Research of coal-direct chemical looping hydrogen generation with iron-based oxygen carrier modified byNaAlO2

This study reports a high-performance modified oxygen carrier (OC) in a three-cycle chemical looping process in which coal is used as the raw feedstock to produce hydrogen. A series of experiments of coal-direct chemical looping hydrogen generation (CLHG) were conducted in a batch fluidized bed reactor, in the absence or presence of the NaAlO2. The experimental results indicated that the carbon conversion and hydrogen yield reached 87.0% and 1.30 L center dot g(-1), respectively, when the coal/oxygen carrier (Fe4Al6) mass ratio was 1:20. However, FeO was the main product of the reduction process with Fe4Al6, which limits the production of hydrogen during steam oxidation. Therefore, NaAlO(2)was used to improve the reaction performance of the OC. The carbon conversion and hydrogen production of NaAlO2-loaded oxygen carriers were 10.7% and 9.6% higher than Fe4Al6, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and temperature-programmed reduction (TPR) techniques were used to characterize the oxygen carriers. According to the XRD analysis results, the addition of 5 wt% NaAlO(2)can generate NaFeO2. The unique layer structure of NaFeO(2)can loosen the structure between Fe(2)O(3)and Al2O3. Thus, the surface morphology and pore structure of the oxygen carrier were improved, which are responsible for the enhancement in reactivity rather than the catalytic effects of the alkali metal. The cycle performance of the Na0.5Fe4Al6 remained stable after multi-redox cycles, and no serious sintering phenomena were observed; in addition, the carbon conversion and hydrogen yield remained above 86% and 1.40 L center dot g(-1), respectively.