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The organic acids present in petroleum, commonly called “naphthenic acids” (NA), are identified as carboxylic acids of the general formula “RCOOH”, where R represents a hydrocarbon chain that does not necessarily show cycloaliphatic structure. The presence of stable oil-in-water emulsions in the crude oils hinders the dehydration process, which is required during the production step. Some compounds, such as the organic acids (NA) present in the crude oils, are involved in the stabilization of the emulsions, because of their amphiphilic structure. The emulsion-breaking process is improved if the organic acids are determined qualitatively and quantitatively. We proposed the study of a quantitative extraction procedure of NA contained in crude oils. First of all, we performed the liquid−liquid extraction of the organic acids, using alcoholic solutions. Because this method did not allow the quantitative recovery of the acids, we developed a separation process based on an ion-exchange resin (QAE Sephadex A25). The isolated acid fraction was then derivatized as methyl esters and quantified by gas chromatography experiments, using the internal standard method allowing the determination of the NA composition. The extraction yield was checked via the total acid number (TAN) measurement, using the standard ASTM D664-95 (IP 177/96), which is the standard method commonly used in the oil industry. The extraction of NA on ion-exchange resins required the preliminary study of a model molecule mixture of carboxylic acids, to ensure the complete control of the procedure. Four crude oil samples that were provided by Total (France) (Y1, Y2, Y3, Y4) were then analyzed. The results confirmed the presence of such acids in the crude oils.

New solubility data for methane, carbon dioxide, and their binary mixtures in pure water were obtained at 344.25 K and from 10 to 100 MPa. A thermodynamic model that combines a cubic equation of state (Peng−Robinson with k ij given in the literature) with the Henry's law approach has been elaborated. It has been shown that the (P,T) functional form of Henry's constant given by the Krichevsky−Kasarnovsky equation is applicable. It involves two important parameters: partial molar volume at infinite dilution and Henry's constant at the vapor pressure of water. Neither of these two parameters is a function of pressure or composition. The Henry's constant correlations of Li and Nghiem and Harvey, and the partial molar volume correlation of Lyckman et al. have been validated using a great number of solubility data.

1. Our objective was to measure the effects of bioturbation and predation on the physical characteristics and biogeochemical processes in river sediments. 2. We investigated the impacts of tubificid worms tested separately and together with an omnivore (Gammarus pulex), which does feed on tubificids, on sediment distribution, water flux, sediment organic carbon, biofilm biomass and microbial activities, and the concentrations of dissolved oxygen, dissolved organic carbon, PO 3À 4 , NO À 3 , NO À 2 and NH þ 4 in slow filtration sand-gravel columns. We hypothesised that gammarids, which exploit the top 2-3 cm of the sediment, would modify the impact of worms at the sediment surface.3. In experiments both with and without gammarids, bioturbation by the tubificids modified both the distribution of surface particles in the sediment column and water flux. In addition, microbial aerobic (oxygen consumption) and anaerobic (denitrification and fermentative decomposition of organic matter) processes in the sediment were stimulated in the presence of tubificid worms. However, G. pulex did not affect either the density or bioturbation activity of the tubificid worms. 4. Bioturbation by the benthos can be a major process in river habitats, contributing to the retention of organic matter in sediment dynamics. The presence of at least one predator had no effect on bioturbation in sediments. In such systems, physical heterogeneity may be sufficient for tubificids to escape from generalist predators, though more specialised ones might have more effect.

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