Decomposition of dinitrotoluene isomers and 2,4,6-trinitrotoluene in spent acid from toluene nitration process by ozonation and photo-ozonation

Ozone and UV/O3 were employed to mineralize dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) in spent acid from toluene nitration process. The oxidative degradation tests were carried out to elucidate the influence of various operating variables on the performance of mineralization of total organic compounds (TOC) in spent acid, including reaction temperature, intensity of UV (254 nm) irradiation, dosage of ozone and concentration of sulfuric acid. It is remarkable that the nearly complete mineralization of organic compounds can be achieved by ozonation combined with UV irradiation. Nevertheless, the hydroxyl radicals (OH) would not be generated by either ozone decomposition or photolysis of ozone under the experimental condition of this study. According to the spectra identified by gas chromatograph/mass spectrometer (GC/MS) and further confirmed by gas chromatograph/flame ionization detector (GC/FID), the multiple oxidation pathways of DNT isomers are given, which include o-, m-, p-mononitrotoluene (MNT) and 1,3-dinitrobenzene, respectively. In addition, oxidative degradation of 2,4,6-TNT leads to a 1,3,5-trinitrobenzene intermediate.