(142h) Numerical Investigation of the Effect of Surfactants On the Dynamics of the Organic Drops in Water Column

Chemical dispersants are widely used to counter the adverse effects of oil spills on the environment. Surfactants are the active ingredients in dispersants which cause reduction in interfacial tension resulting in the production of smaller oil droplets. Surfactant distributes between the bulk phase (water) and the interface to achieve equilibrium between the two phases.

   In this study we present a numerical model which captures the effect of surfactant on the dynamics of the hydrocarbon droplets. In the preliminary results we show how the variation in concentration of surfactant affects the terminal settling velocities of Carbon tetrachloride droplets in water. The system under consideration consists of 0.02 ml (d_p = 3.4 mm) CCl₄droplets, containing 0. 2M of acetic acid, settling in an extraction column of internal diameter 3cm and length 70cm, containing water with surfactant TritonX-100. Numerical simulations are carried out at different concentrations of surfactant in the bulk phase. As the concentration of surfactant in continuous phase remains constant in each case, a uniform interfacial tension prevails across the droplet surface. The relation between the bulk surfactant concentration and interfacial tension is established using Langmuir-Szyszkowski equation. The results are compared with those obtained in the experiments conducted by Chen et al. (“Adsorption Behavior of surfactants and mass transfer in single drop extraction”, January 2000,Vol 46. No1,AICHE Journal, pp.160-168). The mass transfer coefficients for transfer of acetic acid from droplet to continuous phase are taken from the data provided in the experiment.

We also present a model which is applicable in scenarios of continuous spray of surfactant on the swarm of hydrocarbon drops. In this case, the concentration of surfactant in the continuous phase is not constant. A convection-diffusion equation is included in the model to capture the transport of surfactant from continuous phase to dispersed phase and depending on the surfactant concentration at the interface, the interfacial tension is calculated. The results are extended to the system with droplets resulting from the breakup of a liquid jet. Applications of this model can be found in understanding the deep water oil spill scenarios.