This study focused on the separation of two immiscible liquids as continuous and dispersed phases. The study observed the matter of dropdropping coalescence at the Interfaceinterface, while separating caustic soda and disulfide compounds in the gravity separator. This phenomenon is a part of the Merox unit. A digital high-frame rate camera was used for measuring the drop coalescence time. The drops of dimethyl disulfide were directed toward caustic soda as the continuous phase. By applying the experiment design methods and influential independent variables. The, the effect of drop size and physical properties on coalescence time, were investigated. The volume of fluid method has been used for modeling the drops of the dispersed phase that were released from the nozzle toward the interface and the results were compared with experimental data. By conducting these experiments and, measuring the drop coalescence time with the mother phase at the interface and by fitting the coalescence time curve based on the independent variables, the desired nonlinear equation was achieved. A comparison between experimental data and reported correlation was done and had a maximum deviation of 15.1%.