Enthalpies Of Mixtures Research Articles

Excess molar enthalpies for mixtures of supercritical CO 2 and linalool

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and linalool were measured at conditions of temperature and pressure typical of supercritical extraction processes: 313.15 and 323.15 K and 7.64, 10.00 and 12.00 MPa. The measurements were carried out using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy are large. Mixtures formed by low-density carbon dioxide and linalool show very exothermic mixing and excess molar enthalpies exhibit a minimum in the CO 2-rich region. The lowest H m E values (≈−4000 J mol −1) are observed for mixtures at 313.15 K and 7.64 MPa. Mixtures formed by high-density carbon dioxide and linalool show considerably endothermic mixing (≈400–600 J mol −1) in the linalool-rich region and moderately exothermic mixing for the other compositions. On the other hand, H m E at 7.64 MPa and 313.15 and 323.15 K varies linearly with CO 2 mole fraction in the two-phase region where a gaseous mixture and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. Results are analyzed in terms of phase equilibria, pure carbon dioxide density and CO 2–terpene molecular interactions. Excess molar enthalpies are simultaneously correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state and the classical mixing rule. The significance of these large variations of H m E with temperature and pressure in the design of supercritical fluid deterpenation processes is discussed.

Void fraction in horizontal bulk flow boiling at high flow qualities

In this work, a new thermodynamic prediction of the vapor void fraction in bulk flow boiling, which is the core process of many energy conversion systems, is analyzed. The current heat balance is based on the flow quality, which is closely related to the measured void fraction, although some correlation for the vapor–liquid velocity ratio is needed. So here, it is suggested to work with the “static“ or thermodynamic quality, which is directly connected to the void fraction through the densities of the phases. Thus, the relation between heat and the mixture enthalpy (here based on the thermodynamic quality instead of the flow one) should be analyzed in depth. The careful void fraction data taken by Thom during the “Cambridge project” for horizontal saturated flow boiling with high flow qualities (⩽0.8) have been used for this analysis. As main results, first, we have found that the applied heat and the increment of the proposed thermodynamic enthalpy mixture throughout the heated duct do not agree, and for closure, a parameter is needed. Second, it has been checked that this parameter is practically equal to the classic velocity ratio or “slip” ratio, suggesting that it should be included in a true thermodynamic heat balance. Furthermore, it has been clearly possible to improve the “Cambridge project” correlations for the “slip” ratio, here based on inlet pressure and water velocity, and heat flux. The calculated void fractions compare quite well with the measured ones. Finally, the equivalence of the suggested new heat balance with the current one through the “slip” ratio is addressed. Highlighted is the same new energetic relation for saturated flow boiling that has been recently confirmed by the authors for Knights data, also taken during the “Cambridge project”, which include not only horizontal but also vertical upwards flows with moderate outlet flow quality (⩽0.2).

A new heat balance for flow boiling

AbstractRecently, one of the authors suggested calculating void fraction, an essential element in thermal‐hydraulics, working with the “thermodynamic” quality instead of the usual “flow” quality. However, the standard heat balance is currently stated as a function of the “flow” quality. Therefore, we should search a new energy balance between the mixture enthalpy, based on “thermodynamic” quality, and the absorbed heat. This work presents the results of such analysis based on accurate measurements of the axial profile of the cross‐sectional average void fraction in the region of boiling with subcooling for water at medium and high pressures taken by Moscow Power Institute (MPI) and Argonne National Laboratory (ANL). As main results, we find that, under uniform heat flux, the mixture enthalpy suffers an abrupt reduction of its slope upon passing saturation point, and a new slip ratio could balance heat with such mixture enthalpy. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Prediction of saturated liquid enthalpy of refrigerant mixtures

New corresponding temperature and corresponding enthalpy of refrigerant mixtures were defined. The relationship between saturated liquid corresponding enthalpy and corresponding temperature of refrigerant mixtures accorded with that of pure components. The characteristic parameters of saturated liquid enthalpy difference of refrigerant mixtures were calculated by three methods according to the different application conditions. The generalized equation of saturated liquid enthalpy of refrigerant mixtures was presented. The calculated values were compared with the values in literature for five ternary and binary refrigerant mixtures, namely R404A, R407A, R407B, R32/R134a, and R410A. The overall average absolute deviation was less than 1.0%.

