Application of the wilson-equation to azeotropic mixtures

Stephan, K. and Wagner, W., 1985. Application of the Wilson-equation to azeotropic mixtures. Fluid Phase Equilibria, 19: 201-219. The Wilson model is appropriate to describe low pressure phase equilibria. For binary mixtures only two parameters are needed. A diagram was developed, based on the Wilson model, allowing us to distinguish azeotropic from nonazeotropic binary systems. To apply this diagram the Wilson constants, and in addition the vapour pressure or boiling temperature and the molar entropy of vaporization of the pure componentes must be known. A few examples for the application of the method are discussed.     

The prediction of isobaric phase equilibria for non-ideal multicomponent mixtures from heat of mixing data

A method for predicting isobaric binary and ternary vapor—liquid equilibrium data using only isothermal binary heat of mixing data and pure component vapor pressure data is presented. Three binary and two ternary hydrocarbon liquid mixtures were studied. The method consists of evaluating the parameters of the NRTL equation from isothermal heat of mixing data for the constituent binary pairs. These parameters are then used in the multicomponent NRTL equation to compute isobaric vapor—liquid equilibrium data for the ternary mixture. No ternary or higher order interaction terms are needed in the ternary calculations because of the nature of the NRTL equation. NRTL parameters derived from heat of mixing data at one temperature can be used to predict vapor—liquid equilibrium data at other temperatures up to the boiling temperature of the liquid mixture.For the systems studied this method predicted the composition of the vapor phase with a standard deviation ranging from 1–8% for the binary systems and from 4–12% for the ternary systems.     

Solubility prediction of drugs in water-polyethylene glycol 400 mixtures using Jouyban-acree model

A numerical method is proposed for predicting solubility of drugs in water-PEG 400 mixtures based on the Jouyban-Acree cosolvency model. The accuracy of the proposed method is evaluated by computing mean percentage deviation (MPD) and compared with that of log-linear model of Yalkowsky. The overall MPDs of the Jouyban-Acree model and the most accurate version of Yalkowsky's model are 39.8 (+/-46.7) % and 175.8 (+/-266.4) %, respectively, and the mean difference is statistically significant (p < 0.0005). The proposed method produces acceptable residual distribution and the probability of solubility prediction with residual log of solubility <0.5 unit is 0.86. The applicability of the proposed method could be extended for predicting the solubility of drugs in water-PEG 400 mixtures at various temperatures. The impact of various log P values computed using different software is also studied and the results of ANOVA revealed that there are no significant differences between the accuracy of the predicted solubilities employing various log P values.     

差热分析求可逆相变焓的模拟研究

就样品的比热在相变前后均是温度函数的一般情况 ,通过动态地模拟DTA测量样品所经历的整个相变过程 ,验证了DTA中该相变潜热公式及相应的面积方法的正确性。证明对于可逆相变 ,采用文章所建议的面积法 ,把升降温过程中测得的相变潜热取一算术平均值 ,可最大限度地减少由于样品内温度梯度及样品比热是温度函数所带来的测量误差     

The prediction of isothermal phase equilibria for non-ideal multicomponent mixtures from heats of mixing

A method is presented for predicting both vapor—liquid and liquid—liquid equilibria for multicomponent mixtures using heat of mixing data for the constituent binary pairs together with pure component vapor pressures. Its application to two highly non-ideal hydrocarbon ternary systems is discussed. The parameters of the hybrid local composition model of Renon and Prausnitz, known as the NRTL equation, were evaluated from heat of mixing data for the three binary pairs in each of the two ternary systems. The parameters thus obtained were used in the multicomponent form of the NRTL equation to predict the ternary vapor—liquid equilibrium data for the completely miscible system cyclohexane(1)—n-heptane(2)—touluene(3) and for the partially miscible system acetonitrile(1)—benzene(2)—n-heptane(3) without the need for any ternary or higher order parameters.This method predicted compositions of the single phase region of the partially miscible ternary system with a standard deviation of 10%. It also predicted compositions for the fully miscible system with a standard deviation of 4.6%. Total pressure curves for the partially miscible and miscible ternaries were predicted with standard deviations of 6.6% and 4.5% respectively. Poor predictions of the binodal curve for the partially miscible region were obtained. The method offers a means of predicting the whole range of ternary phase equilibria for miscible systems.     

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.     

The heat of adsorption of water on nonporous hydrophilic carbon adsorbents in the model of two-stage adsorption

The behavior of integral and differential heats of adsorption of water in the region of transition from the first stage of adsorption (formation of clusters) to the second stage (formation of a stretched liquid film) was considered. The curve of integral heat of adsorption has an inflection at the transition point, and the differential heat of adsorption changes jumpwise. The values of these effects were estimated by the simplest model of formation of one and two hydrogen bonds between a water molecule and an adsorption center on the surface of the carbon adsorbent. Curves of differential heat of adsorption with transition points for real systems are presented. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1479–1483, August, 1999.     

