Improving oxygen permeation of MIEC membrane reactor by enhancing the electronic conductivity under intermediate-low oxygen partial pressures

Abstract

Oxygen chemical potential decreases continuously across a mixed ionic-electronic conducting membrane as one side is fed with air and the other side is fed with methane for syngas production. At a certain position in the membrane bulk, the oxygen chemical potential is intermediate-low, i.e. corresponding to an oxygen partial pressure of 10−10–10−15atm. Insufficient electronic conductivity at an intermediate-low oxygen chemical potential may limit the oxygen transport across the membrane bulk under the syngas production condition. In this work, a new ceria based dual-phase membrane 75wt% Ce0.85Sm0.15O1.925 – 25wt% Sm0.6Sr0.4Cr0.3Fe0.7O3−δ (SDC–SSCF) was prepared as a membrane reactor for the syngas production. The conductivities of SDC–SSCF, 75wt% Ce0.85Sm0.15O1.925 – 25wt% Sm0.6Sr0.4Al0.3Fe0.7O3−δ (SDC–SSAF, as a control material) and related single-phase materials were investigated under various oxygen partial pressures. SDC–SSAF has enough high electronic conductivity under high and low oxygen partial pressures but limited electronic conductivity under the intermediate-low oxygen partial pressure, thus the low electronic conductivity limits the ambipolar diffusion in the membrane bulk. However, the electronic conductivity of SDC–SSCF is high enough in the whole range of oxygen partial pressure compared with the ionic conductivity. As a result, the oxygen permeation flux through a 0.5-mm-thick SDC–SSCF membrane is high up to 7.6mLcm−2min−1 at 950°C for the syngas production, which is 1.8 times that of the SDC–SSAF membrane under the same condition. In addition, the SDC–SSCF membrane reactor was steadily operated for 220h, and reached >95% methane conversion and >98% CO selectivity. The scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses reveal the good stability of SDC–SSCF as a membrane reactor.