High Yttria-Zirconia and Yttria Ceramics for Petrochemical Reverse-Flow Reactor Applications

Reverse-flow reactors achieve the desired hydropyrolysis reaction of natural gas and other hydrocarbon feeds at very high temperatures of up to 2000 degrees C, which enables the production of many high-value chemicals. To identify refractory ceramic materials suitable for constructing key components of the reactor, the full range of solid solutions between zirconia and yttria having 18 to 100mol% yttria have been tested in a laboratory reactor. Conventional yttria-stabilized zirconia (YSZ) materials having 8mol% Y2O3 appear to accommodate reactor thermal severity, but are prone to a new form of corrosion termed ceramic dusting that is observed when pyrolysis and oxidation cycles are alternated under reverse-flow conditions. Yttria and high yttria-zirconia ceramics having similar to 80mol% or more yttria suppress ceramic dusting corrosion in steam-free pyrolysis environments. The addition of low levels of steam of similar to 5% to the pyrolysis gas stream increases the stability of YSZ materials substantially, so that the stability threshold is closer to 40mol% Y2O3 in the yttria-zirconia system. The two approaches can be combined to optimize reactor performance. Key experimental results are presented and discussed taking into account the thermodynamic phase stability of the different phases.