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Palladium and silver-palladium composite membranes have been obtained by deposition on ceramic supports using a modified electroless plating process.
Investigated supports are asymmetric alumina tubular membranes, with pore size ranging from 20 nm to 500 nm, supplied by various manufacturers. Deposits have been performed both on the external and on the internal surface of the supports. The deposition process consists of the following consecutive steps: • support cleaning • activation using PdCl 2 and SnCl 2 solutions plating • in-flow deposition of palladium by electroless • in-flow silver deposition by electrodeposition • thermal treatment in order to obtain the alloy formation ss has been properly optimized and a procedure to recover palladium from spent solutions the complete bit good penetration and anchorage of the metal layer onto the alumina supports, and appear imulating synthesis gas zation of end seals allowed obtaining H impurities absorbed on membrane surface (e.g. chlorides, carbon, etc.) can strongly ecrease H 2 permeability. lian Electrical System under the Contract Agreement established with the Ministry Decree of March 23 rd , 2006. Each step of the proce has been developed. Thermal treatment conditions (temperature and time) have been optimized according to a simple uni- dimensional model. X-ray diffraction measurements have been performed in order to verify formation of the alloy; in addition SEM micrographies have been made to verify its morphology. Using the procedure described above Pd and Pd-Ag membranes 5 to 10 micron thick have been obtained. Deposits exhi pinhole free. Permeation tests have been performed in a pilot loop with the above-mentioned membranes. Tests have been carried out both with single gases (H , N , He, CO ) and with gas mixtures s 2 2 2 composition, up to 370°C and with a transmembrane pressure ranging from 1 to 5 bar. H 2 permeability and selectivity in the 200-370°C temperature range has been determined. Membranes exhibit good temperature stability; however, it has been found that selectivity is mainly limited by the presence of gas leakages through the end seals at the metal/ceramic interface. Optimi 2 selectivity versus He and CO 2 of 300 and 800, respectively, at 310°C. Furthermore, tests performed with gas mixtures simulating synthesis gas composition indicate that, for temperatures below 300°C, CO absorption on membrane surface determines a marked decrease in H 2 permeation (reversible poisoning), due to the occupation of sites available for H 2 dissociation. In general, for temperatures below 300°C, d Acknowledgments This work has been financed by the Ministry of Economic Development with the Research Fund for the Ita
31 Dicembre 2007
Centrali elettriche per la coproduzione di energia elettrica e idrogeno: progettazione di base (P4 (PROD))