Recovery of dinitrotoluenes and trinitrotoluene from spent acid of toluene nitration process by solvent extraction

Extraction using hexane or heptane solvent was employed to recover dinitrotoluene (DNT) isomers and 2,4,6-trinitrotoluene (TNT) from spent acid after toluene nitration process. Multiple stages experiments were conducted to elucidate the influence of various operating variables on the performance of removal of organic compounds from spent acid, including extracting temperature, volume ratio of solvent versus acid, spent sulfuric acid concentration and organic compounds content of the feedstock. It was found that organic compounds extracted reached nearly 78%, of which solubility in spent acid depends strongly upon the sulfuric acid concentration. In both cases of hexane and heptane, the extracting priority of organic compounds is in the following order: 2,3-DNT > 2,6-DNT > 3,4-DNT > 2,4-DNT > 2,4,6-TNT. Furthermore, this method established is promising for regeneration of spent acid preliminarily.