Coal-direct chemical looping hydrogen generation with BaMnO3 perovskite oxygen carrier

Abstract

Coal-direct chemical looping hydrogen generation (CDCLHG) is a novel process that uses coal to directly produce H2 with inherent CO2 capture. A key issue is to find out suitable oxygen carriers for this process. In this study, perovskite was proposed as the oxygen carrier for CDCLHG, and a series of Mn-based and Fe-based perovskite oxides were synthesized by a sol-gel method for CDCLHG reactions in a fixed-bed reactor. The results showed that BaMnO3 was an optimal oxygen carrier for CDCLHG, which could obtain H2-rich gas (>85%) with a high H2 gas production rate, about 13 times higher than that in char steam gasification. Further tests showed that the optimal reaction temperature and O/C ratio were 850 °C and 1: 0.05, respectively. XRD and XPS patterns indicated that part of the lattice oxygen in BaMnO3 could convert to the carbonate oxygen in BaCO3 during the fuel oxidation stage (FO stage) and obtained BaMnO3-δ with plentiful oxygen vacancies in it. The BaMnO3-δ could partially restore its lattice oxygen in the reduction of steam stage (RS stage) and completely recover its initial structure in the air calcining stage (AC stage). SEM images showed that the decrease of BaMnO3 reaction performance after 9 cycles was mainly due to ash accumulation.