Solubility In Supercritical Fluids Research Articles

Determining the Solubility of Organic Compounds in Supercritical Carbon Dioxide Using Supercritical Fluid Chromatography Directly Interfaced to Supercritical Fluid Solubility Apparatus

The solubilities of benzoin and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride in supercritical fluid carbon dioxide have been measured using static supercritical fluid solubility apparatus directly interfaced to supercritical fluid chromatography (SFC). The method involves increasing the pressure of supercritical fluid carbon dioxide in controlled steps to produce a series of saturated sample solutions that are sequentially analyzed by online SFC. The system requires minimal manual sample manipulation stages and facilitates a self-validation check procedure. Solubility data for benzoin was determined at 308 and 318 K through the pressure range of 12–24 MPa using 2 MPa steps. Solubility data for 3,3′,4,4′-benzophenonetetracarboxylic dianhydride was determined at 328 and 343 K through the pressure range 15–27.5 MPa using 2.5 MPa steps. The Mendez-Santiago and Teja model has been successfully applied to correlate all sets of experimental solubility data.

Interfacing supercritical fluid solubility apparatus with supercritical fluid chromatography operated with and without on-line post-column derivatization: Determining the solubility of caffeine and monensin in supercritical carbon dioxide

An interface has been developed that enables the direct coupling of a continuously stirred high pressure vessel with on-line supercritical fluid chromatography (SFC). The system provides a rapid means to determine the solubility of organic compounds in supercritical fluid carbon dioxide (SF-CO2). The method involves increasing the loaded vessel pressure in controlled steps to produce a series of progressively more saturated sample solutions for on-line SFC solubility measurements. The method was validated by obtaining mole fraction solubility data for caffeine in SF-CO2 at four different temperatures ranging from 313K to 343K through the pressure range 10–28MPa. For caffeine, SFC detection was performed at 254nm. The solubility of monensin in SF-CO2 was determined using SFC with post-column derivatization. Vanillin served as derivatizing agent with SFC detection at 520nm. Mole fraction solubility data for monensin was obtained at 313K and 328K through the pressure range 10–27.5MPa.

A five-parameter empirical model for correlating the solubility of solid compounds in supercritical carbon dioxide

The correlation of solute solubility in supercritical fluids is crucial for the development of supercritical applications. Many models have been developed to calculate the solubility of solid compounds. In this work, a new five-parameter empirical model was proposed for correlating solute solubility in supercritical carbon dioxide (SCCO2). The new model successfully correlated solute solubility of 45 compounds (1130 data points) in SCCO2, which were collected from literature published between 2010 and 2015. A comparison of the 14 most common empirical models (Chrastil, Adachi-Lu, del Valle–Aguilera, Sparks, Gordillo, Jouyban, Garlapati-Madras, Ch-Madras, Kumar-Johnston, Méndez Santiago-Teja, Hozhabr, Keshmiri, Khansary) and the proposed model showed that the overall average absolute relative deviation of the proposed model is the lowest (5.16%).

Foaming of polymers with supercritical fluids: A thermodynamic investigation

The foaming of polymers using supercritical fluids was investigated, both, from a theoretical and an experimental point of view. Key thermodynamic phenomena that take place during the foaming process were described using the Non Random Hydrogen Bonding (NRHB) equation-of-state, such as the supercritical fluid solubility in the polymer matrix and the plasticization profile of the polymer–supercritical fluid system. Moreover, the NRHB model was combined with the classical nucleation theory in order to describe the energy barrier for nucleation. Subsequently, the foaming of the well-defined polystyrene–CO2 system was experimentally studied. Porous polystyrene structures were prepared using supercritical CO2 as foaming agent at various pressure and temperature conditions that refer to constant amount of dissolved fluid (CO2) inside the polymer matrix, or to constant initial energy barrier for nucleation. The experimental results, which were discussed in the light of the aforementioned theoretical investigation, reveal that at pressure and temperature conditions of constant equilibrium solubility of CO2 inside the polymer matrix, the average pore diameter decreases with increasing foaming temperature, mainly due to the formation of more pores, which is a consequence of the decrease in the energy barrier for nucleation. Furthermore, at conditions that refer to constant initial energy barrier for nucleation, all the produced porous structures presented similar pore diameters and cell population densities, regardless of the foaming temperature. Finally, it is concluded that the energy barrier for nucleation determines the morphology of the final porous structure to a large extent, although other processing parameters, such as the foaming temperature (or pressure) and the amount of the dissolved fluid, may also influence the cell size.

