CatSys: Catalytic Gas Phase Process Systems

The CatSys project focuses on the optimal design of processes for the production of commodity chemicals such as Cl₂, HCN and NH₃ by (electro-) catalytic gas phase reactions at low energy consumption, utilizing a close combination of mathematical modeling with experimental data at different process levels. Thereby, the PSE group has strong interactions with national and international research groups (Prof. T. Turek, Technical University Clausthal, Prof. M.R. Singh, University of Illinois at Chicago, Dr. A.Z. Weber, Berkeley National Laboratory) and leading chemical companies such as Evonik and Covestro. As an example, a novel electrochemical gas phase HCl oxidation process is briefly presented herein.

The electrochemical oxidation of HCl, a major industrial by-product in processes using Cl₂ as feedstock, to convert it back to Cl₂ with renewable electricity constitutes a sustainable recycling concept (Figure left). Exergy analysis at the process level, considering distillative or absorptive HCl/Cl₂ separation strategies, showed significant exergy savings [1-3] compared to the state-of-the-art industrial process (Figure middle), but also highlighted that the major optimization potential is at the reactor level [1,2,4]. A dynamic, 1D agglomerate model, coupled with reaction microkinetic analysis and HCl mass transfer [5], underlined the kinetic origin of the limited reactor performance [6]. Extension of the model to the full reactor level [7], indicated the importance of thermal management, the optimization of which may provide a 90% increase in the limiting current (Figure right). A numerical crossover model [8] confirmed that the cathode performance is in addition impaired by the HCl permeation through the membrane, effectively mitigated by the incorporation of a chloride-insensitive Rh_xS_y cathode that led to the operation of a lab scale gas phase electrolyzer above 5 kA/m² for the first time.

Figure: (Left) Scheme for the utilization of renewable energy sources for the recycling of HCl to Cl2 [1]. (Middle) Contributions of the different units to the exergy demand of the state-of-the-art process (shaded) and a novel ionic liquid separation process (filled) [2]. (Right) Simulated polarization curves of the full reactor with standard thermal resistance and optimized reactor operation [7]. — Figure: (Left) Scheme for the utilization of renewable energy sources for the recycling of HCl to Cl₂ [1]. (Middle) Contributions of the different units to the exergy demand of the state-of-the-art process (shaded) and a novel ionic liquid separation process (filled) [2]. (Right) Simulated polarization curves of the full reactor with standard thermal resistance and optimized reactor operation [7].

Figure: (Left) Scheme for the utilization of renewable energy sources for the recycling of HCl to Cl₂ [1]. (Middle) Contributions of the different units to the exergy demand of the state-of-the-art process (shaded) and a novel ionic liquid separation process (filled) [2]. (Right) Simulated polarization curves of the full reactor with standard thermal resistance and optimized reactor operation [7].

Publications

[1] Bechtel, S., Vidaković-Koch, T., Sundmacher, K. (2018). Chem. Eng. J., 346, 535.

[2] Bechtel, S., Song, Z., Zhou, T., Vidaković-Koch, T., Sundmacher, K. (2018). Comput. Aided Chem. Eng., 44, 2167.

[3] Bechtel, S., Vidaković-Koch, T., Sundmacher, K. (2018). PCT/EP2018/082752.

[4] Bechtel, S., Vidaković-Koch, T., Sundmacher, K. (2019). Chem.-Ing. -Technik, 91 (6), 795.

[5] Bechtel, S., Sorrentino, A., Vidaković-Koch, T., Weber, A. Z., Sundmacher, K. (2019). Electrochim. Acta, 324, 134780.

[6] Martínez, I.G., Vidaković-Koch, T., Kuwertz, R., Kunz, U., Turek, T., Sundmacher, K. (2014). Electrochim. Acta, 123, 387.

[7] Bechtel, S., Vidaković-Koch, T., Weber, A. Z., Sundmacher, K. (2020). J. Electrochem. Soc. 167, 013537.

[8] Bechtel, S., Crothers, A. R., Weber, A. Z., Kunz, U., Turek, T., Vidaković-Koch, T., Sundmacher, K. (2021). Electrochim. Acta, 365, 137282.