Kinetics of the Absorption of Hydrogen by LaNi sub 5 H/sub X//N-Undecane Suspensions. Part I. The H sub 2 /LaNi sub 5 H/sub X//N-Undecane System

摘要

Isothermal kinetic studies of the absorption of hydrogen by LaNi sub 5 H/sub x/ suspended in n-undecane have been performed. The rate limiting process is the dissolution of H sub 2 in the solvent. A general rate equation is given, dH sub 2 /dt = 1/2 ks (a''-a'), where ks is the rate constant for the absorption of H sub 2 by the solvent; (a''-a') represents a thermodynamic driving force which is determined by the equilibrium solubility of H sub 2 in the solvent and the equilibrium absorption plateau pressure of the solid. The rate constant is defined as k/sub s/ = A/sub s/exp(-E/sub s//RT) where E/sub s/ is the activation energy for dissolution of H sub 2 in the solvent and is equal to 11.0 +- 1.1 kJ/mol H sub 2 . The pre-exponential, A/sub s/, is a function of the efficiency of the gas-liquid contact. The rate equation should have general utility and can be used with other hydrides suspended in n-undecane as long as the rate limiting process is unchanged. A new method for the study of fast reactions involving the dissolutions of H sub 2 in liquids is discussed. The H sub 2 absorption and desorption rates are well within the range required for practical applications. 10 references, 3 figures, 2 tables. (ERA citation 09:032780)