Modeling and optimization of adsorption behavior of lactic acid onto zirconium-based metal-organic framework: response surface methodology (RSM)

Abstract

ABSTRACT Lactic acid is readily generated in bacterial fermentations; however, a significant amount of processing and expenses are required for the purification of lactic acid in the fermentation broth. In this work, the sorption of lactic acid from a simulated broth has been studied by utilizing zirconium-based metal-organic framework (Zr-UiO-66 MOF) that acts as a prominent adsorbent due to its specific geometries and functional groups. The morphological, and structural properties of the prepared MOF are investigated using different characterization techniques such as Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) pattern, Fourier transform infrared (FTIR) analysis, and Brunauer-Emmett-Teller (BET) analysis. The characterization results demonstrate the accuracy of the synthesis procedure. In order to achieve an efficient lactic acid separation process, it is essential to determine the optimal operational conditions. To address this, response surface methodology (RSM) was employed to devise an approach for optimizing five crucial process parameters for achieving the optimal response in lactic acid recovery removal. These parameters include initial LA concentration (ranging from 1 to 36 mg.L−1), pH (3–10), temperature (25 to 55 °C), adsorbent mass (0.25 to 1 g), and contact time (10 to 240 min). The RSM analysis revealed that the quadratic model provided the best fit for the experimental data, with a high coefficient of determination (R2). Three validation trials were carried out to determine the precision of the optimization process, leading to a maximum adsorption efficiency of 97.7% being reached under the optimized conditions (initial concentration = 18.5 mg.L−1, pH = 6.5, adsorbent mass = 0.625 g, contact time = 240 min, and temperature = 40 °C).