Control structure selection of increased-pressure extractive distillation process for DMC-MeOH azeotropic mixture

Producing dimethyl carbonate (DMC) as a green chemical with the desired purity is important in the industry. Although studies on the steady-state design of energy-efficient extractive distillation processes are important for the purification of DMC-methanol (DMC-MeOH) azeotropic mixtures, the dynamic controllability of these processes is also critical in the case of feed condition changes, and it should be investigated carefully. Results of the limited studies in the literature show that changing the operating pressures in extractive distillation processes might have different effects on the dynamic controllability of different systems. Thus, in this study, alternative control strategies are developed for a recently proposed increased-pressure extractive distillation process to separate DMC-MeOH mixture. All control structures are designed using inferential temperature controllers, which have a general acceptance in industrial applications. Effects of different ratio controllers are investigated by evaluating the dynamic responses of control structures for disturbances in feed flowrate and composition. Two metrics including integral absolute error and steady-state deviation of purities are used in the evaluation of alternatives. Results of dynamic simulations show that a control structure including reflux ratio controller is not a suitable strategy for this process. It is demonstrated that a control structure including reflux to feed ratio controller for both distillation columns is necessary for the robust and efficient control of a pressure-increased extractive distillation process. These efficient dynamic results support the economic advantage of increased-pressure extractive distillation process separating DMC-MeOH azeotropic mixtures.