Adsorption deformation of a microporous AR-V carbon adsorbent during the adsorption of <Emphasis Type="Italic">n</Emphasis>-hexane

Adsorption isotherms of n-hexane and adsorption deformation isotherms of an AR-V carbon adsorbent are measured in a pressure range of 1 Pa to 20 kPa at temperatures of 254.8–353 K. It is found that, except for the initial pressure range (p < 800 Pa), the relative linear deformation increases with increasing pressure and decreases with increasing temperature. At temperatures of 254.8, 273.2, and 293 K, the curves of adsorption and adsorption deformation exhibit hysteresis in the region close to the saturated vapor pressure. It is noted that, at pressures below 800 Pa, microporous AR-V carbon adsorbent undergoes contraction in the range of high temperatures. It is revealed that the contraction range of the adsorbent with respect to pressure gradually narrows with decreasing temperature and degenerates at 254.8 K.     

Viscosity Arrhenius Activation Energy and Derived Partial Molar Properties in 1,4-Dioxane + Water Binary Mixtures from 293.15 to 323.15 K

The knowledge and prediction of physicochemical properties of binary liquid mixtures is of great importance for understanding intermolecular interactions. Viscosities (η) have been investigated by using density (ρ) and kinematic viscosity (ν) measurements for 1,4-dioxane + water (D–W) mixtures over the entire range of mole fractions under atmospheric pressure, at 311.15, 316.15 and 320.15 K, in order to increase the studied temperatures range available from the literature and to improve the investigations. The viscosity Arrhenius activation energy of 1,4-dioxane + water mixtures was calculated from the present experimental viscosity measurements, and those presented in a previous work at only four temperatures, and for three temperatures in the present work, over the entire range of composition in the temperatures range from 293.15 to 323.15 K. Based on the partial molar activation energy from the Arrhenius equation for viscosity, interactions between water and 1,4-dioxane molecules are discussed. Comparison between some reduced Redlich–Kister functions covering the composition domain shows the existence of two distinct behaviors.     

Heat capacity,saturation vapor pressure,and thermodynamic functions of ethyl esters of C<Subscript>3</Subscript>–C<Subscript>5</Subscript> and C<Subscript>18</Subscript> carboxylic acids

The heat capacities of ethyl propanoate (EPr), ethyl n-pentanoate (EPen), and ethyl n-octadecanoate (ethyl stearate, ESt) were measured by vacuum adiabatic calorimetry in the temperature range of 6 to 373 K. Triple point temperatures, fusion enthalpies and entropies, and purity of the samples of the sub-stances under study were determined. The saturation vapor pressures for EPr and EPen were determined by comparative ebulliometry in an atmospheric pressure range of 4.0 to 101.7 kPa. The normal boiling points and vaporization enthalpies vs. temperature were obtained. The standard thermodynamic functions (S, H, and G) were calculated for the condensed and ideal gas states on the basis of the experimental data. The vapor pressures of the atmospheric range were extrapolated to entire ranges of the liquid phases of EPr and EPen using the principle of corresponding states and the combined processing of pT parameters and low-temperature differences in the heat capacities of an ideal gas and liquid.     

Thermodynamic and experimental study of the interaction of silicon and carbon monoxide: Synthesis of silicon carbide nanofibers

The reaction of crystalline silicon with carbon monoxide to produce silicon carbide was studied. Thermodynamic simulation of the equilibrium phase composition of the nSi-mCO system was carried out in the range 300–2000 K (27–1727°C). Conditions required for silicon carbide was carried out applying various experimental modes (n, m, and T) and possible pathways of the reactions were determined. Interaction between crystalline silicon and carbon monoxide formation in a temperature range of 1000–1450°C. The order of the reaction in CO was found to be close to unity. Silicon carbide nanofibers with thicknesses of from 5 to 100 nm were synthesized and characterized by powder X-ray diffraction, mass-spectral elemental analysis, and scanning electron microscopy. A possibility of synthesizing high-purity silicon carbide fibers were experimentally evaluated.     

The low-temperature heat capacity and saturation vapor pressure of ethyl ester of butanoic acid

The heat capacity, thermodynamic properties of fusion, and purity of the ethyl ester of butanoic acid were determined by adiabatic calorimetry in the temperature range from 8 to 372 K. The pT-parameters of the ester for the equilibrium liquid-vapor were measured by comparative ebulliometry in the “atmospheric” range of pressure from 10.8 to 101.7 kPa. The obtained data were used to derive the normal boiling temperature (T _n.b), the enthalpies of vaporization at T = 298.15 K and T _n.b, and the main thermodynamic functions (changes of S, H, G) in the crystal and liquid states of the temperature interval studied and in the ideal gas state at T = 298.15 K. The experimental vapor pressures of the narrow temperature interval, ΔT = 62 K were extended to the entire range of the liquid, T _cr − T _tp⁰ = 394.3 K, from the triple, T _tp⁰, to the critical, T _cr, temperatures.     

