A continuous model of a rotating disc column for glycerol recovery in soap production

Since many years Rotating Disc Contactors (RDC) are adopted, in large scale plants of soap production, for recovery glycerol from soap solution. However no literature related to the modeling of this equipment is reported. Also equilibrium data and solution properties are not available. Here a theoretical approach to the problem is adopted. As usual in these kind of equipments axial dispersion widely affects the separation efficiency. Fluid-dynamic aspects (e.g. drop size, velocity and hold-up of the dispersed phase), mass transfer and axial dispersion coefficients affects column behavior. A mechanistic approach is proposed for their evaluation. Model predictions concerning glycerol, NaOH, NaCl concentrations and column hold-up have been compared with experimental data obtained from a commercial column. The results appear to be satisfactory. Part of the proposed methodology is fairly general and can be extended to the modeling of other liquid-liquid extractors like for instance the rotating buckets contactors (Dente and Bozzano 2004).