Carbon dioxide solubility in aqueous potassium salt solutions of l-proline and dl-α-aminobutyric acid at high pressures

In the present work, the solubility of CO₂ in aqueous solutions of potassium prolinate (KPr) and potassium α-aminobutyrate (KAABA) was measured at temperatures (313.2, 333.2, and 353.2) K and CO₂ partial pressures up to 1000 kPa for amino acid salt concentrations: KPr, w = (7.5, 14.5, and 27.4 wt%) and KAABA, w = (6.9, 13.4, and 25.6 wt%). It was found that the CO₂ absorption capacities of the studied amino acid salt systems were considerably high and comparable with that of industrially important alkanolamines including monoethanolamine. The CO₂ loadings in aqueous potassium α-aminobutyrate at high pressures were also found to be generally higher than the loadings in aqueous potassium prolinate. A modified Kent–Eisenberg model was applied to correlate the CO₂ solubility in the amino acid salt solution as function of CO₂ partial pressure, temperature, and concentration. The model gave good representation of the (vapour + liquid) equilibrium data obtained for the amino acid salt systems studied, and provided accurate predictions of the solubility.     

Solubility of hydrogen in toluene for the ternary system H2 + CO2 + toluene from 305 to 343 K and 1.2 to 10.5 MPa

The solubility of hydrogen in toluene in the presence of the compressed CO₂ at the temperatures from 305 to 343 K and the pressures from 1.2 to 10.5 MPa was measured by using a continuous flow technique. The obtained data indicate that more hydrogen could be dissolved in toluene at the pressures higher than a certain value depending on temperature and the molar ratio of H₂ to CO₂ in gas. The Peng–Robinson equation of state associated with the van der Waals mixing rule were found to correlate the VLE data of the ternary system H₂ + CO₂ + toluene satisfactorily. From the volume expansion resulted from the dissolution of CO₂ in toluene calculated by the proposed model, it was found that hydrogen solubility was generally increased with increasing volume expansion. A large volume expansion was required to enhance hydrogen solubility when the mole fraction of hydrogen in gas was low.     

High pressure measurement and CPA equation of state for solubility of carbon dioxide and hydrogen sulfide in 1-butyl-3-methylimidazolium acetate

Removal of acid gases such as CO₂ and H₂S from natural gas is essential for commercial, safety and environmental protection that demonstrate the importance of gas sweetening process. Ionic liquids (IL) have been highly demanded as a green solvent to remove acid gases from sour natural gas and capturing of CO₂ from flue gases. In this work, the solubility of CO₂ in 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) is measured at temperatures (303.15, 328.15, 343.15) K and pressure range of (0.1 to 3.9) MPa. Moreover, the experiments are carried out for simultaneous measurements of (CO₂ + H₂S) (70% + 30% on a mole basis) solubility in the same ionic liquid at T = (303.15, 323.15, 343.15) K and a pressure range of (0.1 to 2.2) MPa. To model the solubility of acid gases in IL, both physical and chemical equilibria are applied so that the (vapour + liquid) equilibrium calculation is carried out through Cubic-Plus-Association (CPA) EoS. The reaction equilibrium thermodynamic model is used in liquid phase so that the chemical reaction is taking place between IL and acid gasses. The Henry’s and reaction equilibrium constants are obtained though optimization of the solubility data. Using CPA EOS, the pure parameters of [bmim][acetate] are optimised and consequently using these parameters, gas partial pressure calculation is performed for the (CO₂ + IL) and (CO₂ + H₂S + IL) systems. For the (CO₂ + IL) system, the percent average absolute deviation (AAD%) of 4.83 is resulted and for the (H₂S + CO₂ + IL) system the values of 18.8 and 13.7 are obtained for H₂S and CO₂, respectively.     

Experimental study of high pressure phase equilibrium of (CO2 + NO2/N2O4) mixtures

Experimental bubble pressure, as well as liquid density of (CO₂ + NO₂/N₂O₄) mixtures are reported at temperatures ranging from (298 to 328.45) K. Experiments were carried out using a SITEC high-pressure variable volume cell. Transition pressures were obtained by the synthetic method and liquid density was deduced from measurement of the cell volume. Correlation of experimental results was carried out without considering chemical equilibrium of NO₂/N₂O₄ system. (Liquid + vapour) equilibrium was found to be accurately modelled using the Peng–Robinson equation of state with classical quadratic mixing rules and with a binary interaction coefficient k_ij equal to zero. Nevertheless, modelling of liquid density values was unsatisfactory with this approach.     

