Isobaric Solubility Research Articles

Solvent selection in physical supercritical fluid deposition

Physical supercritical fluid deposition is a method of thin film deposition that does not rely on in-situ chemical reactions. Instead, the technique relies on a maximum in the isobaric saturation solubility to deposit material onto a heated substrate. As such, a strong understanding of the saturation solubility is crucial to designing a successful deposition procedure. Here, we report the first study on the problem of solvent selection in physical supercritical fluid deposition, developing qualitative categories of a solvent-solute systems by studying poly(3-hexyl thiophene) (P3HT) solutions at supercritical pressures. Overpowered solvents exhibit high saturation solubilities and do not exhibit a maximum in the isobaric solubility as exemplified by pentane. Underpowered solvents exhibit extremely low saturation solubilities and as such are not suitable for this deposition technique as demonstrated by a fluorocarbon solvent. Optimum solvents are characterized by moderate saturation solubilities, showing a maximum in the isobaric saturation solubility with respect to temperature. This behavior is demonstrated with a chlorofluorolefin solvent. We also demonstrate the properties of mixtures formed by these three classes of solvents. The mixture of an optimum solvent with an overpowered solvent appears effective for physical supercritical fluid deposition, whereas the mixture of an overpowered and underpowered solvent does not. In sum, the work demonstrates guidelines to solvent selection that will allow for the deposition of a wider range of materials.

Modeling cobalt (III) acetylacetonate and iron (III) acetylacetonate solubilities in supercritical CO2 with PC-SAFT based on experimentally-determined solid–liquid equilibria in organic solvents

A methodology to model the solubilities of metal complexes in supercritical CO2 is indispensable for effectively designing the supercritical CO2-based deposition method. Herein, the solubility of two metal acetylacetonates (acac), Co(acac)3 and Fe(acac)3, in supercritical CO2 was modeled based on the perturbed-chain statistical associating fluid theory (PC-SAFT) and experimentally-determined solid–liquid equilibria in organic solvents. This modeling approach is more predictive than conventional cubic-type equations of state or semi-empirical correlation models. The pure-component parameters of PC-SAFT for metal acetylacetonates are obtained by fitting the obtained solubility data to four typical organic solvents (toluene, acetone, 2-butanone, and ethyl acetate). By applying these PC-SAFT parameters, the model satisfactorily reproduced the solubilities of the metal complexes in supercritical CO2, particularly under low-temperature conditions even with the kij (binary interaction parameter) set to 0 in the combining rule. The isobaric solubilities can also be described by PC-SAFT by generalizing the temperature dependence of kij.

Estimating the solubility of salsalate in supercritical CO2 via PC-SAFT modeling using its experimental solubility data in organic solvents

In this work, a methodology was studied for estimating the solubility of salsalate, an active pharmaceutical ingredient of non-steroidal anti-inflammatory drugs, in supercritical CO2 (scCO2) using the experimental data of its solubility in organic solvents and perturbed-chain statistical associating fluid theory (PC-SAFT)-based modeling. This type of modeling is more predictive than conventional semi-empirical correlation models and cubic-type equations of state. The PC-SAFT pure-component parameters of salsalate were determined by fitting its solubility data in organic solvents, which were newly measured in this work. The PC-SAFT parameters obtained thus were then applied to estimate the solubility of salsalate in scCO2. This approach can adequately reproduce the experimental values of the isothermal and isobaric solubilities of salsalate in scCO2 over a wide range of temperatures and pressures even when the binary interaction parameter (kij) is set to zero.

Modeling the solubility of non-steroidal anti-inflammatory drugs (ibuprofen and ketoprofen) in supercritical CO2 using PC-SAFT

A method to estimate the solubilities of two non-steroidal anti-inflammatory drugs (NSAIDs), ibuprofen and ketoprofen, as active pharmaceutical ingredients (APIs) in supercritical CO2 (scCO2), was examined using perturbed-chain statistical associating fluid theory (PC-SAFT), which is more predictive than conventional methods that use cubic-type equations of state and semi-empirical correlation models. The values of the three PC-SAFT pure-component parameters of the API were adjusted to the solubility in organic solvents and determined. These parameters were then applied to estimate the solubility of the API in scCO2. The PC-SAFT solubility calculations almost reproduced the experimental values over a wide pressure range, even when kij (the binary interaction parameter) was set to zero. Furthermore, the isobaric solubility of scCO2 was successfully described by PC-SAFT using the generalized kij.

