Experimental investigation of double-stage membrane reformer (DSMR) for enhanced hydrogen production via methanol steam reforming

Abstract

Methanol steam reforming (MSR) provides an effective option for on-site hydrogen generation through a membrane reformer (MR) equipped with the Pd-based membrane for H₂ separation from the mixture gas produced during MSR. However, a major obstacle toward scale-up and commercialization is the restricted mass and heat transfer across the catalyst bed. Additionally, a substantial quantity of hydrogen is emitted in the retentate that goes unrecovered. Therefore, in the present study, we have used the structured SiC foam coated with Cu-Fe/Al₂O₃-Zn-ZrO₂ (AZZ, Cu-Fe = 50:50 mol ratio, and AZZ = 70:15:12) catalyst to intensify the radial heat and mass transfer inside the reactor. Further, a multi-pass membrane separator (MPMS) is introduced on the retentate side of the MR to recover the leftover hydrogen, the integrated system is termed as a double-stage membrane reformer (DSMR), functioning as a standalone H₂ production and separation module, to effectively separate the unrecovered H₂ from the retentate stream of the MR. The performance of the DSMR was optimized at different temperatures (573–673 K), pressures (100–300 kPaG), weight hourly space velocity (WHSV, 12.23 to 48.92 ${\text{kg}}_{\text{feed}}{h}^{‐1}{\text{kg}}_{\text{catalyst}}^{‐1}$), and varying membrane areas (65–495 cm²). The Cu-Fe/AZZ/SiC catalyst was tested in all three configurations for comparison including traditional reformer (TR), MR, and DSMR at 300 kPaG of pressure, 673 K of temperature, 3/1 of S/C ratio, 187 cm² of membrane area, and 12.23 kg_feed h⁻¹ kg⁻¹_catalyst of WHSV. Following the performance testing a higher methanol conversion is obtained in the case of DSMR. For instance, the methanol conversion of ∼75 % is achieved in the case of DSMR compared to ∼57 % in MR and ∼53 % in TR. Moreover, H₂ recovery of more than 74.5 % is achieved in DSMR which is 8.5 % higher compared to MR. This is attributed to the enhanced hydrogen recovery in DSMR which helped to achieve higher methanol conversion according to the Le Chatelier's principle. This dual-stage configuration improved hydrogen separation and encouraged equilibrium shifting toward the desired product.