Combining multivariate curve resolution and lumped kinetic modelling for the analysis of lignin degradation by copper-catalyzed Fenton-like systems

Abstract

Lignin degradation by Cu(II)-catalyzed Fenton-like systems was studied around neutral pH. Kinetic runs were carried out under dark conditions, at 60 °C and using Cu(II) concentrations below 0.1 mM. The surface response methodology was used to evaluate the effect of reaction conditions on the system behavior. The time required to achieve an absorbance reduction of 80% at 280 nm (t_80%) was used as a response variable. To further characterize the process, time-resolved UV-vis absorption spectra, TOC decrease, and H₂O₂ consumption were measured. Key spectral contributions and the main kinetic trends under different reaction conditions derived from multivariate curve resolution by alternating least squares (MCR-ALS) in combination with the corresponding TOC and H₂O₂ profiles were used to develop a pseudo-mechanism for lignin degradation. The numerical resolution of the kinetic model was used to fit, by nonlinear regression, the rate constants that better explain MCR-ALS data as well as both TOC and H₂O₂ profiles. Results show an efficient lignin mineralization at reasonable timescales, with the minimum t_80% being 60 min under the most effective conditions. In addition, the lumped kinetic mechanism based on MCR-ALS decomposition of UV-vis spectra properly reproduced the experimental trends and allowed a comprehensive analysis of the organic carbon evolution associated with both the residual lignin and potentially toxic aromatic intermediates. Moreover, the proposed modeling strategy is valuable for technical purposes since it predicts not only the overall treatment rates but also those conditions required to minimize the contribution of secondary reactions that lead to the inefficient consumption of H₂O₂.