Effect of Organic Alkalis on Interfacial Tensions of Surfactant/Polymer Solutions against Hydrocarbons

Abstract

The dynamic interfacial tensions (IFTs) of enhanced oil recovery (EOR) surfactant/polymer/organic alkali systems against a homologous series of alkanes have been investigated by a spinning drop interfacial tensiometer. Two organic alkalis with different molecular sizes, ethanolamine (EA) and diethanolamine (DEA), two surfactants with high interfacial activity, heavy alkyl benzenesulfonate (HABS) and petroleum sulfonate (SLPS), and two kinds of polymers, partly hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM), were employed to study the real mechanisms controlling the IFT behavior. The experimental results show that the addition of organic alkali may affect the dynamic IFTs of surfactant solutions through different mechanisms. First, the possible reaction of organic alkali with the oil-soluble components in industrial surfactants will influence the surface active spices at the interface and enhance the dynamic behavior. Second, the hydrophilic–lipophilic balance (HLB) of the surfactant may vary, and the surfactant may become more water-soluble because of the ionization of oil-soluble components, especially for HABS. Finally, the organic counterion with larger molecular sizes may affect the arrangement of interfacial surfactant molecules. For both HABS and SLPS surfactants, interfacial interactions between the hydrophobic part of surfactants and the hydrophobic blocks of HMPAM will reduce the interfacial concentration of surfactant monomers by forming aggregates and result in an obvious increment of the IFT value. On the other hand, HPAM will obviously enhance the water solubility of the surfactant/organic alkali solutions and reduce the IFT values for the hydrocarbons with lower alkyl carbon number (ACN).