(318b) Empowering Carbon Negative Bio-Chemicals with Advanced Electrochemical Separations

Succinic acid has the potential to become a central platform molecule for renewable and bio-based polyesters.¹ The biomass based polyesters synthesized from succinic acid can substitute petrochemically made polymers while having 34-40% less climate impact.² A key feature of succinic acid is that the prokaryotic strains like Basfia succiniciproducens or Actinobacillus succinogenes have the ability to utilize CO2 as a secondary carbon substrate under anaerobic conditions. This brings the opportunity to make the industrial succinic acid production a carbon sink and provide carbon capture capacity that creates synergies with other industries like bioethanol or cement.

However, efficient downstream technologies with low process carbon footprints are necessary to preserve the carbon capture capacity of bio-succinic acid production. In contrast, most techno economic studies recommend to focus on the development of aerobic and low pH tolerant yeast strains.⁴ A low pH fermentation reduces the complexity of the downstream processing at the expense of CO2 emissions from the up-stream. The newly emerging electrochemical separation technologies^5–9 allow a waste free separation of succinic acid. We compared the state of the art downstream technologies for succinic acid purification with in situ separation by electrochemical pH swing extraction. First, we investigate the thermodynamic limits of the microbial metabolism in prokaryotic and eukaryotic host cells and identify a tradeoff between microbial energy demand for product export under low pH conditions and high carbon conversion yields which require a neutral pH in the fermentation. Second, we quantify the effect of these limits on a process scale by comparing different conceptual process designs for succinic acid purification in an extension of a previous techno economic assessment. The electrochemical pH swing separation revealed the potential to maintain the negative carbon emission balance for succinic acid production, while also reducing the water consumption and waste footprint in comparison to the state of the art technologies.¹⁰ Finally, we implemented a dynamic process model in MATLAB to validate the feasibility of in situ product removal by electrochemical pH swing extraction and electrochemical pH control of a dual substrate (glycerol and CO2) succinic acid fermentation.¹¹ In a sensitivity analysis we compared the reaction kinetic of the fermentation with the kinetics of a pH swing electrolysis with integrated reactive extraction of succinic acid by tertiary amines. The sensitivity study shows that the electrolysis is the rate limiting step for product recovery but significantly faster than the production rate of the fermentation, thus making electrochemical pH-control feasible. We applied the dynamic model to investigate the potential to operate the succinic acid production with a closed base recycle loop. The results show that if concentrated feedstock is available, the consumption of pH control agent in the fermentation is reduced by 88% and the fresh water demand can be reduced by 99% compared to the open loop process.¹¹ The electrification of succinic acid downstream processing, when operated with renewable electricity, turns bio-succinic acid into a carbons sink for other industries and thereby provides a promising perspective for industrial carbon integration.

Literature Cited

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7. Gausmann M, Kocks C, Doeker M, Eggert A, Maßmann T, Jupke A. Recovery of succinic acid by integrated multi-phase electrochemical pH-shift extraction and crystallization. Separation and Purification Technology. 2020;240(240):116489.

8. Gausmann M, Kocks C, Pastoors J, Büchs J, Wierckx N, Jupke A. Electrochemical pH-T-Swing Separation of Itaconic Acid for Zero Salt Waste Downstream Processing. ACS Sustainable Chem. Eng. 2021;9(28):9336–9347.

9. Gausmann M, Gössi A, Bertram F, Riedl W, Schuur B, Jupke A. Electrochemical membrane-assisted pH-swing extraction and back-extraction of lactic acid. Separation and Purification Technology. 2022;289(3):120702.

10. Gausmann M, Jupke A. Techno economic assessment of downstream technologies for carbon negative bio-succinic acid production. Manuscript in preparation. 2022.

11. Gausmann M, Kiefel R, Jupke A. Dynamic modeling of electrochemical pH swing extraction for in situ separation of succinic acid reveals biorefinery integration potential. Manuscript in submission. 2022.