First principles predictions of thermophysical properties of refrigerant mixtures

We present pair potentials for fluorinated methanes and their dimers with CO(2) based on ab initio potential energy surfaces. These potentials reproduce the experimental second virial coefficients of the pure fluorinated methanes and their mixtures with CO(2) without adjustment. Ab initio calculations on trimers are used to model the effects of nonadditive dispersion and induction. Simulations using these potentials reproduce the experimental phase-coexistence properties of CH(3)F within 10% over a wide range of temperatures. The phase coexistence curve of the mixture of CH(2)F(2) and CO(2) is reproduced with an error in the mole fractions of both phases of less than 0.1. The potentials described here are based entirely on ab initio calculations, with no empirical fits to improve the agreement with experiment.     

Application of a new equation of state to liquid refrigerant mixtures

A new general equation of state recently reported for pure liquids has been developed to predict the volumetric and thermodynamic properties of six binary and two ternary liquid refrigerant mixtures (including HCs and HFCs mixtures) at different temperatures, pressures, and compositions. The results show this equation of state can be used to reproduce and predict different thermodynamic properties of liquid refrigerant mixtures within experimental errors. The composition dependence of the parameters of this equation of state has been assumed as quadratic functions of mole fraction. Using these mixing rules, the agreement between calculated and experimental densities is better than 0.6% for binary mixtures and 2.3% for ternary mixtures. To compare the performance of this new equation of state against other well-known methods such as the COSTALD method, the density of some refrigerant mixtures, for which the parameters of COSTALD were available, has been computed and compared with those of this new equation of state.     

Prediction of homogeneous azeotropes by Wilson equation for binary HFCs and HCs refrigerant mixtures

A simple approach based on Newton's method using Wilson activity coefficients equation and Antoine equation is proposed to determine the binary homogeneous azeotropes for hydrofluorocarbons (HFCs) and hydrocarbons (HCs) mixtures. With the known Wilson parameters at a certain temperature, the azeotropic composition at this temperature range can be evaluated. Only one point of the measured VLE data is required to evaluate the Wilson parameters firstly if they are unavailable. The method is verified with six binary systems, which are ethane (HC-170) + trifluoromethane (HFC-23), difluoromethane (HFC-32) + propane (HC-290), pentafluoroethane (HFC-125) + propane (HC-290), 1,1,1,2-tetrafluoroethane (HFC-134a) + n-butane (HC-600), 1,1,1-trifluoroethane (HFC-143a) + n-butane (HC-600) and propane (R290) + 1,1,1,2,3,3,3-heptafluoropropane (R227ea) mixtures. Good agreements are found between the calculated results and reference data.     

The geometric minimum action method for computing minimum energy paths

An algorithm is proposed to calculate the minimum energy path (MEP). The algorithm is based on a variational formulation in which the MEP is characterized as the curve minimizing a certain functional. The algorithm performs this minimization using a preconditioned steepest-descent scheme with a reparametrization step to enforce a constraint on the curve parametrization.     

Computing all the azeotropes in refrigerant mixtures through equations of state

Azeotropic mixtures of fluorocarbon (FC) and hydro fluorocarbon (HFC) with hydrocarbons are gaining popularity as drop-in substitutes for CFCs and HCFCs. A method to compute all the azeotropes in a refrigerant mixture through the equation of state approach is described. The method allows prediction of all the azeotropes in a refrigerant mixture and is in close agreement with the experimental data. Both the vapor and the liquid phase non-idealities are incorporated through fugacity coefficients modeled using Peng–Robinson–Stryjek–Vera equation of state with Wong-Sandler and van der Waals mixing rules. Homotopy continuation based methodology guarantees computation of all the solutions of necessary and sufficient condition of azeotropy in multicomponent refrigerant mixtures. The method establishes the pressure dependency of azeotropic composition allowing prediction of bifurcation pressure where refrigerant azeotropes may appear or disappear and predicts azeotropes at elevated pressures. The approach is independent of equation of state and mixing rules but rely on their ability to represent the phase behavior. The approach is tested with R23–R13, propane–R227ea binary mixtures and a ternary mixture of R32–R125–R143a.     