Densities and Apparent Molar Volumes of NaOH(aq) to the Temperature 623 K and Pressure to 30 MPa

Densities of NaOH(aq) solutions with molalities between 0.033 and 6.047 mol⋅kg⁻¹ were measured with a vibrating-tube densitometer at temperatures between 373 K and 623 K and pressures from near the saturation vapor pressure of water to 30 MPa. Apparent molar volumes, V _φ, calculated from the measured densities in this work were well represented with the Pitzer ion-interaction treatment up to T = 523 K. Above that temperature the formation of ion pairs must be taken into account to describe correctly the molality dependence of V _φ and for the reliable extrapolation of V _φ to infinite dilution. Standard-state thermodynamic properties for the ion formation reaction were taken from recently published electrical conductivity measurements. A comparison with previous correlations of volumetric properties of NaOH(aq) is presented covering the full range of pressure and temperature.     

The ionization of aqueous ammonia to 300°C in KCl media

A potentiometric technique using a hydrogen electrode concentration cell with flowing solutions was employed to study the ionization of ammonia over the temperature range 50–295°C in KCl media from 0.04 to 3.3m. The isothermal pressure coefficient of the ionization reaction was obtained at pressures up to 100 bars and temperatures to 250°C in these same media, and was found to vary as the square root of the ionic strength within the experimental error. Smoothing functions have been presented which also fit selected published data on the ammonia ionization reaction with a standard error of fit of 1.8 times the assigned uncertainties. Thermodynamic parameters for the reaction have been tabulated at rounded temperatures, and ionic strengths at the saturation vapor pressure. A limit is given for the association quotient of HCl at 300°C in 3m KCl based on these data.     

Phase separation in the (R4N)2[Nd(NO3)5]-hydrocarbon solvent-chloroform systems at various temperatures

Phase diagrams were studied for (R₄N)₂[Nd(NO₃)₅]-C _n H_{2n + 2}-chloroform liquid ternaries (where R₄N⁺ is trialkylbenzylammonium and n = 10, 12, 14, or 15) at T = 298.15−333.15 K. (R₄N)₂[Nd(NO₃)₅]-C _{n H2n + 2} binaries are two-phase liquid systems at all temperatures in this range. One phase (phase I) is an almost pure hydrocarbon solvent. The other (phase II) is enriched in (R₄N)₂[Nd(NO₃)₅]. The C _n H_{2n + 2} solubility in phase II decreases with increasing the alkyl chain length of the hydrocarbon solvent and increases with increasing temperature. The title liquid ternaries are characterized by a homogeneous solution field and a two-phase liquid solution field. One phase is enriched in (R₄N)₂[Nd(NO₃)₅] and chloroform; the other is enriched in the hydrocarbon solvent. Liquid-liquid phase separation fields enlarge with increasing C _n H_{2n + 2} alkyl chain length and slightly narrow with increasing temperature. Critical solution points at fixed temperatures depend on C _n H_{2n + 2}. Original Russian Text ? A.K. Pyartman, V.A. Keskinov, P.V. Zaitsev, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 3, pp. 531–534.     

PVT properties of an alternative biofuel: dimethyl ether

Dimethyl ether is an important chemical material and it has many engineering applications. It is a clean and economical alternative fuel and an ozone-friendly refrigerant. In this work, its PVT properties have been object of study. In particular, the experimental work was performed both in the two-phase region and in the superheated vapor region phase by means of the isochoric method. The isochoric measurements were carried out at temperatures from 219 K to 363 K and at pressures from 22 kPa up to 1,740 kPa. A total of 159 points, both in the two phase (71 points) and in the superheated vapor region (88 points) were obtained. The present experimental PVT data contribute to the deeper knowledge of the behaviour of the fluid both in the superheated vapour and in the saturation pressure region and to the development of a new equation of state.     

Volumetric properties of 1-iodoperfluorohexane+<Emphasis Type="Italic">n</Emphasis>-octane binary system at several temperatures

New densities are reported over the whole composition range for 1-iodoperfluorohexane+n-octane system at temperatures from 288.15 to 308.15 K at atmospheric pressure. These data have been used to compute the excess molar volumes, V _m ^E. Large positive V _m ^E values have been obtained over the entire range of composition, which increases when the temperature rises. The experimental data were used to calculate the isobaric thermal expansivity, and the quantities (∂V _m ^E/∂T)_p and (∂H _m ^E/∂p)_T. Furthermore, the results have been used to investigate the volumetric prediction ability of the equations of state Soave–Redlich–Kwong, Peng–Robinson, Patel–Teja and Soave–Redlich–Kwong with volume translation.     

