Thermal effect of carboxylic acids in the degradation by photo-Fenton of high concentrations of ethylene glycol

The degradation by Fenton and photo-Fenton of high concentrations of ethylene glycol (1000–25,000 mg/L), similar to those found in wastewater has been studied. Strongly exothermic reactions led to temperature increments up to 70–94 °C. In most experiments, temperature increments favored radical formation that provided almost complete mineralization. Oxalic, formic and acetic acids were identified as degradation intermediates. The obtained results indicate that the radicals formed in the degradation of formic and acetic acids with H2O2 were responsible for the exothermic reactions. Nonetheless, Fe–oxalic complexes inhibited the previous reactions by slowing down the process in such a way that complete mineralization did not occur until those complexes were degraded.FTIR studies allowed the identification of some of the complexes and species formed in the process.

. Photo-Fenton degradation of 11,600 ppm of ethylene glycol (as TOC ■). Evolution of: intermediates (as carbon concentration) ( formic, oxalic and acetic acid) and temperature (♢). [H2O2] = 120 g/L, [Fe2+] = 200 ppm.Figure optionsDownload as PowerPoint slideFigure optionsDownload as PowerPoint slideFigure optionsDownload as PowerPoint slideFigure optionsDownload as PowerPoint slideHighlights
► Highly concentrated ethylene glycol was mineralized in minutes.
► Some reaction intermediates produced highly exothermic reactions.
► Fe–oxalate complexes slow down the process.
► The temperature rise is responsible for the mineralization achieved.