Nonylcyclohexanol polyethoxylate, a greener alternative of nonylphenol polyethoxylate endows sodium oleate solution high salt tolerance

Abstract

Nonylphenol polyethoxylate (NPEOn) has been expected to enhance salt tolerance of system containing carboxylates, but banned in countries recently. Herein, a group of new surfactants, nonylcyclohexanol polyethoxylate (NCEOn) was formulated with sodium oleate (NaOA) into binary surfactant systems, to investigate their interaction towards salt tolerance, phase behavior, interface tension and lime soap dispersing requirement in brine with comparison of NPEO10. The results indicate that the salt tolerance of NaOA-NCEOn system increased with increasing NCEOn concentration and EO number, following the order towards the salts: SO42- > Cl- for anions and Na+ > Mg2+ > Ca2+ for cations, respectively. Moreover, cloud point (CP) of NaOA-NCEOn system was increased by adding NaOA but decreased by introducing inorganic salts, respectively. The influence strength of cationic ions on CP decline was in the order: Na+ < Mg2+ < Ca2+. The thermodynamic parameters at CP explains the difference in salt tolerance of NaOA towards monovalent and divalent cations. Notably, the NCEO11(0.02 %)-NaOA (0.05 %) system exhibited similar or superior salt-tolerance in NaCl (20 %) or CaCl2 (2 %) brine, as NPEO10 did. The solubility of NaOA in saline (0.1 %-5%) was up to thousand folds of that in water, suggesting NCEOn a green substitute for NPEO10 in the field.