NSERC-DFG SUSTAIN: Biological and electrochemical process design for biocatalytic CO2 conversion

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Biocatalytic conversion processes represent a promising contribution to a sustainable circular economy due to mild operating conditions compared to existing processes, simple biocatalyst cultivation, and the possibility to reach a complete conversion of the feed gas without necessary expensive loop management. In opposite to traditional fermentation processes that are based on starch feedstock, synthesis gas fermentation uses gaseous C1-substrates and offers great flexibility regarding the feedstock. The fermentation reaction is catalyzed by a chemolithoautotrophic microorganism, and the final products of a future process chain could be high value chemicals like fuels, chemicals, lipids and proteins. Anaerobic acetogens are possible microorganisms used for gas fermentation, and they are well investigated and already successfully in use at industrial pilot scale and commercial plants for anaerobic syngas fermentation. Anaerobic acetogens are able to produce acetate or ethanol as intermediates through the fixation of CO2 via the so-called Wood-Ljungdahl pathway. This project deals with the development, the estimator and control design, and the optimization of a novel novel electro-bio hybrid process for the conversion of CO2 to high-value products. This will include the implementation of the concepts at a test-rig. For this, it aims to combine the expertise of the involved partners from KIT Karlsruhe, Germany and Queen’s University, Ontario, Canada. A major goal of this investigation is to increase the overall process efficiency. Important contributing factors are composition of the synthesis gas, gas flow rate, pH, cell density in the reactor and process pressure. Electrochemical processes are to be integrated to provide a hybrid solution to CO2 conversion in which the electrochemistry can be used to control feed composition. The SANDRA test-rig, which includes a continuously operated stirred tank reactor for the fermentation of the microorganism Clostridium ljungdahli, has been set up by the Institute of Catalysis Research and Technology of KIT will serve as experimental proof-of-concept. Establishment of a stationary state in this biological system is slow due to the long residence time of the liquid phase and possible adaptation processes of the microorganisms. The purely empirical optimization of reactor operation is therefore extremely time-consuming. Continuous control involving suitable estimator or soft-sensor concepts of reactor operation to achieve an optimal operating condition with respect to a meaningful objective such as total carbon fixation, would help to drastically reduce reactor operating times while providing valuable information about the system, which is desperately needed for a future knowledge-based scale-up of the new technology.