Impact of Catalyst Deactivation on a Carbon Dioxide Methanation "Power-to-Gas" Process: Deactivation Kinetic Study and Reactor Modelling

<>Impact of catalyst deactivation on a carbon dioxide methanation “Power-to-Gas” process: deactivation kinetic study and reactor modelling <>Eduard Alexandru Morosanu^a,b, Albin Chaise^b, Alain Bengaouer^b, Samir Bensaid^a,*

^a Department of Applied Science and Technology (DISAT), Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy.

^b Laboratory of Heat-Exchanger Reactor, Univ. Grenoble Alpes, CEA, LITEN, DTBH, Grenoble F-38000, France

* Corresponding author. E-mail address: samir.bensaid@polito.it

Power to synthetic natural gas (SNG) is a candidate technology to be used for long term storage of renewables (wind and solar). In the past years this technologie has received much interest from the scientific community and a consistent number of demonstrator plants have been built over the years. One of the aspects that need investigation is the ability of the system to maintain the productivity and quality of the gas in time. Decrease in the conversion rate has been observed and it is generally attributed to the loss of the catalyst activity. Some studies are present in scientific literature on the phenomena causing catalyst deactivation (i.e. sintering). However, few publications linking the decrease in kinetics with the reactor performance evolution can be found for the SNG process. In this work we’ve performed an experimental campaign on a commercial catalyst to determine the deactivation kinetics for the CO₂ methanation system. The deactivation law was then used in transient model to evaluate the performance in time of the reactors.

A set of 100h long tests at different temperatures were performed (example reported in Figure 1), with final restoring of the original temperature to determine the true deactivation effect.

Figure 1: Example of long-term test results.

Inlet: 60% H₂, 16% CO₂ and 20% N₂; pressure: 5 bar; temperature: 425 °C; duration: ~ 100 h.

Sintering was determined to be the deactivation mechanism (BET surface reduction and Nickel particle diameter increase). In literature sintering processes are modelled using first or second order general power low expression (GPLE). The experimental data was best fitted by a second order GPLE. Adiabatic and cooled reactors with different geometries were simulated using the deactivation law in a model developed in COMSOL. The adiabatic reactor exhibited a high decrease in time of the performance due to the high temperature reached. The cooled reactor showed a relevant decrease during the first hours caused by the exothermal high temperature peak. Afterwards the peak diminished in intensity and broadened. This caused the reduction of the deactivation kinetics and stabilization of the reactor performance.