HYDROLYSIS AND OXIDATION OF ACETAMIDE IN SUPERCRITICAL WATER

This paper describes the development of acetamide destruction kinetics in supercritical water. The experimental conditions included temperatures between 400 and 525-degrees-C and pressures between 230 and 335 atm. The empirical rate equations for the hydrolysis and the overall reaction (hydrolysis + oxidation by hydrogen peroxide) were determined as follows: (hydrolysis) r = -(10(2.2) +/- 10(1.3)) exp((-51000 +/- 5600)/RT)[acetamide]1 and (overall reaction) r = -(10(3.6) +/- 10(2.5)) exp((-68000- +/- 3800)/RT)[acetamide]1, where the activation energies were in joules per mole and [acetamide] was in moles per liter. First-order kinetics with respect to the acetamide concentration properly described both the hydrolysis and overall reaction rates. The hydrolysis reaction proceeded more rapidly than the oxidation. Therefore, the role of supercritical water as an active reactant should be recognized. The residual byproducts formed from the hydrolysis or the overall reaction of acetamide were acetic acid and ammonia. The effects of hydrogen peroxide concentration and the reaction pressure on the reaction rate were negligible. Therefore, the use of an oxidant slightly above the stoichiometric demand may be sufficient in SCWO processes. The negligible pressure effect implies that, to minimize construction costs associated with containing high pressure, the pressure may be kept as low as possible. Also, the negligible pressure influence may add flexibility for controlling the retention time without loss of destruction efficiency.