Oxidative steam reforming of ethanol over Ru-Al_2O_3 catalyst in a dense Pd-Ag membrane reactor to produce hydrogen for PEM fuel cells

摘要

This study focuses on the influence of oxygen addition on ethanol steam reforming (ESR) reaction performed in a dense Pd-Ag membrane reactor (MR) for producing hydrogen directly available for feeding a polymer electrolyte membrane fuel cell (PEMFC). In particular, oxygen addition can prevent ethylene and ethane formation caused by dehydration of ethanol as well as carbon deposition. The MR is operated at 400 ℃, H_2O:G_2H_5OH = 11:1 as feed molar ratio and space velocity (GHSV) ～2000 h~(-1). A commercial Ru-based catalyst was packed into the MR and a nitrogen stream of 8.4 × 10 ~(-2) mol/h as sweep gas was flowed into the permeate side of the reactor. Both oxidative ethanol steam reforming (OESR) and ESR performances of the Pd-Ag MR were analyzed in terms of ethanol conversion to gas, hydrogen yield, gas selectivity and CO-free hydrogen recovery by varying O_2:C_2H_5OH feed molar ratio and reaction pressure. Moreover, the experimental results of the OESR and ESR reactions carried out in the same Pd-Ag MR are compared in order to point out the benefits due to the oxygen addition. Experimentally, this work points out that, overcoming O_2:C_2H_5OH = 1.3:1, ethanol conversion is lowered with a consequent drops of both hydrogen yield and hydrogen recovery. Vice versa, a complete ethanol conversion is achieved at 2.5 bar and O_2:C_2H_5OH = 1.3:1, whereas the maximum CO-free hydrogen recovery (～30%) is obtained at O_2:C_2H_5OH = 0.6:1.