Hydrogen production by steam methane reforming in membrane reactor equipped with Pd membrane deposited on NiO/YSZ/NiO multilayer-treated porous stainless steel

In this study, we prepared a Pd composite membrane with high hydrogen permeance and thermal stability on a tubular porous stainless steel (PSS) support by ethylene diamine tetraacetic acid-free electroless plating. The conventional yttria-stabilized zirconia (YSZ) was replaced with a NiO/YSZ/NiO multilayer as the diffusion barrier, and the latter was introduced on a PSS tube (diameter of 12.7 mm, length of 450 mm, and surface area of 175 cm²). A long-term thermal stability test revealed that the NiO/YSZ/NiO multilayer significantly reduced the growth rate of nitrogen leakage. The test was carried out for ~1150 h on a 2.5-µm thick Pd membrane deposited on a NiO/YSZ/NiO/PSS tube (diameter of 25.4 mm, length of 450 mm, and surface area of 350 cm²). The hydrogen permeance obtained at the end of the test was 3.81 × 10⁻³ mol m⁻² s⁻¹ Pa^−0.5, and the H₂/N₂ selectivity was ~87 at a temperature of 773 K and pressure difference of 101.3 kPa. The rate of increase in nitrogen leakage during the test was 3.05 × 10^–11 mol m⁻² s⁻¹ Pa^−0.5 h⁻¹, which demonstrated the ability of the NiO/YSZ/NiO multilayer to mitigate nitrogen leakage. To produce hydrogen using the Pd composite membrane reactor, steam methane reforming was conducted under the following operating conditions: pressure, 430–1114 kPa; temperature, 883 K; and gas hourly space velocity, 1000 h⁻¹. The reaction yielded a methane conversion and hydrogen recovery of 75.1% and 97.9%, respectively. The permeate stream was composed of 93.1 vol% H₂, 0.6 vol% CO, 1.8 vol% CH₄, and 4.5 vol% CO₂. The gas composition of the permeate stream was suitable for use as fuel in a high-temperature polymer electrolyte membrane fuel cell.