CO2 Binary System Research Articles

Experimental validation on the phase separation for the 2-(Diisopropylamino)ethyl methacrylate and Poly[2-(diisopropylamino)ethyl methacrylate] in supercritical CO2

Using an intense pressure flexible volume apparatus, the phase transition equilibrium of the two-component mixture consisting of 2-(diisopropylamino)ethyl methacrylate (2DIPAEMA) + supercritical carbon dioxide (Sc CO2), as well as poly(2-(diisopropylamino)ethyl methacrylate) [P(2DIPAEMA)] with various co-solvents (propylene, propane, 1-butene, butane, and dimethyl ether), was investigated. Additionally, the three-component system P(2DIPAEMA) + 2DIPAEMA (0.0, 0.0245, 0.0523, 0.1036 mol fraction) + Sc CO2 was studied at a specific temperature range of 313.2 K to 454.5 K and an upper-pressure limit of 171.03 MPa. The dew-point, critical-point, and bubble-point equilibria data for the 2DIPAEMA + Sc CO2 binary system at a temperature interval of 313.2–393.2 K and a pressure limit of 21.61 MPa were measured. At low co-solvent concentrations, the solubility transition curve in the three-component P(2DIPAEMA) + Sc CO2 + co-solvent system (comprising propylene, propane, 1-butene, butane, and dimethyl ether) shows a cloud pressure curve that increases as temperature decreases. However, at higher concentrations, cloud pressure decreased rapidly, but a minor change in cloud pressure with temperature was recorded, indicating a homogeneous single-phase behavior resembling a type-I phase diagram. The van der Waals one-fluid mixing rule was employed to compare the experimentally calculated data with the computed and modelled data of the Peng–Robinson mathematical equation. It was discovered that the computed values were consistent with the experimental values. The RMSD for the (Sc CO2 + 2DIPAEMA) system was 4.37 % at five different temperatures. The critical parameter of the pure component, 2DIPAEMA, was estimated using the Joback-Lyderson approach.

Cryogenic Solid Solubility Measurements for HFC-32 + CO2 Binary Mixtures at Temperatures Between (132 and 217) K

Accurate phase equilibrium data for mixtures of eco-friendly but mildly-flammable refrigerants with inert components like CO2 will help the refrigeration industry safely employ working fluids with 80 % less global warming potential than those of many widely-used refrigerants. In this work, a visual high-pressure measurement setup was used to measure solid–fluid equilibrium (SFE) of HFC-32 + CO2 binary systems at temperatures between (132 and 217) K. The experimental data show a eutectic composition of around 11 mol % CO2 with a eutectic temperature of 131.9 K at solid–liquid–vapour (SLVE) condition. Measured SLVE and solid–liquid equilibrium data were used to tune a thermodynamic model implemented in the ThermoFAST software package by adjusting the binary interaction parameter (BIP) in the Peng–Robinson equation of state. The tuned model represents the measured melting points for binary mixtures with a root mean square deviation (RMSD) of 3.2 K, which is 60 % less than achieved with the default BIP. An RMSD of 0.5 K was obtained using the tuned model for the mixtures with CO2 fractions over 28 mol % relative to an RMSD of 3.4 K obtained with the default model. The new property data and improved model presented in this work will help avoid solid deposition risk in cryogenic applications of the HFC-32 + CO2 binary system and promote wider applications of more environmentally-friendly refrigerant mixtures.

Investigating the solution behavior of CO2 in ester based on a hybrid of ANN technology and PS method

ABSTRACT Artificial neural networks (ANNs) are artificial intelligence tools, and pattern search (PS) is a method for solving optimization problems. Although these two technologies have been extensively used in the chemical and engineering fields, they have limitations. This study proposes a methodology based on a hybrid of ANN technology and PS method to investigate the solution behavior of carbon dioxide (CO2). Five CO2-ester binary systems are selected as the model systems to demonstrate the point of interest. The results reveal that this methodology can overcome the defects of the two technologies and develop their advantages, thereby providing a satisfactory description of the solubility data of CO2 in these esters. The proposed methodology can be applied to a series of CO2 binary systems and is helpful in selecting a suitable absorbent for CO2 capture technology.

