Solubility In Supercritical Fluids Research Articles

Solubilities in supercritical fluids

Abstract Solubilities in supercritical fluids are of great importance in a wide variety of applications. These applications include: production of controlled drug delivery systems, powder processing, pollution prevention and remediation, methods for spraying paints and coatings, precipitation/crystallization processes, bioseparations, and food processing. Examples of some of these applications will be given. Supercritical fluid processes make use of the significant variation of solubility with pressure when the solvent is a supercritical fluid. This permits the accomplishment of many processes that would be otherwise very difficult to achieve. To fully understand the benefits of such processes, one must understand the phase behavior of such systems. The types of phase behavior that can be observed will be discussed, along with the ways that this behavior can be used to modify solubilities in such fluids. There have been many methods proposed for the experimental determination of solubilities in supercritical fluids. These will be reviewed in general, and recommendations for preferred methods given. Solubilities in supercritical fluids can be correlated and predicted by making use of thermodynamic calculations involving equations of state, as well as by other methods. The various methods will be reviewed, and recommendations given for various applications.

Titanyl phthalocyanine solubility in supercritical acetone

A simple technique is proposed for measuring solids solubilities in supercritical fluids. This technique is based on the specific properties that supercritical fluids forms homogeneous mixtures and have gas-like diffusivities and viscosities. The proposed technique was validated by measuring silicon dioxide solubility in supercritical water. The results showed good agreement with literature data. Titanyl phthalocyanine solubility in supercritical acetone was measured at temperatures ranging from 235 to 280 °C and acetone densities from 0.25 to 0.48 g cm −3. Solubilities varied from 0.64 g kg −1 at 235 °C and 0.25 g cm −3 to 3.81 g kg −1 at 280 °C and 0.41 g cm −3. A solvation reaction model for the description of temperature and solvent density dependence of the solubilities was used to correlate the data.

Calculations of solid solubility in supercritical fluids using a simplified cluster solvation model

A simplified cluster solvation model was employed in this study to correlate the solid solubility in supercritical fluids. Based on the concept of cluster solvation, several supercritical molecules were associated with a solid solute in chemical equilibrium. Solid solubility was calculated by applying the equilibrium criteria for the cluster formation process. This simplified model has two temperature-independent binary parameters. It is observed that the overall deviation in solid solubility calculations of binary systems from this model is comparable to that from other semi-empirical models with more optimally fitted parameters. This simplified cluster solvation model was extended to ternary and multi-component calculations by directly using the parameters from binary correlation results. Without any additional parameter, the predicted accuracy is still acceptable. Application of this model to systems with co-solvent has also been examined. A general trend for the variation of the effective association number with co-solvent concentration is observed.

An experimental technique for measuring high solubilities of dyes in supercritical carbon dioxide

The solubilities of colour index (C.I.) disperse orange 3, red 324, blue 79 and quinizarin were measured at the temperatures of 353.2, 373.2, 393.2 K between 18 and 30 MPa with a ‘flow method’ conceived for determination of high solubilities in order to avoid the flow instability problems connected with dye precipitation. The comparison of results with the literature underlines the advantage of this new technique: higher solubility values are obtained especially at the most severe operating conditions. Experimental data for disperse orange 3 were also compared with similar results obtained by the authors using a ‘batch method’ in a previous work. The comparison of the results shows how the ‘flow method’, even though adapted for high solubility measurements, reveals to be the simplest and more efficient technique to evaluate dye solubility in supercritical fluids.

Synthesis of Fluorinated and Hydrocarbon Ester Functionalized Poly(p-phenylenes) and Their Solubility in Supercritical Fluids

