Recovery of levulinic acid from aqueous solutions with anion exchange resins

In this MS thesis, the recovery of levulinic acid from aqueous solutions by four different commercial anion exchangers was investigated. Effects of several parameters on the process efficiency were probed while kinetic, thermodynamic, and equilibrium studies were performed. The weak basic anion exchange resins, named as Amberlite IRA-67, Lewatit MP-62 and Lewatit MP-64; and a strong basic anion exchanger, named as Lewatit M-500 were tested in the study. The pH of the media significantly influenced the process efficiency. The highest separation efficiency was obtained at the natural pH of the solution (pH=2.1) with the weak basic anion exchangers and at pH=5 with the strong basic anion exchange resin. Kinetic studies showed that the system reached the equilibrium by 60 min. with Amberlite IRA-67 and Lewatit MP-62, 30 min. with Lewatit MP-64, and 50 min. with Lewatit M-500. In addition, it was observed that the kinetic data were observed to follow the pseudo second order kinetic model. For all resins, the adsorption percent decreased with the increase in temperature and the ΔH˚ and ΔG˚ had negative values. This means that the process was spontaneous and had an exothermic nature with these resins. Separation efficiency was seen to increase with the increase in resin dose and decrease with the levulinic acid concentration. The maximum adsorption capacity (438.7 mg LA/g resin) and separation efficiency (100%) were obtained with Lewatit MP-62. The equilibrium data obtained with the weak basic anion exchangers were observed to be in agreement with the Langmuir isotherm model. The highest R2 value was reached with the Freundlich isotherm model for Lewatit M-500. However, it was estimated that an acceptable fit could be provided with this resin and the Langmuir model. Therefore, a more detailed isotherm analysis was advised to be done performed in order to understand the mechanism of the process carried out with Lewatit M-500.