Pd encapsulated and nanopore hollow fiber membranes: Synthesis and permeation studies

• Published in: Journal of membrane science Vol. 290; no. 1; pp. 182 - 195
• Main Authors: Nair, Balamurali Krishna R., Harold, Michael P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2007
• Subjects: Gas separation; Hollow fiber; Hydrogen; Membrane reactor; Palladium; Membrane reactor; Gas separation; Palladium; Hydrogen; Hollow fiber
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2006.12.028

New types of supported Pd membranes were developed for high temperature H 2 separation. Sequential combinations of boehmite sol slip casting and film coating, and electroless plating (ELP) steps were designed to synthesize “Pd encapsulated” and “Pd nanopore” membranes supported on α-Al 2O 3 hollow fibers. The permeation characteristics (flux, permselectivity) of a series of unaged and aged encapsulated and nanopore membranes with different Pd loadings were compared to those of a conventional 1 μm Pd/4 μm γ-Al 2O 3/α-Al 2O 3 hollow fiber membrane. The unaged encapsulated membrane exhibited good performance with ideal H 2/N 2 separation factors of 3000–8000 and H 2 flux ∼0.4 mol/m 2 s at 370 °C and a transmembrane pressure gradient of 4 × 10 5 Pa. The unaged Pd nanopore membranes had a lower initial flux and permselectivity, but exhibited superior performance with extended use (200 h). At the same conditions the unaged 2.6 μm Pd nanopore membrane had a H 2 flux of ∼0.16 mol/m 2 s and separation factor of 500 and the unaged 0.6 μm Pd nanopore membrane had a H 2 flux of ∼0.25 mol/m 2 s and separation factor of 50. Both nanopore membranes stabilized after 40 h of operation, in contrast to a continued deterioration of the permselectivity for the other membranes. An analysis of the permeation data reveals a combination of Knudsen and convective transport through membrane defects. A phenomenological, qualitative model of the synthesis and resulting structure of the encapsulated and nanopore membranes is presented to explain the permeation results.