Abstract
The non-catalytic supercritical water oxidation (SCWO) of phenol was modeled using Gopalan-Savage and Thornton-Savage global and network rates. Comparison of experimental data for the phenol conversion with the numerical predictions of this study indicated very close compatibility. Applying the validated model, the phenol conversion and selectivity of various products were studied as a function of effective parameters such as feed phenol concentration, reactor residence time, feed temperature, and feed oxygen concentration. The results of modeling analysis show that an appropriate elevated temperature range (460°C < T <500°C) and long residence time (≈90 s) reduce the concentration of hazardous products (i.e., dimers, dibenzofuran, dibenzo-p-dioxin) and maximize the selectivity of environmental benign products such as water and carbon dioxide. Also, high oxygen concentration (≈0.01 mol/L) increase water and carbon dioxide yield. Moreover, high feed phenol concentrations cause a shortcoming for the SCWO system in terms of phenol conversion and selectivity of desirable environmental products. As a consequence, the feed phenol concentration of ≤2 × 10−3 mol/L is recommended as the appropriate condition.
Acknowledgements
The financial support provided for this project by Isfahan University of Technology (IUT) is gratefully acknowledged.
Nomenclature
| A | M0.58-a-b.s−1 | pre-frequency factor |
| CA | mol/m3 | reactant concentration |
| [CA o] | mol/m3 | feed reactant concentration |
| CP,H2O | kJ/mol.°C | constant pressure heat capacity for water |
| D | m | reactor diameter |
| Ea | kJ/mol | activation energy |
| Ft | mol/s | feed molar flow rate |
| G | g/s.m2 | mass velocity |
| hw | kJ/s.m2. °C | convective heat transfer coefficient |
| ΔH | kJ/mol | enthalpy change |
| K | s−1(mol/lit)1-n | rate constant |
| i | (-) | Number of reaction |
| L | m | reactor length |
| NPec | (-) | Peclet number (uIL/Dz) |
| P | bar | pressure |
| mol/m3.s | rate of reaction of component A per unit volume | |
| rPhenol | mol/m3.s | global rate reaction |
| T | °C | temperature |
| u | m/s | interstitial fluid velocity |
| U | W/m2.k | overall heat transfer |
| V | m3 | reactor volume |
| x | (-) | conversion |
| z | m | reactor axial dimension |
| (-) | experimental data | |
| (-) | model predicted data | |
| (-) | average of the experimental data |
| Greek letters | ||
| ρ | kg/m3 | fluid density |
| ρp | kg/m3 | particle density |
| μ | kg/m.s | fluid viscosity |
| (-) | stoichiometric coefficient of A in each reaction | |
| τ | (s) | residence time |
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