Energy-saving Design for the Separation of Two Azeotropic Mixtures

In this thesis, energy-saving design for the separation of azeotropic mixtures will be discussed. For the separation of azeotropicmixture, tert-buyl alcohol (TBA) and water, there are several alternative designs, including heterogeneous azeotropic distillation, azeotropic dividing-wall column (A-DWC) and extractive distillation system, all are investigated in order to save the steam cost and the total annual cost (TAC). For the separation using heterogeneous azeotropic distillation, since large amount of the top vapor of the heterogeneous azeotropic column is requied to generate, more energy is needed for the reboiler.For the separation using A-DWC, the lower part of it can be treated as two stripping columns, compared to the original heterogeneous azeotropic distillation design, the condenser of the preconcentrator is removed and therefore energy carried by the top vapor is conserved, which resulting in lower capital cost and utility cost. Finally, extractive distillation system using glycerol as entrainer with a feed-effluent heat exchanger (FEHE) is considered to be the most economic design. For the separation of the n,n-dimethylacetamide (DMAC) and acetic acid (HAC), the process design of the pressure-swing distillation and extractive distillation is proposed. In addition to use the conventional entrainer triethylene glycol (TEG), using pure ionic liquid 1-butyl-3-methylimidazolium Bis [(trifluoromethyl) sulfonyl]-imide ([BMIM][TF2N]) and mixed entrainer ([BMIM][TF2N] and TEG) is investigated too. The result showed that the most promising method is the extractive distillation system using pure ionic liquid [BMIM][TF2N] as entrainer, and then is the extractive distillation system using the mixed entrainer ([BMIM][TF2N]：TEG=0.6：0.4). In summary, for a particular azeotropic mixture, there are more than one ways to achieve the separation task. However, significant savings on the steam cost and TAC can be achieved if the most suitable separation method can be selected.