Phase Equilibria Of Carbon Dioxide Research Articles

Thermodynamic modeling of gas hydrate phase equilibrium of carbon dioxide and its mixture using different equations of states

In this work, the fugacity-based approach of the Klauda and Sandler model was used to predict the equilibrium conditions of gas hydrates formation for carbon dioxide and its mixtures with nitrogen, methane, ethane, and propane. In order to calculate the Langmuir constants and empty hydrate vapor pressure, the correlations presented by Munck et al., (1988) and Dharmawardhana et al., (1980) were used, respectively. Hence, six well-known equations of state (EOS) including PR, PRSV, SRK, PT, VPT and translated and consistent versions of the Peng-Robinson (tc-PR) had been used to calculate the thermodynamic properties. The thermodynamic modeling results were compared with numerous experimental data in the literature. These results showed that although all EOSs could successfully predict the equilibrium pressure of carbon dioxide, there is a deviation, less than 3.3 %, in all of them. In the case of mixture hydrates, such as CO2/CH4 and CO2/C2H6, the equilibrium pressures from the models had a good agreement with experimental data, except for PT EOS with a relatively high average absolute deviation in CO2/CH4 mixture hydrates. The predicted equilibrium pressure from the different EOSs showed excellent results for structure I, including CO2/C3H8 mixture hydrates. In addition, it has been concluded that this modeling can’t predict the equilibrium pressure structure I of CO2/N2 mixture hydrate at high pressures.

Experimental Phase Equilibria of Carbon Dioxide and Methane Hydrates in the Presence of 2-Propanol and Sodium Chloride

Experimental Phase Equilibria of Carbon Dioxide and Methane Hydrates in the Presence of 2-Propanol and Sodium Chloride

High-pressure phase equilibria of carbon dioxide + 1,4-dioxane binary system

New isothermal vapor–liquid equilibrium (VLE) data for the carbon dioxide + 1,4-dioxane system are reported at four temperatures (323.15, 333.15, 343.15, and 353.15) K and pressures up to 122.7 bar. The critical curve was also measured up to 158.8 bar and 420.15 K. Phase behavior measurements were performed in a high-pressure windowed cell with variable volume, using a static-analytical method with phases sampling by rapid online sample injectors (ROLSI) coupled to a gas chromatograph (GC) for analysis. The experimental results of this study are compared with the scarce available literature data. The new and all available literature data for the carbon dioxide + 1,4-dioxane binary system are modelled with the cubic Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) equations of state (EoS) with classical van der Waals mixing rules (two-parameter conventional mixing rules, 2PCMR). The modeling showed that SRK and PR models can accurately predict the phase behavior of the system studied.

Semi-clathrate hydrate phase equilibria of carbon dioxide in presence of tetra-n-butyl-ammonium chloride (TBAC): Experimental measurements and thermodynamic modeling

The promotion effect of TBAC on the dissociation condition of the studied system is determined under the present experimental data. A combination of the van der Waals–Platteeuw solid solution theory, binding mean spherical approximation electrolyte model and modified Peng–Robinson equation of state is used for calculation of the hydrate, aqueous solution and gaseous phases properties, respectively. The results are also compared with the experimental data for other salts such as tetra-n-butyl-ammonium bromide (TBAB) and tetra-hydro furan (THF). A good agreement between the model predictions and experimental data is found with an absolute average relative deviation of 13.1%.

Phase Equilibria of Carbon Dioxide, Propane Hydrate in the Presence of Glucose and Fructose

Phase equilibrium data for the hydrates formed in four three-component systems: CO2 + glucose + water system, CO2 + fructose + water system, C3H8 + glucose + water system, C3H8 + fructose + water system were measured in pressures range of (0.24 to 4.57 MPa) and temperatures range of (274.9 to 283.1 K) at 5% and 10% mass fraction of additives. The experimental data were determined using an isochoric pressure-search method. The effects of glucose (or fructose) on CO2 and C3H8 hydrate formation condition were studied. The addition of glucose or fructose increase the equilibrium pressure of the CO2 and C3H8 to form hydrate, and the presence of 10 mass% concentration of glucose (or fructose) showed more remarkable inhibition effect on CO2 and C3H8 hydrate formation.

An equation of state for solid–liquid–vapor equilibrium applied to gas processing and natural gas liquefaction

The analytical equation of state for the representation of solid, liquid, and vapor (SLV-EoS), proposed by Yokozeki, has been applied to the representation of phase equilibrium of substances involved in gas processing and in the natural gas liquefaction process. A new procedure for the parameters regression has been set up in order to achieve a better representation of phase equilibrium. This new procedure has been applied for obtaining new parameters for the original SLV-EoS equation, with the van der Waals attractive term. Different attractive terms have also been studied, in order to achieve an optimized representation for solid–liquid, solid–vapor, and liquid–vapor equilibrium of pure substances. The obtained equations have been used for representing phase equilibrium of carbon dioxide, methane, ethane, and propane in a wide range of temperature and pressure. The new equations have also been applied to the description of phase equilibrium, involving also solid phases, of the mixtures methane–carbon dioxide, ethane–carbon dioxide, and propane–carbon dioxide.

