Vapour-liquid equilibrium data for binary mixtures of some new refrigerants

The acceptance of the Montreal Protocol has led to a timetable for the phasing out of chlorine-containing refrigerants and their replacement by new chlorine-free materials. For many applications a pure alternative refrigerant can not be found with the appropriate properties and refrigerant mixtures have been considered. In order to model the properties of these refrigerant blends accurate vapour-liquid equilibrium (VLE) data are required over the range of temperature and pressure of interest to the refrigeration engineer. In this paper we report VLE data for six binary mixtures of the new hydrofluorocarbon refrigerants over a wide range of temperatures and pressures. The six mixtures are: R32/R125, R32/R143a, R32/R134a, R125/R143a, R125/R134a and R143a/R134a. Results for R32/R125 and R32/R134a were obtained down to at least −30°C and were done in duplicate. The raw data were correlated to two models using Maximum Likelihood techniques. One of the models was then used to predict azeotropic compositions for three of the mixtures (R32/R125, R32/R143a and R125/R143a) and the approximate composition of a ternary saddle point azeotrope.     

Molar excess free energy of mixing of 1-propanol or 2-propanol with cyclohexane at 298.15 and 308.15 K in terms of association model with a Flory contribution term

Excess molar Gibbs free energies of mixing for 1-propanol or 2-propanol + cyclohexane over the whole composition range at 298.15 and 308.15 K have been calculated from vapour pressure data measured by static method. The data have been analysed in terms of a Mecke-Kempter association model with a Flory contribution term.     

Measurements and correlation of vapour-liquid equilibria of 2-butanone and hydrocarbons binary systems at two different pressures

Consistent isobaric vapour-liquid equilibrium data have been measured for 2-butanone + n-hexane, 2-butanone + n-heptane, and 2-butanone + 2,2,4-trimethylpentane at two different pressures. All binary systems present a minimum boiling azeotrope at both pressures, and show that the azeotropic compositions are weakly dependent on pressure. The equilibrium data were correlated using the Wilson, NRTL, and UNIQUAC models for which the parameters are reported.     

Vapour-liquid equilibrium of the acetone---methanol system in the presence of KSCN and comparison with other salts

The effect of KSCN at salt mole fractions of 0.01–0.05 and at saturation on the VLE of the binary acetone-methanol system has been experimentally investigated at 101.32 kPa using a modified Othmer equilibrium still. The experimental data were correlated by the electrolytic NRTL model [B. Mock, L.B. Evans and C.C. Chen, AIChE J., 32 (1986) 1655–1664], the extended UNIQUAC equation [B. Sander, A. Fredensland and P. Rasmussen, Chem. Eng. Sci., 41 (1986) 1171–1183] and the modified Wilson and NRTL models proposed by Tan [T.C. Tan, AIChE J., 31 (1985) 2083–2085; Chem. Eng. Res. Des., 65 (1987) 355–366; Trans. Inst. Chem. Eng., 68 (1990) 93–102]. The results were compared with those obtained by Tan's predictive models. A crossover between the salting-out and salting-in effects on acetone and a non-azeotropic minimum in the temperature-composition diagram were observed at low and high salt concentrations. Based on the solubility data in the mixture, comparisons with the effect of other salts on the same mixed solvent were made.     

Vapor-liquid equilibrium predictions of refrigerant mixtures from a cubic equation of state with a G-EoS mixing rule

A modified excess Gibbs energy model which is based on the local composition concept and assigns a single energy parameter per pair of components, is incorporated into the G^E—EoS thermodynamic formalism for vapor-liquid equilibrium (VLE) calculations of simple and complex refrigerant mixtures. One temperature set of data close to 273 K is used to obtain the model's parameters, which are used to extrapolate the VLE at other temperatures and pressures. A one-parameter form of the model based on the Wong-Sandler mixing rule is presented for several simple systems. The physical significance of the model's energy parameter is connected to the preference of the mixture for like to unlike interactions. The model is applied for VLE predictions of the ternary system R14-R23-R13, and the results are compared to calculations using the 3PWS model [H. Orbey. S.I. Sandler, Ind. Eng. Chem. Res. 34 (1995) 2520–2525] and the van der Waals mixing rule. Modelling of a few complex systems with only three data points given at each temperature is shown with a two parameter version of our model on the basis of the Huron-Vidal mixing rule.     

