Oxidative coupling of methane in a modified γ-alumina membrane reactor

Methane oxidative coupling experiments were conducted in a porous gamma -alumina membrane reactor using Mn-W-Na/SiO2 catalyst, and its performance was compared with a packed reactor operated at similar conditions. The gamma -alumina membrane tube was thermally stabilized by treating the membrane tube with La(NO3)(3) aqueous solution and calcining at 900 degreesC. Non-uniform oxygen permeation was achieved by partially coating the outer surface with a high-temperature glaze. C-2 yields up to 27.5% were obtained in the membrane reactor. The experimental results clearly demonstrated that it was beneficial to distribute the feed of oxygen along the reactor length for the methane oxidative coupling reactions. Although the membrane reactor showed lower methane conversion at the same reaction conditions, it gave higher C-2 selectivity and C-2 yield at similar methane conversions. The helium flow rate was varied in the membrane and co-feed reactors to keep the temperature, methane flow rate, and oxygen flow rate constant. At the same methane conversion the membrane reactor gave 10% higher C-2 yield and 30% higher C-2 selectivity than the co-feed reactor. At similar C-2 yield and C-2 selectivity, the methane conversion of the membrane reactor was 15% lower than that of a co-feed reactor. The oxygen flow rate was varied in the membrane and co-feed reactors to keep conversion constant at the same temperature, methane flow rate, and helium flow rates. At the same methane conversion, the membrane reactor gave about 3% higher C-2 yield and selectivity than the co-feed reactor. Higher helium flow rate gave higher C-2 selectivity and yield, whereas changing methane flow rate did not significantly affect the reactor performance. (C) 2000 Elsevier Science Ltd. All rights reserved.