Characterisation of gas-liquid interfaces related to offshore produced water treatment: Interfacial activity of model components

Abstract

The amount of produced water during oil production is increasing as oil fields mature. Produced water is the largest source of pollution in the production phase, and can be treated by a method known as gas flotation. To increase the efficiency of this method, the surface tension between the produced water and air should be as high as possible. In this study, acid solutions were used as model produced water to investigate how salinity, pH, and the structure and concentration of surfactants influence the surface tension. The acids studied are 4-heptylbenzoic acid, decanoic acid, and 3-cyclopentylpropionic acid. Two models are used to investigate the limiting transport mechanisms of short-time-limit adsorption. The measurements were done by means of a Du Nöuy ring tensiometer and a maximum bubble pressure tensiometer. The results indicate that the surface tension of the surfactants decrease when salt is added to the solution. The structure of the surfactant is highly important, as longer chained surfactants have shown to have a higher tendency to adsorb at the interface. The presence of a benzene ring in the hydrocarbon chain has shown to reduce the surface tension. Increasing the pH of a solution of 3-cyclopentylpropionic has shown to cause an increase in surface tension. The results also indicate that an adsorption barrier is present at concentrations above the CMC, and in surfactant solutions in absence of salt.