Solubility of carbon dioxide in aqueous solution of 2-amino-2-methyl-1-propanol and piperazine

In this work, new experimental results of the vapour-liquid equilibrium (VLE) of CO₂ in aqueous 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ) have been presented in the temperature range of 298-328 K and PZ concentration range of 2-8 mass%, keeping the total amine concentration in the solution at 30 mass%. The partial pressures of CO₂ were in the range of 0.1-1450 kPa. A thermodynamic model was developed to correlate and predict the VLE of CO₂ in aqueous AMP + PZ. The electrolyte nonrandom 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 experimental data from this work and data available in the literature were used to regress the ENRTL interaction parameters. The model predictions are in good agreement with the experimental data of CO₂ solubility in aqueous blends of this work as well as those reported in the literature. The current model can also predict speciation, heat of absorption, pH of the CO₂ loaded solution, and amine volatility.     

Acid gases partial pressures above a 50 wt% aqueous methyldiethanolamine solution: Experimental work and modeling

Aqueous amine solutions are widely used in the industry for acid gas removal. In order to treat natural gas or refinery process streams, an accurate knowledge of solubility data of carbon dioxide, hydrogen sulfide and other sulfur species in aqueous amine solutions is required. In this paper, new equilibrium measurements on 50 wt% aqueous methyldiethanolamine solution with CO₂ and H₂S have been produced. A simple way to correlate the data has been searched and found. First, a model proposed by Posey et al. in 1996, then a Deshmukh–Mather model are used to correlate “vapor–liquid” equilibria. The Posey et al. model lacks accuracy to represent the experimental data, especially for high loadings. The Deshmukh–Mather model shows good agreement as long as the total loading (H₂S + CO₂) does not reach 1.0.     

Thermodynamic modeling of the vapor–liquid equilibrium of the CO2/H2O mixture

In order to evaluate the feasibility of CO₂ sequestration in geological formations detailed knowledge of the mutual solubilities of the CO₂/H₂O system is required. In this work we employ three models, which all involve the well-known Peng–Robinson equation of state, to study the CO₂/H₂O phase equilibrium, with emphasis on the solubility of CO₂ in the aqueous phase and the solubility of H₂O in the CO₂-rich phase. The considered models include the Peng–Robinson equation of state coupled with the conventional van der Waals one fluid mixing rules or the universal mixing rules, and the cubic-plus-association equation of state that uses the Peng–Robinson equation of state in order to account for the usual attractive and repulsive forces and an extra association term to account for the strong hydrogen bonding interactions. The required model parameters are calibrated using experimental data up to 1500 bar for pressure, and up to 673 K for temperature. To improve the accuracy of the proposed models we consider two temperature ranges. Temperatures lower than 373 K are of interest to the geological CO₂ sequestration, while higher temperatures are of interest to fluid-inclusion studies. Good agreement is obtained between the experimental and the correlated solubilities.     

Solubility of H2S in 1-(2-hydroxyethyl)-3-methylimidazolium ionic liquids with different anions

The solubility of hydrogen sulfide in a series of 1-(2-hydroxyethyl)-3-methylimidazolium ([HOemim]⁺)-based ionic liquids (ILs) containing different anions, viz. hexafluorophosphate ([PF₆]⁻), trifluoromethanesulfonate ([OTf]⁻), and bis-(trifluoromethyl)sulfonylimide ([Tf₂N]⁻) at temperatures ranging from 303.15 to 353.15 K and pressures of up to about 1.8 MPa was measured by a volumetric based static apparatus. The solubility data were correlated using two models: (1) the Krichevsky–Kasarnovsky equation and (2) the extended Henry's law combined with the Pitzer's virial expansion for the excess Gibbs energy. Henry's law constants (at zero pressure) in mole-fraction and molality scales were obtained at different temperatures by means of these two models. Using the solubility data, the partial molar thermodynamic functions of solution, i.e. Gibbs energy, enthalpy, and entropy were calculated. Comparison showed that the solubility of H₂S is greater than that of CO₂ in the corresponding ILs studied in this work and that the solubility of both gases increases as the number of trifluoromethyl (–CF₃) groups in the anion increases, i.e. the solubility behavior of both gases follows the order [HOemim][Tf₂N] ≥ [HOemim][OTf] > [HOemim][PF₆] > [HOemim][BF₄].     

