Effect of Additives on the Cloud Point of the Octylphenol Ethoxylate (30EO) Nonionic Surfactant

Abstract

The effect of different additives on the cloud point (CP) of an octylphenol ethoxylate (OPEO30) aqueous solution was investigated. The CP of OPEO30 is higher than 100 C due to its approximately 30 oxyethylene units per molecule, which limits its use in cloud point extraction (CPE) procedures at room temperature. However, the presence of additives can promote a decrease in CP, allowing its use in CPE. Halide presence decreased the CP of OPEO30 in the following order F-[Cl-[Br-. It was also observed that the addition of divalent anions resulted in a more pronounced salting-out effect than monovalent anions. Blends of OPEO30 and its counterpart with 7.5 units of ethylene oxide (OPEO7.5) were also investigated, and it was verified that the CP of OPEO30 decreased linearly with increasing OPEO7.5 concentration, showing that mixing surfactants is a strategy to be explored. In the presence of small amounts of alcohols that are partially soluble in aqueous solution, such as isobutanol and pentanol, cloudiness was observed at temperatures below the CP of pure OPEO30 solution.