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Successive Loadings of Reactant in the Hydrogen Generation by Hydrolysis of Sodium Borohydride in Batch Reactors

Pages: 153-159

M. J. F. Ferreira¹, V. R. Fernandes², C. M. Rangel³, L. Gales⁴, and A. M. F. R. Pinto^*,5

¹INEGI - Instituto de Engenharia Mecânica e Gestão Industrial, Rua Dr. Roberto Frias 378, 4200-465 Porto, Portugal
²INETI - Unidade de Electroquímica de Materiais, Estrada do Paço do Lumiar, 1649-038 Lisboa, Portugal
³Laboratório Nacional de Energia e Geologia- LNEG/ Fuel Cells and Hydrogen, Estrada do Paço do Lumiar, 1649-038 Lisboa, Portugal
⁴IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto & ICBAS -
Instituto de Ciências Biomédicas Abel Salazar, Largo Prof. Abel Salazar 2, 4099-003 Porto, Portugal
⁵CEFT - Centro de Estudos de Fenómenos de Transporte, Departamento de Engenharia Química,
Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal

Received: April 2, 2009 , Accepted: June 6, 2009

Abstract:
In this paper, for the first time, an experimental investigation is presented of five successive loadings of reactant alkaline solution of sodium borohydride (NaBH4) for hydrogen generation, using an improved nickel-based powder catalyst, under uncontrolled ambient conditions. The experiments were performed in two batch reactors with internal volumes of 0.646 l and of 0.369 l. The compressed hydrogen generated, at pressures below hydrogen critical pressure, gives emphasis on the importance of considering solubility effects during reaction, leading to storage of hydrogen in the liquid phase inside the reactor. The present work suggests that the sodium metaborate by-product formed by the alkaline hydrolysis of NaBH4, in a closed pressure vessel without temperature control, is NaBO2.xH2O, with x ≥ 2.
The data obtained in this work lends credit to x ≈ 2, which was discussed based on the XRD results, and this call for increased caution in the definition of the hydrolysis reaction of NaBH4 up to temperatures of 333 K and up to pressures of 0.13 MPa.

Keywords:

Sodium borohydride; nickel-based catalyst; hydrogen generation; hydrogen storage; high pressure; fuel cell.