Photocatalytic Degradation of 4-chlorophenol in Water: a Kinetc Study

SATUF, M.L.; BRANDI, R.J.; CASSANO, A.E.; ALFANO, O.M.

Río de Janeiro, Brasil

Congreso; 2º Congreso de Ingeniería Química del Mercosur y 4º Congreso del Mercosur de Ingeniería de Sistemas y Procesos - ENPROMER 2005; 2005

Universidade Federal do Rio de Janeiro, Brazil

Keywords: 4-chlorophenol, detoxification, photocatalysis, titanium dioxide, kinetics. Chlorophenols are widely used in the chemical industry. In particular, 4-chlorophenol (4-CP) is involved in the synthesis and transformation of many drugs, pesticides and dyes. Due to their toxicity and resistance to biodegradation, they represent an important source of water pollution. Heterogeneous photocatalysis has emerged as an efficient method to degrade this kind of chlorinated aromatics. The main advantage of photocatalysis over traditional detoxification methods is that pollutants can be completely mineralized without leaving behind any hazardous residues. In this work, we study the degradation of 4-CP in aqueous solution using ultraviolet light and titanium dioxide in suspension. Experiments were carried out in a slurry reactor placed in the loop of a batch recycling system. Radiation was supplied by ultraviolet lamps situated on both sides of the reactor. A kinetic expression to model the degradation rate of 4-CP is proposed. This expression involves the evaluation of the radiation field inside the reactor. From the numerical solution of the radiation field, the local volumetric rate of photon absorption (LVRPA) can be calculated. The values of the LVRPA at each point inside the reactor are required to model the effect of radiation on the reaction rate. Experimental runs were performed at different levels of catalyst concentration, incident radiation and pH. The parameters involved in the proposed kinetic expression were estimated from the experimental data by means of a non-linear regression procedure. The quantum efficiency of the process as a function of pH was also evaluated. The kinetic expression shows explicitly the dependence of the reaction rate with the LVRPA and the catalyst concentration.