Liquid-liquid extraction-based process concepts for recovery of carboxylic acids from aqueous streams evaluated for dilute streams

In this manuscript carboxylic acid extraction processes are reviewed and compared on energy efficiency, especially in situations with very low carboxylic acid concentrations. Production of carboxylic acids by fermentation rather than petrochemical routes aims at reducing dependency on petroleum resources. Wastewater streams are potential carbon sources for fermentation. However, their limited carbon content results in low carboxylic acid concentrations (∼1 wt%) that render separation of waste-derived carboxylic acids challenging. This necessitates implementation of cost-effective separation concepts. The incentive to review liquid-liquid extraction (LLX)-based processes for carboxylic acids was to evaluate their applicability to low carboxylic acid concentrations. Although a thorough study of recent solvent developments was beyond the scope of this work, a brief discussion on their families supported the LLX-based process developments that were assessed in terms of energy demand by simulating their thermal unit operations with Aspen Plus. They were simulated both under their reported conditions and with their initial concentration set to 1 wt%. A process proposed by Urbas (1983) that makes use of CO2, CO2-switchable solvents and low-boiling organic solvents outperformed the others for low carboxylic acid feed concentrations. With a heating duty of about 36 MJ/kgproduct, it could recover both volatile and non-volatile carboxylic acids from fermentation broths with 1 wt% initial carboxylic acid loading. Future developments in the field may be based on this process design, but with more environmentally friendly solvents such as the bio-based furan derivatives.