High-pressure phase behaviour of the binary system {CO2 + cis-decalin} from (292.75 to 373.75) K

The phase behaviour of the {CO₂ (1) + cis-decalin (2)} binary system has been experimentally studied at temperatures ranging from (292.75 to 373.75) K. Saturation pressures, ranging from (15.9 to 490.5) bar, were obtained using a variable volume high-pressure cell by visual observation of phase transitions at constant overall composition. For this system, no literature data are available and the results obtained in this study reveal the occurrence of vapor–liquid, liquid–liquid, and vapor–liquid–liquid phase transitions in the investigated temperature range. A total of 133 experimental points are reported including bubble points, dew points, liquid–liquid phase equilibria, and coordinates of the three-phase line. The experimental data can be reasonably predicted by the PPR78 model in which the temperature-dependent binary interaction parameter is calculated by a group contribution method.     

Carbon dioxide-methane mixture adsorption on activated carbon

In this work, we report new experimental data of pure and binary adsorption equilibria of carbon dioxide and methane on the activated carbon RB2 at 273 and 298 K. The pressure range studied were 0–3.5 MPa for pure gases and 0–0.1 MPa for mixtures. The combination of the generalized Dubinin model to describe the pure CO₂ and CH₄ isotherms with the IAST (Ideal Adsorbed Solution Theory) for the mixtures provide a method for the calculation of the binary adsorption equilibria. This formulation predicts with acceptable accuracy the binary adsorption data and can easily be integrated in general dynamic simulation of PSA (pressure swing adsorption process) adsorption columns. It involves only three parameters, independent of the temperature, and directly determined with only one adsorption isotherm of CO₂.     

Modeling the vapor–liquid equilibria of polymer–solvent mixtures: Systems with complex hydrogen bonding behavior

The vapor–liquid equilibria of binary polymer–solvent systems was modeled using the Non-Random Hydrogen Bonding (NRHB) model. Mixtures of poly(ethylene glycol), poly(propylene glycol), poly(vinyl alcohol) and poly(vinyl acetate) with various solvents were investigated, while emphasis was put on hydrogen bonding systems, in which functional groups of the polymer chain can self-associate or cross-associate with the solvent molecules. Effort has been made to explicitly account for all hydrogen bonding interactions. The results reveal that the NRHB model offers a flexible approach to account for various self- or cross-associating interactions. In most cases model's predictions (using no binary interaction parameter k_ij = 0) and model's correlations (using one temperature independent binary interaction parameter, k_ij ≠ 0) are in satisfactory agreement with the experimental data, despite the complexity of the examined systems.     

Equation of state for the NH3−H2O system

An equation of state (EOS) for the NH₃–H₂O system has been developed. This EOS incorporates a highly accurate end-member EOS and on an empirical mixing rule. The mixing rule is based on an analogy with high order contributions to the virial expansion for mixtures. Comparison with experimental data indicates that the mixed system EOS can predict both phase equilibria and volumetric properties for this binary system with accuracy close to that of the experimental data from 50°C and 1 bar to critical temperatures and pressures.     

Concentrated electrolyte solutions at high temperatures and pressures

A survey is given of recent experimental results obtained from high-temperature, high-pressure investigations with water, aqueous solutions, and ionic fluids. Data on the static dielectric constant of water to 550°C and 5 kbar are given and discussed with respect to their relation to water structure. Infrared and Raman spectra of HDO in pure water have been obtained to 400°C and 4 kbar, which give information on hydrogen bonding. Xe–H₂O and CO₂–H₂O mixtures were investigated in the infrared. Ni(II) and Cu(II) complexes were investigated by absorption spectroscopy in aqueous solutions of high chloride content to 350°C and 2–6 kbar. The gas-liquid critical point of ammonium chloride was found at 880°C and 1635 bars. This fluid appears to be predominantly ionic even in the critical region. The possibility of converting pure polar fluids such as ammonia and water into concentrated ionic solutions by self-ionization at very high pressures is mentioned.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

High-pressure vapor–liquid and vapor–liquid–liquid equilibria in the carbon dioxide + 1-heptanol system

Vapor–liquid equilibria (VLE) and vapor–liquid–liquid equilibria (VLLE) data for the carbon dioxide + 1-heptanol system were measured at 293.15, 303.15, 313.15, 333.15 and 353.15 K. Phase behavior measurements were made in a high-pressure visual cell with variable volume, based on the static-analytic method. The pressure range under investigation was between 0.58 and 14.02 MPa. The Soave–Redlich–Kwong (SRK)-EOS coupled with Huron–Vidal (HV) mixing rules and a reduced UNIQUAC model, was used in a semi-predictive approach, in order to represent the complex phase behavior (critical curve, LLV line, isothermal VLE, LLE, and VLLE) of the system. The topology of phase behavior is qualitatively correct predicted.     