Excess molar enthalpies for binary mixtures related to supercritical antisolvent precipitation: Carbon dioxide + N-methyl-2-pyrrolidone

An isothermal high-pressure flow calorimeter has been used to measure excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and N-methyl-2-pyrrolidone (NMP) under conditions of temperature and pressure typically used in supercritical CO 2 antisolvent precipitation (SAS): 313.15 and 338.15 K and 9.48, 15.00 and 20.00 MPa. Mixtures showed exothermic mixing; excess molar enthalpies exhibited a minimum in the CO 2-rich region. The effects of pressure and temperature on the excess molar enthalpy of CO 2 + NMP are large. The lowest H m E values (≈−4500 J mol −1) were observed for mixtures at 338.15 K and 9.48 MPa. On the other hand, H m E at this condition of temperature and pressure varies linearly with CO 2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition are in equilibrium. These data were analyzed in terms of phase equilibria data and critical locus for CO 2 + NMP and the related SAS experiments. Very exothermic excess molar enthalpies were obtained for conditions of temperature and pressure with marked coalescence phenomena for micro and submicro particles of tetracycline, amoxicillin and ampicillin produced by SAS. Excess molar enthalpies here reported and those previously measured at 298.15 K and 7.50, 10.60 and 12.60 MPa were correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state and the classical mixing rule with two binary interaction parameters.

(Vapour+liquid) equilibria and excess molar enthalpies for binary mixtures containing N,N-dialkylamides and 1-chloroalkanes

Abstract Isothermal (vapour + liquid) equilibria (VLE) and excess molar enthalpies H m E have been measured for liquid (N,N-dimethylformamide or N,N-dimethylacetamide + 1-chlorobutane, or + 1-chlorohexane, or + 1-chlorooctane mixtures). The VLE data have been reduced using the Redlich–Kister equation taking into consideration the vapour phase imperfection in terms of 2nd molar virial coefficients. The experimental results show that both H m E and G m E are positive and increase with increasing chain length of the 1-chloroalkane.

Partial molar enthalpy properties and correlation of excess molar enthalpy data of acetonitrile + diethylamine or S-butylamine mixtures at various temperatures and atmospheric pressure

Experimental data of excess molar enthalpy ( H m E ) of binary mixtures of acetonitrile + diethylamine or S-butylamine mixtures as a function of composition at 288.15, 293.15, 298.15 and 303.15 K at atmospheric pressure have been used to calculate excess partial molar enthalpy and partial molar enthalpy of each component as a function of composition as well as partial molar enthalpy properties at infinite dilution. The Flory and Prigogine–Flory–Patterson (PFP) theories were applied to correlate the H m E data. The results of the calculations as well as the influence of temperature and isomers chain on the partial molar enthalpy properties are discussed.

Excess molar enthalpies for mixtures of supercritical carbon dioxide and 1,8-cineole

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and 1,8-cineole were measured at 308.15, 313.15 and 323.15 K and 7.64 MPa and at 308.15 and 323.15 K and 10.00 MPa using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy of [CO 2 ( x) + 1,8-cineole (1 − x)] are large. Mixtures at 308.15 K and 10.00 MPa show slightly endothermic mixing in the 1,8-cineole-rich region and moderately exothermic mixing for x > 0.2. Excess molar enthalpies become very exothermic at the other conditions of temperature and pressure studied. The lowest H m E values (≈−4900 J mol −1) are observed for CO 2-rich mixtures at 313.15 K and 7.64 MPa. These data are examined together with phase equilibria and critical parameters previously reported for [CO 2 + 1,8-cineole]. The large negative values of H m E are related to the carbon dioxide change of state from that of a low-density fluid to that of a liquid-mixture component in CO 2-rich mixtures.

