Methanol oxidation in supercritical water

Anitescu, G., Zhang, Z., and Tavlarides, L., Kinetic study of methanol oxidation in supercritical water, Indust. Eng. Chem. Res., 38(6), 2231-2237, 1999. 

Steeper, R.R., Methane and methanol oxidation in supercritical water chemical kinetics and hydrothermal flame studies, Sandia Rep., Sand96-8208.UC-1409, 1-150, 1996. 

Tester JW, Welby PA, Holgate HR. Revised global kinetic measurements of methanol oxidation in supercritical water. Ind Eng Chem Res 1993 32 236-239. 

Tester JW, Webley PA, Holgate HR. Revised global kinetic measurements of methanol oxidation in supercritical water. Ind Eng Ch R 1993 32(l) 236-239 Helling RK, Tester JW. Fundamental kinetics and mechanisms of hydrogen oxidation in supercritical water. Combust Sci Technol 1993 88(5-6) 369-397. 

Fundamental Kinetics of Methanol Oxidation in Supercritical Water... 

Webley, P. A. Tester, J. W. (1989) Fundamental Kinetics of Methanol Oxidation in Supercritical Water. In Supercritical Fluid Science and Technology, K. P. Johnston and J. M. L. Penninger, Ed. American Chemical Society Washington, DC, Vol. 406 pp 259-275. 

KINETIC STUDIES OF METHANOL OXIDATION IN SUPERCRITICAL WATER AND CARBON DIOXIDE... 

Chapter 18. Kinetic studies of methanol oxidation in supercritical water... 

Webley PA, Tester JW, Holgate HR. Oxidation kinetics of ammonia and ammonia-methanol mixtures in supercritical water in the temperature range 530-700°C at 246 bar. Ind Eng Chem Res 1991 30 1745-1754. 

The destruction of hazardous chemical wastes by oxidation in supercritical water is a promising new technology which has several advantages over conventional methods of toxic chemical waste disposal. Although the feasibility of the supercritical water oxidation process has been demonstrated, there is little kinetic information available on the underlying reaction mechanisms. We have recently determined the oxidation kinetics of several model compounds in supercritical water, and now report on our results of the oxidation of methanol, a conunon industrial solvent, in supercritical water. Globd kinetic expressions are presented and our attempts to model the reaction using a free-radical mechanism with 56 elementary reactions are discussed. The inability of the elementary reaction model to represent oxidation in supercritical water is demonstrated and future model modifications are discussed. 

Free-radical reactions are also promoted. Fujii et al. (2011) show that oxidation of methanol by in supercritical water involves both HOO and HO in a chain reaction. 

Savage PE, Rovira J, Stylski N, Martino CJ. Oxidation kinetics for methane/methanol mixtures in supercritical water. J Supercrit Fluids 2000 17 155—70. 

Fourteen oxidation runs were conducted to determine the oxidation kinetics of methanol in supercritical water. The temperature range covered was 450—550 0 at a pressure of 243 atm (24.6 MPa). Reactor residence times ranged from 8.5 to 12.4 seconds. The oxidation run at 450 0 resulted in such low conversions of methanol (<1%) that experimental errors were too large to draw any quantitative conclusions. The data from this run were not included in... 

The Arrhenius plot for an assumed first-order oxidation of methanol in supercritical water is shown in Figure 1 where error bars shown are at the 98% confidence limit. Also shown is the weighted least-equares regression line to the data, where the weights were taken as proportional to kj/a (H). The... 

Table I. Summary of Experimental Clonditions and Results for Oxidation or Methanol in Supercritical Water...

Figure 1. Arrhenius Plot for the First-Order Oxidation of Methanol in Supercritical Water.

The above considerations indicate that the oxidation of methanol in supercritical water in our operating range is probably a free-radical mechanism. It is of interest therefore to compare our results with gas—phase methanol oxidation studies. Major differences will highlight the role played by water in the oxidation process. 

K. A. Smith and J. W. Tester, Critical Review of Kinetic Data for the Oxidation of Methanol in Supercritical Water, J. Supercrit. Fluids, 34, 249-286 (2005). 

Consequently, the vast majority of SCF applications are based on CO2 near the GL critical point, with a possible admixture to support the ability for solvating dipolar components. The extraction of carcinogenic aromatic hydrocarbons and their nitro derivatives from diesel particulates by CO2 + toluene or methanol SCF can serve as an example. CO2 based SCF also helps in cleaning polyethylene from undesired polymer additives. In a similar way one can consider technologies focused on so called h q)er-coal, an extremely pure and environment friendly fuel for turbines in power plants. Recently, the first power plants based on this idea are being constructed in China. The removal of pesticides from meat, decaffeinated coffee and denicotinized cigarettes are the next society-relevant applications. Noteworthy is the h q)er-oxidation with supercritical water and bitumens extraction based on supercritical toluene. The latter system is also used for the liquefaction of coal. ... 

There are not many measurements of elementary reactions with free radicals in supercritical water. Two examples are the addition of OH radical to nitrobenzene [114] and the reaction of the OH radicals with methanol [115]. The experimental rate constants for hydrogen abstraction from methanol by OH radicals are significantly higher than the values used by a variety of researchers for modeling oxidation of methanol in supercritical water using detailed chemical kinetics models [115]. 

Figure 7.5 Most important reaction pathways of the oxidation of methanol in supercritical water at 377°C with an excess of oxygen after 100 s reaction time [118). Calculated using the model of Brock et al. (94). Printed with kind permission of Kluwer Academic Publishers [116])...

Ehiring our investigations of the oxidation in supercritical carbon dioxide, water and carbon dioxide, more than 500 experiments were conducted in the temperature range of 300 -550°C, with reaction times between 10-50 seconds and with the model compounds methanol, ethanol, toluene, triethanolamine, formic acid, acetic acid, and formaldehyde. Usually the differences between reactions in supercritical watCT, supa-critical carbcMi dioxide and wet carbon dioxide are rath small but in some cases they are significant and interesting (to be published elsewhere, see also [5]). Complete conversion as in the case of SCWO can be reached in supercritical CO2 as well [5], so a coupling of extraction and oxidation is of into est for application. 

High-pressure oxidation in carbon dioxide shows the same high conversion rates of the model compounds as in oxidation in supercritical v/ater. However small differences are found even if small amounts of water are added to carbon dioxide. The oxidation of methanol at 420°C and 25 MPa leads to a smalls CO content and lower oxygen conversion if small amounts of water are added into the mixture before reaction. 

Oxidation in Supercritical Media. The oxidation of methane in supercritical water has been examined in the presence or absence of metal catalysts. In many cases, the major product is carbon dioxide. However, some papers reported moderate yields and selectivities for methanol (eq. (15)) (27). 

Lee JH, Foster NR. Direct partial oxidation of methane to methanol in supercritical water. J Supercrit Fluids 1996 9 99-105. 

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