Formaldehyde, sodium hydroxide hazard

Douglas R. Chrisope; Peter E. Rogers
Agricultural Group, Monsanto Co., St. Louis

Chemical & Engineering News (9 Jan 1995) Vol. 73, No. 2, pp. 2.

We recently became aware of an unexpected hazard in our operations and would like to alert others to a situation that may be relatively common. Our investigation was prompted by a recent paper [E. C. Ashby et al., J. Am. Chem. Soc., 115, 1171 (1993)] that established conditions under which formaldehyde reacts with sodium hydroxide to give formic acid and hydrogen quantitatively. Typically, conditions also exist in which both this reaction and the classical Cannizzaro reaction proceed simultaneously. Ashby showed that reaction of 4 M NaOH with 15 mM formaldehyde led to production of hydrogen from 31% of the formaldehyde, the remainder going to normal Cannizzaro products. We wish to report that with only 0.5 M NaOH, 1-2% of the 20 mM formaldehyde present in our system is converted to hydrogen, which can create a significant safety hazard.

Monsanto manufactures, ships, and stores solutions of organic acid sodium salts that initially contain residual formaldehyde levels of 300-700 ppm and NaOH at about 1.5 weight %. Laboratory studies with these solutions revealed that they did generate hydrogen gas in a steady fashion, and if stored in a confined space, it would be possible to exceed the lower explosive limit (LEL) of 4.2 mol % for hydrogen in air. Monsanto has detected hydrogen in the headspace of railcars and storage tanks at levels below the LEL. In view of these results, actions to render inert and to dilute the vapor space of these systems have been taken.

It seems likely that other manufacturing operations might contain the necessary conditions to generate hydrogen by this pathway. We urge others to consider this a possibility in systems where hydroxide and any aldehyde without .alpha.-hydrogens are both present. If such a situation does exist, we would recommend conducting appropriate testing or lab studies.

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