- 學位論文
醋酸乙酯反應蒸餾及含雜質醋酸去水化之研究
Studies on Ethyl Acetate Reactive Distillation and Dehydration of Acetic Acid Having Impurities
摘要
本論文共分成醋酸乙酯反應蒸餾與含有雜質之醋酸去水程序之研究兩大部分。吾人於醋酸乙酯程序中，探討了不同莫飛板效率情況下所產生之多重穩態現象。並且透過操作變數的轉換，使用有機相回流比，可以成功的避免多重穩態的產生。並且透過此方式重新探討設計時各塔板增加變化之情形與反應速率常數的關係。於反應段中，塔板數變化受板效率下降之情況影響較為輕微，而精餾段中，其板數增加的情況則較傳統蒸餾塔與板效率成反比例為多，故此，設計時板效率實為一重要考量因素。此外，吾人也探討了不同控制架構與控制點下，醋酸乙酯程序的動態響應與擾動排除範圍。透過閉環靈敏度分析加上傳統開環靈敏度分析的策略，調動原始僅有傳統開環靈敏度分析下的控制點，可以得到更好的動態效果及其較小的穩態偏差值。而從研究中也顯示RD雙點溫控架構比單點溫控架構有其較大之擾動排除範圍。此外也探討了不同觸媒下，醋酸乙酯程序的穩態設計與動態響應。從研究中發現，雖然均相觸媒之反應速率較慢，但在穩態設計上，與異相觸媒相比，有稍低之年總成本。然而在其動態響應上，因反應速率較慢，故此需要較長的滯留時間，導致其動態較慢，且對擾動排除之效果差於異相觸媒。故此，可以瞭解不同的反應動力式，對反應蒸餾系統的組態無關，但對其動態響應有著很大的影響。 吾人於含有雜質之醋酸去水程序研究中，探討在含有對位二甲苯雜質的情況下，醋酸去水程序的熱力學性質。可以發現在含有雜質時，系統被蒸餾曲面分割成為兩個區域，故此，系統是否含有雜質對穩態設計有很大的影響。且透過進料位置影響的探討可以發現，使用建構於不含雜質組態下的進料位置處理含有雜質之系統，需要額外增加50%的能量耗費。故此，可以透過移動進料位置，降低其年總成本與塔底再沸器熱負載量之消耗。 最後，吾人對醋酸去水程序進行動態的分析與控制。從動態的脈衝測試中發現，在不含雜質與含有雜質系統最佳之操作點上，不含雜質之系統為穩定之穩態點；然而對於含有雜質之系統，透過分枝曲線的分析可以發現，含有雜質之系統中含有兩個穩態點，一個是穩定的而另一個是不穩定的，而最佳之操作點為不穩定之穩態點。由於透過成本的考量，此系統需操作於不穩定之穩態上，且透過雙點溫控架構可以使其穩定。至於動態現象上的研究，則發現當進料雜質含量過低時，其系統反而需要耗費很大的再沸器熱負載能量，吾人提出透過觀測塔中溫度之變化，以執行關閉側分流之策略，有其良好的成效且可應用於其他擾動排除。
並列摘要
This dissertation consists of two parts: esterification of ethyl acetate (EtAc) via reactive distillation (RD) and the dehydration of acetic acid containing impurities. In the first part, a homogeneous catalytic reactive distillation is focused. First, the effect of the Murphree plate efficiency (MPE) on the dynamics of such a reactive distillation is investigated. Output multiplicity was found while the organic reflux flow rate is a manipulation variable. However if reflux ratio is chosen as the new manipulating variable, this output multiplicity can be eliminated. Furthermore, the stage numbers in the RD are not inversely proportional to the MPE exactly. Second, alternative ways to improve control of an EtAc reactive distillation process are explored. In order to save energy and maintain the operating point at the original steady-state, closed-loop sensitivity plus open-loop sensitivity analysis is found effective in developing control systems for good control performance. As a result of the analysis, feasible ranges for control are also presented. Third, comparison between the optimal designs and control of homogeneous and heterogeneous catalytic reactive distillations is made. The homogeneous catalytic RD process has higher capital but less energy cost than the heterogeneous one, but, the former has less concern on the issues of catalyst installation and replacement. As for the control, heterogeneous catalytic process has faster response and lower steady-state offset than the homogeneous one. In the second part, the process flowsheets with and without tiny impurity of (p-xylene) PX or (m-xylene) MX are considered in the optimal design of acetic acid dehydration column via heterogeneous azeotropic distillation. First, the simulation results show that dramatic differences in the base-case conditions occur upon adding 0.1 mol% of PX or MX impurity in the feed. Over 50% more TAC and operating energy are needed to operate this column with side stream due to these impurities in the feed. However, by considering feed tray location as an additional variable in the optimal design, significant savings in total annual cost can be obtained. Second, The bifurcation phenomenon was found in the case of feed with impurity, no matter the column has a side stream r not. this phenomenon was not found for the case of feed without impurity. For the former, the column should be operated at the optimal case, and, a dual-point temperature control strategy is needed. Notice that this optimal case is an open-loop unstable. In that case, PX concentration inside the column needs to be maintained in order to keep the composition profile following the path with more PX in the bottom part of the column. To ensure an energy-efficient operation, a side stream operating strategy is devised to preserve PX inside the column. The proposed overall control strategy is tested under various feed disturbances. High-purity products can still be obtained despite disturbances.