Optimization of protocatechuic acid adsorption onto weak basic anion exchange resins: kinetic, mass transfer, isotherm, and thermodynamic study

Protocatechuic acid (PCA) is an important carboxylic acid since it is broadly utilized in the industry. Separation of PCA from the fermentation broth has been a great matter of interest. Weak basic anion exchange resins perform well at fermentation broth pH, and thus they have been widely utilized to separate carboxylic acids from the fermentation broth and aqueous solutions. In this study, the adsorption behavior of PCA onto weak basic anion exchange resins, Amberlite IRA-67 (IRA-67), Amberlite XAD-4 (XAD-4), and Amberlite A-21 (A-21), has been examined with several aspects like contact period, PCA concentration, adsorbent quantity, and temperature. The central composite face-centered design from response surface methodology (RSM) has been used to ascertain the optimum conditions. The resins were compared with activated carbon (AC) at optimum conditions. The central composite face-centered design of RSM presented the best adsorption capacity results which can be obtained under optimum conditions of 1542.20 mg L-1 initial acid concentration, 0.2 g adsorbent amount, and 298.2 K temperature. Under these conditions, IRA-67, AC, A-21, and XAD-4 showed the highest adsorption capacities of 36.27, 32.96, 30.54, and 6.71 mg g(-1), respectively. IRA-67 was ranked first, followed by AC, A-21, and XAD-4 in terms of the adsorption capacity. Four kinetic models, namely pseudo-first-order, pseudo-second-order, Elovich, and Weber-Morris intra-particle diffusion models, were matched with the experimental data to find the mechanism that governs the adsorption process of PCA onto the resins. The mass transfer mechanism of PCA onto the resins has been examined by external and internal diffusion coefficients, and the Biot number. The commonly used two-parameter isotherm models, namely Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Halsey, Jovanovich, Florry-Huggins, and Harkin-Jura, were fit to the experimental data. The outcomes of this study displaced that the resins IRA-67 and A-21 are quite effective in removing PCA from its aquatic environment, whereas XAD-4 is less effective in terms of the adsorbent capacity.