Evaluation of the Compatibility of EPDM and IIR I. Specific heat capacity

The thermal effect of mixing of EPDM and IIR was studied by differential scanning calorimetry over the temperature range between 335 and 435 K. O'Neill's method was used for calculating the specific heat capacity with alumina as standard. The greater the butyl rubber content, the lower the heat capacity. The presence of butyl rubber induces a marked thermal instability because of isobutylene units. It is possible that a rearrangement occurs in the molecular sequence, accompanied by secondary reactions involving free radicals. The contribution of each component to the cP of the tested polymeric systems is discussed. Differences between theoretical and experimental specific heat capacities increase as the operation temperature is raised. The relationship between the contributions of the two components to the specific heat capacity values of mixtures can be described by a first order equation, named the law of reciprocal thermal affinity. This aspect can be ascribed to the interaction of various reacting entities, which form certain units with low molar heat capacity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Overall analysis of first‐order phase transitions in some alkyloxycyanobiphenyl liquid crystals

Measurements of pressure, molar volume and specific heat as functions of temperature in the isotropic (I) phase as well as in the smectic A (SmA) and nematic (N) mesophases of some alkyloxycyanobiphenyl compounds (nOCB, n = 6–10) were carried out using differential thermal analysis under pressure, densitometry, X‐ray powder diffraction and modulated differential scanning calorimetry. Thermodynamic properties, such as latent heats and volume jumps at the different phase transitions, were determined. The coherence of this whole set of data was tested using pressure–temperature data through the slopes associated to their phase transitions, extrapolated at normal pressure in the light of the Clausius–Clapeyron equation.     

Correlation for prediction of vapor pressures of pure fluids incorporating renormalization group formulations with corresponding-states principle

A simple correlation for predicting the vapor pressures of coal liquids between the freezing and critical points, and extending to normal fluids, has been developed on the basis of renormalization group theory and phenomenological scaling theory. The Clapeyron equation has been reduced to the integral form

to represent vapor pressure using a generalized correlation developed by Sivaraman et al. (1983) for the prediction of latent heats of vaporization of normal fluids and coal-liquid model compounds. L*, the dimensionless latent heat of vaporization, andΔz, the difference between the compressibility factors of the saturated vapor and liquid, are given by the corresponding-states correlations

and

based on the formulations of Pitzer et al. (1955). A simple expression for the latent heat of vaporization developed by Torquato and Stell (1982) is incorporated into this correlation. The vapor-pressure correlation has been tested successfully for 23 pure-component systems including aromatic and heterocyclic compounds often found in coal liquids and shale oil in the region 0 〈 ε = (T_c-T)/T_c 〈 0.69. The deviations in the predicted vapor pressures are in the range 0.11–5.45%.     

Water-methanol-benzene ternary system. Thermochemical experiment and computer simulation

Solution heats have been measured for benzene dissolved in mixtures of water with methanol at 25°C. The resulting values are compared with data for water-methanol-aniline, water-acetonitrile-benzene, and water-acetonitrile-aniline systems. Computer simulations have been performed for binary mixtures of water with methanol and dilute solutions of benzene in these mixtures. Thermodynamic and structural characteristics of solutions were obtained by calculations. The enthalpy of benzene transfer from water into a mixed solvent correlates with the relative deviation of the local composition from the mean composition of the mixture.     

An equation of state for hydrochloric acid solutions

Gibbons, R.M. and Laughton, A.P., 1984. An equation of state for hydrochloric acid solutions. Fluid Phase Equilibria, 18:61–68.A modified Redlich-Kwong-Soave (RKS) equation is presented for hydrochloric acid solutions. It is shown that the equation with one binary parameter predicts the azeotropic behaviour of the system accurately and the heats of solution within 10%. These results suggest that the new equation can be applied to a wide range of polar systems.     

Melting of polymers by non-isothermal, temperature-modulated calorimetry: analysis of various irreversible latent heat contributions to the reversing heat capacity

This paper provides an analysis of contributions to the apparent, reversing heat capacity when measured by temperature-modulated differential scanning analysis (TMDSC) with an underlying heating rate in the temperature range where irreversible transitions with latent heats occur. To deconvolute the data of a TMDSC scan into a total and reversing part, it is common practice to use the sliding averages and the first harmonics of the Fourier series of temperature and heat-flow rate. Under certain conditions, this procedure produces erroneous reversing contributions which are detailed by experiment and simulation. Unless the response to the temperature modulation is linear, the total heat-flow rate is stationary, and the transition is truly reversible and occurs only once during the temperature scan, one cannot expect a true deconvolution of total and reversible effects. In the presence of multiple, irreversible transitions within a modulation period, however, each process involving latent heat can increase the modulation amplitude, as demonstrated by computer-simulation of polymer melting. As a result, the multiple transitions may give erroneously high latent heats when integrating the apparent reversing heat capacity with respect to temperature.     