Studies on ion exchange equilibria and kinetics VI. Prediction of ion exchange equilibria of UO 2 2+ −Na+−H+ ternary system

Experimental data are reported for the ion exchange equilibria of the binary systems UO ₂ ²⁺ –H⁺, UO ₂ ²⁺ –Na⁺ and Na⁺–H⁺, and of the ternary system UO ₂ ²⁺ –Na⁺–H⁺ on a strong acid cation exchange resin 001X7 at 25 °C. It is found that the equilibria for any pairs of ions are essentially the same in binary and ternary mixtures and that the prediction method proposed by our laboratory for SO ₂ ^2– –Cl^––NO ₃ ^– -201X7 strong base anion exchange resin system is also applicable to the ternary system studied in this paper. The predictions of the ternary system UO ₂ ²⁺ –Na⁺–H⁺ based solely on the binary data without using resin phase activity coefficients are consistent with the experimental data.     

Experimental determination and calculation of the critical curves for the binary systems of CO2 containing ketone, alkane, ester and alcohol, respectively

A set of variable-volume autoclave with a quartz window was used for the experimental determination of the high-pressure phase equilibria and critical curves. The critical temperatures, pressures, densities and mole volumes in the region near the critical point of CO₂ were examined for eleven binary systems of supercritical CO₂ (SC CO₂) with different kinds of substances (ketone, alkane, ester and alcohol), respectively. The critical curves of the above binary systems were also calculated using an equation of state. The equation consists of a hard body repulsion term and an additive perturbation term, which takes care of the attractive molecular interaction. The calculated data were compared with the experimental data, and yielded good agreements. At the same time, the values of the adjustable parameters, λ, k_σ and k_? were obtained. The critical curves of the above eleven binary systems at higher temperatures and pressures all belong to type I.     

Measurement and modeling of high-pressure (vapour + liquid) equilibria of (CO2 + alcohol) binary systems

An apparatus based on a static-analytic method assembled in this work was utilized to perform high pressure (vapour + liquid) equilibria measurements with uncertainties estimated at <5%. Complementary isothermal (vapour + liquid) equilibria results are reported for the (CO₂ + 1-propanol), (CO₂ + 2-methyl-1-propanol), (CO₂ + 3-methyl-1-butanol), and (CO₂ + 1-pentanol) binary systems at temperatures of (313, 323, and 333) K, and at pressure range of (2 to 12) MPa. For all the (CO₂ + alcohol) systems, it was visually monitored to insure that there was no liquid immiscibility at the temperatures and pressures studied. The experimental results were correlated with the Peng–Robinson equation of state using the quadratic mixing rules of van der Waals with two adjustable parameters. The calculated (vapour + liquid) equilibria compositions were found to be in good agreement with the experimental values with deviations for the mol fractions <0.12 and <0.05 for the liquid and vapour phase, respectively.     

Measurement and modeling of high-pressure (vapor + liquid) equilibria of (CO2 + alkanol) binary systems

Complementary isothermal (vapor + liquid) equilibria data are reported for the (CO₂ + 3-methyl-2-butanol), (CO₂ + 2-pentanol), and (CO₂ + 3-pentanol) binary systems at temperatures of (313, 323, and 333) K, and at pressure range of (2 to 11) MPa. For all (CO₂ + alcohol) systems, it was visually monitored that there was no liquid immiscibility at the temperatures and pressures studied. The experimental data were correlated with the Peng–Robinson equation of state using the quadratic mixing rules of van der Waals with two adjustable parameters. The calculated (vapor + liquid) equilibria compositions were found to be in good agreement with the experimental data with deviations for the mole fractions <8% and <2% for the liquid and vapor phase, respectively.     

Constant-Volume Heat Capacity of H2O + Na2CO3 Solutions Near the Critical Point of Pure Water

The results of new isochoric heat capacity measurements of H₂O + Na₂CO₃ solutions as a function of temperature along several isochores in the near-critical region of pure water are reported. The measurements cover temperatures from 331 to 661 K at Na₂CO₃ mole fraction 0.008869. The experiments were performed at seven densities between 245 and 875 kg-m^–3. The measurements were made in a high-temperature, high-pressure, adiabatic, and nearly constant-volume calorimeter. Uncertainties of the isochoric heat capacity measurements are estimated to be 1–2% in the liquid phase, 2–3% in the vapor phase, and 4–5% near the critical point. Measurements were made in the two-phase (vapor–liquid, liquid–solid, vapor–solid) and three-phase (vapor–liquid–solid) regions. Two peaks in isochoric heat capacity have been found near the critical point of pure water. One of the peaks at T _S1 occurs on the three-phase (L–V–S) curve and another peak at T _S2 corresponds to a two-phase (L–S or V–S) curve. The experimental values of phase transition temperatures T _S() on each isochore was determined. Uncertainty in the phase transition temperature measured was no greater than ±0.03 to 0.05 K.     