Modelling of phase equilibria for associating mixtures using an equation of state

In the present work, the group contribution with association equation of state (GCA-EoS) is extended to represent phase equilibria in mixtures containing acids, esters, and ketones, with water, alcohols, and any number of inert components. Association effects are represented by a group-contribution approach. Self- and cross-association between the associating groups present in these mixtures are considered. The GCA-EoS model is compared to the group-contribution method MHV2, which does not take into account explicitly association effects. The results obtained with the GCA-EoS model are, in general, more accurate when compared to the ones achieved by the MHV2 equation with less number of parameters. Model predictions are presented for binary self- and cross-associating mixtures.     

Prediction of global vapor-liquid equilibria for mixtures containing polar and associating components with improved renormalization group theory

Our recently improved renormalization group (RG) theory is further reformulated within the context of density functional theory. To improve the theory for polar and associating fluids, an explicit and complete expression of the theory is derived in which the density fluctuation is expanded up to the third-order term instead of the original second-order term. A new predictive equation of state based on the first-order mean spherical approximation statistical associating fluid theory (FMSA-SAFT) and the newly improved RG theory is proposed for systems containing polar and associating fluids. The calculated results for both pure fluids and mixtures are in good agreement with experimental data both inside and outside the critical region. This work demonstrates that the RG theory incorporated with the solution of FMSA is a promising route for accurately describing the global phase behavior of complex fluids and mixtures.     

Liquid-liquid phase equilibria for some polystyrene-methylcyclohexane mixtures

Liquid-liquid cloud point diagrams of solutions of nearly monodisperse samples of polystyrene (PS), and binary mixtures of nearly monodisperse PS’s, both in methylcyclohexane (MCH), were determined for several polymer molecular weights (M_w) at 0.1 MPa. The bimodal mixtures (PS[M_w(1),ρ(1)] + PS[M_w(2),ρ(2)], M_w(1)=90×10³ g/mol, M_w(2)=13×10³ g/mol, 5.78 × 10³ g/mol, and 2.2 × 10³ g/mol, ρ=1.06) were prepared constraining 〈M_w〉=38.6×10³ g/mol, ρ=M_w/M_n is the polydispersity index. In each case the cloud point curves (CPC’s) for the bimodal mixtures are strongly skewed, lying well above CPC for 〈M_w〉 when φ<φ_CRITICAL, and below CPC for 〈M_w〉 when φ>φ_CRITICAL; φ is volume fraction polymer in the polymer/solvent mixture. The experimental results are discussed in the context of empirical and mean-field representations.     

Phase diagrams of crystalline adducts containing two volatile components

The phase relationships in binary systems forming a crystalline addition compound are obtained by means of classical thermodynamic arguments for the case in which both components are volatile. This approach can be applied to inclusion compounds and to other low-stability addition compounds existing only in the solid phase. The results are consistent with those already known for clathrates containing a volatile guest and a non-volatile host, and for symmetric systems, such as racemic compounds. The temperature range in which the adduct undergoes a congruent sublimation depends on the ratio of the vapor pressures of the two components. A relation has been found to exist between the properties of the pure components, the melting behavior and the enthalpy of formation of the adduct.     

DISQUAC predictions of phase equilibria,molar and standard partial molar excess quantities for 1-alkanol+cyclohexane mixtures

Literature data for phase equilibria: vapor-liquid VLE, liquid-liquid LLE, and solid-liquid SLE; molar excess Gibbs energies G ^E , molar excess enthalpies H ^E ; activity coefficients _i and partial molar excess enthalpies H _i ^E,o at infinite dilution for 1-alkanol (1)+cyclohexane (2) mixtures are examined by the DISQUAC group contribution model. For a more sensitive test of DISQUAC, the azeotropes, obtained from the reduction of the original isothermal VLE data, are also examined for systems characterized by hydroxyl, alkane and cyclohexane groups. The alkane/cyclohexane and alkane/hydroxyl interaction parameters have been estimated previously. The cyclohexane/hydroxyl interaction parameters are reported in this work. The first dispersive parameters increase regularly with the size of the alkanol; from 1-octadecanol they are constant; an opposite behavior is encountered for the third dispersive parameters, which are constant from 1-dodecanol. The second dispersive parameters decrease as far as 1-propanol and then increase regularly; from 1-octadecanol they are constant. The quasichemical parameters are equal to those for the alkane/hydroxyl interactions. Phase equilibria, the molar excess functions, and activity coefficients at infinite dilution are reasonably well reproduced. Poor results are found for H _i ^E,o and DISQUAC predictions for H _i ^E,o are strongly dependent on temperature.     

