5579 r2010 American Chemical Society pubs.acs.org/EF Energy Fuels 2010, 24, 5579–5585 : DOI:10.1021/ef1008743 Published on Web 09/14/2010 Identification of a Novel Ester Obtained during Isolation of C 80 (“ARN”) Tetraprotic Acids from an Oilfield Pipeline Deposit P. A. Sutton, † B. E. Smith, ‡ D. Waters, ‡ and S. J. Rowland* ,† † Petroleum and Environmental Geochemistry Group, Biogeochemistry Research Centre, University of Plymouth, Plymouth, Devon PL4 8AA, United Kingdom, and ‡ Oil Plus Limited, Dominion House, Kennet Side, Newbury, Berkshire RG14 5PX, United Kingdom Received July 8, 2010. Revised Manuscript Received August 12, 2010 Solid deposits in some oilfield pipelines and oil-processing equipment include calcium salts of C 80-82 polycyclic tetracarboxylic acids (“ARN” acids) probably originating from Archaea. It is thought that such deposits form once calcium in seawater comes into contact with crude oils containing the acids, under relevant conditions. The deposits may cause restriction or blockage of pipelines and equipment, with considerable consequent costs for downtime and cleaning. The accurate measurement of the concentra- tions of the acids in oils is an important requirement for the development of mathematical models for the prediction of the formation of oilfield deposits. We have now identified, in a deposit from one North Sea oilfield pipeline, in addition to the known C 80-82 polycyclic tetracarboxylic acids, a hitherto unreported ester of C 80 (“ARN”) acids. We report the evidence for the identification and suggest reasons for the occurrence of the ester. Quantitative analyses which exclude determination of such esters may under- estimate the potential for oils to cause flow problems. Calculations for computer models based on such data might then be in error. Introduction The identification of unusual C 80-82 polycyclic tetra- carboxylic acids, probably originating from Archaea, in solid deposits in some oilfield pipelines and oil-processing equip- ment, long proved to be a major analytical challenge. 1 None- theless, the acids were eventually isolated, and mixtures of regioisomers were identified by nuclear magnetic resonance spectroscopy and mass spectrometry (MS). 2-4 Some workers coined the term “ARN” acids to describe the compounds. 1 It is thought that such insoluble deposits form once calcium in seawater comes into contact with crude oils containing the acids, under relevant conditions. 5 These calcium-acid depos- its may cause restriction or blockage of pipelines and equip- ment, with considerable consequent costs for downtime and cleaning; therefore, attempts at chemical analysis of the distri- butions and concentrations of the acids in oils and deposits have assumed considerable commercial importance. A wide range of techniques has been applied, principally involving detection by various forms of MS, following extraction steps, such as the use of ion-exchange resins. 6 Although few, if any, calibrated methods for the measurement of the acids in oils have been published, it has been noted that, while “ARN” acids can at least be detected in many oils, 7 they are notably absent from others. Some analyses have also shown the presence of more complex mixtures of C 60þ unidentified acids in oils. 8 The accurate measurement of the concentrations of the acids in oils is likely to be a very important requirement for the development of mathematical models for the prediction of the formation of oilfield deposits. 9 Upon examination of a pipeline deposit from a North Sea oilfield, we have now identified, in addition to the known C 80-82 polycyclic tetracarboxylic acids, a hitherto unreported ester of C 80 (“ARN”) acids. We now report the evidence for the identification and suggest a reason for the occurrence of the ester. Quantitative analyses that exclude determination of such esters may underestimate the potential for oils to cause oil flow problems. Calculations for computer models based on such data might then be in error. Experimental Section General solvents (n-hexane, cyclohexane and propan-2-ol) were obtained from Rathburn Chemicals, Scotland, or Fisher Scientific U.K. (diethyl ether) and were HPLC-grade. Liquid chromatography/mass spectrometry (LC/MS)-grade solvent (Chromosolv propan-2-ol, Sigma-Aldrich U.K., Ltd.) and buffers (formic acid, Fisher Scientific U.K.; ammonium acetate, Sigma- Aldrich U.K., Ltd.) were used for electrospray ionization/mass spectrometry (ESI/MS). A sample of crude polycyclic tetracarboxylic acids (hereafter denoted “crude acids”) was isolated from a North Sea oilfield *To whom correspondence should be addressed. Telephone: þ44- 1752-584557. E-mail: srowland@plym.ac.uk. (1) Baugh, T. D.; Grande, K. V.; Mediaas, H.; Vinstad, J. E. SPE Tech. Pap. 93011, 2005. (2) Smith, B. E.; Sutton, P. A.; Lewis, C. A.; Dunsmore, B.; Fowler, G.; Krane, J.; Lutnaes, B. F.; Brandal, O.; Sjoblom, J.; Rowland, S. J. J. Sep. Sci. 2007, 30, 375–380. (3) Lutnaes, B. F.; Brandal, B.; Sjoblom, J.; Krane, J. Org. Biomol. Chem. 2006, 4, 616–620. (4) Lutnaes, B. F.; Krane, J.; Smith, B. E.; Rowland, S. J. Org. Biomol. Chem. 2007, 5, 1873–1877. (5) Sorbie, K. S.; Shepherd, A.; Smith, P. C.; Turner, M.; Westacott, R. E. Proceedings of the Chemistry in the Oil Industry IX; Manchester, U.K., Oct 31-Nov 2, 2005. (6) Mohammed, M. A.; Sorbie, K. S. Colloids Surf., A 2009, 349,1–18. (7) Brocart, B.; Bourrel, M.; Hurtevent, C.; Volle, J.-L.; Escoffier, B. J. Dispersion Sci. Technol. 2007, 28, 331–337. (8) Mapolelo, M.; Stanford, L. A.; Rodgers, R. P.; Yen, A. T.; Debord, J. D.; Asomaning, S.; Marshall, A. G. Energy Fuels 2009, 23, 349–355. (9) Mohammed, M. 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