Power-to-Gas (PtG) processes are of major importance for the defossilisation of global economies in general and the chemical industry in particular. The intermittency of renewable energy sources necessitates the long-term chemical storage of electricity in the form of chemicals, which can be achieved through dynamically operated PtG processes. Part of such a process is the CO2 methanation, in which hydrogen and carbon dioxide are converted into methane, synthetic natural gas. However, the dynamic operation of such heterogeneously catalysed processes poses distinct challenges and has recently attracted increasing attention within the reaction engineering community.
Figure 1. HPR-20 EGA, Hiden Analytical.
This study presents a detailed experimental investigation into the dynamic behaviour of CO₂ methanation in a tubular profiling reactor. A key feature of the work is the simultaneous, spatially and temporally resolved measurement of gas-phase composition and temperature inside the catalyst bed, enabling direct insight into reaction dynamics that are usually inaccessible with typically employed laboratory reactors. A capillary positioned at the center of the fixed bed allows defined sampling of gaseous samples, which are analysed by a mass spectrometer with high temporal resolution. The reactor is subjected to dynamic step changes in the feed. The temporal response is measured at different axial positions and combined during post-processing to obtain spatiotemporal profiles across the reactor. Through this sophisticated methodology, several transient effects could be resolved across the reactor including the following key findings:
- Direct observation of reactant and product progression inside the reactor: The measurements reveal how reactant consumption and product formation propagate through the catalyst bed following a step change in feed, depending on the applied reaction conditions. Methane is formed sequentially along the reactor length, while the depletion of the reactant carbon dioxide is enhanced by adsorption, leading to an initial over-stoichiometric decrease.
- Transient selectivity effects: During the early phase following a feed switch, the selectivity toward carbon monoxide changes significantly. This behaviour is likely a result of coverage-dependent reaction rates and the dynamic interplay of the consecutive reverse water–gas shift (rWGS) and CO methanation reactions within the reaction network.
- Temperature overshoot phenomena: Upon the reactive step, the reactor temperature increases rapidly and subsequently decreases toward the steady-state temperature profile. This behaviour can be attributed to the increasing coverage of the catalyst surface during the step, which facilitates higher reaction rates and, consequently, a larger release of heat at the beginning of the applied step.
- Implications: The combined spatiotemporal concentration and temperature profiles provide a unique, high-quality dataset that can be used to validate detailed reactor models and to develop advanced kinetic descriptions under dynamic operating conditions.
Overall, this research clearly demonstrates the value of internal reactor measurements for uncovering reaction dynamics that remain hidden in conventional experiments. By resolving concentration and temperature gradients with high fidelity, the study provides essential insights that support improved mechanistic understanding, more reliable modelling, and ultimately the optimisation and scale-up of methanation reactors operated under flexible, renewable-driven conditions.
Project Summary by: Prof. Dr.-Ing. Thomas Turek, Institute of Chemical and Electrochemical Process Engineering, Leibnizstr. 17, 38678 Clausthal-Zellerfeld, Germany.
Paper Reference: Küchen, G. and Turek, T. (2026). Measuring Spatiotemporal Concentration and Temperature Profiles in a Tubular Fixed‐Bed Reactor for CO 2 Methanation. ChemCatChem, 18(1). DOI: 10.1002/cctc.202501636.
Hiden Product: HPR-20 EGA.