Competition of Viscosity Correlation Equations in Isobutyric Acid + Water Binary Mixtures Near and Far Away from the Critical Temperature

Shear viscosity deviations Δη have been investigated by using density (ρ) and kinematic viscosity (ν) measurements for isobutyric acid + water (IBA + W) mixtures over the entire range of mole fractions at atmospheric pressure and at two temperatures (301.15 and 315.15 K). This study extends the temperature range from the five other temperatures investigated in a previous work, 1.055 K≤(T−T _c )≤14.055 K, both far from and close to the critical temperature. This system exhibits very large positive values of Δη due to increased hydrogen bonding interactions and the correlation length between unlike molecules in the critical region, and to very large differences between the molar volumes of the pure components at low temperatures. The results were also fitted with the Redlich–Kister polynomial equations and the recently proposed Herráez correlation equation. Comparisons between the two models at different temperatures and number of parameters are discussed. We note that, in this system where the shear viscosity η as a function of mole fraction (x ₁) of IBA presents a maximum, experimental data are in agreement with the two correlation models when more than three parameters are employed, especially for temperatures far from the critical temperature.     

Low-temperature Data for Carbon Dioxide

Summary. We investigated empirical data for the vapor pressure (154≤T≤196 K) and the heat capacity (12.52≤T≤189.78 K) of solid carbon dioxide. A computer algebra system (CAS) was used for all calculations. From the numerical point of view, we have adopted a cubic piecewise polynomial representation for the heat capacity and reached an excellent agreement between the available empirical data and the calculated ones. Furthermore, we have obtained values for the vapor pressure and heat of sublimation at temperatures below 195 right down to 0 K. The theoretical key prerequisites are: 1) Determination of the heat of sublimation of 26250 J · mol⁻¹ at vanishing temperature and 2) Elaboration of a ‘linearized’ vapor pressure equation that includes all the relevant properties of the gaseous and solid phases. It is shown that: 1) The empirical vapor pressure equation derived by Giauque & Egan remains valid below the assumed lower limit of 154 K (a similar argument holds for Antoine’s equation), 2) The heat of sublimation reaches its maximum value of 27211 J · mol⁻¹ at 58.829 K and 3) The vapor behaves as a (polyatomic) ideal gas even for temperatures below 150 K.     

Low-temperature Data for Carbon Dioxide

We investigated empirical data for the vapor pressure (154≤T≤196 K) and the heat capacity (12.52≤T≤189.78 K) of solid carbon dioxide. A computer algebra system (CAS) was used for all calculations. From the numerical point of view, we have adopted a cubic piecewise polynomial representation for the heat capacity and reached an excellent agreement between the available empirical data and the calculated ones. Furthermore, we have obtained values for the vapor pressure and heat of sublimation at temperatures below 195 right down to 0 K. The theoretical key prerequisites are: 1) Determination of the heat of sublimation of 26250 J · mol⁻¹ at vanishing temperature and 2) Elaboration of a ‘linearized’ vapor pressure equation that includes all the relevant properties of the gaseous and solid phases. It is shown that: 1) The empirical vapor pressure equation derived by Giauque & Egan remains valid below the assumed lower limit of 154 K (a similar argument holds for Antoine’s equation), 2) The heat of sublimation reaches its maximum value of 27211 J · mol⁻¹ at 58.829 K and 3) The vapor behaves as a (polyatomic) ideal gas even for temperatures below 150 K.     

Isopiestic Determination of the Osmotic and Activity Coefficients of K<Subscript>2</Subscript>HPO<Subscript>4</Subscript>(aq), Including Saturated and Supersaturated Solutions,at <Emphasis Type="Italic">T</Emphasis>=298.15 K

The osmotic coefficients of K₂HPO₄(aq) have been measured at T=298.15 K by the isopiestic vapor pressure method over the range of molalities from 1.3846 mol⋅kg⁻¹ to 13.939 mol⋅kg⁻¹ (oversaturation) with CaCl₂(aq) as the reference solution. The molalities and osmotic coefficients of saturated solutions in equilibrium with K₂HPO₄⋅xH₂O(cr) were measured simultaneously by the same method. Available literature osmotic coefficients of K₂HPO₄(aq) at T=298.15 K, and our new experimental data, were combined and modeled using an extended form of Pitzer’s equation and the Clegg-Pitzer-Brimblecombe equation based on the mole-fraction-composition scale. These equations were used to calculate the activity coefficients of K₂HPO₄(aq) at T=298.15 K.     

