The amount of acidic crude oils produced worldwide is increasing. These oils introduce problems throughout the hydrocarbon value chain due to their high content of carboxylic acids, examples of which are naphthenate deposition in production facilities and refinery corrosion. In order to deal with these problems, it is often necessary to isolate the carboxylic acids in different fluid streams or solids to allow further analysis without interference from other compounds. This paper presents and verifies an ion-exchange method that can be used for selective isolation of carboxylic acids from crude oils, distillate fractions and other organic solvent. The efficiency and selectivity of the method have been demonstrated as >98 mol-% using two synthetic carboxylic acids. Its usefulness for isolation of carboxylic acids from solids and non-organic solvents has also been demonstrated, exemplified by calcium naphthenate deposits and water. Introduction Among the oilfields found and developed around the world, an increasing fraction contains naphthenic acids and has a high TAN-value (Total Acid Number). Producing and refining high-TAN crude oils introduces a number of problems, e.g. calcium naphthenate deposition in process facilities offshore,1–4 and corrosion in refinery equipment.5 In order to understand the mechanisms behind these and other naphthenic acid-related problems, it is of utmost importance that the acids can be isolated selectively, thereby allowing for thorough characterization of the acids. Through the years, a number of works dealing with isolation and characterization of acids in crude oils, base oils, oil shale, etc. have been published. The different methods are most easily grouped into the categories solid/liquid extraction,6–12 liquid/liquid extraction,13 and chromatography.14,15 Methods for direct extraction of acids from water are also described.16–18 The idea of using a sugar-based QAE Sephadex A-25 ion exchange resin (Acid-IER) was presented to Statoil by private consultant Bjørn A. Ardø, who also worked with Statoil to develop the idea into a working procedure for isolating carboxylic acids from crude oils. The fact that it is sugar-based makes the IER hydrophilic, and, therefore, more selective towards carboxylic acids than hydrophobic IERs. The present paper describes the Acid-IER method in detail, and gives examples of its use for isolating acids from a crude oil and its distillates as well as from water and calcium naphthenate deposits. The high efficiency and selectivity of the Acid-IER method has been demonstrated using two synthetic acids dissolved in an acid-free crude oil. Laboratory equipment The experimental set-up and equipment used during carboxylic acid isolation are ordinary laboratory equipment, e.g. filter funnels, filtering flasks, and round flasks. During the filtering process two filter paper qualities were used - 5891 Black Ribbon and 5893 Blue Ribbon from Schleicher & Schuell - hereafter referred to as coarse and fine filter paper, respectively. Solvent evaporation was done using a rotavapor (Labrota 4003 equipped with rotacool and rotavac, Heidolph). The rotation and temperature set points were 120 rpm and 60°C, respectively. The pressure was reduced gradually to 35 mbar. The acids were dried further in a heating chamber (60°C) until the weight was stable.

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By using a new furnace design, M(3)AlF(6) (M = Na, K, Cs) and mixtures of small amounts of AlF(3) in FLiNaK (46.5 mol % LiF, 11.5 mol % NaF, 42 mol % KF) and CsF-KF eutectic have been investigated over a wide temperature range (25-1050 degrees C) by Raman spectroscopy. The peak positions and their relative intensities have been measured as a function of temperature. In FLiNaK, up to 750 degrees C, the bands shift gradually to lower wavenumbers, and their halfwidths increase in agreement with published data. However, it is shown from solubility measurements and Raman data that, in these conditions, the mixture is not totally molten and the spectra correspond mainly to AlF(6)(3-) in the solid state. When the mixture is completely molten, a new band appears clearly on the high-frequency side of the main band of the spectrum, and its intensity grows up when the temperature is increased. The present results are a clear confirmation of the dissociation of AlF(6)(3-) into AlF(5)(2-) and AlF(4)(-) that our study of the Raman bands of the fully melted systems MF-AlF(3) (M = Na, K, Li) previously suggested. On these systems, it is then important to know if the spectra belong mainly to solid or liquid fluoroaluminates before drawing any conclusion concerning the liquid phase structure.

Calcium naphthenate deposition is among the most challenging obstacles to high production regularity for oilfields where acidic crude oils are produced. Until now it has generally been acknowledged that the deposit is made up of calcium soaps of the naphthenic acids in the crude oil, though with a slight overrepresentation of the lighter acids. In this paper, however, we demonstrate that this is not the case. Through a combination of several analytical techniques - the most important being Potentiometric Titration, LC/MS, NMR, and VPO - the ARN acid has been identified as the dominating constituent of these deposits. The ARN acid is a family of 4-protic carboxylic acids containing 4 - 8 unsaturated sites (rings) in the hydrocarbon skeleton with mole weights in the range 1227–1235 g/mol. The mole weight of the homologous ARN acids series are 1227, 1229, 1231, 1233, 1235 (basic structures) + n×14 (n = number of additional CH[2]-groups in hydrocarbon skeleton).The ARN acid with mole weight 1231 has C[80]H[142]O[8] as empirical formula. The present paper describes the different analytical methods leading to the ARN acid discovery. Furthermore it discusses possible ARN structures and methods for quantitative ARN detection in crude oils. The ARN acid has proved to be the main component in naphthenate deposit from oilfields offshore Norway, Great Britain, China and West Africa.The implications of the discovery to current calcium naphthenate treating strategies will be briefly discussed. Introduction An increasing share of the oilfields found and developed around the world falls in the category "high-TAN crudes", i.e. contains significant amounts of carboxylic (mainly naphthenic) acids. Producing and refining high-TAN crude oils introduces a number of problems, among which calcium naphthenate deposition in process facilities is the most serious production issue.[1–4] The mechanistic understanding of calcium naphthenate deposition is still very limited, though. It is generally acknowledged that a reaction takes place between naphthenic acids in the oil and calcium ions in the water. The reaction product, calcium naphthenate, is basically insoluble in either of the phases and, hence, precipitates out and accumulates at the oil/water interface. Although this simple model describes the naphthenate deposition phenomenon nicely, it doesn't give any clue as to why the acids in the deposit do not resemble the acids in the crude oil (Mediaas et al.[5] have titrated acids isolated from a calcium naphthenate deposit sample and from the corresponding crude oil to show that the average mole weight of the former is significantly lower than that of the acids in the crude oil; 330 and 430 g/mol, respectively). Furthermore, in some cases, it takes only a few parts per million of a naphthenate inhibitor to suppress naphthenate deposition from oil and water containing 2 wt% naphthenic acids and 0.1 wt% calcium, respectively.[1] Together, these observations indicate that some rigid selection criteria direct which naphthenic acids are active in the naphthenate deposition process. These are nothing but field observations confirming laboratory experiments showing that high pH (~10 or higher) and high reactant concentrations are needed for detectable amounts of ordinary organic (including naphthenic) acids to deposit as calcium salts.[2] ConocoPhillips and Statoil have cooperated for several years to unravel the fundamental secrets of calcium naphthenate deposition. Our working hypothesis has been that the reason for the above described "discrepancies" between the model and field- and laboratory observations is that one or more specific structural elements need to be present in a naphthenic acid in order to render it receptive to deposition upon contact with calcium-containing water at pH ~6. The objective has been to identify structural keys that enable naphthenic acids to deposit as calcium naphthenate under production conditions. The first fruit of this cooperation - the identification of the ARN acid as a prerequisite for calcium naphthenate deposition - was presented at the ACS National Meeting in August 2004.[6] In this paper we will elaborate somewhat more on the ARN acid discovery before we present our present ideas regarding the structure of the ARN acid.