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.     

Photocleavage of dimers of coumarin and 6-alkylcoumarins

The cleavage of four coumarin dimers, the syn-head-to-tail (ht) dimer of parent coumarin (syn-ht-CC1), the anti- and syn-hh dimers of 6-methylcoumarin (anti-hh-CC2 and syn-hh-CC2, respectively) and the anti-hh dimer of 6-dodecylcoumarin (anti-hh-CC3), was studied by UV–vis and IR spectroscopy and HPLC upon direct 254 nm irradiation as well as sensitized excitation. The quantum yield of dimer splitting is Φ_sp = 0.1–0.3 in various solvents and the effects of structure and solvent polarity are small. In certain solvents some of the dimers produced CO₂ along with the monomers in the splitting reaction. Electron transfer from dimers to the triplet state of sensitizers, such as benzophenone or 9,10-anthraquinone, was observed in acetonitrile.     

Phase equilibrium for ozone-containing hydrates formed from an (ozone + oxygen) gas mixture coexisting with gaseous carbon dioxide and liquid water

The paper reports the three-phase (gas + aqueous liquid + hydrate) equilibrium pressure (p) versus temperature (T) data for a (O₃ + O₂ + CO₂ + H₂O) system and, for comparison, corresponding data for a (O₂ + CO₂ + H₂O) system for the first time. These data cover the temperature range from (272 to 279) K, corresponding to pressures up to 4 MPa, for each of the three different (O₃ + O₂)-to-CO₂ or O₂-to-CO₂ mole ratios in the gas phase, which are approximately 1:9, 2:8, and 3:7, respectively. The mole fraction of ozone in the gas phase of the (O₃ + O₂ + CO₂ + H₂O) system was from ∼0.004 to ∼0.02. The modified pressure-search method, developed in our previous study [S. Muromachi, T. Nakajima, R. Ohmura, Y.H. Mori, Fluid Phase Equilib. 305 (2011) 145–151] for p–T measurements in the presence of chemically unstable ozone, was applied, having been further modified for dealing with highly water-soluble CO₂, for the (O₃ + O₂ + CO₂ + H₂O) system, while the conventional temperature-search method was used for the (O₂ + CO₂ + H₂O) system. The measurement uncertainties (with 95% coverage) were ±0.11 K for T, ±6.0 kPa for p, and ±0.0015 for the mole fraction of each species in the gas phase. It was confirmed that, at a given CO₂ fraction in the gas phase, p for the (O₃ + O₂ + CO₂ + H₂O) system was consistently lower than that for the (O₂ + CO₂ + H₂O) system over the entire T range of the present measurements, indicating a preference of O₃ to O₂ in the uptake of guest-gas molecules into the cages of a structure I hydrate.     

Performance of a bench-scale membrane pilot plant for the upgrading of biogas in a wastewater treatment plant

A bench-scale membrane pilot plant for upgrading biogas generated at a municipal wastewater treatment plant was constructed and operated for extended periods of time. The raw biogas was available at 45–60 psia (3.1–4.1 bar) and contained 62.6 mol% CH₄, the balance being mainly CO₂ and a large number of organic impurities. The operation of the pilot plant was tested with two identical hollow-fiber modules for periods of over 1000 h (41 days) with each module. One of the hollow-fiber modules was tested at an average pressure of about 525 psia (36 bar) and at stage-cuts of 0.34–0.41, and the other module at about 423 psia (29 bar) and at stage-cuts of 0.36–0.39. The flow rates of the biogas feed were 30–36 ft³/h (2.4×10⁻⁴–2.8×10⁻⁴ m³/s) and 21–24 ft³/h (1.7×10⁻⁴–1.9×10⁻⁴ m³/s), respectively. The CH₄ concentration in the retentate stream (the upgraded biogas) was raised in these tests to 92–95 mol% CH₄. The performance of the pilot plant was stable over the entire test periods. An even higher CH₄ concentration of 97 mol% was reached in short-term tests at a stage-cut of 0.46. The raw biogas had to be pretreated to prevent the condensation of organic impurities which tended to dissolve the hollow fibers. Upgraded biogas containing over 90 mol% CH₄ produced in a large-scale membrane separation plant could be used for the generation of electricity. At the same time, the permeate (waste) stream would contain over 15 mol% CH₄ and could be used for heating applications.     

High pressure phase equilibrium for δ-tocopherol + CO2

Vapour–liquid equilibrium compositions were measured for mixtures of δ-tocopherol and carbon dioxide, at pressures from 9 up to 27 MPa, and four temperatures between 306 and 333 K. The system exhibits liquid–liquid equilibrium at high pressures, similarly to previous results for mixtures of α-tocopherol with carbon dioxide. The results were correlated with the Peng–Robinson equation of state, using the Panagiotopoulos–Reid combination rules.Comparison of the solubilities of δ-tocopherol and α-tocopherol in supercritical carbon dioxide was performed using Chrastil’s equation to correlate the data. The number of solvent CO₂ molecules per solute molecule was calculated in both cases. An enthalpy of solvation per mole of CO₂ of −10 kJ mol⁻¹ was obtained.     

