Supercritical fluid extraction of acetic acid, alcohols and other amphiphiles from acid-water mixtures

Common supercritical fluid solvents cannot effectively extract highly water-soluble contaminants from either soils or waters. Two questions then arise: (1) how effective is SCF extraction from aqueous solution of contaminants only slightly soluble in water, when highly soluble organics are present; and (2) how will the extractability of the highly soluble contaminant be affected by the slightly soluble one? We have explored SCF extractions of this type, the solvent being CO2 at 7-17 MPa and temperatures to 323 K, for a range of amphiphilic or surfactant compounds including simple alcohols (1-hexanol and I-octanol), longer chain oxyalcohols (polyethylene glycol-200 and the methyl ether of polyoxyethylene-3), and a fluorinated polyether carboxylate. Acetic acid was used as the model contaminant of high aqueous solubility. We found that the presence of the amphiphiles decreases the already limited extractability of acetic acid from aqueous solution by SCF-CO2; this was especially true of materials regarded as nonionic or anionic surfactants. Meanwhile, the presence of acetic acid apparently decreased the extractabilities of alcohols by CO2, especially for alcohols of higher molecular weight. Possible reasons for this behavior and its implications for SCF extraction of natural waters are discussed. (C) 1997 Elsevier Science B.V.