Naphthenic acids in Brazilian petroleum: Extraction and analysis
Ana Maria Geller1, Liliane Dailei Almeida Gruber, Maria Silvana Aranda Moraes, Flaviana Cardoso Damasceno, Claudia Alcaraz Zini, Elina Bastos Caramão
1 Inorganic Chemistry, University of Rio Grande do Sul
P.11 in Poster Session
Most of the Brazilian oils and their derivatives are heavy and slightly acidic. This acidity may impart lower prices for crude oils. New challenges, such as the characterization of heavy and extra heavy pre-salt layer and offshore oils, which may result in a high production in a near future, are also important driving forces for the improvement of analytical approaches. Naphthenic acids (NA) are considered responsible for corrosion in the liquid phase of the petroleum refining, and the levels of acidity measured by the TAN (Total Acid Number), has been receiving special attention in recent research about their content and nature. As correlations between TAN and naphthenic acids structures are generally very poor, more detailed analyses of naphthenic acids are needed to better understand the relation among physical effects due to naphthenic acids and their composition/concentration. The development of an ideal analytical method for quantifying NA (general formula CnH2n+ZO2, where n is the carbon number and Z specifies the hydrogen deficiency resulting from ring formation) has been impeded by the complexity of these mixtures. For each n and Z combination there are numerous possible isomers, and the challenges of differentiating naphthenic acids from other naturally-occurring organic acids. Several methods of NA extracting were tested for two fractions of Brazilian oil with high acidity. The NA extracts were derivatized with N-Methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide (MTBDSTFA). The MTBDSTFA has been usually employed as a derivatizing agent to facilitate the analyses of naphthenic acids in commercial preparations. NA are transformed in their t-butyldimethylsilyl esters and after analyzed by mono dimensional Gas Chromatography (1D-GC) and also by GC´GC (comprehensive two-dimensional Gas Chromatography). In the GC × GC procedure, two columns are connected by an interface called modulator. The second dimension (second column) is usually a high speed separation and it combines, therefore, a high power of separation with a reduced time of analysis. Among its advantages, there is a significant improvement in resolution and peak capacity in addition to increased sensitivity.