Effect of brine salinity on the partitioning, distribution and corrosion inhibition performance of a quaternary amine corrosion inhibitor

Surfactant corrosion inhibition performance in water–oil environments is influenced by complex relationships between their physical properties, solution chemistry and interfacial characteristics. The existence of polar heads/nonpolar tails influences both the preferential distribution of the surfactant between the two media as well as the phase in which micellisation occurs. Both phenomena affect the efficiency of the surfactant inhibitor and its adsorption at the metal-solution interface. To demonstrate the complexity of such interactions, the effect of brine salinity on the critical micelle concentration (CMC) and partitioning/distribution behaviour of a quaternary amine corrosion inhibitor (alkyldimethylbenzylhexadecylammonium chloride, or BAC-C₁₆) in a brine and toluene system (at 1:1 ratio) was explored. All experiments were conducted at 50 °C and pH4 over varying salinities (0.1, 1 and 10 wt%) of NaCl brine. Both CMC and partitioning characteristics of BAC-C₁₆ are significantly affected by aqueous phase salinity, with an inversion of the partitioning response observed between concentrations of 0.1 and 1 wt% NaCl. The effect of BAC-C₁₆ partitioning/distribution behaviour on corrosion inhibitor performance was examined using rotating cylinder electrode experiments. The results illustrate that in order to establish the true corrosion inhibition behaviour, consideration of the chemical distribution characteristics is crucial.