(Vapour + liquid) equilibria (VLE) of CO2 in aqueous solutions of 2-amino-2-methyl-1-propanol: New data and modelling using eNRTL-equation

This work presents new experimental results for carbon dioxide (CO₂) solubility in aqueous 2-amino-2-methyl-1-propanol (AMP) over the temperature range of (298 to 328) K and CO₂ partial pressure of about (0.4 to 1500) kPa. The concentrations of the aqueous AMP lie within the range of (2.2 to 4.9) mol · dm^?3. A thermodynamic model based on electrolyte non-random two-liquid (eNRTL) theory has been developed to correlate and predict the (vapour + liquid) equilibrium (VLE) of CO₂ in aqueous AMP. The model predictions have been in good agreement with the experimental data of CO₂ solubility in aqueous blends of this work as well as those reported in the literature. The current model can also predict speciation, heat of absorption, enthalpy of CO₂ loaded aqueous AMP, pH of the loaded solution, and AMP volatility.     

Prediction of water content of sour and acid gases

Estimating the feasibility of acid gas geological disposal requires the knowledge of the water content of the gas phase at moderate pressures and temperatures (typically below 50 MPa, below 380 K) and up to 6 mol NaCl. In this paper, a non-iterative model is developed to predict the water content of sour and acid gases at equilibrium with pure water and brine. This model is based on equating the chemical potential of water and using the modified Redlich–Kwong equation of state to calculate the fugacity of the gas phase. The water content of pure CH₄, CO₂ and H₂S are represented with average absolute deviations of less than 3.36, 7.04 and 8.4%, respectively. Experimental data of the water content of mixtures of the acid gases were reproduced with average absolute deviations of less than 6.32%.     

High-pressure phase behavior of CO2 + 1-butyl-3-methylimidazolium chloride system

The phase behavior of carbon dioxide (CO₂) and the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) was measured and correlated at high pressures up to ∼40 MPa and at temperatures between 353.15 K and 373.15 K. The solubility data of CO₂ in [bmim][Cl] were obtained by observing the bubble point pressure at specific temperatures. A variable-volume view cell, which is a high-pressure equilibrium apparatus, was used to measure the CO₂ + [bmim][Cl] system solubility under varying pressure and temperature conditions. In addition, liquid–liquid–vapor (LLV) three-phase behavior was investigated using the equilibrium cell to be able to determine the classification of phase-behavior type by Scott and Van Konynenburg. Based on the LLV phase behavior, this system most likely has type III phase-behavior which is common for IL + CO₂ systems. The resulting data showed that CO₂ dissolved well in the IL at low CO₂ concentrations, but that the pressure derivative of CO₂ solubility dramatically decreased as the mole fraction of CO₂ was increased. The experimental data were well fitted by the Peng–Robinson equation of state with a quadratic mixing rule and cubic parameters estimated by the Joback method.     

Gas solubility of H2S in aqueous solutions of N-methyldiethanolamine and diethanolamine with 2-amino-2-methyl-1-propanol at 313, 343, and 393 K in the range 2.5–1036 kPa

The gas solubility of hydrogen sulfide in aqueous solutions of 32.5 wt.% N-methyldiethanolamine (MDEA) and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol, at 313.15, 343.15, and 393.15 K, has been measured, using a volumetric method for the analysis of the liquid phase, over a range of pressure from 2.5 to 1036 kPa. The experimental results of the gas solubility are given as the partial pressure of H₂S against its mole ratio α (mol H₂S/mol total alkanolamine) and mole fraction of H₂S at each temperature studied. Enthalpies of solution of H₂S have been derived from the pressure-temperature concentration data. Experimental solubility data obtained in our laboratory for H₂S and CO₂ are compared, and it is possible to establish that the aqueous solutions of MDEA, DEA, and AMP studied in this work are highly selective towards H₂S under the same conditions of pressure and temperature.     

