Prediction of enthalpies of vaporization based on modified Randič indices. Esters

In the work a prediction method based on modified Randi? indices to estimate the enthalpies of vaporization under standard conditions Δ_vapH⁰(298.2) is proposed for esters with different structures and numbers of ester groups. It is shown that the proposed method enables the prediction of enthalpies of vaporization of esters with an accuracy as good as experimental.     

Prediction of vaporization enthalpies based on modified Randič indices. Aldehydes and ketones

A method to predict the vaporization enthalpies of aldehydes and ketones of different structures under normal conditions is proposed based on the modified Randi? method.     

Prediction of the vaporization enthalpy based on modified Randič indices. II. Polyatomic alcohols

The vaporization enthalpy of polyatomic alcohols with different structures under normal conditions is calculated using a modified Randič method. The vaporization enthalpy of polyatomic alcohols is shown to largely depend on the number of hydrogen bonds formed by alcohols.     

Prediction of the enthalpy of vaporization based on modified Randi? indices. Ethers

A method to predict the enthalpies of vaporization of ethers with various structures under normal conditions using a modified Randič method is proposed.     

Prediction of the vaporization enthalpy based on modified Randi? indices. I. Monohydric alcohols

The vaporization enthalpy of monohydric alcohols with different structures under normal conditions is calculated using a modified Randič method with an error comparable to the experimental one. The energy of hydrogen bonds in alcohols is determined and shown to be constant and independent on the alcohol structure. Original Russian Text Copyright ? 2009 by E. L. Krasnykh __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 3, pp. 577–581, May–June, 2009.     

Prediction of the vaporization enthalpy based on modified randič indices. III. Carbonic acids

The vaporization enthalpies of mono- and dicarbonic acids with different structures are calculated under normal conditions using the modified Randič method and the energies of hydrogen bonds. The results demonstrate good agreement between the experimental and calculated data.     

Low-temperature heat capacity of β-glycine and a phase transition at 252 K

Low-temperature heat capacity of unstable -glycine was measured in a temperature range 5.5 to 295 K, and thermodynamic functions were calculated. At very low temperatures, heat capacity fits a sum of cubic (Debye) and linear terms: C_p=aT+bT ³. The linear contribution increases with temperature and disappears at the second-order phase transition near 252 K which was observed for the first time.     

Melt–vapor phase transition in the lead–selenium system at atmospheric and low pressure

The boiling temperature and the corresponding vapor phase composition in the existence domain of liquid solutions were calculated from the partial pressures of saturated vapor of the components and lead selenide over liquid melts in the lead–selenium system. The phase diagram was complemented with the liquid–vapor phase transition at atmospheric pressure and in vacuum of 100 Pa, which allowed us to judge the behavior of the components during the distillation separation.     

Calculation of pVT and vapor–liquid equilibria of copolymer systems based on an equation of state

A molecular thermodynamic model for copolymers and their mixtures has been established by adopting the hard-sphere-chain fluid as a reference and a square-well (SW) term as well as an association term as a perturbation. The latter is introduced to consider various associating functions in a chain-like molecule based on the shield-sticky model of chemical association. The model adopts five molecular parameters, i.e. r_i, σ_ii ε_ii/k, δε_ii/k and ω_ii, for a polymer species i, where the last two are responsible for association. These parameters can be obtained from the pVT data of the corresponding molten homopolymer i. The model can be used to correlate pVT data for molten copolymers with an adjustable parameter describing the interaction between different polymer species. The model can also be used to calculate vapor–liquid equilibria (VLE) for copolymer solutions with three adjustable interaction parameters.     

Prediction of the auto-ignition temperature of binary liquid mixtures based on the quantitative structure–property relationship approach

Journal of Thermal Analysis and Calorimetry - The auto-ignition temperature (AIT) is one of the most important parameters in flammability risk assessment and management in the chemical process....     

Separation of chiral phosphorus compounds on the substituted P-cyclodextrin stationary phase in normal-phase liquid chromatog-raphy

The separation of enantiomers of a series of eighteen novel nitrogen mustard linked phosphoryl diamide derivatives was investigated on the prepared phenyl carbamate derivative β-cy-clodextrin bonded phase in normal-phase HPLC. Some of the enantiomers could be separated in baseline. The chiral recognition mechanism was also suggested for the separation of chiral phosphorus organic compounds.     

