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

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. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.