Supercritical water oxidation partial

A simple model of lumped kinetics for supercritical water oxidation included in the partial differential equations for temperature and organic concentrations allows to qualitatively simulate the dynamic process behavior in a tubular reactor. Process parameters can be estimated from measured operational data. By using an integrated environment for data acquisition, simulation and parameter estimation it seems possible to perform an online update of the process parameters needed for prediction of process behavior. 

Gasification of Liquidized Biomass Supercritical Water Using Partial Oxidation... 

The calculations have been done not only for stoechiometric combustion conditions, but also for negative oxygen balances, which are relevant for partial combustion conditions and for thermal decomposition reactions. By taking into account an excess of water, also the reaction products of a supercritical water oxidation can be calculated. 

In the wet oxidation process, materials partially or completely dissolve into a homogeneous, condensed-phase mixture of oxygen and water, and chemical reactions between the material and oxygen take place in the bulk water phase. This condensed-phase makes wet oxidation an ideal process to transform materials which would otherwise be non-soluble in water to a harmless mixture of carbon dioxide and water. Since oxidation reactions are also exothermic, the high thermal mass of supercritical water makes this reaction medium better suited for thermal control, reactor stability, and heat dissipation. The purpose of this research was to establish a new method for selectively oxidizing waste hydrocarbons into new and reusable products. 

Partial wet oxidation or controlled wet oxidation is, in a sense, similar to that of catalytic oxidation. Catalytic oxidation provides a conventional catalyst in order to boost and control the oxidative reaction, whereas wet oxidation provides a favored atmosphere for the reaction to occur. More accurately, catalytic oxidation provides a surface upon which intimate contact between the reactants takes place compared to the thermodynamic (or fluid dynamic) contact provided by wet oxidation. In wet oxidation, it can be said that the supercritical water phase acts as the "catalyst for the reaction. 

Lilac, W.D. Lee, S. Kinetics and mechanisms of styrene monomer recovery from waste polystyrene by supercritical water partial oxidation. Adv. Envi. Res. 2001, 6, 9-16. 

Complete oxidation in supercritical water occurs at a high rate usually, complete conversion to carbon dioxide is achieved in the reaction time of about 1 min for most organics. New applications of supercritical water are emerging where only partial oxidation is carried out and oxygenated hydrocarbons are produced. Here, the reaction time has to be limited to the order of seconds. 

Richter and Vogel oxidized cyclohexane in supercritical water for a varying reaction time from 5 to 80 sec range. The partial oxidation resulted in the desired cyclohexanone product, but the yield was very low (Fig. 7). The by-products included carboxylic acids, carbon monoxide, and carbon dioxide. 

Richter, T. Vogel, H. The partial oxidation of cyclohexane in supercritical water. Chem. Eng. Technol. 2002, 25 (3), 265-268. 

Masaru Watanabe, Hiroshi Inomata, Mitsumasa Osada, Takafumi Sato, Adschiri, Kunio Arai. (2003), Catalytic effects of NaOH and ZrO2 for partial oxidative gasification of -hexadecane and lignin in supercritical water. Fuel. 82,545-552. 

G. T. Hong and M. H. Spritzer, Supercritical Water Partial Oxidation, Proceedings of the 2002 U.S. DOE Hydrogen Program Review, NREI7CP-610-32405, 2002. 

A more complex degradation takes place when this process is applied to PVC. The authors propose that PVC depolymerization under supercritical water conditions proceeds in accordance with a mechanism consisting of four different pathways (i) dehydrochlorination and partial oxidation, (ii) dehydrochlorination and chain scission, (iii) dehydrochlorination and total oxidation, and (iv) hydrochlorination. In the reaction products, high yields of vinyl chloride, 1,1-dichloroethane and 1,2-dichloroethane are detected, especially at short reaction times, whereas longer times favour total oxidation products. 

Other possible oxidative treatments for the feedstock recycling of plastic and rubber wastes include partial oxidation with organic peroxides and decomposition by reaction with oxygen by thermooxidation or under supercritical water conditions. However, these latter alternatives have so far not been widely investigated. 

Show feasibility of supercritical water partial oxidation (SWPO) in pilot-scale preliminary testing. 

General Atomics is developing Supercritical Water Partial Oxidation (SWPO) for the efficient and environmentally advantageous gasification of and hydrogen production from low-grade fuels such as biomass, municipal/solid waste (MSW) and high-sulfur coal. 

Using direct mixing with supercritical water for heat-up of a biomass slurry entering the reactor is problematic because a relatively large amount of supercritical water is required. This dilutes the biomass slurry and requires oxidation of most of the biomass to attain the desired final temperature of about 650°C. Limited preheat and partial oxidation have been established as the preferred means of heat-up. 

Spritzer, M.H. and GT Hong, "Supercritical Water Partial Oxidation", Presented at the Annual Peer Review Meeting, USDOE Hydrogen Program, Golden, CO, May 2002. 

Hong, GT and M.H. Spritzer, "Supercritical Water Partial Oxidation", 2002 Annual Report to USDOE Hydrogen Program, available at www.eren.doe.gOv/hydrogen/docs/2002toc.html. 

Hamley PA, Ilkenhans T, Webster JM, et al Selective partial oxidation in supercritical water the continuous generation of terephthahc acid from para-xylene in high yield. Green Chem 4 235-238, 2002. http //dx.doi.org/10.1039/b202087b. 

---