Eletrorefinaria de produtos de alto valor agregado a partir da oxidação eletroquímica da lignina: hidrogênio verde, ácidos carboxílicos e ácido vanílico

Abstract

A growing concern for issues related to environmental impacts has intensified the search for technologies in effluent remediation, renewable energies, and sustainable sources of chemical precursors. Electrochemical oxidation for promoting the reforming of organic effluents can be an alternative for obtaining high-value industrial chemical reagents. The main challenges are associated with the high energy cost of oxidative remediation processes, which can be minimized with renewable energy sources such as wind and photovoltaic. In this research, a reactor with a divided flow by an anionic ion exchange membrane was used, separating the anodic and cathodic compartments. As anodic electrodes, the following were used: Nb/BDD (Niobium/Boron-Doped Diamond) and DSA® (Ti/TiO2, RuO2, and IrO2), with a Ni-Fe mesh (Nickel-Iron) as the cathode, were used for remediating synthetic lignin effluents (a residue from the production process). The oxidative cleavage of lignin resulted in the generation of carboxylic acids in the anodic compartment and green hydrogen in the cathodic compartment. Using a BDD electrode, the best results were achieved with the following concentrations under experimental conditions of 0.5 mol L-1 NaOH and J=100 mAcm-2: oxalic acid 86.03 mgL-1, acetic acid 15.67 mg L-1, formic acid 8.64 mg L-1, and vanillic acid 0.6795 mg L-1. With a DSA electrode, electrode coupled to an electrodialysis separation system, the best results were observed: malonic acid 1800 mg L-1, oxalic acid 27 mg L-1, formic acid 0.4 mg L-1 and acetic acid 2.3 mg L-1. The electrodialysis system proved to be efficient in concentrating the acids produced, with efficiency ranging from 45 to 95%. The best results in relation to green hydrogen production were: 2.59 L in experiments with BDD anode under experimental conditions (1 mol L-1 NaOH and J = 100 mAcm-2) and 2.93 L in experiments with DSA anode, under experimental conditions (0.5 mol L-1 NaOH and J = 100 mAcm-2). In this context, the results obtained show that promoting electrorefinery in lignin-based effluents is a viable alternative for obtaining value-added products, such as carboxylic acids widely used in industry and green hydrogen.