Frédéric Plantier

Acoustic method for measuring asphaltene flocculation in crude oils

Abstract With a view to evaluate the risk of asphaltene to flocculate in crude oils, an experimental device based on an acoustic technique of phase comparison has been developed. The operational method and the results concerning the influence of the precipitant concentration on crude–solvent mixtures at 323 K and atmospheric pressure thus obtained are presented. On the basis of the measurements carried out, it is shown that flocculation caused a sufficiently important change in the output phase signal which thus can be used as an indicator of the phenomenon.

Nonlinear parameter (B/A) measurements in methanol, 1-butanol and 1-octanol for different pressures and temperatures

Experimental determinations versus pressure of the nonlinear acoustic parameter B/A have been conducted for methanol, 1-butanol and 1-octanol in the pressure range 0-50 MPa and temperature range 303.15-373.15 K. These measurements proceed from an experimental technique based on a phase comparison method allowing to measure the change in sound speed with the pressure for an isentropic process. The value of B/A is found to decrease with increasing pressure and seems to be an increasing function of temperature. A comparison with the data determined numerically by the classical thermodynamic method has also been performed.

Measurement under high pressure of the nonlinearity parameter B/A in glycerol at various temperatures

An experimental study of some assorted glycerol properties is carried out in order to determine, under high static pressure, the glycerol nonlinearity parameter B/A against temperature by a modified isentropic method. The static pressure and temperature ranges exploited in this experimental investigation, of various glycerol properties, are extended respectively from 0.1 to 100 MPa and from 10 to 100 degrees C. The static pressure step of two consecutive measurements is 10 MPa and the temperature step is 10 degrees C. The measured values show that, in glycerol, the density rho(0) and the infinitesimal ultrasonic wave velocity c(0) increase monotonically with the imposed static pressure and decrease monotonically with temperature. The present investigation shows that the nonlinearity parameter B/A is a function of the imposed static pressure and temperature. The accuracy of the measured B/A values is estimated at about +/-2%.

Measurement of the B/A nonlinearity parameter under high pressure: Application to water

An experimental apparatus was developed to measure, over a wide range of pressure, the acoustical nonlinear parameter B/A with an uncertainty of 2.2% in order to study the influence of pressure on the value of this parameter in liquids. The experimental technique rests on an improved thermodynamic method which uses a highly sensitive phase comparison technique to measure the change in speed of sound with pressure. The apparatus was then used to measure B/A in water within the pressure range from 0.1 to 50 MPa and at temperatures of between 303.15 and 373.15 K. The data obtained were compared with those in the literature which come from numerical derivation of speed of sound measurements.

Note: Temperature derivative of the refractive index of binary mixtures measured by using a new thermodiffusion cell

A thermodiffusion cell is developed for performing Soret experiments on binary mixtures at high pressure and in the presence of a porous medium. The cell is validated by performing experiments at atmospheric pressure. The experiments are performed by applying different temperature gradients to binary mixtures in order to determine their thermal contrast factor. These measurements provide a first demonstration of the good reproducibility of this kind of measurements upon calibration.

Measurements under high pressure of ultrasonic wave velocity in glycerol

Glycerol has been the subject of significant scientist interest. Indeed, glycerol is a polyalcohol and the presence of three hydroxyl groups per molecule makes glycerol a complex system to explore. The purpose of this investigation is to measure under high pressure the ultrasonic wave velocity in glycerol, from which a number of important thermodynamic properties could be derived and determined as a function of pressure and temperature. Pressure and temperature ranges exploited in this experimental investigation of various glycerol properties, are extended from 0.1 MPa to 100 MPa and from 10°C to 100°C, respectively. A high pressure measurement cell equipped with temperature and pressure monitoring and control instrumentation is used. A time of flight method is exploited to measure, under high pressure, the ultrasonic wave velocity at different temperatures. The resulting experimental data of ultrasonic wave velocity in glycerol combined with measurements at atmospheric pressure, of density, specific heat and the thermal expansion coefficient are used to derive density at elevated pressures. As isentropic compressibility is linked to ultrasonic wave velocity and density by means of the Newton-Laplace equation, this intrinsic physical property is easily deduced. These results led to the behavior of each property as a function of temperature and pressure.

