Steam reforming of bio-oil stabilized with ethanol over a Ni/MgAl2O4 catalyst in a Pd-membrane reactor

A new membrane reactor (MR) has been used in the steam reforming (SR) of a feed of raw bio-oil stabilized with 25 wt% ethanol over a Ni/MgAl₂O₄ catalyst, comparing the results (yield of H₂ and byproduct gases) to those reached in a conventional reactor (CR). The reaction setup involves two steps in series: a down-flow tube (at 500 ºC) for the vaporization of the feed and controlled removal of pyrolytic lignin (PL) from the oxygenates in the bio-oil, followed by an up-flow reactor provided with a composite Pd membrane supported on a porous stainless steel (PSS) tube containing a CeO₂ intermediate layer (Pd/CeO₂/PSS). In the MR configuration (with permeate pressure of 0.2 bar absolute), a H₂ yield of 82 % was achieved at 550 ºC, space time of 2.8 h, S/C ratio of 1.55 and 3 bar in the retentate (reactor). This result significantly improves those reached in CR, even at 1 bar and 600 ºC. The S/C ratio in the feed must be limited in the MR configuration to avoid restrictions in H₂ flux through the Pd-membrane caused by a higher gas dilution and concentration-polarization effect, as observed when the S/C ratio is increased up to 2.2. Similarly, a higher retentate pressure has a negative effect on the H₂ yield due to its negative impact on the equilibrium of methane SR, that overcomes its benefits on the H₂ permeation through the membrane. A promising performance of the membrane and catalyst has been obtained, thus demonstrating good prospects for their use in the sustainable production of H₂ from lignocellulosic biomass.