Measurement of bubble point pressures and critical points of carbon dioxide and chlorodifluoromethane mixtures using the variable-volume view cell apparatus

The bubble point pressures and the critical points of carbon dioxide (CO₂) and chlorodifluoromethane (HCFC-22) mixtures were measured by using a high-pressure experimental apparatus equipped with a variable-volume view cell, at various CO₂ compositions in the range of temperatures above the critical temperature of CO₂ and below the critical temperature of HCFC-22. The experimental bubble point pressure data were correlated with the Peng-Robinson equation of state (PR-EOS) to estimate the corresponding dew point compositions at equilibrium with the bubble point compositions. The experimentally measured bubble point pressures and the mixture critical points gave good agreement with those calculated by the PR-EOS. The variable-volume view cell equipment was verified to be an easy and quick way to measure the bubble point pressures and the mixture critical points of high-pressure compressible fluid mixtures.     

Prediction of vapour pressure of aqueous solutions of single and mixed electrolytes

A simple method is proposed for estimating the vapour pressures of aqueous single electrolyte solutions at 25°C. The method is based on a single empirical parameter, K. The treatment is extended to include different temperatures as well as solutions of mixed electrolytes. The estimation of vapour pressures in mixed solutions requires knowledge of the K values of constituent electrolytes and the vapour pressure of aqueous solutions of two reference electrolytes, viz. LiBr and NH₄NO₃ at 25°C. The calculated vapour pressures of single and mixed electrolyte solutions are in agreement with experimental data within 1.6% in general.     

Solubility of isobutane and propane in polyethylene at high temperatures and low pressures

A novel procedure was developed to measure the solubility of isobutane and propane in both low and high-density polyethylene at temperatures to 500°F (260°C) and vapor pressures from 1 to 1500 torr (33 psia). These measurements represent the first known solubility measurements at these combined extremes of pressure and temperature. Excellent agreement was found when our data were extrapolated to higher pressures and compared with data from another source. In the temperature and pressure regions of interest in this work, the linear isotherms were fit with a form of the Flory–Huggins equation. With the equation in that form we can now estimate the ratio of solubilities of two solutes in a given polymer from pure solute data only. We can also predict the absolute solubility of nonpolar solutes in polyethylene at various temperatures and pressures using only critical temperatures and acentric factors of the solutes.     

The critical temperatures and pressures of thirty organic compounds

Critical temperatures and pressures of some organic compounds were measured. There is good agreement between the observed critical pressures and values obtained by extrapolation of equations representing the variation of vapour pressure with temperature in the region of the normal boiling point. An incremental scheme relating critical temperatures to normal boiling points is described and is used for the correlation of the critical temperatures, obtained in this and other investigations, of more than 150 compounds.     

Viscosity of organic liquids at elevated temperatures and the corresponding vapour pressures

This work involved the measurement of the viscosities of pure organic liquids at temperatures ranging from 353.15 K to 463.15 K and at the corresponding vapour pressures. A rolling ball viscometer was used where considerable emphasis was given to achieve simplicity and rapidity in obtaining results, without sacrificing the accuracy. Considering the forces affecting the motion of the ball inside the viscometer tube, an equation for the calibration of the viscometer at the same working temperature was derived. The constants of this equation were determined using benzene as the reference liquid, and the dependency of the constants on the temperature was also established. Comparing the derived equation with published ones demonstrated its adequacy in both the streamline and transition flow conditions. The liquids studied were toluene, methanol and n-hexane. In some cases, the results compared reasonably well with published data while in others, deviations of up to 15% were found. Nine equations were tested with the experimental results for the prediction of the viscosity of these liquids. It was found that the 3-constant Agrawal and Thodos empirical equation gave the least average deviation.     

Thermal effects in polytetrafluoroethylene at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for polytetrafluroethylene (PTFE, Teflon) in the reference temperature range from 294° to 381°K and in the pressure range from 13.8 to 200 MN/m². The thermal effects were found to be higher at the reference temperature approximating the transition temperatures of 19° and 30°C than at higher reference temperature. The data were analyzed by determining the predicted thermoelastic coefficients derived from the Thomson equation (?T/?P = αT/ρC_p). A curvefitting analysis showed that the empirical curve, (?T/?P) = ab(ΔP)^b?1, described the experimental thermoelastic coefficients obtained from the experiments. The fact that no agreement was found between the predicted and the experimental coefficients is due to the physical changes in PTFE at the transition temperatures. The relationship between the thermal effects and the chain molecular motion is discussed by including dynamic mechanical analysis and differential scanning calorimetry DSC measurements for the PTFE samples.     

