Multi-Objective Optimization and Control of Lactic Acid Purification via Bidirectional Reactive Distillation

Abstract The lactic acid (LA) monomer serves as the precursor to the biodegradable polymer poly(lactic acid) (PLA). However, the separation of high-purity LA from fermentation broths remains a significant challenge. In the present work, a reactive distillation (RD) process was proposed for the separation and purification of LA. Furthermore, process intensification was achieved through thermal coupling, leading to the development of two distinct thermally coupled RD configurations. Based on a multiobjective genetic algorithm (MOGA), comprehensive optimization was conducted for both the conventional reactive distillation (CRD) process and the thermally coupled intensified processes, with optimization objectives including economic indicator, environmental impact, and thermodynamic efficiency. The results demonstrate the effectiveness of the thermal coupling strategy in reducing the energy consumption and enhancing the process performance. Specifically, thermal coupling between the RD column and subsequent separation columns achieves a 20.25% improvement in thermodynamic efficiency, 11.40% reduction in total annualized cost, and 27.99% decrease in CO2 emissions, as compared with the baseline process utilizing CRD. Additionally, control performance assessment was performed for the two complex thermally coupled RD processes, and the corresponding control structure adapting temperature as an indirect composition indicator was designed. Dynamic response analysis under feed flow rate and feed composition disturbances confirmed the effectiveness and robustness of the proposed control structure.