Predicting the solubilities of metal acetylacetonates in supercritical CO2: Thermodynamic approach using PC-SAFT

Solubilities of metal precursors in supercritical carbon dioxide (scCO2) are needed to effectively design the scCO2-based deposition method. Herein, a method for predicting the solubilities of metal acetylacetonate (acac) precursors in scCO2 was developed using the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state. Three PC-SAFT pure-component parameters viz., the segment diameter, segment number, and dispersion energy, for two metal acetylacetonates (Cr(acac)3 and Cu(acac)2) were determined by adjusting their values to the measured solubilities in organic solvents. The PC-SAFT parameters of Cr(acac)3 and Cu(acac)2 were then applied to predict the experimentally determined metal precursor solubilities in scCO2 from the literature. The PC-SAFT predictions accurately described the experimental solubilities in scCO2 over a wide range of pressures and temperatures even if the binary interaction parameter kij was set to 0. The isobaric solubilities in scCO2 were also calculated with the generalized kij values, which provided a successful PC-SAFT description.

Thermodynamic model for mineral solubility in aqueous fluids: theory, calibration and application to model fluid‐flow systems

Geofluids(2010)10, 20–40AbstractWe present a thermodynamic model for mineral dissolution in aqueous fluids at elevated temperatures and pressures, based on intrinsic thermal properties and variations of volumetric properties of the aqueous solvent. The standard thermodynamic properties of mineral dissolution into aqueous fluid consist of two contributions: one from the energy of transformation from the solid to the hydrated‐species state and the other from the compression of solvent molecules during the formation of a hydration shell. The latter contribution has the dimension of the generalized Krichevskii parameter. This approach describes the energetics of solvation more accurately than does the Born electrostatic theory and can be extended beyond the limits of experimental measurements of the dielectric constant of H2O. The new model has been calibrated by experimental solubilities of quartz, corundum, rutile, calcite, apatite, fluorite and portlandite in pure H2O at temperatures up to 1100°C and pressures up to 20 kbar. All minerals show a steady increase in solubility along constant geothermal gradients or water isochores. By contrast, isobaric solubilities initially increase with rising temperature but then decline above 200–400°C. This retrograde behavior is caused by variations in the isobaric expansivity of the aqueous solvent, which approaches infinity at its critical point. Oxide minerals predominantly dissolve to neutral species; so, their dissolution energetics involve a relatively small contribution from the solvent volumetric properties and their retrograde solubilities are restricted to a relatively narrow window of temperature and pressure near the critical point of water. By contrast, Ca‐bearing minerals dissolve to a variety of charged species; so, the energetics of their dissolution reactions involve a comparatively large contribution from volume changes of the aqueous solvent and their isobaric retrograde solubility spans nearly all metamorphic and magmatic conditions. These features correlate with and can be predicted from the standard partial molar volumes of aqueous species.The thermodynamic model can be used over much wider range of settings for terrestrial fluid–rock interaction than has previously been possible. To illustrate, it is integrated with transport theory to show quantitatively that integrated fluid fluxes characteristic of crustal shear zones are capable of precipitating quartz or calcite veins from low‐ and medium‐grade metamorphic conditions, at a geothermal gradient of 20°C km−1. For subduction zones, modeled by a geotherm of 7°C km−1, the required fluid fluxes are one to two orders of magnitude lower and predict enhanced efficiency of mass transfer and metasomatic precipitation in comparison with orogenic settings. The new model thus can be applied to shallow hydrothermal, metamorphic, magmatic and subduction fluids, and for retrieval of dependent thermodynamic properties for mass transfer or geodynamic modeling.

Measurement and correlation for solubilities of alkali metal chlorides in water vapor at high temperature and pressure

A flow type apparatus was designed and constructed to measure the solubilities of salts in water vapor at high temperature and pressure. The apparatus was equipped with an additional pure water line to prevent the clogging by precipitated solid salts at the outlet of an equilibrium cell. The solubilities of sodium chloride and potassium chloride in water vapor were measured at 623–673K and 9.0–12.0MPa. In order to verify the soundness of this method and the performance of the apparatus, the experimental results for the solubilities of sodium chloride at 673K were compared with the literature data. The present data are in good agreement with the literature data. The solubilities of sodium chloride are similar to those of potassium chloride at the same temperatures and pressures. The isobaric solubilities decrease with increasing temperature at the experimental pressure range. The experimental results of solubilities were correlated by a solution model. The molar volumes and the energy parameters of salts were treated as adjustable parameters and were optimized with the present and literature data. The adjusted energy parameters for salts can be related to a linear function of the temperature. The correlated results show good agreement with the experimental data.

