444057 Explaining the Paradox of Asphaltene Precipitation with n-Alkanes

Monday, April 11, 2016
Exhibit Hall E (George R. Brown )
M. R. Islam and Chau-Chyun Chen, Chemical Engineering, Texas Tech University, Lubbock, TX

Explaining the paradox of asphaltene precipitation with n-alkanes
Md Rashedul Islam and Chau-Chyun Chen
Department of Chemical Engineering, Texas Tech University
Paraffins, specifically alkanes, promotes asphaltene precipitation when they are blended with
asphaltene-containing petroleum fluids. The alkane/oil volume ratio required for onset of
asphaltene precipitation increases with the carbon number and yields a maxima. Experimental
study indicates that the maxima lays at C7[1] or between C8 -- C10 [2]. However, precipitation
yield decreases asymptotically with increase of the carbon number even if excessively high
alkane/oil volume ratio is used [3]. For example, n-pentane be a better solvent for asphaltene
than n-hexane in regard of both onset of precipitation and precipitation yield. However, high
carbon number alkane beyond the maxima, n-hexadecane for instance, can be a better solvent at
onset of precipitation point and a poorer solvent in regard of precipitation yield than n-
pentadecane. A thermodynamic explanation for this paradox is necessarily important to find the
compatibility of bitumen or crude oil with paraffinic hydrocarbons. In this work, this paradox is
explained by the aggregation thermodynamics of asphaltene precipitation [4]. Both the enthalpy
and entropy of mixing are investigated to explain the effect of paraffin carbon number on
asphaltene precipitation. Athabasca and cold lake bitumen samples are studied.
[1] G. Hotier and M. Robin, "Action de divers diluants sur les produits pétroliers lourds:
mesure, interprétation et prévision de la floculation des asphalténes," Oil & Gas Science and
Technology, vol. 38, pp. 101-120, 1983.
[2] I. A. Wiehe, H. W. Yarranton, K. Akbarzadeh, P. M. Rahimi, and A. Teclemariam, "The
paradox of asphaltene precipitation with normal paraffins," Energy & fuels, vol. 19, pp.
1261-1267, 2005.
[3] D. L. Mitchell and J. G. Speight, "The solubility of asphaltenes in hydrocarbon solvents,"
Fuel, vol. 52, pp. 149-152, 1973.
[4] M. Wang, Y. Hao, M. R. Islam, and C. C. Chen, "Aggregation Thermodynamics for
Asphaltene Precipitation," AIChE Journal, Submitted.

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