Hydrate phase equilibrium in the system of (carbon dioxide + 2,2-dimethylbutane + water) at temperatures below freezing point of water

The four-phase equilibrium conditions of (vapor + liquid + hydrate + ice) were measured in the system of (CO₂ + 2,2-dimethylbutane + water). The measurements were performed within the temperature range (254.2 to 270.2) K and pressure range (0.490 to 0.847) MPa using an isochoric method. Phase equilibrium conditions of hydrate formed in this study were measured to be at higher temperatures and lower pressures than those of structure I CO₂ simple hydrate. The largest difference in the equilibrium pressures of structure I CO₂ hydrate and the hydrate formed in the present study was 0.057 MPa at T = 258.3 K. On the basis of the four-phase equilibrium data obtained, the quintuple point for the (ice + structure I hydrate + structure H hydrate + liquid + vapor) was also determined to be T = 266.4 K and 0.864 MPa. The results indicate that structure H hydrate formed with CO₂ and 2,2-dimethylbutane is stable exclusively at the temperatures below the quintuple temperature.     

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.     

Effect of compressed CO2 on crystallization and melting behavior of isotactic polypropylene

Compressed gases such as CO₂ above their critical temperatures provide a highly tunable technique that has been shown to induce changes in phase behavior, crystallization kinetics and morphology of the polymers. Gas induced plasticization of the polymer matrix has been studied in a large number of polymers such as polystyrene, and poly(ethylene terephathalate). The knowledge of polymer–gas interactions is fundamental to the study of phenomena such as solubility and diffusivity of gases in polymers, dilation of polymers and in the development of applications such as foams and barrier materials.In this paper, we describe the interactions of compressed CO₂ with isotactic polypropylene (PP). Crystallization of various PPs in presence of compressed CO₂ was evaluated using a high pressure differential scanning calorimeter (HPDSC). CO₂ plasticized the polymer matrix and decreased the crystallization temperature, T_c by ∼8 °C for PP at a pressure of 650 psi CO₂. The decrease as a function of pressure was −0.173 °C/bar and did not change with the molecular architecture of PP. Both crystallization kinetics and melting behavior are evaluated.Since solubility and diffusivity are important thermodynamic parameters that establish the intrinsic gas transport characteristics in a polymer, solubility of CO₂ in PP was measured using a high-pressure electrobalance and compared with cross-linked polyethylene. At 50 °C, solubility followed Henry’s law and at a pressure of 200 psi about 1% CO₂ dissolved in PP. Similar solubility was achieved in PE at a pressure of 160 psi. Higher solubility of CO₂ in PE is attributed to its lower crystallinity and lower T_g, than PP. Diffusion coefficients were calculated from the sorption kinetics using a Fickian transport model. Diffusivity was independent of pressure and PE showed higher diffusivity than PP. Preliminary foaming studies carried out using a batch process indicate that both PP and PE can be foamed from the solid state to form microcellular foams. Cell size and cell density were ∼10 μm and 10⁸ cells/cm³, respectively in PE. Differences in morphology between the foams for these polymers are attributed to the differences in diffusivity.     

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.     

Molecular spin ladders self-assembly from [Ni(dmit)2]− building blocks: Syntheses,structures and magnetic properties

Two ion-pair compounds, consisting of 1-(4′-R-benzyl)pyridinium ([RBzPy]⁺, R = NO₂ (1) and Br (2)) and [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithion-4,5-dithiolato), have been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into two-leg ladder through terminal S⋯S interactions in 1, lateral S⋯S interactions in 2. The weak H-bonding interactions of C–H⋯S were observed in 2, while only weak van de Waals interactions between anion and cations in 1. The magnetic susceptibilities measured in 2–300 K indicate AFM exchange interaction domination both two compounds. A peculiar magnetic transition at ∼100 K was observed in 1. An AFM ordering below ∼11 K was found in 2, and the best fit to magnetic susceptibility above 45 K in this compound, using a dimer model with s = 1/2, give rise to Δ/k_B = 36.1 K, zJ = −0.91 K, C = 3.2 × 10⁻³ emu K mol⁻¹ and χ₀ = −4.0 × 10⁻⁶ emu mol⁻¹ with g of 2.0 fixed.     