Solubility predictions for copolymer systems

With the many possible composition combinations possible for copolymers there is a critical need to develop methods of predicting the properties of these materials. This paper examines the applicability of popular, current vapor–liquid equilibria prediction models in characterizing the solubility of solvents in copolymers. In some cases anomalous behavior is observed where the solubility of the solvent in the copolymer is greater than or less than in either of the composite homopolymers. Two popular UNIFAC models and the group-contribution, lattice-fluid equation of state (GCLF-EoS) have been evaluated for this application. In general the UNIFAC models showed a better capability than the GCLF-EoS. There is a need for more sophisticated methods for predicting the complex interactions that can be present in copolymer systems.     

Thermodynamics of liquid mixtures containing n-alkanes and strongly polar components: VE and C P E of mixtures with either pyridine or piperidine

Excess molar volumes V _E and excess molar heat capacities C _P ^/E at constant pressure have been obtained, as a function of mole fraction x₁, for several binary liquid mixtures belonging either to series I: pyridine+n-alkane (C_lH_2l+2), with l=7, 10, 14, 16, or series II: piperidine+n-alkane, with l=7, 8, 10, 12, 14. The instruments used were a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. V ^E of pyridine+n-heptane shows a S-shaped composition dependence with a small negative part in the region rich in pyridine (x₁>0.90). All the other systems show positive V ^E only. The excess volumes increase with increasing chain length l of the n-alkane. The excess molar heat capacities of the mixtures belonging to series II are all negative, except for a small positive part for piperidine+n-heptane in the region rich in piperidine (x₁>0.87). The C _P ^/E at the respective minima, C _P ^/E (x_1,min ), become more negative with increasing l, and the x_1,min values range from about 0.26 (l=7) to 0.39 (l=14). Most interestingly, mixtures of series I exhibit curves of C _P ^/E against x₁ with two minima and one maximum, the so-called W-shape curves.Dedicated to Professor A. Néckel on the occasion of his 65^th birthday. Communicated in part at the XVII^èmes Journées de Calorimétrie, d'Analyse Thermique et de Thermodynamique Chimique, Ferrara, Italy, 27–30 October, 1986.     

Heterogeneous extended langmuir model with multiregion surfaces for adsorption of mixtures

The multiregion or multisite adsorption theory is applied to the heterogeneous extended Langmuir (HEL) model for predicting adsorption from mixtures. A new model, multiregion HEL (MR-HEL), is derived. MR-HEL is thermodynamically consistent. It uses the same three parameters for each component of the mixture as in the HEL model. Examples, including eight binary and one ternary systems, show that both MR-HEL and HEL yield satisfactory results for relatively ideal systems with like components. For nonideal and highly nonideal mixtures, however, MR-HEL reduces the total average deviation for the predicted amount adsorbed for each component by more than 50% in comparison with the original HEL model. The improvement by MR-HEL is significant. Moreover, the new model predicts not only an azeotrope for binary system CO(2)+C(3)H(8) that shows strong nonideal behavior but also the correct azeotropic composition.     

Molecular simulation of the high-pressure phase equilibria of binary atomic fluid mixtures using the exponential-6 intermolecular potential

Molecular simulation results using the exponential-6 intermolecular potential are reported for the phase behaviour of the atomic binary mixtures of neon+xenon, helium+neon, helium+argon and helium+xenon. These binary mixtures exhibit both vapour–liquid and liquid–liquid phase equilibria up to very high pressures. Comparison with experiment indicates good overall agreement. The results indicate that the exponential-6 intermolecular potential is a useful generic potential for molecular simulation.     