An improved perturbed hard-sphere equation of state

The Carnahan–Starling–Patel–Teja (CSPT) equation of state was revisited to improve the fitting accuracy of vapour–liquid equilibrium data of pure fluid substances. By setting the pseudo-critical compressibility factor and the correction coefficient in the attractive parameter as the temperature-dependent variables, the fitting accuracies of the vapour pressures and the saturated liquid-phase densities from the new CSPT increased significantly compared with the Patel–Teja equation of state (PT) and the Peng–Robinson equation of state (PR) and the original CSPT model. The new CSPT combined with temperature-dependent functions was applied to the vapour–liquid equilibrium data available for 45 pure substances. The results indicate that the new CSPT model can accurately reproduce the experimental vapour–liquid equilibria in the whole temperature and pressure range. The successful calculations of the PVT in the critical region suggest the new CSPT has wide applicability. The new CSPT model is also superior to PR and the original CSPT for calculating the phase behaviour of binary mixtures.     

CO2/CH4 mixed gas separation using poly(ether-b-amide)-ZnO nanocomposite membranes: Experimental and molecular dynamics study

Poly (ether-b-amide) (PEBA) mixed matrix membranes (MMMs) filled by different amounts of nano ZnO (up to 1 wt %) were synthesized and their gas separation performance was evaluated for CO₂, CH₄ and N₂ pure gas and their binary mixtures. The ZnO-filled PEBA MMMs were characterized using ATR-FTIR, FESEM, AFM, TGA, DMTA, XRD and Mechanical tensile strength analyses. Generally, it was revealed that 0.5 wt % loading of ZnO into the polymer matrix caused a ZnO−PEO interaction; while ZnO–ZnO self-association hindered the interaction for the MMMs with other loadings of ZnO. As a result, PEBA-ZnO 0.5 wt % MMM possessed a higher glass transition temperature (T_g). Therefore, the CO₂ permeability through PEBA-ZnO 0.5 wt % enhanced 27% than simple PEBA membrane. Moreover, all the fabricated MMMs were simulated by molecular simulation. Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods were also applied to simulate the structural and gas transport properties of the membranes. The RDF, XRD, T_g, FFV and density analysis were compared with experimental results. Also, a binary mixture of CO₂:CH₄ (10:90) was used to determine CO₂ permeability and CO₂/CH₄ selectivity, which were considerably reduced compared to single gas experiments. Moreover, the solubility of the binary gas mixture, the energy distribution and density distribution of both gases within the simulated cell were calculated by molecular simulation.     

Thermodynamic study of perfluorohexane + ether mixtures: VLE, LLE, and H

Vapour–liquid equilibria (VLE), liquid–liquid equilibria (LLE), and excess enthalpies (H^E) of binary mixtures of perfluoro-n-hexane plus an ether (diethyl, dipropyl, dibutyl, butyl methyl, and butyl ethyl ether), have been determined using a head-space gas-chromatographic technique, a turbidimetric apparatus, and a heat-flow calorimeter, respectively. A recently designed titration technique and calculation procedure have been used to obtain H^E from heats of solution. The observed liquid–liquid coexistence curves have been compared with those predicted by the activity coefficients γ_i and their temperature dependence. All mixtures are strongly endothermic (H^E > 0) and show large positive deviations from ideality (G^E > 0), which increase with the size of the ether. Molecular interactions have been examined by calculating and discussing solvation functions and Kirkwood–Buff (KB) integrals. Perfluorohexane proved to be an inert molecule that interacts with ethers more weakly than hexane.     

Modeling CO2 solubility in Aqueous Methyldiethanolamine Solutions by Perturbed Chain-SAFT Equation of State

CO₂ capture by aqueous alkanolamines treating is one of the prevalent methods to reduce carbon dioxide emissions and to help environmental problems. For realizing more the thermodynamics of the CO₂–MDEA–H₂O, the PC-SAFT equation of state was used to simulate the absorption of carbon dioxide by MDEA (methyldiethanolamine). A correlation for temperature-dependent binary interaction parameter were calculated by excess enthalpy data for aqueous MDEA at low temperatures (lower than 350 K), and then this binary interaction parameter used to predict phase equilibria of ternary aqueous mixtures of MDEA with carbon dioxide. Smith–Missen algorithm and PC-SAFT EOS have been used to determine concentration of species in chemical equilibrium and physical equilibrium, respectively. In addition, for determining parameter sets of MDEA, vapor pressure and saturated liquid density data were used and different and probable association schemes were considered in parameter estimations. Results show 4(2:2, 0:0) association scheme for MDEA and 4(2:2) association scheme for water have better agreement with binary and ternary VLE experimental data.     

