Performance evaluation of hematite oxygen carriers in high purity hydrogen generation from cooking oil by chemical looping reaction

Abstract

Chemical Looping Reforming (CLR) of cooking oil combining with Chemical Looping Hydrogen (CLH) for synthesis gas and high purity hydrogen production was performed with different hematite oxygen carriers. Results revealed the sample with higher content of Fe2O3 and ZnO displayed better reactivity. Zn2+ in hematite can promote the releasing of active lattice oxygen [O·] to improve carbon conversion efficiency and atomic selectivity based on metal synergistic effect. The highest carbon conversion efficiency 47.36% with H2/CO ratio closed to 2 and syngas yield 1.19 L/g were achieved in CLR stage. Accordingly, the maximum H2 concentration of 93.8% and yield of 444.3 ml/g were obtained in the subsequent CLH stage. It was revealed that the reduction of Fe species in oxygen carrier was a stepwise process in order of Fe3+→Fe2+→Fe0 in CLR reaction, whereas, the lattice oxygen O2− diffused outward from bulk to surface of oxygen carrier, transforming to chemical adsorption oxygen O2− and O− to participate reactions. The hematite oxygen carriers displayed irregularly blocky and porous structure. Meanwhile, sintering phenomena was not observed in the used samples. The BET surface area of oxygen carrier in four reaction stages increased from 1.727 to 2.703 m2/g.