Naphthenic acids were identified as the main corrosive species in acidic crudes, although they represent less than 3% wt. The determination of naphthenic acid concentration in oils is one of the first tasks for naphthenic corrosion studies, being expressed still by the total acid number (TAN). However, the TAN is not directly correlated to the corrosivity of naphthenic acids, and therefore it is important to study the naphthenic composition and the corrosion associated with TAN values. Herein, the corrosion process was evaluated on an AISI 316 steel surface immersed in two crude oil samples (G and J) with distinct TAN values (0.33 and 3.10 mg KOH g(-1)) by optical microscopy, atomic force microscopy (AFM) and Raman spectroscopy during a total period of 36 days. For light microscopy images, the naphthenic corrosion is evidenced only on the AISI 316 steel surface from 21 days of exposure to sample J. On the other hand, AFM measurements predicted the real stage'' of naphthenic corrosion, evidenced by topographic and phase images from 21 days for crude oil G and 14 days for sample J. Raman spectra also corroborated AFM data, wherein three corrosion products were identified: goethite (alpha-Fe(OOH), magnetite (Fe3O4), and hematite (Fe2O3). The correlation between the naphthenic corrosion and the TAN values was evaluated from negative ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry data that showed a wider range of DBE distribution (from 1 to 17) and higher naphthenic acid species concentration for the crude oil with higher corrosion power. (C) 2014 Elsevier Ltd. All rights reserved.

The analysis of hydrocarbon using atmospheric or ambient ionization techniques still remains a challenge in mass spectrometry. Traditionally, the ionization occurs via protonation or deprotonation and thus the molecules of interest must have a basic or acidic group to generated [M+H](+) or [M-H](-) ions. To overcome such limitation, it is proposed a simple, easy, fast and powerful analytical methodology to ionize saturated (linear and branched), unsaturated, and cyclic hydrocarbons as well as polyaromatic hydrocarbons by atmospheric pressure chemical ionization (APCI) using small hydrocarbons as reagents in a FT-ICR mass spectrometer. These molecules may be present in hydrocarbon fraction samples and paraffin/crude oil blends. Among the APCI hydrocarbon reagents, isooctane provided the best results when compared to pentane, hexane, cyclohexane and heptane. The method renders the ionization of hydrocarbons to yield [M-H](+) ions with no associated fragmentation using nitrogen as sheath gas. (C) 2015 Elsevier Ltd. All rights reserved.

Naphthenic acids are recognized as the main corrosive species in acidic crude oils, although they represent less than 3 wt%. Alternative methods have been developed in an attempt to remove naphthenic acids from the oil, however, their implementation in petrochemical industry still represents a challenge. Herein, a sub-product of the steel industry, steel slag, is evaluated as an economic alternative catalyst and environmentally feasible to remove naphthenic acids present in crude oils. A high-acidity crude oil (TAN = 4.79 mg KOH g(-1) and S = 1.022 wt%) was submitted to thermo-catalytic process at 300 and 350 degrees C during 2, 4 and 6 h and its degradation products were monitored by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron mass spectrometry (FT-ICR MS), total acid number (TAN) and total sulfur. The main crystalline phases detected by X-ray diffractometry in the catalyst were calcite (CaCO3), silica (SiO2) and magnesia (MgO). Among them, the MgO contributes effectively to promote the thermo-catalytic decarboxylation of naphthenic acid species, with a TAN reduction of 43.50% (4.79 -> 1.89 mg KOH g(-1)) from the original oil to the degraded oil obtained after treatment at 350 degrees C for 4 h. Acid species with lower pK(a) values were selectively removed with the ESI(-)FT-ICR MS data confirming an increase in the DBE values from 1-5 to 5-18 for O-2 class. Therefore, the catalyst selectively promoted the removal of naphthenic acids via (i) neutralization reaction; (ii) cracking reaction and (iii) MgCO3 formation from CO2 molecules produced by a previous thermal decarboxylation reaction. (C) 2015 Elsevier Ltd. All rights reserved.