Roland Solimando

Thermodynamics of crystallization of sodium sulfate decahydrate in H2O–NaCl–Na2SO4: application to Na2SO4·10H2O-based latent heat storage materials

Abstract In this paper, we present a methodology for the prediction of the crystallization enthalpy of mirabilite (Na 2 SO 4 ·10H 2 O) from supersaturated H 2 O–NaCl–Na 2 SO 4 solutions. Required thermodynamic properties of H 2 O–NaCl–Na 2 SO 4 such as dissolution enthalpies, phase equilibria and heat of hydration of Na 2 SO 4 are represented or determined using Pitzer’s ion-interaction model. Measurements of crystallization enthalpies at various temperatures and concentrations were made in a SETARAM C80D calorimeter by mixing H 2 O–Na 2 SO 4 and H 2 O–NaCl–Na 2 SO 4 solutions supersaturated relatively to mirabilite with a seed crystal of Na 2 SO 4 ·10H 2 O once the thermal equilibrium was reached. Good agreement was obtained between experimental and predicted values of crystallization enthalpies. Furthermore, we have studied the influence of NaCl used as an additive regarding the heat storage capacity of supersaturated H 2 O–Na 2 SO 4 solutions.

Thermodynamics of mixtures formed by polycyclic aromatic hydrocarbons with long chain alkanes

Thermodynamic properties of polycyclic aromatic hydrocarbons (PAH) and long chain alkanes determine the phase behaviour of heavy petroleum fractions. Studying thermodynamic excess functions of these systems is difficult and consequently experimental data available in the literature are scarce. Enthalpies of mixing of 13 PAH-alkane systems at temperature above the melting point of both components are reported in this paper. Morever, 13 solid-liquid equilibria of the same family of systems are presented. Experimental results were correlated using S.S.F. model (Rogalski and Malanowski, 1977). Several regularities observed in the liquid-solid phase diagrams of the systems studied are discussed

Use of Pitzer's model to calculate thermodynamic properties of aqueous electrolyte solutions of Na2SO4 + NaCl between 273.15 and 373.15 K

Abstract Pitzers model has been used to calculate various thermodynamic properties of NaCl–Na2SO4–H2O system. A methodology taking into account enthalpy and solubility data has been proposed. This leads to the proposal of a unique set of parameters allowing simultaneous representation of dissolution enthalpies, activity coefficients and solubility data in binary and ternary systems.

Dissolution enthalpy of NaCl in water at 25°C, 45°C and 60°C. Determination of the Pitzer's parameters of the {H2ONaCl} system and the molar dissolution enthalpy at infinite dilution of NaCl in water between 25°C and 100°C

The dissolution enthalpy of sodium chloride in water was measured until saturation at 24.4°C, 44.3°C and 59.2°C using a C80D differential calorimeter (SETARAM). The experimental data were fitted using Pitzers ion interaction model and the value of the dissolution enthalpy per mole of salt at infinite dilution was found at each temperature by treating ΔsolH∞ as adjustable parameter. Using these calorimetric measurements, the analytical expression of the variation of Pitzers parameters were established with respect to temperature. The validation of this expression is made by the measurement of vapour equilibrium of binary solution {H2ONaCl} closed to saturation. Excellent agreement between experimental and calculated values of water activity has been found using our Pitzers model parameters.

Modifying the Peng Robinson equation for a homogeneous representation of pure fluid PVT properties

Abstract Peng-Robinson volume corrected equation was modified to yield homogeneous representation of PVT properties of pure fluids. A correcting term which significantly contributes only in the vicinity of the critical point was added. The resulting equation is not cubic any longer but preserves general characteristics of cubic EOS far from the critical point and yields, at the same time, very satisfactory representation of near critical fluid properties.

Heat capacity estimations using equations of state

Abstract Five equations of state accurately expressing the vapor pressures of hydrocarbons were used to estimate Δ C p , the difference between liquid and ideal gas heat capacities. It was observed that two equations of state giving equally accurate vapor pressures can yield very different Δ C p estimates. The consequences are investigated and discussed.

Modelling of the phase behaviour of mixtures in the critical region using the augmented Peng-Robinson equation of state

Abstract The Peng-Robinson equation extended to the PVT property representation in the critical point neighbourhood (PRA equation) was used to calculate binary pressure-composition and pressure-density diagrams. The modified excess function at constant packing fraction model was used to take into consideration binary interactions. In the case of binary systems exhibiting the mixture critical point, calculation results were satisfactory and substantially improved with respect to those obtained using the volume corrected Peng-Robinson (PRC) equation.

Thermodynamic study of magnesium sulfate crystallization: application of Pitzer model and quinary diagrams

AbstractExtracting valuable salts from reverse osmosis reject brine may be a solution to reduce environmental risk of this effluent if discarded. Isothermal evaporation (25°C) allows recovering many salts like gypsum, halite, and magnesium salts (epsomite, hexahydrite). In this paper, magnesium sulfate crystallization was studied, for this purpose two different quinary diagrams were used to draw the crystallization path. Furthermore, the application of Pitzer model and the use of Phreeqc program were required, respectively, to calculate electrolytes solubility product and to simulate the evaporation steps. Experimentally, X-ray diffraction was adopted to identify the nature of recovered solid phases. The different results of this study are almost similar and confirm the crystallization of epsomite and hexahydrite at the end of evaporation process.