Nickel-iron modified natural ore oxygen carriers for chemical looping steam methane reforming to produce hydrogen

Abstract

Chemical looping steam methane reforming (CL-SMR) is a promising and efficient method to produce hydrogen and syngas. However, oxygen carrier (OC) prepared by synthesis are complex, expensive and poor mechanical performance, while natural ore OCs are low activity and poor selectivity. In order to avoid these problems, Ni/Fe modification of natural ores were proposed to improve the reactivity and stability of OC to CL-SMR. The results indicated that the modified calcite recombined and improved the structural phase during the reaction, enhancing performance and inhibiting agglomeration. Moreover, high ratio of iron to nickel was easy to sinter and decline the OC performance. In addition, with the increase of steam flow, both CH4 conversion and carbon deposition decreased. Thereinto, the highest H2 concentration, CH4 conversion efficiency and H2 yield were obtained when the ratio of steam to OC was 0.05. Furthermore, CH4 flow rate had a great impact on CL-SMR performance. When the ratio of CH4 to OC was 0.04, it achieved the highest CH4 conversion efficiency of 98.96%, the highest H2 concentration of 98.83% and the lowest carbon deposition of 3.23%. However, the carbon deposition increased with the increase of CH4 flow rate. After a long-time chemical looping process, the Ni/Fe modified calcite showed a consistently stable performance with average H2 concentration of 93.08%, CH4 conversion efficiency of 88.03%, and carbon deposition of 2.15%.