Techno-Economic Analysis of Alternative Designs for Low-pH Lactic Acid Production

Lactic acid production is highly affected by the fermentation pH. The need for neutralizing agents and the salts produced during fermentation have a significant impact on the overall process performance. Changing the neutralizing agent and allowing lower pH fermentation can improve the process profitability. This work investigates the impact of fermentation parameters and evaluates the process economics of alternative downstream processing designs to produce lactic acid. The results show that low-pH fermentation (pH = 3.86) was profitable (internal rate of return, IRR > 10%) at a fermentation yield of 0.97 g/g sucrose. Decomposing the salt subproduct to reduce the environmental burden associated with gypsum disposal has a significant impact on the economic performance, resulting in a lower IRR than the other designs. Although the salt decomposition process has a high energy demand, it is compensated by the savings obtained in the downstream processing, thus resulting in a similar overall energy demand when compared to conventional reactive distillation. A novel process configuration with ammonium sulfate subproduct shows potential for 3 p.p. higher IRR and up to 30% lower fuel demand in comparison with the conventional process. Therefore, alternative downstream processes could drive low-pH fermentation to outperform the conventional process without any neutralizing agent.