Removal of imidazolium- and pyridinium-based ionic liquids by Fenton oxidation

• Published in: Environmental science and pollution research international 2018-12, Vol.25 (35), p.34930-34937
• Main Authors: Gomez-Herrero, Esther, Tobajas, Montserrat, Polo, Alicia, Rodriguez, Juan J., Mohedano, Angel F.
• Format: Article
• Language: English
• Subjects: Advanced Oxidation Processes for Water/Wastewater Treatment; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Biodegradability; Biodegradation; Borates - chemistry; Carbon dioxide; Chains; Chemical oxygen demand; Chlorides; Conversion; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental Health; Environmental science; Free radicals; Hydrogen peroxide; Hydrogen Peroxide - chemistry; Hydroxylation; Imidazoles - chemistry; Ionic liquids; Ionic Liquids - chemistry; Ions; Iron - chemistry; Models, Chemical; Organic acids; Organic Chemicals; Oxidation; Oxidation process; Oxidation-Reduction; Pyridinium; Pyridinium Compounds - chemistry; Waste Water Technology; Water Management; Water Pollution Control
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1007/s11356-017-0867-4

The oxidation of imidazolium (1-hexyl-3-methylimidazolium chloride, HmimCl) and pyridinium (1-butyl-4-methylpyridinium chloride, BmpyrCl) ionic liquids (ILs) by Fenton’s reagent has been studied. Complete conversion was achieved for both ILs using the stoichiometric H 2 O 2 dose at 70 °C, reaching final TOC conversion values around 45 and 55% for HmimCl and BmpyrCl, respectively. The decrease in hydrogen peroxide dose to substoichiometric concentrations (20–80% stoichiometric dose) caused a decrease in TOC conversion and COD removal and the appearance of hydroxylated oxidation by-products. Working at these substoichiometric H 2 O 2 doses allowed the depiction of a possible degradation pathway for the oxidation of both imidazolium and pyridinium ILs. The first step of the oxidation process consisted in the hydroxylation of the ionic liquid by the attack of the ·OH radicals, followed by the ring-opening and the formation of short-chain organic acids, which could be partially oxidized up to CO 2 and H 2 O. At H 2 O 2 doses near stoichiometric values (80%), the resulting effluents showed non-ecotoxic behaviour and more biodegradable character (BOD 5 /COD ratio around 0.38 and 0.58 for HmimCl and BmpyrCl, respectively) due to the formation of short-chain organic acids. Graphical abstract ᅟ