Experimental and Predicted Solubilities of HFC134a (1,1,1,2-Tetrafluoroethane) in Polyethers

Experimental solubilities were determined for 1,1,1,2-tetrafluoroethane (HFC134a) in triethylene glycol dimethyl ether and in tetraethylene glycol dimethyl ether at 101.33 kPa refrigerant partial pressure in the low-temperature range (258.15−298.15 K). The experimental device was adapted from an apparatus commonly used to measure slightly soluble gases. Because HFC134a was highly soluble in the two polyglycols, the mole fraction of the refrigerant was calculated by the φ−γ method and the symmetrical criteria for the components. The solubilities of the refrigerant in the two solvents were very similar. The thermodynamic quantities related to the solution process were also obtained from the solubility data. The isobaric solubilities predicted by the original and Dortmund UNIFAC versions were compared with the experimental values to test the interaction parameters of Kleiber (Fluid Phase Equilib. 1995, 107, 161) and Kleiber and Axmann (Comput. Chem. Eng. 1998, 23, 63).

V olatileC alc: a silicate melt–H 2O–CO 2 solution model written in Visual Basic for excel

We present solution models for the rhyolite–H 2O–CO 2 and basalt–H 2O–CO 2 systems at magmatic temperatures and pressures below ∼5000 bar. The models are coded as macros written in Visual Basic for Applications, for use within Microsoft ® Excel (Office’98 and 2000). The series of macros, entitled V olatileC alc, can calculate the following: (1) Saturation pressures for silicate melt of known dissolved H 2O and CO 2 concentrations and the corresponding equilibrium vapor composition; (2) open- and closed-system degassing paths (melt and vapor composition) for depressurizing rhyolitic and basaltic melts; (3) isobaric solubility curves for rhyolitic and basaltic melts; (4) isoplethic solubility curves (constant vapor composition) for rhyolitic and basaltic melts; (5) polybaric solubility curves for the two end members and (6) end member fugacities of H 2O and CO 2 vapors at magmatic temperatures. The basalt–H 2O–CO 2 macros in V olatileC alc are capable of calculating melt–vapor solubility over a range of silicate-melt compositions by using the relationships provided by Dixon (American Mineralogist 82 (1997) 368). The output agrees well with the published solution models and experimental data for silicate melt–vapor systems for pressures below 5000 bar.

Chain length effects on aqueous alkane solubility near the solvent’s critical point

Free energy of hydration calculations for butane and octane were conducted at several state points. A relatively new method of performing the alkane insertion was used and it was found to perform quite well. Our preliminary simulation results are in good agreement with the recent equation of state (EOS) predictions of Yezdimer et al. [Chem. Geol. 164 (2000) 259] and suggest that at near-critical conditions the isobaric solubility curves for a series of alkane chain molecules may unexpectedly reverse.

Ti(IV) hydrolysis constants derived from rutile solubility measurements made from 100 to 300°C

Using a Au–Ir hydrothermal reaction cell and dilute buffer solutions to control pH, the isobaric solubility of rutile (TiO 2) was measured over a broad pH range from pH 1 to 13 between 100 and 300°C. The solubility data were regressed to derive the cumulative and stepwise hydrolysis constants for Ti(IV) in aqueous solution. The data were accurately modeled using the hydrolysis species: Ti(OH) + 3, Ti(OH) 4(aq) and Ti(OH) − 5. The following cumulative ( K s3, K s4, K s5) hydrolysis constants (log K and error, reactions written with respect to the solid oxide) and stepwise ( K 34, K 45) hydrolysis constants (log K and error) were determined by regression: 100°C 150°C 200°C 250°C 300°C log K s3 −5.44(0.032) −5.42(0.106) −5.28(0.055) −5.03(0.046) −4.61(0.112) log K s4 −7.72(0.150) −7.66(0.202) −7.57(0.153) −7.93(0.202) −7.92(1.11) log K s5 −17.8(0.068) −17.1(0.138) −16.4(0.132) −15.9(0.018) −15.4(0.057) log K 34 −2.28(0.153) −2.24(0.228) −2.29(0.162) −2.90(0.207) −3.31(1.12) log K 45 −10.1(0.165) −9.42(0.245) −8.86(0.202) −7.95(0.203) −7.43(1.11) These data are required to model the chemical behavior of Ti(IV) in aqueous solutions and provide a baseline for the Ti-solubility-limited dissolution of titanates.

