Degradation mechanisms of organic compounds in molten hydroxide salts: a radical reaction yielding H2 and graphite

• Published in: RSC advances Vol. 13; no. 29; pp. 19955 - 19964
• Main Authors: Lecomte, Florent, Ana Gabriela Porras Guiterrez, Huvé, Marielle, Moissette, Alain, Sicoli, Giuseppe, Rollet, Anne-Laure, Daviero-Minaud, Sylvie
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 04.07.2023; The Royal Society of Chemistry
• Subjects: Carbon dioxide; Carbonates; Carboxylic acids; Chemical Sciences; Chemistry; Degradation; Graphite; Hazardous materials; Hazardous wastes; Hydroxides; Molten salts; Neoprene; Organic compounds; Oxidation; Reaction products; Recycling; Residues
• ISSN: 2046-2069
• DOI: 10.1039/d3ra02537c

Molten salts are used in various waste treatments, such as recycling, recovery or making inert. Here, we present a study of the degradation mechanisms of organic compounds in molten hydroxide salts. Molten salt oxidation (MSO) using carbonates, hydroxides and chlorides is known for the treatment of hazardous waste, organic material or metal recovery. This process is described as an oxidation reaction due to the consumption of O2 and formation of H2O and CO2. We have treated various organic products, carboxylic acids, polyethylene and neoprene with molten hydroxides at 400 °C. However, the reaction products obtained in these salts, especially carbon graphite and H2 without CO2 emission, challenges the previous mechanisms described for the MSO process. Combining several analyses of the solid residues and the gas produced during the reaction of organic compounds in molten hydroxides (NaOH–KOH), we demonstrate that these mechanisms are radical-based instead of oxidative. We also show that the obtained end products are highly recoverable graphite and H2, which opens a new way of recycling plastic residues.