The solubility of pure CO2, CH4, and N2 in the mixture of choline-2-pyrrolidine carboxylic acid ([Cho][Pro]) and polyethylene glycol (PEG200) (mass ratio = 1:2) was measured experimentally at temperatures from 308.15 to 338.15 K and pressures up to 28 bar, in which [Cho][Pro] is an ionic liquid and PEG200 is a cosolvent with the purpose to decrease the viscosity. It was found that [Cho][Pro]/PEG200 showed a good selectivity for CO2/CH4 and CO2/N2 separation. The measured experimental data points from this work and others were further used to estimate the thermodynamic properties including the Henry's law constants for the gases in [Cho][Pro]/PEG200, the equilibrium constant for the reaction between CO2 and [Cho][Pro], the CO2 absorption enthalpy in [Cho][Pro]/PEG200, and so forth. The consistent results of the CO2 absorption enthalpy at infinite dilution prove the reliability of the thermodynamic properties obtained in this work. The thermodynamic properties of [Cho][Pro]/PEG200 were further compared with other three typical absorbents, and the absorption enthalpy is nearly half of that for 30 wt % MEA aqueous solution. At the same time, the theoretical amount of absorbents needed for [Cho][Pro]/PEG200 is much lower than that of H2O scrubbing. This shows that [Cho][Pro]/PEG200 is a promising absorbent
Using the ion-selective electrode method with a concentrated electrolyte solution added continuously, the mean activity coefficients of HCl in the HCl + NH4Cl + H2O system were experimentally measured at 298.15 and 313.15 K and at five molality fractions of NH4Cl (y2 = mNH4Cl/(mHCl + mNH4Cl) from 0.1 to 0.9. The measurements were made by an electrochemical cell using a H glass ion-selective electrode and a chloride solid-state ion-selective electrode. It was found that the influence of NH4+ on the H glass ion-selective electrode could be neglected up to 1.3 molkg-1, and this pair of ion-selective electrodes was suitable for determining the activity coefficients of HCl in the system. A new set of Pitzer mixing parameters, correlated from the experimental results, was used to calculate the activity coefficients for HCl in the system from 293.15 to 313.15 K up to 3.0 molkg-1.
The molar enthalpies of mixing for binary systems of choline chloride (chcl)/urea deep eutectic solvents (mole ratios of 1:1.5, 1:2, and 1:2.5) with water were measured at 308.15 and 318.15 K under atmospheric pressure with an isothermal calorimeter. The binary mixture of (chcl/urea (1:2.5) + water) showed endothermic behavior over the entire range of compositions, while the binary mixtures of (chcl/urea (1:1.5) + water) and (chcl/urea (1:2) + water) showed endothermic behavior first and then was changed to be exothermic with increasing content of deep eutectic solvents. The Redlich–Kister (RK) equation and the nonrandom two-liquid (NRTL) model were used to fit experimental molar enthalpies of mixing. The NRTL model with the fitted parameters was further used to predict the vapor pressure for the three systems and was compared with the experimental data from literature. For the binary mixtures of (chcl/urea (1:2) + water), the predicted vapor pressure agreed well with the experimental data only when the temperature was lower than 333.15 K and the mole fraction of chcl/urea (1:2) was lower than 0.1. Otherwise, the deviation increased greatly with an increase of the amount of chcl/urea (1:2).
The activities of methanol, ethanol, 2-propanol, and 1-butanol in poly(ethylene glycol) methacrylate (Mn = 360) solutions have been measured by the isopiestic method at 298.15 K. Sodium iodide and calcium chloride were used as the isopiestic standards for the calculation of activities. The original equation of Flory−Huggins and the modified Flory−Huggins equation with concentration-dependent interaction parameters have been used for the correlation of the experimental solvent activity data. The strength of interaction between different alcohols and the polymer was discussed on the basis of the obtained Flory−Huggins interaction parameters. The reliability of the two local-composition models, NRTL and NRF, were also assessed by fitting the experimental activity data to these models. All of these models satisfactorily present the obtained experimental activity data
Experimental liquid-liquid equilibria for various dibasic ester + solvent + water systems were obtained at 297 K. These systems are suggested as possible substitutes in applications where chlorocarbons and aromatic hydrocarbons are used. The dibasic esters can also be used as novel solvents in separation techniques.
