Thermal abatement of nitrogen-containing hydrocarbons by non-catalytic supercritical water oxidation (SCWO) (original) (raw)
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Chemosphere, 2017
Supercritical water oxidation (SCWO) process of 14 N-containing compounds was investigated with residence time of 150 s, at a stable pressure of 24 MPa, temperatures of 350-500 o C and 500% excess oxygen, resulted in total nitrogen (TN) removal from 41-96%. The products of N-containing species were mainly N 2 , nitrate, ammonium, as well as hardly nitrite or NO X. The yield distributions of nitrate and ammonium were different: the main nitrate concentrations were obtained from the compounds containing nitro-group and diazonium, like nitrobenzene, 2-nitrophenol and eriochrome blue black R (EBBR); the predominant ammonium yields were achieved from amino-group and N-heterocyclic compounds, such as aniline, 5-chloro-2methylaniline, 3,4-dichloroaniline, 1-methylimidazole, 1,10-phenanthroline, cyanuric acid, indole and 2,3-indolinedione. It is interesting that 2-nitroaniline, possessing both nitro-and amino-group, would dominantly decompose into N 2. To explore the relationship between TN removal and molecular structural characteristics, density functional theory (DFT) method was used to calculate molecular descriptors of all 14 N-containing compounds. The correlation results showed that among all the fifteen molecular descriptors, q(C)-, q(C-H) + and F(0) x greatly affects temperature behavior of
Supercritical water oxidation of nitrogen compounds with multi-injection of oxygen
The Journal of Supercritical Fluids, 2013
A supercritical water oxidation (SCWO) process with oxidant multi-injection was studied in a continuous flow system in which the same amount of oxidant feed is split between two points -a first injection at the reactor inlet and a second injection at one of the three different positions along the reactor. Under the same operating conditions, this multi-injection configuration showed advantages over the system with a single oxidant entry. Moreover, oxidant dosage in a SCWO reactor is a key aspect in energy management.
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...
Industrial & Engineering Chemistry Research, 2000
Supercritical water oxidation (SCWO) has been shown to be an effective method for the treatment of industrial wastes. Organic compounds containing nitrogen are very usual in industrial wastes, and therefore, it is necessary to study the oxidation behavior of such compounds in order to improve the applicability of this technology to wastewaters and sludges. In this paper, oxidation parameters of several nitrogen-containing compounds in supercritical water such as aniline, acetonitrile, pyridine, and the intermediate stable compound ammonia are studied, using 2-propanol as auxiliary fuel. SCWO of feedstreams containing 2-propanol and the nitrogenous compound was carried out using a pilot-plant scale, based on a continuous-flow reactor system. Results show that for these compounds suitable conditions for SCWO are the following: reaction temperature in the range 600-700°C; stoichiometric amount of oxygen at residence time of 40 s. In these conditions, compound concentration in the effluent is below detection limits, TOC removal is greater than 99.97%, and N removal is greater than 97%.
Analysis of an elementary reaction mechanism for benzene oxidation in supercritical water
Proceedings of the Combustion Institute, 2000
A benzene supercritical water oxidation (SCWO) mechanism, based on published low-pressure benzene combustion mechanisms and submechanisms describing the oxidation of key intermediates, was developed and analyzed to determine the controlling reactions under SCWO conditions of 750-860 K, 139-278 bar, and equivalence ratios from 0.5 to 2.5. To adapt the combustion mechanisms to the lower temperature (Ͻ975 K) and higher pressure (Ͼ220 bar) conditions, new reaction pathways were added, and quantum Rice-Ramsperger-Kassel theory was used to calculate the rate coefficients and, hence, product selectivities for pressure-dependent reactions. The most important difference between the benzene oxidation mechanism for supercritical water conditions and those for combustion conditions is reactions in supercritical water involving C 6 H 5 OO predicted to be formed by C 6 H 5 reacting with O 2 . Through the adjustment of the rate coefficients of two thermal decomposition pathways of C 6 H 5 OO, whose values are unknown, the model accurately predicts the measured benzene and phenol concentration profiles at 813 K, 246 bar, stoichiometric oxygen, and 3-7 s residence time and reproduces the finding that the carbon dioxide concentration exceeds that of carbon monoxide at all reaction conditions and levels of benzene conversion. Comparison of the model predictions to benzene SCWO data measured at several different conditions reveals that the model qualitatively explains the trends of the data and gives good quantitative agreement without further adjustment of rate coefficients.
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%.
Journal of Hazardous Materials, 2011
Spray incineration and supercritical water oxidation (SCWO) processes have been used for detoxifying waste organic fluids in the University of Tokyo. In this study, we aim to elucidate the environmental aspects of these waste treatment processes by life cycle assessment (LCA). Through the investigation of actual plants, the inventory data and other characteristics of actual plants were collected and analyzed. To confirm the potential of SCWO, three modification types of the process and operation were considered and assessed on the basis of estimated inventory data. The results demonstrate that spray incineration has less environmental impact than SCWO in all scenarios. However, SCWO has various advantages for installation as a treatment process in universities such as negligible risk of creating dioxins and particulate matter. Proper choice of the treatment method for organic waste fluid requires a comprehensive analysis of risks. Spray incineration poses the risk of providing dioxins and particulate matter, while SCWO has such risk at negligible level. This means that waste including concerned materials related to such emission should be treated by SCWO. Using the right technologies for the right tasks in the detoxification of hazardous materials should be implemented for sustainable universities.