Thermodynamics of aqueous solutions of methyldiethanolamine and diisopropanolamine

The vapour–liquid equilibrium (VLE) of the systems of water + methyldiethanolamine (MDEA) and water + diisopropanolamine (DIPA) was measured at several temperatures with a static total pressure apparatus. The solid–liquid equilibrium (SLE) of the same systems was measured at low amine concentrations by means of two experimental methods: a visual method and a Differential Scanning Calorimeter (DSC). The activity coefficients of water + MDEA were modelled with the NRTL equations. The model parameters were regressed from VLE, SLE and excess enthalpy data from this work and from the literature. The model developed in this work was compared with models found in the literature. The NRTL equations were also used to model the activity coefficients of the system of water + DIPA. The model parameters were fitted from the VLE and SLE data measured in this work.     

Solubility and thermodynamics of carbon dioxide in aqueous ethanol solutions

Solubilities of carbon dioxide in aqueous ethanol solutions, determined at 15, 20, 25, 30 and 35°C at atmospheric pressure, show a minimum at each temperature. Thermodynamics functions for the solution process were calculated and compared with the predictions of the Pierotti gas solubility theory. The abnormal behavior of these solutions is demonstrated.     

Solubility of trifluoroethoxyphthalocyanines and -subphthalocyanines in liquid and supercritical carbon dioxide

In an analysis of the solubility of a wide range of phthalocyanines (Pcs) and its analogues (SubPcs) in liquid and/or supercritical CO₂, compounds with trifluoroethoxy substituents were found to exhibit high solubility. To our knowledge, this is the first example of Pc compounds soluble in 100% CO₂. This unprecedented unique property of trifluoroethoxy substituted Pcs might have particular applications in catalysis in organic reactions as well as dyes for solar cells by CO₂ delivering coatings.     

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.     

Solubility of iodopropynyl butylcarbamate in supercritical carbon dioxide

Supercritical carbon dioxide has been considered an appropriate alternative for extraction and purification process of cosmetics, pharmaceuticals, food supplements and natural products. Solubility information of biological compounds is essential for choosing supercritical fluid (SCF) processes. The solubility of iodopropynyl butylcarbamate (IPBC), a fungicide and anti-dandruff agent, was measured in supercritical carbon dioxide with a high pressure apparatus equipped with a variable volume view cell at 313.15, 323.15, and 333.15 K and at pressure between 80 and 35 MPa. The experimental data were correlated well with Peng–Robinson equation of state (PR EOS) and quasi-chemical nonrandom lattice fluid model.     

Solubility data for benzene in aqueous solutions of methyldiethanolamine (MDEA) and of diglycolamine (DGA)

Specially designed equipment based on a static-analytic method with Rolsi™ pneumatic samplers for on line gas chromatograph analysis has been used for this work. Operating pressures and temperatures are between 0.3 and 10 MPa and between 293 and 393 K. Vapor pressures over liquid-liquid mixtures and benzene solubility data are reported herein for benzene with amine aqueous solutions (methyldiethanolamine (MDEA) and diglycolamine (DGA)). Modelling of solubility data is achieved using a simple model based on activity coefficients.     

Experimental determination of the solubility of aromatic compounds in aqueous solutions of various amines

A new apparatus to measure solubility data of aromatics in aqueous solutions has been designed. It is based on a static-analytic method with Rolsi™ pneumatic samplers for on line gas chromatograph analysis. Operating pressures and temperatures are between 0.3 and 10 MPa and between 293 and 393 K.

Solubility measurement results are reported for several aromatic compounds (benzene, toluene, ethylbenzene and xylene) in different amine aqueous solutions (monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), diglycolamine (DGA)). Several influent parameters are studied (temperature, total pressure, etc.).     

The solubility of water in mixtures of dimethyl ether and carbon dioxide

This paper reports measurements of the solubility of water in liquid and supercritical fluid mixtures of dimethyl ether and carbon dioxide. The measurements were made by extracting water under saturation conditions using premixed liquid dimethyl ether–carbon dioxide mixtures. Results are reported for temperatures of 313.8 K and 333.3 K at 9.0 MPa and 15.0 MPa. Results are fitted to the Peng–Robinson cubic equation of state with mixing rules according to Wong and Sandler, using binary interaction parameters fitted to the literature data for the respective binary systems: dimethyl ether–water; dimethyl ether–carbon dioxide; and carbon dioxide–water. Liquid densities for dimethyl ether–carbon dioxide mixtures, measured using a coriolis flow instrument, are also reported.     

