Bernard Siffert

Chemical nature and water/oil emulsifying properties of asphaltenes

Abstract Asphaltenes which differ in their abilities to form water/oil emulsions were analysed by acidimetry, infrared and nuclear magnetic resonance spectroscopies. Asphaltenes which easily form such emulsions are loosely packed molecules and exhibit a marked acid/base imbalance.

Surface characteristics of aluminas in relation with polymer adsorption

Abstract Inverse gas chromatography (IGC) was applied to the characterization of the surface properties (dispersive component (γSD) of surface energy, and acid/base interaction parameter (ISP) of a series of aluminas differing not only in specific surface area, but also in content of impurities (Si, Ca, Na, Mg). It is shown that both γSD and ISP are very sensitive in the presence of impurities. The adsorption of poly(vinyl chloride) and of poly(methyl methacrylate) from a butanone solution on the different samples was investigated. The amount of polymer which adsorbs on the powder depends on the acid/base characteristics of both polymers and Al2O3 samples.

Structure and water—oil emulsifying properties of asphaltenes

Abstract Alphaltenes were selected on the basis of their capacity to form water—oil emulsions. They were characterized by electron microscopy, surface group analysis, g.p.c. and low-angle X-ray scattering. It appears that the high stability of water-oil emulsions is related to the ‘structuring’ capacity of asphaltenes at the water-oil interface. Some asphaltenes are able to form regularly stacked layers, resembling the behaviour of surfactant liquid crystals.

Sodium carboxylate adsorption onto TiO2: Shortest chain length allowing hemimicelle formation and shear plane position in the electric double layer

Abstract The adsorption of short chain sodium alkylcarboxylates onto TiO2 was investigated. Three adsorption processes, dependent on the nature of existing charges and the dissociation state of carboxylates were demonstrated: electrostatic attraction, spreading at the surface, and, in certain circumstances, formation of hemimicelles. The last mentioned species can form if the alkyl chains contain at least four carbon atoms. The electrostatic attraction occurs on positively charged TiO2 and, consequently, extensive adsorption takes place at pH values below the IEP. Although the adsorption of the various carboxylate ions remains the same at concentrations less than 2 × 10−2 M, electrokinetic investigations showed that the zeta-potential decreases when the adsorbate contains more than three carbon atoms. This result can be interpreted either in terms of a shift of the shear plane or the appearance of hydrodynamic brake forces. It was inferred therefrom that the shear plane is situated at a distance Δ of 4 A from Sterns plane (the length of the CH3CH2CO2− anion, i.e., one or two water molecule thicknesses).

STUDY OF THE STABILITY OF BITUMEN EMULSIONS BY APPLICATION OF DLVO THEORY

Abstract The stability of bitumen emulsions was compared with the chemical and interfacial properties of the bitumens. The chemical properties of the bitumens were studied by determining their asphaltenes and resins contents and the interfacial properties by measuring the zeta potential of bitumen dispersions in acid water. The DLVO theory was applied to evaluate the stability of the emulsions. This theory was improved by taking account of additional interaction energies: hydrophilic and hydrophobic interactions (extended DLVO theory). Experimental results showed that it is possible to predict the stability of the emulsions from the chemical and interfacial properties of the bitumens. It seems that the resins/asphaltenes ratio affects the dispersion and emulsion stability by controlling the distribution of polar components inside the bitumen during the dispersion or emulsion manufacturing.

Relationship between electrical charge and flocculation of heavy oil distillation residues in organic medium

Abstract A relationship between the electric charge and the stability of heavy oil distillation residues dispersed in organic medium has been established. The origin of the electric charge is a consequence of an electron transfer between the organic solid particles and the liquid organic phase. By hydroviscoreduction, both the electric charge and the resistance against flocculation are increased. An interaction parameter ISL is defined predicting the behavior of practical systems.

INFLUENCE OF WATER ON THE RETENTION OF ORGANIC PROBES ON CLAYS STUDIED BY IGC

Oil recovery is strongly related to the wettability of reservoir rocks that are formed of quartz grains attached by mineral hydroxides and clay minerals. Illites and kaolinites are the most active due to their high specific surface areas and electrical charge densities. Therefore, these minerals’ relative affinities for oil or water when in contact with a water-oil mix are of great importance. In order to model such a complex system, we used a mix of organic model molecules of the oil constituents and water vapor. Their interactions were estimated by inverse gas chromatography (IGC). IGC experiments were performed using a carrier gas with controlled humidity. By means of IGC at infinite dilution conditions, the dispersive component of the surface energy, γsd, was determined. A strong decrease of γsd, due to water molecules shielding the highest-energy sites, was observed. The energetic surface heterogeneity of the clays was examined using IGC at finite concentration conditions, allowing the determination of organic probe adsorption isotherms in the presence of water. From these isotherms, adsorption energy distribution functions were computed for propanol-2 and pyridine probes. Water mainly modifies the illite distribution functions, whereas practically no change was observed in the case of kaolinite. This observation is related to the higher hydrophilicity of illite as compared with kaolinite, and explains the different behaviors of the 2 clay families in oil reservoirs.

Relationship between the chemical properties of bitumens and their colloidal properties in water

The chemical properties of different bitumens were characterized by determining their asphaltene and resin contents and acid-base properties by carrying out titrations in organic media. Furthermore, the colloidal properties of the bitumens in water, i.e. their electrical interfacial properties, were evaluated by measuring the zeta potentials of bitumen dispersions in water. Comparison between the chemical and colloidal properties of the bitumens shows that it could be possible to predict the dispersion stability from the chemical properties of the bitumens. The resins/asphaltenes ratio can affect the dispersion stability by controlling the arrangement of the bitumen components inside the droplet and also at the interface during dispersion manufacture.

Effect of mineral impurities on the charge and surface potential of coal: Application to obtaining concentrated suspensions of coal in water

Abstract The surface charge of pulverized coal particles in water at different pH values was studied and the surface potential was shown to reach —50 mV at 20°C. The surface charge essentially originates from the presence of mineral impurities. The effect of these mineral impurities on the surface potential of the coals was then studied: the point of zero charge was a direct function of the SiO2/ Al2O3 molar ratio of the mineral impurities contained in the coal (linear dependency). These mineral impurities have a majority effect in creating an electric double-layer shell around the coal particles. Having found this, we were able to prepare stable, fluid concentrated suspensions (up to 72% coal by weight) in water in the presence of sodium tripolyphosphate and sodium lignosulfonate, which are also stabilizers and thinners of concentrated suspensions of clay (drilling muds, for example).

Adsorption at the solid—solution interface and micelle formation in water of the poly(oxyethylene—styrene—oxyethylene) triblock copolymer

Abstract ABA-type copolymers composed of polystyrene (PS) as the B block and polyoxyethylene (POE) as the A block, having weight fractions (nps) of PS and Mn values in the ranges 16–35% and 12000–27000 respectively, were synthesized by sequential anionic polymerization. Micelle formation in water by triblock copolymers in the concentration range 10−5–1 g dm−3 was investigated by fluorescence probing (FP) and small-angle X-ray scattering (SAXS) methods. The data obtained by the FP method indicate that the CMC is extremely small and not observable over the concentration range studied. The micelle size determined by SAXS was found to increase with the total copolymer chain length. The results are in good agreement with the Star model, and a power-law dependence is found between the radius of gyration R of the micelles and the Mn values of the copolymers investigated. Adsorption measurements from water onto titanium dioxide particles were made with copolymer concentrations ranging from 10−1 to 1 g dm−3. The maximum amount adsorbed and the surface density were found to decrease with increasing nps and molecular weight of the PS block respectively.