Solubility in SCF

Applications The majority of SFE applications involves the extraction of dry solid matrices. Supercritical fluid extraction has demonstrated great utility for the extraction of organic analytes from a wide variety of solid matrices. The combination of fast extractions and easy solvent evaporation has resulted in numerous applications for SFE. Important areas of analytical SFE are environmental analysis (41 %), food analysis (38 %) and polymer characterisation (11%) [292], Determination of additives in polymers is considered attractive by SFE because (i) the SCF can more quickly permeate throughout the polymer matrix compared to conventional solvents, resulting in a rapid extraction (ii) the polymer matrix is (generally) not soluble in SCFs, so that polymer dissolution and subsequent precipitation are not necessary and (iii) organic solvents are not required, or are used only in very small quantities, reducing preparation time and disposal costs [359]. 

To model the solubility of a solute in an SCF using an EOS, it is necessary to have critical properties and acentric factors of all components as well as molar volumes and sublimation pressures in the case of solid components. When some of these values are not available, as is often the case, estimation techniques must be employed. When neither critical properties nor acentric factors are available, it is desirable to have the normal boiling point of the compound, since some estimation techniques only require the boiling point together with the molecular structure. A customary approach to describing high-pressure phenomena like the solubility in SCFs is based on the Peng-Robinson EOS [48,49], but there are also several other EOS s [50]. 

In this work we investigate such interactions by fluorescence spectroscopy. Probe molecules such as 2-naphthol and its 5-cyano-derivative are effective chromophores for studying acid/base interactions since both are relatively strong photo-acids. In addition, 2-naphthol is a common solute for which SCF solubility and physical property data exist. Ultimately, spectroscopic information will be used to develop a clearer picture of the specific interactions which induce large cosolvent effects on solubility in SCF solutions. 

Table I. Effects of cosolvents including simple liquids, complexing agents and surfactants on solubilities in SCFs at 35 C...

Pressure is not the best independent variable with which to represent solubilities in SCFs. The quite confused representation of Figure 2.3-l(a) can be improved if the same solubility isotherms are plotted against the vapor density (i.e. the SCF density), as in Figure 2.3-1(b). This smooth dependence is embedded in a simple equation proposed by Chrastil [7] and recently modified by Mendez-Santiago and Teja [8] to correlate solubility of solids in SCFs ... 

Organic compounds become soluble in SCFs to form a homogeneous reaction phase, leading to high reactivity and selectivity. 

Because enzymes are not soluble in SCFs it should be possible to disperse free enzyme in the SCF and recover the enzyme without the need to immobilize it on a support. 

Many enzymes are stable and catalyze reactions in supercritical fluids, just as they do in other non- or microaqueous environments. Many enzymes are more stable in supercritical fluids than in aqueous solutions. However, enzymes are not soluble in SCFs therefore enzymatic catalysis in SCFs is always heterogeneous. 

Drug properties, such as solubility and partitioning of the dmg into SCF, determine the properties of the particles formed. When SCF is intended as an antisolvent, if the drug is soluble in SCF under the operating conditions, it will then be extracted into SCF and will not precipitate outl . ... 

Palmitic acid and its derivatives have, depending on the temperature and pressure, reasonable solubility in SCFs. In particular, liquid phase components have an acceptable... 

SCE-based processes such as GAS process, SAS process, aerosol solvent extraction system (ASES), SEDS address low solubility of the compounds in SCCO2. In these processes, the drug, polymer, or both are dissolved in an organic solvent to form a solution. Solvents used may include dimethyl sulfoxide, N-methyl pyrrolidone, methanol, ethanol, acetone, chloroform, or isopropanol. To successfully produce ASD, the drug and polymer should exhibit limited solubility in SCF and the organic solvent should be miscible with carbon dioxide. Collection of the precipitated particles in the antisolvent is carried out in the same vessel where solvent extraction takes place. The particles are collected on a filter unit located at the bottom of the vessel. 

Compound/ polymer solubility in SCF Required Not required Not required Not required Preferred... 

The extracted sample must have fine solubility in SCFs. SCFs (CO2) is more suitable for fat-soluble chemical constituents. The solubility of samples in SCFs can be modified by adding cosolvent (such as 1-10 % methanol), which can enhance the polarity of SCFs (CO2) to extract moderately polar compounds. 

The main advantage of SCCO2 lies in the easiness of the possible downstream processing. Separating products from reactants can be greatly facilitated by the ease with which the solvent power of SCF solvents can be adjusted. By coupling a series of depressurization steps at the outflow of the reaction vessel, it is possible to selectively fractionate products and residual substrates of a reaction [9]. The fluid can be recycled after repressurizing. Different methods are described for the calculation of solubility in SCFs [10-13]. 

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