A modified van der Waals type equation of state

A cubic equation of the van der Waals type is presented with the critical compressibility factor taken as substance dependent. Input requirements are Pitzer's acentric factor and the critical temperature and pressure. Parameter b is treated as independent of temperature, and the temperature dependence of parameter a is given by an expression similar to that proposed by Soave. A test on vapour pressure is presented for more than one hundred substances and on liquid density for 65 substances and comparisons are given with results of Soave's and Peng-Robinson's equations. Representation of vapour pressure, particularly at low pressures, and of the liquid density has been improved. The equation is restricted to non-associating compounds.     

Phase equilibria in the H2/CO2 system at temperatures from 220 to 290 K and pressures to 172 MPa

Phase equilibria in the system H₂/CO₂ have been studied experimentally using a vapor-recirculating apparatus. Measurements of vapor and liquid phase compositions were made for ten temperatures ranging from 220 to 290 K and pressures to 172 MPa. The mixture critical line and the pressure-temperature trace of the three-phase region solid-liquid-vapor have been located. The three-phase region and the critical line intersect at T ? 234.8 K and P ? 198 MPa to form an upper critical end point. Experimental results have been compared with previous studies and with predictions of three equations of state, Peng-Robinson, Redlich-Kwong and Deiters. Expressions have been derived for temperature dependent critical parameters that account for quantum effects in H₂, in calculations for H₂/X systems using the Peng-Robinson equation.     

Tetralin vapour pressure at elevated temperatures

Vapour pressure of tetralin was measured at elevated temperatures up to 661 K. The experimental vapour pressure data obtained from this work and the literature have been correlated by multiple regression resulting in the equation: $\text{log P =}\text{?2549}\text{T?1.022}\text{× 10}{}^{\mathrm{?3}}\text{T + 7.804}$. This equation can be used to predict tetralin vapour pressure between the normal boiling point and the critical point with maximum error of ≈3%.     

A method for correlating and extending vapour pressure data to lower temperatures using thermal data: Vapour pressure equations for some n-alkanes at temperatures below the normal boiling point

Vapour pressures for many liquids are available in the range 50–760 torr but accurate determinations at lower pressures are frequently absent. Extrapolation based on purely empirical equations is hazardous and a convenient method is proposed for extrapolating such data to lower temperatures by utilizing readily available thermal data. The method is based on thermodynamically exact relationships. It has the advantage over previous such approaches that it makes greatest use of data, such as ideal gas and liquid heat capacities at around the temperature at which the vapour pressure is required, which are likely to be available. When applied to the n-alkanes C₆–C₁₆ from the normal boiling temperature down to a reduced temperature of 0·41 the method leads to a convenient vapour equation of the form ln p⁰ = alnT + bT ? (d/T) + E.The constants in this equation have been obtained in a systematic way from the available thermal, volumetric and vapour pressure data for these alkanes. These constants, together with vapour pressures and latent heats at 25°C calculated from them, are listed. Agreement between the calculated quantities at 25°C and experimental values (where available) is good.     

Investigation of bubble-point vapor pressures for mixtures of an endothermic hydrocarbon fuel with ethanol

Bubble-point vapor pressures and equilibrium temperatures for several mixtures with different mass fractions of a kerosene based endothermic hydrocarbon fuel (EHF) and ethanol were measured by comparative ebulliometry with inclined ebulliometers. Correlation between vapor pressures and equilibrium temperatures by the Antoine equation was given with satisfactory precision. The bubble-point lines of pressure versus composition at different temperatures and temperature versus composition at different pressures were obtained. The pseudo binary systems of EHF+ethanol appear with very large positive deviations from Raoult's law. It follows that the addition of ethanol had a critical effect on the vapor pressure of fuels. Ethanol may be an effective oxygenated hydrocarbon additive to adjust the volatility of EHF.     

Interaction model for the critical pressures of aliphatic hydrocarbon mixtures

An interaction model is proposed for the prediction of the critical pressures of multicomponent aliphatic hydrocarbon mixtures which may include methane. This model utilizeg a series consisting of terms of increasing order which has been truncated beyond the fifth interaction term. After a number of algebraic manipulations, the excess critical pressure for these multicomponent mixtures has been represented as follows The nonmethane interaction coefficients A_ij, B_ij, C_ij and β_ijk and the methane interaction coefficients A_1j, B_1j, C_1j, D_1j and β_1jk have been expressed as functions of the critical pressure parameter, π_ij. The resulting relationships permit the evaluation of these interaction coefficients for a multicomponent system and from its composition, the critical pressure of the mixture is calculated. The critical pressures of several binary and multicomponent aliphatic hydrocarbon mixtures have been calculated and have been compared with experimental values. For 99 binary methane-free mixtures representing 11 systems, the average deviation is 3.23%. For 46 binary mixtures representing six methane systems, the average deviation becomes 4.41 %. For 36 multicomponent aliphatic hydrocarbon mixtures containing from three to six components, the average deviation is found to be 3.18%.     

