Phase relations of o- and p-chlorobenzoic acids in hydrotrope solutions

The separation of chlorobenzoic acids from their mixtures of o- and p-components in hydrotrope solutions was investigated. The aqueous solubilities of o- and p-chlorobenzoic acids in different concentrations of sodium cumene sulfonate and sodium butyl monoglycol sulfate solutions at different temperatures were determined by the mass disappearance method. The ternary solid-liquid-phase equilibrium diagrams for the o-chlorobenzoic acid + p-chlorobenzoic acids + water system with sodium cumene sulfonate and sodium butyl monoglycol sulfate as hydrotropes, incorporating several hydrotrope isoplethal curves and the two-component saturation and eutectic tie lines, were constructed. The sensitivity and feasibility of the proposed process are examined by carrying out solubilization and equilibrium precipitation experiments with the mixtures of various compositions, including the eutectic composition. With both these hydrotropes 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%) crystals of chlorobenzoic acid were obtained from precipitation of noneutectic mixtures of o- and p-chlorobenzoic acids in their primary crystallization region.