兩類共沸混合物分離之節能設計

Abstract

本文探討各類共沸混合物分離之節能設計流程。首先討論共沸物質三級丁醇(tert-butyl alcohol,TBA)和水之各種分離設計流程，包括非均勻相共沸蒸餾(heterogeneous azeotropic distillation)、共沸隔牆塔(azeotropic dividing-wall column)與萃取蒸餾 (extractivedistillation)系統，並透過熱整合的方式節能。若採用非均勻相共沸蒸餾系統，則非均勻共沸蒸餾塔塔頂需產生高流率的汽相出流，造成該塔再沸器之高能秏。若採用共沸隔牆塔系統，隔牆塔的下半部分可視為兩根氣堤塔，故與原來之非均勻相共沸蒸餾系統比較，預濃縮塔的冷凝器被移除，節省了原來冷凝其汽相流所需的能秏及冷凝器之設備成本 (capital cost)。最後發現以甘油 (glycerol)作為萃取劑 (entrainer) 之萃取蒸餾系統，並加上一進料/出流熱交換器(feed-effluent heat exchanger, FEHE) 進行熱整合之設計流程最具經濟效益。 本文亦針對二甲基乙醯胺 (n,n-dimethylacetamide, DMAC) 與醋酸 (acetic acid, HAC)共沸系統的各種分離方法，討論以變壓蒸餾 (pressure swing distillation)、萃取蒸餾系統之程序設計。其中萃取蒸餾系統，除了討論採用傳統有機溶劑三甘醇 (triethylene glyceol, TEG) 作為萃取劑的系統外，也會對分別以純離子液體 (ionic liquid) 1-butyl-3-methylimidazolium Bis [(trifluoromethyl) sulfonyl]-imide ([BMIM][TF2N]) 以及混合溶劑 ([BMIM][TF2N]和TEG) 作為萃取劑的系統進行探討。結果發現以純離子液體[BMIM][TF2N] 作為萃取劑之萃取蒸餾系統最為節能，其次則為以混合溶劑 ([BMIM][TF2N] 和TEG) 作為萃取劑之萃取蒸餾系統。 藉由討論上述之兩個共沸物之節能設計流程，能發現儘管對於特定的混合物系統可以用不只一種方式來完成分離，但若是能夠選擇使用最適合之分離方式則可以大幅節省蒸汽費用與年度總成本。

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.