Dynamic Operation of Power-to-X Processes Demonstrated by Methanol Synthesis

Chemical energy storage in the context of so-called Power-to-X (PtX) processes will play a key-role in the future energy system due to the increasing power production from renewable energy and the urging defossilization of industry and transport sector. Among possible PtX products, methanol produced from carbon dioxide (CO2) and sustainably produced hydrogen (H2) is going to play a key-role due to its high relevance in the global fuel and chemical market.
Compared to conventional methanol synthesis based on fossil feedstocks, methanol synthesis based on CO2-rich gas streams captured from industrial processes, biomass processing or ultimately captured from air is subjected to decreased equilibrium conversions, inhibited reaction kinetics and an accelerated catalyst aging. Moreover, the production of H2 from water electrolysis operated with renewable power and the coupled CO2-supplying industrial process can impose dynamic fluctuations to syngas supply unknown to the current-state-of-the-art. For these new boundary conditions, design of the synthesis reactor and operation of the process become more challenging and do demand for detailed models for each unit operation in the synthesis process. However, for the kinetic simulation of the synthesis reactor under these conditions only scarce knowledge exists in the scientific community. Thus, a detailed kinetic description of the reaction network in industrial reactors is required to enable methanol synthesis from sustainable resources in the future. To tackle that deficit, this work used a scale-flexible simulation platform to design a miniplant facility with the reactor reproducing the thermochemical behavior of an industrial steam cooled tube bundle reactor with a high agreement. An innovative analytical concept using the highly resolved fiber optic temperature measurement to analyze the axial temperature profile in the reactor combined with an FTIR product composition measurement was implemented to derive a kinetic model for reactor- and process design validated over the complete range of relevant load conditions for Power-to-Methanol (PtM) processes. Comparison to kinetic models obtained from literature highlighted both the scientific value of methodical approach implemented in this work
and the high relevance of the herein proposed kinetic model for the practical implementation of PtM processes. Furthermore, the validation of the dynamic reactor model implemented in this work by a exemplary load change performed with the miniplant showed a high level of agreement between the experimental data and the simulation results. Thus, the scientific potential of the herein proposed miniplant validation approach for the investigation of stationary and dynamically operated PtX processes could be demonstrated.