Studies on oxidative coupling of methane using high-temperature proton-conducting membranes

A solid oxide proton conducting SrCe0.95Yb0.05O3-x (SCYO) membrane has been applied to methane oxidative coupling in a laboratory membrane reactor using disc-shaped membrane specimen equipped with porous silver electrodes. The investigations were carried out at 750 degrees C and atmospheric pressure and covered variations of feed gases (methane versus helium or air), water vapor pressure, and electrical current. Under the conditions tested, the SCYO-membrane was found to exhibit both substantial oxide ion as well as proton conductivity and electronic conductivity as well. The addition of small amounts of water on the air side, up to 25 mbar partial pressure, led to a significant decrease of conversion at virtually constant C-2-selectivity whereas the addition of small amounts of water on the hydrocarbon side caused methane steam reforming, producing a three-to fourfold increase of conversion while sharply decreasing C-2-selectivity. By applying up to 10 mA current to the cell, the rate of methane consumption could be enhanced to about three times the open circuit rate, however, associated with a small reduction of C-2-selectivity.