Entrainer co-solvent effects of supercritical solvents

Entrainers, modifiers, and co-solvents are basically mixed solvent systems and provide another dimension to supercritical fluid extraction. The entrainers enhance the solubility of the low volatile substance in the solvent, provide selective solubility in multi-solute instances, and enhance the sensitivity of the solubility and selectivity to temperature, pressure, and composition. The entrainers may be reactive and are also useful as slurrying media. Table 21.1.4 shows representative data on the effect of entrainers on vapor liquid systems that has been systematically studied by Brunner s group. Kumik and Reid as well as Johnston s group present data for dense gas-solid systems. 

Hexadecanol( 1) - octadecane(2) - entrainer - Hexadecanol(l) - octadecane(2) - entrainer -  

Although entrainers provide the aforementioned added advantages, they also bring forth more eomplex process flowsheets. The separation of extract from entrainer and entrainer from the supercritical component are not as easy and as sharp as in the instances without entrainer. The selection of entrainer is based on thermodynamic, environmental, and economic considerations. The solute-entrainer and entrainer-supercritical separations are the key from the processing perspective.  

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Phenol, a common priority pollutant, was extracted from two environmental matrices, soil and water, using near critical and supercritical carbon dioxide. The primary objective of this study was to determine the distribution of the contaminant between the soil or water and the supercritical phase, and the effect of soil moisture and co-solvents on the distribution coefficients. Static equilibrium extractions were performed on dry and wetted soil contaminated with 1 wt.% phenol and on water containing 6.8 wt.% phenol. Supercritical carbon dioxide (with and without en-trainers) was chosen as the solvent for the study. An appropriate entrainer for dry soil extractions (methanol) ffiffered from that found for aqueous extractions (benzene). However, soil moisture was found to have a significant impact on the effectiveness of en-trainers for soil extractions of phenol. Entrainers appropriate for extracting wetted soil were found to be the same as those advantageous for aqueous extractions. Benzene was also extracted from dry and wetted soil to investigate the extractability of a hydrophobic compound. 

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