Eletrooxidação de resíduos reais como estratégia simultânea para produção de compostos de alto valor agregado: ácidos carboxílicos e hidrogênio verde

Abstract

With the increase in population, we see emerging new challenges in various sectors of society. This scenario of change has given rise to the 2030 Agenda, which addresses the goals of sustainable development. Issues such as the increase in domestic effluents, growing food demands, and the consequent rise in industrial waste, including various biomasses, as well as the use of fossil fuels, stand out as significant environmental challenges that require more sustainable solutions for the future. In this context, the electro-refinery emerges as an attractive proposal to tackle these problems. By employing clean energy, it enables the conversion of materials considered waste into value-added products. Thus, this work aims to transform real domestic effluent, in this case, the wash water from a washing machine, and an industrial residue, the liquid from cashew nut-shell, into value-added products, such as carboxylic acids, while simultaneously cogenerating green hydrogen. Cells divided by polymeric electrolyte membranes, both Proton Exchange Membrane (PEM) and Anion Exchange Membrane (AEM), were used, with BDD/Nb electrodes as anode and Ni-Fe stainless steel mesh as cathode. In the treatment of washing machine effluent, two different electrolytes (0.1 mol L-1 H2SO4 and 0.1 mol L-1 Na2SO4) were tested, also varying the current densities (7.5, 15, 30, and 60 mA cm-2). The results reveal the production of high-value-added products, especially carboxylic acids, with emphasis on the selectivity to acetic acid, reaching 45.7 mg L-1. Furthermore, the generation of green H2 was observed, with approximate volumes of 0.8 L after 150 minutes. When using the liquid from cashew nut-shell, different conditions were explored, such as current density (40, 70, and 100 mA cm-2), electrolyte concentration and nature (0.125, 1.0, and 2.0 mol L-1 NaOH and 0.05 mol L-1 Na2SO4), and substrate concentration (0.01, 0.05, and 0.1% v/v). It was found that all variables influence the production of carboxylic acids and the energy efficiency of green H2, with substrate concentration being the most significant variable in acid production and current density in green H2 production. As substrate concentration increases, it was possible to achieve acetic acid production rates of 565.4 mg L-1, and at higher current densities, green H2 volumes of 1.8 L were observed after 240 min. Thus, the viability of electrorefinery-based technology is evidenced by the selective electrochemical transformation of organic pollutants from waste into value-added products, such as green H2 and carboxylic acids. This advancement represents a promising step towards a circular economy, contributing to environmental sustainability