Pure and mixed gas permeation tests were performed on Pd-based hydrogen selective membranes at different experimental conditions. In particular the permeance of pure hydrogen as well as of binary and ternary mixtures containing hydrogen, nitrogen and methane was measured at temperatures ranging from 673 to 773 K, and at pressure differences up to 6 bar. The membranes, supplied by NGK insulator Ltd. Japan, were formed by a selective Pd-Ag layer (20%wt Ag) deposited on a tubular ceramic support, and showed very high hydrogen permeance and a practically infinite selectivity toward hydrogen. Interestingly the permeance values measured in pure gas experiments resulted always higher with respect to those obtained in permeation tests with gas mixtures; in the latter case, moreover, the permeate flux significantly deviates from Sieverts’ law suggesting the existence of non negligible resistances to hydrogen transport in the gas phase, in addition to that offered by the metallic membrane. Experiments performed at increased feed flow rates, showed also an increase in hydrogen permeance thus revealing the importance of the concentration polarization effects inside the module. Gas phase mass transport coefficients were calculated and used to determine the role of such a resistance in the overall mass transport process. The Sherwood number was also evaluated and was found to follow a boundary layer type of correlation.

Influence of the gas phase resistance on hydrogen flux through thin palladium–silver membranes

CATALANO, JACOPO;GIACINTI BASCHETTI, MARCO;SARTI, GIULIO CESARE
2009

Abstract

Pure and mixed gas permeation tests were performed on Pd-based hydrogen selective membranes at different experimental conditions. In particular the permeance of pure hydrogen as well as of binary and ternary mixtures containing hydrogen, nitrogen and methane was measured at temperatures ranging from 673 to 773 K, and at pressure differences up to 6 bar. The membranes, supplied by NGK insulator Ltd. Japan, were formed by a selective Pd-Ag layer (20%wt Ag) deposited on a tubular ceramic support, and showed very high hydrogen permeance and a practically infinite selectivity toward hydrogen. Interestingly the permeance values measured in pure gas experiments resulted always higher with respect to those obtained in permeation tests with gas mixtures; in the latter case, moreover, the permeate flux significantly deviates from Sieverts’ law suggesting the existence of non negligible resistances to hydrogen transport in the gas phase, in addition to that offered by the metallic membrane. Experiments performed at increased feed flow rates, showed also an increase in hydrogen permeance thus revealing the importance of the concentration polarization effects inside the module. Gas phase mass transport coefficients were calculated and used to determine the role of such a resistance in the overall mass transport process. The Sherwood number was also evaluated and was found to follow a boundary layer type of correlation.
2009
J. Catalano; M. Giacinti Baschetti; G. C. Sarti
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/79102
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