Degradation mechanisms of organic compounds in molten hydroxide salts: a radical reaction yielding H(2) and graphite

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 O(2) and formation of H(2)O and CO(2). 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 H(2) without CO(2) 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 H(2), which opens a new way of recycling plastic residues.