Dimethyl carbonate (DMC) and methanol (MeOH) form a binary minimum-boiling homogeneous azeotrope, and thus conventional distillation cannot achieve complete separation. The extractive distillation (ED) with o-xylene as a heavy entrainer in our recent work possesses significant energy saving and achieves a high purity of 99.9% DMC compared with the pressure-swing distillation (PSD). For a fair comparison, both ED and PSD were evaluated against the same minimum product specifications (DMC ≥ 99.5 wt% and MeOH ≥ 98.0 wt%), noting that the recovered MeOH stream was recycled to the reactive distillation column rather than treated as a final product. However, the dynamic performance of this ED is still unclear, and all the benefits of the ED are reasonable only under good dynamic controllability. In this work, the dynamic controllability of the ED process was compared with that of the PSD one. Both processes were evaluated under a unified temperature-control philosophy, including conventional fixed R. Closed-loop dynamic simulations were performed under ±10% step disturbances in feed flowrate and composition. It was revealed that under the tested disturbances, DMC purity was maintained close to the high-purity target (≈99.9 wt%) in the ED process, whereas larger deviations and a lower attainable DMC purity were obtained in PSD. The results provide a control-oriented basis for the selection and further development of special distillation schemes for MeOH/DMC azeotropic separation.
Sui et al. (Tue,) studied this question.