Solubilities of four macrolide antibiotics in supercritical carbon dioxide and their correlations using semi-empirical models

Accurate experimental determination of a solid drug’s solubility in supercritical fluids and its correlation is crucially important to the development of supercritical technologies for the pharmaceutical industry. In the present work, the solubilities of azithromycin, erythromycin, clindamycin and clarithromycin in supercritical carbon dioxide were measured at temperatures ranging from (308 to 348) K and pressures from (12.2 to 35.5) MPa using a static method. The mole fraction solubilities ranged from 2.7×10−5 to 11.46×10−5. The crossover region was observed for azithromycin, clarithromycin, clindamycin and erythromycin from 13.8 to 14.0MPa, 15.0 to 15.2MPa, 14.8 to 15.2MPa and 16.8 to 17.1MPa, respectively. Solubility data were correlated using four semi-empirical density-based models (Chrastil, Kumar, Johnston, Bartle and Mendez-Santiago and Teja models). The average absolute relative deviations ranged from 1.7 to 7.4; 2.07 to 8.1; 7.21 to 10.37 and from 5.13 to 9.44 for Chrastil, Bartle, K–J and M–T models, respectively. The results showed that by using three temperature-independent parameters these models can be applied for satisfactory solubility predictions at different pressures and temperatures. A comparison among the four models revealed that the K–J and Chrastil models gave much better correlation of the solubilities in comparison with other models. Using the correlation results, the heat of drug–CO2 solvation and that of drug vaporization was separately approximated in the range of −13.56 to −23.12 and 33.07–47.65kJmol−1. The correlation results showed good agreement with the experimental data.

過渡応答法による超臨界流体中の化合物の拡散係数の測定および溶解度と部分モル体積の推算

過渡応答法による超臨界流体中の化合物の拡散係数の測定および溶解度と部分モル体積の推算

Mathematical-thermodynamic solubility model developed by the application of discrete Volterra functional series theory

Based on the discrete form of Volterra functional series in approximation of multivariable functions, a mathematical model proposed for the modeling of solute solubility in supercritical fluids with four independent variables, which can be regarded as the general form of majority of available empirical models in literatures. As far as we know, it is the first time the thermodynamic-mathematical development of empirical models is presented. A substantial number of data points for different solutes and solvents is used to analyze the performance and reliability of the proposed model. Peng–Robinson equation of state together with the two adjustable parameters van der Waals mixing rule, as an example of theoretical models, and a number of recent empirical models, as examples of empirical/statistical models, were considered to demonstrate the superiority of the proposed model. The particle swarm optimization (PSO) was used for determination of the optimum coefficients of all models. The results were obtained and discussed in details.

A simple correlation to predict drug solubility in supercritical carbon dioxide

The availability of easy correlation of drug solubility in supercritical fluids without time-consuming calculations and difficult is crucially important for improvement of supercritical technology in pharmaceutical industries. This work proposes a new correlation to predict drugs solubility in CO2. The main advantages are its simplicity and minimal input data, namely temperature and density. The proposed drug solubility correlation in CO2 has better performance (lower AARE%) respect to eight other empirical equations. Due to data sets, the mean AARE for the proposed model was 6.88%.

Development and evaluation of a new semi-empirical model for correlation of drug solubility in supercritical CO2

The accurate determination of drug solubility in supercritical fluids and its correlation are crucially important for development of supercritical technology in pharmaceutical industries. In this research, a new empirical equation was proposed to correlate solute solubility with temperature, pressure and density of pure supercritical CO2. The accuracy of the proposed model in comparison with six other empirical equations was evaluated using 25 published solubility data sets by calculating the average absolute relative deviation (AARD). Due to these data sets, the mean AARD for the proposed model was 10.64 (±4.18); where, the values for other equations were 13.97 (±6.79), 13.16 (±6.31), 13.33 (±5.36), 14.64 (±13.94), 29.62 (±20.28) and 12.64 (±6.04). To validate proposed model, the solubility of Clobetasol Propionate (CP) and Desoxycorticosterone acetate (DC) as two corticosteroids was measured and modeled at temperatures ranging from 315 to 345K and pressures from 152 to 305bar by a static method. The acquired mole fraction results varied in the range of 1×10−6 to 2.1×10−5 for CP and 5×10−6 to 1.03×10−4 for DC. The AARD of proposed model for CP solubilities was 4.95% and for DC was 5.29% that was in reasonable range according to other published solubility data.