High pressure phase behavior and modeling of CO2–propyl acrylate and CO2–propyl methacrylate systems

High pressure phase behavior are obtained for CO₂–propyl acrylate system at 40, 60, 80, 100 and 120 °C and pressure up to 161 bar and for CO₂–propyl methacrylate systems at 40, 60, 80, 100 and 120 °C and pressure up to 166 bar. The solubility of propyl acrylate and propyl methacrylate for the CO₂–propyl acrylate and CO₂–propyl methacrylate systems increases as the temperature increases at constant pressure. The CO₂–propyl acrylate and CO₂–propyl methacrylate systems have continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of CO₂ and propyl acrylate or propyl methacrylate. The CO₂–propyl acrylate and CO₂–propyl methacrylate systems exhibit type-I phase behavior with a continuous mixture critical curve.The experimental results for CO₂–propyl acrylate and CO₂–propyl methacrylate systems are modeled using both the statistical associating fluid theory (SAFT) and Peng–Robinson equations of state. A good fit of the data are obtained with SAFT using two adjustable parameters for CO₂–propyl acrylate and CO₂–propyl methacrylate systems and Peng–Robinson equation using one and two adjustable parameter for CO₂–propyl acrylate and CO₂–propyl methacrylate system.     

Phase equilibria in ternary (carbon dioxide + tetrahydrofuran + water) system in hydrate-forming region: Effects of carbon dioxide concentration and the occurrence of pseudo-retrograde hydrate phenomenon

In the present work, the three- and four-phase hydrate equilibria of (carbon dioxide (CO₂) + tetrahydrofuran (THF) + water) system are measured by using Cailletet equipment in the temperature and pressure range of (272 to 292) K and (1.0 to 7.5) MPa, respectively, at different CO₂ concentration. Throughout the study, the concentration of THF is kept constant at 5 mol% in the aqueous solution. In addition, the fluid phase transitions of L_W–L_V–V → L_W–L_V (bubble point) and L_W–L_V–V → L_W–V (dew point) are determined when they are present in the ternary system. For comparison, the three-phase hydrate equilibria of binary (CO₂ + H₂O) are also measured. Experimental measurements show that the addition of THF as a hydrate promoter extends hydrate stability region by elevating the hydrate equilibrium temperature at a specified pressure. The three-phase equilibrium line H–L_W–V is found to be independent of the overall concentration of CO₂. Contradictory, at higher pressure, the phase equilibria of the systems are significantly influenced by the overall concentration of CO₂ in the systems. A liquid–liquid phase split is observed at overall concentration of CO₂ as low as 3 mol% at elevated pressure. The region is bounded by the bubble-points line (L_W–L_V–V → L_W–L_V), dew points line (L_W–L_V–V → L_W + V) and the four-phase equilibrium line (H + L_W + L_V + V). At higher overall concentration of CO₂ in the ternary system, experimental measurements show that pseudo-retrograde behaviour exists at pressure between (2.5 and 5) MPa at temperature of 290.8 K.     

Phase compositions and saturated densities for the binary systems of carbon dioxide with ethanol and dichloromethane

The compositions and densities of the liquid and vapor phases of two binary systems at equilibrium were measured on a new experimental apparatus over a range of temperatures and pressures. The studied systems are: CO₂–ethanol at 313.2 and 328.2 K; CO₂–dichloromethane at 308.2, 318.2 and 328.2 K and for pressures ranging from ambient up to ca. 9 MPa. Some of our measurements are critically compared with corresponding literature values. These measurements are ideally suited for testing equation-of-state models. The recently developed quasi-chemical hydrogen-bonding (QCHB) model was used for correlating the experimental data. A satisfactory agreement was obtained between experimental and calculated phase compositions and saturated densities.     

Equilibrium solubility of carbon dioxide in a 30 wt.% aqueous solution of 2-((2-aminoethyl)amino)ethanol at pressures between atmospheric and 4400 kPa: An experimental and modelling study

New experimental equilibrium data were obtained for the solubility of carbon dioxide in an aqueous solution with 30 wt.% of 2-((2-aminoethyl)amino)ethanol (AEEA) at temperatures ranging from (313.2 to 368.2) K and CO₂ partial pressures ranging from above atmospheric to 4400 kPa. A thermodynamic model based on the Deshmukh–Mather method was applied to correlate and predict the CO₂ solubility in aqueous AEEA solutions. The binary interaction parameters and equilibrium constants for the proposed reactions were determined by data regression. Using the adjusted parameters, equilibrium partial pressures of CO₂ were calculated and compared with the corresponding experimental values at the selected temperatures and pressures. Values of carbon dioxide solubility at other temperatures reported in the literature were also calculated. The average absolute deviation for all of the data points was found to be 8.2%. The enthalpy change of the absorption of CO₂ in the 30 wt.% aqueous solution of AEEA was also estimated with our model.     

