The outer-inner loop mechanism of alkali carbonate-modified BaFe₂O₄ during the biomass char chemical looping partial oxidation and hydrogen generation (CLPH) process

Chemical looping partial oxidation and hydrogen generation (CLPH) process of biomass can produce inherently separated syngas, demonstrating significant potential applications. To further enhance the quality of the separated syngas, specially, CO selectivity and H₂ purity. K₂CO₃/Na₂CO₃, which are recognized as effective catalysts for gasification, were mechanically mixed with BaFe₂O₄ and the performance of the K/Na modified BaFe₂O₄ during CLPH process were comprehensively investigated. The results indicated an increase in solid–solid reactivity, CO selectivity and hydrogen purity after the K/Na modification. While the effects of K/Na are not the more the better, the optimal K₂CO₃/Na₂CO₃ loading amount is 3 wt.%/1 wt%. Under optimal conditions (3 K-BFO), CLPH process achieved a production of 1106.5 ml/g·char CO with a selectivity of 65 % and 1820.3 ml/g·char H₂ with almost 99 % purity. An Outer-Inner loop mechanism for carbonate modified CLPH process was proposed. The outer loop comprised the reduction and oxidation process of OC. The inner loop involves the cycle of K species, during CLPH process, the K₂CO₃ initially functions as the catalyst, then decompose into KFeO₂ after the partial oxidation reaction. In the steam reactor, KFeO₂ absorbs carbon released during the steam oxidation process and turned back into K₂CO₃, and thus regenerating the catalyst while purifying the hydrogen. Additionally, due to the volatilization of carbonate during the cycle process, catalytic activity will decline after two cycles, while it can be readily restored by the supplement of K₂CO₃.