- 學位論文
複合式萃取-蒸餾系統之共沸混合物分離的節能設計與控制
Design and Control of Azeotropic Separation by Energy-Saving Hybrid Extraction-Distillation System
摘要
本文探討複合式萃取-蒸餾系統應用於共沸混合物之節能設計與控制，與其它分離方法相比 (如共沸蒸餾、萃取蒸餾以及變壓蒸餾)，溶劑萃取仍然是最優選的分離方法之一，它的特點在於分離原理是透過物質在不同溶劑中溶解度的差異，藉由選擇合適的溶劑使得溶液呈現不互溶之兩相液體，因此主要分離過程可以通過萃取塔來進行而無須消耗額外的能源，為該系統帶來巨大的經濟潛力。本文共介紹了兩類共沸混合物系統進行分析與討論，包括乙醇/苯以及四氟丙醇/水之系統，此二程序使用之熱力學模型不僅滿足三成分液-液平衡線之實驗數據，同時也能完整地預測出雙成分氣-液平衡之行為，顯示出其模擬程序之可信度。 在乙醇/苯之分離系統中選用甘油作為重溶劑，經由液-液平衡原理將溶液中之乙醇提取出來，由於萃取相必定殘留些許的苯，且乙醇並非為該蒸餾區域中之穩定節點，因此可延伸出兩種蒸餾序列，以獲得符合純度規格之乙醇與回收甘油以便重複使用，除此之外也考慮到重溶劑之特性，引入程序熱整合與真空系統於製程中，進一步降低整體之操作成本，而在品質控制上則是基於開環靈敏度測試與閉環靈敏度測試的結果，提出無須濃度控制器之整廠控制架構，並證實在此控制策略上可有效地排除進料干擾，維持兩產品之設計規格。 本文也針對四氟丙醇/水系統，探討以甲基叔丁基醚 (MTBE) 以及異丙醚 (DIPE) 作為輕溶劑之分離程序，藉由溶劑的夾帶將四氟丙醇引入至萃取相，而高純度的水則由萃餘相中離開，充分運用兩相之間的不互溶性來突破蒸餾邊界的限制，同時也考量到液-液萃取可行之密度差進行完整的經濟分析，除此之外，為了得到更加嚴謹之動態響應，利用分相槽之串聯設計模擬萃取塔單元，實現以壓力驅動模組進行動態討論，並分析流量驅動模組與壓力驅動模組之暫態響應，進一步探索複合式萃取-蒸餾系統之動態視野。
並列摘要
Design and control of azeotropic mixture separation process by energy-saving hybrid extraction-distillation system was investigated in this thesis. Compared with other separation methods (i.e., azeotropic distillation, extractive distillation and pressure-swing distillation), solvent extraction remains to be one of the most preferable separation methods because the separation is achieved through their relative solubilities in two different immiscible liquid phases without energy usage. Thus, by utilizing a hybrid extraction-distillation separation process, huge economic potential is expectable with the finding of an effective solvent. In this work, two kinds of azeotropic mixture systems were analyzed and discussed, including ethanol/benzene and 2,2,3,3-tetrafluoro-1-propanol/water systems. The thermodynamic models used in both processes not only satisfy the experimental data of ternary liquid−liquid equilibrium, but also precisely predict the behavior of binary vapor-liquid equilibrium, showing the credibility of the simulated processes. In the ethanol/benzene separation system, glycerol was selected as a heavy solvent, which is used to extract ethanol from benzene by the principle of liquid-liquid equilibrium. Since the extract phase inevitably contains some residual benzene and besides, ethanol is not a stable node in the operating distillation region, two alternative distillation sequences was proposed to obtain ethanol product at the purity specification and also purified glycerol for recycling back to the extraction column. Considering the nature of the heavy solvent, heat integration within process streams and operation in vacuum condition were taken into account for the design of the energy-saving cases. Furthermore, the quality control loops were established based on the results of open-loop and closed-loop sensitivity tests without the need of any online composition measurement. It was found that both ethanol and benzene products can be maintained at high purity despite having large feed disturbances. For the separation of 2,2,3,3-tetrafluoro-1-propanol (TFP) and water, using methyl tert-butyl ether (MTBE) or diisopropyl ether (DIPE) as light solvent was proposed. By solvent entrainment, TFP is introduced into the extract phase, while high purity water is removed from the raffinate phase. This process fully utilized the heterogeneity of components to overcome the limitations of distillation boundary, and the feasible density difference of liquid-liquid extraction was also considered for complete economic analysis. Furthermore, in order to perform a more rigorous investigation on the dynamic simulations of this system, several decanters were put in series to simulate the extraction unit in the pressure-driven module. The transient responses of the flow-driven module and the pressure-driven module were analyzed respectively to further explore the dynamic horizon of the hybrid extraction-distillation system.