Abstract:

Citric acid is a widely used organic acid and an important intermediate in the tricarboxylic acid (TCA) cycle, where carbohydrates are oxidized to carbon dioxide. The objective of this study is to design and simulate an industrial process for citric acid production using molasses as a low-cost carbon source through fermentation by Aspergillus niger. Molasses samples, obtained from the Kenana Sugar Factory, Sudan, were analyzed in the laboratory to assess their chemical and physical properties, including sugar content, ash, and reducing sugars, to confirm their suitability as a fermentation substrate. The fermentation medium was formulated by supplementing molasses with essential nutrients such as urea, magnesium and calcium sulfates, vitamins, and legume soaking water as a natural phosphate source. The results of fermentation experiments were performed in 10-liter bioreactors under optimal conditions of 30 °C, pH 4.5, and 150 rpm, producing 38.5 g/L of citric acid after 7 days. For process scale-up, modeling, and optimization, SuperPro Designer® (Version 4.53) was used to simulate the entire production chain, including media preparation, fermentation, solvent extraction (MIBK), crystallization, and drying stages. The results showed that the mathematical model predicted a citric acid yield of 2063.6 kg per batch with an efficiency of 84.7%, while the process simulation achieved 7574.5 kg per batch under ideal conditions with 100% efficiency and a reduced fermentation time of 5 days. The solvent recovery efficiency was very high at 99.05%, indicating effective separation and reuse of MIBK. Overall, the study demonstrates that integrating experimental work with mathematical modeling and process simulation significantly improves process understanding and confirms that industrial-scale production of citric acid from molasses using Aspergillus niger is feasible, efficient, and environmentally sustainable.