Effect of Some Petroleum Sulfonate Surfactants on the Apparent Water Solubility of Organic Compounds

Water solubility enhancements of 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT) and 1,2,3-trichlorobenzene (TCB) by some commercial petroleum sulfonates (Petronate L, Petronate HL, and Pyronate 40) were studied at room temperature. Unlike conventional surfactants, the petroleum sulfonate surfactants are mixtures of sulfonated hydrocarbons and free mineral oils, which form stable emulsions in water and thus behave much like a bulk organic phase in concentrating organic solutes. The extent of solubility enhancement is linearly proportional to the concentration of the petroleum sulfonate-oil (PSO) emulsion, in contrast with the effect of a conventional surfactant in which a sharp inflection occurs in the vicinity of the critical micelle concentration (CMC). The enhancement effect of the PSO surfactant is 1.5–3 orders of magnitude greater than that of ordinary surfactant monomers below the CMC. The partition coefficient of the solute between the emulsified PSO phase and water (K_em) is closely related to the nonpolar content of the PSO surfactant; the normalized K_em values are about the same order of magnitude as the solvent (octanol)-water partition coefficients of the solutes. The data suggest the potential impact of an emulsified phase on the transport and fate of organic contaminants in situations where spilled or waste oils may be emulsified by surfactants.