Treatment of chlorophenols-bearing wastewaters through hydrodechlorination using Pd/activated carbon catalysts

The catalytic hydrodechlorination of 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol in aqueous solution over Pd/ activated carbon catalysts (0.5% w/w Pd) was studied in a fixed bed reactor. The reactor was fed with a 100 mg/l solution of chlorophenol and a H-2/N-2 (1:1) gas stream. The ranges studied for temperature, pressure and space-time were 25-100 degreesC, 1.8-6.0 bar and 14-55 kg h/mol, respectively. A commercial and some home-made catalysts were tested. The carbon supports were subjected to oxidation with nitric acid and sodium persulfate. Chlorophenols conversion was found to peak for pressure values approximate to2.4 bar. In these conditions, an increase of reaction temperature increases conversion. In the runs carried out at high space-time both the reactants conversion and the selectivity towards end chain reaction products was enhanced. The oxidation of the carbon support with nitric acid prior to impregnation improves conversion. At the optimum conditions (2.4 bar, 75 degreesC and nitric acid oxidation of carbon support) conversion values over 95% were reached for all chlorophenols. As a result of this treatment the toxicity of the initial solutions was reduced by more than 90%. (C) 2004 Elsevier Ltd. All rights reserved.