Solubility of carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

In this work, the phase behaviour of the binary system of carbon dioxide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf₂N]) has been studied experimentally. The equipment used for the experiments is the Cailletet set-up, based on visual observations of phase transitions of systems with constant overall composition. Results are reported for carbon dioxide concentrations ranging from 12.3 to 59.3 mol%, and within temperature and pressure ranges of 310–450 K and 0–15 MPa, respectively. The data reveal an extremely high capacity of the selected ionic liquid for dissolving CO₂ gas, for example, reaching up to about 60 mol% within the above-mentioned pressure and temperature range. Also, the solubility of CO₂ in the ionic liquid [emim][Tf₂N] is compared to the solubility of CO₂ in the ionic liquid [emim][PF₆], an ionic liquid that shares the same cation.     

Experimental study on equilibrium solubility (at low partial pressures), density, viscosity and corrosion rate of carbon dioxide in aqueous solutions of ascorbic acid

In this paper, ascorbic acid as a new carbon dioxide (CO₂) absorbent was investigated. The equilibrium solubility of CO₂ into 0.5, 1 and 1.5 mol dm⁻³ (M) aqueous ascorbic acid solutions were measured experimentally with a stirred batch reactor at total atmospheric pressure over the CO₂ partial pressure ranging from 0 to 45 kPa and temperatures between 298 and 313 K. The results of the gas solubility are presented as loading capacity (mol CO₂/mol ascorbic acid) as function of partial pressure of CO₂ for all experimental runs. Experimental results showed that solubility of CO₂ increases with increase in molar concentration of ascorbic acid solution at a given temperature and decreases with increase in temperature at a given concentration. The densities and viscosities of the ascorbic acid solutions were measured at the same conditions of the solubility measurement. Some corrosion rate tests were also performed on carbon steel at temperature of 308 K. It was observed that viscosity and corrosion rate increase when the molar concentration of ascorbic acid solution increases.     

Solid–liquid phase equilibria in the systems K2SO4–MSO4–H2O (M = Co,Ni, Cu) from ambient to enhanced temperatures

Reviewing the literature solubility isotherms in the ternary systems K₂SO₄–MSO₄–H₂O (M = Co, Ni, Cu, Zn) revealed a lack at ambient temperatures. The solid–liquid phase equilibria have been determined in the systems K₂SO₄–MSO₄–H₂O (M = Co, Ni, Cu) at T = 313 K. With increasing bivalent metal sulfate concentration, the solubility of potassium sulfate rises until the two-salt point is reached. Reciprocally, the solubility of the bivalent metal sulfate hydrates (CoSO₄·7H₂O, α-NiSO₄·6H₂O, CuSO₄·5H₂O) increases with rising potassium sulfate concentration. In all three systems the double salts of Tutton's type K₂SO₄·MSO₄·6H₂O (M = Co, Ni, Cu) are formed.     

Measuring the solubility of CO2 and H2S in sulfolane and the density and viscosity of saturated liquid binary mixtures of (sulfolane + CO2) and (sulfolane + H2S)

The density and viscosity of liquid sulfolane saturated (loaded) with single CO₂ and H₂S gases were measured simultaneously with the solubility of the single CO₂ and H₂S gases in sulfolane at temperatures ranging from (303.15 to 363.15) K and pressures of up to about 2.4 MPa using a new experimental set-up developed in our laboratory. The experimental density and viscosity values were correlated using a modified Setchenow-type equation. It was observed that the density and viscosity of mixtures decrease by increasing temperature and acid gas solubility (loading) in sulfolane. Acid gas loading has a much profounder effect on the viscosity of solutions than on their density, i.e. at a concentration of 1 mol CO₂/H₂S per kg of sulfolane the density decreases by less than 3%, but viscosity decreases by more than 30%. Results show that at fixed temperature and pressure H₂S is more than four times as soluble as CO₂ in sulfolane. The measured solubility and density values were respectively used to obtain Henry’s law constants and partial molar volumes at infinite dilution for dissolution of CO₂ and H₂S gases in the liquid sulfolane at the temperatures studied. The Henry’s law constants obtained at different temperatures were used to determine infinite dilution partial molar thermodynamic functions (Gibbs free energy, enthalpy and entropy) of solution. The measured solubility data were correlated by using a model comprised of the extended Henry’s law and the Pitzer’s virial expansion for the excess Gibbs free energy.     

