Hydrothermal defluorination of fluorobenzene in the presence of sodium hydroxide

Abstract

Since fluorinated organic compounds are widely used in various industries, generating large amounts of waste, an effective disposal method is increasingly demanded. In this study, fluorobenzene (FB) as a model fluorinated compound was subjected to high-pressure liquid water in a small bomb-type batch reactor in the presence of alkaline additives under hydrothermal conditions. Defluorination proceeded under alkaline hydrothermal conditions, with NaOH or KOH as the most effective additives tested. The major products were fluoride ions and phenol recovered in the aqueous product solution. For example, 90% fluorine from FB in fluoride ion form and 90% of phenol were recovered in a 1.2 mol kg⁻¹ NaOH solution at 573 K for 120 min. The defluorination reaction was found to proceed via ipso substitution. The rate was expressed by second-order reaction kinetics with respect to concentrations of FB and OH⁻ with an activation energy of 113.4 kJ mol⁻¹ and a pre-exponential factor of 8.52 × 10¹² mol kg⁻¹ min⁻¹.