Reduction of acrolein by elemental iron: kinetics, pH effect, and detoxification

Acrolein is a highly toxic alpha,beta-unsaturated aldehyde that is widely used as a biocide, a cross-linking agent, and an intermediate in the chemical industry, among other applications. In this study we investigated the reductive transformation of acrolein by elemental iron and evaluated the feasibility of using iron to detoxify acrolein. At acidic and neutral pH, acrolein was transformed by iron through reduction of the C=C double bond to propionaldehyde. The reduction appeared to involve the chemisorption of acrolein to the iron surface followed by reduction of adsorbed acrolein. Both the adsorption and reduction rate constants decreased with increasing pH. Between pH 7.0 and 7.4, the acrolein adsorption rate constant decreased precipitously, resulting in a sharp decline in its removal rate. At higher pH, acrolein disappeared rapidly in control without iron, presumably due to reversible, base-catalyzed hydration. At equilibrium, approximately 93% of acrolein was hydrated, corresponding to an equilibrium constant of 13. Acrolein at 25 mg/L completely inhibited aerobic respiration; in contrast, its reduction product propionaldehyde was biodegradable. This suggests that elemental iron may be used to pretreat acrolein-containing wastes prior to aerobic biodegradation. To our knowledge, this is the first report of reduction and detoxification of an alpha,beta-unsaturated aldehyde by elemental iron.