Monomers of the structure 2,5-dichloro-1,4(RO 2 C) 2 benzene, where R = CH 2 CF 2 CF 3 (la), -(CH 2 ) 2 CH 3 (1b), -CH 2 CH 2 (CF 2 ) 5 CF 3 (1c), and -(CH 2 ) 7 CH 3 (1d), were prepared and characterized in the study. Polymerization by the Ni-catalyzed/Zn-mediated homocoupling methodology afforded poly(p-phenylenes) 2a-2d. The polymers obtained after precipitation into methanol showed molecular weights (M n , relative to polystyrene standards) in the range 7000-13 000. The regiochemistry in the polymer was deduced to be approximately 70% head-to-tail with the remainder head-to-head. The polymers displayed excellent solubility in common polar organic solvents such at THF and chloroform. The poly-(p-phenylenes) 2a and 2b showed no solubility in supercritical ethane, propane, butane, and carbon dioxide even at 190 °C and 35 000 psia. Polymer 2d was remarkably soluble in the supercritical hydrocarbon solvents at low pressures (1000 psia). However, 2d does not dissolve in supercritical carbon dioxide. The fluorinated poly(p-phenylene) 2c dissolved in the supercritical hydrocarbons at pressures below 6000 psia, and it dissolved in carbon dioxide at pressures as low as 1000 psia at 25 °C.

Solubility of the Drugs Bisacodyl, Methimazole, Methylparaben, and Iodoquinol in Supercritical Carbon Dioxide

Fluids have been used before for the extraction and chromatography of drugs, but only a few literature references are available on drug solubility in supercritical fluids. The objective of this work concerned the experimental determination of the equilibrium solubilities of four compounds used as drugs (bisacodyl, methimazole, methylparaben, and iodoquinol) in supercritical carbon dioxide at temperatures ranging from (308 to 348) K and pressures from (122 to 355) bar. The measurements were performed using a simple and reliable static method. Iodoquinol showed solubilities below the range in which reliable data can be obtained with the used method. Bisacodyl, methimazole, and methylparaben solubilities were successfully correlated using a semiempirical model. Correlation of the results shows good self-consistency of the data obtained. Crossover pressures were observed for all compounds.

Synthesis of controlled‐release products in supercritical medium

AbstractControlled‐delivery products have recently received considerable attention. They prolong the drug's therapeutic effect, keeping its concentration between the therapeutic and toxicity limit. The final product must be free of residual solvent, even with nontoxic solvents, to provide its constant property that does not change with natural evaporation of the solvent. A major cost item in the synthesis of controlled‐release drugs is to remove this solvent to acceptable limits. To eliminate the production step involving the organic solvent from the overall process, the drug was introduced into the polymer matrix using supercritical carbon dioxide (scCO2) as the carrier solvent and swelling agent. This study focuses on the impregnation of a biodegradable polymer matrix with 5‐fluorouracil for chemotherapy and β‐estradiol estrogen hormone therapy. Swelling of the polymer matrix, solubility of drug components in scCO2 and the adsorption isotherm/partition coefficients in the presence of scCO2 were studied. To investigate the single‐component supercritical adsorptive synthesis of controlled‐delivery products, accurate experimental techniques to measure drug‐component solubilities in supercritical fluids and adsorption isotherms in the presence of supercritical fluids were developed. Solubility data of these drugs in scCO2 at 35–55°C and 101–220‐bar were reported. The adsorption equilibrium constants/partition coefficients were presented for these drug components on poly‐dl‐lactide‐co‐glycolide (PLGA) at the same conditions. To understand the effect of operating variables on the total drug loading and to predict the drug‐loading breakthroughs, a flow over a flat plate model was developed that accounts for the polymer swelling, the partitioning of the drug component between the supercritical and polymer phases, and the polymer diffusivity. Experimental isotherm data with and without the polymer were incorporated into the model to isolate the system response from the polymer response to determine impregnation efficiencies.

Spectroscopic measurement of solid solubility in supercritical fluids

AbstractDifferent in situ spectroscopic techniques, including infrared, ultraviolet, and fluorescence, were developed to measure the solubility of organic solids in supercritical carbon dioxide (scCO2). These techniques are applicable over a wide range of concentrations, as low as 10−6 or 10−7 mol fraction, where the conventional flow method is ineffective and less accurate. No separate calibration is required; in fact, the molar absorptivity is determined at the saturation point as an additional benefit. While this technique requires more time per data point, it is more accurate and unbiased than traditional methods at lower concentrations. The Patel‐Teja equation of state was used to correlate the data and expand the data for the ternary system. Data are reported for anthracene, 1,4‐naphthoquinone, and 2‐naphthol in scCO2 and CO2 with methanol cosolvent at 313 K and a pressure range from 7 to 21 MPa.