Phase equilibrium of PVAc + CO2 binary systems and PVAc + CO2 + ethanol ternary systems

The cloud point and bubble point isopleths were measured for poly(vinyl acetate) (PVAc) + CO2 binary systems and PVAc + CO2 + ethanol ternary systems using a supercritical CO2 phase equilibrium apparatus. A transition point measurement device was designed to accurately determine the cloud point pressures by measuring the resistance variation of a photoresistor. The effects of the temperature, pressure, components, and polymer molecular weight on the phase behavior of these binary and ternary systems were investigated. We found that the transition point pressure increased with increasing temperature and molecular weight of PVAc, the cloud point isopleths for the PVAc + CO2 binary systems are upper critical solution pressure (UCSP) type, the cloud point pressures moved downwards with the addition of ethanol to PVAc + CO2, and the cloud point pressures decreased with increasing PVAc + ethanol concentration at a fixed mass ratio of 1:7. The perturbed-chain statistical associating fluid theory equation of state (PC-SAFT EOS) was used to investigate the phase behavior of these binary and ternary systems by adjusting the binary interaction parameter, kij. The modeling shows a very good agreement with the experimental data.

Application of Highly Accurate Phase-Equilibrium Models for CO2 Freezing Prediction of Natural Gas System

It is of great engineering significance to find an accurate model to predict CO2 freezing and avoid plugging in the light hydrocarbon separation process of natural gas. Research starts from CO2 freezing in simple CH4–CO2 binary systems. By use of a traditional model based on the Antoine equation, the calculated freezing temperature in liquid–solid equilibrium (LSE) is not as accurate as that in vapor–solid equilibrium (VSE). Then a new thermodynamic method of reference state of hypothetical fluid is used to replace LSE model based on the Antoine equation to calculate solid CO2 fugacity. The improved phase-equilibrium model based on GERG-2008 is proved to be the most accurate one to calculate CO2 freezing temperature, in which the Antoine equation is used in VSE model while reference state method is used in LSE model. Compared with experimental data, the calculated results also show a higher accuracy in complex natural gas system. Besides, the improved phase-equilibrium model is applied in the actual light...

Measurement and correlation of vapor-liquid equilibria for a binary system containing 1-butyl-3-methylimidazolium tridecafluorohexylsulfonate and carbon dioxide

Using a high-pressure variable-volume view cell, the vapor-liquid equilibria of the binary system CO2 and 1-butyl-3-methylimidazolium tridecafluorohexylsulfonate ([BMIM][TDfO]) were determined. The CO2 mole fraction ranged from 0.104 to 0.952 over a temperature range of 298.2-323.2 K. Both the Peng-Robinson and Soave-Redlich- Kwong equations of state were applied with two different mixing rules to correlate with the experimentally obtained results. Increasing the alkyl chain length in perfluorinated sulfonate anion mother structure from methyl to hexyl markedly increased the CO2 solubility. To investigate the effect of the number of fluorine atoms in the anion on the phase behavior of imidazolium-based ionic liquid, these experimental results were then compared with those reported in previous experimental studies of 1-alkyl-3-methylimidazolium cations-including ionic liquid+CO2 binary system.

Electrolyte CPA equation of state for very high temperature and pressure reservoir and basin applications

