Investigation on POM reaction in a new perovskite membrane reactor

A perovskite-type oxide of Ba_0.5Sr_0.5Co_0.8Fe_0.2 O_3-δ (BSCFO) shows mixed (electronic/oxygen ionic) conductivity at high temperatures. Membrane made of the oxide has high oxygen permeability under air/helium oxygen partial pressure gradient. At 850°C, oxygen permeation rate maintained about 1.15 ml/cm²min for more than 1000 h under ambient air/helium oxygen gradient. A membrane reactor constructed from the oxide membrane was applied for the partial oxidation of methane (POM) to syngas, LiLaNiO_x/γ-Al₂O₃ with 10 wt.% Ni loading was used as the packed catalyst. At the initial stage, oxygen permeation rate, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation rate to reach its steady state. A membrane reactor made of BSCFO was successfully operated for POM reaction at 875°C for about 500 h without failure, with methane conversion of >97%, CO selectivity of >95% and oxygen permeation rate of about 11.5 ml/cm²min. Under membrane reaction condition, the POM reaction mechanism was suggested to obey the CRR (complete combustion of CH₄ to CO₂ and H₂O and a subsequent reforming reaction of the residual CH₄ and with CO₂ and H₂O to CO and H₂) mechanism.