To study the effects of type and content of cosolvent as well as temperature on the properties of two well-known deep eutectic solvents (DESs), i.e., ChCl/EG (choline chloride + ethylene glycol at a molar ratio of 1:2) and ChCl/Gly (choline chloride and glycerol at a molar ratio of 1:2), the density and viscosity of the mixtures of ChCl/EG or ChCl/Gly with methanol (MeOH) and water (H2O) over the whole compositional range at temperatures from 288.15 to 323.15 K as well as the molar enthalpy of mixing for the mixtures of ChCl/EG or ChCl/Gly + MeOH were experimentally measured. The excess molar volume, viscosity deviation, and excess molar Gibbs energy of activation were further calculated to study the effects of temperature, types of cosolvent and DES, and their contents on the nonideal behavior of these pseudobinary systems. The molar enthalpy of mixing measured in this work was further compared with those with H2O as the cosolvent reported in the literature. It shows that the mixing of these two DESs with MeOH is exothermic, which is opposite compared to those mixed with H2O. Additionally, the nonrandom two-liquid model and Gibbs–Helmholtz equation were combined to represent the experimental results of the enthalpy of mixing.
To study the effect of water on the properties of choline chloride (ChCl)/urea mixtures (1:2 on a molar basis), the density and viscosity of ChCl/urea (1:2) with water were measured at temperatures from 298.15 K to 333.15 K at atmospheric pressure, the CO2 solubility in ChCl/urea (1:2) with water was determined at 308.2 K, 318.2 K, and 328.2 K and at pressures up to 4.5 MPa. The results show that the addition of water significantly decreases the viscosity of ChCl/urea (1:2), whereas the effects on their density and CO2 solubility are much weaker. The CO2 solubility in ChCl/urea (1:2) with water was represented with the Nonrandom-Two-Liquid Redlich–Kwong (NRTL-RK) model. The excess molar volume and excess molar activation energy were further determined. The CO2 absorption enthalpy was calculated and dominated by the CO2 dissolution enthalpy, and the magnitude of the CO2 dissolution enthalpy decreases with the increase of water content.
The adsorption equilibria of propylene and ethylene on 15 commercial activated carbons at 101.3 kPa and 313 K were investigated. The adsorption amount of propylene and ethylene on these adsorbents varied greatly from a minimum of 1.593 mmol·g−1 for propylene and 1.430 mmol·g−1 for ethylene to a maximum of 4.528 mmol·g−1 for propylene and 3.100 mmol·g−1 for ethylene. Characteristics of these activated carbon adsorbents such as the Brunauer−Emmett−Teller (BET) surface area, micropore area, external surface area, total pore volume, micropore volume, and average pore diameter were determined by a volumetric method. The adsorption amount of the two alkenes on these 15 carbon samples were correlated with their physical parameters. Both the BET surface area and micropore volume have an effect on their adsorption.
The phase diagram for the poly(ethylene glycol) dimethyl ether (PEGDE) + Na2SO4 + H2O system at 298.15 K using PEGDE with a molar mass of 2000 was determined. Compositions of the liquid−liquid and the liquid−liquid−solid equilibria were determined using calibration curves of refractive index of the solutions, and atomic absorption (AA) and X-ray diffraction analyses were made on the solids. The solid phase in equilibrium with the biphasic region was anhydrous Na2SO4. An empirical nonlinear three-parameter expression developed by Merchuk was used for reproducing the experimental binodal data at T = (288.15, 298.15, 308.15, and 318.15) K, and the fitting parameters were obtained for the corresponding temperatures. The effects of temperature on the binodal curve were also studied, and it was observed that the area of the biphasic region increased slightly with an increase in temperature. The experimental tie-line compositions at the aforementioned temperatures were fitted to both the Othmer−Tobias and Bancroft and Setschenow-type equations. Correlation coefficients for all equations are reported.
The complete phase diagram for the poly(ethylene glycol) dimethyl ether 2000 (PEGDME2000) + Na2CO3 + H2O system at 298.15 K was determined. Experimental liquid−liquid equilibrium phase diagrams, tie lines, and plait points were obtained for the ternary system. Compositions of the liquid−liquid and the liquid−liquid−solid equilibria were determined from calibration curves of refractive index of the solutions, and atomic absorption (AA) and X-ray diffraction analyses were made on the solids. Binodal curves were described using the Merchuk equation at T = (288.15, 293.15, 298.15, 308.15, and 318.15) K, and the fitting parameters were obtained for the corresponding temperatures. The effects of temperature on the binodal curve were also studied, and it was observed that the area of the biphasic region increased slightly with increase in temperature. Also, the tie lines were fitted to both the Othmer−Tobias and Bancroft and Setschenow-type equations. Correlation coefficients for all equations are reported.