In this work, an electrolyte version of the Cubic Plus Association (eCPA) equation of state has been adapted to systems containing CH4, CO2, H2O and NaCl (up to 5molal) at pressures up to 200MPa and temperatures up to 773K for salt-free systems and 573K for salt-containing systems. Its purpose is to represent the phase behavior (including salting-out effect and critical point) and the phase densities in a range of temperature and pressure encountered in deep reservoirs and basins. The goal of the parameterization proposed is not to reach a very high accuracy for phase equilibrium and volumetric properties, but rather to develop a semi-predictive approach to model the phase and volumetric behavior of this system while allowing an easy extension to other compounds.Without salt, predictions for pure component vapor pressures and liquid molar volumes present an average absolute deviation (AAD) lower than 3% compared to experimental reference values. The pure component molar volumes out of saturation show an AAD lower than 4%. The highest deviations in densities are observed as expected in the vicinity of the critical coordinates of pure water and this effect increases when gases or salts are added to the system. For each binary system, CH4+CO2, CH4+H2O and CO2+H2O, binary interaction parameters have been fitted to correctly represent the shape of the fluid phase envelopes (including all critical points) in the entire temperature and pressure range considered (219K to 633K and up to 250MPa). The methane concentration in both phases of the CH4+CO2 binary system is represented with an AAD lower than 9%. The methane solubility in water is represented within 16% and 8% for the methane content of the vapor. The CO2 solubility in water is within 26%, while the CO2 in the vapor phase shows an average deviation of 12%. All molar volumes are represented with an AAD lower than 3%. The few VLE experimental data for the CH4+CO2+H2O ternary system are fairly well predicted with the model without extra parameter, which confirm the ability of the eCPA equation of state to be extended to multi-component systems. In the presence of salts, gas+ion binary interaction parameters have been fitted, and all phase equilibrium are qualitatively correctly described, and more specifically the salting out effect. The solubility of methane or CO2 in brines, up to 5molal, is represented with an AAD of 33% in a large temperature and pressure range (up to 673K and 150MPa). It should be noticed that for high temperatures, experimental data are relatively scarce and not always consistent. No data exist for water content of the vapor phase in these conditions.The new eCPA model can be easily extended to other components (including ions) to better represent real fluid behavior in very deep reservoir conditions.

Densities and Viscosities of 1-butyl-3-methylimidazolium Hexafluorophosphate [bmim][PF6] + CO2 Binary System: Determination and Correlation

A gas-dissolving device was designed and connected to the falling-body viscometer, which was used to determine the viscosities of liquids in our lab before. The equipment can be used to determine the gas composition, the densities and viscosities of the solution at the same time. The densities and viscosities of [bmim][PF6] + CO2 binary system were determined in the temperature range of 313.2 to 413.2 K and pressure range of 5.0 to 25.0 MPa by the equipment. Then the viscosities of [bmim][PF6] + CO2 binary system at constant temperature, constant pressure, and different temperature and pressure were correlated, respectively. For the correlation at different temperature and different pressure for different concentration mixtures the average relative deviation ARD is 0.037.

Vapour–liquid equilibrium data for the hydrogen sulphide (H2S) + carbon dioxide (CO2) system at temperatures from 258 to 313 K

From the design of acid injection scheme to the impact of hydrogen sulphide in CCS scheme, knowledge of the phase behaviour of the hydrogen sulphide+carbon dioxide is essential. In this communication, new isothermal vapour–liquid equilibrium measurements for the binary system H2S–CO2 have been conducted at 258.41K, 273.15K, 293.47K and 313.02K in the pressure range from 1.0 to 5.5MPa. The experimental method used in this work is of the static-analytic type, taking advantage of two magnetic capillary samplers (Rolsi™, Armines’ Patent) developed in the CTP laboratory. This experimental method allows the sampling in both liquid and vapour phases and their analysis by GC. The data were obtained with uncertainties within ±0.02K, ±0.002MPa, and 0.006 for molar compositions. It is demonstrated that both the Peng–Robinson (PR) equation of state (classical or the P-PR78 version) or the Soave–Redlich–Kwong (SRK) equation of state combined with the classical mixing rule and appropriate binary interaction parameters were able to satisfactorily describe the phase behaviour of the H2S–CO2 binary systems.

Measurement and mathematical modeling of solubility of buttery-odor substance (acetoin) in supercritical CO2 at several pressures and temperatures

The solubilities of acetoin (3-hydroxy-2-butanone), a frequently used buttery-odor compound in supercritical carbon dioxide (SC-CO2) at several pressures and temperatures were measured in this work. The measurements were conducted in a static-analytic mode at several pressures ranging from 8MPa to 28MPa and four temperatures of 313.15K, 323.15K, 333.15K, and 343.15K. The equilibrium was established for 3–4h. The solubilities of acetoin in SC-CO2 increased with increasing both pressure and temperature beyond the crossover pressure at 8MPa. Two density-based models namely Chrastil and Del Valle-Aguilera and Peng–Robinson equation of state (PR-EOS) with quadratic and Stryjek–Vera mixing rules were used to represent experimental solubilities and to describe phase behavior of the system. Both Chrastil and Del Valle-Aguilera models were able to correlate experimental solubility data satisfactorily with absolute average relative deviation (AARD) of 0.27%. Similarly, the phase equilibrium behavior of acetoin+supercritical CO2 binary system can be well interpreted by PR-EOS with quadratic (AARD of 0.11%) and Stryjek–Vera mixing rules (AARD of 0.08%).

