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Influence of support characteristics on gas permeation of Pd composite membranes

pubblicazioni - Articolo

Influence of support characteristics on gas permeation of Pd composite membranes

composite membranes Pietro Pinacci*, Maria Broglia* Euromembrane 2009 Montpellier France, 6-10 Settembre 2009 POSTER SESSION * ERSE SpA Palladium alloy membranes are widely studied for CO 2 capture and hydrogen separation from synthesis gas in membrane reactors. Due to the considerable cost of palladium, efforts have been made to obtain low thickness deposits on cheaper materials, such as macro-porous metals, by various techniques, including electroless plating [1]. However, high operating temperatures (>350-400°C) and long exposure times can determine the diffusion of substrate metals (e.g. iron) into the palladium layer and, subsequently, a significant decrease of hydrogen permeance and selectivity. To avoid this problem, the support should be modified, introducing a suitable barrier layer such as a grown-on oxide obtained by a proper thermal treatment. The characteristics of the modified support, including pore size distribution and surface rugosity, strongly affect the thickness of the palladium layer that should be deposited in order to obtain a dense and stable membrane [2]. The objective of this work is, therefore, to optimize the surface characteristics of commercial metallic supports in order to minimize the thickness of the deposited palladium layer. Investigated supports are tubular AISI 316L supports, with a nominal pore size of 0.1 micron, supplied by two different manufacturers. Supports have been machine polished with a diamond paste in order to reduce surface rugosity. Supports have been then oxidized by a proper thermal treatment and, thereafter, palladium has been deposited by electroless plating in successive baths. At the end of each bath, the helium permeance of the membranes at room temperature has been determined. Membranes have been considered as dense and, consequently, palladium deposition stopped, when helium permeance has been reduced below 10 -9 mol/sec/m 2 /Pa. Finally membrane permeation tests in single gases (He and H 2 ) have been performed in the 300-450°C temperature range, in order to check their performances (permeance and selectivity) and stability. Experimental allowed to optimize the preparation procedure of the membrane. The surface rugosity of the support was decreased of a factor up to six without significantly affecting its mass transfer resistance and, at the same time, the Pd layer thickness has been reduced more than a factor 2 (from 25 down to 11 microns) while maintaining good stability and performances at temperature,

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