Vapor–liquid phase equilibrium of carbon dioxide with mixed solvents of DMSO + ethanol and chloroform + methanol including near critical regions

A visual and volume-variable high-pressure phase equilibrium analyzer was used for measuring the vapor–liquid phase boundaries of the ternary systems containing carbon dioxide and mixed solvents of dimethyl sulfoxide (DMSO)+ethanol or chloroform+methanol at temperatures from 298.15K to 348.15K over wide composition ranges including near critical points. Four pseudo-binary systems of carbon dioxide plus mixed solvents with constant molar ratios of DMSO/ethanol=3/7, 5/5, 7/3, and chloroform/methanol=1/2, were studied in this work. The critical conditions at each investigated temperature were estimated from the experimental isothermal phase boundaries by interpolation. The Peng–Robinson equation of state with the two-parameter van der Waals mixing rules was applied to calculate the phase boundaries. The experimental values were compared with the predicted results from the Peng–Robinson equation using the binary interaction parameters determined from the vapor–liquid equilibrium data of the constituent binaries. The agreement is reasonably well for carbon dioxide+chloroform+methanol, but obvious overestimations are found near the critical regions of carbon dioxide+DMSO+ethanol, especially at higher temperatures.

An extended Peng‐Robinson equation of state for carbon dioxide solid‐vapor equilibrium

AbstractThe Peng‐Robinson equation of state (PR EoS) for liquid‐vapor equilibrium is extended to model the solid‐vapor (sublimation) and solid‐liquid (melting) phase equilibria for carbon dioxide (CO2). The sublimation behavior is modeled through the re‐formulations of the empirically based analytical expressions for the two temperature dependent parameters, a and b in the PR EoS. The melting phase behavior on the other hand is modeled by the coupling of the original and the extended PR EoS and equalization of solid and liquid phase fugacities. Analytical expressions derived based on the extended PR EoS are used to determine thermodynamic and phase equilibrium derivative properties for solid/vapor CO2. These include internal energy, enthalpy, heat capacity, thermal expansion, and isothermal compressibility coefficients as well as the adiabatic speed of sound. In most cases good agreement with the available experimental data is obtained covering the pressure and temperature ranges 0.1–100 MPa and 100–300 K. A pressure/temperature phase equilibrium diagram for solid‐liquid‐vapor CO2 is constructed to demonstrate the overall performance and the limitations of the two EoS as compared to the experimental data spanning the triple point up to 100 MPa pressure. It is shown that the application of the PR EoS along the CO2 sublimation line gives rise to significant errors. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd

Calculation of the high pressure phase equilibrium in hyperbranched polymer systems with the lattice-cluster theory

Currently, the lattice-cluster theory (LCT) is the most convenient thermodynamic tool to describe the branching influence on the phase equilibrium of hyperbranched polymer systems. Unfortunately, until now all applications of the LCT to such systems were restricted to moderate pressure because of the assumption of a rigid lattice. However, there is also a compressible version of the LCT known since a long time. Here, unoccupied lattice sites (voids) are permitted to make the system compressible. Thus, a binary system A+B is treated as ternary system A+B+C where C represents the voids. In this paper, the very complex equations are essentially simplified resulting in an applicable notation. On this base a LCT equation of state is developed and applied to the calculation of the high pressure phase equilibria of carbon dioxide+Boltorn U3000 and of propane+Boltorn H3200. The polymers are fatty acid modified Boltorn H30 molecules (hyperbranched polyester of generation number g=3). The calculated results agree reasonably well with the experimental data from literature.

Methanol Inhibition Effect on Hydrate-Containing Phase Equilibria of Carbon Dioxide and Water

In this work, we investigated the inhibition effect of methanol on the carbon dioxide hydrate-forming conditions in two and three phases. The effect of the amount of carbon dioxide relative to the aqueous methanol solution was also studied to examine the effect of the overall composition on hydrate-forming conditions. In the three-phase region at pressures from (5.0 to 20.0) MPa, the measured isobaric dissolution temperature of hydrate was found to increase as the loading ratio of carbon dioxide increases at the same methanol content, indicating a decreased inhibition effect of methanol. In two-phase region at the pressure of (6.0 and 10.0) MPa, however, the measured solubility of water was found to be unaffected by methanol of 0.200 mass fraction. CSMGem (Sloan and Koh, Clathrate Hydrates of Natural Gases, 3rd ed.; CRC Press: Boca Raton, FL, 2007) calculations qualitatively agree with the present data sets.

