Synthesis, oxygen permeation study and membrane performance of a Ba0.5Sr0.5Co0.8Fe0.2O3-delta oxygen-permeable dense ceramic reactor for partial oxidation of methane to syngas

Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCFO) oxide was synthesized by a combined ED TA-citrate complexing method. The partial substitution of Sr in SrCo0.8Fe0. 2O3-delta by Ba led to obvious improvement in the phase stability of the ma terial at high temperatures. Under an air/helium oxygen gradient, the oxyge n permeation fluxes of BSCFO were considerably high, a permeation flux appr oximate to1.6 ml/cm(2) min was achieved for a 1.5 mm. membrane at 950 degre esC, when P'(O2) = 0.21 atm and P " (O2) = 0.05 atm. The oxygen permeation was rate-determined mainly by oxygen bulk diffusion under non-reducing envi ronment within the membrane thickness (1.5-1.8 mm) and temperature range (8 00-900 degreesC) investigated. The oxygen permeation flux kept at 1.1-1.2 m l/cm(2) min under ambient air/helium oxygen gradient during more than 1000 h operation. However, at lower temperatures, the permeation flux slowly dec reased in an exponential relationship with time, which was possibly due to the phase decomposition of the material. Two membrane configurations and th ree cases were investigated for the partial oxidation of methane to syngas in a planar BSCFO reactor with LiLaNiOx/gamma -Al2O3 as the reforming catal yst. The decrease in the distance between membrane surface and the reformin g catalyst led to increase in the oxygen permeation fluxes and the role of surface exchange at the reaction membrane side in the oxygen permeation rat e determination. High temperature treatment made some catalyst deposit onto the membrane surface, which led to a change of the oxygen exchange mechani sm at the reaction side membrane surface, and resulted in an increase in ox ygen permeation flux and decrease in activation energy of oxygen surface ex change. The stable long-term performance of the membrane reactor demonstrat ed that the permeation was still controlled by surface oxygen exchange of t he reaction side membrane surface after the high temperature treatment. At 875 degreesC, a permeation flux of 11.5 ml/cm(2) min, methane conversion of 97-98%, and CO selectivity of 95-97% were achieved. (C) 2001 Elsevier Scie nce B.V. All rights reserved.