Catalytic calcium-looping reforming of biogas: a novel strategy to produce syngas with improved H₂/CO molar ratios

Anaerobic digestion to acquire biogas is currently the most widely used approach to dispose of vast anthropogenic biowastes. However, effective strategies, except for power generation in the energy sector, to utilize the waste-derived biogas resource are lacking. Herein, we propose a new thermochemical biogas transformation process, catalytic calcium-looping reforming of biogas, to produce syngas with a controllable molar ratio of H₂ to CO. In this process, the conventional CH₄ dry reforming reaction is decoupled into the separate CH₄ dissociation reaction to acquire H₂ and reverse Boudouard reaction to acquire CO, respectively. Results showed that the proposed process was able to produce a H₂-rich stream at a yield of 175.4mmol_H2/gNi with a H₂/CO molar ratio of 5.6 at 700 °C, followed by a high-purity CO stream at a yield of 155.4 mmol_CO/g_Ni at 800 °C in one biogas reforming cycle. It is shown that the reaction between CO₂ and the carbon species with a graphitic ordering is the rate-determining step of the proposed biogas reforming process. Despite the scope for improvement of process stability, the proposed catalytic calcium-looping reforming of biogas has been experimentally demonstrated to be a promising strategy to inherently control the molar ratio of H₂ to CO during syngas production.