Failure mechanisms of ceramic membrane reactors in partial oxidation of methane to synthesis gas

In the course of generating synthesis gas (H2, CO) from methane, we have observed two types of fractures occurring on the Sr(Co, Fe)Ox-type oxygen membrane reactors. The first type occurred shortly after the reaction started and the second type often occurred days after the reaction. To determine the causes of these fractures, we have examined the starting material and fractured membranes using a combination of X-ray diffraction and thermogravimetric analyses. We found that the first type of fracture was the consequence of an oxygen gradient in the membrane, pointing from the reaction side to the air side. This causes a lattice mismatch inside the membrane, leading to fracture. The second type of fracture, however, was the result of a chemical decomposition. We found that the Sr(Co, Fe)Ox-type membrane had been reduced to SrCO3, and elemental Co and Fe by the synthesis gas generated in the reaction. The decomposition causes enormous expansion leading to a large crack along the axis of tube.