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Ind. Eng. Chem. Res. 1993,32, 236-239
Revised Global Kinetic Measurements of Methanol Oxidation in Supercritical Water New data are presented for methanol oxidation rates in supercritical water to update and correct earlier measurements taken in our laboratory. A revised global rate expression with Arrhenius parameters and a full interpretation of these new data are provided in light of a systematic temperature measurement error discovered in the earlier set of experiments. Motivation and Scope Repeated references have been made to preliminary measurements of methanol oxidation rates in supercritical water based on experiments carried out in our MIT laboratory (Tester et al., 1993). The most prominent of these are a frequently cited Los Alamos National Laboratory report by Rofer and Streit (1989) and an ACS monograph paper by Webley and Tester (1989). In later publications (Webley et al., 1990,1991),we mentioned that new kinetic measurements had been made to correct a systematic temperature measurement error in our tubular reactor system. The data and rate expressions reported earlier (Rofer and Streit, 1989; Webley and Tester, 1989) must therefore be considered invalid. Although a global rate expression for methanol oxidation with Arrhenius parameters was given by Webley et al. (1991), the actual data were not presented or discussed. The objectives of this Research Note are 3-fold: (1) to document completely these new results; (2) to discuss in detail how we corrected the original data set to account for the systematic temperature measurement error; and (3) to present revised global rate parameters based on the combined data set.
heat-transfer rates from the fluidized sand bath were higher, this misplacement of the thermocouple bead would not have resulted in as large temperature measurement error. However, because actual transfer rates were lower, a significant error resulted. Oxidation experiments in reactor T2 used an Omega (type K, Model No. CAIN116U-12)ungrounded thermocouple sheathed in a l/lS-in. (1.59 mm) 0.d. Inconel tube where the bead was located at the bottom of the sheath. By repeating runs with the T2 reactor over the same temperature range studied with the T1 reactor, we were able to estimate an average systematic error of +26 "C for the T1 reactor system temperature. The methodology used to obtain this estimate is described in the subsection on Effect of Temperature in the Data Analysis and Interpretation section of this paper. In all, 20 experiments conducted in the tubular reactor systems (T1 and T2) and one run in the packedbed reactor (P)are reported in this paper. Other experiments were carried out but results are not reported due to large carbon balance errors, oxygen limitations, or conversions that were too high or too low to permit data regression.
Experimental Conditions and Procedures The oxidation of methanol in supercritical water was investigated over the temperature range 450-550 "C at 246 bar (3550 psig). Methanol and oxygen feed concentrations ranged from 1.28 X to 5.68 X mol/L and
