Unveiling the role of operating conditions for pure hydrogen production from ethanol steam reforming in a vacuum-assisted Pd membrane reactor

The use of a membrane reactor (MR) is an effective solution for improving H 2 production in reforming processes because the selective separation of H 2 from the reaction medium overcomes thermodynamic equilibrium constraints. This study investigates the effect of operating conditions upon the enhancement of H 2 production by ethanol steam reforming (ESR) over a Ni/MgAl 2 O 4 catalyst through the use of a MR reactor with the permeate side operated under vacuum to produce a pure H 2 stream. The reactor is provided with a Pd membrane supported on a porous stainless steel (PSS) tube containing a CeO 2 intermediate layer (Pd/CeO 2 /PSS), which is 100% selective for H 2 permeation. The effects of pressure (1–3 bar), temperature (500–550 °C), ethanol concentration (12.5–20 mol%), and the steam/ethanol (S/E) molar ratio (3–6) are analyzed experimentally in both a conventional reactor (CR) and a MR The results show that, conversely to the CR, increasing the pressure has a positive effect in the MR, because the beneficial effect of pressure on H₂ permeation overcomes its negative impact on the SR equilibrium, which allows obtaining a H 2 yield higher than the predicted thermodynamic equilibrium values in the CR. Ethanol dilution and high S/E ratios improve H 2 yield in the CR, and although the former reduces the H₂ flux in the MR, the H 2 production remains high, allowing to achieve H₂ yields of up to 69% and H 2 recoveries of 83% under adequate conditions (550 °C, 3 bar, S/E ratio of 6, and 12.5% ethanol), with a H 2 purity of 100% in the permeate stream. The permeability of the membrane decreased due to carbon deposition, which was reversible by manual cleaning to some extent. This work demonstrates the effectiveness of the MR for intensifying the ESR process over Ni/MgAl 2 O 4 catalyst when using moderate pressure and high values of ethanol dilution and S/E ratio. • A 100% H 2 selective composite Pd/CeO 2 /PSS(porous stainless steel) membrane was synthetized. • Reaction temperature has low effect on the H 2 enhancement in the MR and the H 2 recovery. • The dilution of ethanol and the increase in S/E ratio slightly increase the H2 yield. • 69% H 2 yield and 83% H 2 recovery achieved at 550 °C, 3 bar, S/E of 6, 12.5% ethanol. • Permeability loss by carbon deposition was partially reversible by manual cleaning.