Hydrogen gas mixture separation by CVD silica membrane

In this work we investigate the performance of high flux chemical vapour deposition (CVD) silica membranes for the separation of gas mixtures containing H₂ and CO₂ at various temperatures. The membranes were prepared by a counter diffusion CVD method where tetraethyl orthosilicate (TEOS) and O₂ were used as reactants. Single gas permeation resulted in activated transport for the smaller kinetic diameter gases (H₂ and He) whilst the larger kinetic diameter gases (CO₂ and N₂) showed negative activation energy. The single gas permeation of H₂ increased from 5.1 × 10⁻⁷ to 7.0 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ in the temperature range 100–400 °C, and H₂/CO₂ and H₂/N₂ selectivities reached 36 and 57 at 400 °C, respectively. The H₂ purity in the permeate stream also increased with temperature for H₂:CO₂ binary gas mixture, thus being beneficial for H₂ diffusion. H₂ competitively permeated through the membrane at a several range of gas mixtures, and a saturation level was achieved at H₂:CO₂ 60:40 feed concentration, where the diffusion of CO₂ molecules became negligible delivering ∼99% H₂ purity in the permeate stream. These results substantiate that the counter diffusion CVD method produced thin silica film membranes with a very precise pore size control, in particular suggesting a narrow pore distribution with average pore radius of about 3.1 Å.     

Phase equilibria of imidazolium ionic liquids and the refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a)

A number of applications with ionic liquids (ILs) and hydrofluorocarbon gases have recently been proposed. Detailed phase equilibria and modeling are needed for their further development. In this work, vapor–liquid equilibrium, vapor–liquid–liquid equilibrium, and mixture critical points of imidazolium ionic liquids with the hydrofluorocarbon refrigerant gas, 1,1,1,2-tetrafluoroethane (R-134a) was measured at temperatures of 25 °C, 50 °C, 75 °C and pressure up to 143 bar. The ionic liquids include 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf₂N]), 1-hexyl-3-methyl-imidazolium hexafluorophosphate ([HMIm][PF₆]), and 1-hexyl-3-methyl-imidazolium tetrafluoroborate ([HMIm][BF₄]). The effects of the anion and cation on the solubility were investigated with the anion having greatest impact. [HMIm][Tf₂N] demonstrated the highest solubility of R-134a. The volume expansion and molar volume were also measured for the ILs and R-134a. The Peng–Robinson Equation of State with van der Waals 2-parameter mixing rule with estimated IL critical points were employed to model and correlate the experimental data. The models predict the vapor–liquid equilibrium and vapor–liquid–liquid equilibrium pressure very well. However, the mixture critical points predictions are consistently lower than experimental values.     

Isothermal vapour–liquid equilibria in the binary and ternary systems consisting of an ionic liquid, 1-propanol and CO2

Vapour–liquid equilibrium measurements for binary and ternary systems containing carbon dioxide, 1-propanol, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquids are presented in this work. The binary CO₂ + 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide system at 313.15 K at pressure range from 2 to 14.4 MPa was examined. The obtained phase envelop shows that even at low pressure of CO₂ the solubility of the gas in the ionic liquid is high. The ternary phase equilibria were studied at 313.15 K and pressures in the range from 9 to 12 MPa. The ternary phase diagrams show that higher CO₂ pressure diminishes the miscibility gap.     

