SEPARATION OF CHLOROBENZOIC ACIDS THROUGH HYDROTROPY

The separation of o- and p-chlorobenzoic acids from their mixtures was investigated using hydrotrope solutions. The aqueous solubilities of o- and p-chlorobenzoic acids in different concentrations of hydrotrope (i.e., sodium butyl monoglycol sulfate) at different temperatures wer e determined by the weight disappearance method. The ternary solid-liq uid-phase equilibrium diagram for the o-chlorobenzoic acid-p-chloroben zoic acid-water system with the same hydrotrope, incorporating several hydrotrope isoplethal curves and two-component saturation and eutecti c tie-lines, was constructed. The sensitivity and feasibility of the p roposed process were examined by carrying out solubilization and equil ibrium precipitation experiments with the mixtures of various composit ions, including the eutectic composition. The precipitation kinetics o f pure o- and p-chlorobenzoic acids from their hydrotrope solutions we re studied in a laboratory-scale agitated precipitator. The nucleation and growth rates are correlated in terms of significant process varia bles using power law models. With this hydrotrope it was possible to e nrich p-chlorobenzoic acid significantly in the product crystalline ph ase from the eutectic composition in a single stage. Highly pure (>99. 0%) chlorobenzoic acid crystals were obtained from precipitation of no neutectic mixtures of o- and p-chlorobenzoic acids in their primary pr ecipitation region of the ternary phase equilibrium diagram.