Separation and Purification Technology 67 (2009) 158–165 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Modeling of a pilot-scale trickle bed reactor for the catalytic oxidation of phenol Qiang Wu a , Xijun Hu a,∗ , Po Lock Yue a , Jian Feng b , Xi Chen b , Huiping Zhang c , Shizhang Qiao d a Department of Chemical Engineering, Hong Kong University of Science & Technology, Hong Kong, China b Department of Control Science & Engineering, Zhejiang University, Hangzhou 310027, China c School of Chemical and Energy Engineering, South China University of Technology, Guangzhou 510640, China d ARC Centre for Functional Nanomaterials, University of Queensland, Brisbane QLD 4072, Australia article info Keywords: Modeling Trickle bed reactor Mass transfer Wet air oxidation Copper/activated carbon catalyst abstract A mathematical model was developed to simulate the catalytic wet air oxidation (CWAO) of aqueous phenol in a trickle bed reactor (TBR). Both ‘axial dispersion’ and ‘plug flow’ models were proposed. ‘Steady-state’ mass transfers across different phases inside the reactor have all been considered in parallel with oxidation reactions catalyzed by heterogeneous copper catalyst supported on activated carbon. The changes in the concentrations of oxygen and phenol in various phases were thus depicted as a function of bed length. In order to validate the accuracy of the established TBR model, a series of experiments on phenol oxidation were performed on a pilot-scale TBR containing 5.6l of catalysts. The model was found able to give satisfactory predictions for nearly half of all the runs. The discrepancies between the experimental and modeling results were investigated for the less promising runs. It was also noticed that similar simulation results could be attained from ‘axial dispersion’ model against ‘plug flow’ model. Following the discussion on the changes of phenol and oxygen concentrations in the various phases, it is finally concluded that the performance of the TBR of this study depends largely on gas-to-liquid mass transfer process. Further suggestions with regards to reactor optimization are also proposed on the basis of experimental outcome. © 2009 Elsevier B.V. All rights reserved. 1. Introduction To detoxify highly polluted industrial wastewater of low biodegradability, over the past decades, a number of studies have been given to the application of wet air oxidation (WAO) tech- nique for wastewater treatment, as reviewed by Mishra et al. [1]. WAO refers to the process in which liquid pollutants are oxi- dized by oxygen at elevated temperature (125–320 ◦ C) and pressure (0.5–20 MPa). It is advantageous over conventional biological meth- ods in the respect that high concentration non-biodegradable toxic substances can be degraded with high efficiency. Nevertheless, the operational cost of a typical WAO is tremendously high, owing to the need to escalate system pressure and temperature. In view of this, more recently, researchers have been focusing on the devel- opment of a certain catalyst by which the same goal of oxidizing organic pollutants can be achieved at mild pressure and temper- ature. These attempts give rise to the catalytic wet air oxidation (CWAO) process [2–18]. ∗ Corresponding author. Tel.: +852 23587134; fax: +852 23580054. E-mail address: kexhu@ust.hk (X. Hu). CWAO process can be conducted either in a batch or in a contin- uous reactor, the latter of which attracts more attention due to its more operational convenience and treatment flexibility. Trickle bed reactor (TBR) is one of the ideal continuous reactor options and the mathematical simulation of a CWAO process taking place in TBR has been widely conducted. Some of the major findings in this regard have been summarized in the following. On the basis of their studies on the mass transfer coefficients of gas-to-liquid and liquid-to-solid processes in TBR, Goto and Smith [19] established both ‘axial dispersion’ and ‘plug flow’ models to predict the conversion rate of oxidizing formic acid by oxygen at temperatures of 212–240 ◦ C and pressure of 40 atm. The discrep- ancies between the two models were found negligible and the modeling results were in accordance with experimental data. This work concluded that, in term of their effects on the conversion rate, four mass transfer resistances are listed from the most to the least significance: gas-to-liquid mass transfer, intra-particle diffu- sion, liquid-to-solid (particle) mass transfer and axial dispersion. Bergault et al. [20] also observed that the hydrogenation of ace- tophenone in a TBR is much more sensitive to the mass transfer of gas-to-liquid than that of liquid-to-solid. The reviews conducted by Al-Dahhan et al. [21] and Wu et al. [22] further suggested that the incomplete wetting should also be taken into account as one 1383-5866/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2009.03.021