Raman spectroscopic measurement of oxidation in supercritical water .2. Conversion of isopropyl alcohol to acetone

The oxidation of isopropyl alcohol in supercritical water has been investigated using Raman spectroscopy. Results for species concentration as a function of residence-time are presented for temperatures ranging from 400 to 480 degrees C at constant pressure, 24.4 +/- 0.3 MPa, and constant equivalence ratio, 0.88 +/- 0.02. Acetone has been identified as the principal intermediate formed and subsequently destroyed, during the oxidation process. By assuming first-order kinetics for the destruction of both isopropyl alcohol and acetone, effective first-order rate constants have been determined from fits of the experimental data. Assuming Arrhenius behavior, the fits yield rate constants for isopropyl alcohol, k(eff,ipa) = 3.255 x 10(22)(s(-1)) exp[-301.1(kJ . mol(-1))/RT], and for acetone, k(eff,ace) = 1.948 x 10(10)(s(-1)) exp[-137.7(kJ . mol(-1))/RT]. These results indicate that for temperatures greater than 425 degrees C, the destruction of isopropyl alcohol proceeds faster than that of acetone.