Polymeric surfactants for enhanced oil recovery. Part III—interfacial tension features of ethoxylated alkylphenol‐formaldehyde nonionic surfactants

Abstract

The interfacial tensions (IFT) of four low molecular weight groups of ethoxylated octylphenol‐, dodecylphenol‐, tetradecylphenol‐ and hexadecyl‐phenol—formaldehyde polymeric surfactants were determined using the spinning drop method. Some noteworthy features of the interfacial behaviour of dilute aqueous solutions of 16 of these compounds and homologous hydrocarbons are discussed. An important feature is that these surfactants behave similarly to monomeric ones in their hydrocarbon scan, that is they have a minimum IFT value against a particular member of a homologous hydrocarbon series. The magnitudes of the tension at minimum (γmin) values obtained in this study are of the order of ‘ultralow’ (10−2‐10−3 mNm−1). The nmin values of these polymeric nonionic surfactants decrease with increasing hydrophilicity, that is decrease with the increase of ethylene oxide units condensed per mole of alkylphenol unit in the polymeric surfactants studied. In this case, the downward shift in nmin is smaller and apparently not linearly related to the number of EO units. Increasing the hydrophobicity of these polymeric nonionics, that is increasing the length of the alkyl chain from C8 to C16, resulted in an increase in the nmin values obtained. For each of the investigated groups, the lowest γmin values are obtained with polymeric surfactants having the highest EO content. The optimum low tension performance occurs at the low end of the equivalent alkane carbon number scale (at EACNs below 6). Under the influence of added electrolytes these EACNs were shifted to higher values.

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“…However, the IFT* tended to decrease when the EACN value of the oil increased. From the research by Barakat et al (1989) [62], it is known that each nonionic surfactant is suitable for a different EACN. The IFT* trend steadily declined, and then increased again when the hydrophobicity of the oil increased [62].…”

“…From the research by Barakat et al (1989) [62], it is known that each nonionic surfactant is suitable for a different EACN. The IFT* trend steadily declined, and then increased again when the hydrophobicity of the oil increased [62]. Therefore, the IFT* results of our study are likely within the first part of this rend.…”