Solubility of carbon dioxide in pentaerythritol tetraoctanoate

In this paper, solubility measurements of CO₂ in pure pentaerythritol tetraoctanoate (PEC8) between 273 and 343 K are presented. The experiments were performed according to the static, synthetic method. The data are represented using the Peng–Robinson equation of state with the Huron–Vidal mixing rules and the UNIQUAC equation for the excess Gibbs Energy (g^E) at infinite pressure. This system shows immiscibility in liquid phase, with lower critical end point (LCEP) at T = 268 ± 0.1 K and xCO₂=0.98±0.001$x_{\text{C}{\text{O}}_2}=0.98\pm 0.001$ and upper critical end point (UCEP) at the critical point of pure CO₂.     

High-pressure phase behaviour of binary (CO2 + nicotine) and ternary (CO2 + nicotine + solanesol) mixtures

This work paper presents vapour–liquid equilibrium (VLE) data for binary (CO₂ + nicotine) and ternary (CO₂ + nicotine + solanesol) mixtures, at 313.2 K and 6, 8 and 15 MPa. The (CO₂ + nicotine) system exhibits three phases (L₁L₂V) in equilibrium at 8.37 MPa. It is estimated that this system most likely follows the type-III phase behaviour. In the ternary system, the presence of solanesol in the vapour phase was detected only at the pressure of 15 MPa. At this pressure, partition coefficients and separation factors for solanesol/nicotine were calculated for different initial nicotine/solanesol compositions and a strong influence of composition was found. The results were modelled using the Peng–Robinson equation of state (PR EOS) coupled with the Mathias–Klotz–Prausnitz (MKP) mixing rule (PR–MKP model). Good correlations of the binary data, particularly in the case of the (CO₂ + nicotine) mixture, were obtained. However, the model could not correlate the ternary data.     

Experimental analysis and modeling of CO2 solubility in AMP (2-amino-2-methyl-1-propanol) at low CO2 partial pressure using the models of Deshmukh–Mather and the artificial neural network

The equilibrium solubility data for CO₂ in aqueous solution of AMP have been determined at temperatures from 293 K to 323 K, partial pressures from 17.47 kPa to 69.87 kPa and concentrations of AMP from 1 M to 4 M. The experimental results show that the solubility of CO₂ in AMP increases with partial pressure and decreases with temperature and concentration of solvent. Two different mathematical models have been used to analyze the solubility of CO₂ in AMP including those of Deshmukh–Mather and the artificial neural network. The modeling results indicate that the neural network modeling provides a better prediction of experimental CO₂ loadings than the Deshmukh–Mather model when compared with experimental results in this work. Therefore, this new modeling method can be useful in predicting the results of CO₂ absorption and its accuracy is comparable with those of thermodynamic models which are used widely.     

Vapour–liquid equilibrium for β-myrcene and carbon dioxide and/or hydrogen and the volume expansion of β-myrcene or limonene in CO2 at 323.15 K

Vapour–liquid equilibrium measurements for binary and ternary (carbon dioxide + β-myrcene and carbon dioxide + β-myrcene + hydrogen) systems have been carried out at 323.15 K and pressures in the range from 7 MPa to the critical pressure of the binary mixture and at pressures from 10 to 14 MPa for the investigated ternary systems. Samples from the coexisting phases were taken, and compositions were determined experimentally. Results were correlated using the Peng–Robinson and the Soave–Redlich–Kwong equations of state with the Mathias–Klotz–Prausnitz mixing rule. The set of interaction parameters for the employed equations of state and applied mixing rule for the system of CO₂ + β-myrcene and of CO₂ + β-myrcene + H₂ were obtained. Additionally, the volume expansion of the liquid phase for the binary mixtures (carbon dioxide + β-myrcene and carbon dioxide + limonene) were measured at 323.15 K and at pressures from 4 MPa up to very close to the critical pressure of the mixture. The ratio of liquid phase total volumes at the given pressure and at 4 MPa was calculated.