Excess molar enthalpies of binary mixtures for (tributyl phosphate+methanol/ethanol) at 298.15 K

Abstract Excess molar enthalpies of binary mixtures for tributyl phosphate (TBP)+methanol/ethanol were measured with a TAM air Isothermal calorimeter at 298.15 K and ambient. The results for xTBP+(1–x)CH3OH are negative in the whole range of composition, while the values for xTBP+(1–x)C2H5OH change from positive values at low x to small negative values at high x. The experimental results have been correlated with the Redlich–Kister polynomial. IR spectra of the mixtures were measured to investigate the effect of hydrogen bonding in the mixture.

Excess enthalpies of binary mixtures of some propylamines + some propanols at 298.15 K

The molar excess enthalpies of 1,2- and 1,3-propanediamine + 1- or 2-propanol and 1,2- and 1,3-propanediol + 1- or 2-propaneamine have been determined at 298.15 K using a twin-microcalorimeter for a series of runs over the whole range of mole fractions. All excess enthalpies were large exothermic, in particular, the systems of amines + propanediols were more than −5 kJ mol −1 at the minimum. Primary or secondary alcohols and amines showed systematically different enthalpic behaviors. Equilibrium constant K1 expressed in terms of mole fractions and standard enthalpy of the formation of a 1:1 complex have been evaluated by ideal mixtures of momomeric molecules and their associated complexes.

Molar excess enthalpies of binary mixtures of [tributyl phosphate + {CH 3(CH 2) nOH ( n = 0 to 3)}] at 298.15 K

The excess molar enthalpies ( H m E ) of binary mixtures between tributyl phosphate (TBP) and aliphatic alcohols {CH 3(CH 2) n OH, ( n = 0 to 3)} were measured with a TAM air isothermal calorimeter at 298.15 K and atmospheric pressure. The results of H m E for { xTBP + (1 − x)CH 3OH} are negative but positive for { xTBP + (1 − x)C 3H 7OH} and { xTBP + (1 − x)C 4H 9OH} in the whole range of composition, while the values of H m E for { xTBP + (1 − x)C 2H 5OH} change from positive values at low x to small negative values at high x and the curve become S shaped. The experimental results have been correlated with the Redlich–Kister polynomial equation. The excess partial molar enthalpies at infinite dilution were determined for each mixture. IR spectra of the mixtures were measured to investigate the effect of hydrogen bonding in the mixture.

Excess molar enthalpies for mixtures of supercritical carbon dioxide and limonene

Excess molar enthalpies (HmE) for mixtures of supercritical CO2 and limonene were measured at 308.15, 313.15 and 323.15K and 7.64 and 10.00MPa using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy of [CO2(x)+limonene(1−x)] are large. Mixtures at 308.15K and 10.00MPa show slightly endothermic mixing in the limonene-rich region and moderately exothermic mixing for x>0.5. Mixtures at the other conditions of temperature and pressure studied show exothermic mixing, excess molar enthalpies exhibit a minimum in the CO2-rich region. The lowest HmE values (≈−4500Jmol−1) are observed for mixtures at 313.15K and 7.64MPa. On the other hand, HmE at 7.64MPa and 308.15, 313.15 and 323.15K varies linearly with CO2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. These data are examined together with phase equilibria and critical parameters previously reported for CO2+limonene. Excess molar enthalpies are simultaneously correlated using the Peng–Robinson equation of state and the classical mixing rule with one binary interaction parameter.

Excess enthalpies of binary mixtures of 2-ethoxyethanol with four hydrocarbons at 298.15, 308.15, and 318.15 K : An experimental and theoretical study

New experimental data are reported for the thermodynamic investigation of the intermolecular and intra-molecular hydrogen bonding in 2-ethoxyethanol + hydrocarbons. The excess enthalpies of the mixtures of 2-ethoxyethanol + n-hexane, or cyclohexane, or benzene, or n-octane at three temperatures (298.15, 308.15, and 318.15 K) were measured. The data are correlated with the statistical thermodynamic model non-random hydrogen bonding (NRHB) which accounts for both types of hydrogen bonds and was recently developed by the authors. A single set of hydrogen bonding parameters is used for all the alkoxyethanol systems and for the recently calculated thermodynamic properties. The results showed a satisfactory agreement between experimental and calculated data and the contributions of all different types of molecular interactions were calculated. The intra-molecular hydrogen bonding contribution to the heats of mixing is exothermic and significant. The calorimetric measurements are combined with dielectric ones and the derived Kirkwood factor is used to interpret the physicochemical behaviour of our systems.

