| Alcohol polyoxyethylene ether sulfonates (RO(CH2CH2O)nCH2CH2SO3Na) are a kind of anionic surfactant with anionic-nonionic combined hydrophilic group, which have excellent thermal stability and salt tolerance and are good surfactants for enhanced oil recovery. However, commercial production has not been realized yet due to low yield in synthesis.In this study, coconut alcohol polyoxyethylene ether sulfonate (CAPES) was synthesized by reaction of metallic sodium with coconut alcohol polyoxyethylene(3) ether (AEO3) followed by reaction with 2-chloroethanesulfonate with toluene as solvent. In the first step of the reaction, a yield as high as 95% can be reached by reacting 4h at 120℃at a sodium/AEO3 molar ratio equal to 1:1 under nitrogen protection. In the second step, the yield is significantly affected by the temperature, reaction time and the molar ratio of reactants. By both systematic single-factor tests and orthogonal tests the optimum reaction condition were obtained, or let Na-AEO3 react with 2-chloroethylenesulfonate for 4h at 60℃at an Na-AEO3 /2-chloroethylenesulfonate molar ratio of 1:1.3. The yield at the optimum condition can reach as high as 82%. Characterized by IR and MS spectra, the final product after purification was proved to have molecular structures in good agreement with the mixed homologues of C12/C14 fatty alcohol polyoxyethylene (n) ether sulfonates where n is between 1 to 8. The studies to the properties of CAPES indicate that CAPES has a low cmc, 6.50×10-4 mol/L and a lowγcmc, 32.20 mN/m, and a saturated adsorption of 2.73×10-10 mol/cm2 at air-water interface, which corresponds to a cross-section molecular area of 0.61nm2 at 25℃. It is found that the interfacial activity of CAPES is similar to AES but much better than SDS, and CAPES has a thermal stability of higher than 97% when dissolved in neutral and slightly alkaline aqueous media and set for 96 h at 80oC, which is much higher than that of AES. At 45oC the tolerance of CAPES to NaCl, CaCl2 and MgSO4 in pure water reaches 115, 167 and higher than 300 g/L, respectively, equivalent to that of AES. Using CAPES as surfactant to prepare microemulsions, the optimum salinity and the salt concentration range in which middle phase microemulsions are formed are also equivalent to that of AES. The salt tolerance of CAPES is much better than alkylbenzene sulfonates. By mixing with zwitterionic surfactant CAPES can reduce Daqing crude oil/water interfacial tension to a magnitude of 10-3mN/m at 45oC without adding any alkaline agent or neutral electrolyte. CAPES is thus a significant surfactant applicable in alkali-free surfactant–polymer flooding.
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