Ceramic microreactors for on-site hydrogen production from high temperature steam reforming of propane

Abstract

The steam reforming of hydrocarbon fuels is a promising method for the production of hydrogen for portable electrical power sources. A suitable reactor for this application, however, must be compatible with temperatures above 800 °C to avoid coking of the catalytic structures during the reforming process. Here, ceramic microreactors comprising high surface area, tailored macroporous SiC porous monoliths coated with ruthenium (Ru) catalyst and integrated within high-density alumina reactor housings were used for the steam reforming of propane into hydrogen at temperatures between 800 and 1000 °C. We characterized these microreactors by studying C₃H₈ conversion, H₂ selectivity, and product stream composition as a function of the total inlet flow rate, steam-to-carbon ratio (S/C), and temperature. As much as 18.2 sccm H₂, or 3.3 × 10⁴ sccm H₂ per cm³ of monolith volume, was obtained from a 3.5 sccm entering stream of C₃H₈ at a S/C of 1.095 and temperatures greater than 900 °C. Operating at a S/C close to 1 reduces the energy required to heat excess steam to the reaction temperature and improves the overall thermal efficiency of the fuel processor. Kinetic analysis using a power law model showed reaction orders of 0.50 and −0.23 with respect to propane and steam, respectively, indicating that the rate limiting step in the steam reforming reaction is the dissociative adsorption of propane on the Ru catalyst. The performance of the microreactor was not affected after exposure to more than 15 thermal cycles at temperatures as high as 1000 °C, and no catalyst deactivation was observed after more than 120 h of continuous operation at 800 °C, making these ceramic microreactors promising for efficient on-site hydrogen production from hydrocarbons for use in polymer electrolyte membrane (PEM) fuel cells.