Oxidative steam reforming of methane to synthesis gas in microchannel reactors

Oxidative steam reforming of methane to synthesis gas (syngas) over an alumina supported bimetallic Pt–Rh catalyst was comparatively investigated in coated and packed microchannel reactors. In the first configuration, thin layers of catalysts are coated on opposite walls of a single microchannel, while the second one is described by particulate catalysts packed into an empty microchannel of dimensions identical with the first one. Both geometries are compared on the basis of methane conversion and CO selectivity measured at different values of parameters, namely reaction temperature (773–923 K), molar steam-to-carbon (S/C = 0–3.0) and oxygen-to-carbon (O2/C = 0.47–0.63) ratios in the feed, and contact time (0.36–0.71 mg min cm−3). Although methane conversions are found to be comparable, the coated catalyst gave significantly higher CO selectivities than the packed counterpart in the whole parameter range. Increase in all of the parameter values led to improvement in methane conversion, while CO selectivity increased only with temperature and contact time. Molar H2/CO ratios obtained in the coated microchannel reactor are found to vary between 1.0 and 3.0 which are at least three times smaller than those produced in the packed microchannel reactor. Catalyst deactivation is not detected in both configurations. Stable operation up to 72 h over coated microchannel verified mechanical and chemical stability of the Pt–Rh coating that produced syngas with H2/CO ratio of 2.12 at temperatures lower than employed in industrial reformers. Different flow distribution properties of coated and packed microchannels seem to play roles in affecting the product distribution.

► Methane OSR over Pt–Rh in coated and packed microchannels is compared. ► Both configurations give similar methane conversion levels. ► Coated microchannel gives superior CO selectivity under identical conditions. ► Product H2/CO ratios in packed microchannels are at least three times higher. ► The two product spectra are likely to be affected by different flow distributions.