Separation of close-boiling mixtures by conventional distillation consumes a large amount of energy because of the very high reflux ratio required. Mechanical vapor recompression heat pumps (MVRHPs) can recycle the energy of the vapor and can thus be used in such distillation processes to save energy. Three different distillation schemes, namely, conventional distillation, top MVRHP distillation, and bottom-flashing MVRHP distillation, were simulated for the separation of the closeboiling mixture of n-butanol and isobutanol using Aspen Plus to determine the economically best option. The research results indicate that, compared to conventional distillation, the energy savings for bottom-flashing MVRHP distillation and top MVRHP distillation can reach 67.92% and 72.92%, respectively, and the TACs correspondingly decrease by 71.74% and 75.57%.

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A coupled separation system involving a mechanical vapor recompression heat pump (MVRHP) and double-effect distillation (MED) was proposed. In a case of separating N,N-dimethylacetamide (DMAC)/water mixture, four distillation schemes (i.e., conventional distillation, top MVRHP distillation, double-effect distillation, and double-effect distillation with double MVRHP) were conceptually constructed and simulated by using Aspen Plus with the binary interaction parameters of the NRTL thermodynamic model. We evaluated these four schemes to choose the best one with the goal of the minimum total annual cost (TAC). Compared to the conventional distillation, the TACs for double-effect distillation with double MVRHPs, top MVRHP distillation, and double-effect distillation were decreased by 47.76, 32.23, and 5.45%, respectively. It indicates that the double-effect distillation with double MVRHPs has obvious advantages over the other three distillation schemes in terms of economic efficiency.