A kinetic study for the Fenton and photo-Fenton paracetamol degradation in an annular photoreactor

Abstract

A kinetic model describing Fenton and photo-Fenton degradation of paracetamol (PCT) and consumption of hydrogen peroxide (H₂O₂) was proposed. A set of Fenton and photo-Fenton experiments (18 runs in total) was performed by fixing the initial concentration of PCT to 40 mg L^-1 and varying the initial concentrations of H₂O₂ and ferrous ion, Fe²⁺. The experimental set-up was a well-stirred annular photoreactor equipped with an actinic BL TL-DK 36 W/10 1SL lamp. Experimental results highlighted that PCT is no more detected by HPLC analysis within a minimum reaction time of 2.5 and a maximum reaction time of 15.0 min. Besides, a maximum conversion of total organic carbon (TOC) of 68.5% was observed after 75 min of reaction in case of using UV radiation and the highest concentrations of the Fenton reagents. The experimental data were used to fit the kinetic model. The radiation field inside the reactor was taken into account through the local volumetric rate of photon absorption, evaluated by assuming a line source model with spherical and isotropic emission. The kinetic parameters were estimated by using a non-linear least-squares regression procedure and root mean square errors (RMSE) were calculated in order to validate the feasibility of the proposed model. A good agreement between experimental and predicted data was observed and the lowest values of RMSE resulted in 5.84 and 9.59% for PCT and H₂O₂ normalized concentrations, respectively.

Keywords: AOPs; Annular photoreactor; Design of experiments; Kinetic modeling; LVRPA; Pharmaceuticals.

Fig. 1

Experimental set-up. a Schematic view. b Picture

Fig. 2

Methodological framework followed to estimate the parameters of the proposed kinetic model

Fig. 3

Normalized experimental concentrations of TOC, obtained under dark (□) and irradiated(■) conditions and considering the lowest and highest initial concentrations of Fe²⁺ and H₂O₂$(C_{{\mathrm{Fe}}^{2+}}^{\mathit{\text{to}}}$ and $C_{{\mathrm{H}}_2{\mathrm{O}}_2}^{t0}$): experiments E1 and E10 (a) and experiments E9 and E18 (b), respectively

Fig. 4

Specific consumption of the oxidizing agent as a function of the experiments performed with $C_{{\mathrm{Fe}}^{2+}}^{\mathit{\text{to}}}$ = 5 and 10 mg L⁻¹ and for the three different investigated values of $C_{{\mathrm{H}}_2{\mathrm{O}}_2}^{t0}$ (94.5, 189, 378 mg L⁻¹) under nonirradiated (striped bar chart) and irradiated conditions (solid bar chart)

Fig. 5

Experimental concentrations of paracetamol (○,●) and hydrogen peroxide (Δ,▲) and predicted (▬) and hydrogen peroxide (- -). Dark (○,Δ) and irradiated (●,▲) conditions. a Experiment E6 ($C_{{\mathrm{Fe}}^{2+}}^{\mathit{\text{to}}}$= 7.5 mg L⁻¹ and $C_{{\mathrm{H}}_2{\mathrm{O}}_2}^{t0}$ = 378 mg L−¹), and b experiment E18 $C_{{\mathrm{Fe}}^{2+}}^{\mathit{\text{to}}}$= 10 mg L⁻¹ and $C_{{\mathrm{H}}_2{\mathrm{O}}_2}^{t0}$ = 378 mg L⁻¹)