Development and workflow of a separation process for optimum design: A case of phenylenediamine

An industrial project based upon the multi-scale objective-oriented process development (MOPD) method for developing an optimum process for separating phenylenediamine (PDA) isomers was executed. This article reports the first four (4) steps of that project. In the first step, the solution for this separation problem was conceptualized. It is a distillation-crystallization-hybrid process. The second step is to validate the concept experimentally from the thermodynamic point of view followed by kinetic considerations. It was found that a 2-stage crystallization is required to purify the main product isomers to the desirable specification that is higher than 99.5 mol%. A heat and material balance model was then constructed for analyzing and optimizing various design variables, also used to understand the operability of the process. Finally, with proper HAZOP analysis and detailed engineering, the pilot unit was designed. Throughout the project, all exercises and efforts are well focused with clear objectives, hence there are minimum detours on the execution; furthermore, the clear objectives enhanced the communications among various disciplines tremendously. It is a valuable asset for senior management in the allocation of resources and budgets.