Selective Adsorption for Toluenediamine Recovery from TDA Tar through Surface Modification of Activated Carbon

Abstract

Toluenediamine (TDA) tar, as the heavy fraction from the dinitrotoluene hydrogenation to produce the important product of TDA, contains significant amounts of meta-TDA of 10 - 30 wt.% and is currently incinerated as waste at great cost. In this paper, the adsorption separation technology was adopt for the recovery of meta-TDA from TDA tar with some porous adsorbent materials. The activated carbon has the highest adsorption ratio for ethanol solution of meta-TDA. After treatment by HNO₃ or CH₃COOH, the modified activated carbon has the slightly decreased adsorption capacity for TDA tar of 238.8 mg·g^-1 or 243.3 mg·g^-1 with the meta-TDA selectivity of 96.36 % or 98.15 %. While the activated carbon modified by NaOH or NH₃·H₂O leads to the higher adsorption capacity of 287.9 mg·g^-1 or 261.2 mg·g^-1 for TDA tar with relative lower meta-TDA selectivity of 90.10 % or 96.02 %. The FT-IR and BET results confirm that surface oxygen-containing groups can be created through the acid or alkali modification, which result in enhancing the adsorption selectivity of meta-TDA. The proposed selective adsorption based on modified activated carbon would be an efficient and low-cost separation technology for TDA recovery from TDA tar.