Shrinking-core model for the photo-Fenton oxidation of polystyrene nanoplastics in water

DI LUCA, CARLA; GARCÍA, JORGE; ORTIZ, DAVID; MUNOZ, MACARENA; MARTÍNEZ DE PEDRO, ZAHARA; CASAS, JOSÉ A.

Buenos Aires

Congreso; 11th WORLD CONGRESS OF CHEMICAL ENGINEERING (WCCE11); 2023

Plastic debris, including micro and nano-sized particles, is considered a top environmental problem, and is recognized as an emerging concern that might affect human ability to preserve the availability of safe water supplies in the future. Even though the scale of the problem has driven a large number of scientific investigations, big knowledge gaps seem to linger on the development of both, specific degradation technologies for micro(nano)plastics in water and representative kinetic models1. Fluid-particle reactions are heterogeneous reactions in which a gas or liquids contacts a solid (B), reacts with it, and transform into products. In the shrinking core model, when no ash forms, the reacting particle shrinks during reaction from the surface to the core, finally disappearing2. Herein, the main objective of this work is to predict and describe the kinetics of the photo-Fenton oxidation of polystyrene (PS) nanoplastics in water. Figure 1 displays the preliminary results for the photo-Fenton oxidation of PS nanospheres (D = 140 nm) performed at: T = 25 ºC, t = 2.5 h, pH0 =3, [H2O2]0 =130 mg/L (5 doses, 1 every 0.5 h), [Fe3+]0 =10 mg/L, [PS]0 = 20 mg/L, 500 rpm and 200 W/m2 of irradiance. The reaction progress was monitored in terms of Total Organic Carbon (TOC) concentration and particle size changes by TEM analysis. After 90 min of reaction, the solids were completely converted (XB = 100%), reaching a mineralization level of c.a. XTOC = 90%. From Fig.1A, it can be seen that the reaction rate is controlled by film diffusion (FD), under the operating conditions tested. Figs.1B-C show the development of a particle size distribution, i.e. different conversion levels of PS, as the reaction advances. Further research is being performed in order to: i) address the influence of reaction temperature, PS particle size and stirring speed on the rate-controlling step; ii) characterize the removal mechanism and iii) develop a rate equation to predict and describe the advanced oxidation of PS nanoplastics in water.