Automated apparatus for the rapid determination of liquid–liquid and solid–liquid phase transitions

An automated apparatus developed for the determination of liquid–liquid and solid–liquid equilibrium temperatures with a resolution of 1 mK and a traceable accuracy of 0.01 K is described. The amount of light transmitted through six sample cells placed in a computer controlled thermostat is recorded at heating or cooling rates from 0.075 to 15 K h⁻¹. The construction does not require expensive optic equipment like lasers, glass fibre optics or photomultipliers, but is based on light emitting diodes (LED) as light sources and light dependent resistors (LDR) or photodiodes as detectors. As shown by the discussed examples, the instrument has a wide range of possible applications from the investigation of simple one-component and binary systems to the study of the complicated phase behavior of surfactant solutions.     

Correlation and prediction of salt effects on vapor–liquid equilibrium in alcohol–water–salt systems

A modification of the solvation model of Ohe is proposed for the calculation of vapor–liquid equilibria (VLE) in alcohol–water–salt systems. The modified method employs the Bromley equation to calculate the activity of water in salt solutions, and a one-parameter empirical expression to calculate the activity of the alcohol. The single parameter is obtained by fitting ternary alcohol–water–salt data. The method is simple to use and does not require data on the vapor-pressures of alcohol–salt mixtures that are seldom available in the literature. Experimental data for 17 salts in 36 alcohol–water–salt systems, covering a temperature range from 298 to 375 K, and salt concentrations up to about 8 m, were correlated using the new approach. In all, 69 data sets and 1045 data points were correlated satisfactorily. The method was also used to predict VLE in four ternary alcohol–alcohol–salt systems and one quaternary alcohol–alcohol–water–salt system with satisfactory results.     

Molecular simulation of the phase behaviour of ternary fluid mixtures: the effect of a third component on vapour–liquid and liquid–liquid coexistence

The Gibbs ensemble algorithm is implemented to determine the vapour–liquid and liquid–liquid phase coexistence of dilute ternary fluid mixtures interacting via a Lennard–Jones potential. Calculations are reported for mixtures with a third component characterised by different intermolecular potential energy parameters. Comparison with binary mixture data indicates that the choice of energy parameter for the third component affects the composition range of vapour–liquid substantially. The addition of a third component lowers the energy of liquid phase while slightly increasing the energy of the vapour phase.     

Influence of the anisometry of magnetic particles on the isotropic–nematic phase transition

The influence of the shape anisotropy of magnetic particles on the isotropic–nematic phase transition was studied in ferronematics based on the nematic liquid crystal (LC) 4-(trans-4-n-hexylcyclohexyl)-isothiocyanato-benzene (6CHBT). The LC was doped with spherical or rod-like magnetic particles of different size and volume concentrations. The phase transition from isotropic to nematic phase was observed by polarising microscope as well as by capacitance measurements. The influence of the concentration and the shape anisotropy of the magnetic particles on the isotropic–nematic phase transition in LC are demonstrated here. The results are in a good agreement with recent theoretical predictions.     

The calculation of Cs and Rb conductivities in the region of liquid–plasma transition

The conductivity and thermal conductivity of Cs and Rb are calculated in the liquid phase and in the region between the plasma (gas) and the liquid states. The last area is located at the temperatures higher than the critical one, near the critical point. The Ziman formalism originated from the liquid metal theory was used for the calculations. The results of present calculations were compared with available experiments and calculations of other researchers. It was found that the liquid state formalism can be applied to expanded liquid Cs and Rb at densities higher than the critical one, but another type of models is necessary at lower densities.     

Modelling of high-pressure phase equilibria using the Sako–Wu–Prausnitz equation of state: II. Vapour–liquid equilibria and liquid–liquid equilibria in polyolefin systems

Phase equilibria in binary and ternary polyolefin systems are calculated using the cubic equation of state proposed by Sako–Wu–Prausnitz (SWP). Calculations were done for high-pressure phase equilibria in ethylene/polyethylene (LDPE) systems and for liquid–liquid equilibria (LLE) in systems containing either high-density polyethylene or poly(ethylene-co-propylene). The calculations for the copolymer/solvent systems are compared with those using the SAFT EOS. The two equations of state can describe UCST, LCST as well as U-LCST behaviour with similar accuracy. Whereas, the binary interaction parameter is temperature-independent for SAFT, it is found to be a function of temperature for the SWP model. Moreover, the influence of an inert gas on the LCST of the polyethylene/hexane system is investigated using the SWP EOS. The polydispersity of the different polyethylenes is considered in the phase equilibrium calculations using pseudocomponents chosen by the moments of the experimental molecular weight distributions.