(458f) Switching Bioprocesses into Zero-Waste Virtual Power Plants By Flexible Operation of Electrochemical pH-Swing Extraction Processes

Carboxylic acids are important platform molecules that enable a sustainable chemistry based on renewable resources.¹ Although the biochemistry of the production is well established the successful industrial application is still challenging. As an example the US-Canadian company Bio-Amber, once considered a rising star for their ambition to establish a fermentation based production route for succinic acid had to file for bankruptcy.² This demonstrates that up to today advantages in environmental metrics cannot sufficiently compensate an economic disadvantage of the bio-based production. In order to make bio-based chemistry successful a holistic process development is required and must strive to achieve high yields in the fermentation steps, a low-cost and low-waste separation process and exploit all opportunities to harvest every added value feasible in the process.

We developed an electrochemically driven pH-swing extraction process for the recovery of succinic acid from aqueous solutions.^{3 4} This concept overcomes the issue of salt waste production otherwise encountered during the separation of bio-based succinic acid.⁵ Instead of waste generating acid and base this technology uses electricity to drive the pH-swing extraction. The calculated electricity costs required to operate the electrochemical pH-swing extraction with the current prototype equipment are comparable to the costs for acid, base and waste disposal in state of the art process designs. A more detailed techno-economic assessment of the operational expenses (OPEX) of our electrochemical separation concept and four other process designs proposed in the literature was conducted with ASPENplus. The study revealed a cost advantage of the electrochemical processing route compared to other downstream options. Beyond the promising OPEX values determined for the electrochemical pH-swing process the technology enables utilization of electricity instead of fossil fuel derived heat for the separation of succinic acid.

Preferably the electricity used for the separation should be harvested from renewable sources like wind and solar power. These energy sources are inherently fluctuating and an extensive use of these sources will impose a significant stress on the stability of the power grid in the future. This talk demonstrates how a flexible operation of the electrochemical pH-swing extraction process can turn a bio-based succinic acid production into a virtual power plant. We implemented an algorithm in MATLAB that given the price profile of the electricity market calculates the cost-optimal load profile for the electrochemical unit operations. Modulating the power consumption according to the electricity prices provides a 7% saving on the electricity costs. A dynamic model of the electrochemical pH-swing extraction is used to calculate the electric current density, pump-speed and other operational parameters from the dynamic load profile. With the determined operational parameters the load flexible operation of a 100cm² electrolysis cell was tested experimentally. Throughout the experiment a constant degree of protonation close to 100% was measured, indicating that despite the load flexible operation a constant separation efficiency is viable with the operational conditions suggested with the model.

The developed method enables a load flexible and cost optimal operation of the electrochemical pH-swing extraction of succinic acid. In addition to the cost advantage harvested from times of abundant renewable electricity, hydrogen and oxygen are concurrently produced in the electrochemical pH-swing step. The cost advantage together with the generation of valuable co-products constitute an added value that can improve the overall economic competitiveness of the bio-based succinic acid production. Beyond that, load flexible operation and demand side management of large consumers aids in stabilizing the power grid and will likely become more important in the renewable centered electricity supply of the future.

Acknowledgements

The authors gratefully acknowledge the financial support of the Kopernikus project SynErgie (03SFK3L1-2) by the Federal Ministry of Education and Research (BMBF) and the project supervision by the project management organization Projektträger Jülich (PtJ).

Literature Cited

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