Kinetic Modeling For The Oxidation Of Methanol In Supercritical Water

Supercritical water oxidation (SCWO) is a promising technique for the treatment of organic wastes. The properties(including hydrogen bonding,density,thermal conductivity,diffusion coefficient et al) of supercritical water(SCW) were presented. The characteristic of supercritical water oxidation and the industrial application and the technical expectation of supercritical water oxidation were discussed in detail,and the universal research works on the degradation efficiency,influential factors,oxidation kinetics and reaction mechanism of the organic pollutant in SCWO and water's effect in SCWO were reviewed in the paper.The methanol was chosen as the object of SCWO for studying the kinetics for the oxidation of the organic pollutant in SCW. Based on the reaction mechanism proposed by Brock et.al., the kinetic model was put forward by the application of mass-balance and hypothesis of quasi-steady-state. There were twenty-three kinetic parameters in the kinetic model of methanol in supercritical water oxidation. Twenty-one kinetic parameters were found from the paper or calculated by the application of the formulas. The experimental data were used to correlate the kinetic model and the unknown kinetic parameters were obtained by using Matlab Version 6.1. The unknown kinetic parameters were showed as follow: k3/: Ab=5.48×1013 cm3/mol·s, Ea=1882.7cal/mol, n=0; k5/: Ab=7.33×1014 cm3/mol·s, Ea=60063.1cal/mol, n=0. The concentrations of methanol, formaldehyde,CO and CO2 were calculated using the kinetic model and were compared with the experimental data. The results showed that the calculations are in agreement with the measurements and the error was analysed. For researching the conversion of the reactants and the products of the methanol in SCWO and providing the theoretical direction for the industrialized design of SCWO, the concentrations of methanol ,formaldehyde,CO and CO2 were calculated at the two reaction conditions(t=554℃,P=25MPa,[CH3OH]0=6.6×10-7mol/L,[O2]0=2.5×10-6mol/L,[H2O]0=4.34×10-3mol/L and t=590℃,P=25MPa,[CH3OH]0=5.3×10-7mol/L,[O2]0=2.1×10-6mol/L,[H2O]0=4.03×10-3mol/L). The trend of the concentrations of methanol, formaldehyde,CO and CO2 as a function of the reaction time and the trend of the yields of formaldehyde,CO,CO2 as a function of the methanol conversion were analysed through the chart.(1)The reactions of the methanol in SCWO were sensitive to the reaction temperature. When increasing the reaction temperature, the reactions of the methanol in SCWO were very rapid and the reaction time decreased. (2)In despite of the different reaction temperature and the different reaction time, The trend of concentrations of methanolthe,formaldehyde,CO and CO2 as a function of the reaction time were same. The methanol concentration decreased as increasing the reaction time until the methanol concentration became zone. The formaldehyde concentration earlier increased as increasing the reaction time and decreased affer coming the maximum until the formaldehyde concentration became zone. The CO concentration increased as increasing the reaction time and appreciably decreased affer coming the maximum until the reaction finished. The CO2 concentration continually increased as increasing the reaction time until the reaction finished.