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

• Carboxyl betaines with double alkylpolyoxyetheylene ether chains were synthesized.
• Effects of EO number on solubility and surface activity were evaluated.
• IFT behavior of these products for surfactant-polymer flooding was evaluated.
• Inserting EO groups improves solubility and reduces adsorption loss on sandstone.
• The new surfactants with EO groups keep small cross section area at interfaces.

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 (diC12B), 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 EO groups between the long alkyl chains and head groups, and both homogenous compounds (diC12EnB, n = 2, 3, 4) and a mixture of homologues diC12–14EnB (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 EO 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 (Nmin). Using these surfactants solely ultra low IFT (<0.01 mN/m) can be achieved by diC12E2B, diC12E4B, and diC12–14E2.2B against C13–15, C7–9, and C8–9n-alkanes, respectively, and an order of 10−2 mN/m IFT between Daqing crude oil and connate water can be achieved. However, ultra low IFT between Daqing crude oil and connate water can be achieved by using these surfactants via formulations. In comparison with diC12B the new surfactants with EO groups have both improved aqueous solubility and lower adsorption loss when employed in SP flooding free of alkali.

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