Optimization of 4-chlorophenol regeneration from powdered activated carbon using response surface methodology

In this study, an experimental study aimed at optimizing the factors affecting the regeneration amount of 4-chlorophenol (4-CP) from spent powdered activated carbon (PAC) is presented. For this response surface methodology (RSM) with Box-Behnken design was applied, which identified four variables (acoustic density, NaOH concentration, spent PAC dosage and ethanol concentration) in batch experiments. The physicochemical characteristics of the regenerated PAC under the optimal desorption condition was evaluated using thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and scanning electron microscopy, as compared with the virgin and spent PACs. Among the four variables, acoustic density and ethanol concentration (v/v, %) had stronger effect on the 4-CP desorption (p < 0.001). The predicted optimal 4-CP desorbing amount was 97.43 mg g(-1), and this matched well the observed performance of (96.94 +/- 0.70) mg g(-1), obtained by acoustic density of 0.36 W mL(-1), NaOH concentration of 0.10 mol L-1, spent PAC dosage of 0.93 g L-1 and ethanol concentration (v/v) of 24%. The result of thermogravimetric pyrolysis profiles of regenerated PAC confirmed that the adsorption behavior of 4-CP exhibited a chemisorption feature and desorption process was dominated by chemical reaction. Analysis of FTIR, pore structure and BET surface area demonstrated that ultrasound mainly acted on the surface functionalities, macro-pore and meso-pore structure of PAC. Additionally, the SEM images indicated that cavitation effect affected the surface roughness and surface cavities of PAC. The results here provided an insight into the application of ultrasound to regenerate saturated PAC with 4-CP.