Phase Equilibria of the 1-Hexyl-2,3-dimethylimidazolium Bis(trifluoromethylsulfonyl)imide and Carbon Dioxide Binary System and 1-Octyl-2,3-dimethylimidazolium Bis(trifluoromethylsulfonyl)imide and Carbon Dioxide Binary System

A high-pressure variable-volume view cell was used to measure the phase equilibria of a 1-hexyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([HMMIM][Tf2N]) and CO2 binary system in th...

Intermolecular-Interaction-Dominated Solvation Behaviors of Liquid Monomers and Polymers in Gaseous and Supercritical Carbon Dioxide

The strong desire for the extensive application of supercritical carbon dioxide (scCO2) as an environmentally benign solvent in polymers synthesis and processing has spurred numerous attempts to discern and improve its solvability toward monomers as well as polymers. The detailed solvation processes along with the phase behaviors of a fluorinated liquid monomer (LM) of 2,2,2-trifluoroethyl methacrylate (TFEMA), as well as another 13 non-fluorinated LMs in gaseous and supercritical CO2, were respectively investigated by using a newly built high-pressure ATR-FTIR in situ monitoring system as CO2 pressure stepwise increased from 0 to 38.0 MPa. Interestingly, an unexpected vibrational absorption variation, especially a distinct blue-shift in the in situ FTIR spectra of the functional groups in each LM + CO2 binary system, was generally observed during the solvation process as CO2 pressure increased. A similar variation trend of the vibrational absorption of the C–F bond in the TFEMA + CO2 system was also obtained by ab initio calculation (MP2). We believe that the special evolution of the vibrational absorption is directly rooted in and dynamically induced by the variation of the intermolecular interactions in the LM + CO2 binary systems as the pressure and/or the temperature varied and is closely related to the solvation behaviors of the LM in CO2. Based on this cognition, the solvation mechanism of the LMs in gaseous and supercritical CO2 was systematically demonstrated by introducing the concepts of transition pressure (PT) as well as the resultant forces/interactions of σ(A–B) and σ(B–B). Poly(vinyl acetate) (PVAc), poly(hexafluoropropylene oxide) (PHFPO), and PTFEMA oligomers were prepared and characterized. The proposed mechanism was evaluated by investigating the solvation behaviors of the prepared oligomers and hexafluoropropylene trimer ((HFP)3) in CO2 and was successfully employed to expound the special CO2-philicity of the carbonyl compounds and the fluorinated organics (FOs).

High Pressure Phase Behavior of Carbon Dioxide in Carbon Disulfide and Carbon Tetrachloride

The knowledge about the nature of the interactions between carbon dioxide (CO2) and different organic molecules is of relevance for designing, operating, and optimizing many industrial processes. In fact, numerous studies concerning the interactions of CO2 with other compounds have been presented, using both experimental and theoretical approaches. As part of a continuing effort to fully understand the interactions between CO2 and different compounds, the high pressure phase equilibria of CO2 binary systems containing carbon disulfide (CS2) and carbon tetrachloride (CCl4) were here investigated, involving experimental measurements of high pressure phase equilibria and modeling with the cubic plus association (CPA) equation of state (EoS). The CCl4 and CS2 were chosen due to their similar structure to CH4 and CO2, respectively, allowing to anticipate the interactions between like and unlike molecules that can be found at binary and multicomponent systems constituted by CO2 and/or CH4. It was found that CO2 + CS2 presents strong positive deviations to ideality while the CO2 + CCl4 system presents an almost ideal behavior.

