Process for purification of 3-hydroxy-2-naphthoic acid by selective extraction of 2-naphthol impurity with tributyl phosphate using supported liquid membrane

Abstract

3-Hydroxy-2-naphthoic acid (BON acid) is an important intermediate in the dyestuff and pigments industry. The BON acid produced in conventional way from the Kolbe–Schmitt reaction usually contains 2–5% 2-naphthol impurity. The objective of the work was to selectively remove 2-naphthol from BON acid using tributyl phosphate (TBP). The solubility of 2-naphthol and BON acid in water was modeled using the non random two liquid (NRTL) equation. The hollow fiber supported liquid membrane (HFSLM) was used for the purification. A mathematical model was developed to explain the results. The distribution coefficient of 2-naphthol was significantly higher than BON acid. The distribution coefficient decreased with increase in pH. In HFSLM experiments optimal separation was obtained in the pH range of 7–9. The stability of HFSLM module was investigated. During HFSLM runs separation factors in excess of 200 were obtained. HFSLM studies showed that it was possible to selectively remove 2-naphthol from the mixture, resulting in a significantly higher purity BON acid. Experimental data was adequately correlated using a developed mathematical model. Based on the experiments, a modified purification scheme is proposed.