Glass frit sealing method for macroscopic defects in Pd-based composite membranes with application in catalytic membrane reactors

A method of sealing defects in thin-film Pd-alloy composite membranes using commercially available glass frit powder is detailed. This technique involves application of a low melting point glass frit and in situ firing in inert gas to seal defects on the order of 1 mm in diameter. In this case, a glass frit with a melting point of 560 °C was found to produce stable seals at 520 °C during a 150 h stability test under pure hydrogen. Changing the feed mixture to 50% H2, 25% Ar and 25% steam, however, caused softening and subsequent seal failure at 520 °C. However, stable operation was achieved with water gas-shift mixtures when the temperature was reduced to 400 °C. The seal is demonstrated to be very robust within ammonia decomposition membrane reactors. Even though the frit seal had direct contact with the catalyst bed, it was observed to be stable in an ammonia decomposition reactor at 520 °C. The catalytic membrane reactor obtained 98% conversion, producing above 99% purity hydrogen with a flux of 0.11 mol m−2 s−1 for 150 h with no signs of seal degradation.