Solubility of sulphur dioxide in aqueous electrolyte solutions at higher ionic strengths—Chloride and bromide containing systems

The absorption of sulphur dioxide in chloride and bromide containing electrolyte solutions was measured up to ionic strengths of 5 mol/dm³. The thermodynamic equilibrium of the gas phase and the liquid phase was characterized by UV spectroscopy. UV spectra analysis gave strong evidence for SO₂X⁻ complexes existing in the solutions. Consequently, these compounds were implemented in the reaction scheme for absorption.     

Solubility of carbon dioxide in aqueous solutions of sodium chloride: Experimental results and correlation

The solubility of carbon dioxide in aqueous solutions of sodium chloride was measured in the temperature range from 40 to 160°C, up to 6 mol-kg salt solutions and total pressures up to 10 MPa. Pitzer's⁽¹⁾ equations as well as the Chen and Evans⁽²⁾ model were used to correlate the new data. Results are reported and compared to literature data and correlations.     

Equilibrium conditions of clathrate hydrates formed from carbon dioxide and aqueous acetone solutions

Equilibrium conditions of clathrate hydrates formed from carbon dioxide and aqueous acetone solutions were experimentally measured at temperatures between 269.2 and 281.4 K and pressures up to 3.98 MPa. The acetone concentrations in solutions were investigated from 0.04 to 0.40 mass fractions. The experimental results suggested a transition in hydrate structure from structure I to another structure for acetone solutions between 0.04 and 0.12 mass fractions of acetone. The hydrate structure was suggested to be structure II which was the most stable with a 0.16 mass fraction acetone solution. For more than 0.16 mass fraction of acetone, the equilibrium conditions of the hydrate were shifted to lower temperatures as acetone concentrations increased.     

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.     

Solubility of disperse yellow 54 in supercritical carbon dioxide with or without cosolvent

Extraction of disperse yellow 54 with supercritical carbon dioxide was conducted at 393.2 K and 30 MPa over a wide range of contact times. Saturated solubilities of the disperse dyestuff in supercritical carbon dioxide with or without cosolvent were also measured over the temperature and pressure ranges of 353.2 K to 393.2 K and 15 MPa to 30 MPa. Either ethanol or dimethyl sulfoxide, up to 5 mol%, was used as a cosolvent. As evidenced from the experimental results, the magnitudes of equilibrium solubility can be effectively enhanced in the presence of both two cosolvents. Dimethyl sulfoxide was found to yield higher solubility enhancement. Cosolvent effects were discussed on the basis of the Kamlet-Taft solvatochromic solvent parameters of cosolvents. The saturated solubility data were correlated with the Chrastil and the Mendez-Santiago and Teja equations. The Chrastil model correlated the solubility data to about within the experimental uncertainty. The correlated results of the Mendez-Santiago–Teja model supported the consistency of the solubility data over the entire experimental conditions.     

Phase equilibria of mixed carbon dioxide and tetrahydrofuran hydrates in sodium chloride aqueous solutions

In this work, the competing effects of sodium chloride (NaCl) and tetrahydrofuran (THF) on carbon dioxide hydrate formation are investigated through phase equilibrium measurements. The phase behaviour in the hydrate forming region for the binary system carbon dioxide–water, the ternary systems carbon dioxide–tetrahydrofuran–water and ternary carbon dioxide–sodium chloride–water and, in addition, the quaternary system carbon dioxide–tetrahydrofuran–water–sodium chloride are determined experimentally, using a Cailletet apparatus. All measurements are made in a temperature and pressure region of 275–290 K and 0.5–7.0 MPa, respectively. In these ranges, three different hydrate equilibrium curves are measured namely: H-L_W-V, H-L_W-L_V-V and H-L_W-L_V. The formation of an organic-rich liquid phase in the systems due to a liquid–liquid two-phase split between water and tetrahydrofuran when pressurized with carbon dioxide causes the occurrence of an upper quadruple point (Q₂) to evolve into a four-phase H-L_W-L_V-V equilibrium line. The presence of sodium chloride in the quaternary system enhances the split between the two liquids due to the salting-out effect. It was found that the hydrate promoting effect of tetrahydrofuran is able to suppress the inhibiting effect of sodium chloride especially at lower concentration of sodium chloride.     

