Energy & Fuels 2007, 21, 1309-1316
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Self-Association of Organic Acids in Petroleum and Canadian Bitumen Characterized by Low- and High-Resolution Mass Spectrometry† Donald F. Smith,‡,§ Tanner M. Schaub,‡ Parviz Rahimi,| Alem Teclemariam,| Ryan P. Rodgers,*,‡,§ and Alan G. Marshall*,‡,§ National High Magnetic Field Laboratory, Florida State UniVersity, 1800 East Paul Dirac DriVe, Tallahassee, Florida 32310-4005, Department of Chemistry and Biochemistry, Florida State UniVersity, Tallahassee, Florida 32306, and National Centre for Upgrading Technology, 1 Oil Patch DriVe, DeVon, Alberta, AB T9G 1A8 Canada ReceiVed August 16, 2006. ReVised Manuscript ReceiVed NoVember 8, 2006
We examine solution-phase aggregation for a whole crude oil, whole bitumen, and bitumen distillate fractions by negative-ion electrospray ionization [(-) ESI] detected by both high-resolution [Fourier transform ion cyclotron resonance (FT-ICR)] and low-resolution [linear quadrupole ion trap (LTQ)] mass spectrometry (MS). Aggregate formation for both crude oil and bitumens is concentration-dependent. At high concentrations (i.e., >1 mg/mL), the disruption of noncovalent interactions between heteromultimers by low-energy collisionactivated dissociation (CAD) yields LTQ dissociation mass spectra with molecular-weight distributions identical to those observed by FT-ICR MS analysis at lower concentrations for purely monomeric species. These materials can exist as aggregates in solution even at high dilution (less than 0.1 mg/mL). We demonstrate the concentration and boiling point dependence for multimerization of polar acidic species in the Athabasca bitumen and bitumen distillates. Interestingly, the lowest boiling distillation cut (375-400 °C) displays the highest aggregation tendency, with dimers at concentrations as low as 0.05 mg/mL. Higher boiling point distillation cuts display a decreased aggregation tendency with an increasing cut point. High-resolution negative-ESI FT-ICR MS of the bitumen distillation fractions reveals the elemental composition, and thus the class, type, and carbon number of the multimeric species. Acidic heteroatomic classes for the distillation cut multimers include O4, S1O4, O3, S1O3, N1O2, and N1S1O2. The most abundant multimers for the 375-400 °C distillation cut are O4 species, whereas the 450-475 °C cut contains N1O2 multimers in the highest relative abundance. Changes in multimer heteroatom content as a function of the monomer composition and distillation cut suggest that aggregation depends upon the chemical functionalities of the monomer species.
Introduction The molecular-weight distribution (MWD) of petroleum and petroleum-derived materials is widely debated. Simply, the MWDs determined by various techniques [e.g., size-exclusion chromatography (SEC),1-4 vapor pressure osmometry (VPO),2,4-6 fluorescence depolarization,7-11 and mass spectrometry † Presented at the 7th International Conference on Petroleum Phase Behavior and Fouling. * To whom correspondence should be addressed. Telephone: +1-850644-0529 (A.G.M.); +1-850-644-2398 (R.P.R.). Fax: +1-850-644-1366. E-mail:
[email protected] (A.G.M.);
[email protected] (R.P.R.). ‡ National High Magnetic Field Laboratory, Florida State University. § Department of Chemistry and Biochemistry, Florida State University. | National Centre for Upgrading Technology. (1) Millan, M.; Behrouzi, M.; Karaca, F.; Morgan, T. J.; Herod, A. A.; Kandiyoti, R. Characterizing High Mass Materials in Heavy Oil Fractions by Size Exclusion Chromatography and MALDI-Mass Spectrometry. Catal. Today 2005, 109, 154-161. (2) Domin, M.; Herod, A.; Kandiyoti, R.; Larsen, J. W.; Lazaro, M. J.; Li, S.; Rahimi, P. A Comparative Study of Bitumen Molecular Weight Distributions. Energy Fuels 1999, 13, 552-557. (3) Lazaro, M.-J.; Herod, A. A.; Cocksedge, M.; Domin, M.; Kandiyoti, R. Molecular Mass Determinations in Coal-Derived Liquids by MALDI Mass Spectrometry and Size-Exclusion Chromatography. Fuel 1997, 76, 1225-1233. (4) Miller, J. T.; Fisher, R. B.; Thiyagarajan, P.; Winans, R. E.; Hunt, J. E. Subfractionation and Characterization of Mayan Asphaltene. Energy Fuels 1998, 12, 1290-1298.
(MS)]1,2,4-6,12-21 differ significantly. Many experiments report a low molecular weight (100-2000 Da), but a few experiments suggest a much higher molecular weight (100-50 000 Da or higher). It is known that the tendency for petroleum molecules (including but not limited to asphaltenes) to self-associate complicates the determination of true monomeric MWDs.17,22-32 As a result, analytical techniques that require a high concentra(5) Dickie, J. P.; Yen, T. F. Macrostructures of the Asphaltic Fractions by Various Instrumental Methods. Anal. Chem. 1967, 39, 1847-1852. (6) Acevedo, S.; Gutierrez, L. B.; Negrin, G.; Pereira, J. C.; Mendez, B.; Delolme, F.; Dessalces, G.; Broseta, D. Molecular Weight of Petroleum Asphaltenes: A Comparison between Mass Spectrometry and Vapor Pressure Osmometry. Energy Fuels 2005, 19, 1548-1560. (7) Groenzin, H.; Mullins, O. C. Asphaltene Molecular Size and Structure. J. Phys. Chem. A 1999, 103, 11237-11245. (8) Groenzin, H.; Mullins, O. C. Molecular Size and Structure of Asphaltenes from Various Sources. Energy Fuels 2000, 14, 677-684. (9) Groenzin, H.; Mullins, O. C. Molecular Size and Structure of Asphaltenes. Pet. Sci. Technol. 2001, 19, 219-230. (10) Groenzin, H.; Mullins, O. C.; Eser, S.; Mathews, J.; Yang, M.-G.; Jones, D. Molecular Size of Asphaltene Solubility Fractions. Energy Fuels 2003, 17, 498-503. (11) Buch, L.; Groenzin, H.; Buenrostro-Gonzalez, E.; Andersen, S. I.; Lira-Galeana, C.; Mullins, O. C. Molecular Size of Asphaltene Fractions Obtained from Residuum Hydrotreatment. Fuel 2003, 82, 1075-1084. (12) Larsen, B. S.; Fenselau, C. C.; Whitehurst, D. P.; Angelini, M. Evaluations of Heavy Constituents in Fractions of Petroleum Residues Using Gel Permeation and Field Desorption Mass Spectrometry. Anal. Chem. 1986, 58, 1088-1091.
10.1021/ef060387c CCC: $37.00 © 2007 American Chemical Society Published on Web 12/14/2006
1310 Energy & Fuels, Vol. 21, No. 3, 2007
tion (VPO) or that use solvents that may promote aggregation [gel-permeation chromatography (GPC) and SEC] can yield MWDs that reflect the aggregate molecular weight and not that of the true monomer. MS with various ionization methods has been used extensively to examine the MWD of petroleum. Boduszynski used field ionization/field desorption ionization (FI/FD) to conclude that the upper limit of the MWD of petroleum is approximately 2000 Da.21 Del Rio and Philp found similar distributions (