A Novel Apparatus for Accurate Measurements of Solid Solubilities in Supercritical Phases

A new apparatus for the measurement of solid solubilities in supercritical fluids is described in detail. It is based on an analytical open-flow method: the composition of the phase is obtained by analyses, and the solvent flows continuously through the solid solute. Solubilities of naphthalene in supercritical CO2 in the pressure range of 8−30 MPa are reported for the isotherms 308.15 and 318.15 K. The solubility data are then correlated using three density-based models.

Modelling solubility of solids in supercritical fluids using fusion properties

The modelling of solid solubilities in supercritical fluids is usually performed by means of thermodynamic models based on cubic equations of state together with the use of correlations for estimating the solid properties. However, it was shown in the literature, that the error in sublimation pressure, which is very low for high molecular weight compounds, is in many cases responsible for large deviations between experimental and calculated solubilities. In this work, the sublimation pressure of solids is estimated by using experimental fusion data and liquid–vapour equilibrium properties obtained from an equation of state (EOS). The results provided by this method are compared with those obtained using sublimation pressures from literature. It is shown that this method allows satisfactory solubility predictions when using a reliable EOS.

Revision: Extracción con CO2 a alta presión. Fundamentos y aplicaciones en la industria de alimentos / Review: High pressure CO2 extraction. Fundamentals and applications in the food industry

Supercritical extraction (SFE) is a unit operation that exploits the dissolving power of supercritical fluids (SF) under conditions above their critical temperature and pressure. It is possible to obtain solvent-free extracts using SF and the extraction is faster than using conventional organic solvents. These advantages are due to the high volatility of SF (gases under normal environmental conditions) and improved transport properties (i.e., high diffusivity and low viscosity). When using carbon diox ide (CO,) in particular, moderate-temperature processing and high selectivity towards valuable microconstituents in natural products can be achieved. This article presents a review of transport properties and solubilities in SF, particularly CO2, as well as other underlying factors that are respon sible for the kinetics and phase equilibrium in SFE processes. It also describes the selective CO 2 ex traction of essential oils, pungent principles, carotenoid pigments, antioxidants, antimicrobials, and related substances to be used as ingredients for the food, drug and perfume industries, from spices, herbs and other plant materials. These very important applications are discussed from the point of view of the potential applications of SFE in Latin America. The two most important commercial ap plications of SFE in the food industry, namely hop extraction and coffee decaffeination, are reviewed to a limited extent. Some other potential applications briefly described include extraction and frac tionation of edible fats and oils, purification of solid matrices, and concentration of fermentation broths, fruit juices and other extracts. In most cases CO2 extracts are compared with counterparts obtained using conventional methods.

Predicting the approximate solubilities of solids in dense carbon dioxide

The aim of this paper is the prediction of solid solubilities in supercritical fluids (SCF) on an order-of-magnitude basis. A further aim is to clarify some of the computational aspects of the Boublik and Mansoori equations for the perturbed hard-sphere used in the estimation of solubility. Modelling the solubilities of heavy hydrocarbons and other organics provides an average value for the pair-potential integral function a 12. The latter varies by only ±30% from one solute to the other over relatively wide ranges of pressure ( P) and temperature ( T). Thus, it is possible to use a mean value to estimate approximate solubilities in SCF, which are useful in some stages of engineering work where order-of-magnitude data is sufficient. On the other hand, the (one-parameter) Peng–Robinson equation of state with the interaction parameter optimized for each solute gives no clear guidance.

A Density-Dependent Solute Solubility Parameter for Correlating Solubilities in Supercritical Fluids

A density-dependent solute solubility parameter has successfully correlated solubilities in supercritical fluids (SCFs). Fifteen solutes, including polar and nonpolar compounds, have been studied in up to four SCFs. A two-parameter, linear fit resulted in a median average absolute relative deviation (AARD) of 20%, ranging from 6.1% to 42%, for the 34 systems studied. A three-parameter power fit provided a median AARD of 12%, ranging from 2.3% to 38%.

Solubility of solids in supercritical fluids from the measurements of the dielectric constant: Application to CO2–naphthalene

A new method for the measurement of solid solubilities in supercritical fluids is described in detail. The method is based on the measurement of the dielectric constant of the saturated supercritical solution solvent–solute and that of the supercritical solvent as a function of pressure along different isotherms. Our method is simple, absolute, easy to use, and permits precise measurement of the solubility of solids in supercritical fluids. Solubilities of naphthalene in supercritical CO2 in the pressure range 12–30 MPa are reported along the isotherms 313.15, 318.15, and 323.15 K.

