sodium-hypochlorite and nitrogen-chloride

Five liters of sodium hypochlorite aqueous solution (12 mass%) was poured into 300 L of liquid waste containing ammonium ion of about 1.8 mol/L in a 500 L tank in a plant area; then, two minutes later the solution exploded with a flash on March 30th, 2005. The tank cover, the fluorescent lamp and the air duct were broken by the blast wave. Thus, we have conducted 40 runs of laboratory-scale explosion tests under various conditions (solution concentrations of (NH4)2SO4 and NaClO, temperatures, Pt catalysts, pH, etc.) to investigate the causes for such an explosion. When solutions of ammonium sulfate and sodium hypochlorite are mixed in the presence of platinum black, explosions result. This is ascribable to the formation of explosive nitrogen trichloride (NCl3). In the case where it is necessary to mix these 2 solutions (ammonium sulfate and sodium hypochlorite) in the presence of platinum black, the following conditions would reduce a probability of explosion; the initial concentration of NH4(+) should be less than 3 mol/L and the pH should be higher than 6. The hypochlorite solution (in 1/10 in volume) to be added at room temperature is recommended to be less than 0.6 mol/L.

Topics: Ammonium Sulfate; Chemical Hazard Release; Chlorides; Explosions; Gas Chromatography-Mass Spectrometry; Nitrogen Compounds; Platinum; Sodium Hypochlorite; Spectroscopy, Fourier Transform Infrared; Waste Products

Trichloramine is a volatile, irritant compound of penetrating odor, which is found as a disinfection by-product in the air of chlorinated indoor swimming pools from reactions of nitrogenous compounds with chlorine. Acid amides, especially urea, ammonium ions and α-amino acids have been found as most efficient trichloramine precursors at acidic and neutral pH. For urea a relative NCl(3) formation of 96% at pH 2.5 and 76% at pH 7.1 was determined. Even under sub-stoichiometric molar ratios of Cl/N the formation of NCl(3) is favored over mono and dichlorinated products. However, the reaction kinetics of urea with chlorine is slow under conditions relevant for swimming pools. Also the mass transfer of NCl(3) from water to the gas phase which was calculated by the Deacon's boundary layer model could be shown as a relatively slow process. Mass transfer would take 20 h or 5.8 d for a rough or a quiescent surface of the water, respectively. This is much more than a typical turnover rate of 6-8 h of a treatment cycle of a 25 m swimming pool. Therefore processes to remove NCl(3) and its precursors can help to minimize the exposure of bathers.

Topics: Air Pollutants; Air Pollution, Indoor; Chlorides; Disinfectants; Hydrogen-Ion Concentration; Kinetics; Models, Chemical; Nitrogen Compounds; Phase Transition; Sodium Hypochlorite; Swimming Pools; Urea; Water