(150e) Toluenediamine Production Through Hydrogenation in Methanol Solvent

A feasibility analysis for a new toluenediamine (TDA) production plant was conducted. The production process selected for investigation was the hydrogenation of dinitrotoluene (DNT) in liquid methanol solvent over a nickel catalyst. The product TDA and reactant DNT have much higher boiling temperatures than the solvent methanol and byproduct water, and the boiling points of the reactants and products are too close to allow for sufficient separation. Therefore, the reactor must be sized sufficiently to achieve nearly complete conversion, as the reactant cannot be separated and recycled. Oligomerization of the DNT and TDA occurs at higher temperatures, generating high boiling tars that deactivate the catalyst and contaminate the product streams. Additionally, the thermal instability of DNT, as well as TDA, tars, and other nitrogen containing byproducts necessitate a temperature limit of approximately 350 F in any streams that could potentially contain the least stable component DNT. The composition of water in the product must be no greater than 0.1 weight percent. Two potential alternatives in distillation of the solvent and water from the products were apparent as a result of both a temperature and composition specification in the bottoms product. The first was a single column at high vacuum requiring refrigeration in the condenser, and the second was two separators with a column at atmospheric pressure using cooling water in the condenser before the vacuum column achieving the desired composition. The total annualized cost (TAC) for the single column was $6.361/10⁶, while the TAC for the double column system was less at $4.696/10⁶ due to reduced refrigeration costs. Health and safety hazards were considered in a process safety analysis that outlined concerns for implementing the process. A product price of $1.00 per pound of TDA was calculated to yield sufficient return on investment (ROI) of approximately 51.9% with a payback period of 1.9 years. Production of toluene diisocyanate (TDI) from toluenediamine was considered as the primary use, with an estimated price in 2016 of $1.459 per pound of TDI, validating the assigned price of intermediate TDA. The net present value of the project considering five years of operation after startup is $56.2 MM, or $129.3 MM over an operation lifetime of 14 years.