Adsorptive separations using supercritical frontal analysis chromatography

AbstractMany food products and pharmuceuticals industries are looking to integrating super‐critical extraction and separations processes to fulfill processing needs due to limitations and regulations concerning the use of organic solvents. One such technology, which may affect these industries, is continuous supercritical adsorptive separation, a processing technology similar to the separation process of xylenes developed at UOP. Many products like pharmaceuticals and other human consumables could be processed more economically and with higher purity by supercritical fluid adsorption/desorption processes. Past studies, however, have focused on single‐component adsorption/desorption involving a supercritical mobile phase, whereas adsorptive separations involving super‐critical fluids are multicomponent systems. Accurate experimental techniques, which can determine both multicomponent solubilities in supercritical fluids and multicomponent adsorption isotherms in the presence of supercritical fluids, were developed to investigate the multicomponent supercritical adsorption phenomenon. A dynamic column model developed takes into account column dispersion as well as mass transfer and diffusive resistances. Experimental isotherm data incorporated into the model can predict the breakthrough profiles. An extension of pulse chromatography was used to identify the important hydrodynamic and transport parameters, and operating conditions are identified for optimal separations.

Solubilities in supercritical fluids from the virial equation of state

Solubilities in supercritical fluids from the virial equation of state

Solubilities in supercritical fluids from the virial equation of state

We present a simple treatment of supercritical fluid extraction for binary (solvent-solute) and ternary (solvent-solute-cosolvent) systems. Solubility predictions are made using the virial equation of state. The solute chemical potential is calculated up to fourth order in the fluid density. There are no adjustable parameters: the pressure mixture virial coefficients Bα β, Cα β γ and Dα β γ δ are computed directly from the potentials representing the interactions of solvent, solute and cosolvent molecules. For the purposes of illustration we assume these are of Lennard-Jones form; however, the method is considerably more general, and may be applied even when the potentials are anisotropic. Computer simulations have also been performed, and confirm the accuracy of this approach at densities up to twice the critical density.Our analysis of ternary systems helps to identify the nature of the interactions primarily responsible for entrainer effects.

A Recirculating Equilibrium Procedure for Determining Organic Compound Solubility in Supercritical Fluids. Anthracene in Carbon Dioxide

An instrumental recirculation technique was developed to measure the solubility of organic compounds and thus their potential extractability, in supercritical fluids over the pressure range of 80−500 bar. Anthracene, whose solubility is well defined, was chosen as a model compound to be used in evaluating the recirculation technique. Its solubility in supercritical carbon dioxide was measured at 40, 50, and 60 °C using an off-line spectroscopic technique. The solubility data were found to have good precision and to agree with published results. Anthracene solubility increased with pressure but was more enhanced by higher temperature. An upper crossover pressure of the isotherms due to retrograde vaporization that agreed with theory was found at 142.2 bar.

Predicting Solubilities in Supercritical Fluids

We present a simple treatment of supercritical fluid extraction, including entrainer effects. Solubility predictions are made using the Redlich−Kwong equation of state: parameters for this equation are calculated directly from intermolecular potentials. We have tested our approach in the low-solubility limit by comparing with computer simulations. Good agreement is found for realistic values of the potential parameters describing solute−solvent and solvent−solvent interactions.

Prediction of the Solubility in Supercritical Fluids Based on Supercritical Fluid Chromatography Retention Times

An improved method for the rapid prediction of solubilities of solutes in supercritical fluids is proposed. The method is based on the measured retention times of solutes eluting from packed and capillary supercritical fluid chromatography (SFC) columns. The solubilities in CO2 of four polycyclic aromatic hydrocarbons were estimated with an average error of about ±30% using retention data obtained by packed column SFC. For more polar compounds, which may interact strongly with the stationary phase in packed columns, capillary column SFC gave better results. Agreement to better than 35% was found between the solubilities obtained by this method and those obtained gravimetrically for compounds with a variety of functionalities. Several factors have been investigated, including the relationship between solubility and the reciprocal of the capacity factor, the effect of temperature, and the effect of the stationary phase.