The application of Box–Behnken design for the optimization of protocatechuic acid separation by a reactive extractant trioctylphosphine oxide

Protocatechuic acid (PCA) is a carboxylic acid of great interest since it has several pharmaceutical properties. PCA is either obtained by microbial fermentation or recovered from waste streams of food processing industries. In this study, PCA was separated from its aqueous solutions by a reactive extractant trioctylphosphine oxide (TOPO). Isobutanol, propyl acetate, and ethyl methyl ketone were used with TOPO in the organic phase. The operating parameters have been optimized by Box–Behnken design of response surface methodology. The maximum extraction efficiency of TOPO/isobutanol system was 98.91% under optimum conditions (0.02 mol kg −1 PCA concentration, 50% v/v TOPO amount, and 298.2 K temperature). The maximum extraction efficiency of TOPO/ethyl methyl ketone system was 91.09% under optimum conditions (0.028 mol kg −1 PCA concentration, 50% v/v TOPO amount, and 312.2 K temperature). The maximum extraction efficiency of TOPO/propyl acetate system was 99.05% under optimum condition (0.029 mol kg −1 PCA concentration, 48.51% v/v TOPO amount, and 301.2 K temperature). Lastly, a thermodynamic study has been carried out to reveal the insight mechanism of the reactive extraction processes examined, and the reactions were found to be exothermic in nature.