Co-oxidation of methylphosphonic acid and ethanol in supercritical water (original) (raw)
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The Journal of Supercritical Fluids, 2007
Reaction kinetics of methanol and ethanol oxidation in supercritical water at 520-530 • C and 24.7 MPa were investigated both experimentally and by computational simulation. Furthermore, studies were performed on the oxidation of the two alcohols in binary mixtures. For the methanol system, experimental data showed that the methanol conversion decreased with increasing initial methanol concentration in the low concentration range (from 6.48 × 10 −6 to 3.94 × 10 −5 mol/l), whereas the conversion increased for initial concentrations in the high concentration range (from 2.23 × 10 −4 to 1.55 × 10 −3 mol/l). Kinetic analyses based on the elementary reaction model showed that production of OH from the reaction of H 2 O with HO 2 seemed to play an important role at the low methanol concentrations and that the characteristic dependence of methanol conversion on initial methanol concentration was due to the very high concentration of H 2 O in supercritical water oxidation of methanol. For the binary system, it was found that methanol conversion was accelerated by ethanol addition whereas ethanol oxidation was slightly retarded by the presence of methanol. Calculation with an elementary reaction model could reproduce the phenomenological mutual effects of alcohols with respect to reaction rates, and it was found that the acceleration/retardation effect of conversions could be well characterized by the time profile of OH radical, rather than HO 2 radical.
Journal of Environmental Sciences, 2011
The destruction of methylphosphonic acid (MPA), a final product by hydrolysis/neutralization of organophosphorus agents such as sarin and VX (O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothionate), was investigated in a a bench-scale, continuous concentric vertical double wall reactor under supercritical water oxidation condition. The experiments were conducted at a temperature range of 450-600°C and a fixed pressure of 25 MPa. Hydrogen peroxide was used as an oxidant. The destruction efficiency (DE) was monitored by analyzing total organic carbon (TOC) and MPA concentrations using ion chromatography on the liquid effluent samples. The results showed that the DE of MPA up to 99.999% was achieved at a reaction temperature of 600°C, oxygen concentration of 113% storichiometric requirement, and reactor residence time of 8 sec. On the basis of the data derived from experiments, a global kinetic rate equation for the DE of MPA and DE of TOC were developed by nonlinear regression analysis. The model predictions agreed well with the experimental data. Citation: Veriansyah B, Song E S, Kim J D, 2011. Destruction of methylphosphonic acid in a supercritical water oxidation bench-scale double wall reactor. Journal of Environmental Sciences, 23(4): 545-552
Partial Oxidation of Ethanol in Supercritical Water
Industrial & Engineering Chemistry Research, 2020
Ethanol is partially oxidized in a continuous supercritical water reactor at temperatures from 500 to 530°C, constant pressure of 25 MPa, initial ethanol concentration of 5 wt %, residence times of 3−8 s, and oxidant-to-fuel stoichiometric equivalence ratios of 5, 7.5, and 10%. The experimental conditions are selected to study the regime where ethanol oxidation happens rapidly but below the temperature necessary to initiate hydrolysis reactions. The reactions and interactions of intermediate species can be analyzed, leveraging previous experimental results and the existing body of literature on ethanol hydrolysis, pyrolysis, and oxidation. Higher oxidant concentration increases ethanol destruction and gasification efficiency, although significant coke/char buildup is qualitatively observed within the reactor. Product yields from the experiments are used to infer significant reaction mechanisms, and a pathway is postulated for the counterintuitive formation of char under the studied conditions.
The role of catalyst in supercritical water oxidation of acetic acid
Applied Catalysis B: Environmental, 1997
The oxidation kinetics of acetic acid in supercritical water (l.O2<T,< 1.15 and 1.04<Pr<1.13) was examined in the homogeneous phase as well as in the presence of a solid catalyst consisting of supported copper, zinc, and cobalt oxides. For the conditions studied, the uncatalyzed oxidation reaction was found to be first order in acetic acid and 0.3 order in oxygen, with an activation energy of 182 kJ mall'. The rate of catalyzed oxidation was found to be well described by means of the power-law kinetic formulation based on non-uniform surfaces. It is postulated that oxygen is adsorbed on active sites and that a reaction between adsorbed species and organic molecules from the van der Waals sublayer forms a carbonate complex which further decomposes to carbon dioxide and water. The apparent activation energy of catalyzed oxidation is 110 kJ mol-'. The observed products in uncatalyzed supercritical water oxidation were carbon monoxide, carbon dioxide, and water. The oxidation of acetic acid over transition metal oxides favors the production of carbon dioxide over carbon monoxide.
Water density effects on methanol oxidation in supercritical water at high pressure up to 100MPa
The Journal of Supercritical Fluids, 2011
Reaction kinetics of methanol oxidation in supercritical water at high pressure condition (420 • C; 34-100 MPa; = 300-660 kg/m 3 ) was investigated. Pseudo-first order rate constant for methanol decomposition increased with increasing water density. Effects of supercritical water on the reaction kinetics were investigated using a detailed chemical kinetics model. Incorporating the effect of diffusion in a reduced model revealed that overall kinetics for SCWO of methanol is not diffusion-limited. Roles of water as a reactant were also investigated. The dependence of sensitivity coefficient for methanol concentration and rate of production of OH radical on water density indicated that a reaction, HO 2 + H 2 O = OH + H 2 O 2 , enhanced the OH radical production and thereby facilitated the decomposition of methanol. It is presumed that concentration of key radicals could be controlled by varying pressure intensively.
