The design of vessels and off-gas systems for denitrating acidic radioactive process solutions by reacting nitric acid with sugar requires a fairly accurate determination of the rate of the controlling step. Therefore, the reaction of sugar with concentrated nitric acid was closely examined at temperatures of 100 and 110°C and in the presence of low levels of iron [0 to 0.2 M Fe(III)]. The sugar-acid reaction does not exhibit a single mechanism. However, the overall reaction can be approximated by the following expression:
.The rate coefficient, K(t), as a function of time [K(t) = K0 + K1t] mathematically delineates the change from the rapid initial reaction at high acid concentrations to the slower digestion reaction at low acid concentrations. At the high acid concentrations (>6 M), the rate coefficient approaches K0. The relationship of the rate constant, K0, with Fe(III) at 100°C is K = 0.60 × [0−4 + 5.60 × 10−4[Fe(III)]. Efficiencies of the sugar destruction by nitric acid ranged from 2.56 to 2.93 mol of acid consumed per mole of carbon added. Product off-gases were examined throughout the reaction. Release of CO was fairly constant throughout the reaction, but amounts of CO2 increased as the nitric acid began to attack the terminal carboxylic acids produced from the consumption of sucrose. Voluminous quantities of NO2 were released at the beginning of the reaction, but larger relative concentrations of NO were observed toward the end.
