Kinetics of Hydrogen Formation from Formaldehyde in Basic Aqueous Solutions

Abstract

A phenomenological description of dihydrogen generation from solutions of formaldehyde and glyoxylate in basic aqueous solutions at high ionic strength is presented. Effective rate constants and activation energies for the H{sub 2} production reactions of these two substrates are given. The effect of formaldehyde and NaOH concentrations on the rate of H{sub 2} generation was studied at 23, 45, and 60{degree}C. The reaction is first order in formaldehyde and approaches second order in [OH{sup -}] at low [HCHO]. At high ionic strength the experimental results can be modeled by a reaction mechanism that includes the Cannizzaro reaction in competition with the hydrogen production reaction. To obtain acceptable agreement of the experimental observations with the computational modeling, one needs to invoke a reaction of hydroxide ions with the two deprotonated forms of methylene glycol (the hydrated formaldehyde). The quantitative description of this reaction is important in safety issues of stored high level liquid nuclear waste. 16 refs., 9 figs., 4 tabs.