Energy & Fuels 2009, 23, 3687–3693
3687
Water Enhances the Aggregation of Model Asphaltenes in Solution via Hydrogen Bonding Xiaoli Tan,† Hicham Fenniri,*,‡ and Murray R. Gray*,† Department of Chemical and Materials Engineering, UniVersity of Alberta, Edmonton, Alberta T6G 2G6, Canada and National Institute for Nanotechnology and Department of Chemistry, UniVersity of Alberta, Edmonton, Alberta T6G 2M9, Canada ReceiVed March 15, 2009. ReVised Manuscript ReceiVed May 8, 2009
The self-association properties of two 2,2′-bipyridine derivatives, 4,4′-bis(2-pyren-1-yl-ethyl)-2,2′-bipyridine (PBP) and 4,4′-bis[2-(9-anthryl)ethyl]-2,2′-bipyridine (ABA), in water-saturated solvents were studied as models for petroleum asphaltenes. 1H NMR spectroscopy titration experiments in chloroform established that both compounds self-associate in solution. The addition of water (ranging from 0.43 to 0.86 g/L) increased the thermal stability and the aggregation behavior of PBP and ABA at low concentration (3.06 × 10-4 and 1.28 × 10-3 M, respectively). The chemical shift, line-width, and spin-spin (T2) relaxation time of water protons in these solutions showed that the O-H · · · N hydrogen bonds between the pyridyl nitrogens of PBP/ABA and water were responsible for their aggregation at low concentration, although FTIR spectroscopy suggested that the H-bond between PBP and water was relatively weak. The solubility of water in PBP solutions showed that the number of water molecules per PBP molecule varied between 1 and 2 in water-saturated CHCl3 and that the Gibbs free energy for the exchange of water between the aqueous phase and the solution of PBP was -16 kJ/mol at 22 °C. Water likely enhanced the stability of aggregates by reinforcing π-π interactions via waterbridged intermolecular H-bonding between the pyridyl nitrogen.
Asphaltenes are the densest fraction of petroleum and are separated as solids by the addition of an excess amount of n-alkane to crude oil. The importance of asphaltenes stems from the problems they cause in the petroleum industry.1 They have a great tendency to associate, leading to solid-phase separation, precipitation, and facility plugging problems, as well as catalyst deactivation. Characteristic structural features of asphaltenes molecules are planar polyaromatic cores and polar (sulfur, oxygen, and nitrogen) functional groups, attached to naphthenic rings and aliphatic side chains.2 The associative behavior of asphaltenes in solvents and crude oils has been studied by small angle neutron scattering (SANS),3,4 vapor pressure osmometry (VPO),5 isothermal titration calorimetry (ITC),6 gel permeation chromatography (GPC),7 high quality factor (high-Q) ultrason-
ics,8 and molecular simulations.9 The intermolecular interactions that drive asphaltenes to associate may include electrostatic interactions, van der Waals or dispersion forces between aromatic rings, intermolecular charge transfer, exchange-repulsion interaction, and hydrogen bonding.9,10 However, understanding the behavior of asphaltenes at the molecular level is a challenging task due to the high polydispersity and chemical diversity of this fraction. Due to this complexity, the energetics of self-association of asphaltenes are not clearly defined.1 Asphaltenes are also important in interfacial and colloid sciences, because they play an important role in stabilization of water-in-oil emulsions.11,12 Masliyah and co-workers13 showed that a layer of asphaltenes at the toluene/water interface is strongly bonded with water. Such interaction of asphaltenes with trace amounts of water in bulk organic solvents has been reported previously.14-16 On the basis of calorimetric titration
* To whom correspondence should be addressed. E-mail: hicham.fenniri@ nrc-cnrc.gc.ca (H.F),
[email protected] (M.R.G.); phone: (780) 6411750 (H.F.), (780) 492-7965 (M.R.G.); fax: (780) 641 - 1601 (H.F.), (780) 492-2881 (M.R.G.). † Department of Chemical and Materials Engineering. ‡ National Institute for Nanotechnology and Department of Chemistry. (1) Sheu, E. Y. Energy Fuels 2002, 16, 74–82. (2) Strausz, O. P.; Lown, E. M. The Chemistry of Alberta Oil Sands, Bitumens, and HeaVy Oils; AERI: Calgary, AB, 2003. (3) Gawrys, K. L.; Spiecker, P. M.; Kilpatrick, P. K. Pet. Sci. Technol. 2003, 21, 461–489. (4) Sheu, E. Y.; Liang, K. S.; Sinha, S. K.; Overfield, R. E. J. Colloid Interface Sci. 1992, 153, 399–410. (5) (a) Yarranton, H. W.; Alboudwarej, H.; Jakher, R. Ind. Eng. Chem. Res. 2000, 39, 2916–2924. (b) Agrawala, M.; Yarranton, H. W. Ind. Eng. Chem. Res. 2001, 40, 4664–4672. (6) Merino-Garcia, D.; Andersen, S. I. Pet. Sci. Technol. 2003, 21, 507– 525. (7) Seidl, P. R.; Chrisman, E. C. A. N.; Silva, R. C.; de Menezes, S. M. C.; Teixeira, M. A. G. Pet. Sci. Technol. 2004, 22, 961–971.
(8) Andreatta, G.; Goncalves, C. C.; Buffin, G.; Bostrom, N.; Quintella, C. M.; Arteaga-Larios, F.; Perez, E.; Mullins, O. C. Energy Fuels 2005, 19, 1282–1289. (9) (a) Murgich, J.; Rodriguez, J.; Aray, Y. Energy Fuels 1996, 10, 68– 76. (b) Murgich, J. Mol. Simul. 2003, 29, 451–461. (10) Murgich, J. Pet. Sci. Technol. 2002, 20, 983–997. (11) Fordedal, H.; Schildberg, Y.; Sjoblom, J.; Volle, J. L. Colloids Surf. A: Phys. Chem. Eng. Aspects 1996, 106, 33–47. (12) McLean, J. D.; Kilpatrick, P. K. J. Colloid Interface Sci. 1997, 189, 242. (13) (a) Yan, Z.; Elliott, J. A. W.; Masliyah, J. H. J. Colloid Interface Sci. 1999, 220, 329–337. (b) Zhang, L. Y.; Lopetinsky, R.; Xu, Z.; Masliyah, J. H. Energy Fuels 2005, 19, 1330–1336. (c) Zhang, L. Y.; Xu, Z.; Masliyah, J. H. Ind. Eng. Chem. Res. 2005, 44, 1160–1174. (d) Zhang, L. Y.; Breen, P.; Xu, Z.; Masliyah, J. H. Energy Fuels 2007, 21, 274–285. (14) Andersen, S. I.; del Rio, J. M.; Khvostitchenko, D.; Shakir, S.; Lira-Galeana, C. Langmuir 2001, 17, 307–313. (15) Murgich, J.; Merino-Garcia, D.; Andersen, S. I.; del Rio, J. M.; Lira-Galeana, C. Langmuir 2002, 18, 9080–9086. (16) Khvostitchenko, D.; Andersen, S. I. Energy Fuels 2008, 22, 3096– 3103.
1. Introduction
10.1021/ef900228s CCC: $40.75 2009 American Chemical Society Published on Web 05/26/2009
3688
Energy & Fuels, Vol. 23, 2009
and Fourier-transform infrared (FTIR) spectroscopy, Andersen et al. found that trace amounts of water in the solvent (