Measurement of water activities of alanine + tri-potassium citrate + water system at temperatures between 293.15 and 313 K—Experimental and modeling

Water activity measurements by isopiestic method have been carried out on the aqueous solutions of alanine + tri-potassium citrate (K₃Cit) over a range of temperatures at atmospheric pressure. From these measurements, values of the vapor pressure of solutions were determined. The effect of temperature on the vapor–liquid equilibrium of alanine + K₃Cit + H₂O systems has been studied. The experimental water activities have been correlated successfully with the segment-based local composition Wilson and NRTL models. The agreement between the correlations and the experimental data is good.     

Excess molar enthalpy for methanol,ethanol, 1-propanol, 1-butanol + <Emphasis Type="Italic">n</Emphasis>-butylamine mixtures at 288.15 and 308.15 K at atmospheric pressure

Experimental data of excess molar enthalpy (H _m^E) of binary liquid mixtures containing (methanol or ethanol or 1-propanol, or 1-butanol) + n-butylamine mixtures have been determined as a function of composition at temperatures 288.15 and 308.15 K, at atmospheric pressure, using a modified 1455 PARR mixture calorimeter. The H _m^E values are negative for both systems over the whole composition range. The applicability of the ERAS Model to correlate H _m^E of mixtures studied is tested, and the agreement between experimental and theoretical results is satisfactory. The model results are discussed in terms of the cross-association interactions with temperature variation as well as in terms of the variation of the carbon chain in the alcohols presents in the mixtures.     

Phase compositions and saturated densities for the binary systems of carbon dioxide with ethanol and dichloromethane

The compositions and densities of the liquid and vapor phases of two binary systems at equilibrium were measured on a new experimental apparatus over a range of temperatures and pressures. The studied systems are: CO₂–ethanol at 313.2 and 328.2 K; CO₂–dichloromethane at 308.2, 318.2 and 328.2 K and for pressures ranging from ambient up to ca. 9 MPa. Some of our measurements are critically compared with corresponding literature values. These measurements are ideally suited for testing equation-of-state models. The recently developed quasi-chemical hydrogen-bonding (QCHB) model was used for correlating the experimental data. A satisfactory agreement was obtained between experimental and calculated phase compositions and saturated densities.     

Vapor Pressure and Heat of Sublimation of Crystal Polymorphs

In order to determine the applicability of vapor pressure studies on polymorphic modifications, pairs of enantiotropically related modifications of caffeine, theophylline and carbamazepine were investigated. The studies were performed over a wide temperature range (71 to 191°C) and accordingly over a wide vapor pressure range (0.02 to 400 Pa) using an automatic instrument constructed on the basis of the gas saturation principle. This instrument enables an analytical determination of the main component and the impurities present by the chromatographic separation of the substances transported in the gas flow. Therefore, the real partial pressure of the main component can be measured. Due to the high precision of the applied method it was possible to determine partial pressure curves and the thermodynamic transition temperature — the point at which the vapor pressure of two crystal polymorphs is equal. The thermodynamic transition temperatures of caffeine and theophylline were determined to be 136 and 232°C, respectively. These values are in agreement with experimental or calculated values derived from DSC investigations but are more reliable. Vapor pressure measurements of carbamazepine are only meaningful in the low temperature range due to its decomposition at high temperatures. The thermodynamics, advantages and limits of vapor pressure determinations of polymorphic modifications are discussed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Liquid—vapor equilibrium in the system H2Ar at temperatures from 83 to 141 K and pressures to 52 MPa

Calado, J.C.G. and Streett, W.B., 1979. Liquid—vapor equilibrium in the system H₂Ar at temperatures from 83 to 141 K and pressures to 52 MPa. Fluid Phase Equilibria, 2: 275–282.Experimental measurements of liquid—vapor phase equilibria in the system H₂Ar are reported for thirteen temperatures in the range 83.09 to 141.42 K, and pressures to 52 MPa. The mixture critical line and the pressure—temperature trace of the three-phase line solid—liquid—gas have been located. These lines intersect at T = 84.0 K and P = 52.5 MPa to form an upper critical end point. The pressure—temperature trace of the three-phase line has a temperature minimum at T ? 82.5 K, P ? 20 MPa.     

Determination of the saturation vapor pressure of silicon by Knudsen cell mass spectrometry

Silicon evaporation has been investigated by high-temperature mass spectrometry, and the saturation vapor pressure of silicon over its melt has been determined over the temperature range from 1739 and 2326 K. The saturation vapor pressure data obtained via silicon evaporation from Knudsen cells made of molybdenum, tungsten, molybdenum disilicide-lined molybdenum, and graphite silicided by the gas-phase method are compared. Among these materials, silicided graphite is the most inert toward silicon vapor. The silicon partial pressures measured in the silicided graphite cell are close to the recommended values.