Phenol oxidation in supercritical water in a well-stirred continuous reactor

A well-stirred reactor for phenol and acetic acid oxidation in supercritical water is considered. A mathematical model of an adiabatic reactor is formulated. A numerical algorithm for solving the model equations using the homotopy method is developed. The model takes into account specific features of processes under supercritical conditions, namely, the changes in the thermodynamic properties (enthalpy, heat capacity, and critical parameters) of mixtures with a change in pressure and temperature. The thermodynamic properties are calculated by methods of nonideal thermodynamics. It is shown that there is a multiplicity of steady-state solutions at various reactor performances. The results of numerical analysis of the effect of the inlet flow temperature, the amount of methanol (fuel) fed, and the total pressure on the reactor performance are presented.

Excess molar volumes and excess molar enthalpies of binary and ternary mixtures of 1-butanol, a tertiary amine (tri- n-butylamine or tri- n-octylamine) and n-hexane: Experimental results and ERAS-model calculations

Experimental data at T = 298.15 K and ambient pressure of excess molar volumes V m E and excess molar enthalpies H m E are reported for two ternary and the corresponding binary mixtures of {1-butanol, tri- n-butylamine (TBA), or tri- n-octylamine (TOA), and n-hexane}. A vibrating-tube densitometer was used to determine V m E . H m E was measured using a quasi-isothermal flow calorimeter. The experimental results are used to test the applicability of the ERAS model for describing both thermodynamic excess properties of ternary mixtures containing an alkanol, a tertiary amine and an n-alkane. Qualitative agreement of calculated values with experimental results was achieved using only system-specific parameters determined from binary mixtures. The results are explained in terms of the self-association between alkanol molecules, cross-association between the alkanol and the tertiary amines and structural effects.

Monte carlo investigations of intermolecular interactions in water–amide mixtures

Monte Carlo simulations of water–amides (amide=formamide—FOR, methylformamide—NMF and dimethylformamide—DMF) solutions have been carried out in the NpT ensemble at 308 K and 1 atm. The structure and excess enthalpy of the mixtures as a function of the composition have been investigated. The TIP4P model was used for simulating water and six-site models previously optimized in this laboratory were used for simulating the liquid amides. The intermolecular interaction energy was calculated using the classical 6–12 Lennard–Jones potential plus a Coulomb term. The interaction energy between solute and solvent has been partitioned what leads to a better understanding of the behavior of the enthalpy of mixture obtained for the three solutions experimentally. Radial distribution functions for the water–amides correlations permit to explore the intermolecular interactions between the molecules. The results show that three, two and one hydrogen bonds between the water and the amide molecules are formed in the FOR, NMF and DMF–water solutions, respectively. These H-bonds are, respectively, stronger for DMF–water, NMF–water and FOR–water. In the NMF–water solution, the interaction between the methyl group of the NMF and the oxygen of the water plays a role in the stabilization of the aqueous solution quite similar to that of an H-bond in the FOR–water solution.

Steam Generator Two-Phase-Flow Numerical Simulation with Liquid and Gas Momentum Equations

This work takes place in steam generator flow studies, and we consider here steady-state three-dimensional two-phase (liquid and gas) flows. The main goal is to improve the modeling of kinetic imbalance between the phases. We present a method that solves the mixture (liquid-gas) mass and enthalpy equations, and two momentum equations: one for the mixture and one for the gas. This choice is equivalent to solving the gas and the liquid momentum equations, but it is better suited to the Chorin projection method used for the pressure calculation. Solving two momentum equations instead of solving only the one for the mixture introduces the use of correlations for the gas-liquid friction but avoids the use of a correlation for the drift velocity and opens the way to a finer analysis of the relative dynamic behavior of each phase.

