Design and Control of Dimethyl Carbonate-Methanol Separation via Extractive Distillation in the Dimethyl Carbonate Reactive-Distillation Process

Dimethyl carbonate is ail environmentally benign and biodegradable chemical. It can be produced by a transesterification reaction of methanol with ethylene carbonate, coproducing another useful product, ethylene glycol. A reactive distillation column can be utilized for the complete conversion of ethylene carbonate with methanol in excess. The coproduct, ethylene glycol, is the bottom product while the top product of this reactive distillation column is a mixture of dimethyl carbonate and methanol close to the azeotropic composition. In this paper, an economical separation process via extractive distillation is proposed to obtain pure dimethyl carbonate product and also pure methanol to be recycled to the reactive distillation column. A very simple procedure is proposed in this paper for the quick comparison of alternative entrainer candidates before rigorous process simulation is conducted. Aniline is found to be a very effective entrainer to enhance the relative volatility between methanol and dimethyl carbonate. A problem with small heavy-boiler impurities in the feed stream of the extractive distillation process is also pointed Out, with a practical Solution given for this problem. Simple overall control strategy of this process is also proposed to maintain product purity despite various feed disturbances. Only one tray temperature control loop is required for each of the columns.