High pressure phase equilibrium of carbon dioxide and benzaldehyde binary system

The high-pressure phase equilibria of carbon dioxide+benzaldehyde binary system were measured at temperatures from 298.55 to 345.15K and pressures from 2.20 to 14.96MPa. The experimental method used in this work was a static-analytical method with liquid and vapor phase sampling. The experimental results are discussed and compared with available literature data. The experimental data were correlated with the Peng–Robinson equation of state (PR EoS) using classical van der Waals (two-parameter conventional mixing rule) mixing rules, which could correlate well the binary phase behavior with an average absolute relative deviation of 3.4%.

Phase equilibria of carbon dioxide and methane gas-hydrates predicted with the modified analytical S-L-V equation of state

Gas-hydrates (clathrates) are non-stoichiometric crystallized solutions of gas molecules in the metastable water lattice. Two or more components are associated without ordinary chemical union but through complete enclosure of gas molecules in a framework of water molecules linked together by hydrogen bonds. The clathrates are important in the following applications: the pipeline blockage in natural gas industry, potential energy source in the form of natural hydrates present in ocean bottom, and the CO2 separation and storage. In this study, we have modified an analytical solid-liquid-vapor equation of state (EoS) [A. Yokozeki, Fluid Phase Equil. 222–223 (2004)] to improve its ability for modeling the phase equilibria of clathrates. The EoS can predict the formation conditions for CO2- and CH4-hydrates. It will be used as an initial estimate for a more complicated hydrate model based on the fundamental EoSs for fluid phases.

Vapor‐Liquid Phase Equilibria for Carbon Dioxide+Isopentanol Binary System at Elevated Pressure

AbstractHigh‐pressure vapor‐liquid phase equilibrium data for carbon dioxide+isopentanol were measured at temperatures of 313.2, 323.1, 333.5 and 343.4 K in the pressure range of 4.64 to 12.71 MPa in a variable‐volume high‐pressure visual cell. The experimental data were well correlated with Peng‐Robinson equation of state (PR‐EOS) together with van der Waals‐2 two‐parameter mixing rule, and the binary interaction parameters were obtained. Henry coefficients and partial molar volumes of CO2 at infinite dilution were estimated based on Krichevsky‐Kasarnovsky equation, and Henry coefficients increase with increasing temperature, however, partial molar volumes of CO2 at infinite dilution are negative and the magnitudes decrease with temperature.

Phase equilibria of carbon dioxide + 1-nonanol system at high pressures

Vapor–liquid–equilibria (VLE) and vapor–liquid–liquid equilibria (VLLE) data for the carbon dioxide + 1-nonanol system were measured at 303.15, 308.15, 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 1.15 and 103.3 bar. The Soave–Redlich–Kwong (SRK) equation of state (EOS) coupled with both classical van der Waals and a Gibbs excess energy ( G E ) mixing rules was used in semi-predictive approaches, in order to represent the complex phase behavior (critical curve, liquid–liquid–vapor (LLV) line, isothermal VLE, LLE, and VLLE) of the system. The topology of phase behavior is correctly predicted.

High-pressure phase behavior and FT-IR study of poly(methyl methacrylate) + ethanol systems with addition of supercritical CO2

The phase equilibria of carbon dioxide (CO2) + poly(methyl methacrylate) (PMMA; Mw = 15 k) + ethanol ternary systems were measured at temperatures ranging from 293.3 to 359.7 K and pressures up to 14.1 MPa. In order to determine the phase boundary, we observed the cloud points and bubble points by using a variable volume view cell. Furthermore, the dissolution process of PMMA in CO2-expanded ethanol was studied using FTIR spectroscopy. Although both CO2 and ethanol are nonsolvents for PMMA at 303 K, PMMA dissolved in CO2-expanded ethanol. The noticeable band was carbonyl stretching band for PMMA. No peak shifts and/or no contributions were obtained for PMMA in pure ethanol at 303 K, because ethanol is nonsolvent for PMMA. With addition of CO2 in the mixture of PMMA and ethanol, the carbonyl stretching band of PMMA has a weak contribution at lower wave numbers. It is indicated that a strong interaction between PMMA and ethanol via hydrogen bonding exists.