Analysis of the orientational order effect on n-alkanes: Evidences on experimental response functions and description using Monte Carlo molecular simulation

Short-range correlations of the molecular orientations in liquid n-alkanes have been extensively studied from depolarized Rayleigh scattering and thermodynamic measurements. These correlations between segments induce structural anisotropy in the fluid bulk. This phenomenon, which is characteristic of linear chain molecules when the constituting segments are nor freely jointed, but interact through a given angular potential, is then present in the linear n-Cn series, increasing its magnitude with chain length, and it is therefore less relevant or even completely absent in branched alkanes. This intermolecular effect is clearly revealed in second-order excess magnitudes such as heat capacities when the linear molecule is mixed with one whose structure approaches sphericity. The mixing process of different aspect ratio chain molecules is thought to modify the original pure fluid structure, by producing a diminution of the orientational order previously existing between pure n-alkane chains. However, second-order thermodynamics quantities of pure liquids C(P), ( partial differentialv/ partial differentialT)(P), and ( partial differentialv/ partial differentialP)(P) are known to be very sensitive to the specific interactions occurring at the microscopic level. In other words, the behavior of these derived properties versus temperature and pressure can be regarded as response functions of the complexity of the microscopic interactions. Thus, the purpose of the present work is to rationalize the orientational order evolution with both temperature and molecular chain length from the analysis of pure fluid properties. To this aim, we focused on two linear alkanes, n-octane (n-C(8)) and n-hexadecane (n-C(16)), and two of their branched isomers, i.e., 2,2,4-trimethylpentane (br-C(8)) and 2,2,4,4,6,8,8-heptamethylnonane (br-C(16)). For each compound, we propose a combined study from direct experimental determination of second-order derivative properties and Monte Carlo simulations. We performed density rho, speed of sound c, and isobaric heat capacity C(P) measurements in broad ranges of pressure and temperature allowing a complete thermodynamic characterization of these compounds. Monte Carlo simulations provide a link between the molecular scale model and the experimental thermodynamic properties. Additional information about the microscopic structure of the simulated fluid model was derived, through the calculation of the radius of gyration and average end-to-end distances. Orientational order is clearly revealed by the experimental residual heat capacity trend of pure linear alkanes. The close agreement observed between this experimental macroscopic property and the calculated theoretical structural parameters support the conclusion that the orientational order between segments of linear molecules should be regarded as a conformational effect due to the flexibility of the chain.

A novel experimental setup for simultaneous adsorption and induced deformation measurements in microporous materials

A new experimental setup is presented allowing the simultaneous measurement of adsorption isotherms and adsorption-induced deformations. It is composed of a manometric technique coupled with a digital image correlation setup for full-field displacement measurements. The manometric part is validated by comparing adsorption isotherms with those obtained by a gravimetric method. The principles and methods of both adsorption isotherm and induced deformation measurements are presented in detail. As a first application of this new apparatus, the coupling between adsorption and induced deformation is characterised for a microporous media (activated carbon) saturated by pure CO2 (318.15 K, [0-60] bars) and pure CH4 (303.15 K, [0-130] bars). For this very homogeneous porous material, the induced deformation is characteristic of a pure volumetric swelling but the full-field setup may allow the characterisation of the localised pattern of deformation for heterogenous or cracked microporous media.

Thermoresponsive gold nanoshell@mesoporous silica nano-assemblies: an XPS/NMR survey

This work provides a detailed study on the physico-chemical characterization of a mechanized silver-gold alloy@mesoporous silica shell/pseudorotaxane nano-assembly using two main complementary techniques: XPS and NMR (liquid- and solid-state). The pseudorotaxane nanovalve is composed of a stalk (N-(6-aminohexyl)-aminomethyltriethoxysilane)/macrocycle (cucurbit[6]uril (CB6)) complex anchored to the silica shell leading to a silica/nanovalve hybrid organic-inorganic interface that has been fully characterized. The stalk introduction in the silica network was clearly demonstrated by XPS measurements, with the Si 2p peak shifting to lower energy after grafting, and through the analysis of the C 1s and N 1s core peaks, which indicated the presence of CB6 on the nanoparticle surface. For the first time, the complex formation on nanoparticles was proved by high speed (1)H MAS NMR experiments. However, these solid state NMR analyses have shown that the majority of the stalk does not interact with the CB6 macrocycle when formulated in powder after removing the solvent. This can be related to the large number of possible organizations and interactions between the stalk, the CB6 and the silica surface. These results highlight the importance of using a combination of adapted and complementary highly sensitive surface and volume characterization techniques to design tailor-made hybrid hierarchical structured nano-assemblies with controlled and efficient properties for potential biological purposes.

A phase comparison technique for sound velocity measurement in strongly dissipative liquids under pressure

An accurate technique for the sound velocity measurement in strongly dissipative liquids is elaborated. This technique is based upon high sensitive phase detection. Each medium, at a given temperature and pressure, is characterized by a specific phase shift due to the propagation of the ultrasonic wave within the analyzed medium. By tuning the insonation frequency of the ultrasonic signal, a succession of consecutive nulls of the output dc voltage generated by the phase detector is observed. Thus from the obtained series of frequency values, the sound velocity is computed. Numerous organic liquids, such as alcohols and alkanes, have been used to validate this experimental procedure. As the developed method is well suited for the sound velocity measurement in strongly dissipative liquids, measurements of compressional wave velocity in heavy oil are also carried out over the temperature range 10 degrees C to 50 degrees C. The experimental results agree well with those found in the literature. The accuracy of the developed method is estimated at about +/-0.3%.