Dispersed oil droplets from the low-concentration emulsion solution of dodecane-water system were separated using a coalescence column packed with polystyrene bead of 0.5 mm diameter. The separation efficiency defined by the fraction of removed oil droplets were determined by counting the droplet numbers and by varying the column length, the droplet sizes, the feed concentrations. At fixed feed concentrations and solution velocity, the efficiency increases as the column length and particle size increase, but it decreases as the velocity increases.
A mathematical model for the estimation of separation efficiency was proposed under the assumption of two step reactions, coagulation and coalescence.
From the model, the efficiency($E_f$) can be related to the initial concentration and residence time (τ =εL/v) by
$In (1-E_f) - KC_{so}E_f = -KK_c^\tau$
where K and $K_c$ are the rate constants of coagulation and coalescence respectively.
From the data reduction, the parameter model showed the good fittability with the experimental data. Further, coagulation rate constant increases exponentially with the increase of emulsion size, while it decreases with the increase of solution velocity. On the other hand, the coalesence rate constant slightly decreases with emulsion size, but nearly constant within solution velocity examined (0.2 ~ 2 cm/s).
