Potassium Catalytic Effect on Gasification Reactions of Coal and Coal/Biomass Blends under Oxy-combustion Conditions. An Isotopic Study Using 13C18O2

Abstract

In the present study, 20 wt % K2CO3 was added to coal and coal/biomass blends in a 20:80 wt % ratio and subsequently were heating-treated at 600 °C using CO2 or N2 atmospheres. The reactivity under oxy-combustion conditions (21% O2 + 79% CO2) was studied by thermogravimetry, and characterization of chars was carried out by N2 adsorption, scanning electron microscopy, and Raman and X-ray photoelectron spectroscopy. Higher activation energy for impregnated coal/biomass blends compared to impregnated coal was observed, likewise, for materials thermally treated with CO2. It is demonstrated that CO2 gasification takes place together with O2 combustion under oxy-combustion conditions. Isotopically labeled 13C18O2 was used to confirm the participation of CO2 gasification reactions at 450, 500, 550, and 600 °C in both catalyzed and uncatalyzed systems under O2 + CO2. The catalytic effect of potassium promotes CO2 gasification, and the highest CO (12C18O) desorption was obtained with impregnated samples. It is possible to suggest that CO2 gasification reactions follow different reaction pathways in the presence or absence of potassium. The catalytic gasification reaction proceeded preferentially through a molecular CO2 (13C18O2) adsorption route, while the noncatalyzed systems advanced using a dissociative adsorption pathway.