The role of catalyst in supercritical water oxidation of acetic acid (original) (raw)
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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.
The Journal of …, 2011
Sodium titanate was hydrothermally synthesized on the surface of titanium particles in supercritical water. Sodium titanate showed catalytic activity on supercritical water oxidation (SCWO) of acetic acid and promoted oxidation rate greatly comparing to uncatalyzed oxidation. Global rate law based on power-law model and Langmuir-Hinshelwood model could describe experimental results well. In addition, Mars-Van Krevelen model expresses catalytic process well. This suggested that redox reaction over sodium titanate might be a dominant oxidation mechanism, at least, above 450 • C. Deactivated sodium titanate was easily re-synthesized and it recovered catalytic activity. Sodium titanate showed a great potential of a long-term available catalyst in SCWO processes through its cyclic re-activation.
Kinetics of MnO 2 -Catalyzed Acetic Acid Oxidation in Supercritical Water
Industrial & Engineering Chemistry Research, 2000
Acetic acid was oxidized in supercritical water over a bulk MnO 2 catalyst. CO 2 , the complete oxidation product, was produced almost quantitatively. The rate of acetic acid disappearance exhibited saturation kinetics with respect to acetic acid, a maximum with respect to the oxygen concentration, and an independence from the water concentration. We identified a global rate law that was both qualitatively and quantitatively consistent with these experimental results. Using this catalytic rate law and literature rate laws for noncatalytic oxidation of acetic acid in supercritical water, we found that the use of MnO 2 as an oxidation catalyst can reduce the reactor volume required for treatment of aqueous solutions of acetic acid by more than 2 orders of magnitude.
Oxidation catalysis in a supercritical fluid medium
Industrial & Engineering Chemistry Research, 1987
The supercritical fluid (SCF) extraction technique was extended by its application to SCF-solidcatalyzed reactions that otherwise take place in a two-fluid-phase reactor. By use of COz as a solvent, toluene was contacted with air in the presence of redox or acid catalysts and underwent partial oxidation t o primarily benzaldehyde. A screening study of several oxide and mixed-metal oxide catalysts revealed that supported COO, partly oxidized to Co(III), was the most active (10-5/s turnover number) and selective (no multiring condensation products) catalyst. The relative activity of the supported COO catalyst was not unexpected, because the Co2+/Co3+ redox couple is the most effective catalyst for this reaction in solution. The oxide was capable of duplicating the liquid-phase behavior, although at lower activity levels than promoted (for example, with Br-ions) homogeneous cobalt catalysts.
STEPPING STONES TOWARD OXIDATION PROCESSES IN SUPERCRITICAL WATER
Under supercritical conditions (i.e. when the temperature and the pressure of a substance are above its thermodynamic critical point), water becomes a fluid with unique properties that can be used to treat a wide variety of wastes. For example, during Supercritical Water Oxidation (SCWO) organic wastes can be almost fully converted into carbon dioxide and water. Already used in a variety of terrestrial applications (for example onboard ships), SCWO technology, because of its potential for extremely high waste conversion efficiencies, is of great interest in the context of space exploration programs. A SCWO reactor could be used in the treatment of a number of waste streams typically found onboard spacecraft used in long duration missions or as a part of the Environmental Control and Life Support (ECLS) system for an extraterrestrial habitat. As part of the DECLIC program, the first two investigation phases motivated by the potential of future SCWO applications in microgravity have e...
Physicochemical Treatment of Hazardous Wastes, 2003
Supercritical water oxidation (SCWO) reaction is effective in destruction of polychlorinated biphenyls (PCBs) to mineral products of CO 2 , HCl, and H 2 O such that 99.95% conversion of Aroclor 1248 is possible in 54.5 seconds residence time at 823 K and 25.3 MPa. Yet to design and operate SCWO reactors to avoid harmful products formation such as polychlorinated dibenzofurans and dioxins, it is necessary to understand the PCB reaction pathway leading to final products. This study shows the dechlorination reaction pathway of 3344-Tetrach lorobiphenyl (a surro gate for Aroclo r 1248) in methanol solutions. It is suggested that hydrogen species from methanol act as reaction rate enhancers and lead to a series reaction pathway of dechlorination to biphenyl followed by ring-opening oxidation to mineral products. Also, reaction kinetics for this system are presented. These results are of value for reactor design to ensure oxidation of these recalcitrant pollutants in an environmentally safe manner.
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%.
Supercritical water oxidation for the treatment of various organic wastes: A review
The removal of complex organic and chemical industrial wastes is not accessible using conventional treatment methods. Incineration and hydrothermal oxidation under supercritical conditions are two options for dealing with a wide range of hazardous wastes. Incineration is an effective treatment for removing hazardous waste. The main disadvantages of incineration are a source of unwanted emissions and high operating costs. Supercritical water oxidation (SCWO) is considered a green technology for destroying organic waste with friendly environmental emissions. The removal efficiency reached 99.99% within a short residence time. In this review, the treatment of organic waste by SCWO is shown using cofuel and catalysts to enhance the performance of SCWO.
Symmetry
This work reports supercritical water oxidation (SCWO) of organic pollutants in industrial wastewater in the absence and presence of catalysts. To increase the efficiency of the oxidation process, the SCWO of organic compounds in industrial wastewater was performed in the presence of various iron- and manganese-containing heterogeneous catalysts (Fe-Ac, Fe-OH, and Mn-Al). The catalytic and non-catalytic SCWO of organic compounds in wastewater from PJSC “Nizhnekamskneftekhim”, generated from the epoxidation of propylene with ethylbenzene hydroperoxide in the process of producing propylene oxide and styrene (PO/SM), was performed. The effect of operational parameters (temperature, pressure, residence time, type of catalysts, oxygen excess ratio, etc.) on the efficiency of the process of oxidation of organic compounds in the wastewater was studied. SCWO was studied in a flow reactor with induction heating under different temperatures (between 673.15 and 873.15 K) and at a pressure of 2...
OPA oxidation rates in supercritical water
Journal of Hazardous Materials, 2005
Supercritical water oxidation can effectively destroy a large variety of high-risk wastes resulting from munitions demilitarization and complex industrial chemical. An important design consideration in the development of supercritical water oxidation is the information on the oxidation rate. In this paper, the oxidation rate of isopropyl amine (OPA), one of high-risk wastes resulting from munitions demilitarization, was investigated under supercritical water oxidation (SCWO) conditions in an isothermal tubular reactor. H 2 O 2 was used as the oxidant. The reaction temperatures were ranged from 684 to 891 K and the residence times varied from 9 to 18 s at a fixed pressure of 25 MPa. The conversion of OPA was monitored by analyzing total organic carbon (TOC) on the liquid effluent samples. The initial TOC concentrations of OPA varied from 7.21 to 143.78 mmol/ at the conversion efficiencies from 88.94 to 99.98%. By taking into account the dependence of reaction rate on oxidant and TOC concentration, a global power-law rate expression was regressed from 38 OPA experimental data. The resulting pre-exponential factor was 2.46(±0.65) × 10 3 1.37 mmol −0.37 s −1 ; the activation energy was 64.12 ± 1.94 kJ/mol; and the reaction orders for OPA (based on TOC) and oxidant were 1.13 ± 0.02 and 0.24 ± 0.01, respectively.