Thermodynamics of Void Fraction in Saturated Flow Boiling

AbstractRecently, Collado (Proc, IMECE 2001, Symposium on Fluid Physics and Heat Transfer for Macro- and Micro-Scale Gas-Liquid and Phase Change Flows) suggested calculating void fraction, an essential element in thermal-hydraulics, working with the “thermodynamic” quality instead of the usual “flow” quality. The “thermodynamic” quality is a state variable, which has a direct relation with the actual vapor volumetric fraction, or void fraction, through phase densities. This approach provides a procedure for predicting void fraction, if values of “thermodynamic” quality are available. However, the standard heat balance is usually stated as a function of the “flow” quality. Therefore, we should search for a new heat balance between the mixture enthalpy, based on “thermodynamic” quality, and the absorbed heat. This paper presents the results of such analysis based on the accurate measurements of the outlet void fraction measured during the Cambridge project by Knights (1960, “A Study of Two-Phase Pressure Drop and Density Determination in a High-Pressure Steam-Water Circuit,” Ph.D. thesis, Cambridge University Engineering Lab, Cambridge, UK) in the 1960s for saturated flow boiling. In the 286 tests analyzed, the pressure and mass fluxes range from 1.72 MPa to 14.48 MPa and from 561.4 to 1833.33 kgm−2s−1, respectively. As the main result, we find that the slip ratio would close this new thermodynamic heat balance. This has allowed the accurate calculation of void fraction from this balance, provided we can predict the slip ratio. Finally, the strong connection of this new thermodynamic heat balance with the standard one through the slip ratio is highlighted.

Thermodynamics of organic mixtures containing amines. IV. Systems with aniline

Binary mixtures of aniline with benzene, toluene, alkane, alkanol, or N,N-dialkylamide have been investigated in the framework of the DISQUAC model. The reported interaction parameters change regularly with the molecular structure of the mixture components. The model consistently describes a set of thermodynamic properties including liquid–liquid equilibria, vapor–liquid equilibria, and molar excess enthalpies. The two latter properties for ternary systems are well-represented by DISQUAC using binary parameters only (i.e., neglecting ternary interactions). A comparison of DISQUAC results and those obtained from the UNIFAC (Dortmund version) and ERAS models is also shown. The experimental molar excess enthalpies for binary and ternary mixtures are better described by DISQUAC than by UNIFAC. ERAS fails when representing molar excess enthalpies of those binary systems including methanol or ethanol. This may be due to the existence of strong dipolar interactions among aniline molecules as well as to effects related to the equation of state term, evaluated comparing molar excess enthalpies, and molar excess internal energies at constant volume. The study of the aniline systems in terms of the concentration–concentration structure factor also underlines the importance of dipolar interactions in solutions with alkanes or alcohols, which may be due to the high polarizability of the aniline molecule.Key words: thermodynamics, mixtures, aniline, dipolar interactions, structural effects.

Excess molar volumes and excess molar enthalpies of binary and ternary mixtures of (ethanol or 1-butanol), triethylamine and n-hexane

Experimental data at 298.15 K and ambient pressure of excess molar volumes V m E and excess molar enthalpies H m E are reported for two ternary and corresponding binary mixtures of an alkanol (ethanol or 1-butanol), triethylamine (TEA) and n-hexane. A vibrating-tube densitometer was used to determine V m E . H m E was measured using a quasi-isothermal flow calorimeter. The experimental results are used to test the applicability of the ERAS model for describing both thermodynamic excess properties of ternary mixtures containing an alkanol, a tertiary amine and a n-alkane. Qualitative agreement of calculated values with experimental results was achieved using only system-specific parameters determined from binary mixtures. The results are explained in terms of the self-association between alkanol molecules and cross-association between the alkanol and the tertiary amine.