利用液-液分相輔助分離三成分共沸物之設計與控制

Abstract

本研究包含兩個混合物系統，主要探討如何利用三成分混合系統中，本身存在的液-液分相區來協助分離。 第一個系統為異丙醚、異丙醇與水的混合物之分離程序，利用液-液分相結合變壓蒸餾的方式，可使蒸餾邊界遠離進料點，大幅減少塔頂出料流量，使整個系統回流量變少，降低能耗。最後，低壓塔與高壓塔之間做部分熱整合後，所計算出的年度總成本相比使用傳統變壓蒸餾的方式節省 38.6%。本文也討論此熱整合設計流程之動態模擬與控制，在考慮開環路與閉環路敏感度測試後，使用單點板溫控制策略與壓力補償溫度控制策略來做控制，最後進行閉環干擾測試，以確認在干擾之下，整個系統仍能維持高純度之產品規格。 第二個系統為苯、異丙醇與水的混合物之分離程序，此系統包含三個雙成分共沸物及一個三成分共沸物，且蒸餾邊界將三成分相圖分成三個區域。由於進料組成位於液-液分相區中，因此新鮮進料直接進入一分相槽後，可得水相與有機相，兩相位在不同蒸餾區域，分別進入一蒸餾塔後可於塔底得到產物，透過調整蒸餾塔的回流比，使兩塔塔頂出料混合後可位在第三種產物所在的蒸餾區，此混合流進入一蒸餾塔後可於塔底獲得第三種產物，塔頂出料組成則接近三成分共沸物組成，回流至前面與新鮮進料混合後一起進入分相槽。最後，進行部分熱整合並計算其 TAC，結果與傳統變壓蒸餾相比可節省 61.4% 的成本。 藉由討論上述兩個分離設計流程，能發現相比傳統變壓蒸餾，本研究所使用的方法可以大幅降低系統內部整體的回流量來達到減少操作成本的效果。

This work consists of two mixture systems and mainly discusses how to use the existing liquid-liquid phase separation region in the three-component mixture system to assist the separation. The first system is the separation process for the mixture of isopropyl ether, isopropyl alcohol and water. By using liquid-liquid phase separation combined with pressure swing distillation, the distillation boundary can be kept away from the operating point and the distillate flow rate of the column is greatly reduced, so that the recirculation in the system is reduced and the energy consumption is also reduced. Finally, after partial heat integration being performed between the low pressure column and the high pressure, the calculated annual total cost is reduced 38.6% compared to the conventional pressure swing distillation. This study also discusses the dynamic simulation and control of this heat-integrated design process. After considering the open loop and closed loop sensitivity test, the single point temperature control and the pressure compensation temperature control are used, and finally the closed-loop disturbance test is performed to confirm that the system can still maintain high purity product specifications under disturbance. The second system is a separation process for a mixture of benzene, isopropanol and water. The system contains three two-component azeotropes and one three-component azeotrope, and the distillation boundary divides the three-component phase diagram into three regions. Since the feed composition is located in the liquid-liquid phase separation zone, the fresh feed directly enters a decanter, and the aqueous phase and the organic phase are obtained. The two phases, which are in different distillation area, enter a distillation column respectively and the product can be get from the bottom. By adjusting the reflux ratio of the distillation column, the mixture of the two column distillate can be located in the distillation zone where the third product is located. After the mixed stream enters a distillation column, the third product can be obtained at the bottom of the column. The distillate composition is close to the three-component azeotrope composition. The distillate is recycled back to mix with the fresh feed and then goes into a decanter. Finally, partial heat integration is performed and then TAC is calculated. The result shows 61.4% savings in cost compared to conventional pressure swing distillation. By discussing the above two separation design process, it can be found that the method used in this study can greatly reduce the overall recirculation of the system to reduce the operating cost compared with the conventional pressure swing distillation.