Thermodynamic and kinetic properties of <Emphasis Type="Italic">cis</Emphasis>-diammineglycolatoplatinum in different water solvents

The dissolution behavior of cis-diammineglycolatoplatinum (nedaplatin) in saline, water and glucose were studied by a microcalorimetric method. The integral heats and differential heats of the dissolution were measured to establish the equation for the solute and the heats. The corresponding half-life, kinetic and thermodynamic properties of the nedaplatin solutions were determined. The results show that hydrogen bonds could be generated and the dissolution entropy of nedaplatin in different solvents is negative during the dissolution process, so as to enhance the drug stability, but there is an obvious difference in stability in different solvents.     

Pure-component vapour pressures of heavy hydrocarbons containing nitrogen or sulphur using the UNIFAC group-contribution method

A group-contribution model for predicting pure-component vapour pressures, in part based on the UNIFAC method for vapour—liquid equilibria, has been extended to include hydrocarbons of molecular weights below 500 containing nitrogen or sulphur. Good representation is obtained for vapour pressure data in the region 10–2000 mmHg. In addition, the accuracy of the method is tested by prediction of heats of vapourization via the Clausius—Clapeyron equation. The predicted heats of vapourization agree with the experimental values within a few percent. In absence of experimental data, the model may be used to estimate vapour pressures and heats of vapourization for the category of compounds studied.     

Generalized correlation for predicting the kinematic viscosity of liquid petroleum fractions

A two-parameter viscosity model proposed previously for pure liquids is extended to correlate the kinematic viscosity–temperature behavior for liquid petroleum fractions. The coefficients in the viscosity equation are related to the characterization properties of the petroleum fractions and a generalized kinematic viscosity–temperature correlation is then developed, which needs only specific gravity at 15.6°C and 50% boiling point as input parameters. The present method, when tested by predicting the experimental kinematic viscosities of 47 fractions from 15 world crude oils with total 250 data points, yielded reasonable results with an overall average absolute deviation of 4.2%.     

Computer-aided product design of alternative solvents based on phase equilibrium synergism in mixtures

A systematic methodology is proposed to find binary azeotropic mixtures as new alternative solvents for the extraction process of volatile aroma molecules widely used in perfume and cosmetic industries. We investigated the use of the reverse engineering approach with computer-aided product design (CAPD) instead of the traditional “trial and error” approach. First, the design problem is defined from the real functionalities of the classical solvents. The latter are translated into physicochemical properties and the corresponding boundary values for each property are defined. The reverse engineering method coupled with CAPD consists in using optimization techniques for building molecular structures that match as best as possible the complete set of target physicochemical properties, thus defining for each candidate a performance index. Property values are evaluated by using group contribution methods for each molecular structure generated by a CAPD tool or by using database values. Acknowledging the contradictory relationship between two selected physicochemical properties, that is, low boiling temperature and high flash point, which is rarely found in pure components, binary azeotropic mixtures were studied to enhance the global performance of solvent candidates. Dimethyl carbonate used as a solvent for the extraction of aroma molecules from plants exhibits between the boiling temperature and the flash point. It was selected as the key component for designing binary azeotropic mixtures. The global performance of the binary azeotropic mixtures was verified by means of calculations of the vapor–liquid and liquid–liquid equilibrium using modified universal functional activity coefficient (UNIFAC) method as a thermodynamic method.     

Application of azeotropic mixtures as standards in testing gas chromatographic systems and components

Summary The use of specially chosen azeotropes is proposed as standards when testing gas chromatographs, detectors, columns and sample introduction systems. These azeotropic mixtures permit us to minimize the errors due to composition changes during sampling and sample introduction systems (intended for gases or liquids). The potentialities and advantages of such applications are illustrated using the azeotropic mixture of benzene and cyclohexane as an example.     

A systematic solution to the problem of sample background correction in DSC curves

The problem of sample background correction in differential scanning calorimetric curves is addressed in this paper. An equation is derived for the heat capacity of the system, which corresponds to the sample background. Thereby, it is assumed that during the thermal event the system is a two-component mixture of the initial substance and the final product. According to this model, the variation in heat capacity of the system is due both to the increase in the partial concentration of the product at the expense of the initial substance and to the physical change in the specific heats of the two components, resulting from the temperature increase. The final result of the derivation is an integral equation which can be solved by means of a numerical technique. The algorithm used is presented in detail. The model is general, and can be applied to diverse exothermic or endothermic processes. The melting of a semi-crystalline polymer and the cure process of a thermoset are given as demonstrative examples. The method improves the reliability and the reproducibility of the data.     

The Determination of Latent Heats of Vaporization Under Quasi-Isothermal Conditions

A method was devised to evaluate latent heats of vaporization from quasi-isothermal isobaric analysis data. The procedure requires the recording of at least two diagrams: one for the investigated liquid, and the other for a standard liquid with a known latent heat of vaporization. Use of the method to determine the heats of vaporization of some alcohols, with water as standard liquid, led to results close to those previously reported in the literature. The main advantage of the procedure consists in the fact that it requires only small amounts of sample (5–10 mg). This revised version was published online in August 2006 with corrections to the Cover Date.