Evaluation of a Mining Waste as an Oxygen Carrier for Syngas Production Using Chemical Looping in a 3 kWh Fluidized Bed Reactor

The development of chemical looping (CL) technology depends on oxygen carriers; hence, the purpose of this study is to evaluate the potential of an inexpensive, readily available, and unexplored mining waste for syngas synthesis. In this study, we examined the application of chromite overburden, a byproduct of mining, as an oxygen carrier for the chemical looping reforming of methane. The efficiency of the oxygen carrier was assessed at 750 °C by conducting redox cycles in a fluidized bed reactor, using methane and air as reducing and oxidizing agents, respectively. The reactivity study revealed sustained formation of H₂ and CO gases during the reforming process of methane. Phase characterization of the r-oxidized and reduced samples using XRD and SEM unambiguously demonstrated the development of stable phases of chromite and iron oxide, respectively. Phase characterization indicated the formation of a chromite phase after the first oxidation cycle, limiting oxygen transport and slightly reducing the reaction efficiency. The phase analysis showed an overall oxide conversion of 11.11% during the redox cycles. Surface morphologies of unreacted and reacted samples showed no sign of attrition or agglomeration in 20 cycles. Overall, COB achieved a total hydrogen yield of 2736 mL per 10 g OC, with an average H₂/CO ratio of 0.87, proving its effectiveness in multicycle chemical looping reforming (CLR). The gas analysis indicated the reduction reactions followed a 3-stage mechanism, i.e., decomposition of methane into carbon and hydrogen, reduction of Fe oxide by H₂, CO, and C, and auxiliary reactions involving H₂O, CO, CO₂, and C. The present work successfully demonstrates the application of chromite overburden (COB) as an oxygen carrier in the production of syngas via a chemical looping reforming scheme.