Compact apparatus for rapid measurement of high-pressure phase equilibria of carbon dioxide expanded liquids

A new apparatus based on a synthetic method was developed for phase equilibrium measurements. The characteristic features of the apparatus are its light weight (ca. 288 g), variable-volume with a free piston, position sensing device for the piston, precise pressure and temperature control, and a window for visual observation. The inner volume of the cell can vary from 2.5 to 8.8 cm 3. The cell was constructed from titanium so that the composition of the sample can be determined by direct weighing of the cell. The apparatus was designed for temperatures up to 473 K and pressures up to 25 MPa. To confirm the reliability of the apparatus, vapor–liquid equilibria of the carbon dioxide–methanol system were measured. The estimated uncertainties of temperature, pressure, and composition of carbon dioxide were less than ±0.05 K, ±0.02 MPa, ±0.20 wt%, respectively. Bubble-point pressures obtained in this work agreed well with the literature data. Bubble-point pressure data for carbon dioxide with acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBE) were measured at temperatures ranging from 313 to 353 K, and could be correlated well with the Peng–Robinson equation of state. The P– x diagrams at a given temperature for acetone, MEK, and MIBK binaries with carbon dioxide were found to be practically identical.

Phase equilibria of carbon dioxide + poly ethylene glycol + water mixtures at high pressure: Measurements and modelling

Phase equilibria of carbon dioxide + poly ethylene glycol (PEG) of average mol weight 6000 g/mol + water mixtures has been measured by the static method at conditions of interest for the development of Particles from Gas Saturated Solutions (PGSS)-drying processes (pressure from 10 MPa to 30 MPa, temperature from 353 K to 393 K). A thermodynamic model based on the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state has been developed for correlating experimental data. The model is able to predict the composition of the liquid phase with an average deviation of 8.0%. However, the model does not calculate correctly the concentration of PEG in the gas phase. The model is also capable of predicting VLE data reported in the literature of PEG + CO 2 mixtures with PEGs of molecular weights ranging from 1500 g/mol to 18500 g/mol as well as solid–fluid equilibrium of carbon dioxide + PEG mixtures at pressures below 10 MPa.

Experimental Measurements of Hydrate Phase Equilibria for Carbon Dioxide in the Presence of THF, Propylene Oxide, and 1,4-Dioxane

Hydrate phase equilibria have been measured for carbon dioxide + cyclic ethers + water in the temperature range of (270 to 290) K and in the pressure range of (0.2 to 4.7) MPa. Three cyclic ethers, THF, propylene oxide, and 1,4-dioxane, were selected at a mole fraction of 0.03. The stabilization effect of the mixed hydrate was found to be the highest for THF followed by propylene oxide, while no stabilization effect was observed for 1,4-dioxane in the studied temperature and pressure range. The mole fraction effect on hydrate phase equilibria has also been investigated for THF and propylene oxide in the range of x = (0.01 to 0.10).

Phase Behavior of the Mixtures of CO2+ Poly(methyl methacrylate) + Ethanol at High Pressure

Phase equilibria of carbon dioxide (CO2) + poly(methyl methacrylate) (PMMA-15 k, PMMA-120 k) + ethanol ternary systems were measured at temperatures ranging from (293.3 to 359.7) K and pressures up to 14.1 MPa. Furthermore, cloud point temperatures of PMMA + ethanol binary systems were determined at pressures up to 15 MPa. To determine the phase boundary, we observed the cloud points and bubble points by using a variable volume view cell. With the addition of CO2 into the binary PMMA + ethanol mixture, the upper critical solution temperature (UCST) line shifts toward higher pressure and temperature values. At high CO2 concentrations, the lower critical solution temperature (LCST) and UCST curves merge. Further, the liquid–liquid split phenomenon is observed over the entire temperature range.

Phase Equilibria in Carbon Dioxide Expanded Solvents: Experiments and Molecular Simulations

We present complementary molecular simulations and experimental results of phase equilibria for carbon dioxide expanded acetonitrile, methanol, ethanol, acetone, acetic acid, toluene, and 1-octene. The volume expansion measurements were done using a high-pressure Jerguson view cell. Molecular simulations were performed using the Gibbs ensemble Monte Carlo method. Calculations in the canonical ensemble (NVT) were performed to determine the coexistence curve of the pure solvent systems. Binary mixtures were simulated in the isobaric-isothermal distribution (NPT). Predictions of vapor-liquid equilibria of the pure components agree well with experimental data. The simulations accurately reproduced experimental data on saturated liquid and vapor densities for carbon dioxide, methanol, ethanol, acetone, acetic acid, toluene, and 1-octene. In all carbon dioxide expanded liquids (CXL's) studied, the molecular simulation results for the volume expansion of these binary mixtures were found to be as good as, and in many cases superior to, predictions based on the Peng-Robinson equation of state, demonstrating the utility of molecular simulation in the prediction of CXL phase equilibria.