Chemical looping steam methane reforming (CL-SMR) is an emerging technology that enables achievement of both F-T ready syngas and high-purity hydrogen simultaneously without additional separation steps via the cycling of solid oxygen carrier (OC). For the methane oxidation with OC, the product distribution is closely related to the oxygen species of OCs. Generally, the active surface oxygen of OC firstly reacted with CH₄ obtaining CO₂ and H₂O, and then less active lattice oxygen selectively oxidizes CH₄ to CO and H₂. To improve syngas selectivity, the initial formed CO₂ should be minimized. Compared with air oxidation, weak oxidants (H₂O) usually can enhance the syngas selectivity, but cannot completely regenerate the structure of OCs, resulting in the decrease of cyclic stability. It is hard to consider both the cyclic stability and syngas selectivity, because that the regenerated OCs by strong oxidant (air/O₂) inevitably results in the enrichment of active surface oxygen species, thereby decreasing the syngas selectivity. Currently, most works focused on the screening and design of OCs. However, the initial formed CO₂ was hardly avoided over the modified OC, which leads to the decreased syngas selectivity and the increased CO₂ emission.
Here, we proposed a novel chemical looping coupling system for coproducing syngas and hydrogen with in situ CO₂ utilization. It integrates chemical looping combustion, chemical looping reforming, CO₂-H₂O co-splitting, hydrogen production and air oxidation using CH₄ as fuel and iron oxide as oxygen carrier (Fig. 1). In this process, syngas and H₂ purification, in addition to CO₂ capture and storage are no longer necessary. It not only produces high-purity hydrogen and syngas without pollutants and greenhouse gas emissions, but realizes the sufficient utilization of feed and oxygen carriers. A detailed thermodynamic analysis of the proposed chemical looping coupling process was conducted by Aspen Plus. The effects of key parameters, such as feed ratio, temperature, and pressure in each reactor on the process performance were investigated in terms of the utilization of CH₄, the yield and purity of syngas and hydrogen, and the oxygen carrier coupling. In addition, the energy balance was analyzed for the coupling system with heat exchanger network.

Chemical looping; CO2 utilization; Process coupling. Syngas and hydrogen; Thermodynamic analysis