Simulation of Multi-stage Lactic Acid Salting-out Extraction using Ethanol and Ammonium Sulfate

Abstract

Abstract Lactic acid obtained through fermentation is an important chemical in the bioeconomy, especially for the production of the biodegradable polymer polylactic acid. However, its production in a larger scale is hindered by its low concentration in the fermentation broth, low volatility, and temperature sensitivity. These characteristics result in high cost for vacuum evaporation and distillation for water removal. Therefore, alternative methods for lactic acid separation have been studied in the literature, including liquid-liquid extraction methods. Salting-out extraction uses the addition of an inorganic salt to reduce the mutual solubility between water and a solvent, thus resulting in a two-phase system. In this work, salting-out extraction of lactic acid using ethanol as solvent and ammonium sulfate as salt was studied using process simulation to define the process conditions that lead to maximum lactic acid recovery and water removal at one-stage and multi-stage extraction scenarios. The simulations were performed using the electrolyte NRTL activity coefficient model (ELECNRTL) in Aspen Plus v8.6, and one-stage simulation was validated with experimental results published in the literature. The results demonstrate that one-stage extraction can yield up to 87 % lactic acid recovery with 35 % of water removal, while counter-current multi-stage extraction can provide more than 96 % recovery with water removal ranging from 47 % to 57 %, and yet requiring lower ethanol volumes, which demonstrates the need for multi-stage experiments in salting-out extraction to validate its performance.