. The methodology was tested against their measured densities at standard conditions and the solubility parameters determined by fitting the MRS model to yield data collected for bitumen diluted with these solvents. The asphaltene yields modeled using the proposed correlations as input to the MRS model matched the experimental data for all but one of the petroleum solvents and their blends with n-heptane with an overall average absolute deviation and bias of 1.1 wt% and -0.8 wt%, respectively. The MRS model did not match the asphaltene yield from the naphtha.
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Keywords
Asphaltene Precipitation, Modified Regular Solution Model, Multicomponent Solvents, Petroleum Solvents, Solvent Blends, Heavy Oil
Citation
Rivero Sanchez, J. A. (2021). Asphaltene Precipitation from Bitumen/Multicomponent Solvent Mixtures (npublished master's thesis). University of Calgary, Calgary, AB.