Toluene Diamine (TDA) is produced by hydrogenating Dinitrotoluene (DNT) over Palladium catalyst in an isopropyl alcohol (IPA) solvent in an agitated, semi-batch reactor. The "crude" TDA product from the reactor is filtered to remove catalyst and then processed through a distillation train to recover the solvent, remove water, remove heavy "tars", and separate out the ortho-isomer. (The ortho-isomer causes by-product formation in the downstream TDI process.)
Each reactor batch is charged with solvent and catalyst, which is comprised of palladium on a powdered carbon substrate. Once the solvent and catalyst are charged, the reactor is pressured up with hydrogen. When operating pressure is reached, DNT is fed to the reactor until the batch is full. After the reaction is complete, the batch is transferred to a buffer tank for continuous feed to the filtration system and distillation train.
The crude TDA is sent through three sets of filters - a plate and frame filter, a sintered metal filter, and a cartridge filter. The filtered TDA is directed to the IPA column, whcih runs at atmospheric pressure, to recover the solvent overhead. The bottoms of the IPA column are sent to the 1st Water Column, another atmospheric column, for overhead water removal. The bottoms of the 1st Water Column are routed to the 2nd Water Column, which operates under a signifcant vacuum to remove all remaining water overhead. The 2nd Water Column bottoms are transferred to the Diamine Still, a large steam-jacketed flash vessel. The TDA is taken overhead here and routed to the Ortho-Isomer Column. The Diamine Still bottoms are routed to the Tar Stills where the final portion of TDA is removed overhead and the heavy "tars" are sent to a storage tank for incineration. The Ortho-Isomer Column takes the Diamine Still and Tar Still overheads and, under a deep vacuum, separates the TDA ortho-isomer overhead. The final TDA product is the bottoms stream of the column.