The Equilibrium Thermal Physics of Supercritical Fluids

To discover particular features of pure supercritical fluids, important for the supercritical fluid extraction and cleaning technologies, the preprocessed and generalized experimental data from the US National Institute of Standards and Technology (NIST) online database have been analyzed. The soft transition between gas-like and liquid-like structures in pure supercritical fluids has been considered in comparison with the abrupt vapor-liquid phase transition. A rough, diffused and boiling boundary between these structures in conditions of extra high gravity is opposed to a flat vapor-liquid boundary at a moderate gravity. The model for molecular diffusivity in carbon dioxide at temperatures near the critical temperature discovers its proportionality to the monomer fraction density. The cluster fraction based model for small molecular weight solids’ solubility in supercritical fluids has been suggested and successfully compared with the well-known experimental results for the solubility of silica in water.The model shows that at growing pressure the dissolution process has already startedin a real gas and discovers the cluster fractions’ role in the solubility process.

Solubility of sulindac in the supercritical carbon dioxide: Experimental and modeling approach

Solubility measurements of solids in supercritical fluids have been increasingly performed during the past three decades, and semi-empirical models are utilizing as one of the best methods to fit this type of data. For the proper design of supercritical fluid drug process, it is essential to have a sufficient knowledge of the drug solubilities in supercritical fluids particularly carbon dioxide because of its green characterization. In this regards, the solubility of sulindac with IUPAC name of {(1Z)-5-fluoro-2-methyl-1-[4-(methylsulfinyl)benzylidene]-1H-indene-3-yl}acetic acid were examined in the wide ranges of temperature and pressure of 308.15–338.15 K and 160–400 bar, respectively, in supercritical carbon dioxide. The obtained results show the sulindac solubility was in the range of 3.65 × 10−5 to 8.69 × 10−3 mole fraction and additionally was correlated with four density based semi-empirical correlations namely, Mendez-Santiago–Teja, Bartle, Chrastile and Kumar and Johnston methods.

Modeling solubility in supercritical fluids via the virial equation of state

We examine the utility of the virial equation of state (VEOS) for the prediction of the solubility of hexane in supercritical carbon dioxide. We computed virial coefficients up to fourth-order for this mixture at 353.15 K, using Mayer-sampling Monte Carlo applied to established molecular models for carbon dioxide and hexane. At this temperature, neither the third- nor fourth-order VEOS indicate the presence of a critical point for the mixture. However, the VEOS coupled with an ideal-solution treatment for the coexisting subcritical fluid phase (with parameters determined from coexistence data at one pressure) reproduces much of the solubility curve as previously established by Gibbs-ensemble molecular simulation. Comparison of the third- and fourth-order VEOS indicate that the virial treatment is converged at the conditions where it is applied.

A comparison between models based on equations of state and density-based models for describing the solubility of solutes in CO 2

The poor dissolution behaviour of solid drugs in biological environment leads to a low bioavailability. However, the dissolution rate of such drugs can be enhanced dramatically by reduction of the particle size. At present, supercritical fluid based particle size reduction processes are gaining in importance in pharmaceutical technology. For the design of such particle formation processes and the determination of their best operating conditions the knowledge of phase equilibrium and solute solubility in a supercritical fluid is essential. Today, models based on equations of state, together with different mixing rules, are most widely used to correlate and predict the solubility in supercritical fluids. Therefore the accurate knowledge of the required solute data, such as critical parameters, acentric factor, solid molar volume, and sublimation pressure of the solutes is essential. However, the common, non-equation of state based group-contribution methods are mostly empirical and often lead to inconsistent and unreliable results. Thus, due to the lack of information on these data, density-based models are often used for the correlation of experimental solubility data. In this investigation, the solubility of Salicylic acid, of S-Naproxen, of RS-Ibuprofen and of Phytosterol in CO 2 is correlated by different methods: two methods for the pressure–solubility correlation and two methods for the density–solubility correlation. In addition, the influence of solute data predicted by different group-contribution methods is investigated. With the exception of S-Naproxen all systems investigated can be modelled sufficient well with a non-cubic equation of state while a cubic equation of state gives less accurate results. In addition, it is shown that for the solutes investigated, the equation of state based method is very sensitive to the values of the sublimation pressure.

