A New Type of Sulfobetaine Surfactant with Double Alkyl Polyoxyethylene Ether Chains for Enhanced Oil Recovery

A new type of sulfobetaine with double alkyl polyoxyethylene (n) ether chains, dicoconut oil alcohol polyoxethylene (n) ether methylhydroxylpropyl sulfobetaine (diC(12-14)E (n) HSB) was synthesized using a commercial nonionic surfactant, coconut oil alcohol polyoxethylene (n) ether, as raw material and its properties as a surfactant for enhanced oil recovery (EOR) in the absence of alkali was studied. The purified product is a mixture of homologues with mainly C-12/C-12, C-12/C-14 and C-14/C-14 alkyl chains and widely distributed EO chains (n = 2.2 on average) with an average molar mass of 742.6 g/mol. The diC(12-14)E(2.2)HSB has an improved aqueous solubility at 25 A degrees C compared with didodecylmethylhydroxylpropyl sulfobetaine (diC(12)HSB), a homologue without an EO chain, and is highly surface active as reflected by its low CMC (4.6 x 10(-6) mol/L), high saturated adsorption (6.8 x 10(-10) mol/cm(2)) and small cross sectional area (0.24 nm(2)/molec.) at the air/water interface. With a hydrophile-lipophile balance well matched with Daqing crude oil/connate water system, the sulfobetaine can reduce Daqing crude oil/connate water interfacial tension to ultra-low values at 45 A degrees C in the absence of alkali, and displays a low saturated adsorption at the sandstone/water interface (0.0024 mmol/g), reduced by 69 and 92 % respectively in comparison with that of the corresponding carboxyl betaine, diC(12-14)E(2.2)B and its homologue without an EO chain, didodecylmethylcarboxyl betaine (diC(12)B). With these excellent properties diC(12-14)E(2.2)HSB gives a high tertiary recovery, 18.4 % original oil in place, when mixed with other hydrophobic and hydrophilic sulfobetaines in surfactant-polymer (SP) flooding free of alkali. The insertion of EO chains in combination with the replacement of carboxyl betaine by sulfobetaine is therefore very efficient for improving the properties of the double chain hydrophobic carboxyl betaines as surfactants for SP flooding free of alkali.