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.     

Solubility of oxygen, carbon dioxide and water in semifluorinated alkanes and in perfluorooctylbromide by molecular simulation

Solubilities of oxygen, carbon dioxide and water in substituted fluorocarbons perfluoroctylethane (PFOE), perfluorohexylethane (PFHE), perfluorohexylhexane (PFHH) and perfluoroalkylbromide (PFOB) were studied by computer simulation, between 293 and 313 K at 1 bar. The solubilities do not show a marked temperature dependence, are similar in all solvents and have values of the order of 4×10⁻³ for oxygen, 2×10⁻² for carbon dioxide and 3×10⁻⁶ for water, in mole fraction. The gases are slightly less soluble in PFHE when compared with the other solvents, whereas water is slightly more soluble in this liquid. The solubilities were obtained from Henry’s law coefficients, in turn derived from residual chemical potentials of the solutes at infinite dilution obtained by molecular simulation techniques using full atomistic force fields.     

Solubility of novel open-chain crown ether bridged diphosphates in supercritical carbon dioxide

The solubility of newly synthesized chelating agents, i.e., tetraethylene glycol bis (2-ethylhexyl) dimethyl diphosphate (EG4EH), tetraethylene glycol bis (n-octyl) dimethyl diphosphate (EG4Oct), and tetraethylene glycol bis (2-butoxyethyl) dimethyl diphosphate (EG4BOE) in supercritical carbon dioxide (scCO₂) were determined at temperatures ranging from (318.15 to 333.15) K and pressures ranging from (12 to 21) MPa. Solubility increases in the order of EG4Oct (MW = 606.33) < EG4BOE (MW = 582.26) < EG4EH (MW = 606.33), indicating that branched side chains of the ligands play an important part in increasing solubility in scCO₂. Semi empirical density-based models proposed by Bartle and Chrastil were used to correlate the experimental data, and AARD values were calculated to be (1.2 to 2.9)% and (0.40 to 0.93)% for Bartle and Chrastil model, respectively. Additionally, the partial molar volumes of those compounds were estimated following the theory developed by Kumar and Johnston.     

Impact of carbon dioxide on the surface tension of 1-hexanol aqueous solutions

Effects of carbon dioxide presence on the surface tension and adsorption kinetics of 1-hexanol solutions were investigated. Experiments were performed at a range of carbon dioxide vapor pressures and varying concentrations of 1-hexanol aqueous solution. Both dynamic and steady-state surface tensions of 1-hexanol aqueous solution were found to decrease with carbon dioxide pressure, and a linear relationship was observed between the steady-state surface tension and carbon dioxide pressure. To explain the experiments, adsorption and desorption of the two species (1-hexanol and carbon dioxide) from two sides of the vapor-liquid interface were considered. A modified Langmuir isotherm, the modified Langmuir equation of state and the modified kinetic transfer equation were developed. The resulting steady-state and dynamic surface tension data were modeled using the modified Langmuir equation of state and the modified kinetic transfer equation, respectively. Equilibrium constants and adsorption rate constants of 1-hexanol and carbon dioxide were evaluated through a minimization procedure for CO₂ pressures ranging from 0 to 690 kPa. From the steady-state modeling, the equilibrium parameters for 1-hexanol and carbon dioxide adsorption from vapor phase and liquid phase were found unchanged at different pressures of carbon dioxide. From the dynamic modeling, the adsorption rate constants for 1-hexanol and carbon dioxide from vapor phase and liquid phase were found to decrease with carbon dioxide pressure. Some fluctuations in the fitting parameters of the dynamic modeling (adsorption rate constants) were observed. These fluctuations may be due to experimental errors, or more likely the limitations of the model used. A major limitation of the model is related to large differences in adsorption/desorption between initial and final stages of the process, and a single set of property parameters cannot describe both initial and final states of the system. Variations may occur depending on which set of data, of initial or final states, is used in the model predictions over the entire time range.     

Solubility of dilute SO2 and CO2 in dimethyl sulfoxide

The solubility of SO₂ and CO₂ in dimethyl sulfoxide has been determined in the temperature range from 293.15 to 313.15?K and partial pressure of SO₂ from 0.15 to 2.62?kPa, and the partial pressure of CO₂ from 5 to 18?kPa. A solubility model is proposed and the solubilities calculated by the model show good agreement with the experimental data.