Revisiting kinetic parameter estimation in continuous flow reactors: time scale analysis and application to photocatalytically assisted water treatment

RONALD VARGAS; JORGE MARTÍNEZ - GARCÍA; ELENA SÁNCHEZ - BADORREY; MARÍA OJEDA

Congreso; IAHR, 38th World Congress; 2019

International Association for Hydro-Environment Engineering and Research

A proper characterization of the kinetic parameters representative of the water treatment processes is basic for their efficiency. Either chemical or biological in origin, many of these processes manifest a chemical kinetics consistent with rate laws (r = -dC/dt) based on a mathematical structure of the form: r = kKC / (1 + KC), where k and K depends on physicochemical parameters as pH and temperature, C is the reactant concentration and t is the reaction time. This is the case of the Langmuir-Hinshelwood kinetic model describing heterogeneous catalysis. The accuracy of the non-linear regression analysis commonly used to estimate the L-H parameters is often limited by: (i) the heterogeneity and/or low density of the experimental data and (ii) the intrinsic non-linearity of the method. Additionally, in continuous flow reactors where the time evolution of the reactant concentration is often measured in the mixer, the calculated parameters often underestimate the advective-transport corrections. In this work the parameter estimation of the L-H type kinetic models is revisited. By analyzing the natural time scales (NTS) of a general catalytic cycle, we present a method to extract accurate kinetic information based on the linear combination of functions where the weighted parameters were the time scales. The NTS of these phenomena are: (i) the fastest time to perform one run of the catalytic cycle, tfast=kK, and (ii) the slowest time it would take to chemically transform an initial amount of matter, tslow=C0/k. The NTS allows the computation of robust kinetics parameters using a simple linear regression. The benefits of the method have been demonstrated for the heterogeneous photocatalysis of naphthalene, with TiO2 as photocatalyst, in a tubular bench reactor (TBR). The results show that the distribution, density or extension in time of the experimental data does not introduce significant errors in the regression. The dependence of the NTS and the L-H kinetic parameters with irradiance, flow rate, flow regime and concentration of the organic compound has been also evaluated. Additionally, we quantify the hydraulic and advective-transport corrections to the k and K estimations by using a 3D high-resolution computational model of the TBR. The results clarify the relationship between the novel kinetic family concept (KF), the relevant photocatalytic processes and the physical variables that affect the chemical interaction. This work contributes to understand wastewater treatment techniques and apply to new challenges related to the environment, energy and life science.