Modeling of (vapor + liquid) equilibrium and enthalpy of solution of carbon dioxide (CO2) in aqueous methyldiethanolamine (MDEA) solutions

A thermodynamic model was used to estimate enthalpy of solution of carbon dioxide (CO₂) in methyldiethanolamine (MDEA) aqueous solutions. The model was based on a set of equations for chemical equilibria, phase equilibria, charge, and mass balances. Non-ideality in the liquid phase was taken into account by interaction parameters fitted to (vapor + liquid) equilibrium data.The enthalpies of solution of CO₂ were derived from the model using classical thermodynamic relations and were compared to experimental values obtained in previous works.     

Kinetic study of CO2 absorption in aqueous solutions of 2-((2-aminoethyl)amino)-ethanol using a stirred cell reaction calorimeter

In the literature, aqueous 2-((2-aminoethyl)amino) ethanol (AEEA) is identified as a promising solvent for postcombustion CO₂ capture. In this work, the kinetics of CO₂ absorption in the aqueous AEEA, containing a primary and a secondary amino group, is studied over a wide temperature range of 303.15-343.15 K and the amine concentration in the range of 0.47-2.89 M using the fall-in-pressure technique in a stirred cell reaction calorimeter setup with a horizontal gas-liquid interface. The overall rate constants for (AEEA + H₂O + CO₂) reaction system are estimated in the pseudo–first-order reaction regime. The kinetic models based on zwitterion and the termolecular reaction mechanisms are used to predict kinetic rate constants. The experimental kinetic data are better correlated using the zwitterion mechanism (AAD 9.18%) than that of the termolecular mechanism (AAD 10.4%). The density, viscosity, and physical solubility of pure components and aqueous binary mixtures of AEEA are also measured at the similar temperature and concentration ranges of rate kinetics. Empirical models are proposed to predict pure component density and viscosity data with AAD of 0.02% and 7.17%, respectively. The Redlich-Kister model, the Grunberg-Nissan model, and the O'Connell's model are used to correlate experimental density, viscosity, and physical solubility data of the binary mixtures with AAD of 0.034%, 4.92%, and 6.5%, respectively. The reaction activation energy (E_a ∼ 32 kJ/mol) of the (AEEA + H₂O + CO₂) system is calculated from the Arrhenius power-law model using the zwitterion mechanism, which indicates lower energy barrier than that of the reported value for monoethanolamine (∼44 kJ/mol) in the literature.     

Demonstration of a linear composition gradient during water saturation of CO2 in supercritical fluid chromatography

Summary Water was added to CO₂ by saturation to increase the solvation power of the mobile phase in supercritical fluid chromatography. The saturation was performed at a temperature above the boiling point of water (100°C) to increase the amount of water which could be loaded homogeneously into the CO₂ (2.5–3.0 mol% water as compared to about 0.25 mol% water at 25°C). A linear composition of water was produced by altering the density of the CO₂ during saturation. Modifications to the injector and CO₂ transfer lines prevented phase separation as a result of the instrumentation used in capillary supercritical fluid chromatography (SFC). After fitting vapor-liquid equilibria data to pressure, density, and temperature conditions, approximately 2.5–3.0 mol% of water was introduced in a linear gradient at 110°C. The effect of water on SFC performance was evaluated with standard steroid compounds. This paper provides further evidence for the need to examine vapor-liquid equilibria data prior to SFC.     

Modeling the phase equilibria of hydrogen sulfide and carbon dioxide in mixture with hydrocarbons and water using the PCP-SAFT equation of state

The perturbed-chain polar statistical associating fluid theory (PCP-SAFT) equation of state is applied to correlate phase equilibria for mixtures of hydrogen sulfide (H₂S) and carbon dioxide (CO₂) with alkanes, with aromatics, and with water over wide temperature and pressure ranges. The binary mixtures of H₂S–methane and CO₂–methane are studied in detail including vapor–liquid, liquid–liquid and fluid–solid phase equilibria. Very satisfying results were obtained for the binary mixtures as well as for the ternary mixture of H₂S–CO₂–methane using the (constant) interaction parameters of the binary pairs.