Analysis of an elementary reaction mechanism for benzene oxidation in supercritical water

Abstract

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.

Application of an adsorptive-thermocatalytic process for BTX removal from polluted air flow

“…Faulty mineralization or incomplete decomposition of BTX compounds, for example benzene, may lead to production of the compounds such as Phenyl, Oxy phenyl, Dioxy phenyl and Hydroxy phenyl in the initial stages of decomposition. With the subsequent decompositions, they are converted to other organic compounds and eventually when it completely oxidized turns into CO 2 and water [ 33 , 34 ]. With these results and results of BTX mineralization in different pollution loading rates (see Figure 5 b) it can be stated that, the retention time and flow rate were more effective than the pollution loading, due to higher concentration, on the mineralization of the BTX.…”

Review on Mechanisms and Kinetics for Supercritical Water Oxidation Processes

“…Although Yong and Matsunura [100,101] deduced the reaction pathway of benzene decomposition in SCWG that benzene formed phenol and gas, directly or through naphthalene as an intermediate medium, into char and other liquid products, and mainly transformed to phenol under the oxygen-rich condition in SCWO. Dinaro et al [102] [32].…”

“…However, the SCWO reaction process is similar to the gas-phase combustion process in some free radical reactions, and gas-phase combustion has developed numerous DCKMs of organics. Currently, some scholars have developed DCKMs of various compounds based on gas-phase combustion [31,66,72,102,[116][117][118][119][120][121][122][123][124][125][126]. The goal of this section is not to summarize these studies, but to analyze the development and simplification treatment of DCKMs for hydrogen, methanol, acetic acid, benzene and ammonia.…”

Review on an Advanced Combustion Technology: Supercritical Hydrothermal Combustion

“…Without any adjustment of experiment-based parameters, the predicted accuracy of the model was encouraging. On the basis of the detailed gas-phase combustion mechanism of benzene, Dinaro et al realized the accurate prediction of the concentration distribution of benzene and phenol under the condition at 813 K and 24.6 MPa by supplementing the new reaction pathway of C 6 H 5 OO [89]. Queiroz et al modified the kinetic parameters of the overall reaction kinetic model of isopropanol combustion by comparing the axial temperature curves obtained from previous experiments of isopropanol hydrothermal combustion, and thus well reproduced experimental results [34].…”