Solubility measurements of methane and ethane in water at and near hydrate conditions

The isobaric solubility of pure methane and ethane gases in liquid water was measured under different conditions, including hydrate formation points, using a ramping method in which measurements are made through the entire and continuous hydrate formation/decomposition cycle. The work was conducted for methane at 3.45 MPa (500 psia) and temperatures ranging from 17.0 to 0.0°C (290.2 to 273.2 K), and for ethane at 0.66 MPa (95 psia) and a temperature range of 17.0 to 0.0°C (290.2 to 273.2 K). The isobaric solubilities obtained show a significant divergence from (normal) Henry's law solubility as the temperature is lowered. The increase in the solubility is presumably the result of the onset of a sorption process that traps the gas molecules in the water structure. Several sub-processes were observed as the hydrate formation was taking place: (1) the dissolution of the gas in the liquid water, or interstitial solubility, (2) the onset of the sorption sub-process and build-up of the hydrate precursors, (3) the catastrophic formation and the existence of the solid phase with its slushy characteristics, and (4) the solidification of the hydrates, therefore causing the total plugging of the experimental cell.

Fluid phase equilibrium of dilute mixtures of helium in near-critical mercury

The phase behaviour of dilute mixtures of the He in near-critical fluid Hg has been studied within the ranges 69 MPa to 332.5 MPa, 1433 K to 1882 K and amount-of-substance fractions x(He) within the values 0.0018 and 0.1020. A high pressure and high-temperature vessel was filled with known amounts of He and Hg (synthetic method) and heated; an isochoric record of pand Twas made while the temperature was gently decreased and the transition from homogeneous to two-phase systems was indicated by abrupt slope changes in the p-against- Tisochores. Two distinct fluid phases are shown to exist in (helium + mercury) at temperatures and pressures higher than those corresponding to the critical point of pure mercury (“fluid–fluid equilibrium of the first type”) and the system's critical line, beginning at the critical point of pure Hg, runs steeply to higher pressures and temperatures. Solubility values as high as 0.28 mol·dm −3were measured for He in near-critical fluid Hg, in contrast to the much lower values estimated for He dissolved in metallic liquid Hg at sub-critical temperatures. The isobaric solubility of He in Hg increases with temperature for super-critical pressures so that (helium + mercury) shows a positive enthalpy and entropy of dissolution under these conditions. At sufficiently high density, non-metallic near-critical Hg experiences a transition to a metallic state, resulting in a strong repulsive interaction between dissolved He and the surrounding conduction electrons, and hence the isothermal solubility of He decreases.

A method for measurement of solid solubility in supercritical carbon dioxide

A new experimental method has been developed for measuring the equilibrium solubility of heavy solutes in supercritical CO 2. The micro-SFE (supercritical-fluid extraction) is coupled to supercritical-fluid chromatography (SFC), both operating under the same temperature, pressure, and CO 2 flowrate. Naphthalene, biphenyl, and phenanthrene are chosen to verify the method. The isobaric solubilities of the solutes in the temperature range of 308–338 K and pressure from 8. 0 MPa to 12. 0 MPa are determined. The experimental data are in agreement with literature values and exhibit some characteristics of solid-supercritical-fluid binary system phase equilibrium in the near critical region of solvent.

Absorption of hydrogen by vanadium-palladium alloys

Pressure-composition isotherms (273–373K) have been determined for the absorption of hydrogen by a series of six palladium alloys (f.c.c.) in the composition range from 1 to 8 at.% vanadium. At a given hydrogen content, the equilibrium hydrogen pressure progressively increases with vanadium content. Thermodynamic parameters for the absorption of hydrogen are reported at infinite dilution of hydrogen, and for the formation of the nonstoichiometric hydride phase from the hydrogen-saturated alloy. The relative, partial molar enthalpy of solution of hydrogen at infinite dilution increases slightly with vanadium content, e.g., for V(5%)-Pd, Δ H ̄ ° H = −8,500 j H compared with −10,040 j H for palladium. The presence of vanadium, which absorbs hydrogen itself in its normal b.c.c. structure, greatly inhibits the ability of palladium to absorb hydrogen. For example, the isobaric solubility of hydrogen (1 atm, 298 K) decreases from H Pd = 0.7 (palladium) to 0.024 (V(6%)-Pd). The lattice expansion due to the presence of interstitial hydrogen has been determined by X-ray diffraction. From these data it can be concluded that the formation of two non-stoichiometric hydride phases does not occur at vanadium contents greater than 5 at.% (298 K). Electrical resistance has been measured as a function of the hydrogen content of the alloys. The electrical resistance increases more markedly with hydrogen content for these alloys than for any of the palladium alloys previously examined.

Solubility of Cupric Oxide in Pure Water at Temperatures up to 550° C

WE report here work in progress on the measurement of the solubility of metals and metal oxides in pure water, in the temperature range 50°–550° C and at pressures up to 400 bars. The isobaric solubility of cupric oxide at 310 bars is reported here and compared with the 300 bar isobar for silica (quartz).