Global warming potential predictions for hydrofluoroethers with two carbon atoms

Global warming potentials are predicted using computational chemistry and thermodynamics approaches for four hydrofluoroethers where no data have previously been available. We also compare results with the same methodology for six other species. We combine predictions of radiative forcing values from density functional theory computations at the B3LYP/6-31g* level of theory with previous experimentally determined or newly estimated hydroxyl radical-hydrogen abstraction rate constants to obtain these global warming potentials. We find that many of the HFEs studied have lower global warming potentials than the hydrofluorocarbons and chlorofluorocarbons they may soon replace, although other environmental and technical issues may need to be addressed first. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Thermodynamics of binary mixtures containing organic carbonates Part XI. SLE measurements for systems of diethyl carbonate with long n-alkanes: comparison with DISQUAC and modified UNIFAC predictions

Using the available interaction parameters for organic carbonate+alkane mixtures the ability of the DISQUAC and modified UNIFAC group contribution model to predict solid–liquid equilibria (SLE) is investigated. Six sets of the SLE temperatures for diethyl carbonate+n-alkane (octadecane, eicosane, docosane, tetracosane, hexacosane, octacosane) systems have been measured by a dynamic method from 278.65 K to the melting point of the long chain n-alkane. The data have been correlated by three equations: Wilson, UNIQUAC and NRTL. The existence of a solid–solid first-order phase transition in n-alkanes has been taken into consideration in the solubility calculations. The relative standard deviations of the solubility temperature correlation for all measured data vary from 0.31 to 0.34 K and depend on the particular equation used.

The SLE curves are usually well predicted by DISQUAC and modified UNIFAC models with average standard deviation of <1.35 K.     

Simulation studies on mixtures of dipolar with nonpolar linear molecules II. A mixing rule for the dipolar contribution to the Helmholtz energy

In recent equations of state an explicit expression for the dipolar contribution to the Helmholtz energy F_D is used. If such equations are applied to mixtures the problem of mixing rules for F_D arises. As a solution, a “one-fluid dipole moment μ_x” is introduced which is based on perturbation theory. The accuracy of the approach is tested by simulation results for mixtures of dipolar with nonpolar linear molecules. In addition to the simulation runs from Part I (Müller et al. (1994)), results from 97 new NVT simulations are presented. Comparisons of pressures, internal energies, dipole energies and excess free energies from simulations with those obtained from the equation for F_D in combination with the one-fluid dipole moment μ_x shows good to excellent agreement.     

Study of properties of vulcanizates for binary mixtures of polar caoutchouck with polyisoprene

Effect of the extender, commercial N-330 carbon, on strength and thermal properties of vulcanizates for binary mixtures of polar caoutchoucks with polyisoprene was studied.     

Solubility of polycyclic aromatics in binary solvent mixtures using activity coefficient models

Polycyclic aromatic hydrocarbons (PAHs) precipitation is one of the major problems in the hydrocracking units. In this investigation, pyrene and phenanthrene were selected because they were found to be in higher concentrations in the feed to hydrocracking units. Their solubilities were investigated in toluene solvent mixture of iso-octane and heptane over a temperature range from 293 to 323 K. The experimental solubility data were used to predict the interaction parameters for seven different solid–liquid equilibrium models. The following activity coefficient models were used; Wilson, NIBS/Redlich–Kister, UNIQUAC, modified UNIFAC, modified UNIFAC (Dortmund), Flory–Huggins and Sheng. The interaction parameters were expressed as a second-order polynomial function in temperature. In order to test the models, the average absolute deviation percentage (AADP) was used. The overall AADP was found to range from approximately 7 to 14%. The models can be arranged according to their accuracy in a descending order based on AADP as follows: NIBS/Redlich–Kister, Wilson, UNIQUAC, Sheng, Flory–Huggins, modified UNIFAC (Dortmund) and finally modified UNIFAC. All models used in this work gave reasonable results; however, the group contribution models can also be used as a predictive tool for the solubility measurement of pyrene and phenanthrene in other solvents containing the same groups of the solvents used in this study.     

Use of pervaporation for separating azeotropic mixtures using two different hollow fiber membranes

The performance of a “two-membrane column” was demonstrated for the separation of water-ethanol and water-isopropanol azeotropic mixtures. The cellulose acetate and silicone rubber membranes which were employed for the strippers showed opposite permselectivity towards each component of the mixtures. The two strippers were connected together with liquid pumps installed between them. A great increase in overall separation factor (over 100) was obtained. The degree of separation was dependent upon the ratio of feed to reject rate. Azeotropic mixtures were successfully separated by using the two-membrane column. This column is expected to provide us with an energy-saving, high purity separation process