Investigations on oxygen carriers derived from natural ores or industrial solid wastes for chemical looping hydrogen generation using biomass pyrolysis gas

Chemical looping process based on multiple-step redox reactions of oxygen carriers (OCs) holds great promise for producing high purity hydrogen with inherent CO2 separation, however, there is a challenge to prepare environmental-friendly OCs with low-cost. Herein, a series of natural ores and industrial solid wastes were screened and made into Fe-based OCs for chemical looping hydrogen generation (CLHG). The results show that OCs prepared by pyrite cinder (OC-PC) feature 94.8% biomass pyrolysis gas (BPG) conversion and 94.5% CO2 concentration in OCs reduction stage. In hydrogen production stage, OC-PC achieves maximum H2 yield, 3.04 mmol g−1, which is 2∼9 times high than other OCs. The highest H2 purity is approximately 99.99%. Long term testing results indicate that OC-PC has excellent stable activity and anti-sinter ability. OCs prepared by red mud correspond to better BPG conversion (96.0%), however, the H2 yield (0.83 mmol g−1) is much lower than that of OC-PC. For OCs prepared from natural ores, they show unsatisfactory H2 production and BPG conversion compared with OC-PC. OCs prepared by ilmenite are with low specific surface area which restrains the heterogeneous reaction. The content of metal element (Mg, K, Ca) also influences the behavior of OC, which is beneficial for the fuel conversion. Moreover, the distribution of inert, anti-coking ability, oxygen vacancy also influence the sinter, H2 purity and H2 yield. Comprehensively evaluating the OCs performance, pyrite cinder is considered to be the most suitable OC raw material for CLHG.