Properties of ionic liquid HMIMPF6 with carbonates,ketones and alkyl acetates

The densities and refractive indices of the pure ionic liquid (IL) HMIMPF₆ were determined at temperature range from T =(278.15 to 318.15) K for density and from T = (288.15 to 318.15) K for refractive index. The coefficient of thermal expansion of HMIMPF₆ was calculated from the experimental values of density. The densities and refractive indices of binary mixtures involving dimethyl carbonate (DMC), diethyl carbonate (DEC), acetone, 2-butanone, 2-pentanone, methylacetate, ethylacetate, and butylacetate + HMIMPF₆ (1-hexyl-3-methylimidazolium hexafluorophosphate) have been measured at T = 298.15 K and atmospheric pressure. Excess molar volumes and changes of refractive index on mixing for the binary systems were calculated. The miscibility of IL with different organic solvents and (liquid + liquid) equilibrium (LLE) data of binary mixture HMIMPF₆ + DEC have been determined experimentally.     

Hot band spectroscopy of CCO in the C–O stretching region: The (ν1 + 2ν3) − 2ν3 and (2ν1 + ν3) − (ν1 + ν3) bands

Two C–O stretching hot bands, (ν₁ + 2ν₃) − 2ν₃ and (2ν₁ + ν₃) − (ν₁ + ν₃), of the CCO radical in the ground electronic state were measured. These hot bands are red shifted by approximately 70 cm⁻¹ compared to the C–O stretching fundamental. CCO was produced in a discharge through a flowing mixture of carbon suboxide and helium. The spectra were recorded using a diode laser spectrometer. The band origins were determined to be 1904.32512(62) and 1902.69130(56) cm⁻¹ for (ν₁ + 2ν₃) − 2ν₃ and (2ν₁ + ν₃) − (ν₁ + ν₃), respectively. The measurements in this band together with previously reported frequencies in the C–C and C–O stretching regions were analysed to determine harmonic frequencies and anharmonicity constants.     

Gas solubility of CO2 in aqueous solutions of N-methyldiethanolamine and diethanolamine with 2-amino-2-methyl-1-propanol

Gas solubility of carbon dioxide in an aqueous solution of 32.5 wt.% N-methyldiethanolamine and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol has been measured, at 313.15, 343.15, and 393.15 K, over a range of pressure from 3 to 2000 kPa, using a chromatographic method for analysis of the liquid phase. The results of the gas solubility are given as the partial pressure of CO₂ against its mole ratio α (mol CO₂/mol alkanolamine) and its mole fraction at each temperature studied. The solubility of CO₂ in all the systems studied decreases with an increase in temperature and increases with an increase in the partial pressure of CO₂ at a given temperature and it is a function of the concentration of the mixture of alkanolamines in solution. The enthalpy of solution of CO₂ has been calculated from the experimental solubility data.     

Experimental and theoretical investigation of solubility of carbon dioxide in concentrated aqueous solution of 2-amino-2-methyl-1-propanol and piperazine

In this work, new experimental results for the (vapour + liquid) equilibrium (VLE) of CO₂ in piperazine (PZ)-activated concentrated aqueous 2-amino-2-methyl-1-propanol (AMP) are presented for the temperature range of (303 to 328) K and PZ concentration range of (2 to 8) wt.%, keeping the total amine concentration in the solution at 40% and 50 wt.%. The partial pressures of CO₂ are in the range of (0.2 to 1500) kPa. The electrolyte non-random two-liquid (ENRTL) theory has been used to develop the VLE model for the quaternary system (CO₂ + AMP + PZ + H₂O) to describe the equilibrium behaviour of the solution. The CO₂ cyclic capacity of these solvents is determined between the rich and lean CO₂ loadings. It is found that the CO₂ cyclic capacity increases with the addition of PZ in aqueous AMP and also with the increase in AMP concentration in the aqueous solution. However, solid precipitation has been observed for 50 wt.% total amine concentration below T = 318 K for all relative compositions of AMP and PZ in the solvent at higher CO₂ loading. The model results of equilibrium composition, pH of the loaded solution and amine volatility of the mixed solvent system, are also presented.     

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.     

Effect of the temperature on the physical properties of pure 1-propyl 3-methylimidazolium bis(trifluoromethylsulfonyl)imide and characterization of its binary mixtures with alcohols

In this paper, physical properties of a high purity sample of the ionic liquid 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [PMim][NTf₂], and its binary mixtures with methanol, ethanol, 1-propanol, and 2-propanol were measured at atmospheric pressure. The temperature dependence of density, refractive index and speed of sound (293.15 to 343.15) K and dynamic viscosity (298.15 to 343.15) K were studied at atmospheric pressure by conventional techniques for the pure ionic liquid. For its mixtures with alcohols, density, speed of sound, and refractive index were measured at T = 298.15 K over the whole composition range. The thermal expansion coefficient of the [PMim][NTf₂] was calculated from the experimental results using an empirical equation, and values of the excess molar volume, excess refractive index, and excess molar isentropic compressibility for the binary systems at the above mentioned temperature, were calculated and fitted to the Redlich–Kister equation. The heat capacity of the pure ionic liquid at T = 298.15 K was determined using DSC.     

