Synthesis of Didodecylmethylcarboxyl Betaine and Its Application in Surfactant-Polymer Flooding

Enhanced crude oil recovery by chemical flooding has been a main measure for postponing the overall decline of crude oil output in China, and surfactant-polymer (SP) flooding may replace alkali-surfactant-polymer flooding in the future for avoiding the undesired effects of using alkali. In this paper the synthesis of a surfactant with a large hydrophobe, didodecylmethylcarboxyl betaine (diC(12)B), and its adaptability in SP flooding were investigated. The results show that diC(12)B can be synthesized by reaction of didodecylmethyl amine, a product commercially available, with chloroacetic acid in the presence of NaOH, with a resulting yield as high as 80 wt% under appropriate conditions. With double dodecyl chain diC(12)B is highly surface active as displayed by its low CMC, 3.7 x 10(-6) mol L-1, low gamma(CMC), 27 mNm(-1), as well as high adsorption and small cross section area (a parts per thousand currency sign0.25 nm(2)) at both air/water and oil/water interfaces at 25 A degrees C. By mixing with conventional hydrophilic surfactants diC(12)B can be well dissolved in Daqing connate water and reduce the Daqing crude oil/connate water interfacial tension to about 10(-3) mN m(-1) at 45 A degrees C in a wide total surfactant concentration range, from 0.01 to 0.5 wt%. And a tertiary oil recovery, 18 +/- A 1.5 % OOIP, can been achieved by SP flooding using natural cores without adding any alkaline agent or neutral electrolyte. DiC(12)B seems thus to be a good surfactant for enhanced oil recovery by SP flooding.