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Energy & Fuels 2007, 21, 266-273
Comparison of the Composition of Russian and North Sea Crude Oils and Their Eight Distillation Fractions Studied by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: The Effect of Suppression Marjo J. Tera¨va¨inen,† Jaana M. H. Pakarinen,† Kim Wickstro¨m,‡ and Pirjo Vainiotalo*,† Department of Chemistry, UniVersity of Joensuu, Post Office Box 111, 80101 Joensuu, Finland, and Technology Centre, Neste Oil Oyj, Post Office Box 310, 06101 PorVoo, Finland ReceiVed June 27, 2006. ReVised Manuscript ReceiVed September 27, 2006
Normal electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR) mass spectrometry in negative-ion mode has been used to compare the composition of Russian and North Sea crude oils and their eight different distillation fractions (160-210, 210-260, 260-310, 310-360, 360-410, 410-460, 460510, and 510-560 °C). This is the first time that the polar compound distribution, especially species containing O, O2 and N atoms, has been studied as a function of temperature. The results obtained are consistent with measured total acid number and nitrogen values; the North Sea crude oil had higher acid but lower nitrogen content compared to the Russian crude oil. The influence of high acid content on the ionization efficiency of other polar species (O and N) in oil samples is also presented for the first time.
Introduction Crude oil is probably one of the most complex mixtures in the world, and its composition varies widely, depending upon the origin and age. Even oil samples taken from the same oil field may differ from each other. Further, the variability of commercial oil qualities is wide because they are collected from several different fields and sold as mixtures on the market. In appearance, crude oil varies from a light, yellow-brown fluid to a heavy, nearly black solid. Chemically, crude oil predominantly (∼90%) consists of hydrocarbon compounds such as naphthenes, paraffins, and aromatic hydrocarbons. The remainder (∼10%) consists of polar compounds containing N, O, S heteroatoms and metal atoms (only vanadium and nickel exist at concentrations >1 ppm).1,2 Despite the small percentage of polar compounds, over 20 000 different polar organic compounds with different elemental compositions (CcHhNnOoSs) have been found in crude oil.3 These polar compounds sometimes cause problems in oil production, refining and storing such as corrosion, emulsion formation, poisoning of catalysts, coke formation, poisonous and carcinogenic characteristics, and contamination. On the other hand, because oil consumption is continuously increasing, there is a demand to use limited oil reservoirs and heavier fractions more efficiently. Therefore, knowledge of the composition of crude oils from different origins is important for optimizing refining processes. * To whom correspondence should be addressed: University of Joensuu, Department of Chemistry, P. O. Box 111, FIN-80101 Joensuu, Finland. Telephone: +358-13-2513362. Fax: +358-13-2513360. E-mail: pirjo.vainiotalo@ joensuu.fi. † University of Joensuu. ‡ Neste Oil Oyj. (1) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G.; Walters, C. C.; Qian, K.; Mankiewicz, P. Org. Geochem. 2004, 35, 863-880. (2) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G.; Qian, K.; Robbins, W. K. Org. Geochem. 2002, 33, 743-759. (3) Marshall, A. G.; Rodgers, R. P. Acc. Chem. Res. 2004, 37, 53-59.
Naphthenic acids and phenols are the two most common oxygen-containing compound classes in crude oil. There are other minor acidic classes, such as aromatic, olefinic, hydroxyl, and dibasic acids.4 Naphthenic acids are defined as carboxylic acids that include one or more saturated ring structures, with five- and six-membered rings the most common. Besides ringcontaining acids, linear carboxylic acids are often included in the naphthenic acid class. Naphthenic acids are known to be a significant source of corrosion in oil-refining equipment.2,5 Corrosion is associated with the total acid number (TAN), which is defined as the mass of potassium hydroxide (KOH) in milligrams required to neutralize 1 g of crude oil. However, it has been argued that there is no clear correlation between the TAN value and corrosion.6,7 Crude oil contains both neutral and basic nitrogen compounds. Neutral nitrogen compounds include, for example, carbazoles, indoles, and pyrroles, and correspond to less than 30% of all organic nitrogen compounds.8 On the other hand, basic nitrogen compounds include, for example, pyridine and quinoline derivatives. Nitrogen compounds are harmful in oil refining because they decrease the efficiency of catalytic processes and increase product instability during storage.2,5,9-11 The major sulfur(4) Brient, J. A. Commercial utility of naphthenic acids recovered from petroleum distillates. In Symposium on Acidity in Crude Oil, Presented Before the Division of Petroleum Chemistry, Inc., 215th National Meeting, American Chemical Society, Dallas, TX, March 29-April 3, 1998. (5) Wu, Z.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2004, 18, 1424-1428. (6) Tomczyk, N. A.; Winans, R. E.; Shinn, J. H.; Robinson, R. C. Energy Fuels 2001, 15, 1498-1504. (7) Barrow, M. P.; McDonnel, L. A.; Feng, X.; Walker, J.; Derrick, P. J. Anal. Chem. 2003, 75, 860-866. (8) Von Raith, J.; Lanik, A. Erdoel, Erdgas Z. 1982, 98, 169-175. (9) Wu, Z.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2005, 19, 1072-1077. (10) Qian, K.; Rodgers, R. P.; Hendrickson, C. L.; Emmet, M. R.; Marshall, A. G. Energy Fuels 2001, 15, 492-498. (11) Guan, S.; Marshall, A. G.; Scheppele, S. E. Anal. Chem. 1996, 68, 46-71.
10.1021/ef060294v CCC: $37.00 © 2007 American Chemical Society Published on Web 11/16/2006
Comparison of Russian and North Sea Crude Oils
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Table 1. Fractions of Russian and North Sea Crude Oils Studied and Their Yields yield (mass percent) oil
160-210 °C
210-260 °C
260-310 °C
310-360 °C
360-410 °C
410-460 °C
460-510 °C
510-560 °C
Russian North Sea
7.37 7.90
8.65 9.61
9.59 10.13
9.00 8.97
9.16 8.15
6.96 6.15
7.03 7.75
6.16 5.65
Table 2. Composition of the Russian and North Sea Crude Oils TANa Russian North Sea
Nb
Nc
Sd
(mg of KOH/g)
basic (mg/kg)
total (mg/kg)
total (mass percent)
