Pd-based membrane reactors for producing ultra pure hydrogen: Oxidative reforming of bio-ethanol

A membrane reactor consisting of a dense self-supported Pd-Ag tube of wall thickness 60 ?m has been filled with a Pt-based catalyst and used for producing pure hydrogen via oxidative steam reforming of bio-ethanol. The reformer feed stream consisted of water and ethanol with traces of glycerol and acetic acid in order to simulate a liquid waste of dairy industry after fermentation and concentration. The membrane reformer has been characterized through permeation and reaction tests performed at 400 and 450 °C with a reaction (lumen) pressure in the range 100-200 kPa. The hydrogen permeated through the membrane has been collected in the reactor shell by a sweep stream of nitrogen. Permeation tests verified the complete hydrogen selectivity of the thin wall tube membrane and measured permeability values at 400-450 °C of 1-2 mol m-1 s-1 Pa-0.5 accordingly to the literature. In the reaction tests, the capability of the membrane to promote the reaction conversion (shift effect) has been demonstrated. The gas chromatographic analysis of the retentate showed very low concentration of CO and the presence of methane as a main product of side-reactions. At 400 °C the pressure affects significantly the hydrogen production and the hydrogen yield moves from 0.4 to 1 when the pressure increases from 100 to 200 kPa. Significant increase of the hydrogen production has been attained at the higher temperature of 450 °C where maximum values of hydrogen yield (close to 3) have been measured with a lumen pressure of 200 kPa. Under these conditions, the technology of Pd-based membranes is effective for recovering hydrogen from a liquid waste.