Hydrogen production from vegetable oil via a chemical looping process with hematite oxygen carriers

Hydrogen production from vegetable oil via a chemical looping process with hematite oxygen carriers has been carried out in a fixed-bed reactor at 1023.15-1173.15 K. The lattice oxygen release process and crystalline transformation for the oxygen carrier in the reaction process are investigated. Results indicate that the maximum H-2 composition achieved in the chemical looping hydrogen stage is over 91.72% when hematite oxygen carriers consisting of Fe2O3, Al2O3 and SiO2 are used. The active component Fe2O3 in oxygen carriers represents three reduced peaks corresponding to the crystalline form transition from Fe2O3 to Fe3O4. Up to 96.13% of the lattice oxygen in Fe2O3 can be consumed in the reduction process. The deep reduction of FeO to Fe represents a lower reaction rate with the exhaustion of the lattice. The maximum carbon conversion efficiency of vegetable oil of 79.10% when the ratio of water to oil is 1.2 and hydrogen-rich gas with a highest concentration of 91.72% are achieved in the chemical looping reforming stage and H-2 production stage, respectively. The impurities in the gas are ascribed to the carbon deposition and steam reaction in the chemical looping process. The micrographs of fresh and used oxygen carriers present irregular and blocky structures, sintering is not observed after the multi-cycle reaction process. The crystalline form and reaction activity remain stable after 20-cycle experiments, suggesting that the hematite oxygen carrier is a promising candidate for hydrogen generation from vegetable oil via the chemical looping process. (C) 2018 Elsevier Ltd. All rights reserved.