Evaluation of Two Sorbents for the Sorption-Enhanced Methanation in a Dual Fluidized Bed System

Abstract

The unceasing concern for climate change, closely related to the exploitation of fossil fuels, pushes the scientific community to develop new technologies for CO2 capture and utilization (CCU). Moreover, the growth and diffusion of solar energy requires new energy storage systems that put solar fuels at the forefront. Methane seems to be a suitable energy vector, which could both store solar energy and exploit fossil fuel derived CO2. Moreover, methane has the main advantage of an already existing distribution and storage infrastructure. The methanation reaction from hydrogen and carbon dioxide (or monoxide) is generally carried out in staged adiabatic catalytic fixed beds operated at high pressure in order to overcome thermodynamic limitations. A recently proposed alternative pathway is the sorptionenhanced methanation concept, which is based on the employment of a sorbent able to capture in situ the H2O produced during reaction, to shift equilibrium towards the formation of CH4. In this work a CaO, derived from natural limestone, and a commercial 3A Zeolite were tested as sorbent materials for H2O capture in a new configuration for the sorption-enhanced methanation based on the concept of chemical looping in dual interconnected fluidized bed systems. The experimental campaign was aimed at studying the sorbent performance in terms of hydration and dehydration at different operating conditions relevant for catalytic methanation. The results showed that CaO has a good capacity to capture and release steam in the temperature range of interest. Unfortunately, even at the lowest temperatures tested, the sorbent is affected by the presence of CO2, which worsens its performance in terms of H2O capture capacity. The zeolite has a more stable behavior than CaO under all investigated conditions. Comparing the performance of the two materials, the zeolite on average has better capture capacity (0.017-0.049 g/g) than CaO (0.006-0.025 g/g) and it is not affected by deactivation during the cycles.