Modified spectrophotometric method for the determination of selenium in environmental and mineral mixtures using 2,3-diaminonaphthalene

Reaction of selenium with 2,3-diaminonaphthalene was reinvestigated with bromide ion as a catalyst. In acid medium, selenium reacts with the above reagent to form a complex extractable with cyclohexane and with an absorption maximum at 378.5 nm. The molar absorptivity of the complex is 17.5 x 10(3) 1 mol(-1) cm(-1). Beer's law is obeyed in the range 0.5-12 mg 1(-1). The method is reproducible and the standard and relative standard deviation for seven replicate analyses of 2 mg 1(-1) of selenium are 0.05 absorbance units and 2.5%, respectively. The limit of detection is 0.012 mg 1(-1). The method was optimized for the determination of selenium in water, soil, cereal and mineral mixtures and cattle feed and was compared with the reported 2,3-diaminonaphthalene method.     

Assessing thermal hazards of reaction mixtures

A strategy for assessing thermal hazards of chemical manufacturing processes is presented with an emphasis on new developments in the areas of the desired and decomposition reaction research. In the case of the desired reaction, the application of a computer program, CAMEO, for assessing synthetic reaction pathways, and enthalpies, and for evaluating the chemistry of specific failure modes is demonstrated. For the decomposition reaction, an unexpected decomposition destabilization phenomenon in mixtures was observed, which clearly demonstrated the need for chemical/solvent mixture testing to provide reliable thermochemical data for reaction hazard assessment. An application of the reaction mixture hazard evaluation strategy to a chemical process is presented.The authors would like to thank P. R. Kingsley for carrying out the experimental work necessary to complete this project. The authors also wish to acknowledge the support of Eastman Kodak Company in the preparation of this study.     

Mew method for estimating polarity of chemical bonds

For alkali-metal and halogen atoms, a relationship has been established between their electronegativity (EN) and the charge on the atoms. Bond polarities have been determined in molecules and crystals of alkali-metal halides by the method of equalization of ENs of the bond partners. The reasons for differing dimensional behavior of metal and nonmetal atoms upon change in coordination are discussed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2701–2704, December, 1989.     

Use of the magnetic suspension balance for the study of liquid mixtures

Previous contributions to the 9th and 12th V.M.T. Conferences have described the use of microbalances to study the absorption of hydrocarbon vapours by essentially involatile liquid absorbents to determine solution thermodynamic properties. The quartz spring balance is useful over the greater part of the relative vapour pressure range but lacks precision in the lower part of the range as the absorption decreases. In this lower pressure region the greater sensitivity and greater load capacity of the commercial beam vacuum microbalance can be utilised and the measurements extrapolated with confidence to give the activity coefficient for the absorbed vapour at infinite dilution in the liquid absorbent. However, interaction of the volatile hydrocarbons studied with the components of the balance limits the use of the latter balance to the lower pressure region.The Sartorius magnetic suspension balance combines the attributes of these two balances in that it is not affected by the organic vapours studied and provides the load-to-precision ratio that the determination of accurate activity coefficients requires. This enables liquid mixtures with one volatile and one or more involatile components to be studied over the entire concentration range on the one apparatus. Results are reported for the absorption of hexane by squalane (hexamethyl tetracosane) and compared with those previously determined using a quartz spring balance and a Sartorius electronic microbalance. The modifications found necessary to the magnetic suspension balance for this work are described.     

A simple method for estimating activation energy from derivative thermoanalytical curves and its application to thermal shrinkage of polycarbonate

Activation energy can be estimated by a new simple method, in which logarithm of maximum rate of conversion observed at different heating rates is plotted against reciprocal absolute temperature, because the conversion at the maximum rate is approximately independent of the heating rate. The method is applied to thermal shrinkage of polycarbonate, and the estimated activation energy is in good agreement with those obtained by conventional methods.

