Investigation of Lactic Acid Separation by Layered Double Hydroxide: Equilibrium, Kinetics, and Thermodynamics

Abstract

The layered double hydroxide (LDH) with high crystallinity was prepared via the coprecipitation method for studying the separation equilibria of lactic acid. It was characterized by FTIR, XRD, and molecular size analyses. The effects of the amount of LDH, temperature, and initial lactic acid concentration on the separation process have been investigated. Results show that the maximum removal of lactic acid was obtained as 66.49% in the case of 1 g of LDH at 298 K. The isothermal data were fitted to Langmuir, Freundlich, and Temkin adsorption isotherms. Elovich, Lagergren, and pseudo-second-order kinetic model equations were applied. The experimental data were fitted with the Langmuir isotherm according to R-2, which is 0.9894 at 298 K, 0.9972 at 308 K, and 0.9998 at 318 K respectively. Separation depended on initial lactic acid concentration at investigated different temperatures (298 K, 308 K, 318 K) significantly. Standard free energy (Delta G degrees), enthalpy (Delta H degrees), and entropy (Delta S degrees) are calculated. The variation of several thermodynamic parameters was calculated according to thermodynamic analysis.