Dense mixed-conducting ceramic membrane reactor for oxidative coupling of methane

Due to its promise for direct conversion of natural gas (90 vol% of methane) into C{dollar}sb2{dollar} (C{dollar}sb2{dollar}H{dollar}sb4{dollar} and C{dollar}sb2{dollar}H{dollar}sb6{dollar}) products, oxidative coupling of methane (OCM) has attracted tremendous interests and research efforts from both scientific and industrial communities since 1982. However, the C{dollar}sb2{dollar} yields achieved so far for OCM over any solid oxide catalysts in a conventional packed-bed reactor are less than 25% if the C{dollar}sb2{dollar} selectivity are maintained higher than 50%. This is generally believed to be caused by undesired gas phase combustion reactions in which methane and C{dollar}sb2{dollar} products are oxidized into CO{dollar}sb{lcub}rm x{rcub}{dollar}.; A novel dense oxygen semipermeable and catalytically active ceramic membrane reactor (DOS-CA-CMR) is used for OCM reaction in this work. This reactor has the potential to achieve higher C{dollar}sb2{dollar} yield and selectivity for OCM since the oxygen is directed supplied through the oxide solid phase. The mechanism of this reactor and the requirements for the membrane materials are discussed. The experimental work is devoted to the selection, fabrication and test of the suitable membrane materials for the OCM membrane reactor.; In order to search for a membrane material with high oxygen semipermeability, good OCM catalytic properties and high stability under OCM reaction conditions, a conventional packed-bed reactor operated in both cofeed and cyclic modes and a transient TGA measurement system are designed and used to evaluate the suitability of the selected materials (in powder or pellet form) for OCM. With this method it is found that two perovskite-type oxides, {dollar}rm Lasb{lcub}0.2{rcub}Srsb{lcub}0.8{rcub}CoOsb3{dollar} (LSC) and {dollar}rm SrCosb{lcub}0.2{rcub}Fesb{lcub}0.8{rcub}Osb3{dollar} (SCF), might not be suitable for OCM membrane reactor while 25 mol% yttria doped bismuth oxide (BY25) may exhibit good OCM catalytic properties when used in an OCM membrane reactor. It is concluded that the OCM catalytic properties of an oxide is closely related to its ionic and electronic conductivity. A material of good selectivity for OCM reactions may become non-selective as it transfers from a p-type electronic conductor to an n-type one. The oxygen permeation properties of LSC oxide is studied with the transient TGA measurement.; An OCM membrane reactor is designed, constructed and studied in this work. It is also used for the direct measurement of the oxygen permeation fluxes through ceramic membranes. Several membranes are studied in this reactor to test their OCM performance and oxygen permeation properties. Among them, {dollar}rm Smsb2Osb3{dollar} and {dollar}rm Ysb2Osb3{dollar} doped {dollar}rm Bisb2Osb3{dollar}(BYS) membrane exhibits both good OCM catalytic properties and stability under the reaction conditions. In order to achieve a high C{dollar}sb2{dollar} selectivity, the oxygen permeation flux must match with the OCM reaction rate. A high membrane surface to reactor volume ratio is essential to obtain a high C{dollar}sb2{dollar} yield in a dense OCM membrane reactor.