Modeling of electrochemical pH swing extraction reveals economic potential for closed-loop bio-succinic acid production

Abstract

Resource-efficient separation processes are a vital technology for the success of renewable chemicals. Electrochemical pH swing separation has the potential to overcome the unsustainable consumption of acid and base and eventual salt-waste production, which was found a major hurdle in the industrialization of bio-succinic acid production. It furthermore enables the in situ product recovery by reactive extraction and the recycling of an alkaline stream into the fermentation for pH control. A dynamic model of a bio-succinic acid fermentation and electrochemical recovery process is developed. The fermentation is fed with waste glycerol and carbon dioxide, the co-products of biodiesel and bioethanol plants, respectively. Succinic acid is separated by an electrochemically induced pH shift reactive extraction. The model-based investigation of this electrochemical extraction apparatus analyzes kinetic phenomena, operative boundaries, and sensitivities towards changes in the cell geometry. The potential for closed-loop operation of bio-succinic acid fermentation and electrochemical pH swing extraction for product recovery and base regeneration is examined. In contrast to a sequential operation of fermentation and extraction, the in situ product removal of succinic acid allows for utilization of feedstocks with substrate concentrations of up to 99 wt% without the need for an additional diluting water feed. The concentrated feedstock and the electrochemical in situ separation of succinic acid cause a rise in downstream process yield by 26.2% and process productivity by 35.6%. The consumption of pH control agent is reduced by 88.7% compared to the sequential operation.