In-situ hydrogenation of dual function material for integrated CO2 capture and methanation with the presence of steam

Abstract

The impacts of steam on hydrogenation of dual function materials (DFM) for Integrated CO2 Capture and in-situ methanation (ICCM) is a new area requiring detailed investigations prior to industrialization. This work investigated impacts from steams on hydrogenation of Ru-Na2CO3/γ-Al2O3 DFM for ICCM that containing Na2O adsorbent, Ru sites, and γ-Al2O3 support. DFM performance was examined in cyclic reactions as introducing external steam during hydrogenation, and the behaviors of adsorbed CO2 species during hydrogenation were characterized by in-situ DRIFTS and H2-TPSR. CH₄ selectivity decreased sharply from 84.3 % to 1.2 % as increasing external steam concentrations to 20 vol.%, and the conversion of adsorbent component decreased from 298.5 μmol g-1 to 167.1 μmol g-1. b-CO32- and m-CO32- formed at Na2CO3/γ-Al2O3 interface were the carbonate species that could be hydrogenated into CH4, some of which were desorbed into CO2 due to moisture-driven desorption effects. With the presence of external steam in H2 reactants, the conversion of carbonate species is a competing process between hydrogenation and moisture-driven desorption. In ICCM reaction with external steam present, b-CO32- was preferred to be desorbed into CO2; while for m-CO32-, desorption into CO2 by steam and hydrogenation into CH4 proceeded in parallel. Strong moisture-driven desorption effects from steam product were demonstrated in a fixed-bed reactor, which also led to rapid decrease of localized selectivity of CH4 along bed height.