Catalytic oxidation of toxic organics in supercritical water
Applied Catalysis B: Environmental, 1994
Oxidation of Wrne toxic orgamc compounds m aupercntlcal water 18 mvestqated m the presence of a sohd catalyst m an isothermal plug flow fixed-bed reactor Companaon between catalyzed and noncatalyzed oxldatlons mdlcatee that the convenuona are much hqher when the catalyst 18 present It 1s also found that the heterogeneous oxldatlon route forms lest uhxmechte producta durmg the decom-posItion of organic8 such as benzow acid and I-methyl-2-pyrmhdone m carbon dloxlde
The regularities of changes in the activation energy as a function of reduced state parameters, characteristics of the molecular field (dielectric constant, polarity) of the oxidized reactant and the oxidation reaction medium of saturated monohydric alcohols and acids in an aqueous medium under supercritical fluid conditions are revealed. A generalized dependence is obtained for the activation energy as a function of the difference between the polarities of the oxidizable reagent and the reaction medium, which describes the literature data with an acceptable error of ± 25%. The capabilities of the method are confirmed by studies of the kinetics of the oleic acid oxidation by hydrogen peroxide in an aqueous medium under supercritical fluid conditions in the temperature range 673-723К and a pressure of 29.4 MPa. The reaction rate constant and activation energy are determined. The activation energy of the oleic acid oxidation reaction by hydrogen peroxide in an aqueous medium under supercritical fluid conditions Ea =-104.8 kJ*mol-1 differs by no more than 11%.
Catalyst activity, stability, and transformations during oxidation in supercritical water
Applied Catalysis B: Environmental, 2001
We used three different catalysts (bulk MnO 2 , bulk TiO 2 , and CuO/Al 2 O 3) to oxidize phenol in supercritical water in a tubular flow reactor. CuO/Al 2 O 3 was the most active of the three on a mass of catalyst basis whereas MnO 2 was the most active on an areal basis. All three catalysts largely maintained their activities for phenol disappearance and for CO 2 formation throughout more than 100 h of continuous use. MnO 2 and TiO 2 were stable in the sense that no Mn or Ti was detected in the reactor effluent. The CuO/Al 2 O 3 catalyst, on the other hand, was not stable. Both Cu and Al were detected in the reactor effluent. The bulk transition metal oxide materials experienced a 3-4-fold reduction in specific surface area after exposure to supercritical water oxidation (SCWO) conditions, whereas the supported CuO/Al 2 O 3 catalyst experienced a 20-fold reduction. Being used as an oxidation catalyst in supercritical water transformed the bulk MnO 2 into Mn 2 O 3 , the CuO catalyst into Cu 2 O, the Al 2 O 3 support into AlO(OH), and anatase TiO 2 into rutile TiO 2. Of the three materials considered, bulk MnO 2 appears to be the best oxidation catalyst for supercritical water conditions. It is stable under reaction conditions, and it provided high activities and good activity maintenance.
Cooxidation of ammonia and ethanol in supercritical water, part 1: Experimental results
AIChE Journal, 2007
The cooxidative effect of ethanol on ammonia oxidation in supercritical water was studied for a range of temperatures (655-7058C), initial ammonia (1-3 mM), ethanol (0-1.0 mM), and oxygen concentrations (0.7-5.0 mM), corresponding to fuel equivalence ratios ranging from 0.9 to 2.2 for the complete combustion of both organic species. With a stoichiometric amount of oxygen available for complete oxidation, the addition of ethanol on an equivalent molar basis was found to increase ammonia conversion from 20 to 65% at initial concentrations of 1 mM for each reactant, T ¼ 7008C, P ¼ 246 bar, and t ¼ 2.5 s. Nitrous oxide was produced in much larger quantities for ammonia-ethanol cooxidation than for ammonia oxidation. Based on fractional yields of nitrogen product, this amounted to 40-75% for co-oxidation with ethanol versus 4-13% without ethanol present.
Industrial & Engineering Chemistry Research, 2002
The use of laboratory-scale equipment to measure intrinsic oxidation kinetics in supercritical water environments was evaluated in this study. The objectives were two-fold: (1) to compare the use of hydrogen peroxide with dissolved oxygen as an oxidant and (2) to characterize the dynamics and intensity of mixing organic reactant and oxidant streams. Methanol was used as the model organic as the oxidation rate exhibits a first-order dependence according to extensive earlier studies. No statistically significant difference was observed in the reaction rates or product distributions for the use of either dissolved oxygen gas or hydrogen peroxide that was preheated and fully decomposed before mixing with methanol at supercritical water conditions (500°C, 246 bar). The intensity of mixing was shown to be an important factor in determining effective mixing times for the reactant and oxidant. Although hydrodynamic effects are certainly dependent on the design and geometry of the mixing tee in the reactor system, fully turbulent (Re > 10 000) cross-flow between entering oxidant and organic streams was found to reduce mixing times to 1 s or less.