乙酸甲酯水解反應之反應性分隔內壁蒸餾塔架構設計與控制

Abstract

反應性分隔內壁蒸餾塔目前研究文獻並不多見，現有的文獻大都反應程度不佳，我們認為在設計反應性分隔內壁蒸餾塔前，須先針對原有的反應性蒸餾架構設計進行研究，再進一步去做熱整合，如此可以避免在直接設計反應性分隔內壁蒸餾塔時轉化率不佳的問題。在本論文中依照乙酸甲酯水解反應的特性來設計不同反應性分隔內壁蒸餾塔，可改善轉化率及產品純度問題，採用Aspen Plus 11.1及其RadFrac模組進行程序之模擬，藉由程序最小年總成本(TAC)的計算以獲得最適設計的架構。 依照乙酸甲酯水解反應特性設計的反應性分隔內壁蒸餾塔的確改善了反應程度不佳及產品純度問題，比較熱整合架構與未熱整合架構，熱整合架構耗能及年總成本都較原本未熱整合架構低，耗能最高可節省約45%，年總成本最高節省約28%，效果驚人，足見反應性分隔內壁蒸餾塔有其發展潛力，根據研究結果顯示其節能來源是消除了反應蒸餾塔底的再混合效應。

在模擬進行上，本論文提出另一種模組型態之模擬架構，較文獻上簡略模擬更接近實際的分隔內壁蒸餾塔架構，但模擬時較為耗時，因必須不斷疊代壓力以求系統合理性，模擬出來結果較一般文獻模擬方法計算出來的能耗較高，年總成本也較高，但與未熱整合架構相比仍有省能及節省年總成本效益。最後本研究亦討論了此組態下之控制架構，由動態模擬結果發現，雖然可使用的自由度很多，但僅需進料比及再沸器能耗兩個自由度即可解決系統產能及進料組成擾動的問題。

Because the price of the crude oil is arising constantly, the exploitation of energy saving becomes one of the recent focuses in research. Utilizing integrated multi-functional unit to replace some single function units is one effective approach toward this goal. Reactive distillation column (RD) and divided wall column (DWC) are examples of such integration. A further integration of RD and DWC is thus motivated and is called reactive divided wall column (RDWC). The methyl acetate hydrolysis process with RDWC design was first proposed by Sander (2007). However, their work was aimed to illustrate that the concept of RDWC could be physically feasible for industry. From their research, the major products (i.e. methanol and acetic acid) are not as pure as the industrial grade. To overcome this deficiency, the design of RDWC aimed to high quality products and the possible energy savings achievable are studied. In this thesis, traditional RD configurations which contains one RD column and possible separation distillation columns for methyl acetate hydrolysis is studied. In these configurations, RD top condenser contains 10 times catalyst than reactive tray and has total reflux to improve the methyl acetate conversion. Except the methyl acetate, the acetic acid, methanol, and excess reactant water are drawn from the RD bottom and fed into the separation distillation columns. It is found that although the above-mentioned configurations can achieve high product specifications, it needs much more reboiler duty and total annual cost. To decrease the energy consumption and capital cost reduction, the above process is integrated to a RDWC configuration. By simulation, it proves that this RDWC can be an effective design. Compared with the original configuration, the original RD reboiler is removed. From this RDWC design, all energy required is provided by the reboiler of the second column. The resulting RDWC can reduce 45 % energy demand and 25 % total annual cost. It is observed that, to make this major saving possible, this RDWC avoids the remixing effect that used to take place is the original RD bottom.