Calculation of Solubilities for Systems Containing Multiple Non-Volatile Solutes and Supercritical Carbon Dioxide

Most of the investigations on thermodynamic modeling of solid solubility in supercritical fluids are limited to pure nonvolatile solutes. Even with a presence of solid mixtures, it is considered that the different solids in the mixture behave as if they were alone, that is, they do not interact. Results in the literature show that this is true if the molecules of the solutes have symmetry, both in size or polarity. The aim of this work is to present solubility experimental data of a solid mixture (β-carotene/bixin) and supercritical carbon dioxide and to propose a thermodynamic model in order to describe this very asymmetric system. The proposed model is based on the Peng−Robinson equation of state and depends on the critical properties and the binary interaction parameters. The binary interaction parameters between carbon dioxide and β-carotene and between carbon dioxide and bixin were obtained from binary experimental data. For the solid mixture and carbon dioxide the model considers interactions between the solids in the solid phase and relaxes the constraint of equal interaction parameters between the solutes. A new set of experimental data on the solubility in supercritical CO2 of a mixture of bixin and β-carotene (1:1, wt) measured at 40 and 60 °C and pressures up to 350 bar is presented, and its behavior is well described by the proposed model, with a deviation of 18.2% and 44.6% for β-carotene and bixin, respectively, opposed to the model without any solid interaction, which poorly describes the available experimental data (approximately 70% average deviation). This model may be used for solid mixtures even when the solids melt.

Solubility of Nonanoic (Pelargonic) Acid in Supercritical Carbon Dioxide

The solubility of nonanoic acid (also known as pelargonic acid) in supercritical carbon dioxide has been determined at (313.15 and 333.15) K over a pressure range of (10 to 30) MPa. The experimental apparatus was of a flow-type, dynamic design, and the solubility was obtained gravimetrically. The solubility ranged from a pelargonic acid concentration of (0.14 ± 0.07) kg·m−3 (333.15 K, 10.0 MPa) to (25.39 ± 0.61) kg·m−3 (313.15 K, 30.0 MPa). The results showed that the solubility of pelargonic acid at 313.15 K was always greater than at 333.15 K at each pressure considered, a common behavior in liquid + SCF phase equilibria. No supercritical fluid solubility data for pelargonic acid were found in the literature. To ensure the validity of the experimental technique, solubility data for oleic acid were measured and compared to literature values. Oleic acid solubilities agreed with literature data within estimated uncertainties. A modified Adachi−Lu model, in terms of dimensionless variables, was used to corr...

Solubility of some statin drugs in supercritical carbon dioxide and representing the solute solubility data with several density-based correlations

Accurate experimental determination of a solid drug's solubility in supercritical fluids (SCFs) and its correlation is crucially important to the development of supercritical technologies for the pharmaceutical industry. In this work, the solubilities of lovastatin, simvastatin, atorvastatin, rosuvastatin and flovastatin in supercritical carbon dioxide (SC-CO 2) were obtained using a simple static method. The solubility measurements were performed at pressures in the range of 121.6–354.6 bar and temperatures in the range of 308–348 K. The mole fraction solubilities ranged from 1.12 × 10 −6 to 1.45 × 10 −3. Solubility data were correlated using four semi-empirical density-based models (Chrastil model, Bartle model, K–J model and M–T model). The results showed that by using three temperature-independent parameters these models can be applied for satisfactory solubility predictions at different pressures and temperatures. A comparison among the four models revealed that the Bartle and M–T models gave much better correlations of the solubility data with an overall average absolute relative deviation (AARD%) of 6.3 and 8.8%, respectively. Using the correlation results, the heat of drug–CO 2 solvation and that of drug vaporization were separately approximated in the range of 13.2–21.3 and 50.5–101.3 kJ/mol.

