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 were determined by the weight disappearance method. The ternary solid-liquid-phase equilibrium diagram for the o-chlorobenzoic acid-p-chlorobenzoic acid-water system with the same hydrotrope, incorporating several hydrotrope isoplethal curves and two-component saturation and eutectic tie-lines, was constructed. The sensitivity and feasibility of the proposed process were examined by carrying out solubilization and equilibrium precipitation experiments with the mixtures of various compositions, including the eutectic composition. The precipitation kinetics of pure o- and p-chlorobenzoic acids from their hydrotrope solutions were studied in a laboratory-scale agitated precipitator. The nucleation and growth rates are correlated in terms of significant process variables using power law models. With this hydrotrope it was possible to enrich p-chlorobenzoic acid significantly in the product crystalline phase from the eutectic composition in a single stage. Highly pure (>99.0%) chlorobenzoic acid crystals were obtained from precipitation of noneutectic mixtures of o- and p-chlorobenzoic acids in their primary precipitation region of the ternary phase equilibrium diagram.