Vapor–liquid equilibria for the ternary system of carbon dioxide + ethanol + ethyl acetate at elevated pressures

Vapor–liquid equilibrium (VLE) data for the ternary system of carbon dioxide, ethanol and ethyl acetate were measured in this study at 303.2, 308.2, and 313.2 K, and at pressures from 4 to 7 MPa. A static type phase equilibrium apparatus with visual sapphire windows was used in the experimental measurements. New VLE data for CO₂ in the mixed solvent were presented. These ternary VLE data at elevated pressures were also correlated using either the modified Soave–Redlich–Kwong or Peng–Robinson equation of state, with either the van der Waals one-fluid or Huron–Vidal mixing model. Satisfactory correlation results are reported with temperature-independent binary parameters. It is observed that at 313.2 K and 7 MPa, ethanol can be separated from ethyl acetate into the vapor phase at all concentrations in the presence of high pressure CO₂.     

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.     

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.     

High-pressure (vapour + liquid) equilibria for ternary systems composed by {(E)-2-hexenal or hexanal + carbon dioxide + water}: Partition coefficient measurement

A new apparatus based on a static–analytic method assembled in this work was utilised to perform high-pressure (vapour + liquid) equilibria measurements of aqueous ternary systems. This work includes values of isothermal partition coefficients between CO₂ and water of two apple aroma constituents, (E)-2-hexenal and hexanal. Additionally, this work reports new experimental (vapour + liquid) equilibria measurements for the ternary systems (CO₂ + (E)-2-hexenal + water) and (CO₂ + hexanal + water), at fixed liquid phase composition (600 mg · kg⁻¹), at temperatures of (313, 323 and 333) K and at pressures from (8 to 19) MPa. Vapour liquid interphase was checked and monitored visually for all the systems studied in this work. No liquid immiscibility was observed at the composition, temperatures and pressures studied. In order to suggest reasonable operation conditions for fractionation of aromas with dense carbon dioxide, partition coefficients of the aroma compounds between CO₂ and water along with their separation factors from water were calculated. Partition coefficients of (E)-2-hexenal between CO₂ and water were in the range of (6 to 91) and where found to be near six times higher than those of hexanal (9 to 17). Very high separation factors from water were observed (∼10⁴) especially for (E)-2-hexenal. The highest separation factor, for both compounds, was found at a temperature of 313 K and pressures from (12 to 14) MPa.     

The co-solubility of 2-ethylhexanoic acid and some liquid alcohols in supercritical carbon dioxide

The co-solubility in supercritical carbon dioxide of 1-butanol, 1-pentanol, 2-ethyl-1-hexanol, or 1-decanol in the presence of 2-ethylhexanoic acid in the pressure range of 100–180 bar and at 313 or 323 K was measured. The solubility of these alcohols in the presence of 2-ethylhexanoic acid is lower than in the systems alcohol + CO₂ and remains nearly constant in the pressure range of 120–180 bar, with the exception of 1-decanol. The lower selectivities in the ternary systems are explained by strong intermolecular hydrogen bonding between alcohol molecules and 2-ethylhexanoic acid molecules. The FT-IR spectra of mixtures of alcohols and 2-ethylhexanoic acid at a 1:1 mole ratio in the liquid CCl₄ confirmed this conclusion.     

Phase equilibrium data and thermodynamic modeling of the system (CO2 + biodiesel + methanol) at high pressures

The main objective of this work was to investigate the high pressure phase behavior of the binary systems {CO₂(1) + methanol(2)} and {CO₂(1) + soybean methyl esters (biodiesel)(2)} and the ternary system {CO₂(1) + biodiesel(2) + methanol(3)} were determined. Biodiesel was produced from soybean oil, purified, characterized and used in this work. The static synthetic method, using a variable-volume view cell, was employed to obtain the experimental data in the temperature range of (303.15 to 343.15) K and pressures up to 21 MPa. The mole fractions of carbon dioxide were varied according to the systems as follows: (0.2383 to 0.8666) for the binary system {CO₂(1) + methanol(2)}; (0.4201 to 0.9931) for the binary system {CO₂(1) + biodiesel(2)}; (0.4864 to 0.9767) for the ternary system {CO₂(1) + biodiesel(2) + methanol(3)} with a biodiesel to methanol molar ratio of (1:3); and (0.3732 to 0.9630) for the system {CO₂ + biodiesel + methanol} with a biodiesel to methanol molar ratio of (8:1). For these systems, (vapor + liquid), (liquid + liquid), (vapor + liquid + liquid) transitions were observed. The phase equilibrium data obtained for the systems were modeled using the Peng–Robinson equation of state with the classical van der Waals (PR-vdW2) and Wong-Sandler (PR–WS) mixing rules. Both thermodynamic models were able to satisfactorily correlate the phase behavior of the systems investigated and the PR–WS presented the best performance.