Chapter 5 - Use of Cloud Point Extraction with Ethoxylated Surfactants for Organic Pollution Removal

Abstract

Above a given temperature, called cloud point (Tc), the aqueous solutions of most of the polyethoxylated nonionic surfactants separate into two phases: a surfactant-rich one (coacervate) and a dilute one, in which the surfactant concentration is close to its critical micelle concentration (cmc). Therefore, due to the micellar solubilization property of the surfactants, hydrophobic, amphiphilic or even ionic solutes can be extracted into the coacervate above Tc. Thus, cloud point extraction (CPE) implies the existence of a phase separation and the solubilization properties of non-ionic surfactant aggregates. As an answer to the current restricted use of volatile organic compounds (VOC), often toxic, on a large scale, CPE appears as an environmentally friendly, energy-saving process for aqueous effluent purification. This technique, widely adapted in our laboratories to the treatment of various aqueous effluents with alkylphenol ethoxylates or alcohol ethoxylates gives successful results concerning (i) soluble pollutants (phenol, benzyl alcohol, neutral red, methylene blue with maximum extraction yields of 95%, 90%, 99.8%, and 90%, respectively, orange G, humic acids); (ii) dispersed pollutants, for example, oily wastewater and silk-screen printing inks; such a process combines cutting oil (or silk-screen printing ink) emulsion destabilization, and CPE. When applied to the treatment of cutting oils in the presence of granite, the chemical oxygen demand (COD) value of the treated effluent may fall from 55 g O2.L-1 to 1.5 g O2.L-1. In some cases, the addition of an electrolyte allows CPE to operate at lower temperatures, under less energy-consuming conditions. An efficient surfactant regeneration method is proposed following acidic effluent treatment.