A new type of renewable surfactants for enhanced oil recovery: Dialkylpolyoxyethylene ether methyl carboxyl betaines

To avoid side effects in alkali-surfactant-polymer (ASP) flooding due to use of caustic alkalis, surfactant-polymer (SP) flooding free of alkali has been paid more attention in recently years. This calls surfactants more hydrophobic than those used in ASP flooding. A carboxyl betaine with double long alkyls, didodecylmethylcarboxyl betaine (diC(12)B), is such a candidate which behaves very well in reducing crude oil/water interfacial tension (IFT) but suffers from poor aqueous solubility and large adsorption loss by negatively charged sandstone. In this paper a new type of carboxyl betaines derived from renewable materials were synthesized by inserting EC) groups between the long alkyl chains and head groups, and both homogenous compounds (diC(12)E(n)B, n = 2, 3, 4) and a mixture of homologues diC(12-14)E(n)B (n = 2.2) derived from commercially available coconut alcohol polyoxyethylene ether were obtained and their properties as surfactants for SP flooding free of alkali were evaluated. The results show that with increasing EC) number the solubility of the surfactants increases whereas the adsorption loss decreases, and accordingly the hydrophilicity of the surfactants increases, leading to a decrease of their preferred alkane carbon number (N-min). Using (C) 2015 Elsevier B.V. All rights reserved.