Removal of phenols from aqueous streams by the cloud point extraction technique with oxyethylated methyl dodecanoates as surfactants

New oxyethylated methyl dodecanoates with average degrees of oxyethylation (n) ranging between 5 and 14 Idenoted OMD-n) were considered as nonionic surfactants for the removal of phenol, 4-methylphenol, and 4-nitrophenol from aqueous streams by the cloud point extraction technique. The cloud point (denoted CP) strongly increases with the average degree of oxyethylation n but is independent of OMD-n concentration, except at low concentration (i.e., < 10 g.L-1). CP can be related to the surfactant hydrophilicity by the following equation: CP(degreesC) = 20.27 x HLBG - 245.8 (above 10 g.L-1 and in the absence of electrolyte), where HLBG refers to the OMD-n hydrophile-lipophile balance in Griffin's scale. The presence of electrolyte such as NaCl strongly decreases the cloud point [Delta CP/Delta [NaCI] approximate to -(9 +/- 1) degreesC.M-1]. Many parameters influence the extraction of phenols in OMD-n-rich phases, including the characteristics of phenols (hydrophobicity, hydrogen-bond acidity, hydrogen-bond basicity, etc.), the average degree of oxyethylation of OMD-n (i.e., n), the concentration of electrolyte, the settling temperature ( T-set), and overheating (DeltaT= T-set - CP). The distribution coefficients typically range between 20 and 100. Finally, the kinetics of the separation process is limited by the slow coalescence of the fine droplets of surfactant-rich phase formed above CP.