Carbon Deposition and Sintering Characteristics on Iron-Based Oxygen Carriers in the Catalytic Cracking Process of Coal Tar

Abstract

Experiments on carbon black production from coal tar via chemical looping pyrolysis were performed in a fluidized bed reactor using natural hematite, hematite/γ-Al2O3 (Fe/Al), and hematite/NiO (Fe/Ni) composites as oxygen carriers (OCs). After 3 redox cycles, thermogravimetric analysis combined with differential scanning calorimetry results show that, in comparison to natural hematite, the oxidation rate of the Fe/Al OC became faster above 700 °C; however, the oxidation performance of the Fe/Ni OC was always poor. The addition of γ-Al2O3 could effectively inhibit carbon deposition; nonetheless, NiO exhibited the opposite effect. On the basis of the burning temperature, the carbon deposition on reduced OCs was mainly hard coke. The X-ray diffraction analysis showed that NiO was not only more effective than γ-Al2O3 to promote the reduction of Fe2O3 in compound OCs but also increased the sintering trend. The scanning electron microscopy analysis indicated the melting of original grains at the surface of the ...