A chemical looping sorption-enhanced methanation (SEM) process with in situ steam removal, was proposed, based on dual interconnected fluidized bed configuration. The process consists in a system where, continuously, methanation and sorbent hydration occur in one reactor, while regeneration of the exhausted sorbent takes place in the other one. In this work SEM of CO2 (with a stoichiometric feed ratio H2/CO2 = 4) was studied in a batch lab-scale experimental campaign to test the performance at different operating conditions. A conventional Ni/Al2O3 catalyst was used. The chosen sorbents for water capture were commercial zeolites, widely investigated in the literature. Zeolites 3A and 4A were tested in the temperature range 200-250 °C, confirming previous results obtained by hydration tests: zeolite 4A showed only slightly higher capture capacity than zeolite 3A. The narrow range of temperatures investigated is the one compatible with the physical and chemical constraints imposed by water adsorption and methanation kinetics: although the Ni-based catalyst is only active above 200 °C, the sorbent H2O capture capacity strongly decreases with increasing temperature, and above 250 °C a significant worsening occurs. Despite these constraints, a clear enhancement effect, in terms of produced methane, was experienced during SEM compared to the traditional case, ranging from 59% to 27% as the temperature increased from 200 to 250 °C, as expected. The zeolites showed a quite stable and repeatable behaviour. The results highlighted the need of further advances towards better performing and less expensive materials to scale up SEM on industrial scale.
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