Jean-Luc Daridon

Simultaneous estimation of phase behavior and second-derivative properties using the statistical associating fluid theory with variable range approach.

A modified statistical associating fluid theory (SAFT) with variable range version is presented using the family of m-n Mie potentials. The use of this intermolecular potential for modeling repulsion-dispersion interactions between the monomer segments, together with a new method for optimizing the molecular parameters of the equation of state, is found to give a very accurate description of both vapor-liquid equilibria and compressed liquid bulk properties (volumetric and derivative properties) for long-chain n-alkanes. This new equation improves other SAFT-like equations of state which fail to describe derivative properties such as the isothermal compressibility and the speed of sound in the condensed liquid phase. Emphasis is placed on pointing out that the key for modeling the latter properties is the use of a variable repulsive term in the intermolecular potential. In the case of the n-alkanes series, a clear dependence of the characteristic molecular parameters on increasing chain length is obtained, demonstrating their sound physical meaning and the consistency of the new fitting procedure proposed. This systematic method for optimizing the model parameters includes data on the saturation line as well as densities and speed of sound data in the condensed liquid phase, and the results show undoubtedly that the model performance is enhanced and its range of applicability is now widened, keeping in any case a good balance between the accuracy of the different estimated properties.

Liquid–solid equilibria in a decane+multi-paraffins system

Abstract Measurements, performed at atmospheric pressure on mixtures made up of decane plus various distributions of heavy normal paraffins from octadecane to triacontane, were carried out to provide information on wax content (amount and composition) as function of temperature. At various temperatures below the wax appearance temperature, liquid and solid phases in partially frozen mixtures were separated by isothermal filtration and analyzed by gas chromatography. Amount and composition of both phases were then deduced from mass balance after correction of the entrapped liquid in the solid residue. Furthermore, the L–S equilibrium data obtained are compared with the values predicted by means of several models.

The Limitations of the Cloud Point Measurement Techniques and the Influence of the Oil Composition on Its Detection

Abstract In the petroleum industry, cloud points are one of the main guides to evaluate the wax precipitation potential of a fluid. The planning of the exploration of a reservoir or the design of its pipelines are based on the measured cloud points for the reservoir oil. It is known that each measuring technique will provide a different cloud point temperature, yet although some of these techniques seem to be more accurate than others, no definite conclusion was established on how cloud points should be measured. On this work, several cloud point measurement techniques are discussed and compared. It will be shown that some of these techniques, such as viscosity, filter plugging, and differential scanning calorimetry (DSC) can only be used under very favorable circumstances, but it will be argued that because every technique requires some finite, often large, amount of solid to detect the presence of a new phase, the cloud point, defined as the temperature for which the first solid appears in the oil, is not accessible experimentally, and unless a very detailed compositional analysis is available, it is also impossible to predict it accurately with a thermodynamic model. The effect of the paraffin distribution in the oils on the cloud point detection will be discussed, and it will be shown how the compositional information can be used to assess the uncertainty of the measured cloud points.

Measurements and modelling of wax formation in diesel fuels

Wax formation in hydrocarbon fluids at low temperatures is one of the harassing problems faced by the petroleum industry. The prevention of wax formation, the production of diesels more resistant at low temperatures and the design of new and better additives requires a good understanding of the crystallisation behaviour of the paraffin molecules. Better experimental techniques to study the wax formation and reliable thermodynamical models, able to predict the solid‐liquid equilibrium of petroleum fluids, would help to prevent and overcome many of the problems associated with wax deposition. Here, an equilibrium cell previously used with synthetic mixtures is applied to study the influence of the desulphuration on the low temperature behaviour of a Petrogal diesel. The compositions of the solid and liquid phases in equilibrium and the fraction of solids in partly crystallised solutions were measured between 25 and 2208C. The latter was also measured by DSC. The experimental data was modelled using the Predictive UNIQUAC model. It is shown that the model provides an excellent description of the measured phase behaviour for these diesels. The desulphuration of the diesel seems to make it slightly heavier and to increase its wax appearance temperature (WAT). q 2000 Elsevier Science Ltd. All rights reserved.

