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The use of low-dosage inhibitors is an alternative to thermodynamic inhibitors to prevent gas hydrates from plugging oil production pipelines. In this work, quaternary ammonium salts (QAs) with different structures were tested as hydrate plug inhibitors on model systems containing 1/1/4/X proportions (by weight) of water/THF/oil/QA systems. The experimental results suggest that the presence of both small (CH3) groups in their polar moiety and two long alkyl chains in their hydrophobic part has a beneficial effect on their ability to adsorb onto the hydrate surface and form a steric barrier around the hydrate crystals, which limits their agglomeration to larger masses. Above a minimum concentration, the concentration of the double-tailed QAs has no appreciable effect on their ability to prevent hydrates from plugging. Their effectiveness as hydrate plug inhibitors is not dependent on the chain length of the oil.

Dependent upon the conditions of pH and water content, an acidic crude oil may form different type of emulsions with different stability. These oils generally contain large amounts of naphthenic acids, RCOOH, which result from crude oil biodegradation. They also contain heavier compounds such as asphaltenes and resins. All of these amphiphiles may contribute to the formation and stability of emulsions. In this work, an acidic crude oil (total acid number ) 1.25) was distilled in three fractions to separate naphthenic acids from resins and asphaltenes. The influence of pH and water content on the type and stability of emulsions prepared with the crude oil and its fractions was investigated. The role of the light, intermediate, and heavy amphiphiles present in the crude oil on its emulsifying properties has been discussed by comparing the emulsion type and stability diagrams obtained for the different oil phases. It has been found that the type of emulsion is governed by the acidic amphiphiles contained in the intermediate fraction. The stability of oil-in-water emulsions is ensured by electrostatic repulsion between the naphthenates, RCOO -, present at the interface, whereas that of water-in-oil emulsions is due to the amphiphiles contained in the heavy fraction, i.e., asphaltenes and resins.

c Search of efficient additives for CO 2 capture processes using clathrates hydrates. c Experimental results based on phase equilibria, kinetics and visual observations. c Action mechanisms linked to these additives are analysed and discussed. c Mixed CO 2 þ THF hydrate promote the formation of the single CO 2 hydrate. c Potentialities of this combination of additives (SDS þTHF) are demonstrated.

The emulsion stabilizing properties of a low-total-acid-number (TAN) crude oil, which had initially been attributed to asphaltenes and calcite precipitation, were re-analyzed with regard to the role of organic acids. Despite high asphaltenes content, this crude oil exhibits features classically observed with acidic oils, such as the increase in emulsion stability upon pressure decrease/pH increase or the poor efficiency of demulsifiers. The potential for a significant role of organic acids was confirmed by the high interfacial activity of indigenous acids, as extracted from the crude oil by means of an ion-exchange resin. This was further addressed analyzing the molecular chemistry of the interfacial layer and its rheology. The interfacial material was found to be composed of a mixture of asphaltenes and organic acids. These acids exhibit a wide range of structures (mono- versus dicarboxylic, fatty versus naphthenic and benzoic) and molecular weights (from 200 to 700 g/mol), contrary to the medium molecular weight fatty monocarboxylic acids that are generally believed to cause “soap emulsions”. The interfacial rheology is indicative of a 2D gel, with an assumed glass transition temperature of approximately 40 °C. In conclusion, this study shows that a co-precipitation of asphaltenes and organic acids can promote the build up of a very cohesive interface. The disruption of this interface not only requires the drainage of individual molecules but also a collective yield of the gel. This paper is part one of two: it confronts physical and chemical data, the latter being further detailed in an associated paper.

Figure 1. Schematic diagram of the experimental apparatus: (1) hydrate forming reactor; (2) magnetic agitator; (3) thermostatic baths; (4) high pressure gas chromatograph; (5) gas storage vessel; (6) lighting system; (7) video camera; (8) data acquisition system.

h i g h l i g h t s Combination of surfactants and organic additives enhance hydrate-based processes. Action mechanism based on the successive formations of (sII) and (sI) hydrates. THF + SDS is the best association of additives among all the combinations tested. Enclathration rate and selectivity of the separation remain too low for scale-up.