Methanol-enhanced degradation of carbon tetrachloride by alkaline activation of persulfate: Kinetic model

Abstract

Carbon tetrachloride (CT), a chlorinated organic compound widely used in the chemical industry during the 20th century, is nowadays a ubiquitous contaminant in groundwater and in situ technologies for its destruction are required. In this work, the degradation of CT by the alkaline activation of persulfate (PS) has been studied. Among the pool of radical species generated (hydroxyl radicals, sulfate radicals and superoxide radicals), O₂^∙- resulted to be the only species responsible for CT abatement. It has been found that the presence of other solvents less polar than water (hydrogen peroxide, acetone, propanol and methanol) improves CT degradation. Among them, methanol was selected as the most adequate co-solvent, leading to the complete elimination of CT (100 mg L^-1, 24 h) with a moderate unproductive consumption of the oxidant. The degradation of CT increased proportionally with the concentration of this solvent (from 0.1 to 10 g L^-1). The ratio NaOH:PS (from 1 to 8) did not affect the degradation of CT when working with a constant concentration of PS and highly alkaline conditions were maintained. The removal rate of CT increased as the concentration of PS increased (from 20 to 60 g L^-1), while the conversion of this pollutant did not depend on its initial concentration (from 10 to 100 mg L^-1). A kinetic model that considers the concentration of PS, MeOH and CT and can predict the concentration of CT with reaction time at different operating conditions, has been developed from the experimental data.

Keywords: Alkaline activation; Carbon tetrachloride; Kinetic model; Methanol; Persulfate; Superoxide radical.