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Zusammenfassung Die Schätzung der Aktivierungsenergie kann mittels einer neuen Methode erfolgen, bei welcher der Logarithmus der für verschiedene Aufheizgeschwindigkeiten gemessenen maximalen Konversionsgeschwindigkeit als Funktion der reziproken Temperatur aufgetragen wird, da die Konversion bei der maximalen Geschwindigkeit inetwa unabhängig von der Aufheizgeschwindigkeit ist. Das Verfahren wurde beim thermischen Schrumpfen von Polycarbonat angewendet und die geschätzte Aktivierungsenergie liegt in guter Übereinstimmung mit den in herkömmlichen Verfahren ermittelten Werten.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday     

Use of amino acid analysis for estimating the individual concentrations of proteins in mixtures

The concentrations of five individual proteins in a mixture were determined from one amino acid analysis of the mixture by solving for each protein using simultaneous equations. Dried casein and whey were separated into five individual protein components using reversed-phase HPLC. Individual proteins were collected and analyzed for amino acid composition. These data were used as standards. Mixtures of purified proteins were analyzed for total amino acid composition and the concentrations of individual proteins in the mixtures were determined by solving simultaneous equations based on the amino acid analysis composition of the standards.     

Modified method for filling micro-HPLC-columns

Summary A new method is introduced for packing micro-columns with an ID (inner diameter) of 320 m. The advantage of this method is the extraordinary economy of the packing material employed and the high reliability in production. The theoretical plate height ranges from 7 to 8 m for 3 m particles.     

A new computational method for estimating X-ray spectral distributions

A new computational method is described for estimating the exposure-rate spectral distributions of X-rays from attenuation data measured with various filtrations. The estimation problem of X-ray spectra is formulated as the numerical computation of solving a set of linear equation with an ill-conditional nature. In this paper, the singular-value decomposition technique, which differs from the iterative method, is applied to this singular numerical computation problem. The principle of the analysis method is based on that the response matrix of filtrations can be decomposed into some inherent component matrices. X-ray spectral distributions are then represented in a simple combination of some component curves, so that the estimation process can be systematically constructed. The singularity in its computation is removed by selecting the components of the combination, and a performance index is also presented for the optimal selection. The feasibility of the proposed method is studied in detail in a computer simulation using a hypothetical X-ray spectrum produced by assuming experimental conditions. The application results are also shown about the spectral distribution from a 140 kV constant voltage X-ray source.     

Adaptive minimum action method for the study of rare events

An adaptive minimum action method is proposed for computing the most probable transition paths between stable equilibria in metastable systems that do not necessarily have an underlying energy function, by minimizing the action functional associated with such transition paths. This new algorithm uses the moving mesh strategy to adaptively adjust the grid points over the time interval of transition. Numerical examples are presented to demonstrate the efficiency of the adaptive minimum action method.     

A new method for estimating the drying sensitivity of clay

Fourteen clays with different drying sensitivity were selected for developing a rapid method of estimation of their drying sensitivity. The clays were arranged in a series according to results of complex technological tests in a decreasing order of their drying sensitivity. It is proposed to determine only that portion of the losses that is released in the temperature range above the drying temperature, at 100–200°C in order to compare different clays as regards the interlayer moisture lost during drying. A relationship was found between the amount of moisture liberated at temperature up to 200°C, mineralogical composition and drying behaviour of clays. Having determined the amount of the interlayer moisture lost at 100–200°C, it is possible to quantitatively evaluate the content of component adversely affecting the drying sensitivity and predict the drying behaviour of a given clay.     

The thermal behaviour of high-molecular polyoxyethylene-urea binary mixtures

The thermal behaviour (from 20 to 500°C) of high-molecular polyoxyethylene-urea mixtures which formed a molecular complex was investigated by means of a derivatograph. Under the conditions of the investigation, there were no indications of an interaction between the thermal decomposition products and the initial components, or of new intermediates with a thermostabilizing effect. A linear coorelation was obtained between the mass loss at 250°C and the urea content of the mixture, which may be used to determine the urea content of similar mixtures.     

Time-property least-squares spectral method for population balance equations

In multiphase chemical reactor analysis the dispersed phase distribution plays a major role in obtaining reliable predictions. The population balance equation is a well established equation for describing the evolution of the dispersed phase. However, the numerical solution of this type of equations is computationally intensive. In this work, a time-property least squares spectral method is presented for solving the population balance equation including breakage and coalescence processes. In this problem, both property and time are coupled in the least squares minimization procedure. Spectral convergence of the L ² least squares functional and L ² error norms in time-property is verified using a smooth solution to the population balance equation.     

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.