Thermodynamics of aqueous potassium carbonate,piperazine, and carbon dioxide

CO₂ solubility was measured in a wetted-wall column in 0.6–3.6 molal (m) piperazine (PZ) and 2.5–6.2 m potassium ion (K⁺) at 40–110 °C. Piperazine speciation was determined using ¹H NMR for 0.6–3.6 m piperazine (PZ) and 3.6–6.2 m potassium ion (K⁺) at 25–70 °C. The capacity of CO₂ in solution increases as total solute concentration increases and compares favorably with estimates for 7 m (30 wt.%) monoethanolamine (MEA). The presence of potassium in solution increases the concentration of CO₃²⁻/HCO₃⁻ in solution, buffering the solution. The buffer reduces protonation of the free amine, but increases the amount of carbamate species. These competing effects yield a maximum fraction of reactive species at a potassium to piperazine ratio of 2:1.A rigorous thermodynamic model was developed, based on the electrolyte nonrandom two-liquid (ENRTL) theory, to describe the equilibrium behavior of the solvent. Modeling work established that the carbamate stability of piperazine and piperazine carbamate resembles primary amines and gives approximately equal values for the heats of reaction, ΔH_rxn (18.3 and 16.5 kJ/mol). The pK_a of piperazine carbamate is twice that of piperazine, but the ΔH_rxn values are equivalent (∼−45 kJ/mol). Overall, the heat of CO₂ absorption is lowered by the formation of significant quantities of HCO₃⁻ in the mixed solvent and strongly depends on the relative concentrations of K⁺ and PZ, ranging from −40 to −75 kJ/mol.     

Solubility of boldo leaf antioxidant components (Boldine) in high-pressure carbon dioxide

This work contributes to the development of an enrichment process for antioxidant compounds in aqueous alcoholic extracts of boldo (Peumus boldus M.) leaves by using high-pressure CO₂ as the solvent. Specifically we measured the high-pressure solubility (y₂, molar fraction) of a selected bioactive compound in boldo leaves (boldine) in CO₂ as a function of system temperature (298 K ≤ T ≤ 333 K) and pressure (8 MPa ≤ P ≤ 40 MPa). Experimental data was correlated by using a density-based model which is valid for solvent densities >607 kg/m³. Predicted solubility values are low (4 × 10⁻⁷ ≤ y₂ ≤ 6 × 10⁻⁵) but comparable with those of nitrogen-containing organic compounds with similar molecular weight (327.4 Da) and solubility parameter (28.3 MPa^0.5 at 313 K) as boldine.     

CO2 adsorption on granular and monolith carbonaceous materials

We evaluated the CO₂ adsorption capacity on granular and monolith carbonaceous materials, obtained by chemical activation of African palm stones with H₃PO₄, ZnCl₂ and CaCl₂ solutions at different concentrations. Textural properties of the synthesized materials were analyzed using N₂ adsorption measurements at 77 K, the isotherms showed obtaining of materials microporous and moderately mesoporous, with surface areas between 161 and 1700 m²/g and pore volume between 0.09 and 0.64 cm³ g⁻¹. Were observed different behaviors for textural parameters in each series, associated with the activating agent used in the preparation. The materials obtained have a CO₂ adsorption capacity between ∼114 and 254 mg CO₂/g, at atmospheric pressure and 273 K. It was established that the total amount of CO₂ adsorbed under these experimental conditions is defined by the narrow micropore volume (V_n) and increased the total basicity of the materials.     

Solubility of semi-fluorinated and nonfluorinated alkyl dichlorobenzoates in supercritical CO2

Isopleths and solution densities, from ∼25 to 100 °C, are reported for mixtures of CO₂ with semi-fluorinated and nonfluorinated propyl, butyl, octyl, and decyl 2,5-dichlorobenzoates. The maxima in the pressure–composition (P–x) isotherms for the alkyl 2,5-dichlorobenzoates range from 70 to 600 bar and the maxima increase with increasing alkyl chain length at each temperature. When the alkyl side chains are semi-fluorinated, the P–x maxima range from 60 to 175 bar over the same temperature range as with the nonfluorinated analogs. The P–x maxima of the semi-fluorinated 2,5-dichlorobenzoates in CO₂, first decrease as the benzoate alkyl chain is increased from propyl to butyl, but then increase as the alkyl chain length is further increased from butyl to octyl to decyl, although the differences in the maxima at a given temperature between these four semi-fluorinated benzoates are not as great as that observed with the nonfluorinated analogs. Also, the alkyl 2,5-dichlorobenzoate–CO₂ mixtures exhibit three-phase, liquid–liquid–vapor (LLV), equilibria near the vapor pressure curve and critical point of CO₂ whereas three phases are not observed for the semi-fluorinated analogs.     

