A molten salt bath was used to carry out the methane steam reforming reaction in the 800-l000°C range. The rate of methane pyrolysis was also determined under the same conditions to compare it to the rate of steam reforming. The molten salt baths used included a eutectic mixture of sodium pyrophosphate and sodium metaphosphate, a eutectic mixture of potassium pyrophosphate and potassium metaphosphate, a mixture of Na2O, P2O5 and V2O5 and a mixture of Na2O, P2O5 and NiO. Additional experiments were conducted in empty reactors.
It was found that the rate of pyrolysis was not affected by any of the salt systems.The rate of the steam reforming reaction was low, about 10% of the pyrolysis rate, for the empty reactors and for all the salt systems except the system Na2O-P2O5-NiO under reducing conditions. Under reducing conditions, the nickel of this system was reduced to' metallic Ni which catalyzed the CH4-H2O reaction.
X-ray diffraction, electron microscope and electron microprobe analysis studies confirmed the hypothesis that under oxidizing conditions nickel was dissolved in the melt and under reducing conditions solid nickel particles were formed which were suspended in the melt. These particles were exposed to the reactant gases on bubble surfaces.
This novel catalytic steam reforming system is especially suitable for handling residual oils of high sulfur and heavy metal content. The sulfur is captured by the salt melt whereas the nickel catalyst is regenerated by repeated cycles of dissolution into and reduction from the melt.
