The Effects of Intermetallic Diffusion Barrier Layers on Porous Stainless Substrates for the Hydrogen Separation from the Steam Reforming Process

• Main Authors: Pin Jung Chen, 陳品仲
• Other Authors: Kong Wei Cheng
• Format: Others
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/39279034373123368213

碩士 === 長庚大學 === 化工與材料工程研究所 === 96 === The hydrogen energy has become an important energy resource due to the energy and environmental problems. Industrially hydrogen is produced by steam reforming of hydrocarbons such as methane. The methane conversion can be increased to 90% in a membrane reactor using Pd or Pd alloy composites. However, the Pd-Fe alloy created by the diffusion of pores stainless steel substrate components into a palladium membrane by operating temperature greater than 400℃ can reduce the permeability of hydrogen. One solution is to create intermetallic diffusion barrier such as ceramic substrate, which blocks the diffusion of substrate components into the Pd membrane. In this study, oxidation ceramic layers as diffusion layer on Pall/Mott porous stainless steel (PSS) substrate were produced in tube furnace purged with air gas at temperatures from 500-800℃. With an increase in annealed temperature, the average pore diameters of Pall and Mott PSS substrates decreased. The X-ray diffraction patterns of the samples demonstrate the presence of chromium oxide in oxidation layers. Then the Pd membranes were deposited on these PSS substrate with the intermetallic oxidation diffusion barriers. The effective Pd membrane thickness could decrease and also increase the hydrogen permeances. The maximum average hydrogen permeances and selectivity of Pall PSS substrates in this study are 31.8 m3/m2．h．atm0.5 and 4300 (H2/N2), while those of Mott PSS substrate are 21 m3/m2．h．atm0.5 and 1800 (H2/N2) in this study. The Pd membranes had activity for hydrogen separation with temperature kept at 500°C over a period of 200 hours. Hydrogen flux improved about 15-20% after 200 hours operation using the substrates with the intermetallic oxidation diffusion barriers created at 600℃. The hydrogen flux of the samples with diffusion barrier layers prepared in this study improved in a period of 50 hours, and hydrogen flux of these samples became stable after 50 hours for the test of life time. The possible reason is the total effects of the recrtstallization texture of Pd membrane and the generation of Pd-Fe alloys layers, which made hydrogen flux of samples became stable after 50 hours for the test of lifetime.