Oxygen permeation studies in surface Pd-activated asymmetric Ce0.9Gd0.1O1.95 membranes for application in CO2 and CH4 environments

Abstract

Oxygen Transport Membranes (OTMs) present a high potential for being considered in the integration of O2 supply systems in oxyfuel installations, as well as for the conduction of chemical reactions when operating Catalytic Membrane Reactors (CMRs). Several solutions are being prospected for overcoming the main drawbacks regarding materials stability and membrane performance. A highly stable material such as Ce0.9Gd0.1O1.95 (CGO) doped with 2% mol. Co was studied as a 40 μm-thick CGO supported CGO membrane. This membrane was characterized by studying its performance as oxygen permeation membrane for the production of oxygen under oxyfuel conditions and for the conduction of chemical reactions involving CH4. In order to improve oxygen surface reactions and consequently, the oxygen permeation, the membrane was surface activated with the addition of Pd nanoparticles. A broad characterization consisting of the study of O2 production under different environments simulating real application conditions was conducted by subjecting the membrane to Ar, CO2 and CH4 environments in the temperature range of 750 to 1000 °C. A peak oxygen flux of 7.8 ml·min−1·cm−2 was obtained at 1000 °C when using a sweep consisting of 75% CH4 in Ar. This flux corresponds to a 16-fold improvement in the O2 permeation at 1000 °C when sweeping with Ar, with an oxygen flux of 0.47 ml·min−1·cm−2. An oxygen flux of 1.2 ml·min−1·cm−2 was obtained at 1000 °C when feeding with pO2 = 1 atm in feed side. Membrane performance under CO2-containing environments showed a positive effect of CO2 on permeation at 1000–900 °C, reaching up to 0.59 ml·min−1·cm−2 O2 at 1000 °C. A continuous exposure of CO2 during 48 h at 750 °C resulted in a slight J(O2) increase, with a reversible reduction in performance when returning to clean conditions, thus demonstrating high stability of CGO membranes.