Recovery of high purity 2,4-dinitrotoluene from spent mixed acid in toluene nitration process

Two easy practical methods for recovery of high purity 2,4-dinitrotoluene (DNT) from spent mixed acid in toluene nitration process are established. One is the dilution manner which produces high purity crystal of 2,4-DNT (>99 wt.%) by addition of proper amounts of deionized water into the spent mixed acid. The other is a refrigeration method which also evaluates high purity crystal of 2,4-DNT (>98 wt.%) by means of simply cooling down spent mixed acid below 283 K. According to the analysis of gas chromatograph-mass spectrometer (GC-MS), the ingredients of crystals were identified. Further, the influence of dilution procedure, refrigeration treatment, and adjustment of pH value on the performance of abatement of total organic compounds (TOC) were elucidated in this research. It was found that the organic compounds dissolving in aqueous spent mixed acid are in equilibrium with the organic phase of dinitrotoluene isomers. Besides, the solubility of each organic component in spent acid depends upon the concentration of spent sulfuric acid.