Accelerated thermal aging of NBR and other materials under air or oxygen pressures

Accelerated thermal degradation of nitrile-butadiene rubber, ethylene-propylene rubber, low density polyethylene and glass reinforced epoxy resin was studied (a) in air, at atmospheric pressure, and various temperatures and (b) in air or oxygen at various pressures (P > 1 atm) and temperatures. On the basis of the experimental results, a kinetic equation of thermal degradation of investigated materials has been derived.     

Thermal dissociation of Ca(OH)2 at elevated pressures

The equilibrium Ca(OH)₂ ? CaO+H₂O has been studied at pressures of steam up to 50 bars and at temperatures of up to 800° C. The dissociation pressures determined are in agreement with the data derived by some previous workers at pressures of less than one bar but they conflict with data published for higher pressures. The results can be expressed by the relation over the range 530–800°c.     

Combustion of aniline droplets at high pressures

The combustion of aniline droplets is well described by the “d² law” up to about 200 psia. At higher pressures turbulence and flame opacity prevent the reliable measurement of droplet diameter but the burning mechanism appears not to change as long as the pressure is less than the critical pressure of aniline. Above the critical pressure of aniline a completely different combustion mechanism is observed.     

Vapour pressure and vapourisation enthalpy of pyridine N‐oxide

The vapour pressure of pyridine N‐oxide was measured using a boiling point method at different temperatures from 389.02 to 546.33 K and the constants of the Antoine equation for the substance were determined. The vapourisation enthalpy of pyridine N‐oxide at the normal boiling point is calculated to be 58.8 ± 1.8 kJ mol^?1. Based on Othmer's method, the standard enthalpy of vapourisation is estimated to be 66.6 ± 0.1 kJ mol^?1 by using pyridine as the reference substance. Furthermore, Watson equation is employed to verify the reliability of and the results demonstrate that the value of is acceptable. © 2011 Canadian Society for Chemical Engineering     

Miscibility,phase separation,and volumetric properties in solutions of poly(dimethylsiloxane) in supercritical carbon dioxide

Miscibility conditions and volumetric properties of solutions of poly(dimethylsiloxane) in supercritical carbon dioxide have been determined as a function of polymer molecular weight, polymer concentration, temperature, and pressure. Measurements have been conducted in a variable volume view cell equipped with an LVDT sensor to identify the position of a movable piston and thus the internal volume of the cell and consequently the density of the solution at a given pressure and temperature. The demixing data (in the form of P‐T curves for a given concentration, or as P‐x diagrams at a given T) and the density isotherms are presented for solutions of two polymer samples with different molecular weights (M_w = 38,600; M_w/M_n = 2.84 and M_w = 94,300; M_w/M_n = 3.01) at several concentrations in the range from 0.05 to 10 mass % over a temperature range from 302–425 K. Solution densities corresponding to the demixing points also have been identified. Representation of the demixing densities on the density isotherms, i.e., pressure‐density plots is a new methodology that gives a direct assessment of the volumetric expansion the solution must undergo before phase separation. The temperature–composition diagrams generated at selected pressures show that the poly(dimethylsiloxane) + CO₂ solutions display both lower critical solution and upper critical solution type behavior. The lower critical solution temperature moves to lower temperatures and the upper critical solution temperature moves to higher temperatures with decreasing pressure and they eventually merge together at lower pressures forming an hourglass‐shaped region of immiscibility. This behavior is linked to the solvent quality of supercritical carbon dioxide that changes with pressure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1397–1403, 2000     

Vapour-liquid equilibria of hydrogen/coal liquid and methane/coal liquid systems at elevated temperatures and pressures

A cubic equation of state is modified in such a way that prediction of PVT data from 40 model compounds, typical of coal oil, becomes possible with an absolute mean deviation of less than 2% for saturated liquid volumes and vapour pressures > 1 bar. Additional correlations for binary interaction parameters are obtained by an optimization procedure using vapour-liquid euilibrium (VLE) data from known heavy hydrocarbon liquid/light gas systems. When the modified equation is applied to coal-derived liquids, only specific gravity and boiling analysis data of the coal liquids are required, primarily in order to determine the equation-of-state parameters. The proposed equation is shown to allow a good prediction of VLE data for systems consisting of wide-boiling-range coal oils and light gases. Experimental values were obtained at elevated temperatures and pressures with a circulation flow apparatus.