Supercritical extraction of contaminants from soils and sediments

This paper summarizes representative developments in the field of polluted soil/sediment decontamination by supercritical extraction (SCE). The broad accomplishments of SCE through sustained research and its applications as a remedial technology are outlined. This technology basically employs green supercritical fluids (SCFs) such as carbon dioxide (SCCD) and water (SCW) for the extraction of volatile organic compounds (VOCs) and persistent organic pollutants (POPs), which include polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and various pesticides from environmental matrices. Comprehensive data on solute solubilities in SCFs, partition equilibrium of solutes between a solid matrix and SCFs, solute desorption from the matrix, and solute separation from the SCF provide a solid basis to develop models regarding a SCE process. Significant experimental results and various proposed models to interpret the extraction phenomena from soils/sediments are presented. SCE has been developed to be applied as an environmental remedial technology after its successful use in analytical chemistry. This development has occurred because of a need for a rapid, safe and cheap cleanup method. Conventional techniques for the extraction of environmental matrices (e.g. liquid solvent extraction, thermal desorption) are time and solvent/energy consuming. The review attempts to summarize the representative studies about SCE of organic contaminants, advantages and the drawbacks of SCE compared to other remedial technologies, and economic aspects. A short section on the future direction for research in this field and general trends toward commercial applications are also included. This review is also intended as a guide for conducting a remediation study in a systematic and stepwise fashion for determination of the effectiveness of SCE technology in conjunction with other cleanup technologies. Systematically conducted and well-documented remedial studies are important in the investigation/feasibility and design processes. The applicability and inherent limitations of SCE technology to determine its specific suitability are also discussed.

Rapid expansion of supercritical solution with solid cosolvent (RESS-SC) process: Formation of 2-aminobenzoic acid nanoparticle

A high solubility in supercritical fluid is desired for performing rapid expansion of supercritical solutions (RESS) to produce particles. Unfortunately, extremely low solubility of polar compounds in supercritical CO 2 makes RESS unviable for commercial applications. Liquid cosolvents can improve the solubility, but are unsuitable due to the dissolution of particles in expansion chamber. This work uses a solid cosolvent, menthol, for 2-aminobenzoic acid (ABA) solubilization in CO 2. ABA solubility is increased from 57 to 6600 μmol/mol at 236 bar and 50 °C by using menthol-saturated CO 2. The other drawback of the conventional RESS process is the size of the particles obtained which is mostly in the micron range, due to growth by agglomeration in expansion chamber. In rapid expansion of supercritical solution with solid cosolvent (RESS-SC) process, solid cosolvent hinders the particle growth resulting in small nanoparticles. For example, RESS-SC process produced ∼80 nm size ABA particles, which is significantly smaller than ∼610 nm size particles obtained from RESS process. Menthol is easily removed from ABA nanoparticles by sublimation (lyophilization). DSC, XRD and SEM analyses are used to characterize the particles.

A new model for predicting solute solubility in supercritical fluids based on the Wilson equation

In this work, a new model based on the Wilson solution theory was proposed for predicting the solubility of solids in supercritical fluid (SCF) with and without cosolvent(s) of binary and ternary systems via computation of activity coefficients. For binary systems the model contains two adjustable parameters, while for ternary systems there are four adjustable parameters. The calculated results of the proposed model were compared with that of the literature models, and it is shown that the proposed model is a more accurate one.

Cubic equation-of-state correlation of the solubility of some anti-inflammatory drugs in supercritical carbon dioxide

The accurate experimental determination of solid drug solubility in supercritical fluids (SCFs) and its correlation are crucially important to the development of supercritical technologies for the pharmaceutical industry. In this work, the solubilities of flurbiprofen, ketoprofen, naproxen and ibuprofen in supercritical carbon dioxide (scCO 2) were correlated using the Peng–Robinson (PR), Soave–Redlich–Kwong (SRK) and Patel–Teja–Valderrama (PTV) equations-of-state with van der Waals (vdW), Panagiotopoulos–Reid (mrPR) and Mukhopadhyay–Rao (MR) mixing rules. Several modeling and correlation computational programs were developed in Mathematica ®, a powerful symbolic computational language. Correlations were compared and discussed on the basis of the employed equation-of-state and mixing/combining rules. The importance of the estimation methods used for the determination of critical and other drug physical properties (namely drug's sublimation pressure) was also underlined in the discussion of the correlation results quality. A potential helpful procedure (based on simultaneous correlation of one of the critical or physicochemical properties) is suggested, in order to satisfactorily choose property estimation methods to use.