Quantifying the influence of salinity on spontaneous emulsification of hydrocarbons

Abstract

This study has investigated the process of oil-in-water spontaneous emulsification using the hydrophobic force of a non-ionic surfactant (Triton X-114) and inorganic salt additive (NaCl). The cloud point of surfactant solutions with different salt concentrations was examined and show a gradual decrease from 27 °C to 18.5 °C when increasing the salinity from 0 to 5 M. The adsorption of Triton X-114 into the oil-water interface has spontaneously enlarged the surface excess concentration of oil droplet in the system, leading to the decrease in surface tension and the spontaneous formation of oil droplets in water. Increasing the concentration of salt additive caused an increment in ions’ penetration into the hydrophilic layer of surfactants, resulting in the formation of smaller droplets. Increasing the chain-length of the oil from C7 (n-heptane) to C16 (n-hexadecane) produced a decrease of 58.6 % in droplet diameter. According, a newly-proposed model was developed and fitted against experimental data to obtain the best-fitted parameters of maximum droplet size (D0) and ion adsorbent constant (Kion). The data and modelling results verify the influence of the interfacial layer on the emulsions’ size and stability.