High-pressure phase equilibria of {carbon dioxide (CO2) + n-alkyl-imidazolium bis(trifluoromethylsulfonyl)amide} ionic liquids

Ionic liquids (ILs) and carbon dioxide (CO₂) systems have unique phase behavior that has been applied to applications in reactions, extractions, materials, etc. Detailed phase equilibria and modeling are highly desired for their further development. In this work, the (vapor + liquid) equilibrium, (vapor + liquid + liquid) equilibrium, and (liquid + liquid) equilibrium of n-alkyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ionic liquids with CO₂ were measured at temperatures of (298.15, 323.15, 343.15) K and pressure up to 25 MPa. With a constant anion of bis(trifluoromethylsulfonyl)amide, the n-alkyl chain length on the cation was varied from 1-ethyl-3-methyl-imidazolium ([EMIm][Tf₂N]), 1-hexyl-3-methyl-imidazolium ([HMIm][Tf₂N]), to 1-decyl-3-methyl-imidazolium ([DMIm][Tf₂N]). The effects of the cation on the phase behavior and CO₂ solubility were investigated. The longer alkyl chain lengths increase the CO₂ solubility. The Peng–Robinson equation of state with van der Waals 2-parameter mixing rule with estimated IL critical properties were used to model and correlate the experimental data. The models correlate the (vapor + liquid) equilibrium and (liquid + liquid) equilibrium very well. However, extrapolation of the model to much higher pressures (>30 MPa) can results in the prediction of a mixture critical point which, as of yet, has not been found in the literature.     

Salt effects on the partition coefficients of phenol in two-phase mixtures of water and carbon dioxide at pressures from (8 to 30) MPa at a temperature of 313 K

Partition coefficients K_c of phenol between an aqueous solution containing different salts and a compressed CO₂ phase have been determined at T=313 K. For NaCl and (CH₃)₄NBr a pressure range from 8 MPa to around 30 MPa was investigated, for KCl and NaBr measurements were performed at a pressure of 22 MPa. The salt concentration has been varied between (0.25 and 3.0) mol·dm⁻³. With increasing pressure a rise in K_c is observed which typically is also found in systems free of salt. Salting-out was observed for the alkali salts, salting-in has been found for the ammonium salt, both effects increased with increasing salt concentration. From the concentration dependence of the K_c values Setschenow coefficients k_S have been derived. At p>10 MPa values are obtained as found in two phase mixtures of water with other organic solvents at ambient pressure. This conclusion was confirmed with both literature and own experimental data in the case of salting-out by NaCl as well as for the salting-in by (CH₃)₄NBr from measurements with phenol in (water + cyclohexane) at T=313 K.     

Study of the solubility of CO2, H2S and their mixture in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate: Experimental and modelling

New experimental results are presented for the solubility of carbon dioxide, hydrogen sulfide in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈mim][PF₆]) at temperatures range from (303.15 to 353.15) K and pressures up to about 2 MPa. The solubility of the mixture of CO₂/H₂S in [C₈mim][PF₆] under various feed compositions were also measured at temperatures of (303.15, 323.15 and 343.15) K and the pressure up to 1 MPa. The solubility of carbon dioxide and hydrogen sulfide increased with increasing pressure and decreased with increasing temperature and the solubility of H₂S is about three times that of CO₂ in the particular ionic liquid studied. The measured data were correlated using extended Henry’s law included Pitzer’s virial expansion for the excess Gibbs energy, and the generic Redlich–Kwong cubic equation of state proposed for gas/ionic liquid systems. The correlations from the two models show quite good consistency with the experimental data for CO₂/IL and H₂S/IL binary mixtures within experimental uncertainties. For CO₂/H₂S/IL ternary mixtures, the RK model shows better correlation with the experimental values. We also studied the effect of cation alkyl chain length on the CO₂ and H₂S solubility by comparison of the experimental data of this study with those of previous reports. As the cation alkyl chain length became longer, the solubility of CO₂ and H₂S increased in the ionic liquid. Additionally, the influence of the anion on the solubility is studied by comparing the solubility of CO₂ and H₂S in [C₈mim][PF₆] with those in [C₈mim][Tf₂N]. As a result, CO₂ and H₂S have higher solubility in the IL with [Tf₂N]⁻ as the anion.     

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.