Vapor−liquid equilibrium data (water activity, vapor pressure, osmotic coefficient, and activity coefficient) of the mixed electrolyte aqueous solution, 1-ethyl-3-methylimidazolium bromide, [Emim][Br], + tripotassium phosphate, [Emim][Br], + dipotassium hydrogen phosphate, [Emim][Br], + potassium dihydrogen phosphate, and their corresponding binary aqueous solutions have been measured by the isopiestic method at temperature 298.15 K. The osmotic coefficients for binary aqueous solutions were correlated to the Pitzer and modified Pitzer models. From these data, the corresponding mean molal activity coefficients, γ±, have been calculated. The activity coefficients of mixed electrolytes were calculated by Scatchard’s neutral-electrolyte method. The activity results were also satisfactorily fitted to the semiempirical equation.
Speed of sound and density of poly(ethylene glycol) methacrylate 360 (PEGMA) + methanol, + ethanol, + 2-propanol, and + 1-butanol systems have been measured experimentally over the whole range of composition at T = 298.15 K and atmospheric pressure. From these experimental data, the excess molar volumes, isentropic compressibility, and changes in speed of sound and isentropic compressibility have been determined for each composition. The results have been interpreted in light of polymer−solvent interactions and packing effects. Also, the excess molar volumes and the changes of the speed of sound and the isentropic compressibility were fitted to two different variable-degree polynomial equations.
Titanium (Ti) metal has been widely used in orthopedic implants, such as knee replacements and fracture fixation devices, where water is the base fluid of the lubricant. In this work, a series of nonequilibrium molecular dynamics have been carried out to investigate the microstructure and lubrication of water molecules confined in TiO2 nanoslits under shearing. The effects of varying slit gap widths (0.8, 1.2, 1.6, and 2.0 nm) and shear velocities (200, 100, 50, and 10 m/s) on the friction coefficients between TiO2 and water molecules were evaluated to shed light on the role of the confined water molecules on lubrication. Simulation results showed that the friction coefficient decreased as the slit width increased. Detailed analysis of water molecules microstructure revealed that water molecules confined in the slits were layered. Typically, all the water molecules in Layer 1 and some water molecules in Layer 2 could reach the sliding velocity of the wall, which were in agreement with the reported mobility of water molecules absorbed on TiO2 nanoparticles via nuclear magnetic resonance. As the width of slit gap increased, the average lifetime of the H-bonds between water molecules within and beyond Layer 1 reduced and the amount of free water increased accordingly, which caused a decrease in the friction coefficient. This understanding can be used to explain at the molecular scale the observation in our previous atomic force microscope experiment in which the higher roughness in TiO2 reflected a lower friction coefficient.
In this work, we developed a new self-diffusion coefficient model for chain-like fluids, which was coupled with the SE equation to simultaneously describe transport properties (i.e., self-diffusion coefficient and viscosity) using the parameters obtained from thermodynamic properties. In modeling, the self-diffusion coefficient model was developed based on the diffusion coefficient of LJ spherical fluids by incorporating a correction function to describe the characteristics of chain-like molecules. Subsequently, the SE equation was used to calculate the viscosity. Based on the molecular parameters in ePC-SAFT (i.e., segment number N, segment diameter σ, and energy parameter ε/kB), one set of universal parameters was determined from the self-diffusion coefficients and viscosities of 19 n-alkanes (C2H4–C20H42) at various temperatures and pressures. The model reproduces the experimental self-diffusion coefficient data (804 data points) with an average ARD of 8.4% and the experimental viscosity data (1539 data points) with an average ARD of 7.2% for 19 n-alkanes over wide ranges of temperature and pressure. Furthermore, the viscosity and self-diffusion coefficient of the other 17 compounds, including long n-alkanes, branched alkanes, and cyclic compounds, were predicted, and among them, the relatively poor prediction results of branched alkanes and cyclic compounds were further discussed. Finally, the proposed model was extended to ionic liquids, generally providing reliable results for these complex fluids. This study suggests that it is possible to describe the thermodynamic and transport properties with one set of molecular parameters based on ePC-SAFT.