Evaluation of the CO2 behavior in binary mixtures with alkanes, alcohols, acids and esters using the Cubic-Plus-Association Equation of State

Knowledge regarding the high pressure phase behavior of CO2 mixtures is of primary importance for designing, operating and optimizing many industrial processes, such as supercritical fluid extraction for pharmaceutical, food and biodiesel industries and oil recovery enhancement through CO2 flooding.In the present work, it is investigated how the CPA EoS (Cubic-Plus-Association equation of state) can be used for an adequate description of the VLE of an extensive series of CO2 binary systems containing n-alkanes, n-alcohols, esters and n-acids, in a broad range of temperatures and pressures. These families constitute a series of non-self associating, associating and cross-associating components whose potential associative interactions with CO2 are evaluated here.A detailed investigation regarding the differing behavior of CO2 depending on the nature of the second component and how the CPA EoS can best describe them is presented here, namely explicitly considering the CO2 association and also evaluating also its different association schemes.It will be shown that it is important to consider CO2 self- and cross-association to describe the VLE of n-alkane and small alcohol/CO2 systems. However, it is not necessary to consider CO2 association when dealing with systems of heavy alcohols, esters or acids.The CPA EoS provides very good results for the extensive range of CO2 binary systems considered here using, for most of them, single, small, temperature independent, positive and chain length dependent binary interaction parameters.

Micronization by Rapid Expansion of Supercritical Solutions to Enhance the Dissolution Rates of Poorly Water-Soluble Pharmaceuticals

The dissolution of a drug into the biological environment can be enhanced by reducing the particle size of the drug. In this study the rapid expansion of supercritical solutions (RESS) process was employed to micronize racemic ibuprofen, and the dissolution rate of the micronized product in a buffered solution was examined. The chiral nonsteroidal antiinflammatory, racemic ibuprofen, was used as a model drug because its dissolution rate is limited by its poor solubility in water. The phase behavior of the ibuprofen−CO2 binary system was investigated prior to the solubility measurements being undertaken. The solubility of racemic ibuprofen in supercritical CO2 was measured using a dynamic apparatus at pressures between 80 and 220 bar and temperatures of 35, 40, and 45 °C. The solubility data was modeled using the Peng−Robinson equation of state with van der Waals mixing rules. The ratio of R and S isomers in the extract was found to be the same as that in the original material. The solubility of pure optic...

Solubility, in Supercritical Carbon Dioxide, of Paraffin Waxes Used as Binders for Low-Pressure Injection Molding

Paraffin waxes, commonly used as binders in ceramic-forming processes, can be removed from ceramic bodies with supercritical carbon dioxide. Therefore, the solubility of three industrial paraffin waxes (melting at 42, 52, and 62 °C, respectively) in supercritical CO2 was investigated. The concentrations of these paraffin waxes in the solvent-rich phase in equilibrium with the paraffin-rich phase were measured at 343 K in the pressure range 12−30 MPa by using infrared absorption spectroscopy. Some n-alcane−CO2 binaries were also investigated. A model was developed by analogy with polydisperse polymers in solvents. It relates the concentration of the paraffin waxes to the concentration of the pure n-alcanes for n-alcane−CO2 binary systems. This model gives accurate overall concentration values for paraffin−CO2 mixtures and reproduces the n-alcane distribution in the solvent-rich phase.

Development and extension of PSRK/UNIQUAC model to methane and nitrogen gases

Two successful procedures for matching the equation of state (EOS) and the excess Gibbs energy model at zero pressure belong to Michelsen [M.L. Michelsen, Fluid Phase Equilibria, 60 (1990) 213] and Holderbaum-Gmehling [T. Holderbaum, J. Gmehling, Fluid Phase Equilibria, 70 (1991) 251]. These procedures lead to volume independent mixing rules for the mixture parameter a. Michelsen proposed the MHV1 and MHV2 mixing rules and Holderbaum-Gmehling proposed the PSRK mixing rule. Keshtkar et al. [A. Keshtkar, F. Jalali, M. Moshfegian, Fluid Phase Equilibria, 140 (1997) 107] demonstrated the utility of these mixing rules together with UNIFAC and UNIQUAC models for the prediction of high-pressure vapor-liquid equilibrium (VLE) of CO 2-binary systems. Also, they showed that the PSRK/UNIQUAC model gives better VLE results than other models. In this paper, we develop and extend the above model to methane and nitrogen gases. For this purpose, it is required that the missing interaction parameters of model are fitted with experimental VLE data. The VLE calculations show that good agreement between calculated results and experimental data can be produced by using the obtained parameters.