Prediction of solid–fluid phase diagrams of light gases–heavy paraffin systems up to 200 MPa using an equation of state–GE model

Abstract This paper presents a procedure for the simultaneous prediction of fluid–fluid and solid–fluid equilibria of light gases–heavy hydrocarbons systems under pressure. The fluid phases behaviour is described by the modified LCVM, an equation of state–G E model and the solid phase non-ideality is represented by the Wilson equation using the predictive local composition concept. This procedure was tested for several binary and ternary systems as well as multi-component systems leading to a good representation of both fluid–fluid and solid–fluid equilibria with a typical average absolute deviation of 1.5 K for the solid–fluid phase boundary of binary and ternary mixtures and of 0.5 K for multi-component systems. The AAD% in the fluid–fluid phase boundary of multi-component systems is of 3.2%.

A simple correlation to evaluate binary interaction parameters of the Peng-Robinson equation of state: binary light hydrocarbon systems

Abstract Gao, G., Daridon, J.-L., Saint-Guirons, H., Xans, P. and Montel, F. 1992. A simple correlation to evaluate binary interaction parameters of the Peng-Robinson equation of state: binary light hydrocarbon systems. Fluid Phase Equilibria , 74:85-93 A simple correlation to evaluate binary interaction parameters k ij of the Peng-Robinson equation of state for light hydrocarbons mixtures is proposed, as a function only of critical temperature and compressibility factor. The method yields results with an accuracy bordering on that obtained with methods requiring specific adjustments for each binary mixture coefficient k ij .

Wax content measurements in partially frozen paraffinic systems

Abstract Waxy solid content and wax composition were measured as a function of temperature below the onset crystallization temperatures in several synthetic systems made up of a solvent (decane) and a paraffinic heavy fraction. The heavy fraction of the first system studied was made up of a regular series of heavy alkanes ranging from C 18 to C 36 . Whereas in other systems, some intermediate paraffins were removed from the series in order to have various «bimodal» distributions. Experimental data were used to test the capacity of a local composition model to predict solid phase behaviors of these bimodal paraffinic distributions.

Pressure and Temperature Dependence of the Speed of Sound and Related Properties in Normal Octadecane and Nonadecane

The speed of sound was mesured in liquid n-octadecane and n-nonadecane using a pulse technique operating at 3 MHz. The measurements were carried out at pressures up to 150 MPa in the temperature range from 313 to 383 K. The experimental results combined with atmospheric density measurements were then used to evaluate volumetric properties such as the density and the isentropic and isothermal compressibilities up to 150 MPa in the same range of temperature. The density data were fitted with a six-parameter modified Tait equation within the experimental uncertainty.

Phase boundary measurement on a methane + decane + multi-paraffins system

Abstract Phase boundaries between homogeneous liquid phase and two-phase regions, both liquid-vapour and liquid-solid, and the phase boundary between the two-phase liquid - vapour region and the three-phase liquid - vapour - solid region were experimentally determined under pressure on the system methane + decane + heavy fraction using a full visibility sapphire cell. Measurements were performed on different mixtures made up of 90% of the binary mixture methane + decane (with a molar fraction of methane of about 50 %) and 10 % of a heavy fraction composed of various distributions of heavy normal paraffins centered around C 22 . The liquid-solid phase transition was investigated up to 45 MPa and fluid phase boundary was studied in the temperature domain from 293 K to 423 K.

A cubic equation of state model for phase equilibrium calculation of alkane + carbon dioxide + water using a group contribution kij

Abstract Daridon, J.L., Lagourette, B., Saint-Guirons, H. and Xans, P., 1993. A cubic equation of state model for phase equilibrium calculation of alkane + carbon dioxide + water using a group contribution k ij . Fluid Phase Equilibria , 91: 31-54. This paper presents a general procedure for the calculation of phase equilibria of paraffin, CO 2 , water and mixtures thereof based on a modified Peng and Robinson equation of state linked with a group contribution k ij . This procedure gives a good representation of the transitions of pure substances, including water and heavy alkanes (C 10 to C 20 ) as well as carbon dioxide-alkane mixtures. It also provides quite satisfactory results for calculation of mutual solubilities of water and alkanes (or carbon dioxide) in conditions of pressure between 0.1 and 50 MPa and temperature between 293 and 523 K.